Clock timing mismatch compensation in direct sampling receiver

In this paper, we study the impact of clock timing mismatch of analog-to-digital converter in a receiver that employs quadrature bandpass sampling of the radio frequency (RF) signal. It is shown that the clock timing mismatch introduces not only symbol timing offset but also image interference, that is, the interference between in-phase and quadrature signals. Then, a mismatch compensation scheme and a pilot-aided mismatch estimation method are proposed. We also propose a blind estimation method, where the clock timing mismatch can be estimated from the second order statistics of the sampled sequences. Numerical simulations confirm the validity of the proposed methods, even in the presence of unknown channel.