This study aims to enhance flexibility in the communication range of rolling shutter based visible light communication (RS-VLC). One of the main challenges in RS-VLC is the trade-off between the data rate and communication distance. To address this issue, we proposed a method that integrates superimposed iterative transmission with parallel delay transmission. Superimposed iterative transmission overlays two datasets, one optimized for short-range communication and the other for long-range. This strategy enhances communication over longer distances without significantly reducing the data rate at shorter ranges. Meanwhile, the parallel delay transmission sends signals with varying delays simultaneously across multiple LEDs, facilitating efficient transmission. By combining these two techniques, we aim to extend the communication range. Experimental results illustrate that the proposed approach enables data reception at long distances (up to 270cm) while significantly reducing data rate degradation at shorter distances. This effectively mitigates the trade-off between data rate and communication range. Additionally, over communication distances of 50 to 290cm, the average throughput of our method improved by approximately 73% compared to conventional methods.

Recently, physical key replications has become easier, highlighting the growing need for new authentication technologies. This study focused on optical physical unclonable functions (PUFs). Optical PUFs use physical irregularities to generate unique identification information for each device, thereby providing increased tampering resistance. Optical PUFs are highly compatible with optical wireless communication (OWC), and their combination contributes to enhanced communication security. However, conventional optical PUFs face challenges in terms of their implementation complexity and cost. In this paper, a simply implemented scratch-based optical PUF is proposed. In the proposed method, scratches are applied to a transparent optical medium to create unique light paths, thus enabling a simple and practical optical PUF that achieves both high resistance to forgery and ease of implementation. Authentication is performed by comparing light paths images captured by a camera with reference data. To evaluate the decision accuracy of the proposed method, a prototype was developed, and 1.4 × 106trials were conducted. Based on the results, the proposed method exhibited a false negative rate of 8.75 × 10−4and a false positive rate of zero within 300 significant digits, which exceeds the accuracy of typical biometric authentication systems.

This research addresses challenges in visible light communication (VLC) systems that use two orthogonally aligned rolling shutters (RS) image sensors as receivers and an LED array as a transmitter. The study focuses on overcoming burst signal loss caused by unsensed periods between frames in RS image sensors. To improve VLC performance, we propose and compare three different schemes. The first is a conventional approach that superimposes a Barker code synchronization signal on the transmission signal using pulse width modulation (PWM). The second introduces a new method of spatial synchronization by dedicating specific LEDs in an array for synchronization signals. The third scheme extends this spatial approach by incorporating a 4 -level PWM for information transmission to increase data rates. The study aims to evaluate and compare the error rate characteristics of these three schemes, assessing their effectiveness in mitigating burst errors and enhancing overall VLC system performance. This research has potential applications, including vehicle communication, Internet of Things devices, and smartphones.

This study aims to provide flexibility to changes in communication range in rolling shutter based visible light communication (RS-VLC). One of the issues in RS-VLC is the trade-off between the data rate and communication range. To resolve this issue, we proposed a superimposed iterative transmission in which two sets of data, namely, for short-and long-range data, are superimposed and then transmitted simultaneously. At short-ranges, the proposed method can decode both short- and long-range data, thus suppressing data rate degradation. As the communication range increases, the proposed method decodes long-range data (and half of the short-range data), allowing for data reception over longer ranges, albeit at a reduced data rate. The experimental results show that the proposed method achieved data reception at a longer range (up to 130 cm) with suppressing throughput degradation at short-ranges, i.e., it mitigated the trade-off between data rate and communication ranges.

We propose an estimation method of light emitting diode(LED) position with a cross filter (CF) for rolling-shutter (RS) camera. The CF is set in front of the camera lens so that incident light can be scattered into two straight lines extending ±π/4 from the horizontal row of the CMOS image sensor (IS). With the geometry of a right-angled isosceles triangle, our method makes it possible to estimate the coordinates of the LED in the IS plane when the scattered light is captured at two points in a scanline. Furthermore, our method makes it possible rows by rows when multiple LEDs are used or when they are moving. Without the CF, estimation is done only once per frame when the scan of the sequentially activated operation of the RS camera reaches a row that has just captured the whole image of the target LED, and the estimated coordinates are not updated in that frame. Experiments verify that our estimation method works with the estimation error less than 5pixels, and to extend the region of a frame in which estimated coordinates are output, even in a moving environment, while the conventional method (without CF) obtains the estimated coordinates only once when the scan reaches a row that captures entire LED.

This study demonstrates the communication performance of rolling shutter based visible light communication (RS-VLC) using dual camera receivers. In RS-VLC, the modulated signals emitted from the light source are captured as stripes based on the exposure timing difference for each line. Using this sequential exposure mechanism, a data rate higher than the frame rate can be achieved. To achieve higher data rates, we apply M-ary pulse amplitude modulation (M-PAM) to RS-VLC. The challenges for M-PAM in RS-VLC include limitations in the available grayscale range and non-uniform luminance distribution, both of which cause symbol errors. To solve this problem, we use two images in which the light emitting diodes (LEDs) are captured at different positions obtained by dual rolling shutter cameras. In this paper, we propose a method to combine two received signals, demodulate the signal transmitted by M-PAM in RS-VLC, and experimentally confirm the improvement in the symbol error rate (SER).

To improve the operational efficiency of remotely operated vehicles (ROVs) used to investigate ocean resources, this paper focuses on underwater visible light communication using a camera as a receiver (i.e., underwater image sensor communication: UISC). UISC can realize wireless communication underwater, where wireless communication using radio waves is difficult. However, due to the limited area of the ROV, it is hard to increase the number of transmitter LEDs installed on the ROV, resulting in a lower communication speed. We have developed a propeller-type rotary LED transmitter (P-RTx) to solve this problem, assuming that the LEDs are attached to the ROV's thruster. P-RTx is a device that increases communication speed by rotating a blinking LED that transmits data and utilizing the receiver's ability to capture their blinking lights as multiple afterimages. As a result of experiments using a prototype P-RTx, we have achieved error-free communications up to a communication distance of 3.0 m at a communication speed of 3.24 kbps, 72 times faster than the conventional method.

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 10–2in the fundamental frequency range of 300–700 Hz when 16-PSK was adopted for subcarrier modulation.

This study focuses on visible light communication (VLC) using dual rolling shutter (RS) cameras. In VLC using an RS camera as a receiver, called rolling shutter based VLC (RS-VLC), the transmitted signal is projected as stripes on the image when the information is transmitted by an LED at a modulation speed higher than the frame rate. Therefore, the RS-VLC can improve the data rate. However, non-uniform luminance distribution on the image causes communication errors. Because LED light sources emit light radially, the luminance between the center and the edge of the LED in the captured image differs. Specifically, the received signal intensity is strong and good channel conditions can be obtained in the center of the LED, whereas the received signal intensity is weak at the edges, making it difficult to recognize changes in signal amplitude and prone to communication errors. To solve this problem, this study aims to enhance the communication error using dual camera images with misaligned LED positions and selecting the one with the better channel condition from the two received signals.

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.

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.

This paper presents an image sensor communication (ISC) using a digital micromirror device (DMD) projector as a transmitter. In particular, we focus on ISC for intelligent transport systems (ITSs) because DMD projectors are expected to be used in road traffic, such as vehicle headlights, street lights, and traffic signs. The DMD projector controls light patterns by switching tilt of micromirrors at high speed. Compared to the conventional LED array transmitter, DMD projector can design and alter the shape of the light pattern and data rate of transmission more easily. In the proposed system, the data rate can be easily increased by increasing the number of multiplexes. However, as the number of multiplexes is increased, the number of received pixels on the image sensor is decreased, and thus the performance of symbol detection deteriorates. Therefore, the purpose of this paper is to examine the relation between the number of received pixels per cell and communication performance for transmission pattern design. Hence, we experimentally clarify this relation using our prototype system via a DMD projector and a high-speed camera.

A nonlinear transform scheme is proposed to convert M discrete samples of parallel transmission (PT) system into the dynamic range between the transmitter and receiver for image-sensor-based (IS-based) visible light communication (VLC). In the PT system reported in [1], although the M discrete samples incorporating N spatial frequencies through M-point inverse discrete Fourier transform (IDFT) are transmitted by M spatially located transmitters. However, the signal of the PT system is, in essential, orthogonal frequency division multiplexing (OFMD) signal, thus suffering from the drawback of the multicarrier systems, i.e., high peak-to-average ratio (PAPR). With our scheme, the M discrete samples are transformed into the dynamic range between the liquid crystal display (LCD) transmitter and image-sensor (IS) camera receiver. Further, although the M discrete signals are expanded in transforming them, some of the expanded discrete samples are out of the dynamic range. Such out-of-the-range samples are truncated and replaced by the maximum or minimum value, i.e., 255 or 0. Our scheme is carried out for the PT system of the LCD transmitter and a 1000-fps high speed camera receiver which are at the distance of two meters. Experimental results show that our scheme enables the PT system to carry more spatial frequencies with achieving error-free transmission than without the scheme, thus increasing the number of bits per frame.

This paper focuses on high-speed stereo camera 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.

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.

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.

A number of works have been reported on robot control using EMG signals. Control of robots, wheelchairs, and rehabilitation aids using the arms, hands or legs by EMG signals has been quite popular and effective. However, few works have dealt with head-movement control using neck EMG signals. We have built a model that estimates continuous human head movement from neck EMG signals. Our proposed model, which considered not only static but also dynamic effects, effectively suppressed the over/undershoot, and predicted head-rotation movements well. This result indicates that the proposed model has the potential to reconstruct the observed data from neck EMG signals properly.

An electrohydraulic totally implantable artificial heart which has a motor-integrated regenerative pump was developed. The system consists of left and right diaphragm-type blood pumps which are implanted in the thorax with a separately placed electrohydraulic actuator in the abdominal region. The blood pump was designed to have an appropriate anatomical fitting in a human thorax. The actuator is a regenerative pump which is able to pump fluid against a high head. The height, diameter, and weight of the actuator are 32.5 mm, 73 mm, and 350 g, respectively. The rotor-magnet of the brushless DC motor is embedded in the impeller of the regenerative pump in order to miniaturize the actuator and increase durability by reducing the number of moving parts. A 32-b microcomputer controls the motor of the actuator. The detection algorithm of the pumping condition was developed by using the TMSTR (time-sequential multiple-state transition representation) linguistic technique to control the artificial heart correctly and safely. The feasibility of the devices was confirmed by in vivo and in vitro experiments.>