Study of I/Q imbalances in QAM communication systems adopting multi-antenna receivers

Abstract

This paper investigates the inphase/quadrature phase (I/Q) imbalance problem in quadrature amplitude modulation (QAM) communication systems with multi-antenna receivers. Two application scenarios are considered: adaptive beamforming and multi-user detection based on blind source separation (BSS). Our analysis illustrates that, in both scenarios, the effect of the transmitter and receiver I/Q imbalance can be mitigated through straightforward digital signal processing methods. For adaptive beamforming systems, increasing the number of receiver branches automatically suppresses the interference induced by transceiver I/Q imbalances. For the multi-user detection application, a simple alternative expression of the signal model can be adopted, which separately lists the inphase and quadrature phase components of the received signals and the source signals. As a result, the BSS estimation of all user signals can be conducted in the presence of transceiver I/Q imbalances. Simulation results confirmed the effectiveness of the presented I/Q imbalance correction techniques.