The Method of Anti-Multipath for Recombination CDMA Users Based on Chip Waveform Compensation

Abstract

In cognition radio system, the technology using CDMA users with controllable spectrum nulls as cognitive user possess the advantage of both CDMA and cognition radio. The existing method to obtain controllable spectrum nulls for cognition CDMA is to use recombination sequence. The autocorrelation performance is turned out to lower through derivation and analysis, which result in the lower of anti-multipath performance of CDMA users with recombination sequence through giving the variance of decision variables at the Rake receiver for asynchronous DSCDMA system in Rayleigh fading channel. Moreover, the performance of antimultipath for CDMA users depended on both chip waveform and spread-spectrum sequence. Thus, the performance of anti-multipath for CDMA users can be compensated by introducing chip waveform with satisfactory autocorrelation performance. The amendatory Hermite function (AHF) was turned out to possess 1properties of fine autocorrelation and cross-correlation, energy concentration in time and frequency domain, which turned out to be appropriate to compensate the antimultipath performance of CDMA users with recombination sequence. What is more, the spectrum nulls of AHF change when the order changes. It means that only the order of AHF used by CDMA users need to be changed when the frequency band of interference or authorized users change. It was turned out that the bit error rate (BER) performance of recombination CDMA users with AHF outweighed that with classic waveforms whenever there were multiple-access interference (MAI), multiple-path interference(MPI), narrow band interference(NBI). The proposed method possesses better performance of anti-MAI, anti-MPI, anti-NBI.