Performance optimisation of indoor SVD-based MIMO-OFDM optical wireless communication systems

Abstract

The performance of multiple-input and multiple-output (MIMO) flip-orthogonal frequency division multiplexing (flip-OFDM) for indoor optical wireless communications (OWCs) is studied here. To improve the system performance in terms of the bit error rate (BER), the singular value decomposition (SVD)-based MIMO technique is applied together with the bit loading technique. The authors, especially, focus on optimising the BER performance of SVD-based MIMO-OFDM OWC systems under the impact of the OFDM symbol design, the configuration of MIMO transmitters, the required data rates, the available bandwidth, and the angular diversity based on tilting receiver photo detectors (PDs). The system BER expressions are analytically derived and verified to be accurate through comparison with simulation results. The authors find that the 9 × 4-MIMO system is the optimal configuration in terms of a large coverage of low BER regions and low computational complexity for the 5 m × 5 m room. In addition, polar angle tilting of PDs can effectively improve the BER performance. Finally, in case of light dimming control with a low total transmit optical power, the system can benefit from a high multiplexing gain with a large tilting polar angle, as indicated by improved condition numbers of MIMO channel matrices.