Multi-user access in wireless optical communication system

In this paper, a multipoint-to-point system consisting K users and a central node over wireless optical communication (WOC) channel is analyzed. The scenario focused on is that there is simultaneous communication from a number of users to the central node. As a powerful solution, we utilize non-orthogonal multiple access (NOMA) technique in the system. Although the superiority of NOMA in radio frequency (RF) system has been greatly considered, the NOMA in WOC still needs further research due to the special features of WOC, especially the non-broadcast nature of optical beam and the vulnerable turbulence channel. With the special features of WOC in mind, system is evaluated in terms of outage probability, bit error rate and ergodic sum rate. In addition, we theoretically prove that NOMA outperforms orthogonal multiple access (OMA), and the performance gain increases with the increase of turbulence strength. Hence, NOMA is more suitable for WOC, especially in strong turbulence channel. Moreover, we also analyze the user pairing scheme. Monte Carlo simulations have been done, which match quite well with the theoretical analysis.