Capacity Enhancement of NOMA‐SWIPT IoT Relay System with Direct Links over Rayleigh Fading Channels

Abstract

It is known that when the direct links between the base station (BS) and the users exist and are nonnegligible, consolidating direct links could significantly enhance the performance of the cooperative relaying systems. Therefore, taking the impact of direct link into account, in this article, we investigate the capacity enhancement of the nonorthogonal multiple access (NOMA) with simultaneous wireless information and power transfer (SWIPT) for the Internet of Things (IoT) relay systems over the Rayleigh fading channels. Specifically, for the considered NOMA‐SWIPT system with direct links, we study a time‐switching energy harvesting (EH) architecture in which a BS transmits two symbols to the two users through the direct links and via an EH‐based relay node. On the receiving user node, we employ maximum ratio combining (MRC) to show the capacity enhancement of the considered system. Moreover, analytical expressions for the Ergodic capacity and Ergodic Sum Capacity are mathematically derived for the MRC and single signal decoding scheme, and the analytical expressions are corroborated with the Monte‐Carlo simulation results. This not only reveals the effect of different EH parameters on the system performance but it also demonstrates the capacity enhancement of the considered NOMA‐SWIPT system compared to a similar system without direct links and to conventional OMA schemes.