论文标题
RIS辅助的无细胞大规模MIMO网络的合作波束形成
Cooperative Beamforming for RIS-Aided Cell-Free Massive MIMO Networks
论文作者
论文摘要
无细胞的大规模多输入多输出(CF-MMIMO)和可重新配置的智能表面(RIS)的组合被认为是提高网络容量并增强覆盖能力的有希望的范式。但是,为了获得RIS AID的CF-MMIMO的全部好处,主要挑战是在基站(BSS),RISS和用户中有效设计合作波束形成(CBF)。首先,我们研究了分数编程,以将加权总和(WSR)最大化问题转换为可拖动的优化问题。然后,采用交替优化框架将转换的问题分解为一个子问题序列,即BSS的混合BF(HBF),RISS的无源BF和用户合并。特别是,乘数算法的交替方向方法用于求解BSS的HBF子问题。具体而言,具有单位模式约束的模拟BF设计通过歧管优化(MO)解决,同时我们为数字BF设计提供了封闭形式的解决方案,该解决方案本质上是凸最小二乘问题。此外,RISS的被动BF和用户的模拟组合是由原始的双重亚级别和MO方法设计的。此外,考虑到常规CF-MMIMO系统中的沟通成本繁重,我们提出了一个部分连接的CF-MMIMO(P-CF-MMIMO)框架,以减少BSS和用户之间的连接数量。为了更好地妥协WSR性能和网络成本,我们将P-CF-MMIMO系统中的BS选择问题作为二进制整数二次编程(BIQP)问题,并开发出轻松的线性近似算法来处理此BIQP问题。最后,数值结果证明了我们提出的算法优于基线算法。
The combination of cell-free massive multiple-input multiple-output (CF-mMIMO) and reconfigurable intelligent surface (RIS) is envisioned as a promising paradigm to improve network capacity and enhance coverage capability. However, to reap full benefits of RIS-aided CF-mMIMO, the main challenge is to efficiently design cooperative beamforming (CBF) at base stations (BSs), RISs, and users. Firstly, we investigate the fractional programing to convert the weighted sum-rate (WSR) maximization problem into a tractable optimization problem. Then, the alternating optimization framework is employed to decompose the transformed problem into a sequence of subproblems, i.e., hybrid BF (HBF) at BSs, passive BF at RISs, and combining at users. In particular, the alternating direction method of multipliers algorithm is utilized to solve the HBF subproblem at BSs. Concretely, the analog BF design with unit-modulus constraints is solved by the manifold optimization (MO) while we obtain a closed-form solution to the digital BF design that is essentially a convex least-square problem. Additionally, the passive BF at RISs and the analog combining at users are designed by primal-dual subgradient and MO methods. Moreover, considering heavy communication costs in conventional CF-mMIMO systems, we propose a partially-connected CF-mMIMO (P-CF-mMIMO) framework to decrease the number of connections among BSs and users. To better compromise WSR performance and network costs, we formulate the BS selection problem in the P-CF-mMIMO system as a binary integer quadratic programming (BIQP) problem, and develop a relaxed linear approximation algorithm to handle this BIQP problem. Finally, numerical results demonstrate superiorities of our proposed algorithms over baseline counterparts.