Outage Probability Analysis of Rate Splitting Multiple Access-Based Hybrid Satellite-Terrestrial Relay Network with Relay Selection

In this paper, we investigate the outage performance of rate-splitting multiple access (RSMA)-based hybrid satellite-terrestrial relay network (HSTRN) with relay selection. We focus on two relay selection strategies, i.e., partial and two-stage relay selection. The satellite-terrestrial relay channels and the terrestrial relay-user channels follow the shadowed Rician and Nakagami- $m$ fading, respectively. The effect of imperfect channel state information (CSI) is also taken into account. The exact and asymptotic outage probability expressions are derived, and the diversity gains and coding gains are obtained. Simulation results validate the derived outage probability expressions. The power allocation optimization problem is formulated in terms of user fairness with the help of derived asymptotic outage expressions. Moreover, the RSMA-based system is compared with the nonorthogonal multiple access (NOMA)-based system. It has been shown that the RSMA-based system outperforms the NOMA-based system, especially when the number of users is high.