On the performance 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 (VLC) system. Analytical expressions of the system performance are derived for two separate scenarios. In the scenario of achieving guaranteed quality of service (QoS), the outage probability of each user is studied and the effect of power allocation coefficients on the system coverage probability is investigated. In the scenario of providing opportunistic best-effort service, system ergodic sum rate is formulated based on a fixed power allocation (FPA) strategy. Both simulation and analytical results demonstrate that, in the first scenario, the maximum coverage probability can be achieved through the exhaustive search (ES) method to find the optimum set of power allocation coefficients. In the second scenario, it is shown that unlike orthogonal multiple access (OMA) techniques, NOMA can achieve a higher system capacity for a larger number of users. Also, the performance of NOMA can be further enhanced by choosing LEDs with a suitable semi-angle. When compared with OMA, NOMA can increase the system capacity by 125% if LEDs with 30° semi-angle are used.