Demonstration of Performance Improvement in Multi-User NOMA VLC System Using Joint Transceiver Optimization

Abstract

The bit error ratio (BER) performance of a non-orthogonal multiple access (NOMA) visible light communication (VLC) system is poor due to the unequal distances between adjacent points in the superposition constellation (SC). In this paper, we propose a novel scheme to improve the BER performance by adjusting parameters to change the shape of SC at the transmitter and by adjusting the parameters of successive interference cancellation (SIC) decoding at the receiver simultaneously, which is called a SC and SIC adjustment (SC-SIC-A) scheme. For multi-user NOMA VLC system, we derive the closed-form BER expression for each user, where the modulation format is four-quadrature amplitude modulation. According to the derived BER expressions, we formulate an optimization problem that minimizes the average BER for all users by adjusting the obtained parameters of SC and SIC decoding via differential evolution algorithm. The improvement of capacity performance is investigated consequently. In order to verify the feasibility and effectiveness of the proposed SC-SIC-A scheme, we carried out theoretical analysis, Monte Carlo simulation and experiments of two-user and three-user NOMA VLC systems. Results show that the SC-SIC-A scheme outperforms the existing schemes in NOMA VLC system, where the signal-to-noise ratio (SNR) reductions to achieve BER of 10−3 are 1.3 dB and 0.8 dB for both users in the two-user NOMA VLC system, respectively, and the SNR reductions to achieve BER of 10−3 are 5.7 dB, 4.3 dB and 4.6 dB for all users in the three-user NOMA VLC system, respectively.