I/Q imbalance calibration for higher self-interference cancellation levels in Full-Duplex wireless transceivers

This paper investigates a Full-Duplex transceiver using an active cancellation technique where an additional transmit chain is employed to create the self-interference cancellation signal. Both transmitters and also the receiver are impaired by frequency-dependent I/Q imbalance with different parameters. It is shown how an I/Q parameter deviation in these chains deteriorates the achievable self-interference suppression level. Three different types of pre-equalization units, with variable complexity degree and different implementation approach, are then introduced and investigated. These units correct the I/Q imbalance and retain the self-interference level to its value as in a perfectly I/Q matched full-duplex transceiver. They can even be used to fully calibrate the I/Q imbalance. Simulative results show that self-interference suppression levels of more than 71 dB can be achieved.