Integrated Satellite-Terrestrial Networks With Coordinated C-NOMA and Relay Transmission

For the cooperative nonorthogonal multiple access (C-NOMA)-aided integrated satellite-terrestrial network (ISTN), an outage is inevitable if the channel from the satellite to the weak user is in deep fade. To handle this issue, this article proposes to deploy relay nodes to assist the communication, specifically, the relay and strong user forward information, which is sent from the satellite, to the weak user. After that, the weak user can boost its received signal strength by utilizing maximum ratio combining. In this context, we further study two kinds of relay protocols, i.e., decode-and-forward (DF) and amplify-and-forward (AF). For each protocol, the closed-form and asymptotic expressions of the outage probability (OP) are derived and then, based on the asymptotic OP, the diversity order is analyzed. Results indicate the DF protocol is preferable to the AF from the OP aspect although it incurs more computational load. Besides, the diversity order of the proposed ISTN is identical to that of C-NOMA and twice that of the relaying network. Simulation results clarify the superiority of the proposed scheme.