Rate-Splitting Multiple Access: Fundamentals, Survey, and Future Research Trends

Abstract

Rate-splitting multiple access (RSMA) has emerged as a novel, general, and powerful framework for the design and optimization of non-orthogonal transmission, multiple access (MA), and interference management strategies for future wireless networks. By exploiting splitting of user messages as well as non-orthogonal transmission of common messages decoded by multiple users and private messages decoded by their corresponding users, RSMA can softly bridge and therefore reconcile the two extreme interference management strategies of fully decoding interference and treating interference as noise. RSMA has been shown to generalize and subsume as special cases four existing MA schemes, namely, orthogonal multiple access (OMA), physical-layer multicasting, space division multiple access (SDMA) based on linear precoding (currently used in the fifth generation wireless network-5G), and non-orthogonal multiple access (NOMA) based on linearly precoded superposition coding with successive interference cancellation (SIC). Through information and communication theoretic analysis, RSMA has been shown to be optimal (from a Degrees-of-Freedom region perspective) in several transmission scenarios. Compared to the conventional MA strategies used in 5G, RSMA enables spectral efficiency (SE), energy efficiency (EE), coverage, user fairness, reliability, and quality of service (QoS) enhancements for a wide range of network loads (including both underloaded and overloaded regimes) and user channel conditions. Furthermore, it enjoys a higher robustness against imperfect channel state information at the transmitter (CSIT) and entails lower feedback overhead and complexity. Despite its great potential to fundamentally change the physical (PHY) layer and media access control (MAC) layer of wireless communication networks, RSMA is still confronted with many challenges on the road towards standardization. In this paper, we present the first comprehensive tutorial on RSMA by providing a survey of the pertinent state-ofthe-art research, detailing its architecture, taxonomy, and various appealing applications, as well as comparing with existing MA schemes in terms of their overall frameworks, performance, and complexities. An in-depth discussion of future RSMA research challenges is also provided to inspire future research on RSMAaided wireless communication for beyond 5G systems.

Secure Beamforming Design for Rate-Splitting Multiple Access in Multi-antenna Broadcast Channel with Confidential Messages

“…Receivers then reconstruct the original messages by extracting the intended common part from the decoded common message and combine it with the decoded private message [21]. RSMA enables a more flexible interference management approach of partially decoding the interference and partially treating the interference as noise, and it has been shown to bridge and outperform space division multiple access (SDMA) and power-domain non-orthogonal multiple access (NOMA) [20,[22][23][24][25]. Furthermore, the performance advantage of RSMA has also been demonstrated in terms of robustness against imperfect CSIT [26,27] and user mobility [28], SE [20], EE [29], user fairness [30], reliability [31], QoS enhancements [20], etc.…”

Weighted Sum-Rate Maximization for Rate-Splitting Multiple Access Based Secure Communication

“…Receivers then reconstruct the original messages by their extracted part of the decoded common message and their separate private message [7]. Rate-splitting multiple access (RSMA) therefore enables a more flexible interference management approach of partially decoding the interference and partially treating the interference as noise, and it has proved to be capable of bridging and outperforming space division multiple access (SDMA) and power-domain non-orthogonal multiple access (NOMA) [8][9][10][11][12]. Furthermore, the performance advantage of RSMA has also been demonstrated in many aspects, such as robustness [13], SE and EE [14].…”

Rate Splitting Multiple Access Aided Mobile Edge Computing in Cognitive Radio Networks

“…It is well known that uplink NOMA with the SIC receiver can achieve only several separated points on the rate boundary of multiple access channels, whereas uplink rate splitting multiple access (RSMA) can achieve the full rate boundary [10]. Recently, RSMA technique has been investigated for various wireless communications scenarios (see [11] and references therein). Motivated by this, we have proposed a CR-inspired rate splitting scheme to enhance the outage performance and user fairness for uplink NOMA systems [12].…”