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arXiv 2402.18231eess.SP
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无蜂窝 MIMO 网络中非相干联合传输的联合波束赋形设计与流分配

Joint Beamforming Design and Stream Allocation for Non-Coherent Joint Transmission in Cell-Free MIMO Networks

Xi Wang, Xiaotong Zhao, Juncheng Wang, You Li, Qingjiang Shi

AI总结:

针对无蜂窝 MIMO 网络 NCJT 的 WSR 最大化问题,提出低交互 RWMMSE 波束赋形及可收敛的 RWMMSE-LSA 联合流分配算法,性能与收敛时间均优于现有方法。

摘要:

我们考虑在以用户为中心的无蜂窝 MIMO 网络中,通过联合波束赋形和流分配来最大化非相干联合传输(NCJT)的加权和速率(WSR)。在该网络中,分布式接入点(AP)被组织成簇,以传输不同信号来服务每个用户设备(UE)。我们首次考虑实际网络中 UE 最大接收流数量的共同限制,并在每个 AP 发射功率约束下,构建了一个用于 WSR 最大化的联合波束赋形与发射流分配问题。由于发射流的整数数量决定了波束赋形器的维度,该联合优化问题是混合整数且非凸的,其决策变量相互耦合,本质上是 NP 难的。本文首先针对固定流数量下的 WSR 最大化,提出了一种分布式、低交互的约简加权最小均方误差(RWMMSE)波束赋形算法。所提出的 RWMMSE 算法显著减少了跨网络交互需求,并具有当前最低的计算复杂度,其复杂度随发射天线数量线性扩展,同时不会对 WSR 造成任何损失。我们从联合波束赋形与流分配问题中获得启发,对决策变量进行解耦并松弛混合整数约束。随后,我们提出了一种联合波束赋形与线性流分配算法,称为 RWMMSE-LSA,该算法产生闭式更新,具有线性流分配复杂度,并保证收敛到原始联合优化问题的驻点。仿真结果表明,与当前最佳替代方案相比,我们提出的算法在 WSR 性能和收敛时间两方面均取得了显著的性能增益。

英文摘要:

We consider joint beamforming and stream allocation to maximize the weighted sum rate (WSR) for non-coherent joint transmission (NCJT) in user-centric cell-free MIMO networks, where distributed access points (APs) are organized in clusters to transmit different signals to serve each user equipment (UE). We for the first time consider the common limits of maximum number of receive streams at UEs in practical networks, and formulate a joint beamforming and transmit stream allocation problem for WSR maximization under per-AP transmit power constraints. Since the integer number of transmit streams determines the dimension of the beamformer, the joint optimization problem is mixed-integer and nonconvex with coupled decision variables that is inherently NP-hard. In this paper, we first propose a distributed low-interaction reduced weighted minimum mean square error (RWMMSE) beamforming algorithm for WSR maximization with fixed streams. Our proposed RWMMSE algorithm requires significantly less interaction across the network and has the current lowest computational complexity that scales linearly with the number of transmit antennas, without any compromise on WSR. We draw insights on the joint beamforming and stream allocation problem to decouple the decision variables and relax the mixed-integer constraints. We then propose a joint beamforming and linear stream allocation algorithm, termed as RWMMSE-LSA, which yields closed-form updates with linear stream allocation complexity and is guaranteed to converge to the stationary points of the original joint optimization problem. Simulation results demonstrate substantial performance gain of our proposed algorithms over the current best alternatives in both WSR performance and convergence time.

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