The technology of Reconfigurable Intelligent Surfaces (RISs) has lately attracted considerable interest from both academia and industry as a low-cost solution for coverage extension and signal propagation control. In this paper, we study the downlink of a multi-cell wideband communication system comprising single-antenna Base Stations (BSs) and their associated single-antenna users, as well as multiple passive RISs. We assume that each BS controls a separate RIS and performs Orthogonal Frequency Division Multiplexing (OFDM) transmissions. Differently from various previous works where the RIS unit elements are considered as frequency-flat phase shifters, we model them as Lorentzian resonators and present a joint design of the BSs' power allocation, as well as the phase profiles of the multiple RISs, targeting the sum-rate maximization of the multi-cell system. We formulate a challenging distributed nonconvex optimization problem, which is solved via successive concave approximation. The distributed implementation of the proposed design is discussed, and the presented simulation results showcase the interplay of the various system parameters on the sum rate, verifying the performance boosting role of RISs.
翻译:重新配置的智能表面技术最近吸引了学术界和工业界的极大兴趣,认为这是一个低成本的扩大覆盖面和信号传播控制解决方案。在本论文中,我们研究了由单干基站(BS)及其相关单干基站用户以及多个被动的LISS组成的多细胞宽频通信系统的下行链路。我们假定,每个BS控制单独的RIS并进行交错频率分解传输(OFDM)。不同于以前将RIS单元要素视为频率加速阶段转换器的各种工作,我们把它们模拟为Lorentzian共振器,并联合设计BS的电力分配以及多个RIS的阶段配置,目标是使多细胞系统达到总和率最大化。我们制定了一个具有挑战性的分布式的非电解波优化问题,通过连续的组合近似度来解决。讨论拟议的设计在分布式实施,并介绍了模拟结果,展示了系统参数在总和率上的相互作用,核查了性能增强作用。