Performance Analysis of Massive MIMO in Non-Ideal Settings

Licentiate thesis, 2015

Recent years have witnessed an unprecedented explosion in mobile data traffic, due to the expansion of numerous types of wireless devices, which have enabled a plethora of data-hungry applications. Novel techniques, such as massive multiple-input multiple-output (MIMO) systems, represent potential candidates to support these formidable demands. However, massive MIMO systems will be a viable solution only if low-cost and energy-efficient hardware is deployed, which is particularly prone to impairments such as in-phase and quadrature-phase imbalance (IQI). Moreover, it has been theoretically shown that the benefits of massive MIMO can be reaped under Rayleigh fading conditions which is an another idealistic assumption. In this thesis, we investigate the performance of massive MIMO systems in non-ideal hardware and channel settings. We begin with by studying the impact of IQI on massive MIMO systems. We consider both the cases whereof the receiver has perfect channel state information (CSI) and estimated CSI. Important insights are gained through the analysis of system performance indicators, such as achievable rates and channel estimation. Finally, we investigate the impact of sparse propagation channels on massive MIMO by deriving the achievable rates of linear receivers. Paper A considers the uplink of a single-cell multi-user MIMO system with IQI. Particularly, the effect of IQI on channel estimation is investigated. Moreover, a novel pilot-based joint estimator of the augmented MIMO channel matrix and IQI coefficients is described and then, a low-complexity IQI compensation scheme is proposed which is based on the IQI coefficients' estimation and it is independent of the channel gain. The performance of the proposed compensation scheme is analytically evaluated by deriving a tractable approximation of the ergodic spectral efficiency (SE) assuming transmission over Rayleigh fading channels with large-scale fading. Finally, by deriving asymptotic power scaling laws, and proving that the SE loss due to IQI is asymptotically independent of the number of BS antennas, we show that massive MIMO is resilient to the effect of IQI. Paper B, considers the uplink of a single-cell massive MIMO system operating in sparse channels with limited scattering. This case is of particular importance in most propagation scenarios, where the prevalent Rayleigh fading assumption becomes idealistic. We derive analytical approximations for the achievable rates of maximum-ratio combining (MRC) and zero-forcing (ZF) receivers. Furthermore, we study the asymptotic behavior of the achievable rates for both MRC and ZF receivers, when N and K go to infinity under the condition that N/K -> c ≥ 1.