MMSE equalization in presence of transmitter and receiver IQ imbalance

The wide spread of low-cost fabrication technologies gives rise to unpredictable imperfections associated with the analog stages which perform the frequency conversion. More specifically, it is well known that such stages suffer from the in-phase (I) and quadrature (Q) imbalance. In this paper, with reference to a single-carrier time-dispersive noisy channel, we address the receiver design when both the transmitter and the receiver are affected by the IQ imbalance, and we propose to resort to the widely linear filtering in order to improve the performances of the conventional minimum mean square error (MMSE) linear equalizer. The results show that the adoption of WL filters allows one to achieve considerable gains both in terms of MMSE and symbol error rate, with a limited increase in the computational complexity of the equalization stage.