Broadband interference excision in spread spectrum communication systems via fractional Fourier transform

We demonstrate the use of the fractional Fourier transform (FRFT) in excising broadband, linear FM (chirp) type interferences in spread spectrum communication systems. This method is predicated on the fact that the FRFT perfectly localizes a linear FM signal as an impulse when the angle parameter of the transform matches the sweep rate (chirp rate) of the linear chirp signal. Therefore, a transform domain thresholding can often eliminate linear-FM type interferences without severely affecting the desired part of the received signal. Thus we propose a preprocessing of the received signal by an FRFT-based excision scheme prior to demodulation. The simulations demonstrate that this technique often improves the bit error performance of the receiver when compared to the case where there is no preprocessing.