Performance Analysis of Three User Cooperative NOMA

Cooperative non-orthogonal multiple access (NOMA) enhances the spectral efficiency and massive connectivity in wireless systems. In this paper, we present a performance analysis of a decode-and-forward cooperative NOMA system, comprising of a base station (BS) and three user equipments (UEs). One of the UEs, which is located far away from the BS, has a weak link to the BS, and the other two near UEs alternately relay the messages to the far UE. We analyse the outage probability, which is defined as the probability that the message transmission rate to the UEs falls below a pre-determined threshold, and derive closed-form expressions for it. We observe that as the rate threshold increases, outage probability increases for all the UEs. Also, it is observed that at low and high SNRs, the outage probability at the far UE reduces as its link strength to BS reduces.