Interference mitigation in spread spectrum communication systems using time-frequency distributions

The capability of the time-frequency distributions (TFDs) to properly represent a single as well as multiple component signals in time and frequency permits the application of a new approach for interference excision in spread spectrum communication systems. The instantaneous frequency (IF) estimate from the TFD is used to construct a finite impulse response filter that reduces the interference power with a minimum possible distortion of the desired signal. The proposed technique is therefore a case of open-loop adaptive filtering. Three- and five-coefficient zero-phase excision filters are considered. Closed-form expressions of the improvement of SNR at the receiver correlator output using the TFD-based adaptive filtering are derived for two extreme cases of time-varying interferers, namely, those of fixed frequency sinusoids and randomly changing instantaneous frequencies. Simulation results including the bit error rates are presented for both swept and frequency hopping jammers.