Chaotic complex spreading sequences for asynchronous DS-CDMA. I. System modeling and results

Abstract

This paper and its companion are devoted to the evaluation of the impact of chaos-based techniques on communications systems with asynchronous code division multiple access. Sequences obtained by repeating a truncated and quantized chaotic time series are compared with classical m-sequences and Gold sequences by means of a performance index taken from communication theory which is here defined and thoroughly discussed. This analysis reveals that, unlike conventional sequences, chaotic spreading codes can be generated for any number of users and allocated bandwidth. Numerical simulations are reported, showing that systems based on chaotic spreading sequences perform generally better than the conventional ones. Some analytical tools easing the comprehension of these advantages are here summarized and proved in Part II where formal arguments are developed and discussed to ensure general applicability of chaotic spreading codes.

Detection performance of chaotic spreading LPI waveforms

“…In order to improve the covertness of the communications, noise-like chaotic spreading sequences can be used to conceal the signals. Chaotic sequences are usually generated using discrete chaotic maps, such as the logistic map, triangular map, and exponential map [6]- [8]. The logistic map is one of the simplest and most widely studied (1) where , , and is called a bifurcation parameter.…”

“…Depending on the value of , the dynamics of this system can change dramatically, exhibiting periodicity or chaos. For , the sequence is periodic with a period for some integer ; while for , the sequence is, for all practical purposes, nonperiodic and nonconverging [2], [6]- [8]. The histogram of the noise-like chaotic sequences in some cases has been proven to follow a certain probability density distribution (pdf) [2].…”

“…Recently, the signal interception problem is also studied with a self-recovering receiver for DS SS signals with unknown spreading codes and its performance is analyzed and presented in [5]. To improve the security of the DS SS systems, nonbinary and nonperiodic chaotic sequences, which have been investigated in [2] and [6]- [8] are desirable for covert communications because their pseudo-random waveforms can be very useful in disguising signals as noise. Another advantage of using chaotic sequences is the large number of available spreading sequences for multiple-access applications [2].…”

Bifurcations and Chaos Generation from 1D or 2D Circuits Including Switches

“…Then, during the two last decades, many researchers have tried to nd applications to chaotic signals, which also look like random signals. Some applications concern the use of chaotic signals for secure transmissions, telecommunications and image processing [19] [24]. It appears that all chaotic signals cannot be used in such applications.…”

Performance Analysis of MC-CDMA Sytems Using Chaotic and Conventional Spreading Sequences

“…Therefore the main advantages of their usage are increased security of the transmission and also ease of generation and visualization of great number of sequences [24]. Generation of chaos is described in [22,23,25], Direct Sequence Spread Spectrum (DSSS) CDMA with chaotic sequences is described for example in [14], Direct Sequence (DS) CDMA is described in [15][16][17][18][19][20][21] and MC/DS CDMA is described in [4]. Chaos is a deterministic, random-like process found in non-linear dynamical system, which is non-periodical, non-converging and bounded.…”