Abstract:

To improve the energy efficiency of muhipath signals, a subchip muhipath search method based on the fractional Fourier transform （FrFT） is proposed, in which Chirp signals are used as pilot signals and muhipath Chirp signals are processed by FrFT at receiver side. Then, according to the linear relationship between the multipath relative delay in time domain and the difference in peak positions of muhipath Chirp signals in FrFT domain, the relative delays between muhipath Chirps are calculated after detecting the peak positions, with a search resolution equal to the reciprocal of the bandwidth of Chirp signals. Thus, the Chirp signal with a bandwidth lager than that of direct sequence spread spectrum （DSSS） signal can be used to search subchip muhipath. Simulated results show that the proposed method helps to effectively calculate the relative delays of subchip multipath and greatly improves the BER （ Bit Error Rate） performance of DSSS receiver after the equal-gain-combining process of the recognized subchip multipath.

Key words: direct sequence spread spectrum, multipath propagation, fractional Fourier transform, Chirp signal