Research On Multi-user Access In Indoor Visible Light Communication System

Visible light communication (VLC) is a new type of wireless communication in recent years. VLC combines the illumination and communications, and appends the data transmission to the LED illumination facilities, which transmits information through the LED illuminant lighting and shading with high speed. Compared with the RF wireless communication, the indoor VLC has much advantage such as wide available bandwidth, without authorization, without electromagnetic radiation, high security and so on, so indoor VLC can be used in some places such as hospital, gas station, and engine room etc. At present, the indoor VLC networking is one of the hot researches. In a multiuser access case, because the number of light detector integrated in a LED terminal is limit, multiple user requests access at the same time will produce collision, which reduces the efficiency of communication system. Therefore, in indoor VLC networking system, how to avoid the collision, and how to effectively complete multi-user access, become the problems need to solve. In this paper, a hybrid multiple access protocol-CSMA/TDMA protocol is presented, which can effectively solve the problem of multi-user access.This paper first introduces the basic theory of indoor VLC, and analyzes the key technologies of current research in VLC systems. Then it introduces the basic multiple access protocols, and analyzes the advantages and disadvantages of each protocol. On this basis, this paper proposes a CSMA/TDMA protocol, and describes the frame structure and protocol in detail. And then discusses the protocol operation process and problems of CSMA period and TDMA period. The relevant parameters of hybrid protocol are analyzed and derived, and expressions of the relevant performance indicators are obtained. Finally, aiming at the proposed protocol, the collision probability, the duration of CSMA period and the system throughput under various conditions are simulated and analyzed. Simulation results show that the proposed protocol can well solve the problem of multiple user access in VLC, and that the protocol is feasible.