I/Q Imbalance Aware Widely-Linear Receiver for Uplink Multi-Cell Massive MIMO Systems: Design and Sum Rate Analysis

Abstract

In-phase/quadrature-phase (I/Q) imbalance is one of the most important hardware impairments in communication systems. It arises in the analogue parts of direct conversion radio frequency (RF) transceivers and can cause severe performance losses. In this paper, I/Q imbalance (IQI) aware widelylinear (WL) channel estimation and data detection schemes for uplink multi-cell massive multiple-input multiple-output (MIMO) systems are proposed. The resulting receiver is a WL extension of the minimum mean square error (MMSE) receiver and jointly mitigates multi-user interference and IQI by processing the real and the imaginary parts of the received signal separately. The IQI arising at both the base station (BS) and the user terminals (UTs) is then taken into account. The considered channel state information (CSI) acquisition model includes the effects of both estimation errors and pilot contamination, which is caused by the reuse of the same training sequences in neighboring cells. We apply results from random matrix theory to derive analytical expressions for the achievable sum rates of the proposed IQI aware and conventional IQI unaware receivers. Our simulation results show that the performance of the proposed IQI aware WLMMSE receiver in a system with IQI is close to that of the MMSE receiver in an ideal system without IQI. Moreover, our results for the sum rate of the IQI unaware MMSE receiver reveal that the performance loss due to IQI can be large and, if left unattended, does not vanish for large numbers of BS antennas.

Optimal Least Squares Estimator and Precoder for Energy Beamforming Over IQ-Impaired Channels

“…Noting it, sum rate limits in downlink (DL) MU MISO systems under IQI and CE errors were derived in [10]. In contrast [11], [12] were targeted towards the joint CE and IQI compensation in uplink (UL) MISO systems. More recently, performance analysis of dual-hop statistical channel state information (CSI) assisted cooperative communications was conducted via simulations in [13] to incorporate the effect of IQI.…”

“…corresponding to the means and variances of amplitude and phase errors (in radians) are similar [26], [27], we set ∆ g = ∆ φ = Φ g = Φ φ = ∆ = 0.4, for each of the 8 IQI parameters.…”

Research on I / Q Unbalanced Channel Reciprocity Calibration Algorithm in Massive MIMO System

“…I / Q imbalance is caused by the non-ideal characteristics of the wireless transceiver circuit, which is present in the process of upconversion and down-conversion. The result is, the amplitude gain of the I / Q branch of the signal is not equal or the phase is not orthogonal [7,8]. In the presence of the I / Q imbalance, the channel will lose its reciprocity even if the radio channel itself remains unchanged during an uplink and downlink subframe interaction.…”

IQ Imbalance in Multiuser Systems: Channel Estimation and Compensation

“…Although several IQI compensation algorithms have been proposed, especially for the case of single-input single-output (SISO) systems [11]- [13], little is still known for the case of massive MIMO systems. To the best of our knowledge the only relevant works are [8], [14]- [18]. Specifically, [8] studied the sensitivity of massive antenna arrays to RF IQI by elaborating on the design of singleuser beamforming schemes; moreover, [14] proposed augmented spatial post-processing linear minimum-mean-squareerror (LMMSE) filters for mitigating the effect of IQI in the uplink receiver.…”

“…Specifically, [8] studied the sensitivity of massive antenna arrays to RF IQI by elaborating on the design of singleuser beamforming schemes; moreover, [14] proposed augmented spatial post-processing linear minimum-mean-squareerror (LMMSE) filters for mitigating the effect of IQI in the uplink receiver. Finally, [16]- [18] proposed widely linear precoding algorithms for massive MIMO systems with IQI. However, none of these works proposed practical channel estimation and low complexity IQI compensation schemes, while a detailed performance analysis is also missing from the literature.…”