Polar Coded RSMA: An Efficient Approach for Enhancing Effective Throughput in Internet of Things

Rate-splitting multiple access (RSMA) is a flexible multiple access scheme that leverages the advantages of superposition coding to enhance user throughput, making it particularly advantageous for Internet of Things (IoT) scenarios. In this article, we consider practical coding and modulation schemes, and develop an analytical method to analyze effective throughput with finite block lengths and QPSK modulation. First, an analysis of the polarization effect between users in the RSMA system is conducted, with the impact of finite length coding taken into consideration. Thereafter, the effective throughput is proposed as the optimization objective. Effective throughput, which accurately reflects both system throughput and error probability, is a pivotal metric for designing IoT systems. Subsequently, to address this optimization problem, we propose an alternating optimization method that leverages successive convex approximation (SCA) and convex optimization in an iterative manner to find feasible solutions. Utilizing the optimized coding rates and precoding matrices, we design a polar-coded RSMA scheme for IoT application. Numerical results demonstrate that under QPSK modulation, RSMA can achieve up to a 33.08% gain in effective throughput compared with NOMA/SDMA, while polar-coded RSMA can reach up to 98.71% of the optimal performance target.