Rejection of narrowband interference in DS spread spectrum systems using two-stage decision feedback filters

The further improvement of the direct sequence spread spectrum (DSSS) receiver proposed by Dukic et al. (1990), using decision feedback (DFB) filter, in reducing the narrowband interference (NBI) is presented. In the first stage of this new receiver, the conventional demodulator is followed by a DFB filter, the role of which is to produce the NBI reference signal. The reference derived in this manner is the input signal to the two-sided adaptive transversal (AT) filter, this being used as a NBI rejection filter. The performance of such a receiver has been analyzed in term of the output error probability. The results obtained show that this two-stage DFB filter techniques enhance the immunity of the new DSSS receiver against NBI, relative to the previously reported receivers using linear and nonlinear NBI rejection methods