Efficient downlink MU-MIMO VLC systems with NOMA-OTFS modulation for indoor applications

Abstract

In optical wireless communication (OWC), visible light communication (VLC) has shown great potential and attractive performance in indoor environments. However, the limited modulation bandwidth of VLC technologies poses performance restrictions. We propose a new approach for downlink communication utilizing multiple-input multiple-output (MIMO) technology. Our approach integrates non-orthogonal multiple access (NOMA) with orthogonal time frequency space modulation (OTFS) to improve transmission performance, particularly for low mobility when using NOMA-OTFS. Our proposed work focuses on the crucial stage of NOMA with successive interference cancellation (SIC), which involves equalization using efficient schemes, such as decision feedback equalizer (DFE), frequency-domain zero-forcing linear equalizer, and minimum mean square error-SIC at the receiver. Through extensive experimentation, it is observed that the DFE with SIC outperforms other equalizers, demonstrating a lower outage probability and a better BER. The effectiveness of the optimized analytical algorithm for ML-based downlink NOMA-OTFS modulation is confirmed through theoretical BER validation. Moreover, the simulation findings indicate that, in a multiuser (MU) scenario, the proposed NOMA-OTFS exhibits a high performance compared with traditional NOMA combined with orthogonal frequency division multiplexing in downlink MU-MIMO VLC systems. This performance advantage is observed for both MIMO and multiple-input single-output multiplexing techniques with power allocation of the users, specifically in terms of BER improvement and peak-to-averagepower ratio reduction.