Separation of cochannel signals under imperfect timing and carrier synchronization

In this paper, we propose a complete receiver for separating cochannel sign als in a time-division multiple-access type system when the timing and carr ier synchronization are imperfect or only nominally accomplished. The recei ver is all digital, data aided, assumes the presence of multiple antennas a t the receiver, and has three functional components. The first part compute s the timing offsets of the different cochannel users through a maximum lik elihood search. The second part uses a bank of filters on an oversampled ve rsion of the baseband signals to obtain a new symbol rate sampled signal in which the different users are all synchronous but are still spatially mixe d and rotated with unknown carrier offsets. The third part uses an extended Kalman-filter-based algorithm to estimate the parameters of this model and to separate and decode the transmitted signals of the different users. The performance of this receiver is demonstrated with simulations, This work i s significant in the context of smart antenna technology, considered as a p otentially significant improvement to wireless systems, since it is a compl ete solution encompassing flat fading, timing error, and frequency offsets for multiple cochannel users.