Low-complexity gain and phase I/Q mismatch compensation using orthogonal pilot sequences

In up-to-date receiver architectures the gain and phase mismatch between the I and Q signal paths may degrade significantly the overall link performance. An alternative cost effective solution to expensive analog components with small tolerances, which make the I/Q mismatch effect negligible, consists in estimating and compensating it through appropriate digital signal processing techniques. In this paper we derive a novel low-complexity data-aided scheme for jointly estimating the carrier phase offset, the I/Q phase mismatch, and the gain of the I and Q branches following the maximum likelihood criterion and adopting as training symbols an orthogonal sequence. The performance analysis proves that the proposed estimator is low-complexity, asymptotically efficient and capable of compensating considerable I/Q mismatch values in the demanding scenario of both uncoded and coded multi-level QAM transmissions.