Reconfigurable intelligent surface (RIS) is a revolutionary technology for sixth-generation (6G) networks owing to its ability to manipulate wireless environments. As a frequency-selective device, RIS can only effectively shape the propagation of signals within a certain frequency band. Due to this frequency-selective property, the deployment of RIS in cellular networks will introduce a complicated base station (BS)-RIS-user association issue since adjacent BSs operate at different frequency bands. In this paper, with the consideration of the frequency-selective characteristics of RIS, we aim to jointly optimize BS-RIS-user association, active beamforming at BSs, and passive beamforming of RIS to maximize the sum-rate of a RIS-assisted cellular network. We first leverage $l_0$-norm to efficiently integrate BS-RIS-user association with active and passive beamforming. Then, we adopt fractional programming (FP) and block coordinate descent (BCD) methods to deal with logarithmic and fractional parts and decouple the joint association and beamforming design problem into several sub-problems. Efficient algorithms which combine $l_0$-norm approximation, majorization-minimization (MM), and alternating direction method of multipliers (ADMM) are developed to alternately solve the sub-problems. Extensive simulation results illustrate the importance of BS-RIS-user association optimization in RIS-assisted cellular networks and verify the effectiveness of the proposed joint association and beamforming design algorithm.
翻译:重新配置智能表面(RIS)是第六代(6G)网络的一个革命性技术,因为它有能力操纵无线环境。作为一个频率选择装置,RIS只能有效地影响信号在某个频率波段内的传播。由于这种频率选择特性,在蜂窝网络中部署RIS将引入一个复杂的基站(BS)-RIS-用户联系问题,因为相邻的BS波段在不同频率波段运作。在本文件中,考虑到RIS的频率选择特性,我们的目标是联合优化BS-RIS用户协会、在BSs公司积极进行模拟,以及被动地调整RIS网络,以最大限度地提高RIS辅助手机网络的总和率。我们首先利用美元-美元-诺姆在蜂窝网络中有效地整合BS-IS-用户与主动和被动波段波段相融合的关系。然后,我们采用小程序(FP)和块协调的回程(BCD)方法来处理对数和分数部分部分部分的特性,并分解联合和将设计问题转换成若干次流动的联,将RIS-辅助性网络的交错化成若干次(IM-辅助性网络的联合-辅助性网络-辅助性网络-辅助网络-辅助性网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络,以尽量优化网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网络网),以尽量最大最大最大最大最大最大最大联合,以最大限度地网络网络网络网络,以最大限度地计算。我们,我们调,我们调,把BS-BS-BS-MMMMMDRMDMMMDMDMLMLMLMDMDMDMDMDMDMDMDMDMDMD 的升级式的升级制的主要方向,将G-MDG-G-CRMLMDMLMDMLMLMLMLMDGMLMLMDMDGMDMDRM 和MDGMDRMDRM 和M 的升级制,将合并,把M 和MDMDMDMDMDM 和M 和M 的升级制式的升级制