Symbol Error Analysis for Integrated Satellite-Terrestrial Relay Networks with Non-orthogonal Multiple Access under Hardware Impairments

As a promising approach to increase spectrum efficiency and user fairness, non-orthogonal multiple access (NOMA) technique, with strong potential for applications in integrated satellite-terrestrial relay networks (ISTRNs), has been considered as a vital part of the future wireless network architecture. However, studies on the symbol error performance of NOMA-based ISTRNs with multiple relays and multiple users are still in their infancy. In this study, we propose a dual-user NOMA-based ISTRN architecture with hardware impairments to all nodes. This study uses the opportunistic scheduling scheme to select the optimal relay for the relaying system with a decode-and-forward protocol and maximum ratio combination technique to improve the signal quality. We also use a shadowed Rician distribution to model fading in the satellite channels, while the terrestrial channels are assumed to follow a Nakagami-
m
fading distribution. In addition, the impacts of the path loss and beam pattern on the system are considered. Closed-form expressions are derived for the average symbol error rate (SER) for near and far users. We verify that the numerical results agree with the theoretical calculations and demonstrate the superiority of the proposed architecture with decode-and-forward protocol compared with the case where line-of-sight links are used to transmit signals alone and with the case using amplify-and-forward protocol. Finally, we analyze the effect of some critical parameters on the average SER of the considered system and present some helpful insights in relation to engineering design.