A novel approach of generating chaotic spread spectrum sequence

In order to enhance ability of combating Multiple Access Interference (MAI) and improve system capacity in multi-user CDMA system, a new system model, which consists of two Multiple Forward Networks (2-MFNN) in series, is proposed to achieve optimum spreading sequences minimizing MAI. The former reconstructs chaotic attractor to generate Chaos Sequences, and the latter further simulates a transform relation to make Chaos Sequences from the former have better cross-correlation and auto-correlation. The method meets the condition of generating optimum spreading sequences minimizing MAI. Due to the disadvantage of conventional BP (Back-Propagation) learning algorithm used to MFNN, Clonal selection algorithm (CLONAL), which has the competence of searching for globally optimal or near-optimal solutions for multi-peak value function, is used as learning algorithm of MFNN. Whether the sequences generated by the system model have chaotic characteristic, is tested by Lyapunov Number, and the performance of output sequences of 2-MFNN is evaluated by using of root-mean-square of correlation function of all sequences. Simulation results Indicate that the sequences obtained by 2-MFNN not only possess chaotic characteristic but also has better correlation., It can be served as generator of good sequences for great capability CDMA system.