Adaptive lattice filters for narrowband interference rejection in DS spread spectrum systems

In the presence of narrowband interference, the performance of direct sequence (DS) spread spectrum communication systems can be improved by using various types of interference rejection filters. The performance of a DS spread spectrum receiver employing a lattice filter for interference rejection is analysed. The filter parameters are adjusted using the stochastic gradient lattice algorithm. For ease of analysis, the adaptive lattice filter is modelled as an optimal Wiener filter followed by an additive misadjustment noise. Analytical expressions for the reflection coefficients and general expressions for the minimum mean square error and the variance of the misadjustment noise are presented. An expression for the system bit error rare, which takes into account, the filter misadjustment noise is derived and numerical results are presented