Performance Evaluation of Non-Orthogonal Multiple Access in Visible Light Communication

In this paper, the performance of non-orthogonal multiple access (NOMA) is characterized in a downlink visible light communication system for two separate cases. In the case of guaranteed quality of service (QoS) provisioning, we derive an analytical expression of the system coverage probability and show the existence of optimal power allocation coefficients on two-user paired NOMA. In the case of opportunistic best-effort service provisioning, we formulate a closed-form expression of the ergodic sum rate, which is applicable for arbitrary power allocation strategies. The probability that NOMA achieves higher individual rates than OMA is derived. Also, we give an upper bound of the sum rate gain of NOMA over OMA in the high signal-to-noise ratio regime. Both the theoretical and simulation results prove that the performance gain of NOMA over OMA can be further enlarged by pairing users with distinctive channel conditions. We also find out that the choice of light emitting diodes (LEDs) have a significant impact on the system performance. In the case of guaranteed QoS provisioning, the LEDs with larger semi-angles have better performance; while in the case of opportunistic best-effort service provisioning, the LEDs with 35° semi-angle give nearly optimal performance.