Cell-free massive multiple-input multiple-output (MIMO) is a promising network to offer huge improvement of the achievable rate compared with conventional cellular massive MIMO systems. However, the commonly adopted Shannon-type achievable rate is only valid in the long block length regime that is not applicable to the emerging short-packet communication. To realize ultra-reliable and low-latency communication (URLLC) in cell-free massive MIMO systems, we optimize the precoding vector at the access points (APs) to maximize the minimum user rate in both the centralized and decentralized fashion. The design takes into account the impact of URLLC and we propose path-following algorithms (PFA) to address the considered problem which generates a sequence of advanced feasible points and converges to at least a locally optimal solution of the design problem. Moreover, we investigate the requirement of the precoding schemes, the length of the transmission duration, the number of antennas equipped at each AP, and the size of each AP cluster on the URLLC rate. Numerical results show that the decentralized PFA precoding can achieve 80\% of the 95\%-likely URLLC rate of the centralized precoding and 89\% of the average URLLC rate with only 12\% computational complexity of the centralized precoding.
翻译:与传统的大型蜂窝式巨型巨型IMIM系统相比,无细胞的大规模多投入产出(MIMO)是一个大有希望的网络,可以大大改善可实现的速率。然而,通常采用的香农型可实现速率只有在对新兴短包装通信不适用的长块长度制度下才有效。为了在无细胞的大型IMIMO系统中实现超可靠和低纬度通信(URLLC),我们优化了在接入点的预编码矢量,以便在集中和分散方式上最大限度地提高最低用户率。设计考虑到了URLLC的影响,我们提出了遵循路径的算法(PFA),以解决所考虑的问题,即产生一系列先进的可行点,并至少汇集到当地最佳的设计问题。此外,我们调查了预编码计划的要求、传输时间长度、每个APA配备的天线的数量以及每个APLC费率上的AP组的规模。数字表明,分散的PAFA前编码可以达到89-类似LCRCRRRRRRRC标准中,即中央级LACRLAC标准前的95-八十九九十九八十九八八八八八的中央级和中央级LC标准。