Non-Orthogonal Multiple Access for RIS-Assisted mmWave Multicast Transmission

To enhance the wireless channel quality of the worst user and further improve spectral efficiency for multicast transmission, this letter proposes a non-orthogonal multiple access (NOMA) and reconfigurable intelligent surface (RIS)-assisted joint multicast and unicast transmission approach (NR-JMU) for mmWave system. We investigate the impact of the decoding order of successive interference cancellation (SIC) and formulate the joint multicast and unicast transmission problem to maximize the multicast spectral efficiency (MSE) while ensuring the reliability of the unicast user. And then, an enhanced semidefinite relaxation based triple alternation optimization algorithm (eSDR-TAO) is propsoed to figure out the optimal active beamforming, passive beamforming and power allocation. Simulation results show that eSDR-TAO exhibits fast and stable convergence performance. The results also indicate that the SIC decoding order is related to the unicast rate requirement, and unicast-first improves the MSE up to 124.5% and 15%, compared with the orthogonal multiple access and multicast-first, respectively.