Asymptotic Optimality of Massive MIMO Systems Using Densely Spaced Transmit Antennas

TL;DR

This paper proves that in massive MIMO systems with densely spaced antennas, simple QPSK transmission can asymptotically achieve channel capacity as antenna spacing approaches zero, highlighting a new approach for system design.

Contribution

It demonstrates the asymptotic optimality of QPSK in massive MIMO with densely spaced antennas, under idealized array assumptions.

Findings

QPSK achieves channel capacity asymptotically as antenna spacing tends to zero.

Densely spaced antenna arrays can realize capacity with simple modulation schemes.

The result is analogous to faster-than-Nyquist signaling in communication systems.

Abstract

This paper investigates the performance of a massive multiple-input multiple-output (MIMO) system that uses a large transmit antenna array with antenna elements spaced densely. Under the assumption of idealized uniform linear antenna arrays without mutual coupling, precoded quadrature phase-shift keying (QPSK) transmission is proved to achieve the channel capacity of the massive MIMO system when the transmit antenna separation tends to zero. This asymptotic optimality is analogous to that of QPSK faster-than-Nyquist signaling.