Lee Byung Moo
School of Intelligent Mechatronics Engineering, Sejong University, Seoul 05006, Korea.
Sensors (Basel). 2017 Dec 29;18(1):84. doi: 10.3390/s18010084.
Massive multiple-input multiple-output (MIMO) systems can be applied to support numerous internet of things (IoT) devices using its excessive amount of transmitter (TX) antennas. However, one of the big obstacles for the realization of the massive MIMO system is the overhead of reference signal (RS), because the number of RS is proportional to the number of TX antennas and/or related user equipments (UEs). It has been already reported that antenna group-based RS overhead reduction can be very effective to the efficient operation of massive MIMO, but the method of deciding the number of antennas needed in each group is at question. In this paper, we propose a simplified determination scheme of the number of antennas needed in each group for RS overhead reduced massive MIMO to support many IoT devices. Supporting many distributed IoT devices is a framework to configure wireless sensor networks. Our contribution can be divided into two parts. First, we derive simple closed-form approximations of the achievable spectral efficiency (SE) by using zero-forcing (ZF) and matched filtering (MF) precoding for the RS overhead reduced massive MIMO systems with channel estimation error. The closed-form approximations include a channel error factor that can be adjusted according to the method of the channel estimation. Second, based on the closed-form approximation, we present an efficient algorithm determining the number of antennas needed in each group for the group-based RS overhead reduction scheme. The algorithm depends on the exact inverse functions of the derived closed-form approximations of SE. It is verified with theoretical analysis and simulation that the proposed algorithm works well, and thus can be used as an important tool for massive MIMO systems to support many distributed IoT devices.
大规模多输入多输出（MIMO）系统可利用其大量的发射天线来支持众多物联网（IoT）设备。然而，实现大规模MIMO系统的一大障碍是参考信号（RS）的开销，因为RS的数量与发射天线数量和/或相关用户设备（UE）成正比。已有报道称，基于天线组的RS开销降低对大规模MIMO的高效运行非常有效，但确定每组所需天线数量的方法仍存在问题。在本文中，我们提出了一种简化的确定方案，用于为降低RS开销的大规模MIMO系统确定每组所需的天线数量，以支持众多物联网设备。支持众多分布式物联网设备是一种配置无线传感器网络的框架。我们的贡献可分为两部分。首先，对于存在信道估计误差的降低RS开销的大规模MIMO系统，我们通过使用迫零（ZF）和匹配滤波（MF）预编码，推导出了可实现频谱效率（SE）的简单闭式近似。该闭式近似包括一个可根据信道估计方法进行调整的信道误差因子。其次，基于该闭式近似，我们提出了一种高效算法，用于为基于组的RS开销降低方案确定每组所需的天线数量。该算法依赖于所推导的SE闭式近似的精确反函数。通过理论分析和仿真验证，所提出的算法效果良好，因此可作为大规模MIMO系统支持众多分布式物联网设备的重要工具。
