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Theoretical Performance Limits of Chaotic Spreading Sequences in DS-CDMA Systems
FIRB - RBAU01E5SF, 2003-2004

In the literature, many works on spreading sequences based on the chaotic theory have shown their good performance if applied to multiple access systems based on code division in asynchronous environment, where delays and phases of the received signals are random due to the mobility and the statistic channel fluctuations. On the other hand, these works have been mainly addressed to systems with simple receivers, like those based on a correlator or a Rake filter. Even if for such as receivers considerable advantages in terms of capacity or of communication quality, if a chaotic system is used, have been shown, a basic step to be done is the study of the system performance when the receiver is more complex and then more intelligent. A first consideration concerns with a certain orthogonality between the gain due to the receiver intelligence and the statistic features of the spreading sequences which are responsible of the multiple access capacity; on the other hand, some preliminary works on the receivers based on interference cancellation show that, even if the advantage given by the chaotic sequences decreases with the increase of the receiver complexity, this advantage does not become vanishing even if the complexity reaches infinity. This statement is the starting point of this research. The target is to completely modify the analysis approach, so that the study does not start from a particular reception structure, but a general and optimal one is assumed, independently from the possibility to be implemented, in order to investigate the performance bound of the chaotic approach in this contest. Interesting is the system capacity, in the sense of the Shannon capacity, and the possibility to move in the plain of the receiver complexity with respect to the capacity, so that some optimal or suboptimal design criteria can be given. These criteria should consider even the effect of the sequence synchronization, which is necessary in order to obtain information from the multiplied flow.

The project has the aim to investigate the capacity of complex reception structures by considering a multiple access scheme based on a code division in asynchronous environment and spreading sequences realized by means of a chaotic approach. The project steps are: identification of the figures of merit and of the general structure of the receiver; study of mathematic models in order to evaluate the asymptotic and finite in time and in space receiver performance; identification of project parameters and optimization of the chaotic sequence set; realization of system simulators/emulators in order to prove the approach effectiveness.
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