Analysis and Design of Common Channel Precoding Algorithms for RSMA

This paper explores a communication system based on rate-splitting multiple access, aiming to improve spectral efficiency in multi-user networks. In systems with rate splitting messages split into common and private parts, allowing more efficient resource allocation across users. The paper presents a mathematical model and optimization problem for designing the common stream precoder, which plays a key role in ensuring optimal data transmission across multiple users. Two common stream precoding algorithms are proposed: one based on singular value decomposition and another using gradient descent. These algorithms are designed to optimize the common stream precoder and enhance spectral efficiency. A numerical experiment is conducted on a 2×2 multiple input single output system, using a zero-forcing precoder for private streams. The results show that the proposed algorithms outperform traditional methods and multi-user multiple input multiple output systems in terms of average spectral efficiency. This demonstrates the potential of rate splitting multiple access for improving network performance, offering a more efficient use of resources and higher throughput.