Spectrum and Energy Efficiency of Massive MIMO for Hybrid Architectures With Phase Shifter and Switches in IoT Networks

Massive multiple-input–multiple-output (MIMO) systems provide efficient connectivity services for a large number of industrial Internet of Things (IoT) devices. To support numerous IoT devices, this article considers downlink hybrid architecture massive MIMO systems with phase shifters-based and switches-based cases, in which the data stream is first sent to the digital domain and then processed by the analog domain. zero-forcing (ZF) receivers are considered under the assumption of perfect channel state information (CSI). For hybrid architecture MIMO systems under quantized phase shifters and switches, we derive asymptotic approximations of the spectrum efficiency (SE) for massive MIMO systems using random matrix theory and then we propose an iterative algorithm to generate corresponding analog processing matrix, which can be used arbitrary quantized phase shifters. With the help of derived theoretical SE and realistic power consumption model, we further evaluate the total energy efficiency (EE) and provide insights into the tradeoffs between the SE and total EE. Finally, Monte Carlo simulation results are presented to substantiate our theoretical analysis results and showcase that the hybrid architecture provides higher total EE compared to existing all-digital architectures, but its achievable SE is lower than that of the hybrid architecture. Furthermore, the results also show that the switchbased hybrid architecture have ability to achieve the enhanced EE performance with large number of base station antennas and low-signal-to-noise ratio regimes compared to quantized phase shifters.