Abstract
Rate splitting multiple access (RSMA) is a promising approach that has gained momentous attention in the field of wireless communications. With the increasing demand for higher data rates and reliable connections, traditional multiple access approaches like SDMA, NOMA have limitations in terms of interference management as well as channel state information uncertainty. The effectiveness of the RSMA has been recognized in addressing these limitations and providing improved performance in multi-antenna systems. RSMA ruptures user messages into common as well as private parts – the common part is decoded by all users to mitigate interference while the private part is decoded only by the intended user. This bridges orthogonal and non-orthogonal multiple access schemes. Benefits of RSMA include optimal performance in many scenarios, robustness against imperfect CSIT, lower feedback overhead and complexity compared to alternatives. RSMA has many potential applications in 6G use cases like mMTC, URLLC, V2X, and integrated sensing-communications. Ongoing research is still needed, especially on implementation and standardization. The current study focuses on the notion of rate splitting, the benefits of RSMA, working principle of RSMA, implementation challenges, RSMA's implementation in 5G and beyond, a comparison with other multiple access techniques, as well as its problems and future trends in wireless networks.
TopIntroduction: Understanding The Concept Of Rate Splitting
Traditional multiple access methods confront various obstacles in satisfying the growing needs of wireless communication. One of the most significant difficulties is the network's inadequate capacity and speed. Traditional systems are struggling to deliver optimal performance as the number of connected devices grows and the need for high-speed data transfer grows. Interference between users is also a serious concern. Multiple users broadcasting at the same time in busy wireless networks can generate interference, resulting in poor signal quality and lower overall network performance. This interference not only affects the individuals concerned, but also neighbouring users, resulting in a domino effect that reduces the overall network's performance. Rate Splitting Multiple Access (RSMA) (Y. Mao et al.,2018) is an innovative method for addressing the shortcomings of classic multiple access systems. The RSMA standard incorporates the idea of rate splitting, which divides the transmission rate into many simultaneous data streams. This one-of-a-kind feature enables each user to transmit and receive data at the same time, greatly enhancing network capacity and throughput. The rate splitting approach used in RSMA is based on the superposition coding concept. The splitting ratios are determined by a unique set of power and rate allocation characteristics provided to each user. RSMA offers more efficient utilisation of available resources by intelligently dividing the transmission rate, resulting in increased spectral efficiency and enhanced overall network performance.
Research interest in RSMA (B. Clerckx et al., 2016) has increased rapidly since 2017, with over 150 conference and journal papers published on the topic. Initial works focused on formulating the concept of rate-splitting for the MIMO broadcast channel and interference channel, and analysing theoretical performance bounds that demonstrate significant gains over SDMA and NOMA. Recent RSMA research can be categorized as: a) System Design: Optimizing RSMA system parameters like power allocation, beamforming vectors, message splitting, and decoding order. Both sum-rate maximization and max-min fairness formulations have been studied. b) Performance Analysis: Analysing performance of RSMA (B. Clerckx et al., 2020) in various wireless network scenarios like Cloud-RAN, integrated access and backhaul, Internet of Things, vehicle-to-vehicle links, and aerial platforms. RSMA demonstrates consistent gains over SDMA and NOMA in both theoretical capacity and numerical evaluations across these scenarios. c)Implementation Challenges: Key issues being addressed include optimization complexity, signalling overhead for channel state information acquisition, self-interference in full-duplex RSMA, integration with advanced PHY layer techniques like index modulation, and prototyping testbeds. d)Future Networks: Studying synergistic combinations of RSMA with promising 6G technologies like reconfigurable intelligent surfaces, cell-free Massive MIMO, THz communications, integrated sensing and communication, and machine learning.