Signal Processing in Massive MIMO With IQ Imbalances and Low-Resolution ADCs

This paper proposes a massive multiple-input multiple-output (MIMO) with low-precision in-phase quadrature-phase (IQ) (de-)modulators and low-resolution analog-to-digital convertors, and develops uplink baseband algorithms for the proposed MIMO system. The IQ imbalance parameters are recovered by a two-stage method. At the first stage, the base station (BS) antennas acquire phase-shifted versions of their imbalance parameters after receiving some predefined training sequence emitted by a specific transceiver that is near to the BS and shares flat-fading channels between itself and the BS. At the second stage, the phase shifts from the first stage are estimated by the specific transceiver through receiving a common sequence transmitted by the BS antennas alternatively. In order to jointly handle the IQ imbalance and nonlinear quantization loss, the IQ-imbalanced multiuser (MU)-MIMO with single-antenna users is first converted into an IQ-balanced MU-MIMO with dual-antenna users. Then, two kinds of channel estimator and multiuser detectors are constructed for the equivalent IQ-balanced system based on the spectral projected gradient method and vectorized message passing de-quantization algorithm. Our numerical results validate the effectiveness of the above baseband algorithms, and show that the proposed massive MIMO is more energy-efficient than the conventional one when the channel coherence time is long enough.