Narrow-band interference rejection using real-time Fourier transforms

An analysis is presented of a BPSK-PN (binary phase shift-keyed with pseudonoise) demodulator when present narrowband interference is attenuated using transform domain filtering. The signal of interest is a wideband direct-sequence spread-spectrum signal (DS-SS). The interference is a narrowband signal which may be of high power and which is either intentionally or unintentionally collocated in frequency and interfering with the signal of interest. The effect of windowing the input signal by a rectangular or Hamming windows as well as the use of an overlap and save scheme is presented. It is shown that the Hamming window far outperforms the rectangular window, and that the interference is for all purposes completely eliminated when the Hamming window is used in conjunction with the overlap and save scheme. The criterion used to evaluate the effectiveness of the different interference rejection techniques is the bit error rate (BER) as measured at the output of the demodulator.