Advanced DSP for I/Q imbalance compensation in a low-IF receiver

Quadrature downconversion to a very low-IF frequency is a promising idea but it has one serious problem. Unavoidable imbalances in the analog front-end between the I- and Q-branches result in finite and usually insufficient rejection of the image frequency band which causes interference. We carry out a signal analysis of an imbalanced low-IF receiver and propose a novel baseband correction structure utilizing an adaptive interference canceller. Theoretical and simulation results are provided in order to evaluate the performance of the proposed idea. The results indicate that the I/Q imbalance can be effectively compensated during the normal operation of the receiver, even in the rapidly changing case, as long as a linear system model for the imbalance is valid