Image sensor communication (ISC), derived from visible light communication (VLC) is an attractive solution for outdoor mobile environments, particularly for intelligent transport systems (ITS). In ITS-ISC, tracking a transmitter in the image plane is critical issue since vehicle vibrations make it difficult to selsct the correct pixels for data reception. Our goal in this study is to develop a precise tracking method. To accomplish this, vehicle vibration modeling and its parameters estimation, i.e., represetative frequencies and their amplitudes for inherent vehicle vibration, and the variance of the Gaussian random process represnting road surface irregularity, are required. In this paper, we measured actual vehicle vibration in a driving situation and determined parameters based on the frequency characteristics. Then, we demonstrate that vehicle vibration that induces transmitter displacement in an image plane can be modeled by only Gaussian random processes that represent road surface irregularity when a high frame rate (e.g., 1000fps) image sensor is used as an ISC receiver. The simplified vehicle vibration model and its parameters are evaluated by numerical analysis and experimental measurement and obtained result shows that the proposed model can reproduce the characteristics of the transmitter displacement sufficiently.

We propose a service differentiation scheme for optical burst switching (OBS) with the scheduling algorithm Horizon. In the proposed scheme, in addition to the latest horizon used in the conventional Horizon, we introduce the second latest horizon and use them for reservation preemption. Burst priority order is perfectly guaranteed according to the burst class information informed by its control packet if the arrival time of the burst is later than the second latest horizon and earlier than the latest horizon. Since the extra offset time is no longer needed for service differentiation, the burst blocking probability and the data latency will be reduced. We assume a multi-hop network with ring topology where bursts traverse five intermediate nodes, and evaluate the performance in terms of the end-to-end and hop-by-hop burst blocking probabilities. Simulation results show that the proposed scheme can achieve service differentiation with smaller blocking probability than the extra-offset-time-based scheme with Horizon. Furthermore, we show that the proposed scheme preserves service differentiation even in multi-hop environments.

A new class of visible light communication (VLC) systems, namely image sensor (IS) based VLC systems, has emerged. An IS consists of a two-dimensional (2D) array of photodetectors (PDs), and then VLC systems with an IS receiver are capable of exploiting the spatial dimensions invoked for transmitting information. This paper aims for providing a brief survey of topics related to the IS-based VLC, and then provides a matrix representation of how to map a series of one dimensional (1D) symbols onto a set of 2D symbols for efficiently exploit the associate grade of freedom offered by 2D VLC systems. As an example, the matrix representation is applied to the symbol mapping of layered space-time coding (L-STC), which is presented to enlarge the coverage of IS-based VLC that is limited by pixel resolution of ISs.

We propose an interference avoidance architecture using uneven spreading as a media access mechanism for optical code division multiple access (OCDMA). While an equal-intensity pulse sequence encoded with the spreading sequence assigned to each node is transmitted for a “1” bit in conventional OCDMA with on-off keying (OOK), the proposed architecture creates an uneven-intensity pulse sequence where one of the pulses has higher intensity than the others. The high-intensity pulse allows source nodes to use increased sensing threshold for channel sensing, which leads to an increase in the number of chip offsets available for collision-free transmission. Our receiver with a hard limiter (HL) allows destination nodes to receive the transmission without false positives. Interference avoidance performance is examined by deriving the collision probability and comparing it with the conventional interference avoidance with equal-intensity spreading. Our numerical results show that our architecture has lower collision probability, shorter time required for channel sensing, higher throughput, higher bit rate, and supports more nodes than the conventional one for a fixed collision probability.

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 [10], 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 [11] 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.

Visible light communication (VLC) and visible light ranging are applicable techniques for intelligent transportation systems (ITS). They use every unique light-emitting diode (LED) on roads for data transmission and range estimation. The simultaneous VLC and ranging can be applied to improve the performance of both. It is necessary to achieve rapid data rate and high-accuracy ranging when transmitting VLC data and estimating the range simultaneously. We use the signal modulation method of pulse-width modulation (PWM) to increase the data rate. However, when using PWM for VLC data transmission, images of the LED transmitters are captured at different luminance levels and are easily saturated, and LED saturation leads to inaccurate range estimation. In this paper, we establish a novel simultaneous visible light communication and ranging system for ITS using PWM. Here, we analyze the LED saturation problems and apply bicubic interpolation to solve the LED saturation problem and thus, improve the communication and ranging performance. Simultaneous communication and ranging are enabled using a stereo camera. Communication is realized using maximal-ratio combining (MRC) while ranging is achieved using phase-only correlation (POC) and sinc function approximation. Furthermore, we measured the performance of our proposed system using a field trial experiment. The results show that error-free performance can be achieved up to a communication distance of 55 m and the range estimation errors are below 0.5m within 60m.