Optimum multilevel chaotic sequences for asynchronous DS-CDMA systems over Rician selective fading channel

The BER performances of asynchronous DS-CDMA systems using conventional matched-filter receiver and multilevel chaotic spreading are estimated over a Rician fading selective channel. The paper completes the results of previous works dedicated to the optimization of system's BER performances by controlling the chaotic sequence generator. It is showed that a family of PWAM (Piece-Wise Affine Markov) maps named (n, t) - tailed shifts can generate sequences that optimize the performances of the DS-CDMA system under different load and channel fading conditions. Even though these works considered the multilevel quantization for the system performance analysis, the optimum case was identified only for the binary sequences, stating that the multilevel sequences offer no improvement over the classical sequences. The present paper shows that in the case of (n, t) - tailed shifts sequences the optimum performances are reached not only for a binary quantization, but for any number of quantizing levels.