Few-Mode Based Beam Shaping for Multi-User Indoor Optical Wireless Communications With Time-Slot Coding

We propose a novel indoor optical wireless communications (OWC) system using few-mode based beam shaping integrating time-slot coding (TSC) scheme to serve multiple users simultaneously. We simulated an indoor OWC system incorporating single-sideband (SSB) 16 quadrature amplitude modulation (16-QAM) modulated signals in a multi-user environment employing few-mode based beam shaping with single-photodetector (PD) and multi-PD reception with maximum ratio combining (MRC), respectively. The results show that for both single-PD and multi-PD receptions, the bit-error-rate (BER) performance can be significantly improved at different positions within the cell and the size of the effective coverage (BER−3) can be increased by 4 times by employing few-mode based beam shaping scheme at 1:1.79 power ratio between LP01 mode and LP11 mode, compared to conventional OWC systems without few-mode based beam shaping scheme. In addition, the system tolerance to signal overlapping can also be enhanced with the proposed few-mode based beam shaping. The optimal power ratios of LP01 mode and LP11 mode when achieving the maximum effective coverage under 7% and 20% HD-FEC thresholds for single-PD and multi-PD reception have also been investigated. Furthermore, the tolerance to the interval delay with 0.23 and 0.28 symbols can be achieved in single-PD and multi-PD reception, respectively.