Multiuser downlink communication for MIMO-VLC system using spatial modulation and optical orthogonal codes

Abstract

In this paper, a novel multiuser spatial modulation (SM) scheme is proposed and applied in downlink multiple input-multiple output (MIMO) visible light communication (VLC) system. In the transmitter side, each user's temporal symbol is first modulated onto user specific optical orthogonal code (OOC), then being emitted by the specific LED that is activated by its spatial symbol. At the front end of each user terminal (UT), array of photodetectors (PDs) convert optical into electrical signal, then chip-level detection scheme is employed to eliminate multiuser interference (MUI). Two computationally attractive detection algorithms are then proposed: Maximum likelihood (ML) algorithm premises on jointly estimating both temporal and spatial symbols. While the two-stages algorithm first identifies the index of the activated LED followed by a M-ary PAM demodulator to extract the desired user's spatial and temporal symbols sequentially. Extensive Monte Carlo simulations are undertaken to evaluate system performance in terms of the overall symbol error rate (SER). It is demonstrated that the chip-level detection scheme can effectively alleviate MUI and both ML and the two-stages detection algorithms work reliably in various scenarios. Hence, it is promising to apply the proposed scheme in multiuser MIMO-VLC system.