Massive MIMO Systems With Non-Ideal Hardware: Energy Efficiency, Estimation, and Capacity Limits

TLDR

Large‑scale antenna arrays can dramatically improve energy and spectral efficiency through enhanced spatial resolution and array gain, and massive MIMO systems exhibit channel decorrelation that enables strong signal gains with minimal inter‑user interference. The study aims to assess whether conventional system models remain valid in the asymptotic regime that underpins these massive MIMO benefits. To this end, the authors introduce a new system model that explicitly incorporates general transceiver hardware impairments at both the base‑station arrays and the single‑antenna user equipments. They find that hardware impairments impose finite ceilings on channel‑estimation accuracy and on uplink/downlink capacity, with the capacity chiefly limited by UE hardware while array‑side impairments vanish asymptotically and pilot contamination becomes negligible; moreover, the vast degrees of freedom in massive MIMO can be leveraged to reduce transmit power or tolerate larger impairments, enabling the deployment of inexpensive, energy‑efficient antennas.

Abstract

The use of large-scale antenna arrays can bring substantial improvements in energy and/or spectral efficiency to wireless systems due to the greatly improved spatial resolution and array gain. Recent works in the field of massive multiple-input multiple-output (MIMO) show that the user channels decorrelate when the number of antennas at the base stations (BSs) increases, thus strong signal gains are achievable with little inter-user interference. Since these results rely on asymptotics, it is important to investigate whether the conventional system models are reasonable in this asymptotic regime. This paper considers a new system model that incorporates general transceiver hardware impairments at both the BSs (equipped with large antenna arrays) and the single-antenna user equipments (UEs). As opposed to the conventional case of ideal hardware, we show that hardware impairments create finite ceilings on the channel estimation accuracy and on the downlink/uplink capacity of each UE. Surprisingly, the capacity is mainly limited by the hardware at the UE, while the impact of impairments in the large-scale arrays vanishes asymptotically and inter-user interference (in particular, pilot contamination) becomes negligible. Furthermore, we prove that the huge degrees of freedom offered by massive MIMO can be used to reduce the transmit power and/or to tolerate larger hardware impairments, which allows for the use of inexpensive and energy-efficient antenna elements.