In this thesis, a new narrow-band interference rejection technique in spread spectrum CDMA systems is proposed and its effect on the code acquisition in the presence of narrow-band interference is discussed. The proposed technique is based on the generalized likelihood ratio test of the pre-whitened received signal, where soft decision feedback filter is used as a pre-whitening filter and the interferer is assumed as a Gaussian autoregressive process in AWGN channel. Specifically, the structure of the proposed technique is a soft decision feedback filter followed by a RAKE combiner. The filter coefficients are updated using the adaptive LMS algorithm. The bit error rate performance of the proposed technique is compared with the previous narrow-band interference techniques' by Monte Carlo simulations. The simulation results show that the proposed technique outperforms the previous technique for multi user communications.
Regarding the code acquisition in the presence of narrow-band interference, the simulation results show that the rejection of narrow-band interference aids the code acquision when the interferer's power is high. When the interferer's power is low, implementing prediction error filter for interference rejection results in worse acquision performance than no interference rejection filter is used, but the proposed technique improves the acquisition peformance.
