Performance metrics for windows used in real-time DFT-based multiple-tone frequency excision

The capability of direct-sequence spread-spectrum receivers to reject narro wband interference can be significantly improved by eliminating narrowband energy in the received signal through a real-time discrete Fourier transfor m (RT-DFT) process, However, the loss in received signal strength due to th is frequency excision process can be significant. In this paper, we present a theoretical framework for evaluating the performance of alternative comb inations of time weighting functions (windows), fractions of overlap in ove rlap-and-add architectures, and frequency-domain mapping algorithms, The se nsitivity loss due to time weighting is presented for variable overlaps and several different windows. A. set of window metrics is defined that provid es a means of calculating distortion losses for an arbitrary number of inte rfering tones with uniformly distributed center frequencies, Theoretical re sults are confirmed by simulation. These results can be used to compare sen sitivities of alternative RT-DFT frequency excision direct-sequence spread- spectrum systems and to calculate the standoff range of a finite number of in-band tone emitters.