  In this paper, a multipoint-to-point system consisting K users and a central
node with non-orthogonal multiple access (NOMA) technique over free space
optical (FSO) channel is characterized for two cases. In the case of guaranteed
user's quality of service (QoS), the outage probability is derived. Another
case is that user's QoS is determined by their own channel conditions. The
developed analytical results of ergodic sum data rate show that NOMA
outperforms orthogonal multiple access (OMA). Besides, the power control scheme
is proposed, and results show that the power control scheme has great influence
to the user's QoS. Monto Carlo simulation has been done, and it matches quite
well with the theoretical analysis.
