Power Minimization for Uplink RIS-Assisted CoMP-NOMA Networks With GSIC

To accommodate the stringent requirements of massive connectivity and ultra-high throughput, both reconfigurable intelligent surface (RIS) and non-orthogonal multiple access (NOMA) have been perceived as the key techniques for future communication networks. In this paper, a versatile framework is conceived to boost transmit power efficiency for RIS-enabled multi-group NOMA networks in the presence of coordinated multi-point (CoMP) reception and imperfect successive interference cancellation (SIC). Particularly, a group-level SIC (GSIC) method is proposed to eliminate the decoded group’s interference together with the well-designed transceivers to mitigate the aggregated interference, including the intra-group interference, the residual interference caused by imperfect SIC, and the interference of NOMA users decoded later. According to the novel framework, a power minimization problem is formulated by collaboratively optimizing the transmit power and the phase shifts. To render the problem tractable, an alternating scheme is developed to optimize the transmit power and the phase shifts iteratively. Specifically, the transmit powers for the users in the same group are devised by a parallel iteration algorithm, whilst the phase shifts are optimized by a sequential rotation method. In simulations, it is shown that the proposed scheme requires less transmit power than various benchmark methods under the constraint of each user’s quality of service.

I. Introduction

Since 2019, the deployment of the fifth generation (5G) wireless network has been gradually rolled out worldwide. In regard to the development law of “using one generation, developing one generation”, the investigation on the sixth generation (6G) communication system has drawn substantial attention from both academic and industrial communities. Several well-known research institutions have issued 6G white papers, wherein reconfigurable intelligent surface (RIS) has been recognized as a promising technique for 6G [1]. Specifically, RIS is a passive device without the capacity of signal processing, which can be easily deployed on building facades, roadside billboards, and so on. By manipulating the phases of incident signals, RIS has the ability of creating favourable radio propagation environment in an energy-efficient and cost-effective manner [2]. It has been reported that both system throughput and power efficiency can be significantly enhanced by the deployment of RISs [3], [4].