Rate-Splitting Multiple Access and Dynamic User Clustering for Sum-Rate Maximization in Multiple RISs-Aided Uplink mmWave System

Abstract

In this paper, a reconfigurable intelligent surfaces (RISs)-aided millimeter wave (mmWave) uplink (UL) rate-splitting multiple access (RSMA) system is investigated which targets to achieve better rate performance and enhanced coverage capability for multiple users. The considered UL RSMA model splits the rate for each user by dividing their message into multiple parts and hence exploits all the necessary degrees of freedom to achieve maximum capacity region and high user fairness. In particular, we focus on the sum-rate maximization for considered UL RSMA system subject to joint optimization of power allocation to the UL users and beamforming design, i.e., active receive beamforming at the base-station (BS) and passive beamforming at multiple RISs. To efficiently mitigate high inter-node interference in multi-user scenario, we first provided a low-complex user pairing scheme based on k-means clustering and then develop an effective low-cost alternating optimization framework to solve the joint optimization problem sub-optimally by decoupling the problem into different sub-problems of power allocation and beamforming design. Specifically, the sub-problems of power allocation and beamforming design are solved using successive convex approximation, Riemannian manifold and fractional programming techniques. Later, the unified solution based on block coordinate descent (BCD) algorithm is proposed. Extensive numerical simulations validate that the user-clustering effectively significantly improves the performance gain and the considered RSMA system outperforms the conventional multiple schemes in terms rate and user-fairness. Also, the exploitation of spatial correlation among each RIS elements i.e., non-diagonal phase-matrices at each RIS achieve better performance that conventional diagonal phase-matrices setting.

Coverage, Throughput, and Energy Efficiency Enhancement in Beamspace Massive MIMO System with Lens Antenna Array Using ORP and RSMA

“…The problem in (21) is nonconvex owing to constraints C3 and C4. Therefore, it is necessary to introduce the variables α m,n and β m,n to handle constraints C3 and C4, respectively.…”

“…To this end, the nonconvex feasible sum throughput optimization problem (21) can be reframed into the following approximated convex problem:…”

“…RSMA is a type of power-domain non-orthogonal multiple access technique that is based on the multi-antenna rate-splitting technique, where each message is divided into a common segment and a private segment, and the common segments of all the PUTs are encoded into a common message and the private segment of each PUT is encoded into a private message. Then the common message is overlaid on top of each PUT's private message [16]- [21]. RSMA has been shown to increase the achievable degrees of freedom (DoF) when the channel state information error at the transmitter (CSIT) decreases with increasing signal-to-noise ratio (SNR) [17].…”

Symbol error probability of mmWave communications with transmit antenna selection and RISs under the impacts of hardware impairments

“…Additionally, RIS‐oriented mmWave design has shown great promise in overcoming the limitations of traditional beamforming techniques, providing more flexible and adaptable wireless connectivity 17–19 . Moreover, the mathematical analysis of RISs‐assisted mmWave communications was also conducted 13,20 . More specifically, the sum rate, outage probability, and throughput formulas of RISs‐assisted mmWave communications were derived to analyze the system behaviors.…”

“…[17][18][19] Moreover, the mathematical analysis of RISs-assisted mmWave communications was also conducted. 13,20 More specifically, the sum rate, outage probability, and throughput formulas of RISs-assisted mmWave communications were derived to analyze the system behaviors. Besides the great benefits of RISs, a performance loss induced by high frequencies of the mmWave band was also investigated.…”