Interpolation Lattice Filters for Narrowband Interference Cancellation in PN Spread Spectrum Communication Systems

Previous work on the adaptive lattice filters for narrowband interference rejection in a direct sequence (DS) spread spectrum communication system has centered around the use of one-sided prediction only. For two-sided interpolation, that is known to achieve better interference rejection than its one-sided counterpart, only the least-mean-squared (LMS) algorithms have been considered thus far in the literature. However, the LMS algorithm has an extremely slow convergence rate. Consequently, the two-sided interpolation filters using the LMS algorithm may not be applicable for suppression of narrowband interference with a time-variant frequency. In this paper, an order-recursive QR-decomposition-based least squares lattice (QRD-LSL) interpolation filter is presented as a solution to the narrowband interference rejection in a DS spread spectrum system. Computer simulation results show that the QRD-LSL interpolation filters can achieve excellent performance in terms of convergence speed as well as SNR improvement for a multiple tone interference with random phase and second-order autoregressive (AR) interference.