Minimal Noise Variance Decoder for Uncoordinated Multiple Access in VLC

This paper proposes an uncoordinated multiple access scheme for visible light communications (VLC) with positioning capability. The sinusoidal-based codes, proposed only for visible light positioning systems, are generalized in this paper by using a novel decoder design. The proposed scheme does not need a central unit to coordinate the transmission of the transmitters. Transmitters can be asynchronous with one another and with the receiver. Each transmitter is allocated a unique codeword with $L$ chips for a system with up to $frac{L-1}{2}$ transmitters where $L$ is prime. Due to the linear growth in complexity with respect to number of transmitters, our proposed scheme is feasible for systems with large numbers of transmitters. Simulation results show that the proposed decoder significantly outperforms Zero-Forcing decoder. Moreover, for a system with $16$ transmitters and average transmitting optical power of $500$ lm, the proposed scheme achieves 2.6 bits/ chip as equivalent to the system throughput with average probability of error less than $10^{-6}$.