Cooperative Rate-Splitting Multiple Access in Heterogeneous Networks

Rate-splitting multiple access (RSMA) has been considered as a promising technology to improve spectral efficiency of wireless communication systems. However, in heterogeneous networks (HetNets), the achievable rate in RSMA is limited by cross-layer interference and the rate of the user with the worst channel condition. To address this issue, we propose a cooperative RSMA (C-RSMA) scheme where the user with the high-quality channel acts as a full-duplex relay to assist in transmitting common stream to the user with weak signals. We formulate the resource allocation problem of C-RSMA in a two-layer HetNet, aiming to maximize the downlink sum rate of all small cell users. The problem is firstly decoupled into the subchannel matching problem and the rate optimization problem. Then, a transfer exchange matching algorithm and a successive convex approximation-based algorithm are proposed to solve these two subproblems, respectively. Simulation results show the sum rate of the proposed C-RSMA scheme is on average 10.1% higher than that of RSMA, and 18.0% higher than that of cooperation nonorthogonal multiple access.