Chaotic Spread Spectrum Sequences For Asynchronous Cdma Systems

CDMA is a main technique of the third generation wireless personal communication system. It adapts to the method of spread spectrum (SS).Spread spectrum communication uses much larger bandwidth than original information required and it uses pseudo noise (PN) sequences modulate.so the quality of the SS sequence affects the system performances directly.The discovery of chaotic dynamic system broad the way of study of PN sequence. Chaos is a convinced and random kind course that appears in the nonlinear system. It is an unperiod and an irregular course. It is not convergence but dose have a bound,while it is sensitive to its initial value. For all these special performance,chaos has an excellent outlook in the application of telecommunication,especially in the generation of PN sequence.In this paper,we have a deep discuss in DS-SS system,analysis the structure of the system, then we come to the PNsequence used in DS-SS system and introduce chaos to the study of PN sequence.We take Logistic sequence as representative with traditional Gold sequence.In the comparison we study their performance of balance performance of run,performance of auto-correlation,performance of cross-correlation, performance of side lobe,performance of peak value.We can come to a conclusion that chaotic sequence is adapt to the spreading codes of DS-CDMA.We improve the key performance of chaotic PN sequence by filtration,and get sequence that better than common chaotic sequence and traditional Gold sequence.We find that Chebyshev sequence has excellent. We study chaotic sequence on the MATLAB's simulink platform.We analysis bit error rate of different kinds chaotic spreading spectrum sequence in MAI and MPI.The feasibility and superior performance of chaotic spreading spectrum technology used to DS-CDMA communication system has been greatly proved.