Joint Estimation for I/Q Imbalance and Multipath Channel in Millimeter-Wave SC-FDE Systems

Abstract

A single-carrier frequency-domain equalization (SC-FDE) system operating at 60-GHz millimeter-wave band suffers from in-phase (I) and quadrature (Q) imbalance, which refers to the mismatch between the I and Q branches in analog front-end processing. The I/Q imbalance incurs unwanted image interference on top of the desired signal and can severely degrade system performance if left uncompensated. In this paper, a training-based approach is proposed to estimate and compensate for the I/Q imbalance in the SC-FDE system. First, we derive the likelihood function capturing the I/Q imbalance and multipath channel. By iteratively maximizing the likelihood function, we can simultaneously and separately estimate the I/Q imbalance and the multipath channel. Then, with the estimate of the I/Q imbalance, the corresponding image interference is removed by simple substitution. Finally, we use the channel estimate to conduct equalization in the frequency domain, as is done in the conventional SC-FDE without the I/Q imbalance. It is shown through simulations compliant with the IEEE 802.11ad Standard that the proposed approach can effectively mitigate the adverse effect of I/Q imbalance and, consequently, can achieve the performance very close to the ideal case without I/Q imbalance.