I/Q Imbalance Calibration for Higher Self-Interference Cancellation Levels in Full-Duplex Wireless Transceivers

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1st International Conference on 5G for Ubiquitous Connectivity
Ramez Askar1, Nidal Zarifeh1, Benjamin Schubert2, Wilhelm Keusgen2, Thomas Kaiser1
1: Institute of Digital Signal Processing, Faculty of Engineering, University of Duisburg-Essen
2: Fraunhofer Heinrich Hertz Institute

    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.