We consider a dynamic time division duplex (DTDD) enabled cell-free massive multiple-input multiple-output (CF-mMIMO) system, where each half-duplex (HD) access point (AP) is scheduled to operate in the uplink (UL) or downlink (DL) mode based on the data demands of the user equipments (UEs). The goal is to maximize the sum UL-DL spectral efficiency (SE). We theoretically establish the sub-modularity of the sum SE, which allows us to develop a new, low complexity, greedy algorithm for the combinatorial AP scheduling problem, with guaranteed optimality properties. We also consider pilot sequence reuse among the UEs to limit the channel estimation overhead. In CF systems, all the APs estimate the channel from every UE, making pilot allocation problem different from the cellular case. We develop a novel algorithm that iteratively minimizes the maximum pilot contamination across the UEs. We compare our solutions, both theoretically and via simulations, against a full duplex (FD) multi-cell mMIMO system. Our results show that, due to the joint processing of the signals at the central processing unit, CF-mMIMO with dynamic HD AP-scheduling significantly outperforms cellular FD-mMIMO in terms of the sum SE and 90% likely SE. Thus, DTDD enabled HD CF-mMIMO is a promising alternative to cellular FD-mMIMO, without the cost of hardware for self-interference suppression.
翻译:我们考虑的是动态时间分解(DDDD)使无细胞的大规模多投入多输出输出(CF-MMIMO)系统(CF-MMIMO)能够实现无细胞的大规模多投入输出(CF-MMIMO)系统,在这个系统中,每个半重复(HD)接入点(AP)预定在上行(UL)或下行(DL)模式下运行,基于用户设备(UES)的数据需求。我们的目标是最大限度地提高UL-DL光谱效率(SE)的总和。我们理论上建立了SE的次模式,使我们能够为组合的AP列表问题开发新的、低复杂性的、贪婪的算法,保证最佳性能。我们还考虑在UD(H)接入点之间试点序列再利用,以限制频道估算间接费用。在CFCFM系统中,所有AP都从每个UE(U)中估算出频道的频道,使试点分配问题不同于手机案例。我们开发了一个新的算法,将UL-DL-DM(理论上和通过模拟)模拟,让我们的解决方案与完全的多解(FD)多细胞 mIM(FM)系统进行比较。我们的结果显示,因为S-IM(S-M)的中央数据处理中可能联合处理SHDM(SEFDFDM)M)的硬值的货币,因为S-M)的内,因此,在S-CM(CFM)极中,极中可能进行大量)的内,因此,我们机的硬(CFDFDFDM)的货币的货币的汇率的汇率的汇率的汇率的汇率处理。