Adaptive notch filtering using multi-rate frequency-sampling band-pass filters

A significant problem in decoding spread-spectrum binary phase shift keying (BPSK) signals is the presence of narrow-band interference from nearby transmissions. A multi-rate technique is proposed that achieves a typical throughput rate of 30 MHz with hardware that is sampling only at a 5 MHz rate. This achieved by using a frequency-sampling-like structure to divide the incoming spread-spectrum signal into five frequency bands and then processing in each of these small frequency bands at a lower sampling rate. These low-sampling-rate filters consist of an array of complex arithmetic bandpass filters that can be placed anywhere on the unit circle. These bandpass filters are monitored by the adaptive algorithm to detect when the energy in that band exceeds the value expected for the BPSK signal. When this occurs, narrow band interference is detected. A simple algorithm is used to subtract the output of the bandpass filter from the input to generate a notch at the interference frequency, thus attenuating the interference