An EKF-based algorithm for PN code tracking in the presence of narrowband interference and multipath

A code-tracking algorithm based on the extended Kalman filter (EKF), that provides both code synchronization and joint estimates of interferer and channel parameters is described. It is assumed that the interference in direct sequence spread spectrum communications can be modeled by an N-th order autoregressive (AR) process and the channel by a finite impulse response (FIR) filter. A composite channel, equivalent to the convolution of the AR coefficients α_n and channel coefficients f_n is constructed, yielding a set of parameters β_m. The received waveform is shown to be a linear function of the α and β coefficients, which can be directly estimated by a Kalman filter. The code delay τ is viewed as a nonlinear parameter, which can likewise be estimated after an appropriate linearization, using the EKF. The performance of the algorithm is evaluated by computing the average bit-error rate (BER) of a digital RAKE receiver that uses the joint delay, channel, and interferer estimates derived from the EKF