Massive MIMO in Real Propagation Environments: Do All Antennas Contribute Equally?

TL;DR

This paper demonstrates that in real massive MIMO channels, antenna selection can significantly reduce the number of RF chains needed without major performance loss, unlike in idealized theoretical models.

Contribution

The study shows that antenna selection based on measured real-world channels can maintain high sum-rate performance with fewer RF chains, offering a practical approach to reduce complexity.

Findings

Antenna selection reduces RF chain requirements in real channels.

Power-based antenna selection performs nearly as well as convex optimization.

Significant complexity reduction is possible with simple antenna selection algorithms.

Abstract

Massive MIMO can greatly increase both spectral and transmit-energy efficiency. This is achieved by allowing the number of antennas and RF chains to grow very large. However, the challenges include high system complexity and hardware energy consumption. Here we investigate the possibilities to reduce the required number of RF chains, by performing antenna selection. While this approach is not a very effective strategy for theoretical independent Rayleigh fading channels, a substantial reduction in the number of RF chains can be achieved for real massive MIMO channels, without significant performance loss. We evaluate antenna selection performance on measured channels at 2.6 GHz, using a linear and a cylindrical array, both having 128 elements. Sum-rate maximization is used as the criterion for antenna selection. A selection scheme based on convex optimization is nearly optimal and used as a benchmark. The achieved sum-rate is compared with that of a very simple scheme that selects the antennas with the highest received power. The power-based scheme gives performance close to the convex optimization scheme, for the measured channels. This observation indicates a potential for significant reductions of massive MIMO implementation complexity, by reducing the number of RF chains and performing antenna selection using simple algorithms.