Multi-Group Multicast Sum-Rate Maximization Based on Reconfigurable Intelligent Surface and D2D for MIMO Communication System

Reconfigurable intelligent surface (RIS) has the characteristics of programmable wireless environments, and device-to-device (D2D) communication can fully utilize network resources. Therefore, in this paper, RIS and D2D technologies are cleverly integrated into multicast multiple-input multiple-output (MIMO) communication system. The goal is to maximize the multi-group multicast sum-rate (SR) by jointly optimizing the orthogonal resource block (ORB) reusing coefficients, beamforming vector of the access point (AP), power assignment of D2D pairs, and reflection coefficients of RIS while meeting the transmission power of the AP, rate requirements of user equipments (UEs), ORBs reusing, and reflecting elements modulus-one constraints. This is a mixed-integer nonlinear programming (MINLP) problem. To solve this problem, we propose a new block coordinate descent (BCD)-based algorithm to decouple the original optimization problem into four sub-problems. Firstly, a new directional search algorithm is proposed to effectively optimize ORB reuse coefficients. Secondly, based on Cauchy-Schwarz inequality, the value of the beamforming vector is calculated. Next, successive convex approximation (SCA)-based method is adopted to optimize the power assignment of D2D pairs on each ORB. Finally, we develop the auxiliary relaxation approach (ARA) to optimize the reflection coefficients of RIS. The simulation results confirm that compared to existing designs and algorithms, the proposed design can greatly improve the multicast SR, the proposed algorithm is reasonable and efficient.