Low-PAPR Polarity-Split 4-LED MIMO-VLC Transmission with Direct-Channel 4D-ML Detection

Abstract

This paper presents a low-PAPR polarity-split four-LED MIMO-VLC transmission scheme for flat indoor optical channels. The proposed transmitter maps each complex QAM symbol into four nonnegative LED branches by separating the positive and negative polarities of the real and imaginary components. At the receiver, a direct-channel four-dimensional maximum-likelihood detector is used to estimate the transmitted QAM symbol directly from the photodetector-domain received vector. The proposed scheme is compared with GLIM-MAP, OSM-DCO-ML, and OSM-ACO-ML under fair spectral-efficiency settings with cyclic-prefix accounting. Simulation results over 4 x 4 flat MIMO-VLC channel matrices show that the proposed scheme provides a much lower PAPR than GLIM and OSM-ACO, and achieves clear BER gains over OSM-DCO under practical channels. At spectral efficiency = 4, the proposed scheme reduces the ML-search space by about 7.94 times relative to OSM-DCO, while avoiding the OFDM transmitter-side IFFT burden. The results indicate that the proposed scheme is a spectrally efficient and low-complexity flat-channel alternative for low-PAPR MIMO-VLC transmission.