An Analysis on Rate-Splitting Multiple Access for IRS Aided 6G Communication

Abstract

Integrating intelligent reflecting surface (IRS) and Rate-Splitting Multiple Access (RSMA) is an effective solution to improve the spectral/energy efficiency in next-generation (beyond 5G (B5G) and 6G) wireless networks. In this paper, we investigate a rate-splitting (RS)-based transmission technique for an IRSaided communication network involving both near and cell-edge users. In particular, we derive a new architecture called IRS-RS that leverages the interplay between RS and IRS, with an aim to maximize the weighted sum-rate (WSR) of users by selecting the reflecting coefficients at the IRS and designing beamformers at the BS under the constraints of power at the base station (BS), quality of service (QoS) at each user and finite resolution at the IRS. To solve the non-convex WSR maximization problem, we propose an alternating algorithm and compare its performance with baseline non-orthogonal multiple access (NOMA) based transmission for an IRS-aided communication network for both perfect and imperfect CSIT cases. Through numerical results, it is shown that the proposed IRS-RS architecture yields better QoS with respect to the cell-edge users when compared to IRS-NOMA transmission scheme.Index Terms-Intelligent reflecting surface (IRS), rate-splitting (RS), non-orthogonal multiple access (NOMA), beamforming.

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

“…The merits of RSMA in multi-antenna networks have motivated the study of RSMA in IRS-aided communication [126], [127], [134], [199], [200]. The authors of [126] were the first to study RSMA for the MISO BC with multiple IRSs cooperatively assisting the downlink transmission from a BS to multiple users.…”

“…By jointly optimizing the precoders, the message splits of 1-layer RS, and the phase shifts of the IRS to maximize EE, RSMA was shown to achieve a better EE performance than NOMA and OFDMA in the IRS aided MISO BC. 2-layer HRS and IRS-aided transmission strategies are further studied in [134], [199], [200], where the transmission from the BS to the users in each HRS user group is assisted by one independent IRS. RSMA was shown to improve the WSR and outage performance compared to 1-layer RS/MU-LP/NOMA-based IRS transmission strategies.…”

Fully Connected Reconfigurable Intelligent Surface Aided Rate-Splitting Multiple Access for Multi-User Multi-Antenna Transmission

“…• Fully RIS SDMA: This is a special case of the proposed scheme when the power allocated to the common stream is fixed to zero. • Single RIS RSMA: This is the single connected RIS aided RSMA scheme, as studied in [32]. • Single RIS SDMA: This is the conventional single connected RIS aided SDMA scheme, as studied in [22].…”

“…When constraints (10c) and (10d) for scattering matrix Θ are replaced by constraint (6), P 1 reduces to the sum-rate problem of the single connected RIS aided RSMA [32]. When the power allocated to w 0 is fixed to zero, the problem reduces to the sum-rate problem for the conventional single connected RIS aided SDMA [22].…”

IRS-Assisted Rate-Splitting Multiple Access for Overloaded Multiuser MISO Transmission

“…These two research works examined the performance of rate-splitting techniques in IRS-aided communication systems in terms of the outage probability and demonstrated that the proposed schemes outperform the traditional non-RSMA schemes in a multiuser system. In another work [12], the authors analyzed the potential of RSMA for enabling the 6G communications through the use of IRS. They provided an in-depth analysis of the transmitter side of IRS-aided RSMA networks for multiple near and cell-edge users, and compared it with the IRS-assisted non-orthogonal multiple access (NOMA) system in terms of the weighted sum-rate (WSR) with perfect and imperfect CSI at the transmitter (CSIT) cases.…”