Adaptive narrow-band interference rejection in a DS-spread spectrum intercept receiver using transform domain signal processing techniques

One of the most important properties of direct-sequence (DS) spread spectrum signals is their low probability of intercept. Detection of such signals and their features, such as center frequency and chip-rate, is of great interest for an interceptor. However, conventional intercept receivers often fail when the operation is in the presence of narrow-band interference, due to the high probability of false alarm.; An intercept receiver which employs transform domain signal processing (TDSP) is constructed at a center frequency of 200 Mhz with a 30 Mhz bandwidth. This receiver detects DS-BPSK spread spectrum signals in the presence of narrow-band interference by employing adaptive narrow-band interference rejection techniques. The significant improvements in the system performance over conventional detection techniques are shown by presenting both experimental measurements and simulated receiver performance (probability of detection versus false alarm) for two DS spread spectrum signal detection techniques: center frequency feature detection, and total power detection.; The receiver employs one of two transform domain processing techniques for adaptive narrow-band interference rejection. In the first technique the narrow-band interference is detected and excised in the transform domain (adaptive multiple notch filtering). In the second technique, the interference is suppressed using soft-limiting in the transform domain. In both techniques the real-time Fourier transformation is performed using surface acoustic wave chirp filters with 200 Mhz center frequency, 60 Mhz bandwidth, and 60 {dollar}mu{dollar}s delay. The intercept receiver performance is studied for both weighted and unweighted received signals, at various interference-to-signal and signal-to-noise ratios and in the presence of both CW and finite-bandwidth interference.