Country：Japan

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Optical camera communication (OCC) is a type of visible light communication that employs a camera as the receiver. Various flicker-free OCC methods using a general-purpose low-frame rate camera have been proposed. In particular, the undersampling method uses a short exposure camera and a light-emitting diode that blinks faster than the camera's frame rate. Despite the short exposure time, the transmitter has to send a symbol for a frame period or longer because the relationship between the symbol timing of the transmitter and exposure timing of the receiver is indeterminate. We propose resolving this indeterminacy by synchronizing the exposure timing to the transmitter. In the proposed method, the transmitter sends multiple data channels in a frame period by time division multiplexing, and the receiver selects a channel. Then, a single symbol of multilevel phase shift keying is extracted from a single pixel value in a frame. Experiments confirmed that the exposure timing could be synchronized even with a degraded signal-noise ratio and that the receiver could select the desired channel. The proposed method achieved a bit error rate of 10(-6)at a signal-noise ratio of 46.2 dB under various modulation schemes.

DOI： 10.1109/JPHOT.2023.3247908

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DOI： 10.1109/JLT.2022.3218071

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATION ENGINEERS  

An essential issue in image sensor communication (ISC) is reliable and high-speed data transmission. In order to increase the data rate, this study uses pulse-width modulation (PWM). However, the symbol decision for PWM will become challenging with increasing numbers of luminance levels because of pixel saturation. In this study, we mitigate the pixel saturation problem by achieving high dynamic range (HDR) using two high-speed image sensors with varied exposure settings. Furthermore, we proposed HDR combining for signal demodulation. The field trial experiment results show that a throughput of higher than 87.5 kbps within the communication distance of 50 m can be achieved.

DOI： 10.1587/comex.2023XBL0075

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Using a rolling shutter camera as a receiver, visible light communication (VLC) can achieve a significantly higher sampling rate than the frame rate because of its sequential exposure mechanism. This study focuses on optical orthogonal frequency division multiplexing (OFDM) in a rolling shutter based VLC for further high-speed data rates. Because an image sensor is employed, conventional optical OFDM, such as DC-biased optical OFDM (DCO-OFDM), must fit in the grayscale range of 0-255 levels. Therefore, DCO-OFDM suffers from poor error performance owing to its high PAPR. To address this problem, we propose a polarity-separated transmission, in which the bipolar OFDM signal is separated into positive and negative parts and then transmitted by two LEDs simultaneously. Polarity-separated transmission is expected to double the grayscale range, i.e. 0-511, and improve error performance because it reconstructs the original bipolar signal by combining the received signals from two LEDs. We experimentally demonstrate and compare the symbol error rate (SER) performance of DCO-OFDM and polarity-separated transmissions. Consequently, polarity-separated transmission improved the SER performance by 10(-2) in the fundamental frequency range of 300-700Hz when 16-PSK was adopted for subcarrier modulation.

DOI： 10.1109/ISCAS46773.2023.10181518

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

<p>1-bit analog-to-digital converters (ADCs) have low power consumption and can easily speed up the analog-to-digital conversion and sampling. However, due to their resolution of only 1 bit, the nonlinearity between the input with multiple amplitude levels and output is large. With the method of utilizing noise proposed in previous studies, 1-bit ADCs can be linearized to demodulate signals with multi-level amplitude modulation like pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM). In this letter, we construct a receiver circuit using a 1-bit ADC, evaluate its performance, and show its availability through demodulation experiments on 4-PAM signals.</p>

DOI： 10.1587/comex.2022COL0032

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DOI： 10.36227/techrxiv.19446947

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This study proposes a simplified Alamouti-type space-time coding (STC), improving the performance of image sensor communication (ISC) using a rotary LED transmitter. The rotary LED transmitter was developed to increase the data rate of ISC using afterimages of LED lights. The transmitter simultaneously causes the LEDs to blink and rotates them around a vertical axis. Owing to the movement of the blinking LEDs that occurs within the exposure time of the camera, multiple blinking states are captured as afterimages, thus increasing the amount of information that can be received per image. However, with increasing communication distance, the size of the LED light captured on the image sensor decreases. In this case, it is difficult to distinguish each LED blinking state, leading to a degradation of the demodulation performance. To overcome this problem, the proposed STC encodes adjacent angular afterimages as symbol pairs and transmits these symbol pairs using two symbol times. In addition, we simplified the data decoding process by using normalized LED luminance values. We evaluate the demodulation performance of the proposed method through experiments. Compared with conventional coding methods, the proposed STC requires no channel estimation and significantly improves the demodulation performance.

DOI： 10.1109/JPHOT.2021.3137601

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This study investigates a new communication scheme for the event camera-based visible light communication (VLC) using a propeller-type rotary LED transmitter. Conventional camera-based VLC suffers from low data rates and high latency due to the limited camera frame rates. To solve this problem, the event camera has been used as the receiver in VLC. Event cameras detect changes in brightness and asynchronously output these changes as events in microsecond order. The high temporal resolution gives the event camera-based VLC good potential in terms of high speed and low latency. However, when an event camera is used as the VLC receiver, the light of the transmitter needs to be changed constantly. If the transmitter LED is continuously in the same blinking state, the event camera may not output any events and the data could not be recovered until the blinking state changes. To transmit the optical signal for event cameras, we use a propeller-type rotary LED transmitter, which is under development, for the event camera-based VLC. The transmitter rotates the blinking LED in circles and uses the afterimage of LED light to transmit signals. The event camera detects the afterimages and constantly outputs them as a stream of events. We filter the noise events and recover data using signal events. This study verifies the operation for the proposed system through an implementation experiment. As a result, we achieved the communication in the proposed system and provided a basic evaluation of communication quality.

DOI： 10.1109/ICCWORKSHOPS53468.2022.9814467

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATION ENGINEERS  

Most of the previous research on the acquisition of the LED Array transmitter assumes that the onboard receiver approaches the LED transmitter from the car's front. In this study, we considered a case where the vehicle's receiver crosses the LED transmitter. This letter modifies the algorithm using spatial-temporal gradient values to detect LED arrays. As a result, we achieved error-free acquisition and successfully communicated up to 9728 [bits] at a vehicle speed of 25 [km/h].

DOI： 10.1587/comex.2022TCL0008

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DOI： 10.1109/JLT.2021.3106911

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Visible light communication based intelligent transportation systems (ITS-VLC) show great potential for future urban mobility. This study presents a performance evaluation of range estimation between vehicles and infrastructures in an ITS-VLC system. In the proposed ITS-VLC system, it is easy to simultaneously conduct communication and ranging using stereo cameras. However, the stereo camera calibration becomes a problem during simultaneous communication and ranging due to vehicle vibration. Using the data from LED transmitters and stereo cameras, it can obtain multiple measurements of distance. The monocular-stereo fusion algorithm is applied to visible light ranging in the proposed scheme using particle swarm optimization. We employed real data from the field trial experiment and achieved a ranging accuracy of 60 ± 1.0 m.

DOI： 10.1109/IV48863.2021.9575534

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Luminance inversion (LI) is proposed to compensate for nonlinear characteristics between a liquid crystal display (LCD) and an image sensor (IS) camera of the parallel transmission (PT) visible light communication (VLC). In the PT system reported in [1], which incorporates N spatial frequencies with phase shift keying (PSK) through M-point inverse discrete Fourier transform (IDFT), data are transmitted from M different regions of pixels on an LCD spatially in parallel. Since the transfer characteristics between the LCD and IS camera is nonlinear, the received signal at IS camera receiver is distorted. The effect is severe because signals of the PT system are, in essence, the OFDM signal, thus suffering from high peak-to-average ratio (PAPR). To linearize it between the LCD and IS camera, our approach is to calculate a complement of the digital data fed to the driver of the pixel and then to feed the pair of the digital data and its complement to the driver during two successive frames. In the receiver, the difference of the signals during the two frames is calculated for each of the M detected regions on the IS plane, and then they input to the following M-point DFT in the PT system. By introducing this LI process, wider linear characteristics in the PT system is obtained than without LI. Experimental results show that the number of bits per frame that the PT system with LI can accommodate without any error is 315bits/frame and 100bits/frame for 8- and 16-PSK, which are much larger than 12bits/frame and 0bits/frame for the 8- and 16-PSK PT system without LI, respectively.

DOI： 10.1109/ICC42927.2021.9500287

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Publishing type：Research paper (scientific journal)   Publisher：IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences  

DOI： 10.1587/transfun.2020TSF0001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

We discuss herein whether an optical wireless communication (OWC) system can be a candidate for post 5G or 6G cellular communication. Almost once per decade, cellular mobile communication is transformed by a significant evolution, with each generation developing a distinctive concept or technology. Interestingly, similar trends have occurred in OWC systems based on visible light and light fidelity (Li-Fi). Unfortunately, OWC is currently relegated to a limited role in any 5G scenario, but the debate whether this is unavoidable has yet to be settled. Whether OWC is adopted post 5G or 6G is not the vital issue; rather, the aim should be that OWC coexists with 5G and 6G communication technologies. In working toward this goal, research and development in OWC will continue to extend its benefits and standardize its systems so that it can be widely deployed in the market. For example, given that a standard already exists for a visible-light beacon identifier and Li-Fi, a service using this standard should be developed to satisfy user demand. Toward this end, we propose herein a method for visible-light beacon identification that involves using a rolling shutter to receive visible-light communications with a smartphone camera. In addition, we introduce a rotary LED transmitter for image-sensor communication.

DOI： 10.1587/transfun.2020WBI0001

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This study focuses on visible light communication (VLC) using a photodiode as a receiver. Accurate data transmission by this type of VLC is a challenge because the photodiode cannot detect weak light of subthreshold intensity owing to its insufficient light sensitivity. To overcome this problem, we employ a stochastic resonance, which is a nonlinear phenomenon in which the response characteristics of a system improve as its noise intensity increases, for the receiver of this VLC system. We also employ additive light-emitting diode light, which interferes in the photodiode as intentional noise. As an experimental result, the stochastic resonance was achieved by setting the parameters of the noise source appropriately, and we recovered the weak transmitting signal at the receiver.

DOI： 10.1109/ISCAS51556.2021.9401452

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This study describes intelligent transport image sensor communication (ITS-ISC) systems that use LED arrays as transmitters that imitate traffic lights. Three signal-transmission schemes -luminance modulation, spatial modulation, and combined luminance and spatial modulation- use LED array. However, their suitability for ITS-ISC has not been explored yet. Therefore, we compare the communication performance of these three systems under strong saturation and present the results.

DOI： 10.1587/comex.2021ETL0032

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Publishing type：Research paper (scientific journal)   Publisher：2020 IEEE Global Communications Conference, GLOBECOM 2020 - Proceedings  

DOI： 10.1109/GLOBECOM42002.2020.9348012

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Publishing type：Research paper (international conference proceedings)  

Stereo cameras, serving as the 'eyes' of automotive vehicles, can determine the distance between objects and the vehicles. In this paper, stereo cameras are introduced into image-sensor-based visible light communication (IS-VLC) systems, in which the combination of VLC and stereo ranging shows promising prospects for intelligent transport systems. However, one of the problems of IS-VLC stereo ranging is that the luminance level of LEDs in the captured images would greatly affect disparity estimation, which would result in inaccurate range estimation. This paper gives the performance evaluation of this problem using phase-only correlation algorithm with luminance selection. The proposed scheme using stereo cameras exhibited a ranging accuracy of 60± 0.15m in static conditions.

DOI： 10.1109/GCWkshps50303.2020.9367540

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Publishing type：Research paper (scientific journal)   Publisher：2020 IEEE 9th Global Conference on Consumer Electronics, GCCE 2020  

DOI： 10.1109/GCCE50665.2020.9291797

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

In this study, the sequential maximum likelihood decoding (S-MLD) for image sensor based visible light communication, referred to as image sensor communication, is proposed. The conventional system cannot correctly decode degraded captured images. To overcome this problem, S-MLD partitions the LED area on the image into two segments and sequentially creates pseudo-captured images, which imitate all possible LED blinking patterns. This approach is based on MLD for each segment. Moreover, reliability determination is incorporated to improve communication quality. We performed computer simulations and confirmed that S-MLD exhibits superior decoding performance and approximately 90% computational cost reduction compared to the previous MLD.

DOI： 10.1587/comex.2020XBL0058

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Publishing type：Research paper (scientific journal)   Publisher：IEEE International Conference on Communications  

DOI： 10.1109/ICC40277.2020.9148927

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Publishing type：Research paper (scientific journal)   Publisher：2020 Optical Fiber Communications Conference and Exhibition, OFC 2020 - Proceedings  

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Publishing type：Research paper (scientific journal)   Publisher：2020 IEEE 17th Annual Consumer Communications and Networking Conference, CCNC 2020  

DOI： 10.1109/CCNC46108.2020.9045147

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Publishing type：Research paper (scientific journal)   Publisher：Optics InfoBase Conference Papers  

DOI： 10.1364/OFC.2020.Th1K.1

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Publishing type：Research paper (international conference proceedings)  

This paper focuses on high-speed stereo cameraã receivers for visible light communication (VLC) in intelligent transport systems (ITSs), contrary to conventional studies where a single (high-speed) camera is used. An advantage of high-speed stereo cameras as VLC receivers is that both front-facing ranging and wireless communication can be achieved in one device. In this paper, utilizing features of VLC, we consider stereo ranging with high accuracy. Moreover, it is known that an LED transmitter for VLC has specific features, high-luminance and high- speed blinking. This paper proposes stereo ranging by applying LED transmitter detection (utilizing these features) to disparity estimation. Additionally, we introduce subpixel estimation using equiangular line fitting to obtain more accurate disparity. Finally, we experimentally demonstrate that the proposed stereo ranging achieves an accuracy of 60 m ± 0.1 m.

DOI： 10.1109/GLOBECOM38437.2019.9013641

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：2019 8th IEEE International Conference on Connected Vehicles and Expo, ICCVE 2019 - Proceedings  

Emergency services around the world face the problem of increasing patient transportation times. The operation of emergency vehicles is fundamentally different from that of general vehicles; hence, algorithms recommending optimal routes in a conventional way are not always applicable to emergency vehicles. In this study, we analyzed data of inter-vehicle and road-vehicle communication collected at 700 MHz band intelligent transport systems and demonstrated that the overall travel time of emergency vehicles can be reduced by decreasing their travel time at intersections.

DOI： 10.1109/ICCVE45908.2019.8965232

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

We propose a method that establishes a direct wireless link from a transmission source to an out-of-range destination with the assistance of the surrounding communication nodes. In this method, a weak (subthreshold) signal is amplified by utilizing the interference signals transmitted from the surrounding communication nodes. To evaluate the amplification gain, we study the mutual information in a multipath fading channel. As a result, we reveal that the mutual information is enhanced owing to the interference signals, and the proposed method enlarges the radio coverage area of the source node. To understand the enhancement mechanism, we introduce a toy model of the propagation channel and discuss the role of the interference signals. We find that the interference signals allow the subthreshold signals into the detectable region in the signal space. Moreover, the mutual information is maximized at the optimal power of the interference signals. In addition, a detailed discussion of the channel capacity shows that there exists an optimal a priori probability of symbol transmission.

DOI： 10.1109/TVT.2019.2934502

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Publishing type：Research paper (scientific journal)   Publisher：2019 8th IEEE International Conference on Connected Vehicles and Expo, ICCVE 2019 - Proceedings  

DOI： 10.1109/ICCVE45908.2019.8965241

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.14923/transcomj.2018WFP0008

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DOI： 10.1364/OE.27.021565

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

We will introduce an integrated system of visible light communications (VLC) and ranging using high-speed stereo imaging. The system simultaneously decodes VLC signal while its source tracking portion outputs range information.

DOI： 10.1109/PHOSST.2019.8794881

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.14923/transcomj.2018JBR0001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This paper focuses on an image sensor communication system that uses an LED as the transmitter and a high-speed image sensor (camera) as the receiver. Communication in this scheme depends on the quality of images transmitted from the LED to the sensor. If the image becomes unfocused on the way to the receiver, the LED luminance that make up the signal cannot be detected, so the receiver cannot demodulate the signal data. To overcome this problem, this study proposes a novel demodulation scheme to recover data from a degraded image, based on a maximum likelihood decoding (MLD) algorithm. The proposed method creates template images that imitate all possible blinking patterns produced by the LED transmitter, and then calculates the Euclidean distances between pixels in the captured image and the pseudo images for all possible blinking patterns. Finally, the algorithm chooses the image template with the smallest Euclidian distance from the received signal as the recovered data. Though an exhaustive set of image templates must be prepared for the proposed MLD, the number of templates depends on the number of LEDs on the transmitter. Thus, the computational complexity of this method increases as the number of transmitter LEDs increases. To reduce the computational complexity of the proposed MLD algorithm, the binary differential evolution (BDE) algorithm is used, which is a swarm intelligence technique. Computer simulations are used to evaluate the BDE algorithm's usefulness for reducing computational complexity and improving the BER of the communication system.

DOI： 10.1587/nolta.10.173

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

This paper proposes a parallel transmission (PT) system using M-point discrete Fourier transform (DFT) for image-sensor-based (IS-based) visible light communications (VLC). We make use of M-point inverse DFT (IDFT) to generate pulse width modulation (PWM) signals transmitted by M spatially aligned LEDs. The M PWM signals are pre-calculated to give N phase shifted carriers after M-point DFT, where N=\\lfloor(M-1)/2\\rfloor and \\lfloor z\\rfloor stands for the maximum integer not exceeding z. Therefore, the IS receiver of a high-speed camera captures the LEDs to obtain the M inputs to the DFT from the luminance values of the captured LEDs. During a symbol interval equal to the exposure time of the high-speed camera, N\\ \\log-{2}P bits in total are simultaneously transmitted between the LEDs and IS-based receiver, when P-ary PSK is used for all the carriers. We experimentally demonstrate our PT system at the distance of nine meters between M PWM-modulated LEDs and a 2000-fps high-speed camera. Our experimental results validate that PSK symbols are demodulated without errors for smaller values of M and P, with controlling the aperture of the lens of the camera receiver.

DOI： 10.1109/GLOCOMW.2018.8644501

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Publishing type：Research paper (international conference proceedings)  

Light-emitting diodes (LEDs) can add visible light communication (VLC) by high-speed blinking to their original lighting function. VLC using image sensors as receivers is referred to as image sensor communication (ISC). ISC eliminates noise and interference and enables multiple and simultaneous communication; hence it is suitable for outdoor mobile environments such as intelligent transport systems (ITSs). On the other hand, since the communication rate depends on the frame rate, it is difficult to increase. Therefore, the purpose of this study is to increase the communication rate by multilevel pulse width modulation (PWM). When the modulation level is increased, demodulation becomes difficult due to the bit per pixel (bpp) limitation of the image sensor. First, in order to perform efficient luminance extraction in limited bpp, we compare the maximum luminance extraction and the average luminance extraction. Then, we propose improving the nonlinearity between the transmitter and receiver, which is a problem in average luminance extraction suitable for a mobile environment, by applying precoded PWM. Finally, we evaluate effectiveness of precoded PWM experimentally.

DOI： 10.1109/GLOCOMW.2018.8644347

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Stochastic resonance (SR) is a noise-enhancement phenomenon that enables the detection of sub-threshold signals by adding noise and using nonlinear systems. This paper explores the applicability of SR in a BPSK receiver with sub-threshold signals. Although received signals are amplified as a result of the nonlinear behavior of the receiver, they are somewhat distorted. This results in the lower performance of SR receivers in comparison with linear receivers. Employing a parallel network of SR systems is expected to solve this problem. The present theoretical analysis demonstrates that in a certain noise intensity range, the output of the network can fully describe an input sub-threshold signal, and hence, the performance close to that of the linear receivers can be obtained. The effectiveness of the SR receiver was also demonstrated through a numerical example of the bit error rate (BER). However, achieving good BER performance requires an infinite number of arrayed SR systems, which is not realistic in practical systems. A design framework for an SR network with a finite number of elements and an appropriate noise intensity that can realize BER performance close to that in linear systems is also provided.

DOI： 10.1587/nolta.10.106

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This letter proposes a demodulation method using a one-bit comparator for signals processed by multilevel pulse amplitude modulation (PAM). The proposed method is simple and provides an alternative to using an analog-to-digital converter to describe multilevel input signals. Because of the noise present in the transmitted multilevel PAM signal, the two level output of the one-bit comparator shows different statistical behavior for each level of the signal. Thus, it is possible to detect the signal level, or perform symbol decision, based on the maximum likelihood criterion. The present theoretical analysis reveals that reliable demodulation is possible even with a one-bit comparator if the probability mass function of the two-level outputs of each received symbol plus intentionally added noise is known.

DOI： 10.1109/LWC.2018.2831683

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

This tutorial article presents an outline of image sensor communication (ISC) technologies realized by light sources and cameras. It discusses the revision of the IEEE 802.15.7-2011 standard, namely, the IEEE 802.15.7m Optical Wireless Communications Task Group, which has significantly influenced the development of the ISC technology. It also reviews the ISC technical proposals of the task group and compares them with related works. The essential technical considerations of the ISC specifications are presented, and the future directions of research and development are discussed.

DOI： 10.1109/MCOM.2018.1700134

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

This paper proposes an N-stream superimposed system for image-sensor-based visible light communications (ISbased VLC). Based on the principle of m-point discrete Fourier transform (DFT), a phase shift keying (PSK) signal is transmitted over m consecutive time slots mT, where T is a slot duration. In practice, the symbol rate of this paper is R/(m + 1) because a guard slot is inserted every m slots. In the superimposed system, N data streams where the symbol rate of the nth data stream, n = {1, 2,.., N}, is 1/(m+ 1)n-1 times the symbol rate of the first data stream are combined to form a pulse-width modulated (PWM) wave with a period time T. An IS receiver with a camera operating at a frame rate of R/(m+ 1)n-1 fps demodulates data streams whose symbol rate is R/m+ 1)n symbol/s or lower. Our experimental results validate that from a superimposed PWM wave of 500-symbol/s and 125-symbol/s data streams, a 2000-fps camera receiver demodulates both of the two data streams and the 500-fps camera receiver does the 125-symbol/s data stream successfully, without shortening individual error-free transmission ranges, compared with non-superimposed systems in which 500-symbol/s and 125-symbol/s data streams are independently transmitted by different light emitting diode (LED) transmitters and received by 2000-fps and 500-fps camera receivers, respectively.

DOI： 10.1109/GLOCOM.2017.8254784

Research data storage URL： http://ieeexplore.ieee.org/document/8254784/

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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DOI： 10.1587/transfun.E101.A.176

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The present letter discusses a detectability enhancement induced by co-channel interference signals in the polarization diversity reception. The challenge is the detection of weak (subthreshold) signals, the level of which is less than the detection limit of radio receivers. To understand the theory underlying the mechanism in the presented diversity scheme, we introduce an analytic model of a dual polarized antenna array in the fading channel. In addition, the channel capacity in a binary data transmission is derived. As a result, we reveal that the interference-aided diversity reception enables us to detect signals even below the detection limit of the receiver. Moreover, the appropriate source code is needed to achieve the channel capacity because the transmission channel is asymmetric in the present reception scheme.

DOI： 10.1109/LCOMM.2018.2851583

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Language：Japanese   Publishing type：Research paper (international conference proceedings)  

In-vehicle cameras can be used as receivers for visible light communication in addition to their primary functions: for viewing assistance and object recognition. Most studies with this design perform tests via a single high-speed camera that is used as the receiver, but this study employs a receiver that uses a high-speed stereo camera. The reception method developed in this paper effectively utilizes left and right stereo images to improve communication performance. Although the selective diversity reception method proposed in previous work improved communication performance, it cannot deal with cases wherein both the left and right cameras introduce errors. To further improve the communication performance of this system, maximal ratio combining (MRC) diversity is applied to the high-speed stereo camera in this study. Communication performance is then evaluated comparing to the selective diversity reception and conventional single-camera reception by experimental tests conducted under static and driving conditions.

DOI： 10.1109/GLOCOM.2018.8647953

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Publishing type：Research paper (scientific journal)   Publisher：Optics InfoBase Conference Papers  

DOI： 10.1364/SPPCom.2018.SpW2G.6

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Publishing type：Research paper (scientific journal)   Publisher：2018 IEEE Global Communications Conference, GLOBECOM 2018 - Proceedings  

DOI： 10.1109/GLOCOM.2018.8647694

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Publishing type：Research paper (scientific journal)   Publisher：IEEE  

DOI： 10.1109/GLOCOM.2018.8648114

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Most practical visible light communication (VLC) systems being currently deployed with image sensor receivers use intensity modulation and direct detection scheme for outdoor and indoor applications. A number of modulation and coding techniques that are used for image sensor-based VLC systems are presented.

DOI： 10.1109/IPCon.2017.8116086

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

This paper presents a feasibility study of the uplink visible light communication (VLC) beacon system for the universal traffic management system (UTMS). The UTMS is a traffic management system beneath the National Police Agency of Japan. Currently, 55 000 UTMS infrared beacon systems have been installed, and they provide expressway and ordinary road information to cars. However, the data rate is 1 Mbps, and a faster data rate is necessary to support automotive and smart mobility devices. In this paper, we propose an uplink V2I system for the UTMS. The system is designed to match the current beacon system as closely as possible, so that the system can easily be replaced and still provide sufficient bandwidth for future automotive and smart mobility devices. We adopt a photo diode (PD) as the VLC receiver and a commercially available off-the-shelf LED headlight as a transmitter. Unfortunately, the bandwidth of such an LED is usually small, so we consider applying a bit-loading algorithm to direct-current-biased optical orthogonal frequency division multiplexing. To reduce strong background noise, such as from the sun, we narrow down the field-of-view by applying a lens to the PD, which forms a tiny communication area, smaller than the current infrared beacon system. We then consider multiple PDs with the lens to create a similar communication area as the infrared beacon system. As a result, we achieve 3.1-Mbps throughput.

DOI： 10.1109/ACCESS.2017.2759179

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

Image sensor communication (ISC), which is derived from visible light communication (VLC), is a novel form of wireless communication that uses an image sensor as a receiver. ISC is an attractive solution for outdoor mobile environments and is particularly well-suited to intelligent transport systems (ITS). The purpose of this paper is to derive the dominant components of vehicle vibrations and road surface irregularities that induce transmitter displacement in ITS-ICS in paved road scenarios. Such displacements make it difficult for a ISC receiver to select the correct pixels. We measured vehicle vibrations during an actual driving scenario using a six-axis acceleration sensor installed in a smartphone. Using the results obtained, we performed a frequency analysis of the vehicle vibrations and determined the parameters of vehicle vibrations based on the frequency characteristics. This paper explains that the vehicle vibrations that affect the communication performance can be modeled by solely using Gaussian random processes when a high frame rate (e.g. 1000 fps) image sensor is used as the ISC receiver.

DOI： 10.1109/ICCW.2017.7962648

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Asia/Pacific Region
Interview with Takaya Yamazato, Director of the AP Region
This is the fourth article in the series of eight, started in November 2016 and published monthly in the IEEE ComSoc Global Communications Newsletter, which covers all areas of IEEE ComSoc Member and Global Activities. In this series of articles, I am introducing the six MGA Directors (Sister and Related Societies; Membership Services; AP, NA, LA, EMEA Regions) and the two Chairs of the Women in Communications Engineering (WICE) and Young Professionals (YP) Standing Committees. In each article, one by one they present their sector activities and plans.

In this issue, I interview Takaya Yamazato, Director of the Asia/Pacific Region (AP). Takaya is a professor at the Institute of Liberal Arts and Sciences, Nagoya University, Japan. He received the Ph.D. degree from Keio University, Yokohama, Japan, in 1993. From 1993 to 1998 he was an assistant professor in the Department of Information Electronics, Nagoya University, Japan. From 1997 to 1998 he was a visiting researcher in the Research Group for RF Communications, Department of Electrical Engineering and Information Technology, University of Kaiserslautern, Germany. In 2006 he received the IEEE Communication Society Best Tutorial Paper Award. He served as symposium co-chair of ICC 2009 and ICC 2011. From 2008 to 2010 he was the chair of the IEEE ComSoc Satellite and Space Communications Technical Committee and the editor-in-chief of the Japanese Section of IEICE Transactions on Communications. His research interests include visible light communication, intelligent transport systems, stochastic resonance, and open educational resources.

DOI： 10.1109/MCOM.2017.7841463

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DOI： 10.1587/nolta.8.204

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DOI： 10.1587/nolta.8.204

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DOI： 10.23919/APCC.2017.8304093

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DOI： 10.1007/s41650-017-0044-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper discusses the stochastic resonance (SR) effect in a binary communication system for subthreshold signal reception. We focus on the problem of no communication when received signal strength is below receiver sensitivity. Subthreshold signal reception requires a device that exhibits SR, such as a Schmitt trigger or a comparator. Previously, we proposed an alternative three-level device and demonstrated its high performance for subthreshold signal reception in an SR receiver. In the present study, we show that our proposed three-level device outperforms the three devices and discuss reasons for this superior performance. Contributions of our present paper are twofold: first, we analytically derive bit error rate (BER) performances of SR receivers installed with a Schmitt trigger and a comparator;second, we compare performances of the Schmitt trigger, comparator, and three-level device.

DOI： 10.1587/nolta.7.407

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

As a new technology for next-generation vehicle-to-everything (V2X) communication, visible-light communication (VLC) using light-emitting diode (LED) transmitters and camera receivers has been energetically studied. Toward the future in which vehicles are connected anytime and anywhere by optical signals, the cutting-edge camera receiver employing a special CMOS image sensor, i.e., the optical communication image sensor (OCI), has been prototyped, and an optical V2V communication system applying this OCI-based camera receiver has already demonstrated 10-Mb/s optical signal transmission between real vehicles during outside driving. In this paper, to reach a transmission performance of 54 Mb/s, which is standardized as the maximum data rate in IEEE 802.11p for V2X communication, a more advanced OCI-based automotive VLC system is described. By introducing optical orthogonal frequency-division multiplexing (optical-OFDM), the new system achieves a more than fivefold higher data rate. Additionally, the frequency response characteristics and circuit noise of the OCI are closely analyzed and taken into account in the signal design. Furthermore, the forward-current limitation of an actual LED is also considered for long operational reliability, i.e., the LED is not operated in overdrive. Bit-error-rate experiments verify a system performance of 45 Mb/s without bit errors and 55 Mb/s with BER &lt; 10(-5).

DOI： 10.1109/JPHOT.2016.2555582

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

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Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

High-speed image sensors, designed for machine vision and control, provide the "eyes" for autonomous and connected vehicle. A noteworthy feature of high-speed image sensors is their ability to be used as a reception device for visible light communication (VLC) signals. Due to the massive number of pixels available and the ability to spatially separate sources, a signal-receiving pixel in the image sensor plane represents the actual position of the transmitter. The VLC signal can be represented not only by a VLC time domain signal but also by the position of the transmitter. In this paper, we propose a robust range estimation scheme that integrates with a VLC function for infrastructure-to-vehicle visible light communication (I2V-VLC). The scheme is composed of an LED array transmitter and a high-speed image sensor receiver. It measures a range by taking phase-only correlation (POC) and avoids vehicle vibration from road irregularity. Field trials confirm an accuracy range of 0.3 m, even on rough road conditions, with the measurement time of 2 ms, which is much faster than that of light detection and ranging (LIDAR).

DOI： 10.1109/ICCW.2016.7503808

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Digital signage, which is advertising media using a liquid crystal display (LCD), is increasing in popularity. One possible application is wireless communications between digital signage and viewers. We focus on image-sensor-based visible light communication (VLC). Image-sensor-based VLC requires only an image sensor (IS), which is common equipment in smart phones. In the proposed method, an information signal is displayed on LCD. However, embedding the information signal into an advertisement may decrease the quality. We propose blue color difference modulation to make such signals imperceptible. We implemented a VLC system between digital signage and IS to demonstrate, the effectiveness of the proposed modulation in a real environment.

DOI： 10.1109/PIMRC.2016.7794761

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We focus on the road-to-vehicle visible light communication (VLC) that system is composed of a LED matrix as a transmitter and a high-speed camera as a receiver. In this VLC system, intensity of each LED cannot be determined from received image directly in case that the receiver is distant from the transmitter. In previous research, a method to estimate intensity of the LED from received image is proposed. In this method, intensity of LED is estimated by using Moore-Penrose pseudo-inverse matrix of coefficient matrix, which expresses relation between intensity of LEDs and pixel values. However, the coefficient matrix changes every moment because it is determined by positional relation between the receiver and the LED traffic light in VLC system. In this paper, we propose a method to estimate position of the LED matrix using simulated images. We measure sensitivity distribution of image sensor to generate simulated images. We evaluated degree of similarity between simulated images and real images.

DOI： 10.1109/APSIPA.2016.7820809

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Spatial modulation (SM) is introduced into layered space-time coding (L-STC) used in image sensor (IS)-based visible light communication (VLC) systems. STC was basically investigated for extending the communication range of the IS-based VLC link [1], although it is out of the range when IS receivers are at the long distance from the LED array of the transmitter where the number of pixels capturing the transmitter on the image plane is less than the number of LEDs of the array. Furthermore, L-STC was done in [2] for increasing the reception rate with improving the pixel resolution while the receiver was approaching the transmitter. In this paper, SM is combined into L-STC by mapping additional information bits on the location of the pair of STC bit matrices of each layer. Experimental results show that additional SM bits are extracted with no error, without deteriorating the reception quality of and shrinking the transmission range of the original L-STC.

DOI： 10.1109/PIMRC.2016.7794763

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Complex interleaved orthogonal design (CIOD) can offers diversity gain to the part of the source in spatial modulation which has single radio frequency (RF) front-end at the transmitter despite multiple-input multiple-output, but emits the undesired component out-of-band. For the reducing out-of-band emission, we give up indicating the information source by the antenna switching and increase both the interleaver size and the antenna switching interval. The increase reduces the discontinuities in the waveform and out-of-band emission. We propose such a scheme as transmit diversity with single RF front-end using CIOD. The diversity gain of the proposed scheme is equivalent to the case for CIOD. Moreover, we evaluate the increase of out-of-band emission and confirm that of the proposed scheme compared to the ideal case is only 3dB.

DOI： 10.1587/comex.2015XBL0170

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This invited paper focuses on a high-speed image sensor as a visible light communication (VLC) reception device to develop the intelligent transport systems (ITS) application using VLC technique. We refer to the VLC using a high-speed image sensor as image-sensor-based VLC. A major advantage of the image sensor is the ability to spatially separate multiple sources. Based on this ability, we proposed several methods for the image-sensor-based VLC in our previous researches. Especially, we focused on unique characteristics of the image sensor and proposed the hierarchical coding and the overlay coding to improve the data reception performance. However, to perform the image-sensor-based VLC in an actual environment, the receiver has to acquire the VLC transmitter from captured images before recovering data. Namely, the VLC transmitter acquisition and tracking are critical problem. the image-sensor-based VLC technique. This invited paper introduces two proposed methods to acquire the VLC transmitter from images captured by the image sensor.

DOI： 10.1109/OECC.2015.7340210

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

This paper demonstrates the feasibility of layered space-time coding (STC) in an outdoor image-sensor-based (IS-based) visible light communication (VLC) system. We examined that for low-resolution IS-based VLC channel where intensity-modulated signals from two different light emitting diodes (LEDs) are detected by one pixel of an IS, STC allows us to decouple them; thus, succeeding to receive them with no errors. Consequently, STC offers extended transmission distance to pixel-resolution-limited IS-based VLC links. In the layered STC presented in this paper, additional bit streams are laid on the 2(n) x 2(n) LED array for increasing the transmission rate per symbol duration for the case where the pixel resolution is improved. A prototype of a three-layered STC is built with an 8 x 8 LED array, where each of the LEDs is modulated at 1 kb/s and a high-speed camera with IS operating at 1000 fps. Our experimental results validate that the two additional bit streams (layer-2 and -3), aligned in the layer-1 STC matrix pair, are extracted with no errors when the receiver comes within 155 and 55 m, respectively, from the LED array, without decreasing 210 m of the transmission distance of layer-1 bit stream.

DOI： 10.1109/JLT.2015.2470091

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The concepts of vehicle-to-vehicle and vehicle-to-infrastructure (V2X) communications technologies using visible light communications (V2X-VLC) are introduced. Advantages of image sensor as a VLC receiver will be presented along with two important our findings.

DOI： 10.1109/PHOSST.2015.7248248

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Publishing type：Research paper (scientific journal)   Publisher：Journal of the Institute of Electronics, Information and Communication Engineers  

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Channel modeling is critical for the design and performance evaluation of visible light communication (VLC). Although a considerable amount of research has focused on indoor VLC systems using single-element photodiodes, there remains a need for channel modeling of VLC systems for outdoor mobile environments. In this paper, we describe and provide results for modeling image sensor based VLC for automotive applications. In particular, we examine the channel model for mobile movements in the image plane as well as channel decay according to the distance between the transmitter and the receiver. Optical flow measurements were conducted for three VLC situations for automotive use: infrastructure to vehicle VLC (I2V-VLC); vehicle to infrastructure VLC (V2I-VLC); and vehicle to vehicle VLC (V2V-VLC). We describe vehicle motion by optical flow with subpixel accuracy using phase-only correlation (POC) analysis and show that a single-pinhole camera model successfully describes these three VLC cases. In addition, the luminance of the central pixel from the projected LED area versus the distance between the LED and the camera was measured. Our key findings are twofold. First, a single-pinhole camera model can be applied to vehicle motion modeling of a I2V-VLC, V2I-VLC, and V2V-VLC. Second, the DC gain at a pixel remains constant as long as the projected image of the transmitter LED occupies several pixels. In other words, if we choose a pixel with highest luminance among the projected image of transmitter LED, the value remains constant, and the signal-to-noise ratio does not change according to the distance.

DOI： 10.1109/JSAC.2015.2432511

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Stochastic resonance (SR) is an interesting phenomenon in that noise enhances system response. Despite attractive phenomenon of SR that noise enhances system response, enhancement of the weak signal below device sensitivity, and few researchers have addressed the SR effect in communication systems. This paper discusses the SR effect in communication systems. We focus on the problem in which communication cannot be established when the received signal strength is below receiver sensitivity. The purpose of this study is to evaluate the bit error rate (BER) performance of the SR receiver and reveal the SR effect in communication systems. We propose an analysis method for the SR receiver using a non-dynamical device that exhibits SR effect. The numerical results show that the SR effect can improve the BER compared to a system without SR. The contribution of the paper is two folds: The first contribution of our present study is that the BER of the SR receiver using a non-dynamical device can analytically be derived. The second contribution of our study is that the number of samples per symbol, the received signal amplitude, and the receiver sensitivity are three important parameters. We further derive the maximum performance gain by the SR system. Although our focus is on primary communication systems; however, our findings can be applied to other systems.

DOI： 10.1587/nolta.6.303

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Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we focus on the image sensor based vehicle-to-infrastructure visible light communication (V2I-VLC) for Intelligent Transport System (ITS). In this communication system, individual detection and tracking of multiple transmitters is critical. In other words, it is identification of the LED headlight between the frames. However, when occlusion occurs due to vehicle's movement, it becomes NLOS. I have the problem that it comes to have difficulty in identification of LED headlight then. Therefore, in this paper, we propose LED identification method that predict the position of the LED headlight on the image sensor when occlusion occurs. I install a high-speed camera in the roadside and test it and evaluate proposal technique. As a result, false negative rate is 1.38%,false positive rate is 3.26%. I confirmed that I could perform LED identification even if occlusion occurred.

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper proposes Alamouti-type space time (ST) coding to visible light communication (VLC) using light emitting diodes (LEDs) and image sensor-based direct detection with a high-speed camera. Although multiple LEDs of an array are used as transmitters to communicate to individual pixel elements of an image sensor which act as multiple receive elements, the received signal is essentially the image of the transmitting element, whose size in pixel reduces with distance. When the receiver captures the LED array at a distance where images of two neighboring LEDs in the array are not separated at the image plane, such distortion depreciates the symbol decision quality. Our proposed scheme aims at expanding the communication range limited by the pixel resolution of image sensor. Our implemented prototype demonstrates that ST coding is feasible to achieve 48-meter error-free transmission range while the repetition transmission achieves 26-meter error-free range.

Language：Japanese  

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In this paper, we focus on the image sensor based vehicle-to-infrastructure visible light communication (V2I-VLC) for Intelligent Transport System (ITS). In this communication system, individual detection and tracking of multiple transmitters is critical. In other words, it is identification of the LED headlight between the frames. However, when occlusion occurs due to vehicle's movement, it becomes NLOS. I have the problem that it comes to have difficulty in identification of LED headlight then. Therefore, in this paper, we propose LED identification method that predict the position of the LED headlight on the image sensor when occlusion occurs. I install a high-speed camera in the roadside and test it and evaluate proposal technique. As a result, false negative rate is 1.38%,false positive rate is 3.26%. I confirmed that I could perform LED identification even if occlusion occurred.

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：English  

The present paper considers receiving characteristics of an image-sensor-based visible light communication (VLC) using an LED and a high-speed-image sensor. In general, a size of LED on an image decreases with increasing a communication distance. In this case, the receiver is difficult to recover data because the intensity of brightness of LED (i.e., luminance) cannot be enough recognized from the image. However, the previous studies about the image-sensor-based VLC have not enough discussed the communication distance and the recognition of LED on the image, i.e., the receiving characteristics. We focus on the communication distance and investigates the relationship between the distance and the receiving characteristics in the image-sensor-based VLC.

Language：English   Publishing type：Research paper (scientific journal)  

We propose a road-to-vehicle Visible Light Communication (VLC) system for ITS. Here, the communication between road and a vehicle is approached using an LED array as a transmitter and an on-vehicle high-speed camera as a receiver. Modulation is conducted at the transmitter by blinking LEDs in high frequency and demodulation is conducted at the receiver by capturing the blinking patterns of the transmitter, by processing the high-speed camera images captured in high frame rate. This paper proposes an effective image processing method for capturing those blinking patterns. Out door communication experiments of the proposed VLC system are also present.

Language：English   Publishing type：Part of collection (book)   Publisher：Cambridge University Press  

Overview Image sensors are used in digital cameras and a large number of imaging devices for industrial, media, medical, and consumer electronics applications. An image sensor consists of a number of pixels
each pixel contains a photodiode (PD), which is generally used as a receiver in visible light communications (VLC). Thus, an image sensor consisting of a number of pixels can also be used as a VLC receiver. A particular advantage of using image sensors, due to the massive number of available pixels, is the ability to spatially separate sources. Owing to the spatial separation of multiple sources, the VLC receiver uses only the pixels that sense LED transmission sources, discarding other pixels, including those sensing ambient noise. The ability to spatially separate sources also provides an additional feature to VLC, i.e., the ability to receive and process multiple transmitting sources. In this chapter, we introduce VLC using an image sensor [1]. After presenting an overview of image sensors in Section 9.2, we introduce the use of an image sensor as a VLC receiver in Section 9.3. We provide a design of an image sensor based VLC system in Section 9.4. In Sections 9.5 and 9.6, we respectively introduce the following two unique applications of VLC systems using an image sensor: (1) massively parallel visible light transmission that can theoretically achieve a maximum data rate of 1.28 Gigabits per second
and (2) accurate sensor pose estimation that cannot be realized by a VLC system using a single-element PD. Applications of image sensor based communication are also presented in Section 9.7 for traffic signal communication, position measurements in civil engineering, and bridge position monitoring. Finally, in Section 9.8, we summarize our conclusions.

DOI： 10.1017/CBO9781107447981.009

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We focus on the road-to-vehicle visible light communication that system is composed of LED matrix as transmitter and high-speed camera as receiver. In proposed method, there are two problems. First problem is in case of long distance. It is difficult to receive data correctly because neighboring LEDs on the received image are merged due to less number of pixels and/or blurring by defocus. In this paper, we propose estimation method of LED intensity from merged image. We evaluated the method by measuring Bit Error Rate and confirmed effectiveness of the method. We also performed real time communication and succeeded to extend communication distance from the previous work by applying the method. Second problem is that, the transmitting rate has been reduced to half of the frame rate of the camera, to avoid intersymbol interference because of exposure time of camera frame. We propose a method to improve the communication rate. The transmitting rate is set same to receiver's frame rate, and the sent data is estimated from pattern mixed image. Using 8b/10b encoding instead of conventional reversal pattern to reduce the flickering of transmitter's lighting is also proposed.

DOI： 10.1109/APSIPA.2015.7415396

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper proposes a novel data detection scheme based on the occurrence of blurred output images in image-sensor-based visible light communication systems. This system's receiver suffers from an inability to detect correct LED luminance values and demodulation of data because the captured image blurs owing to defocusing. The proposed method assumes that the light emitted by all LEDs that is diffused by the blur can be approximated by applying a Gaussian filter and expresses all LED luminance values as convolution equations based on this diffusion of the LED light. We estimate each LED light's condition by simultaneously solving these convolution equations and recover data according to the estimated result. To confirm the accuracy of the proposed method, we conduct computer simulations and an implementation experiment to evaluate the bit error rate performance of the proposed method.

DOI： 10.1109/GLOCOMW.2015.7414144

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper demonstrates the feasibility of layered space-time coding (STC) in an outdoor image-sensor-based (IS-based) visible light communication (VLC) system. We examined that for low-resolution IS-based VLC channel where intensity modulated signals from two different light emitting diodes (LEDs) are detected at one pixel on the image plane, STC allows to decouple them, thus receiving data with no errors. Consequently, STC offers extending the transmission distance. In the layered STC presented here, additional bit streams are aligned in the 2(n) x 2(n) LED array for increasing the transmission rate per symbol duration for the case where the spatial resolution is improved. A prototype of three layered STC is built with an 8 x 8 LED array, where each of the LEDs is modulated at 1 kbps and a high-speed camera with IS operating at 1000 fps. Our experimental results validate that additional bit streams (layer-2 and -3), aligned in the layer-1 STC matrix pair, are extracted with no errors when the receiver comes within 155m and 55 m, respectively, from the LED array, without decreasing 210m of the transmission distance of layer-1 bit stream.

DOI： 10.1109/ICC.2015.7249124

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DOI： 10.1587/nolta.6.520

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This invited paper focuses on a high-speed image sensor as a visible light communication (VLC) reception device to develop the intelligent transport systems (ITS) application using VLC technique. We refer to the VLC using a high-speed image sensor as image-sensor-based VLC. A major advantage of the image sensor is the ability to spatially separate multiple sources. Based on this ability, we proposed several methods for the image-sensor-based VLC in our previous researches. Especially, we focused on unique characteristics of the image sensor and proposed the hierarchical coding and the overlay coding to improve the data reception performance. However, to perform the image-sensor-based VLC in an actual environment, the receiver has to acquire the VLC transmitter from captured images before recovering data. Namely, the VLC transmitter acquisition and tracking are critical problem. the image-sensor-based VLC technique. This invited paper introduces two proposed methods to acquire the VLC transmitter from images captured by the image sensor.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer New York LLC  

We propose a road-to-vehicle Visible Light Communication (VLC) system for ITS. Here, the communication between road and a vehicle is approached using an LED array as a transmitter and an on-vehicle high-speed camera as a receiver. Modulation is conducted at the transmitter by blinking LEDs in high frequency and demodulation is conducted at the receiver by capturing the blinking patterns of the transmitter, by processing the high-speed camera images captured in high frame rate. This paper proposes an effective image processing method for capturing those blinking patterns. Out door communication experiments of the proposed VLC system are also present.

DOI： 10.1007/s13177-014-0079-y

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Image Information and Television Engineers  

In this paper, we discuss optical cammera communication systems using digital signage, which is composed of a liquid crystal display (LCD). The digital signage, which is used as a transmitter, displays advertisement contents as visual information. The optical camera communication system using digital signage has to transmit data information not to obstruct the visual information. In this paper, we propose blue color difference modulation for the optical camera communication system using digital signage. We clarify the performance of the proposed system by data transmission experiments.

DOI： 10.11485/itetr.39.38.0_21

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Language：Japanese   Publishing type：Research paper (scientific journal)  

We have been proposed cooperative diversity receiving ABBA code as cooperative diversity via simple relaying with QOSTBC(Quasi-Orthogonal Space-Time Block Code). This scheme offers codinggain by permutation of space-time coded signal sequences in the relay nodes. So the relay nodes don't need carrier recovery and complete the signal process in the intermediate frequency band. In this paper we discuss two improved scheme with various channel model. These schemes improve the previous scheme without loss of the merit in its relay process. Moreover we sum up cooperative diversity via simple relaying with QOSTBC to discuss these schemes with various channel model. We evaluate effect of these scheme in terms of signal matrixes and simulate bit error rate of the prposed and improved scheme with with various channel model, respectively.

Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper proposes Alamouti-type space time (ST) coding to visible light communication (VLC) using light emitting diodes (LEDs) and image sensor-based direct detection with a high-speed camera. Although multiple LEDs of an array are used as transmitters to communicate to individual pixel elements of an image sensor which act as multiple receive elements, the received signal is essentially the image of the transmitting element, whose size in pixel reduces with distance. When the receiver captures the LED array at a distance where images of two neighboring LEDs in the array are not separated at the image plane, such distortion depreciates the symbol decision quality. Our proposed scheme aims at expanding the communication range limited by the pixel resolution of image sensor. Our implemented prototype demonstrates that ST coding is feasible to achieve 48-meter error-free transmission range while the repetition transmission achieves 26-meter error-free range.

Language：English   Publishing type：Research paper (scientific journal)  

Visible light communication (VLC) using light-emitting diodes (LEDs) is drawing much attention. There are two types of VLC reception devices, a photodiode and an image sensor. VLC using image sensor is called image sensor based VLC. As the receiver only uses the image sensor pixels that sense LED transmission sources and discards other pixels, including those sensing noise sources, image sensor based VLC is an attractive solution for outdoor mobile applications. However, little evidence is available for channel modeling of image sensor based VLC in mobile outdoor environments, especially for motion modeling of VLC transmitter. In this paper, we propose a motion model of VLC transmitter. In particular, we consider three cases; infrastructure-to-vehicle VLC (I2V-VLC), vehicle-to-infrastructure VLC (V2I-VLC), and vehicle-to-vehicle VLC (V2V-VLC). As a result, we show that the motion model of the VLC transmitter on the captured image for the three aforementioned situations (i.e., I2V-VLC, V2I-VLC, and V2V-VLC) can be expressed in the identical pinhole camera model.

Language：Japanese   Publishing type：Research paper (scientific journal)  

We have been proposed cooperative diversity receiving ABBA code as cooperative diversity via simple relaying with QOSTBC(Quasi-Orthogonal Space-Time Block Code). This scheme offers coding gain by permutation of space-time coded signal sequences in the relay nodes. So the relay nodes don't need carrier recovery and complete the signal process in the intermediate frequency band. In this paper, we discuss two improved scheme with various channel model. These schemes improve the previous scheme without loss of the merit in its relay process. Moreover, we sum up cooperative diversity via simple relaying with QOSTBC to discuss these schemes with various channel model. We evaluate effect of these scheme in terms of signal matrixes and simulate bit error rate of the prposed and improved scheme with with various channel model, respectively.

Language：English  

The present paper considers an optical spatial channel in visible light communication (VLC) using LED and a high-speed camera. In general, the optical spatial channel affects the communication performance. However, the previous studies have not enough discussed the channel for VLC. This study focuses on the communication distance, which is one of channel parameters, and investigates the relationship between the distance and a receiving characteristic in the VLC.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper demonstrates the feasibility of layered space-time coding (STC) in an outdoor image-sensor-based (IS-based) visible light communication (VLC) system. We examined that for low-resolution IS-based VLC channel where intensity modulated signals from two different light emitting diodes (LEDs) are detected at one pixel on the image plane, STC allows to decouple them, thus receiving data with no errors. Consequently, STC offers extending the transmission distance. In the layered STC presented here, additional bit streams are aligned in the 2^n × 2^n LED array for increasing the transmission rate per symbol duration for the case where the spatial resolution is improved. A prototype of three layered STC is built with an 8 × 8 LED array. Our experimental results validate that additional bit streams (layer-2 and -3), aligned in the layer-1 STC matrix pair, are extracted with no errors when the receiver comes within 155m and 55m, respectively, from the LED array, without decreasing 210m of the transmission distance of layer-1 bit stream.

Language：English  

In image sensor based VLC, transmitter acquisition and tracking are critical issue. However, the fluctuation of the VLC transmitter in the image plane caused by vehicle movement, complicates correct data reception. Therefore, in this paper, we present results of channel fluctuation measurements for infrastructure-to-vehicle VLC (I2V-VLC), vehicleto- infrastructure VLC (V2I-VLC), and vehicle-to-vehicle VLC (V2V-VLC). We analyze channel fluctuation in terms of optical flow from measured data.

Authorship：Lead author   Language：Japanese  

可視光通信とは，LEDを人の目に分からないほど高速に点滅（変調）させることで情報伝送を行う通信のことである．可視光通信では発光ダイオード（light emitting diode: LED）を送信デバイスに用いるのだが，LEDはものすごい勢いで普及が進みつつあり，それこそ至る所にある．つまりLEDにデータ伝送機能を追加する可視光通信はユビキタスのインフラ基盤になりうるのである．

Language：English  

Light-emitting diode (LED) transmitters based optical wireless communication (OWC) systems offer the potential for new generation communication systems. Particularly, an image sensor based OWC systems consist of the LED transmitters and camera receivers are expected to contribute to intelligent transport system (ITS) for driving supports. For high achievable data rates, orthogonal frequency division multiplexing (OFDM) based OWC systems have attracted a great deal of attention. Despite attractive features of optical OFDM, only few attempts have so far been made to adopt it as a modulation scheme of an image sensor based OWC system. There remains a need for an evaluation of adopting an optical OFDM to the image sensor based OWC systems. Another important issue needs to be addressed is the performance degradation due to a frequency response of an actual image sensor device, especially a signal attenuation loss in higher frequency. In addition to such loss, a narrow band noise generated by its circuits also degrades the performance. The purpose of this paper is to investigate BER performances of the optical-OFDM using an actual image sensor device, the optical communication image sensor (OCI). From simulation results, it is found that the frequency response and the narrowband noise at 12MHz of the OCI lead to the significant reduction of BER performances. Additionally, the results shows that ACO-OFDM shows a little better performance compared to DCO-OFDM with the same bandwidth efficiency.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

For improvement of the coded modulation, we propose the signal sets with triangular constellation and label shaping. The proposed signal set can gain the merits of them despite of a few signal points and a simple modification. We indicate the channel capacity, PAPR (Peak to Average Power Ratio), BER (Bit Error Rate) in case of BICM-ID (Bit Interleaved Coded Modulation with Iterative Decoding) and PAPR with band limited of the 7APSK (Amplitude and Phase-Shift Keying) and modified 14APSK. Especially, the results shows modified 14APSK we proposed can improve 16QAM (Quadrature Amplitude Modulation) in terms of BER and PAPR, simultaneously.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we proposed a transmit diversity with a simple transmitter. Specifically, we connect simplex RF (Radio Frequency) circuits with two antennas and transmit the signals whose phases are rotated and IQ component are interleaved alternately via two antennas. In the receiver, the signals with the signal space diversity are received in spite of the simple transmitter. So we can achieve space diversity and reliable wireless communications. In the performance evaluation, we confirm the 4dB gain at BER=10^<-2> in bit error rate performance.

Authorship：Lead author   Language：Japanese  

This paper presents the visible light communication using image sensor and its application to intelligent transport systems (ITS). As an example, mage-sensor based VLC for automotive application that is currently carried out by the author is also introduced. The paper is a continuation of the paper by Prof. Matsumoto, "Evaluation of optical wireless communication," and by Prof. Haruyama, "Recent trends of visible light communication," appeared on 2014 March issue of Microoptics News.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In image sensor based VLC for automotive applications, transmitter acquisition and tracking are critical. However, the fluctuation of the VLC transmitter in the image plane caused by vehicle movement, complicates correct data reception. Therefore, in this paper, we present results of channel fluctuation measurements for automotive applications. Especially, we examined the channel fluctuation based on mobile movements in the image plane detected by phase only correlation (POC) in the subpixel accuracy.

Publishing type：Research paper (scientific journal)   Publisher：Information Processing Society of Japan (IPSJ)  

In image sensor based VLC for automotive applications, transmitter acquisition and tracking are critical. However, the fluctuation of the VLC transmitter in the image plane caused by vehicle movement, complicates correct data reception. Therefore, in this paper, we present results of channel fluctuation measurements for automotive applications. Especially, we examined the channel fluctuation based on mobile movements in the image plane detected by phase only correlation (POC) in the subpixel accuracy.

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese  

Language：English  

This study introduces an image sensor based visible light communication (VLC) and its application to pose, position, and range estimations. There are two types of visible-light receiver: a photodiode and an image sensor. A photodiode is usually used as a reception device of VLC, and an image sensor consisting of a large number of pixels can also be used as a VLC reception device. A photodiode detects the signal intensity of incoming light, while an image sensor not only detects the incoming signal intensity but also an accurate angle of arrival of light emitted from a visible light transmitter such as a white LED light. After angles of arrival of light are detected by an image sensor, positioning and data reception can be performed. The ability of an image sensor to detect an accurate angle of arrival will provide attractive applications of VLC such as pose, position calculation, and range estimation. Furthermore, because the image sensor has the ability to spatially separate sources, outdoor positioning even with strong sunlight is possible by discarding the associated pixels of noise sources.

Language：English  

Stochastic Resonance (SR) is well known as a phenomenon in which the weak signal in a nonlinear system can be detected by added noise. We consider the application of SR phenomenon to a wireless communication system. The receiver using SR phenomenon can detect the subthreshold signal which is not detectable by the conventional receiver. The effect of SR receiver has been verified, but it has never been verified in radio frequency which is used by a wireless system. In this paper, we consider the implementation of SR System for Radio Frequency and evaluate its performance of Signal to Noise Ratio (SNR).

Language：Japanese  

Language：English  

Stochastic resonance (SR) enhances system responses by increasing noise. By applying SR to a receiver, a subthreshold signal not receivable by a conventional linear receiver could be received. Previously, we proposed an analysis method of the SR receiver using a comparator, and evaluated its bit error rate performance. The comparator is known as a simple non-dynamical system exhibiting SR. However, a dynamical system can have better performance since it has a memory effect. In this sense, we propose an analysis method of the SR receiver using a Schmitt trigger known as a simple dynamical system, and evaluate its bit error rate performance. A performance comparison of the comparator and the Schmitt trigger is also shown.

Language：Japanese  

In image sensor based VLC for automotive applications, transmitter acquisition and tracking are criti- cal. However, the uctuation of the VLC transmitter in the image plane caused by vehicle movement, complicates correct data reception. Therefore, in this paper, we present results of channel uctuation measurements for automo- tive applications. Especially, we examined the channel uctuation based on mobile movements in the image plane detected by phase only correlation (POC) in the subpixel accuracy.

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This study introduces an image sensor based visible light communication (VLC) and its application to pose, position, and range estimations. There are two types of visible-light receiver: a photodiode and an image sensor. A photodiode is usually used as a reception device of VLC, and an image sensor consisting of a large number of pixels can also be used as a VLC reception device. A photodiode detects the signal intensity of incoming light, while an image sensor not only detects the incoming signal intensity but also an accurate angle of arrival of light emitted from a visible light transmitter such as a white LED light. After angles of arrival of light are detected by an image sensor, positioning and data reception can be performed. The ability of an image sensor to detect an accurate angle of arrival will provide attractive applications of VLC such as pose, position calculation, and range estimation. Furthermore, because the image sensor has the ability to spatially separate sources, outdoor positioning even with strong sunlight is possible by discarding the associated pixels of noise sources.

DOI： 10.1587/transcom.E97.B.1759

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Language：Japanese  

Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)  

A distance estimation scheme for vehicle to infrastructure using visible light communication is discussed. As vehicle vibration severely affect the distance estimation performance, we introduce a new LED lighting patterns for the distance estimation. As the result, we acheive nearly the same distance estimation performance for the case of non-driving.

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

This paper proposes a new LED acquisition method for visible light communication systems using an LED array as a transmitter and a high-speed camera as a receiver for road-to-vehicle communications. The first process of the receiver is to search the target LED array from the captured image (LED array acquisition). This paper focuses on the time-gradient and the space-gradient values in the captured images, and draws both gradient value as a scatter diagram. This scatter diagram enables us to regard the LED acquisition as discriminant analysis. From the above, this paper proposes a new acquisition method and confirms its effectiveness by the experiment in a driving situation.

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

The present article introduces VLC for automotive applications using an image sensor. In particular, V2I-VLC and V2V-VLC are presented. While previous studies have documented the effectiveness of V2I and V2V communication using radio technology in terms of improving automotive safety, in the present article, we identify characteristics unique to image-sensor-based VLC as compared to radio wave technology. The two primary advantages of a VLC system are its line-of-sight feature and an image sensor that not only provides VLC functions, but also the potential vehicle safety applications made possible by image and video processing. Herein, we present two ongoing image-sensor-based V2I-VLC and V2V-VLC projects. In the first, a transmitter using an LED array (which is assumed to be an LED traffic light) and a receiver using a high-frame-rate CMOS image sensor camera is introduced as a potential V2I-VLC system. For this system, real-time transmission of the audio signal has been confirmed through a field trial. In the second project, we introduce a newly developed CMOS image sensor capable of receiving highspeed optical signals and demonstrate its effectiveness through a V2V communication field trial. In experiments, due to the high-speed signal reception capability of the camera receiver using the developed image sensor, a data transmission rate of 10 Mb/s has been achieved, and image (320 x 240, color) reception has been confirmed together with simultaneous reception of various internal vehicle data, such as vehicle ID and speed.

DOI： 10.1109/MCOM.2014.6852088

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Language：Japanese  

Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

I-Scover, officially known as IEICE Knowledge Discovery, is a new reference search engine developed by the Institute of Electronics, Information and Communication Engineers (IEICE). It is not just a system for cross-searching articles published by IEICE. It also aims to maximize significance of the IEICE articles by organically linking related information with the articles, making them accessible on the Internet for many users. With I-Scover, berry-picking exploratory search, which has been difficult with conventional reference search engines, is possible. In this article, we will describe I-Scover in terms of its developmental background and aim, introduce its various features and characteristics, and discuss the promotional activity plan to spread I-Scover, as well as its future development plans.

Publishing type：Research paper (scientific journal)   Publisher：Journal of the Institute of Electronics, Information and Communication Engineers  

Scopus

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：English  

The present paper focuses on an application of Stochastic Resonance (SR) for an LED visible light communication (LED-VLC) receiver. SR is well-known as a phenomenon, which enhances the response by additive noise. We consider that a weak optical signal, which is distorted due to an influence of ambient light noise, can be detected by using SR system. This study makes a simple SR circuit for LED VLC and performs its circuit experiment for exploring the possibility and availability of the LED-VLC receiver using SR system.

Language：Japanese  

This paper proposes Alamouti-type space time (ST) coding to visible light communication (VLC) using light emitting diodes (LEDs) and image sensor with a high-speed camera. Although multiple LEDs of an array are used as transmitters, the received signal is essentially the image of the transmitting element, whose size in pixel reduces with distance. When the receiver captures the LED array at a distance where images of two neighboring LEDs in the array are not separated at the image plane, such distortion depreciates the symbol decision quality. Our proposed scheme aims at expanding the communication range limited by the pixel resolution of image sensor. Our implemented prototype demonstrates that ST coding is feasible to achieve 48,m error-free transmission range while the repetition transmission achieves 26,m error-free range.

Language：Japanese  

This paper focuses on road-to-vehicle visible light communication using an LED array as a transmitter and a high-speed camera as a receiver. In this communication, LED array acquisition has a significant role. The spatio-temporal images are essential for a robust LED array acquisition because the time-gradient and space-gradient values can be an important feature value of an LED array. In this paper, we focus on the time-gradient and the space-gradient values in the captured images and draws both gradient value as a scatter diagram. This scatter diagram enables us to regard the LED acquisition as discriminant analysis. From the above, this paper proposes a new acquisition method and confirms its effectiveness by the experiment in a driving situation.

Language：Japanese  

This paper discusses an issue of estimating the distance between an on-vehicle transmitter and a roadside equipment for vehicular-to-infrastructure visible light communication (V2I-VLC). The system integrates the VLC as well as distance estimation functions. In this paper, we discuss a technique overcoming a vehicle vibration by using a particular transmitting LED pattern and the sub-pixel estimation using the phase-only correlation. As the results, we achieve less than 0.5m errors for the distance up to 60 m by the proposed system.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper proposes Alamouti-type space time (ST) coding to visible light communication (VLC) using light emitting diodes (LEDs) and image sensor with a high-speed camera. Although multiple LEDs of an array are used as transmitters, the received signal is essentially the image of the transmitting element, whose size in pixel reduces with distance. When the receiver captures the LED array at a distance where images of two neighboring LEDs in the array are not separated at the image plane, such distortion depreciates the symbol decision quality. Our proposed scheme aims at expanding the communication range limited by the pixel resolution of image sensor. Our implemented prototype demonstrates that ST coding is feasible to achieve 48m error-free transmission range while the repetition transmission achieves 26 m error-free range.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper proposes Alamouti-type space time (ST) coding to visible light communication (VLC) using light emitting diodes (LEDs) and image sensor with a high-speed camera. Although multiple LEDs of an array are used as transmitters, the received signal is essentially the image of the transmitting element, whose size in pixel reduces with distance. When the receiver captures the LED array at a distance where images of two neighboring LEDs in the array are not separated at the image plane, such distortion depreciates the symbol decision quality. Our proposed scheme aims at expanding the communication range limited by the pixel resolution of image sensor. Our implemented prototype demonstrates that ST coding is feasible to achieve 48m error-free transmission range while the repetition transmission achieves 26 m error-free range.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper discusses an issue of estimating the distance between an on-vehicle transmitter and a road-side equipment for vehicular-to-infrastructure visible light communication (V2I-VLC). The system integrates the VLC as well as distance estimation functions. In this paper, we discuss a technique overcoming a vehicle vibration by using a particular transmitting LED pattern and the sub-pixel estimation using the phase-only correlation. As the results, we achieve less than 0.5m errors for the distance up to 60 m by the proposed system.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper focuses on road-to-vehicle visible light communication using an LED array as a transmitter and a high-speed camera as a receiver. In this communication, LED array acquisition has a significant role. The spatio-temporal images are essential for a robust LED array acquisition because the time-gradient and space-gradient values can be an important feature value of an LED array. In this paper, we focus on the time-gradient and the space-gradient values in the captured images and draws both gradient value as a scatter diagram. This scatter diagram enables us to regard the LED acquisition as discriminant analysis. Prom the above, this paper proposes a new acquisition method and confirms its effectiveness by the experiment in a driving situation.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper focuses on road-to-vehicle visible light communication using an LED array as a transmitter and a high-speed camera as a receiver. In this communication, LED array acquisition has a significant role. The spatio-temporal images are essential for a robust LED array acquisition because the time-gradient and space-gradient values can be an important feature value of an LED array. In this paper, we focus on the time-gradient and the space-gradient values in the captured images and draws both gradient value as a scatter diagram. This scatter diagram enables us to regard the LED acquisition as discriminant analysis. Prom the above, this paper proposes a new acquisition method and confirms its effectiveness by the experiment in a driving situation.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper discusses an issue of estimating the distance between an on-vehicle transmitter and a road-side equipment for vehicular-to-infrastructure visible light communication (V2I-VLC). The system integrates the VLC as well as distance estimation functions. In this paper, we discuss a technique overcoming a vehicle vibration by using a particular transmitting LED pattern and the sub-pixel estimation using the phase-only correlation. As the results, we achieve less than 0.5m errors for the distance up to 60 m by the proposed system.

Language：English  

The present paper focuses on an application of Stochastic Resonance (SR) for an LED visible light communication (LED-VLC) receiver. SR is well-known as a phenomenon, which enhances the response by additive noise. We consider that a weak optical signal, which is distorted due to an influence of ambient light noise, can be detected by using SR system. This study makes a simple SR circuit for LED VLC and performs its circuit experiment for exploring the possibility and availability of the LED-VLC receiver using SR system.

Language：Japanese  

This paper focuses on road-to-vehicle visible light communication using an LED array as a transmitter and a high-speed camera as a receiver. In this communication, LED array acquisition has a significant role. The spatio-temporal images are essential for a robust LED array acquisition because the time-gradient and space-gradient values can be an important feature value of an LED array. In this paper, we focus on the time-gradient and the space-gradient values in the captured images and draws both gradient value as a scatter diagram. This scatter diagram enables us to regard the LED acquisition as discriminant analysis. From the above, this paper proposes a new acquisition method and confirms its effectiveness by the experiment in a driving situation.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We are conducting a study on viheicle-infrastractuctre cooperateive systems using visible light communications for driving safty applications. This paper introduces our studies on such VLC supported ITS systems using a high-speed image sensor as a VLC receiver equiped on a vehicle. The image sensors are now adopted for a lane keeping, an obstables recognition, a range estimation and many other applications. If we could add a VLC function to those safety applications, then a driver can recognize his environment visually and also he recognize his environment by signals transmitted through an LED traffic lights, LED tail lights, LED signage board, etc in a form of VLC signals. Together, it can contribute to more extensive safety driving.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We are conducting a study on viheicle-infrastractuctre cooperateive systems using visible light communications for driving safty applications. This paper introduces our studies on such VLC supported ITS systems using a high-speed image sensor as a VLC receiver equiped on a vehicle. The image sensors are now adopted for a lane keeping, an obstables recognition, a range estimation and many other applications. If we could add a VLC function to those safety applications, then a driver can recognize his environment visually and also he recognize his environment by signals transmitted through an LED traffic lights, LED tail lights, LED signage board, etc in a form of VLC signals. Together, it can contribute to more extensive safety driving.

Language：Japanese  

Visible light communications (VLC) is the latest optical wireless communications technologies that uses low-power light emitting diodes, or LEDs, not only to provide light but also to broadcast data. LEDs are extremely energy-efficient and predicted to become widespread in general lighting application. Because LED is a solid-state lighting device, it can be modulated at high-speed compared with other lighting sources. VLC uses LEDs, which send data by flashing light at speeds undetectable to the human eye.Widespread use of LEDs in traffic applications and growing interest in Intelligent Transport System (ITS) presents an opportunity for VLC. Data transmission using LED traffic lights, LED road illumination, and LED brake lights are typical application.In this paper, an on-going research, road-to-vehicle visible light communication, will be introduced. The LED array, assumed to be an LED traffic light, is used as a transmitter and it sends data to a moving vehicle. By providing data together with a traffic signal that is visible to a driver, a safety driving support can be realized.Finally, the author suggests readers a glimpse of wealth on "dual use of LEDs" and concludes the paper.

Authorship：Lead author   Language：Japanese  

We are conducting a study on viheicle-infrastractuctre cooperateive systems using visible light commu- nications for driving safty applications. This paper introduces our studies on such VLC supported ITS systems using a high-speed image sensor as a VLC receiver equiped on a vehicle. The image sensors are now adopted for a lane keeping, an obstables recognition, a range estimation and many other applications. If we could add a VLC function to those safety applications, then a driver can recognize his environment visually and also he recognize his environment by signals transmitted through an LED traffic lights, LED tail lights, LED signage board, etc in a form of VLC signals. Together, it can contribute to more extensive safety driving.

Language：English  

The present paper proposes a novel multiple-LED-arrays acquisition for an infrastructure-to-vehicle visible light communication (I2V-VLC) using LED arrays (transmitter) and an in-vehicle high-speed image sensor (receiver). In order to achieve a robust detection of LED arrays, we employ the block matching algorithm, which is a way of finding a corresponding position between two successive frames. The proposed method divides a captured image into a number of small domains (blocks) and determines if the LED array is present or absent using the block matching. We perform I2V-VLC experiments with multiple-LED arrays and evaluate the acquisition capability of the proposed method.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

The present paper proposes a novel <I>M</I>-ary modulation scheme based on separation and reconstruction of deterministic chaotic dynamics for noncoherent chaos-based communications. The <I>M</I>-ary modulation scheme can transmit <I>b</I>-bit data at a time by using <I>M</I>=2<I>^b</I> distinct sequences. In order to generate <I>M</I> distinct sequences and recover <I>b</I>-bit data, the proposed system separates the chaotic dynamics having the chaotic sequence by using <I>M</I> interleavers, and reconstructs the original sequence based on the chaotic dynamics from the separated one by using <I>M</I> deinterleavers. In advance, each data symbol among <I>M</I> symbols is allocated to each interleaver-deinterleaver pair. The transmitter selects an interleaver corresponding to a data symbol and separates the order of samples of the chaotic sequence using the selected interleaver. The receiver feeds the received sequence into all <I>M</I> deinterleavers and outputs <I>M</I> reconstructed sequences. The proposed system can reconstruct the original chaotic sequence only when the correct deinterleaver, which becomes paired with the interleaver, is selected. Therefore, the receiver can recover <I>b</I>-bit data by analyzing the chaotic dynamics of each reconstructed sequence. We carry out computer simulations and evaluate performances of the proposed <I>M</I>-ary modulation scheme.

DOI： 10.1587/nolta.5.210

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Light-emitting diode (LED) transmitters based optical wireless communication (OWC) systems offer the potential for new generation communication systems. Particularly, an image sensor based OWC systems consist of the LED transmitters and camera receivers are expected to contribute to intelligent transport system (ITS) for driving supports. For high achievable data rates, orthogonal frequency division multiplexing (OFDM) based OWC systems have attracted a great deal of attention. Despite attractive features of optical OFDM, only few attempts have so far been made to adopt it as a modulation scheme of an image sensor based OWC system. There remains a need for an evaluation of adopting an optical OFDM to the image sensor based OWC systems. Another important issue needs to be addressed is the performance degradation due to a frequency response of an actual image sensor device, especially a signal attenuation loss in higher frequency. In addition to such loss, a narrow band noise generated by its circuits also degrades the performance. The purpose of this paper is to investigate BER performances of the optical-OFDM using an actual image sensor device, the optical communication image sensor (OCI). From simulation results, it is found that the frequency response and the narrowband noise at 12MHz of the OCI lead to the significant reduction of BER performances. Additionally, the results shows that ACO-OFDM shows a little better performance compared to DCO-OFDM with the same bandwidth efficiency.

DOI： 10.1109/APCCAS.2014.7032786

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

In image sensor based VLC, transmitter acquisition and tracking are critical issue. However, the fluctuation of the VLC transmitter in the image plane caused by vehicle movement, complicates correct data reception. Therefore, in this paper, we present results of channel fluctuation measurements for infrastructure-to-vehicle VLC (I2V-VLC), vehicle-to-infrastructure VLC (V2I-VLC), and vehicle-to-vehicle VLC (V2V-VLC). We analyze channel fluctuation in terms of optical flow from measured data.

DOI： 10.1109/APCCAS.2014.7032787

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We focus on the road-to-vehicle visible light communication that system is composed of LED matrix as transmitter and high-speed camera as receiver. Conventionally, the transmitting rate has been reduced to half of the frame rate of the camera, to avoid intersymbol interference because of exposure time of camera frame. We propose a method to improve the communication rate. The transmitting rate is set same to receiver's frame rate, and the sent data is estimated from pattern mixed image. Using 8b/10b encoding instead of conventional reversal pattern to reduce the flickering of transmitter's lighting is also proposed.

DOI： 10.1109/APCCAS.2014.7032788

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The present paper proposes a novel multiple-LED-arrays acquisition for an infrastructure-to-vehicle visible light communication (I2V-VLC) using LED arrays (transmitter) and an in-vehicle high-speed image sensor (receiver). In order to achieve a robust detection of LED arrays, we employ the block matching algorithm, which is a way of finding a corresponding position between two successive frames. The proposed method divides a captured image into a number of small domains (blocks) and determines if the LED array is present or absent using the block matching. We perform I2V-VLC experiments with multiple-LED arrays and evaluate the acquisition capability of the proposed method.

DOI： 10.1109/CCNC.2014.6866634

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Visible light communication (VLC) using light-emitting diodes (LEDs) is drawing much attention. There are two types of VLC reception devices, a photodiode and an image sensor. VLC using image sensor is called image sensor based VLC. As the receiver only uses the image sensor pixels that sense LED transmission sources and discards other pixels, including those sensing noise sources, image sensor based VLC is an attractive solution for outdoor mobile applications. However, little evidence is available for channel modeling of image sensor based VLC in mobile outdoor environments, especially for motion modeling of VLC transmitter. In this paper, we propose a motion model of VLC transmitter. In particular, we consider three cases; infrastructure-to-vehicle VLC (I2V-VLC), vehicle-to-infrastructure VLC (V2I-VLC), and vehicle-to-vehicle VLC (V2V-VLC). As a result, we show that the motion model of the VLC transmitter on the captured image for the three aforementioned situations (i.e., I2V-VLC, V2I-VLC, and V2V-VLC) can be expressed in the identical pinhole camera model.

DOI： 10.1109/GLOCOMW.2014.7063473

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Publishing type：Research paper (scientific journal)  

Web of Science

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper demonstrates the feasibility of binary spatially-modulated space-time (SM-ST) coding in an outdoor image-sensor-based visible light communication (VLC) system. We showed that at the transmission distance where intensity modulated symbols from two different light emitting diodes (LEDs) are detected at one pixel of the image plane of the image sensor, space time (ST) coding enables to decouple the two symbols and to extend error-free transmission distance. We furthermore aim at increasing transmission rate per symbol duration when the spatial resolution is improved when the receiver approaches the LED array of the transmitter, by superimposing space shift keying (SSK) signal with the diagonal and anti-diagonal set of the 2 x 2 matrix onto the LED patterns. We built an experimental testbed with LEDs modulated at 1 kbps and a high-speed camera operating at 1,000 fps. Our experimental results validate that SM-ST coding achieves 30m of the error-free transmission distance for the additional bit based on SSK, without deteriorating the reception quality and range of the space-time coded bits.

DOI： 10.1109/APCCAS.2014.7032784

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Publishing type：Research paper (scientific journal)   Publisher：The Illuminating Engineering Institute of Japan  

Visible light communications (VLC) is the latest optical wireless communications technology that uses low-power light emitting diodes, or LEDs, not only to provide light but also to broadcast data. LEDs are extremely energy-efficient and predicted to become widespread in general lighting application. Because LED is a solid-state lighting device, it can be modulated at high-speed compared with other lighting sources. VLC uses LEDs, which send data by flashing light at speeds undetectable to the human eye. Widespread use of LEDs in traffic applications and growing interest in Intelligent Transport System (ITS) presents an opportunity for VLC. Data transmission using LED traffic lights, LED road illumination, and LED brake lights are typical application. In this paper, an on-going research, road-to-vehicle visible light communication, will be introduced. The LED array, assumed to be an LED traffic light, is used as a transmitter and it sends data to a moving vehicle. By providing data together with a traffic signal that is visible to a driver, a safety driving support can be realized. Finally, the author suggests readers a glimpse of wealth on "dual use of LEDs" and concludes the paper.

DOI： 10.2150/jieij.98.17

Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：Japanese  

This study focuses on the visible light communication(VLC) system using LED and a high-speed camera inorder to develop robust and adaptable communication systemsin the disaster situation, such as an earthquake. Especially, we consider utilization of a flashlight, which is often used in disaster situations, as a transmitter. We develop a simple LED-VLC transmitter using a flashlight and perform a communication experiment using it.

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this paper, we focus on a distance estimation scheme in road to vehicle communicationsystem. We use LED transmitter and high-speed camera. The accuracy of camera based scheme is governedby the size of pixel. Therefore we introduce phase only correlation (POC) to estimate with high accuracy.

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：Japanese  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Technical Committees (TCs) on Ad Hoc Networks (AN) and Ubiquitous and Sensor Networks (USN) have been consolidated in new TC, Ambient Intelligence and Sensor Networks (ASN). USN was the result of integrating two TCs in different societies, Ubiquitous and Real-World Oriented Networking (URON) in Communication Society and Sensor Networks (SN) in Engineering Science Society. The author has been engaged in SN, USN, and ASN. The present article looks back the aims and backgrounds of those TCs. In expectation of the further advancement of ASN, a few concluding remarks are presented.

Language：English  

This talk introduces visible light communication (VLC) for automotive applications using an image sensor. In particular, vehicle-to-infrastructure visible light communication (V2I-VLC) and vehicle-to-vehicle visible light communication (V2V-VLC) are presented. Previous studies have documented the effectiveness of V2I and V2V communication using radio technology for improving automotive safety. In this talk, I identify characteristics unique to the introduced image sensor based VLC as compared to radio wave technology. The advantages of VCL are twofold: the line-of-sight feature of visible light links and an image sensor that provides not only the VLC function but also vehicle safety applications using image and video processing. We present two on-going image sensors based V2I-VLC and V2V-VLC projects.

Language：Japanese  

Noncoherent chaos communications, which do not need to use basis signals (unmodulated carriers) for demodulation, are unique communication systems using characteristics of chaos. However, the communication performance of the noncoherent system is lower as compared with the standard communication systems. Thus, it is important to advance noncoherent system in order to improve its performance. In our previous research, we have proposed a novel error-correcting method using a separation and reconstruction of the chaotic dynamics, which is one of characteristics of chaos. As simulation results, we have confirmed that the advantage gained in BER performance of our error-correcting method is about 2--2.5 dB compared to the conventional one (w/o coding). This paper focuses on a number of transmitting data and a combination of symbols, and analyzes an error-correcting capability for evaluating advantages of the separation and reconstruction of the chaotic dynamics in detail.

Language：Japanese  

Stochastic Resonance(SR) is a nonlinear phenomena in which the Signal-to-Noise Ratio(SNR) is enhanced by an increase of the noise. By using SR, we can detect the weak signal which cannot detect by the conventional receiver. In this paper, we consider the application of SR to the communication systems. we implement the Stochastic Resonance Receiver using Schmitt Trigger as the Stochastic Resonance system. We evaluate the performance of the weak signal responce and we discuss about the weak signal detection.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Stochastic Resonance(SR) is a nonlinear phenomena in which the Signal-to-Noise Ratio(SNR) is enhanced by an increase of the noise. By using SR, we can detect the weak signal which cannot detect by the conventional receiver. In this paper, we consider the application of SR to the communication systems. we implement the Stochastic Resonance Receiver using Schmitt Trigger as the Stochastic Resonance system. We evaluate the performance of the weak signal responce and we discuss about the weak signal detection.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Noncoherent chaos communications, which do not need to use basis signals (unmodulated carriers) for demodulation, are unique communication systems using characteristics of chaos. However, the communication performance of the noncoherent system is lower as compared with the standard communication systems. Thus, it is important to advance noncoherent system in order to improve its performance. In our previous research, we have proposed a novel error-correcting method using a separation and reconstruction of the chaotic dynamics, which is one of characteristics of chaos. As simulation results, we have confirmed that the advantage gained in BER performance of our error-correcting method is about 2--2.5 dB compared to the conventional one (w/o coding). This paper focuses on a number of transmitting data and a combination of symbols, and analyzes an error-correcting capability for evaluating advantages of the separation and reconstruction of the chaotic dynamics in detail.

Language：English  

In this paper, we focus attention on visible light communication systems using an LED array as a transmitter and a high-speed camera as a receiver for road-to-vehicle communications (R2V-VLC) in intelligent transport systems. To implement R2V-VLC, it is necessary for the receiver to search the target LED array from the captured images (LED array acquisition) before data demodulation. We propose a new approach for LED array acquisition. We focus on spatio-temporal image and spatio-temporal cross-section image and show LED array in the spatio-temporal image has high time-gradient value and low space-gradient value. Using such characteristic gradient values, we propose new LED array acquisition method. As the results of the experiment in driving situation, we can achieve acquisition miss rate = 0%.

Language：English  

In this paper, we focus on a distance estimation scheme using camera. Our distance estimation scheme is based on triangulation. The accuracy of camera based scheme is governed by resolution of a camera, or equivalently the size of pixel. Therefore we introduce phase only correlation (POC) to estimate with subpixel accuracy. As a result of experiment, we will show that our scheme achieves less than 0.3m estimation error at the distance of 60m. By using POC, the resolution of estimation reaches nearly 0.02 pixel, much less than one pixel.

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：English  

We consider an application of Stochastic Resonance to wireless communication system. Stochastic Resonance (SR) is well known as a phenomenon in which weak signal in nonlinear system can be detected by added noise. A receiver using Stochastic Resonance (SR Receiver) can detect a weak signal which is not detectable in the conventional receiver. In this paper, we consider the implementation of bi-polar pulse SR Receiver using Schmitt Trigger and evaluate the performance in Signal-to-Noise Ratio (SNR) and Bit Error Rate (BER).

Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：English  

IEICE launched the new metadata search system called "I-Scover" on April 3, 2013. For the time being, I-Scover provides the metadata search service of all papers published in IEICE transactions covering from the first edition published in 1968 up to the present edition, Technical Reports (from 2006) and international conference papers of ISPA and EMC. The total number of searchable contents reaches 150,000. This article briefly introduces I-Scover. Before going to the details, let me start with a quiz. What phrase do you guess if you say "I-Scover" for three times?

Language：Japanese  

Language：Japanese  

Language：Japanese  

In road-to-vehicle visible light communication data is transmitted toward moving vehicles from theLED array installed on roads. Robust data reception and fast communication are possible by using a high-speedcamera as it can reduce the vibration of vehicles. In this road-to-vehicle visible light communication, we proposean integrated system of communication and distance estimation by sending a known data pattern from the LEDarray. On issues which is distance estimation performance deterioration by the vibration of the running vehicle, tryto resolve them using the technique using the phase-only correlation method.

Language：Japanese  

In this paper, we focus attention on road-to-vehicle visible light communication(R2V-VLC) in intelligent transport systems. This system uses an LED array as a transmitter and a high-speed camera as a receiver. To implement R2V-VLC, it is necessary to acquire the target LED array from the captured images at receiver before data demodulation. To achieve accurate aquisition, we analyze LED array by use of Spatio-temporal image. As the result of the analysis, we show the LED array in the spatio-temporal image has high time-gradient value and low space-gradient value. After that we propose a new LED array acquisition method using such characteristic gradient values.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we focus attention on road-to-vehicle visible light communication(R2V-VLC) in intelligent transport systems. This system uses an LED array as a transmitter and a high-speed camera as a receiver. To implement R2V-VLC, it is necessary to acquire the target LED array from the captured images at receiver before data demodulation. To achieve accurate acquisition, we analyze LED array by use of Spatio-temporal image. As the result of the analysis, we show the LED array in the spatio-temporal image has high time-gradient value and low space-gradient value. After that we propose a new LED array acquisition method using such characteristic gradient values.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In road-to-vehicle visible light communication data is transmitted toward moving vehicles from the LED array installed on roads. Robust data reception and fast communication are possible by using a high-speed camera as it can reduce the vibration of vehicles. In this road-to-vehicle visible light communication, we propose an integrated system of communication and distance estimation by sending a known data pattern from the LED array. On issues which is distance estimation performance deterioration by the vibration of the running vehicle, try to resolve them using the technique using the phase-only correlation method.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we focus attention on road-to-vehicle visible light communication(R2V-VLC) in intelligent transport systems. This system uses an LED array as a transmitter and a high-speed camera as a receiver. To implement R2V-VLC, it is necessary to acquire the target LED array from the captured images at receiver before data demodulation. To achieve accurate acquisition, we analyze LED array by use of Spatio-temporal image. As the result of the analysis, we show the LED array in the spatio-temporal image has high time-gradient value and low space-gradient value. After that we propose a new LED array acquisition method using such characteristic gradient values.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In road-to-vehicle visible light communication data is transmitted toward moving vehicles from the LED array installed on roads. Robust data reception and fast communication are possible by using a high-speed camera as it can reduce the vibration of vehicles. In this road-to-vehicle visible light communication, we propose an integrated system of communication and distance estimation by sending a known data pattern from the LED array. On issues which is distance estimation performance deterioration by the vibration of the running vehicle, try to resolve them using the technique using the phase-only correlation method.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In road-to-vehicle visible light communication data is transmitted toward moving vehicles from the LED array installed on roads. Robust data reception and fast communication are possible by using a high-speed camera as it can reduce the vibration of vehicles. In this road-to-vehicle visible light communication, we propose an integrated system of communication and distance estimation by sending a known data pattern from the LED array. On issues which is distance estimation performance deterioration by the vibration of the running vehicle, try to resolve them using the technique using the phase-only correlation method.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In road-to-vehicle visible light communication data is transmitted toward moving vehicles from the LED array installed on roads. Robust data reception and fast communication are possible by using a high-speed camera as it can reduce the vibration of vehicles. In this road-to-vehicle visible light communication, we propose an integrated system of communication and distance estimation by sending a known data pattern from the LED array. On issues which is distance estimation performance deterioration by the vibration of the running vehicle, try to resolve them using the technique using the phase-only correlation method.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we focus attention on road-to-vehicle visible light communication(R2V-VLC) in intelligent transport systems. This system uses an LED array as a transmitter and a high-speed camera as a receiver. To implement R2V-VLC, it is necessary to acquire the target LED array from the captured images at receiver before data demodulation. To achieve accurate acquisition, we analyze LED array by use of Spatio-temporal image. As the result of the analysis, we show the LED array in the spatio-temporal image has high time-gradient value and low space-gradient value. After that we propose a new LED array acquisition method using such characteristic gradient values.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we focus attention on road-to-vehicle visible light communication(R2V-VLC) in intelligent transport systems. This system uses an LED array as a transmitter and a high-speed camera as a receiver. To implement R2V-VLC, it is necessary to acquire the target LED array from the captured images at receiver before data demodulation. To achieve accurate acquisition, we analyze LED array by use of Spatio-temporal image. As the result of the analysis, we show the LED array in the spatio-temporal image has high time-gradient value and low space-gradient value. After that we propose a new LED array acquisition method using such characteristic gradient values.

Language：English  

Stochastic Resonance (SR), known as a noise-enhanced phenomenon, can improve the performance of communication systems. By applying SR in the receiver, it is possible to detect a weak signal that is not detectable in the traditional linear receiver. In the SR systems, the input of multi-carrier has not ever been discussed. So this paper proposes the SR receiver for multi-carrier detection and evaluates its Bit-Error-Rate (BER) performance.

Language：English  

The IEICE launched new metadata search system called I-Scover (http://i-scover.ieice.org) from April 3rd, 2013. I-Scover provides metadata search of the IEICE transactions papers (from its first edition published in 1968), Technical Reports (from 2006) and international conference papers of ISPA and EMC. The total of the contents that can be searched is more than 150,000.This article briefly introduces I-Scover. Before going to detail, let me start with a quiz. What phrase do you guess if you say I-Scover for three times?

Language：Japanese  

Language：Japanese  

Language：English  

This paper focuses on a road-to-vehicle visible light communication (VLC) system using LED traffic light as the transmitter and camera as the receiver. The traffic light is composed of a hundred of LEDs on two dimensional plain. In this system, data is sent as two dimensional brightness patterns by controlling each LED of the traffic light individually, and they are received as images by the camera. Here, there are problems that neighboring LEDs on the received image are merged due to less number of pixels in case that the receiver is distant from the transmitter, and/or due to blurring by defocus of the camera. Because of that, bit error rate (BER) increases due to recognition error of intensity of LEDs To solve the problem, we propose a method that estimates the intensity of LEDs by solving the inverse problem of communication channel characteristic from the transmitter to the receiver. The proposed method is evaluated by BER characteristics which are obtained by computer simulation and experiments. In the result, the proposed method can estimate with better accuracy than the conventional methods, especially in case that the received image is blurred a lot, and the number of pixels is small. &copy; (2013) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

DOI： doi:10.1117/12.2005738

Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：English  

This paper analyzes the performance of the error-correcting method, which was proposed in the previous research, using the separation and the reconstruction of chaos for noncoherent chaos communications. Especially, we focus on a number of transmitting data and a combination of symbols (i.e., data pattern). We consider that the capability of the error correction depends on the number of data and the data pattern because the proposed method performs the error correction using successive data symbols. This study performs simulations for the number of data and the data pattern, and evaluates BER performance of the proposed method.

Language：English  

This paper develops a simple simulator for the visible light communication (VLC) system using a LED traffic light and a camera for intelligent transport systems (ITS). We use image processing techniques for simulating effects of optical spatial channel which is a unique channel in VLC. We describe a system model of the VLC simulator and perform the simulation with various parameters of the image processing.

Language：Japanese  

We consider an application of Stochastic Resonance to wireless communication system. Stochastic Resonance(SR) is well known as a phenomenon in which weak signal in nonlinear system can be detected by added noise. A receiver using Stochastic Resonance(SR Receiver) can detect a weak signal which is not detectable in the conventional receiver. In this paper, we consider the implementation of Bi-Polar Pulse SR Receiver using Schmitt Trigger and the evaluation of the performance in Signal-to-Noise Ratio(SNR) and Bit Error Rate(BER).

Language：Japanese  

Stochastic resonance has an effect of improving the detection by increasing noise in the system. By applying this stochastic resonance in the receiver, it is possible to detect the subthreshold signal which is not detectable in the traditional linear receiver. This paper proposes an analysis method of the stochastic resonance receiver for the detection of the bi-polar pulse, which has good compatibility to stochastic resonance, and evaluates its bit-error-rate performance. And, the optimal noise power which maximizes the effect of stochastic resonance is discussed.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE Computer Society  

This paper focuses on a road-to-vehicle visible light communication (VLC) system using LED traffic lights and high-speed cameras on cars. So as to improve the transmission reliability, an error correcting code like a low-density parity-check (LDPC) is applied to the road-to-vehicle VLC system. The decoder of the LDPC code needs channel information in order to maximize decoding performance. Usually, it is calculated from a signal-to-noise ratio (SNR) or bit error rate (BER) of a channel, where noise is a dominant factor of the channel characteristic. In the road-to-vehicle VLC system, not noise but interference among LEDs decides the channel characteristic. In this paper, we propose a channel information estimation method for the road-to-vehicle VLC system. The proposed method estimates a signal-to-interference ratio (SIR) from the receiving image, and calculates the channel information using the SIR. The proposed method is evaluated by experiment. As a result, the proposed method can achieve almost the same performance with the optimum case, and then maximize the decoding performance. © 2013 IEEE.

DOI： 10.1109/wivec.2013.6698229

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper aims to improve the transmission distance for the road-to-vehicle visible light communication system (R2V-VLC) using LED array and high-speed camera by reducing interference caused at the receiver. As we can transmit multiple data using LED array and high-speed camera, parallel data transmission can be possible. However, due to the diffusion of LED and the finiteness of the pixel size of image sensor, the focused LED will affect not only the actual corresponding pixel but also its surrounding pixels. We call this phenomenon as "interpixel interference (IPI)" and it causes degradation in error rate performance. To mitigate the IPI, we propose IPI cancellation scheme for the R2V-VLC system. As the results of the experiment, we can extend the error-free distance from 40m to 60m by the IPI cancellation.

DOI： 10.1109/wivec.2013.6698237

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society for Engineering Education  

DOI： 10.20549/jseeja.2013.0_268

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：20th ITS World Congress Tokyo 2013  

In this paper, we focus on a distance estimation scheme using camera. Our distance estimation scheme is based on triangulation. The accuracy of camera based scheme is governed by resolution of a camera, or equivalently the size of pixel. Therefore we introduce phase only correlation (POC) to estimate with subpixel accuracy. As a result of experiment, we will show that our scheme achieves less than 0.3m estimation error at the distance of 60m. By using POC, the resolution of estimation reaches nearly 0.02 pixel, much less than one pixel.

Scopus

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper proposes Alamouti-type space time (ST) coding to visible light communication (VLC) using light emitting diodes (LEDs) and image sensor-based direct detection with a high-speed camera. Although multiple LEDs of an array are used as transmitters to communicate to individual pixel elements of an image sensor which act as multiple receive elements, the received signal is essentially the image of the transmitting element, whose size in pixel reduces with distance. When the receiver captures the LED array at a distance where images of two neighboring LEDs in the array are not separated at the image plane, such distortion depreciates the symbol decision quality. Our proposed scheme aims at expanding the communication range limited by the pixel resolution of image sensor. Our implemented prototype demonstrates that ST coding is feasible to achieve 48-meter error-free transmission range while the repetition transmission achieves 26-m error-free range.

DOI： 10.1109/GLOCOM.2013.6831438

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Language：English   Publishing type：Research paper (international conference proceedings)  

This paper focuses on a road-to-vehicle visible light communication (VLC) system using LED traffic light as the transmitter and camera as the receiver. The traffic light is composed of a hundred of LEDs on two dimensional plain. In this system, data is sent as two dimensional brightness patterns by controlling each LED of the traffic light individually, and they are received as images by the camera. Here, there are problems that neighboring LEDs on the received image are merged due to less number of pixels in case that the receiver is distant from the transmitter, and/or due to blurring by defocus of the camera. Because of that, bit error rate (BER) increases due to recognition error of intensity of LEDs To solve the problem, we propose a method that estimates the intensity of LEDs by solving the inverse problem of communication channel characteristic from the transmitter to the receiver. The proposed method is evaluated by BER characteristics which are obtained by computer simulation and experiments. In the result, the proposed method can estimate with better accuracy than the conventional methods, especially in case that the received image is blurred a lot, and the number of pixels is small. © 2013 SPIE-IS&amp
T.

DOI： 10.1117/12.2005738

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Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)   Publisher：20th ITS World Congress Tokyo 2013  

Scopus

Publishing type：Research paper (scientific journal)   Publisher：一般社団法人 電子情報通信学会  

DOI： 10.1587/bplus.6.222

Language：English  

This paper develops a simple simulation program for visible light communication (VLC) systems using LED (Transmitter) and a camera (Receiver). In the simulation, we generate an image of LED array transmitter which consists of LEDs arranged in a square matrix. In addition, effects of optical spatial channel, which is a unique channel in VLC, are constructed by using image processing techniques. We describe a system model of the VLC simulator and carry out the simulation with various parameters of the image processing.

Language：Japanese  

Language：Japanese  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper focuses on a road-to-vehicle visible light communication (VLC) system using LED traffic light as the transmitter and camera as the receiver. The traffic light is composed of a hundred of LEDs on two dimensional plain. In this system, data is sent as two dimensional brightness patterns by controlling each LED of the traffic light individually, and they are received as images by the camera. Here, there are problems that neighboring LEDs on the received image are merged due to less number of pixels in case that the receiver is distant from the transmitter, and/or due to blurring by defocus of the camera. Because of that, bit error rate (BER) increases due to recognition error of intensity of LEDs. To solve the problem, we propose a method that estimates the intensity of LEDs by solving the inverse problem of communication channel characteristic from the transmitter to the receiver. The proposed method is evaluated by BER characteristics which are obtained by computer simulation and experiments. In the result, the proposed method can estimate with better accuracy than the conventional methods, especially in case that the received image is blurred a lot, and the number of pixels is small.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper focuses on a road-to-vehicle visible light communication (VLC) system using LED traffic light as the transmitter and camera as the receiver. The traffic light is composed of a hundred of LEDs on two dimensional plain. In this system, data is sent as two dimensional brightness patterns by controlling each LED of the traffic light individually, and they are received as images by the camera. Here, there are problems that neighboring LEDs on the received image are merged due to less number of pixels in case that the receiver is distant from the transmitter, and/or due to blurring by defocus of the camera. Because of that, bit error rate (BER) increases due to recognition error of intensity of LEDs. To solve the problem, we propose a method that estimates the intensity of LEDs by solving the inverse problem of communication channel characteristic from the transmitter to the receiver. The proposed method is evaluated by BER characteristics which are obtained by computer simulation and experiments. In the result, the proposed method can estimate with better accuracy than the conventional methods, especially in case that the received image is blurred a lot, and the number of pixels is small.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We focus on a road-to-vehicle Visible Light Communication (VLC) system using LED traffic light as the transmitter and high-speed camera as the receiver. Data is sent as two dimensional brightness patterns by controlling each LED of the traffic light individually. At the receiver side, the pattern is captured in the high-speed camera image. It is necessary to find the position of transmitter in the image and to extract the intensity of each LED at high-frame rate in real-time. In this paper, we achieve tracking of the transmitter and intensity extraction in real-time by only software processing on PC.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We focus on a road-to-vehicle Visible Light Communication (VLC) system using LED traffic light as the transmitter and high-speed camera as the receiver. Data is sent as two dimensional brightness patterns by controlling each LED of the traffic light individually. At the receiver side, the pattern is captured in the high-speed camera image. It is necessary to find the position of transmitter in the image and to extract the intensity of each LED at high-frame rate in real-time. In this paper, we achieve tracking of the transmitter and intensity extraction in real-time by only software processing on PC.

Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：English  

This paper focuses on characteristics of the chaotic dynamics and improves our previous errorcorrecting method using them for noncoherent chaos communications. Our previous method is performed by using a chaotic sequence generated according to the chaotic dynamics. In this case, it is very difficult to recover data without a successive sequence based on the chaotic dynamics. We focus on this feature and consider that an improved method separates and reconstructs the chaotic dynamics of the sequence according to a specific rule. Namely, the separation and reconstruction of the chaotic dynamics can be applied for our improved method as additional information. As results of simulations, we have confirmed that the advantage gained in BER performance of our improved method is about 2&#8211;2.5 dB compared to a conventional method (without coding).

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：English  

As for cluster-based wireless sensor networks (WSNs), cluster lifetime is one of the most important subjects in recent researches. Besides reducing the energy consumptions of the clusters, it is necessary to make the clusters achieve equal lifetimes so that the whole network can survive longer. In this paper, we focus on the cluster lifetimes in multi-hop WSNs with cooperative multi-input single-output scheme. With a simplified model of multi-hop WSNs, we change the transmission schemes, the sizes and transmission distances ofclusters to investigate their effects on the cluster lifetimes. Furthermore, linear and uniform data aggregations are considered in our model. As a result, we analyze the cluster lifetimes in different situations and discuss the requirements on the sizes and transmission distances of clusters for equal lifetimes.

DOI： 10.1109/JCN.2012.6292251

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：Japanese  

Language：Japanese  

This paper aims to improve the data rate for the visible light communication system using LED array and high-speed camera. Previously, we have proposed the decoding algorithm using inverted signals for driving situation. However, using this method the data rate become a half, because we transmit original signals and inverted signals alternately for LED array tracking. In this paper, we propose the data rate improving method for overlay coding which is coding method that overlay two data. We confirm that we can improve data rate as compared with the previous method.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

This paper aims to improve the data rate for the visible light communication system using LED array and high-speed camera. Previously, we have proposed the decoding algorithm using inverted signals for driving situation. However, using this method the data rate become a half, because we transmit original signals and inverted signals alternately for LED array tracking. In this paper, we propose the data rate improving method for overlay coding which is coding method that overlay two data. We confirm that we can improve data rate as compared with the previous method.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We are conducting a study on visible light communications (VLC) using an LED traffic light and a high-speed camera equipped in a vehicle. Since we use the camera, we can capture and record surround images of the vehicle while receiving the data transmitted from the LED traffic light. This paper introduces the VLC system we are working on. Especially, this paper describes the advantages of road-to-vehicle VLC when the reception device is composed of high-speed camera.

Language：English  

In road-to-vehicle visible light communication data is transmitted toward moving vehicles from theLED array installed on roads. Robust data reception and fast communication are possible by using a high-speedcamera as it can reduce the vibration of vehicles. In this road-to-vehicle visible light communication, we propose anintegrated system of communication and distance estimation by sending a known data pattern.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In road-to-vehicle visible light communication data is transmitted toward moving vehicles from the LED array installed on roads. Robust data reception and fast communication are possible by using a high-speed camera as it can reduce the vibration of vehicles. In this road-to-vehicle visible light communication, we propose an integrated system of communication and distance estimation by sending a known data pattern from the LED array.

Language：English   Publishing type：Research paper (scientific journal)  

This paper addresses the cluster partitioning problem in wireless sensor networks deployed in a continuous area. We present the model of the network and describe its operational details firstly. Both single-hop and multi-hop transmissions with cooperative Multi-Input Single-Output (MISO) scheme are considered for the inter-cluster communications. Besides, uniform and linear data fusions are discussed. Then the calculations of energy consumptions are derived. Different from other researches, the energy consumptions of intra-cluster communication in each cluster are included and modeled as functions of the cluster size. Finally, we simulate all possible cluster partitions by changing the numbers of clusters and cooperative transmitting nodes, and find the maximal network lifetimes. As a result, the relationships between cluster partitions and network lifetimes are clarified in different situations.

Language：Japanese  

Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Our goal is to make efficient use of the energy and therefore achieve network operation with a high packet delivery ratio, regardless of day, night and weather variations, in solar powered wireless sensor networks. One method to optimize the consumption energy in the entire network is to employ a cooperative transmission scheme in which a node uses another node as a relay, when sending its data. If we do not consider the changes in the harvested energy in the network, the packet delivery ratio declines during nights and cloudy days. In this paper, however, we propose a new relay selection scheme with harvested solar energy prediction to maintain the required high packet delivery ratio by reducing the effect of the weather variations.

Language：Japanese  

Stochastic Resonance (SR), known as a noise-enhanced phenomenon, can improve the performance of commutation systems. In this paper, we present a preliminary study on SR and its application to BPSK receiver. We discuss a basic question arises from a receiver using SR that shall we perform SR process in a radio-frequency (RF) band or in a baseband (BB)? As results, we found that SR process in RF band shows better Bit Error Rate (BER) performance. This comes from the fact that a down conversion process that reduces the signal amplitude causes weak noise suppression by SR. While a double frequency term obtained also by the down conversion process do not affect much to the noise reduction performance.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we discuss on visible light communications using an LED array as the transmitter and a highspeed camera as the receiver. LED array , composed of many LEDs, transmits information by flashing LEDs, unfortunately an LED light diffuses around and affects neighboring LEDs. This problem causes degradation in error rate performance. We treat this ploblem as intersymbol interference (ISI) and try to cancel. In this paper, we first propose an area average quantization for the reduction of ISI. Next, we propose a new ISI cancellation method for overlay decoding and evaluate this method.

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we discuss on visible light communications using an LED array as the transmitter and a highspeed camera as the receiver. LED array , composed of many LEDs, transmits information by flashing LEDs, unfortunately an LED light diffuses around and affects neighboring LEDs. This problem causes degradation in error rate performance. We treat this ploblem as intersymbol interference (ISI) and try to cancel. In this paper, we first propose an area average quantization for the reduction of ISI. Next, we propose a new ISI cancellation method for overlay decoding and evaluate this method.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this paper, we focus on reducing intersymbol interference (ISI) and intercarrier interference (ICI) in a highly mobile environment by optimizing the Gaussian pulse shape of Biorthogonal Frequency Division Multiplexing (BFDM). In time-frequency dispersive channels, reducing the signal interference depends on the shaping of signal pulse. BFDM was invented to reduce the interference through a flexible design of signal pulse shaping. However, the shape of Gaussian pulses used in BFDM is not always optimized in every situation and as a result the interference is not always minimized. This research is to optimize the shape of Gaussian pulse. In particular, we optimize the Gaussian pulse in BFDM by maximizing the ratio of the ambiguity function of the transmitter (Gaussian) and its receiver pulses. Numerical results obtained show that the proposed method is effective for the optimization of BFDM. Furthermore, we show that the BFDM outperforms the conventional OFDM in time-frequency dispersive channels.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Our goal is the improvement of the data arrival rate in solar-powered wireless sensor networks. We consider the application of a cooperative transmission scheme that uses a relay node when a node sends data to reduce the consumption of energy of the entire network. In this paper, we propose the selection method of a relay node based on node battery and consumption energy. The overall data arrival rate is improved through the method. However, if we do not consider the variations in energy harvesting, the data arrival rate declines during nighttime. Then, we smooth out the day-and-night data arrival rate variations by introducing the new inactive node reactivation condition to the cooperative transmission scheme and achieve the required high data arrival rate.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：Japanese   Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Cooperative diversity using space-time codes offers effective space diversity with low complexity, but the scheme needs the space-time coding process in the relay nodes. We propose a simple cooperative relay scheme that uses space-time coding. In the scheme, the source node transmits the Alamouti coded signal sequences and the sink node receives the signal sequence via the two coordinated relay nodes. At the relay nodes, the operation procedure is just permutation and forwarding of the signal sequence. In the proposed scheme, none of the relay nodes need quadrature detection and space-time coding and the simple relay process offers effective space diversity. Moreover, simulations show the effectiveness Of the proposed relay process by some simulations.

DOI： 10.1587/transcom.E95.B.643

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Language：Japanese  

In this paper, we discuss road-to-vehicle visible light communications using an LED array as the transmitter and a high-speed camera as the receiver. The visible light communication (VLC) is a wireless communication that a transmitter consists of LED array and it transmit data by Turing LEDs on and off at high speed. We consider applying this VLC technique to the road (infrastructure) -to-vehicle communication for a purpose to support safety driving. So far, we have confirmed effectiveness of the VLC system through static and driving experiments. However, all those experimental results were obtained by off-line processing.

Language：Japanese  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we discuss road-to-vehicle visible light communications using an LED array as the transmitter and a high-speed camera as the receiver. The visible light communication (VLC) is a wireless communication that a transmitter consists of LED array and it transmit data by Turing LEDs on and off at high speed. We consider applying this VLC technique to the road (infrastructure) -to-vehicle communication for a purpose to support safety driving. So far, we have confirmed effectiveness of the VLC system through static and driving experiments. However, all those experimental results were obtained by off-line processing. In this paper, we introduce a real-time processing of the VLC receiver that captures not only the captured images by also the data transmitted from the LED array. The detail of the VLC receiver will be shown at the technology exhibition.

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we discuss road-to-vehicle visible light communications using an LED array as the transmitter and a high-speed camera as the receiver. The visible light communication (VLC) is a wireless communication that a transmitter consists of LED array and it transmit data by Turing LEDs on and off at high speed. We consider applying this VLC technique to the road (infrastructure) -to-vehicle communication for a purpose to support safety driving. So far, we have confirmed effectiveness of the VLC system through static and driving experiments. However, all those experimental results were obtained by off-line processing. In this paper, we introduce a real-time processing of the VLC receiver that captures not only the captured images by also the data transmitted from the LED array. The detail of the VLC receiver will be shown at the technology exhibition.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Visible light communication systems which enable data transmission by blinking LEDs at fast rate attract attention for their applications to Intelligent Transport Systems (ITS). In this paper, we assume that there are multiple information sources and we recognize them with on-vehicle high-speed camera in such systems. To lower probability of false recognition which represents how often non-information sources are recognized as information sources, we propose an improved multiple sources recognition method. We evaluate the proposed method by performing experiments.

Language：English  

Visible Light Communication (VLC) is a wireless communication method using LEDs. In this paper, we use a hybrid sensor designed for VLC which has advantages of photodiode and high-speed camera, that is, high transmission rate and easy detecting of the transmitter. The light receiving section of the sensor consists of communication pixels and video pixels. This sensor can communicate in static environment in previous research. However in dynamic environment, high- speed tracking of the transmitter is essential. We realize the high-speed tracking of the transmitter using the information of the communication pixels. Experimental results show the possibility of communication in dynamic environment.

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper aims to the improve the data rate for the visible light communication system using LED array and high-speed camera. Previously, we have proposed the decoding algorithm using inverted signals for driving situation. However, using this method the data rate become a half, because we transmit original signals and inverted signals alternately for LED array tracking. In this paper, we propose the data rate improving method for overlay coding which is coding method that overlay two data which are called as the long range data and the short range data. In the proposed method, for the long range data, we transmit original signals and inverted signals alternately. On the other hand, for the short range data, we transmit only original signals while we transmit inverted signals of long range data. We confirm that we can improve data rate as compared with the previous method.

DOI： 10.1109/GLOCOMW.2012.6477757

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society for Engineering Education  

DOI： 10.20549/jseeja.2012.0_718

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI PUBLISHING CORPORATION  

This paper addresses the cluster partitioning problem in wireless sensor networks deployed in a continuous area. We present the model of the network and describe its operational details firstly. Both single-hop and multihop transmissions with cooperative Multi-Input Single-Output (MISO) scheme are considered for the intercluster communications. Besides, uniform and linear data fusions are discussed. Then, the calculations of energy consumptions are derived. Different from other researches, the energy consumptions of intracluster communication in each cluster are included and modeled as functions of the cluster size. Finally, we simulate all possible cluster partitions by changing the numbers of clusters and cooperative transmitting nodes and find the maximal network lifetimes. As a result, the relationships between cluster partitions and network lifetimes are clarified in different situations.

DOI： 10.1155/2012/490823

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)  

Web of Science

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The objective of this research is to reduce inter-symbol interference (ISI) and intercarrier interference (ICI) in a highly mobile environment by optimizing the performance of Biorthogonal Frequency Division Multiplexing (BFDM). In time-frequency dispersive channels, reducing the signal interference depends on the shaping of the signal pulse. BFDM was invented to reduce the interference through a flexible design of the signal pulse shaping. However, the shape of the Gaussian pulses used in BFDM is not always optimized in every situation and as a result the interference is not always minimized. This research seeks to optimize the shape of the Gaussian pulse. In particular, we optimize the Gaussian pulse in BFDM by maximizing the ratio of the ambiguity function of the transmitter (Gaussian) and its receiver pulses. Numerical results obtained show that the proposed method is effective for the optimization of BFDM. Furthermore, we show that the optimized BFDM outperforms the conventional OFDM in time-frequency dispersive channels.

DOI： 10.1109/VETECS.2012.6240287

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Visible Light Communication (VLC) is a wireless communication method using LEDs. LEDs can respond in high-speed and VLC uses this characteristics. In VLC researches, there are two types of receivers mainly, one is photodiode receiver and the other is high-speed camera. A photodiode receiver can communicate in high-speed and has high transmission rate because of its high-speed response. A high-speed camera can detect and track the transmitter easily because it is not necessary to move the camera. In this paper, we use a hybrid sensor designed for VLC which has advantages of both photodiode and high-speed camera, that is, high transmission rate and easy detecting of the transmitter. The light receiving section of the hybrid sensor consists of communication pixels and video pixels, which realizes the advantages. This hybrid sensor can communicate in static environment in previous research. However in dynamic environment, highspeed tracking of the transmitter is essential for communication. So, we realize the high-speed tracking of the transmitter by using the information of the communication pixels. Experimental results show the possibility of communication in dynamic environment.

DOI： 10.1117/12.907697

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Language：English  

Solar-powered wireless sensor networks are attracting attention for outdoor long time operation such as environmental monitoring. Even if sensor nodes are charged by solar energy, nodes far from the BS (Base-Station) are stopped due to the lack of energy during nighttime. To prevent this problem, we consider the use of cooperative transmission. In cooperative transmission, energy consumption is balanced among the nodes because of the use of another node as a relay for data transmission of distant nodes. The conventional scheme to select a relay node is based on available battery energy and the expectation of energy consumption of each node. In this paper, we propose a relay selection scheme which is based on the prediction of harvested energy in addition to the available battery energy and the expected value of energy consumption. We evaluate the proposed scheme through packet delivery ratio and show its effectiveness.

Language：Japanese  

In this paper, we conduct a comparison between the Biorthogonal Frequency Division Multiplexing (BFDM) and the Wavelet Based Orthogonal Frequency Division Multiplexing (OFDM) in terms of intersymbol interference (ISI) and intercarrier interference (ICI) reduction in highly mobile environments with assumed time-frequency dispersive channels. ISI and ICI depend largely on the pulse shaping of the signal. BFDM can reduce the signal interference by applying a Gaussian pulse known as a properly localized time-frequency pulse with adaptable characteristics. On the other hand, Wavelet Based OFDM is known to lower interference due to its wavelet basis. In this paper, we propose an optimization method for the Gaussian pulse in BFDM to minimize ISI/ICI by maximizing the ratio of the ambiguity function. In addition, we compare its performance with BFDM and Wavelet Based OFDM.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we conduct a comparison between the Biorthogonal Frequency Division Multiplexing (BFDM) and the Wavelet Based Orthogonal Frequency Division Multiplexing (OFDM) in terms of intersymbol interference (ISI) and intercarrier interference (ICI) reduction in highly mobile environments with assumed time-frequency dispersive channels. ISI and ICI depend largely on the pulse shaping of the signal. BFDM can reduce the signal interference by applying a Gaussian pulse known as a properly localized time-frequency pulse with adaptable characteristics. On the other hand, Wavelet Based OFDM is known to lower interference due to its wavelet basis. In this paper, we propose an optimization method for the Gaussian pulse in BFDM to minimize ISI/ICI by maximizing the ratio of the ambiguity function. In addition, we compare its performance with BFDM and Wavelet Based OFDM.

Language：English  

This paper aims to improve the visible light communication system using LED array and high-speed camera by proposing what we call "overlay coding." "Overlay coding" is a new coding method to realize a hierarchical coding, through which a high-priority data can be received even if the receiver is far from a transmitter. Conventionally, the hierarchical coding has been realized through the wavelet transform that has a limitation of number and disposition of LEDs, and as a result it does not always match with the design of the transmitters (e.g. traffic lights, etc.) used in real life. To solve the limitation problem, we propose a more flexible way of designing the application of LEDs depending on the transmitters. In particular, overlay coding is realized through the procedures of coding and decoding. In coding, we replace one LED with a flexible number of LEDs, and the number depends on whether the data is high-priority or low-priority, then high-priority data and low-priority data are overlaid. In decoding, we first obtain the high-priority data, and then the low-priority data using retrieved high-priority data. The experimental result shows that the distance for receiving error-free data is extended from 30m to 70m in the overlay coding.

Language：English   Publishing type：Research paper (scientific journal)  

This letter investigates the cluster lifetime of single-hop wireless sensor networks with cooperative Multi-Input Single-Output (MISO) scheme. The energy consumptions of both intra-cluster and out-cluster communications are considered. Moreover, uniform and linear data aggregations are discussed. It is found the optimal transmission scheme varies with the distance from the cluster to the base station. More interestingly and novelly, the effect of cluster size on the cluster lifetime has been clarified.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

This letter investigates the cluster lifetime of single-hop wireless sensor networks with cooperative Multi-Input Single-Output (MISO) scheme. The energy consumptions of both intra-cluster and out-cluster communications are considered. Moreover, uniform and linear data aggregations are discussed. It is found the optimal transmission scheme varies with the distance from the cluster to the base station. More interestingly and novelly, the effect of cluster size on the cluster lifetime has been clarified.

DOI： 10.1587/transcom.E94.B.2881

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Language：Japanese  

Language：English  

Our goal is the improvement of the node activity rate in solar-powered wireless sensor networks. We consider the application of a cooperative transmission scheme that uses a relay node when a node sends data to reduce the consumption of energy of the entire network. However, if we do not consider the variations in energy harvesting, the node activity rate declines during nighttime. In this paper, we smooth out the day-and-night node activity rate variations by introducing the new inactive node reactivation condition and achieve the required high node activity rate.

Language：Japanese  

Of the courses, that have been presented in Nagoya University OCW site, are taken up and discussed in terms of how the educative effect can be improved by stimulating student's intellectual curiosity.

Publishing type：Research paper (scientific journal)   Publisher：FIT(電子情報通信学会・情報処理学会)運営委員会  

Intelligent Transport System(ITS) has been proposed to give solutions for traffic problems such as traffic accidents and traffic jams. On the other hand, high frame rate image techniques are getting popular in last several years. In this paper, we propose a Visible Light Communication(VLC) system using high frame rate techniques for Intelligent Transport System. Here, the communication between infrastructure and the vehicle is approached using an LED array as a transmitter and on-vehicle high speed camera as a receiver. The LEDs in the transmitter emit light in 500Hz and the emission patterns are used to achieve communication, capturing them in high frame rate(1000fps) utilizing a high-speed camera. The images captured by high-speed camera are processed to find the transmitter, track the found transmitter, and capture the LED lighting pattern of transmitter in consecutive frames. In our previous work, we proposed algorithms to finding and tracking. In this paper, we introduce method to capture the lighting pattern of the transmitter. Then, out door communication experiments were conducted to confirm the effectiveness of the proposed V LC system.

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society for Engineering Education  

DOI： 10.4307/jsee.59.4_105

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Language：Japanese  

Visible light communication systems which enable data transmission by blinking LEDs at fast rate attract attention for their applications to Intelligent Transport Systems (ITS). In this paper, we assume that there are multiple information sources and we recognize them with on-vehicle high-speed camera in such systems. To distinguish multiple sources, we propose multiple sources recognition method based block matching. We evaluate the proposed method by performing experiments.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Visible light communication systems which enable data transmission by blinking LEDs at fast rate attract attention for their applications to Intelligent Transport Systems (ITS). In this paper, we assume that there are multiple information sources and we recognize them with on-vehicle high-speed camera in such systems. To distinguish multiple sources, we propose multiple sources recognition method based block matching. We evaluate the proposed method by performing experiments.

Language：Japanese  

Language：Japanese  

In this paper, we focus on reducing intersymbol interference (ISI) and intercarrier interference (ICI) in a highly mobile environment by optimizing the Gaussian pulse shape of Biorthogonal Frequency Division Multiplexing (BFDM). In time-frequency dispersive channels, reducing the signal interference depends on the shaping of signal pulse. BFDM was invented to reduce the interference through a flexible design of signal pulse shaping. However, the shape of Gaussian pulses used in BFDM is not always optimized in every situation and as a result the interference is not always minimized. This research is to optimize the shape of Gaussian pulse. In particular, we optimize the Gaussian pulse in BFDM by maximizing the ratio of the ambiguity function of the transmitter (Gaussian) and its receiver pulses. Numerical results obtained show that the proposed method is effective for the optimization of BFDM. Furthermore, we show that the BFDM outperforms the conventional OFDM in time-frequency dispersive channels.

Authorship：Lead author   Language：Japanese  

We are conducting a study on visible light communications (VLC) using an LED traffic light and a high-speed camera equipped in a vehicle. Since we use the camera, we can capture and record surround images of the vehicle while receiving the data transmitted from the LED traffic light. This paper introduces the VLC system we are working on.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

We are conducting a study on visible light communications (VLC) using an LED traffic light and a high-speed camera equipped in a vehicle. Since we use the camera, we can capture and record surround images of the vehicle while receiving the data transmitted from the LED traffic light. This paper introduces the VLC system we are working on.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In highly mobile environments assumed time-frequency dispersive channels, reducing intersymbol interference(ISI) and intercarrier interference (ICI) depends on the signal pulse shape. Biorthogonal Frequency Division Multiplexing (BFDM) is an efficient modulation in terms of designing pulses flexibly. So BFDM can use Gaussian pulse which is a time-frequency well localized. However, the Gaussian pulse shape is not optimized in every channel. In this paper, we optimize the Gaussian pulse shape against the channels by maximizing the ratio of the ambiguity function of the pulses. Numerical result show that the proposed method is effective for the optimization of the Gaussian pulse shape.

Publishing type：Research paper (scientific journal)   Publisher：2011 IEEE Consumer Communications and Networking Conference, CCNC'2011  

DOI： 10.1109/CCNC.2011.5766593

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Authorship：Lead author   Language：English  

Visible light communications (VLC) is the latest optical wireless communications technologies that uses low-power light emitting diodes, or LEDs, not only to provide light but also to broadcast data. LEDs are extremely energy-efficient and predicted to become widespread in general lighting application. It is expected that LED market will reach $29 billion in 2017 that is comparable to today's NAND and DRAM markets [1]. Because LED is a solid-state lighting device, it can be modulated at high-speed compared with other lighting sources. VLC uses LEDs, which send data by flashing light at speeds undetectable to the human eye.

The pioneer of VLC using LEDs is Professor Masao Nakagawa of Keio University. His first paper on this subject appeared in the early 2000, together with his successor Prof. Shinichiro Haruyama, the instructor of this tutorial. Later in 2003, he formed Visible Light Communication Consortium (VLCC). Now VLCC is lead by Prof. Haruyama. Please see the following video, an interview of Prof. Haruyama about VLC, which has been broadcast by NHK World in June 4, 2009. http://www.naka-lab.jp/movie/nhk_world.wmv

So far various experimental VLC systems and prototypes are demonstrated. Such includes 4.8kbps visible light ID as an infrastructure to mobile-terminal application, independent sound transmission through RGB visible lights and 100Mbps VLC wireless LAN system. Using LED array, the data rate of 1 Gbps achieved by Keio University (Prof. Haruyama) that is the fastest at the moment [1]. In terms of longer range, there has been a demonstration by VLCC that achieved 1kbps transmission of the distance 2km, that is the world's longest distance for VLC. Samsung and ETRI are also active in developing VLC applications. They have demonstrated 120Mbps full duplex mobile-to-mobile transmission and 100Mbps signboard transmission. Please see the following video of Nakagawa lab. http://www.youtube.com/watch?v=QEh5f49LsB4

Widespread use of LEDs in traffic applications and growing interest in Intelligent Transport System (ITS) presents an opportunity for VLC. Data transmission using LED traffic lights, LED road illumination, and LED brake lights are typical application. Dr. Yamazato, the instructor of this tutorial, is a leader in VLC application to ITS and he recently achieved 16kbps data transmission and distance up to 70m in a driving situation with a vehicle moving with 30km/h. Today VLC using LED is a hot topic and VLC projects have been initiated in Europe and US. In 2006 Siemens launched VLC project. Later in 2008, European Commission established OMEGA project with a consortium of 20 European partners from industry and the scientific community [3]. Meanwhile, in 2008, the US National Science Foundation has approved a grant of $18.5 million to help establish and the Engineering Research Center focuses on VLC. The members of the Center include the Rensselaer Polytechnic Institute in New York, Boston University and the University of New Mexico. The University of California also have launched five-year research project called the Ubiquitous Communication by Light (UC-Light) that is founded with $3.5 million from the University. The project is anticipated to begin in 2009 and run for five years.

VLC is in the process of standardization by the IEEE 802.15 TG7 and VLCC as well as other standard organizations. The first VLC specification standard was released from JEITA in conjunction with VLCC in 2007. Later in 2008, VLCC released their first specification standard adopting and expanding the IrDA physical layer. IrDA transceiver transmission wavelength (IrDA physical layer) is expanded to accommodate the visible light wavelength. By adapting this specification, the existing IrDA optical modules can be used for VLCC data transmission with slight modification. In January 2009, IEEE 802.15 (Wireless Personal Area Networks) Task Group 7 (Visible Light Communication) has been launched. At the 6th meeting held in November 2009 they adopted the baseline draft text for the development of the 802.15.7 standard.

The goal of this tutorial is to introduce current VLC technology and its trends. Starting with an overview of VLC, participants will learn basics of VLC, on-going standardization activities and VLC. We will provide some experimental results and furthermore detail to enhance VLC application.

Authorship：Lead author   Language：Japanese  

Authorship：Lead author   Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal 3D Time Difference of Arrival (TDOA) positioning, at least four receivers with an unblocked direct path to the transmitter are required. A requirement that is not always met. In this work, a novel method for TDOA positioning using only three receivers is presented. TDOA positioning with three receivers is possible by exploiting the knowledge of some of the indoor features, namely positions of big flat reflective surfaces, for example ceiling and walls. The proposed method was verified using data from a measurement campaign.

Publishing type：Research paper (scientific journal)  

DOI： 10.3169/itej.65.354

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Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal 3D Time Difference of Arrival (TDOA) positioning, at least four receivers with an unblocked direct path to the transmitter are required. A requirement that is not always met. In this work, a novel method for TDOA positioning using only three receivers is presented. TDOA positioning with three receivers is possible by exploiting the knowledge of some of the indoor features, namely positions of big flat reflective surfaces, for example ceiling and walls. The proposed method was verified using data from a measurement campaign.

DOI： 10.1587/transfun.E94.A.964

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Language：Japanese  

Language：Japanese  

Language：Japanese  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

CiNii Research

Language：Japanese  

Language：Japanese  

Language：Japanese  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we discuss on visible light communications using an LED array as the transmitter and a highspeed camera as the receiver. A challenge is that the longer the distance between the transmitter and the receiver, the more reduction in the resolution of the receive image occurs. To solve the problem, we allocate high priority data to low frequency components of spatial frequency. Then, we can receive high priority data even if the receiver is far from the transmitter. For that, we have used the Wavelet transform in our previous researches. However, the conventional scheme limits the number and the disposition of LEDs which can be allocated data. In other words, the hierarchical coding using the Wavelet transform has a low degree of freedom of design. In this paper, to improve a degree of freedom of design, we propose the overlay coding which does not limit the number and the disposition of LEDs.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we consider road-to-vehicle visible light communication systems on driving situation using a LED array transmitter and a high-speed camera receiver. In our previous research, we have proposed inverted signal to track an LED array transmitter. We propose decoding method with inverted signal to improve BER performance. Furthermore, we confirm that we can suppress the flicker of LED in PDF.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we consider road-to-vehicle visible light communication systems on driving situation using a LED array transmitter and a high-speed camera receiver. In our previous research, we have proposed inverted signal to track an LED array transmitter. We propose decoding method with inverted signal to improve BER performance. Furthermore, we confirm that we can suppress the flicker of LED in PDF.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

In this paper, we discuss on visible light communications using an LED array as the transmitter and a highspeed camera as the receiver. A challenge is that the longer the distance between the transmitter and the receiver, the more reduction in the resolution of the receive image occurs. To solve the problem, we allocate high priority data to low frequency components of spatial frequency. Then, we can receive high priority data even if the receiver is far from the transmitter. For that, we have used the Wavelet transform in our previous researches. However, the conventional scheme limits the number and the disposition of LEDs which can be allocated data. In other words, the hierarchical coding using the Wavelet transform has a low degree of freedom of design. In this paper, to improve a degree of freedom of design, we propose the overlay coding which does not limit the number and the disposition of LEDs.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Visible Light Communication(VLC) using LEDs has been proposed as a wireless communication method. As an application of VLC in ITS, we propose a road-to-vehicle visible light communication system using an LED traffic sign as a transmitter and an image sensor as a receiver. For conducting the communication, it is necessary to have high-speed tracking of the LED traffic sign by the image sensor. In this paper, we propose new high-speed tracking method for this system.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Visible Light Communication(VLC) using LEDs has been proposed as a wireless communication method. As an application of VLC in ITS, we propose a road-to-vehicle visible light communication system using an LED traffic sign as a transmitter and an image sensor as a receiver. For conducting the communication, it is necessary to have high-speed tracking of the LED traffic sign by the image sensor. In this paper, we propose new high-speed tracking method for this system.

Language：Japanese   Publishing type：Research paper (scientific journal)  

In Satellite Terrestrial Integrated Mobile Communication System, a single mobile terminal can communicate to both satellite and terrestrial communication systems depend upon his location, QoS and availability of resources among satellite and terrestrial communication systems. But it is hard to achieve high spectrum efficiency of Satellite Terrestrial Integrated Mobile Communication System using fixed resource allocation schemes because variation of satellite traffic and terrestrial traffic is different.

Language：English   Publishing type：Research paper (scientific journal)  

We propose a visible light road-to-vehicle communication system at intersection as an ITS (Intelligent Transport System) technique. In this system, the communication between a vehicle and an LED traffic light is conducted using an LED traffic light as a transmitter and an on-vehicle high-speed camera as a receiver. The LEDs in the transmitter emit light at high frequency, and those emitted light is captured by the high-speed camera for communications. Here, the luminance value of the LEDs in the transmitter should be found, and then it should be tracked in consecutive frames while the vehicle is moving by processing the images from the high-speed camera. In this paper, we propose new algorithms for finding and tracking the transmitter, which result in increased communication speed and data rate compared to the previous methods. Experiments using appropriate images showed the effectiveness of the proposals.

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Language：Japanese  

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electronics, Information and Communication Engineers  

Our goal is improvement of the node activity rate in solar-powered wireless sensor networks. One method to reduce the consumption energy of the entire network is a cooperative transmission that uses a relay node when a node sends data. But if we don't consider the change in harvesting energy, the node activity rate is declined during nighttime. In this paper, we smooth the day-and-night node activity rate by introducing the new inactive node reactivation condition and achieve the required high node activity rate.

Language：English  

In this paper, we focus on a road-to-vehicle visible light communication (VLC) system using LED traffic lights. In this system, an LED traffic light consists of a 2-dimensional LED array (2D LED array), and cars are equipped with high-speed 2-dimensional cameras (2D image sensors). An important issue of this system is frame loss. Sometimes, 2D image sensor in a car fails to get a frame. So as to mitigate the influence of frame loss, we propose to apply erasure coding to the road-to-vehicle VLC system. In the proposed system, a data sequence is encoded by LDPC code whose length is much longer than the size of 2D LED array. In addition, code synchronization is required for the proposed system. We also propose a code synchronization scheme, which makes use of error detection capability of LDPC code. We evaluate the performance of our proposed system, and show that it can recover frame loss for high SNR when less than 8 frames among total 18 frames are lost. In addition, we show that our proposed code synchronization scheme can ignore its errors.

Language：English  

In this paper, we propose the new visible light road-to-vehicle communication system. We use the LED traffic light as the transmitter and the high-speed camera on the vehicle as the receiver. In this system, the data is encoded hierarchically and assign with the each frequency components of the image. We use the DFT for hierarchical encoding considering channel characteristic and quantization of the luminance. The communication experiments were conducted to confirm the effectiveness of the proposed method.

Language：English  

Previous studies on visible light communication uses visually lighting LEDs. However, LEDs are not always lighting. In this paper, we propose visible light communication method using visually non-lighting LEDs. This method enables us to communicate in different situations, e.g. using visually non-lighting tail lamps of cars or visually non-lighting traffic lights. We realize visually non-lighting LEDs by reducing luminescence energy of LEDs according to the brightness in the environment. To reduce luminescence energy of LEDs, we reduce the number of emitting LEDs, increase the interval of emitting, and decrease the luminance of emitting LEDs. In our research we consider the case that the transmitter is tail lamps of cars and the receiver is high-speed camera. We conduct two types of experiments to demonstrate the performance of the proposed system. One is to confirm that LEDs are visually non-lighting. The other is measurement of Bit Error Rate of communication using visually non-lighting LEDs. Experimental results demonstrate that it is possible to make communication using visually non-lighting LEDs. In our future work, we plan to use different sensor devices such as photo diode or CCD in order to decrease the error rate in communication.

Language：English  

Visible Light Communication(VLC) has been introduced as a new wireless communication method. In this paper, we propose a VLC system for Intelligent Transport System (ITS) to communicate between infrastructure and the vehicle. In this system, we use a LED array as a transmitter and on-vehicle high speed camera as a receiver. Here, LEDs in the transmitter emit light in 500Hz and the emission patterns are used to achieve communication, by capturing them using the high speed camera in high frame rate. The images captured by high speed camera are processed to find the transmitter, track the found transmitter, and capture the emission pattern of transmitter in consecutive frames. In our previous work, we proposed algorithms to finding and tracking. In this paper, we introduce method to capture the emission pattern of the transmitter. Then out door communication experiments were conducted to confirm the effectiveness of the proposed VLC system.

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society for Engineering Education  

DOI： 10.20549/jseeja.2011.0_440

CiNii Research

Publishing type：Research paper (scientific journal)  

Web of Science

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Our goal is the improvement of the node activity rate in solar-powered wireless sensor networks. We consider the application of a cooperative transmission scheme that uses a relay node when a node sends data to reduce the consumption of energy of the entire network. However, if we do not consider the variations in energy harvesting, the node activity rate declines during nighttime. In this paper, we smooth out the day-and-night node activity rate variations by introducing the new inactive node reactivation condition and achieve the required high node activity rate.

DOI： 10.1109/PIMRC.2011.6139948

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Publishing type：Research paper (scientific journal)   Publisher：Information and Media Technologies 編集運営会議  

We propose a visible light road-to-vehicle communication system at intersections as an ITS(Intelligent Transport System) technique. In this system, the communication between a vehicle and an LED traffic light is conducted using an LED traffic light as a transmitter and an on-vehicle high-speed camera as a receiver. The LEDs in the transmitter emit light at high frequency, and those emitted light is captured by the high-speed camera for communication. Here, the luminance value of the LEDs in the transmitter should be captured in consecutive frames to achieve communication. For this purpose, first the transmitter should be found, and then it should be tracked in consecutive frames while the vehicle is moving by processing the images from the high-speed camera. In this paper, we propose new algorithms for finding and tracking the transmitter, which result in increased communication speed and data rate compared to the previous methods. Experiments using appropriate images showed the effectiveness of the proposals.

DOI： 10.11185/imt.6.785

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Image Information and Television Engineers  

In this paper, we consider road-to-vehicle visible light communication systems on driving situation using a LED array transmitter and a high-speed camera receiver. In our previous research, we have proposed inverted signal to track an LED array transmitter. We propose decoding method with inverted signal to improve BER performance. Furthermore, we confirm that we can suppress the flicker of LED in PDF.

DOI： 10.11485/itetr.35.9.0_95

Publishing type：Research paper (scientific journal)   Publisher：The Institute of Image Information and Television Engineers  

In this paper, we discuss on visible light communications using an LED array as the transmitter and a highspeed camera as the receiver. A challenge is that the longer the distance between the transmitter and the receiver, the more reduction in the resolution of the receive image occurs. To solve the problem, we allocate high priority data to low frequency components of spatial frequency. Then, we can receive high priority data even if the receiver is far from the transmitter. For that, we have used the Wavelet transform in our previous researches. However, the conventional scheme limits the number and the disposition of LEDs which can be allocated data. In other words, the hierarchical coding using the Wavelet transform has a low degree of freedom of design. In this paper, to improve a degree of freedom of design, we propose the overlay coding which does not limit the number and the disposition of LEDs.

DOI： 10.11485/itetr.35.9.0_89

Publishing type：Research paper (scientific journal)  

Web of Science

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

This paper aims to improve the visible light communication system using LED array and high-speed camera by proposing what we call "overlay coding". "Overlay coding" is a new coding method to realize a hierarchical coding, through which a high-priority data can be received even if the receiver is far from a transmitter. Conventionally, the hierarchical coding has been realized through the wavelet transform that has a limitation of number and disposition of LEDs, and as a result it does not always match with the design of the transmitters (e.g. traffic lights, etc.) used in real life. To solve the limitation problem, we propose a more flexible way of designing the application of LEDs depending on the transmitters. In particular, overlay coding is realized through the procedures of coding and decoding. In coding, we replace one LED with a flexible number of LEDs, and the number depends on whether the data is high-priority or low-priority, then high-priority data and low-priority data are overlaid (section III-B1). In decoding, we first obtain the high-priority data, and then the low-priority data using retrieved high-priority data (section III-B2). The experimental result shows that the distance for receiving error-free data is extended from 30m to 70m in the overlay coding (section IV-B).

DOI： 10.1109/ITSC.2011.6082943

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Image Information and Television Engineers  

Visible Light Communication (VLC) using LEDs has been proposed as a wireless communication method. As an application of VLC in ITS, we propose a road-to-vehicle visible light communication system using an LED traffic sign as a transmitter and an image sensor as a receiver. For conducting the communication, it is necessary to have high-speed tracking of the LED traffic sign by the image sensor. In this paper, we propose new high-speed tracking method for this system.

DOI： 10.11485/itetr.35.9.0_101

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Publishing type：Research paper (scientific journal)   Publisher：2010 IEEE International Conference on Ultra-Wideband, ICUWB2010 - Proceedings  

DOI： 10.1109/ICUWB.2010.5616909

Scopus

Language：English  

In this paper, we propose two dynamic bandwidth allocation (DBA) schemes, a game theory based DBA and a successive DBA, for satellite/terrestrial integrated mobile communication system (STICS). The game theory based DBA allocate the bandwidth according to a utility function based on a weighted demand bandwidth of both satellite and terrestrial system. The successive DBA recursively allocates an unit of bandwidth according to a weighted number of bandwidth unfilled cells of both satellite and terrestrial systems, until the total bandwidth is fulfilled. As results, both DBA outperform the conventional fixed bandwidth allocation scheme. Between two proposed DBA, the successive DBA shows better spectral improvement ratio than the game theory based DBA.

Language：English  

Intelligent transport system has been introduced to reduce traffic problems such traffic accidents and traffic congestions. In this paper, we introduce a receiver for a road to vehicle Visible Light Communication (VLC) system which is proposed as an Intelligent Transport System (ITS) technique. In this system, an on-vehicle high-speed camera is used as a receiver and an LED array is used as a transmitter. VLC is a wireless communication using luminance. Here, transmitter send information by emitting light and receiver receive them by capturing the luminance of emitting LEDs in the array(Luminance: whether each LED is on or off). For capturing the Luminance, it is necessary to find the transmitter and track it in consecutive frames. In our previous works we introduced methods for finding and tracking. In this paper, we shortly explain the proposed transmitter finding and tracking methods and then a new method is proposed for capturing the luminance of LEDs to achieve communication.

Language：English  

Our goal is improvement of the node activity rate in solar-powered wireless sensor networks. One method to reduce the consumption energy of the entire network is a cooperative transmission that uses a relay node when a node sends data. But if we do not consider the change in harvesting energy, the node activity rate is declined during nighttime. In this paper, we smooth the day-and-night node activity rate by introducing the new inactive node reactivation condition and achieve the required high node activity rate.

Language：English  

This paper discusses the visible light road-to-vehicle communication system at intersection as one of ITS (Intelligent Transport System) technique. The communication between a vehicle and an LED traffic light is approached using an LED traffic light as a transmitter, and on-vehicle high-speed camera as a receiver. In this system, it is able to send data by blinking the LEDs of the traffic light in two dimensional patterns, and able to receive them by high-speed camera with image processing [1]. Here, we aim to conduct long-distance high-speed visible light communication. When the distance between transmitter and receiver is far, the image of the LED traffic light captured by on-vehicle high-speed camera is very small. So, if the data are put on two dimension patterns without modification, data would be mistaken, because the two dimension patterns can't be realized correctly. To solve this problem, data are encoded hierarchically before they are lighted by the LED traffic light. This is called as hierarchical encoding that the data are assigned with each spatial frequency.

Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)  

We develop a mathematical framework for the extrinsic information transfer (EXIT) analysis to assess the convergence behavior of maximum a posteriori (MAP)-based joint iterative decoding of correlated sources, which are separately encoded and transmitted over noisy channels. Unlike the previous work, side information about the correlation is not perfectly given at the joint decoder but is extracted from decoder output and updated in an iterative manner. The presented framework provides a convenient way to compare between schemes. We show that it allows us to easily and accurately predict joint decoding gain and turbo cliff position.

Language：English   Publishing type：Research paper (scientific journal)  

Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal Time of Arrival (ToA) positioning, at least three receivers with unblocked direct path to the transmitter are required. A requirement that is not always met. In this work, a novel algorithm for ToA positioning using only two receivers is presented. This is possible by exploiting the knowledge of some of the indoor features, namely positions of big flat reflective surfaces, for example ceiling and walls. The proposed algorithm was tested using data from a measurement campaign.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

We develop a mathematical framework for the extrinsic information transfer (EXIT) analysis to assess the convergence behavior of maximum a posteriori (MAP) based joint iterative decoding of correlated sources which are separately encoded and transmitted over noisy channels Unlike the previous work our approach focuses on the case side information about the correlation is not perfectly given at the joint decoder but is extracted from decoder output and updated in an iterative manner The presented framework provides a convenient way to compare between schemes We show that it allows us to easily and accurately predict Joint decoding gain and turbo cliff position

DOI： 10.1587/transcom.E93.B.3509

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Publishing type：Research paper (scientific journal)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN INST COMMUNICATIONS SCIENCES (K I C S)  

DOI： 10.1109/JCN.2010.6388298

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