Energy Efficiency and Asymptotic Performance Evaluation of Beamforming Structures in Doubly Massive MIMO mmWave Systems

TL;DR

This paper evaluates the energy and spectral efficiency of various beamforming structures in large-scale mmWave MIMO systems, revealing that fully digital beamformers can outperform simpler solutions in energy efficiency, with analog beamforming offering a good trade-off.

Contribution

It provides analytical asymptotic formulas for spectral and energy efficiency of different beamforming structures in massive MIMO mmWave systems, comparing their performance and energy consumption.

Findings

Fully digital beamformers may have higher energy efficiency than simpler solutions.

Analog beamforming can be a good trade-off between performance and complexity.

Analytical formulas for asymptotic efficiency are derived for large antenna regimes.

Abstract

Future cellular systems based on the use of millimeter waves will heavily rely on the use of antenna arrays both at the transmitter and at the receiver. For complexity reasons and energy consumption issues, fully digital precoding and postcoding structures may turn out to be unfeasible, and thus suboptimal structures, making use of simplified hardware and a limited number of RF chains, have been investigated. This paper considers and makes a comparative assessment, both from a spectral efficiency and energy efficiency point of view, of several suboptimal precoding and postcoding beamforming structures for a cellular multiuser MIMO (MU-MIMO) system with large number of antennas. Analytical formulas for the asymptotic achievable spectral efficiency and for the global energy efficiency of several beamforming structures are derived in the large number of antennas regime. Using the most recently available data for the energy consumption of phase shifters and switches, we show that fully-digital beamformers may actually achieve a larger energy efficiency than lower-complexity solutions, as well as that low-complexity beam-steering purely analog beamforming may in some cases represent a good performance-complexity trade-off solution.