Coordinated Direct and Relay Transmission With NOMA and Network Coding in Nakagami-<i>m</i> Fading Channels

Although the use of coordinated direct and relay transmission (CDRT) in non-orthogonal multiple access (NOMA) can extend coverage, its duplicated reduces spectrum efficiency (SE) NOMA. To improve SE, we propose a spectrum-efficient scheme for NOMA-based CDRT over Nakagami- $m$ fading channels. In this scheme, base station (BS) connects with cell-center user (CCU) directly while communicating cell-edge (CEU) via CCU. Then, CCU network coding to process retransmit signals sent by BS first CEU later. Finally, simultaneously broadcast downlink signals. We derive closed-form expressions average fairness index energy (EE) as well asymptotic SE using both perfect imperfect successive interference cancellation (SIC). Simulations verify correctness our theoretical analysis superiority proposed EE.