Sinusoidal-Based Multiple Access Scheme for Visible Light Decentralized Asynchronous System

In some visible light communication (VLC) systems, transmitters are light sources which support not only illumination but also information broadcast and positioning. Since transmit signals in these systems inevitably interfere with each other at receivers, extra devices may be added to synchronize the transmitters, but this impairs an appealing advantage in VLC systems that existing lighting infrastructure can be simply reused. This paper proposes a novel multiple access scheme to realize decentralized asynchronous VLC systems. The proposed scheme allows the transmitters and receivers to be asynchronous. For a system with N transmitters, two unique codewords of L chips are allocated to each transmitter where L is a prime number larger than 4N. In the proposed scheme which is based on pulse-amplitude modulation (PAM), the codewords are modulated in a specially designed way such that the average transmit power is a constant for each transmitter. Our scheme enables the receiver to obtain one channel estimate and one PAM symbol per L chips. Two novel channel estimators are also proposed. Simulation results show that the proposed scheme outperforms other schemes in the literature in terms of bit error rate and system throughput.