Joint estimation of complex gain and fractional delay for Tx leakage compensation in FDD transceivers

This paper deals with a joint estimation algorithm dedicated to the digital compensation of the Tx leakage in FDD transceivers. Such transceivers are affected from transmitter-receiver signal leakage. Combined with non linearity of components in the received path, it leads to a pollution in the baseband signal. The baseband polluting term depends on the equivalent Tx leakage channel, modeling leakages and the received path. In this paper we consider a first-order autoregressive model to approximate Tx-Leakage channel gain variations, and the presence of a fractional delay, modeling propagation effects. We first express asymptotic performance of a gain estimator based on a least-mean-square (LMS) approach in the synchronized case and then derive the influence of the fractional delay. We show that in practice, the fractional delay can not be neglected and we propose a joint estimation of the fractional delay and the cross-channel gain to perform the digital compensation. The proposed method is recursive, online and exhibits low complexity.