Outage Analysis of Alamouti-NOMA Scheme for Hybrid Satellite–Terrestrial Relay Networks

In this article, we investigate the performance of hybrid satellite–terrestrial relay networks with multiuser downlink nonorthogonal multiple access. The satellite applies Alamouti space–time block coding, and users exploit a receive antenna selection technique. Communication between the satellite and users is assumed to be established with the aid of a half-duplex terrestrial relay equipped with multiple receive antennas and operating in amplify-and-forward mode, because of the heavy masking effects attributed to environmental obstacles. Subsequently, the satellite–relay link is exposed to shadowed-Rician fading, whereas the relay–users links undergo Nakagami-
$m$
fading, which is a generic statistical channel model for nonterrestrial networks. To be more practical, we consider imperfect successive interference cancellation. The exact outage probability of each user and the corresponding asymptotic expression at the high signal-to-noise ratio are derived to demonstrate the system performance. The analysis indicates that the shadowing conditions do not affect the array gain when the diversity order is dominated by the multiantenna configuration of the second hop. The theoretical derivations are validated by using Monte Carlo simulations. The numerical results indicate that the proposed scheme significantly improves the performance of each user under various shadowing conditions. It also outperforms orthogonal multiple access when proper power levels are allocated to users.