On the performance of NOMA-based two-way relay network

Non-orthogonal multiple access (NOMA) technique enhances the performance of the two-way relay network (TWRN) by using the rate-splitting strategy, i.e., by transmitting the low-power and high-power symbols simultaneously. Although the rate-splitting improves the spectral efficiency, the successive interference cancellation (SIC) receiver can cause the rate of the high-power symbol to decrease. In this paper, we propose a NOMA-based transmission scheme for a three-time-slot (3T) TWRN which improves the achievable sum-rate by (i) mitigating interference at the SIC receiver of each transceiver before decoding the high-power symbol, and (ii) decoding the low-power symbol based on the maximum-ratio combining (MRC) of the direct and relayed signals. We analyze the proposed scheme in terms of the achievable rate and its asymptotic behavior, and derive a highly accurate upper bound for the ergodic sum-rate. Additionally, we analytically demonstrate that the proposed scheme achieves the maximum rate of the 3T-TWRN. Simulation results validate our theoretical findings and show that the proposed scheme outperforms the conventional NOMA and orthogonal multiple access (OMA) schemes in TWRN.