Joint Interference Rejection/Channel Equalization in DS Spread-Spectrum Receivers using the CMA Equalizer and Maximum-Likelihood Techniques

We consider two direct-sequence (DS) receiver designs for simultaneous rejection of narrowband interference and multipath. The first receiver is based on the generalized likelihood-ratio test (GLRT), where the interferer is modeled as an Nth order circular Gaussian AR process and the channel is assumed to be a tapped delay line. We then derive the ML joint estimator for the channel coefficients and interferer autoregressive parameters. Analytical results for the BER of the GLRT receiver are presented assuming exact knowledge of the received signal covariances. The second receiver uses a transversal adaptive equalizer based on the constant-modulus algorithm (CMA). The advantage of the CMA is that a reference signal is not required, eliminating the need for code synchronization and bit decision feedback. Analytical expressions for BER are then evaluated numerically for the receiver employing the CMA equalizer.