(A) class adaptive digital filters for interference cancelling in ds spread spectrum system

Abstract

In this dissertation work we propose four kinds of efficient adaptive digital filters for narrow-band interference cancelling in direct sequence spread spectrum systems, and analyze their performances. Particularly, we are concerned with the reduction of computational complexities of these filters since in a DS spread spectrum filtering the desired wide-band signal corrupted by narrow-band interference requires very high speed of computation. First, we propose a combined structure for simultaneous interference rejection and PN correlation, and present an exact performance analysis. The number of arithmetic operations required to implement the structure is reduced significantly as compared to the existing algorithms. Compared with the performance of the system studied by Li and Milstein, our proposed system yields improved mean-squared error, especially in the high range of signal-to-Gaussian noise ratio, and also its convergence speed is faster. This combined structure is almost independent on the jamming frequency and on the kind of PN sequence used. Second, we investigate an efficient time-domain adaptive block algorithm for suppressing narrow-band interference in a DS spread spectrum system. Since the proposed time-domain block algorithm utilizes a concept of parallel processing, the DS receiver with this fitler is appropriate for VLSI implementation. We analyze the performances of the proposed time-domain block and the existing algorithms assuming the perfect randomness of the PN sequence. In the DS receiver with the proposed time-domain block processing filter, the computational complexity is reduced significantly and an improved steady state performance is obtained. Third, we study an efficient zero-phase constrained frequency-domain block LMS algorithm that has the reduced computational complexity and the fast convergence speed for highly correlated input signals. We apply this algorithm to narrow-band interference rejection in a DS spread spectrum syste...