Asynchronous direct-sequence ultra-wideband communication using spatiotemporal chaotic sequences

In this work, the authors address the effect of spreading sequences and pulse waveforms on the performance of asynchronous direct-sequence ultra-wideband systems. Regarding spreading sequences, they consider the two cases of short and long sequences. The expression of the multi-user interference (MUI) variance is derived using long sequences at the output of a rake receiver, when propagating through multipath channels. The authors also propose the use of sequences generated with a family of spatiotemporal chaotic systems, namely piecewise coupled map lattices (PCML), as spreading sequences. Such sequences are shown to reduce the MUI variance with regard to independent identically distributed and Gold sets for both short and long sequences. Simulation results show that the use of long PCML codes in additive white Gaussian noise and multipath fading channels results in an improvement of the system average bit error rate, hence an increase of the system capacity in terms of number of active users.