Interference cancellation in MIMO NLOS optical-camera-communication-based intelligent transport systems

Abstract

The ever-increasing number of vehicles at a global level signifies the need for communications between vehicles and the surrounding environment. Visible light communications (VLC) is a viable complementary technology to the congested radio frequency-based wireless systems. In order to increase the reliability of the VLC link, in this paper we propose two novel algorithms based on (i) channel inversion (CI), and (ii) frame subtraction and CI (FSCI) schemes are proposed to successfully extract the data in a non-line-ofsight multiple-input multiple-output spatial division multiplexing optical camera communications system. We have adopted differential modulation and frame subtraction schemes and proposed a unique packet structure to mark the packet and the position of the footprint of transmitters (Txs) in the image frame. We show that, the FSCI scheme with much simpler receiver structures can offer almost the same bit error rate (BER) performance compared with the hybrid selection/equal gain combining (HS/EGC) technique at lower transmit power (illumination) levels of < 13 dBm for a single transmitter(Tx) and improved performance at higher illumination levels of > 20 dBm for multiple Txs. Compared with HS/EGC, CI schemes have a higher tolerance to the spacing between Txs, where the payload threshold level can be set to a fixed value of 0.5.

Optical Camera Communication in Vehicular Applications: A Review

“…H is the channel matrix, which is described by the line-of-sight (LOS) DC channel gain h l c−L OS received at the image sensor h l c−L OS is influenced by the radiation pattern of the transmitter. Let us consider that the light source is Lambertian in nature; then, the radiation pattern of the transmitter is given by [90], [91]…”

“…A im significantly depends on the camera focus, which is further described in Section VII. OCC can also be performed using a non-LOS (NLOS) link [90], [93]- [96], which can be crucial in vehicular applications. An LOS link may not be established between vehicles owing to high mobility in cases wherein an NLOS link uses the portion of the light reflected from a particular surface.…”

Some practical constraints and solutions for optical camera communication

“…However, the path loss is usually much higher than that of an LOS link due to blockage, which limits the achievable data rate and transmission performance. Besides, the output of each pixel is a superposition of contributions from all light sources due to the NLOS nature, which includes additive interference [115].…”

A Demodulation Method Using a Gaussian Mixture Model For Unsynchronous Optical Camera Communication With on-off Keying

“…Indoor VLC, which uses room lights from LEDs as a transmitter, can provide a fast and secure communications system because of the massive number of LEDs and controllability of the illumination area [1], [2], [3], [4]. In addition, great effort has been made to apply VLC to intelligent traffic systems (ITSs) for safer driving and more efficient traffic navigation [5], [6], [7], [8], [9]. Since both of the above applications will utilize LEDs that are already available for room and automotive lighting and traffic Y. Shiraki, T. G. Sato, Y. Kamamoto, and T. Moriya are with NTT Communication Science Laboratories, Nippon Telegraph and Telephone Corporation.…”

“…This enables the receiver to trace moving transmitters and communicate with multiple transmitters simultaneously. By taking advantage of these features, OCC systems have been applied to vehicle-to-infrastructure and vehicle-to-vehicle communications in ITSs [5], [6], [7], [8], [9], positioning systems [13], [14], multichannel acoustic measurement for beamforming via optical wireless microphones [15], [16] and simultaneous biosignal observation of audiences in live concerts [17].…”