Rejection of an FH signal in a DS spread-spectrum system using complex adaptive filters

Abstract

The performance of a direct sequence QPSK spread-spectrum receiver using adaptive filters in the presence of frequency hopped interference is analyzed. The analysis includes both the adaptive prediction error filters and the adaptive transversal filters with two-sided taps. If the product of the instantaneous frequency offset /spl Omega//sub l/, between the jamming signal and the carrier of the spread-spectrum signal, and the sampling period /spl Delta/ is 360/spl deg/ (/spl Omega//sub l//spl middot//spl Delta/=360/spl deg/), the filter gain is reduced to zero. The filter gain G highly depends on the filter adaptation rate /spl mu/. Depending on /spl mu/, G can vary from zero to more than 20 dB for a jammer/signal power ratio (J/S) of 20 dB. If /spl Omega//sub l//spl middot//spl Delta/ is small enough (/spl les/10/spl deg/), the performance of the transversal filter is better than that of the prediction error filter, in the case when /spl mu/ is small. For larger values of /spl mu/ or /spl Omega//sub l//spl middot//spl Delta/, these performances are approximately the same. Numerical results for the hopping sequence of the jamming signal are also presented. Besides the filter gain the analysis of the adaptation rate (time constant) filter misadjustment and the system bit error probability is also included. >