Development of a reverse chaos based CDMA link and fading mitigation

A mathematical model and a simulator for a reverse link of a direct sequence code division multiple access (DS-CDMA) system are developed under the assumption that the spreading signals are binary chaotic sequences which are generated by using a logistic map. The system is analyzed for two channels: the additive white Gaussian noise (AWGN) channel and the AWGN and Rayleigh fading channel. The derived expressions for the probability of error and the bit error rate (BER) curves obtained by simulation for the case when the system is under the AWGN channel show that the system performs very similarly to the classical systems that use Walsh functions for the message bits encoding. However, for the case when the system is under the AWGN and Rayleigh flat fading channel, the theoretical expressions for the probability of error and BER curves obtained by simulation show that the system performs very badly. For a purpose of fading mitigation in this system, the chip interleaving technique is used. In our analysis, a chip interleaver/deinterleaver structure is incorporated into the system. The theoretical findings and simulation results confirm that the proposed chip interleaving technique is an efficient mean to mitigate fading in the reverse link of a chaos based CDMA (CB-CDMA) system.