Outage Performance of C-NOMA-Assisted Cognitive Satellite-Terrestrial Networks.

This paper introduces cooperative non-orthogonal multiple access (NOMA) into a cognitive satellite-terrestrial network to improve the system performance. Specifically, both the secondary transmitter (ST) and the full-duplex (FD) secondary receiver (SR) are proposed to cooperate with the primary user (PU). The ST can transmit superposed signal of primary message from the satellite and the secondary message to the PU and SR simultaneously by NOMA protocol, while the SR also cooperates with the PU to forward the primary message based on the FD protocol. Closed-form approximate expressions for the outage probabilities of the PU and SR are derived. Then, the diversity order of the PU is also obtained. It is shown that the diversity order of the PU can be improved by 1 compared to the existing work that the SR does not cooperate. Monte Carlo simulations confirm the correctness of the theoretical analysis.