Linear vs. bilinear time-frequency methods for interference mitigation in direct sequence spread spectrum communication systems

Time frequency signal representations have been examined for interference mitigation in spread spectrum (SS) communication systems. We implement a direct sequence spread spectrum (DS-SS) system with additive jamming and utilize two distinct time-frequency (t-f) methods to mitigate the interference, namely the shift-covariant class of time frequency distributions (TFD) and the Gabor (1946) transform. The TFD is a bilinear transform and is shown to improve the receiver characteristics in a highly nonstationary jamming environment. The Gabor transform is a linear method that has real-time computational advantages yet has a limited class of jammers against which it performs well. A common feature in these two excision methods is that the t-f points are analyzed with the same time resolutions and frequency resolutions. The performance of both methods under several jamming scenarios is discussed and computational considerations are addressed.