Massive MIMO with Massive Connectivity in Low Power Industrial Internet of Things Networks

In this paper, we investigate the feasibility of using Massive MIMO to provide connectivity to Industrial Internet of Things (IIoT) wirelessly. A 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 (RSs) are heavily reused, which severely compromises the quality of channel estimation for all devices. We show that the attempt by ZF (Zero-forcing) decoding to null out interference from a large number of devices results in very poor performance, while MR (Maximum Ratio) decoding outperforms ZF decoding by a large margin. We provide theoretical closed-form equations of spectral efficiency (SE) for both MR and ZF processing with massive connectivity, and provide various analyses which are useful for designing low power massive IIoT networks using Massive MIMO. Simulation results are provided to validate the theoretical analysis.