On the Energy Efficiency of One-Layer SISO Rate-Splitting Multiple Access

Rate-splitting multiple access (RSMA) combines the concepts of non-orthogonal multiple access (NOMA) and space-division multiple access (SDMA) to provide higher sum-rates (SRs). In particular, one-layer RSMA splits the users' message into two parts: a single common message for all users and a private message for each user. In this work, we consider the problem of maximizing the downlink (DL) energy efficiency (EE) for one-layer RSMA subject to specific quality of service (QoS) constraints and under consideration of a single-input single-output (SISO) system. The solution to this multi-objective problem depends on finding: i) the optimal DL transmit powers, ii) the optimal rate allocation, and iii) the optimal radio frequency (RF) transmit power that must be selected by the base station (BS) so as to obtain the best EE. Thus, we decouple the original problem into three sub-problems that find each part of the solution sequentially. We take advantage of an earlier solution available in the literature for the first two decoupled sub-problems and extend it to an algorithm that maximizes the EE. Numerical results demonstrate consistent performance bounds of our proposed algorithm to the optimal EE values, comparing them to NOMA and orthogonal multiple access (OMA) solutions.