A new spread spectrum scheme combined with a chirp signal in a fractional Fourier transform domain

In a direct-sequence spread-spectrum(DS-SS) system demodulation will be badly affected by interference with the system's central frequency.To solve this problem,the authors proposed a new spread spectrum scheme based on fractional Fourier transform combined with a chirp signal.The chirp signal is applied to spread the spectrum of the binary base band data.Chirp signals with different chirp-rates have the best energy concentration in a corresponding fractional Fourier domain.The location of the best energy concentration in a fractional Fourier domain is different when the chirp-rate of the chirp signal changes.These properties have been used in the proposed scheme,where signals underwent fractional Fourier transform at the receiving end to get the best energy concentration,with demodulation made based on a judgment of the energy concentration's location.Finally,simulation results showed that the performance of the scheme is better than DS-SS for overcoming interference.