Massive MIMO With Massive Connectivity for Industrial Internet of Things

In this paper, we investigate the feasibility of using massive multi-in multi-out (MIMO) to provide connectivity to Industrial Internet of Things (IIoT) wirelessly. Single-cell massive MIMO is used to support a large number of low-power IIoT devices in the uplink simultaneously. To support a large number of devices simultaneously, orthogonal uplink reference signals are heavily reused, which severely compromises the quality of the channel estimation for all devices. We show that the attempt by zero-forcing (ZF) decoding to zero out the interference from a large number of devices results in very poor performance, whereas maximum ratio (MR) decoding outperforms ZF decoding by a large margin. We present theoretical closed-form equations of spectral efficiency for both MR and ZF processings with massive connectivity. Simulation results validate our theoretical analysis. Furthermore, we provide analyses that are useful for designing low-power massive IIoT networks using massive MIMO.