An SCA and Relaxation Based Energy Efficiency Optimization for Multi-User RIS-Assisted NOMA Networks

Abstract

Reconfigurable intelligent surface (RIS) assisted non-orthogonal multiple access transmission can effectively improve the energy/spectrum efficiency in wireless networks. This paper designs a low-complexity scheme to achieve the balanced tradeoff between the sum-rate and power consumption in a RIS-assisted NOMA system, which can be measured by energy efficiency. To solve the formulated problem effectively, the original non-convex problem is first decomposed into two subproblems, i.e., beamforming optimization and phase shift optimization. Alternating optimization is proposed to solve these two subproblems iteratively. In particular, successive convex approximation (SCA) is utilized to convert the non-convex constraints to convex ones. The provided simulation results demonstrate that the proposed scheme can achieve superior performance on energy efficiency compared to the random phase shifts scheme.

Energy-Efficient Design of STAR-RIS Aided MIMO-NOMA Networks

“…Note that ( 35) is not a convex problem because R k,j is not convex with respect to Θ n . Therefore, we optimize the phase shift of the STAR-RIS by using SCA, which is widely used to approximate the non-convex problems into convex ones [37]. The main idea of SCA is to find out the problem whose optimal value is close to that of the original problem with iterations.…”

Joint Phase Shift and Beamforming Design in a Multi-User MISO STAR-RIS Assisted Downlink NOMA Network

“…n k ∼ CN (0, σ 2 ) is the additive white Gaussian noise (AWGN). For traditional NOMA scheme such as [10], successive interference cancellation (SIC) is implemented with a given decoding order of all K users {U 1 , • • • , U K }. Specifically, given two of these K users, denoted by U k and U j , k<j, the U k 's signal is decoded before U j 's one.…”

“…The minimum SINR for each user is 10 dBm. The internal circuit power P c and power amplifier coefficient η are set to 20 dBm and 0.8, respectively [10].…”

“…Compared with orthogonal multiple access (OMA), where the users can only be allowed to transmit or receive the signals on their own channels, NOMA enables users to share the same time slot, frequency domain and channel code [8], [9]. This characteristic significantly improves the spectrum efficiency [1] and enables massive connectivity of the devices in the networks [10]. Inspired by the aforementioned benefits, the aim of this work is to design a multi-user STAR-RIS assisted NOMA network and analyze its energy efficiency performance.…”

“…SCA and SDR were also applied to tackle the optimization of beamforming vectors and phase shifts. Different from [1] and [11], in [10], the RIS-assisted NOMA networks were extended to the multi-user case and the proposed scheme based on the problem relaxation and SCA and it achieved the superior performance in energy efficiency as well. Besides, [12] and [13] also studied the power consumption minimization problem in an RIS-assisted multi-cluster systems, where the concept of central and edge users are proposed.…”