Performance Analysis and Power Allocation for NOMA-Based Hybrid Satellite-Terrestrial Relay Networks With Imperfect Channel State Information

In this paper, we study the multiple-user non-orthogonal multiple access (NOMA) scheme in the hybrid satellite-terrestrial relay networks (HSTRN). The proposed system model takes into account both the decode-and-forward (DF) and amplify-and-forward (AF) protocols at the relay and the imperfection of channel state information (CSI) at all nodes. We analyze the outage performance and investigate the power allocation problem to ensure fairness among users. Specially, we derive the closed-form expressions and the asymptotic expressions at high signal-to-noise-ratios (SNR) region for the outage probability of each user. Based on the asymptotic expressions, the considered non-convex power allocation problem is approximated to a generalized linear fractional programming problem. A low-complexity algorithm is developed to yield an optimal solution. Simulation results demonstrate the validity of theoretical results. The impacts of the channel estimation error and channel fading parameters on the outage performance are analyzed. Comparisons between NOMA and orthogonal multiple access (OMA), as well as between DF and AF protocols are also shown.