This paper aims to enhance underwater visible light communication using a propeller LED transmitter (P-Tx) and receiver camera. Our goal is to improve the operational efficiency of remotely operated vehicles (ROVs) that survey ocean resources. P-Tx is a rotating device with blinking LEDs. By rotating P-Tx, we can generate a pseudo surface with successive light trails (light-trail surface). This technology allows the ROV to track the transmitting ROV and receive data simultaneously without mechanically adjusting the optical axis. However, with increasing distance between P-Tx and the receiver, the light gradually decreases in intensity from the edge of the light-trail surface, causing the receiver to fail to track accurately. This study proposes a robust transmitter detection method that utilizes the characteristics of the light-trail surface and improves the detecting accuracy of P-Tx on the receiving side. We show that the proposed method achieves higher transmitter detection accuracy than the conventional one.

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 paper focuses on underwater visible light communication using a camera as a receiver to improve the operational efficiency of remotely operated vehicles that investigate ocean resources. This technology can realize wireless communication underwater, where wireless communication using radio waves is difficult. However, the optical axes between the transmitter and receiver must be correctly aligned before sending data in the underwater environment. We have developed a propeller LED transmitter (P-Tx) to solve this problem. The P-Tx is a rotating device with blinking LEDs. We can generate a pseudo-surface with successive light trails by rotating the P-Tx. This study calls this pseudo surface a "light-trail surface." The receiver can achieve robust transmitter detection by finding the light-trail surface using image processing without mechanical optical-axis alignment. This study also proposes a modulation method using light-trail surfaces. This study develops a prototype P-Tx and implements the proposed schemes. We then perform ISC experiments using the P-Tx and a camera to verify their communication performance.

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.

Precise positioning is critical in autonomous driving, indoor navigation, and intelligent logistics. With the development of mobile communication technology, indoor base stations (BSs) have been utilized and installed to match indoor signal coverage better. Thus for indoor positioning, cellular signals have emerged as a new option. Ranging through the time of arrival (TOA) is achieved by capturing cellular signals as a signal of opportunity for localization. This approach can only estimate the user equipment (UE) to BS distance when there is just one BS and cannot obtain the two-dimensional (2D) coordinates. In this paper, we combine the fingerprint positioning approach with the signal parameters acquired via cellular signal of opportunity. TOA and one-reflection path are employed as fingerprint features, and 2D localization with a single BS is achieved. A complete signal processing flow is constructed, and the ray tracing method is performed to generate the channel parameters to evaluate the proposed positioning algorithm's performance and match the practical application as closely as feasible. Using the$100\ GHz$carrier frequency that conforms to the sixth generation (6G) communication for simulation, the mean positioning error is$0.312 m$when the fingerprint interval is$0.5 m$. This method provides a feasible solution for 6G indoor positioning scenarios.

This letter proposes a deep-learning-based fingerprinting indoor positioning method, aiming to mitigate catastrophic forgetting in the process of depth transfer learning. Recently indoor positioning methods based on fingerprint have made great development. The deep transfer learning technique has been applied to transfer the positioning network among different scenarios. But catastrophic forgetting is a big challenge during the supervised transfer learning, which results in poor performance of fine-tuned network in source scenario. In order to solve this issue, the proposed method improves the fine-tuning learning procedure according to the importance of network parameters. It can adaptively control the ratio of network parameters by adding regularization factor to loss function. Simulation results show that the proposed method can effectively improve the positioning accuracy in source scenario without reducing the positioning accuracy in target scenario, especially for the transfer learning in multiple scenarios.

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 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.

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.

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 this study, we investigate a positioning-aided scheme using computer vision techniques for image sensor communication (ISC), generally referred to as a visible light communication (VLC) system that utilizes an image sensor (camera). The image sensor in ISC is frequently used as a typical receiver because it has the ability to measure light intensity and distinguish multiple light sources. Additionally, thanks to its ability to detect the angle of arrival of light, the image sensor can estimate its own position using computer vision techniques. The positioning accuracy of ISC is reported to be in sub-meter levels that render visible light positioning (VLP). VLP is one of the most excellent positioning applications in indoor settings as global positioning system cannot provide satisfying indoor positioning services. To apply this significant positioning performance of VLP to our visible light system, we propose a positioning-aided scheme for ISC using computer vision techniques here. In addition, we evaluate the demodulation performance and positioning accuracy of our proposed scheme.

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.

This paper proposes a new demodulation method using a one-bit analog-to-digital converter (ADC). With one bit resolution, a signal having a multilevel signal, such as a quadrature amplitude modulated (QAM) signal, is largely degraded by nonlinearity. To demodulate the signals, a high- resolution ADC is used to receive the signals with high linearity. This study sets out to demodulate the QAM signals using a one-bit ADC, whose resolution is the lowest (one-bit) and possesses outputs of binary (nonlinear) values. We propose to solve the issue by focusing on the statistical characteristics of the output signals of the one-bit ADC combined with noise. The proposed demodulation method is based on maximum a posteriori (MAP) criterion. The theoretical analysis presented illustrates that reliable demodulation is possible even with the one-bit ADC, provided the output probability of the ADC corresponds to each transmitted symbol is known.

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.

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.

The recent increase of wireless devices (i.e., STAtions (STAs)) brings forward an increase of energy consumption. We address the energy consumption issues for STAs in Wireless Mesh Networks (WMNs). One of the available techniques for power-saving is the sleep technique. However, since the common transmission mode from the STA to the server is performed based on end-to-end transmission, this results in increase of energy consumption of the STAs since they cannot enter sleep mode until end-to-end communications are completed. To cope with the issue, we focus on an Access Point equipped with External Storage (APES), which provide end-to-end communication instead of STAs. Using this, STAs can shorten the transmission time and decrease the energy consumption since they communicate with neighboring APES. In this paper, we propose a novel method to select the adequate APES as a proxy server based on the number of STAs and the amount of traffic from STAs. The proposed method effectively transmits data and reduces the energy consumption of the STAs. Moreover, we validate the efficiency of the proposed APES selection method through numerical analysis.

This paper considers a novel error-correcting scheme exploiting chaotic dynamics for noncoherent chaos communication. In our proposed system, two successive chaotic sequences are generated from the same chaotic map; the second sequence is generated with an initial value which is the last value of the first sequence. In this case, successive chaotic sequences having the same chaotic dynamics are created. This feature gives the receiver additional information to correctly recover the information data and thus improves the bit error performance of the receiver. Further, enhanced efficiency also comes from operating on successively modulated data; by involving less redundancy in the error correction system, it can be designed with high coding rate. In this paper, we analyze the scheme's capability, by examining computational times and accuracy rates of error correction, bounds on its capability.

This paper proposes the error-correcting scheme without redundancy sequences based on the chaotic dynamics for noncoherent chaos communications. We generate successive chaotic sequences from the identical chaotic map. And for the next sequence we set the initial value to the end value of the former sequence. By such way we can create the successive chaotic sequences having the same chaotic dynamics. This feature gives the receiver additional information to correctly recover the received noisy signal. Therefore, by analyzing the chaotic dynamics at the receiver, it is possible to improve the error performance without redundancy signal. As results of computer simulations, we confirm about 3 dB gain in BER performance as compared with the conventional suboptimal receiver when using the short chaotic sequence length per 1 bit.

This paper proposes a new noncoherent detection system improved based on the differential chaos shift keying (DCSK) and the correlation delay shift keying (CDSK). In this scheme, a transmitter changes chaotic maps for generating a chaotic sequence efficiently depending on an initial value. Also, the proposed method can choose the chaotic map by a very simple algorithm. In order to investigate the proposed method, computer simulations were carried out and observe the performance.

LEDs are expected as lighting sources for next generation, and data transmission system using LEDs attract attention. In this paper, we present hierarchical coding scheme using LED traffic lights and high-speed camera for intelligent transport systems (ITS) application. Further, if each of LEDs in traffic lights is individually modulated, parallel data transmissions are possible using a camera as a reception device. Such parallel LED-camera channel can be modeled as spatial low-pass filtered channel of which the cut-off frequency varies according to the distance. To overcome, we propose hierarchical coding scheme based on 2D fast Haar wavelet transform. As results, the proposed hierarchical transmission schemes outperform the conventional on-off keying and the reception of high priority data is guaranteed even LED-camera distance is further.