Relay selection schemes for Cooperative NOMA (C-NOMA) with simultaneous wireless information and power transfer (SWIPT)

Non-orthogonal multiple access (NOMA) is considered as an important technique to alleviate the spectral scarcity of wireless networks. Cooperative NOMA (C-NOMA) along with simultaneous wireless information and power transfer (SWIPT) pave paths towards energy and spectral efficient communication networks. This paper investigates SWIPT enabled multiple relay C-NOMA network, where dedicated intermediate relays are energy-constrained and harvest energy from the transmitted source signal. New two-stage relay selection (RS) schemes for C-NOMA with fixed power allocation and dynamic power allocation at relay node are proposed. Analytical expressions and asymptotic expressions of outage probability for proposed schemes and partial RS are derived to evaluate the system performance. Simulation results demonstrate that two stage RS provides the maximum performance gain at high SNR regime, while the partial RS is preferable at low SNR. Based on outage probability difference, a hybrid RS scheme which switches between partial and two-stage is introduced. The important insights of analytical results, such as comparative analysis of relay selection schemes, performance gain over SWITP OMA networks, effect of data rates, effect of relay location, and impact of using SWIPT on the outage performance of C-NOMA networks are discussed.