Analysis of Hierarchical Rate Splitting for Intelligent Reflecting Surfaces-Aided Downlink Multiuser MISO Communications

Abstract

An intelligent reflecting surface (IRS) is an emerging technology in the next-generation (B5G and 6G) wireless communications with the aim of improving the spectral/energy efficiency of the wireless networks. In this paper, we focus on multiple IRS-aided multiuser multiple-input single-output (MISO) downlink network, where each IRS is deployed near to the cell boundary of the cellular network in order to help the downlink transmission to the cell-edge users. To achieve the significant performance benefits provided by the rate-splitting (RS) transmission in multiuser scenario, two-layer hierarchical rate splitting (2L-HRS) technique is deployed at the base station (BS) to serve all the users. Furthermore, we propose an On-Off scheme for controlling the IRSs with practical phase shifts. In order to analyze the performance of the users, we derive the closed-form expressions of outage probability for both cell-edge users and near users. By extensive Monte Carlo simulations, we demonstrate that the proposed design framework outperforms the corresponding one-layer RS (1L-RS), the multiuser linear precoding (MU-LP) and 2L-HRS without IRS. In addition, we reveal the advantages of introducing RS-based IRS in improving the cell-users' performance. The impact of channel estimation errors due to imperfect channel state information, and the various network's parameters, such as the number of reflecting elements and the number of cell-users, on the network performance is demonstrated.INDEX TERMS Intelligent reflecting surface (IRS), rate splitting (RS), multiple-input single-output (MISO), downlink, multiuser.KESHAV SINGH (Member, IEEE) received the M.Sc. degree in information and telecommunications technologies from Athens Information Technology, Greece, in 2009, and the Ph.D. degree in communication engineering from

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.…”

“…• Intelligent reconfigurable surface (IRS) [126], [127], [134]. • Joint communication and radar [117], [139], [140].…”

“…To further reduce the computational complexity, another line of RSMA research focuses on closed-form and lowcomplexity precoder designs [57], [71], [72], [76], [80], [81], [88], [92], [93], [97], [113], [134], which is summarized in this subsection.…”

“…• Weighted matched beamforming (MBF) [72], [76], [81], [92], [93], [97], [113], [134]: The precoder direction pc is designed to maximize the achievable rate of the common stream, which can be formulated as follows…”

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

“…The interplay of RSMA and RIS is first investigated in [25] for multi-user multi-antenna networks, where RIS aided RSMA transmission model achieves higher energy efficiency than NOMA and orthogonal frequency division multiple access (OFDMA). RIS aided RSMA transmission is further shown to enhance the fairness among users [26], reduce the transmit power [27], and achieve superior outage performance [28], [29] over conventional RIS-aided networks. However, all the above works only use the single connected RIS architecture.…”