Simultaneous suppression of multiaccess and narrow-band interference in asynchronous CDMA networks

This paper handles the simultaneous suppression of narrow-band and multiacc ess interference In asynchronous CDMA networks. We consider both linear one -shot detection and block-detection, showing that, in both cases, the prese nce of an external narrow-band interferer generally results in the need for time-varying processing. As to the linear one-shot detectors, we derive bo th a zero-forcing and a minimum mean square error detector, showing that th ey are members of an only family, wherein the optimization criterion is the constrained minimization of a suitably defined output interference energy. We also present a comparative performance assessment between the various d etection strategies, studying the impact of both the optimization criterion and other system parameters, such as the oversampling ratio and the length of the observation window. We also handle the problem of blind and adaptiv e detection. At first we show that the linear one-shot receivers are readil y amenable to a blind implementation, upon off-line estimation of the covar iance matrix of the observables. Next, we consider the problem of an adapti ve implementation of a periodically time-varying minimum mean square error receiver, introducing and assessing a new cyclic recursive least squares (R LS) algorithm: we show that, unlike the conventional RLS algorithms, the ne w algorithm is capable of tracking the periodically time-varying variation of the receiver structure, induced by the presence of a data-like narrow-ba nd interferer.