Performance Improvement of DS-CDMA Systems Using Two Dimensional Bernoulli Chaotic Spreading Sequence

A major goal of a spread spectrum communication system is to protect communication
signals against interference and exploitation by unintended listeners. In fact, Low
Probability of Detection and Low Probability of Intercept are two important parameters
for increasing performance of the system. In DS-CDMA, these goals are reached by
multiplying the data information and spreading sequences. Chaotic sequences, with its
unique properties, have numerous applications in building spreading codes. Before,
using one-dimensional Bernoulli sequence as spreading code is proposed. The main
feature of this sequence is its negative autocorrelation at lag of one. Efficiency of the
system based on these codes will be increased comparing with other known codes. On
the other hand, employing the complex chaotic sequences as a spreading sequence also
has been discussed in several papers. In this paper, the use of two-dimensional Bernoulli
chaotic sequences as a spreading code is proposed. The quality of a multiuser
synchronous and asynchronous DS-CDMA will be evaluated by applying these
sequences in AWGN and fading channel. Simulation results indicate the improved
performance compared with conventional spreading codes like Gold codes and also
other similar complex spreading sequences.