We present a general framework for the characterization of the packet error probability achievable in cell-free Massive multiple-input multiple output (MIMO) architectures deployed to support ultra-reliable low-latency (URLLC) traffic. The framework is general and encompasses both centralized and distributed cell-free architectures, arbitrary fading channels and channel estimation algorithms at both network and user-equipment (UE) sides, as well as arbitrary combining and precoding schemes. The framework is used to perform numerical experiments on specific scenarios, which illustrate the superiority of cell-free architectures compared to cellular architectures in supporting URLLC traffic in uplink and downlink. Also, these numerical experiments provide the following insights into the design of cell-free architectures for URLLC: i) minimum mean square error (MMSE) spatial processing must be used to achieve the URLLC targets; ii) for a given total number of antennas per coverage area, centralized cell-free solutions involving single-antenna access points (APs) offer the best performance in the uplink, thereby highlighting the importance of reducing the average distance between APs and UEs in the URLLC regime; iii) this observation applies also to the downlink, provided that the APs transmit precoded pilots to allow the UEs to estimate accurately the precoded channel.
翻译:翻译后的摘要:
我们提出了一个通用框架来描述支持超可靠低延迟(URRLC)流量的无细胞巨型MIMO系统中可实现数据包误码率。该框架具有通用性,包括集中式和分布式无细胞架构,任意的衰落信道和网络和用户设备(UE)端的信道估计算法,以及任意的合并和预编码方案。该框架被用于在特定的场景下进行数值实验,从而说明了在上行和下行中,与蜂窝结构相比,无细胞结构支持URRLC流量的优越性。此外,这些数值实验提供了以下关于设计无细胞技术支持URRLC的见解:i)为了达到URRLC的目标,必须使用最小均方误差(MMSE)空间处理; ii) 对于每个覆盖区域固定天线数的情况下,集中式无细胞解决方案包括单天线接入点(AP),在上行性能方面表现最佳,从而凸显了在URRLC区域减少AP和UE之间的平均距离的重要性; iii) 如果AP向UE发送预编码的导频序列以使UE可以准确估计预编码信道,则该观察结果也适用于下行。