A Chaotic Direct-Sequence Spread-Spectrum System for Underwater Communication

Abstract-The recent advances in acoustic modem technology have enabled the development of Underwater Acoustic Networks (UAN). Application interests include oceanographic information gathering, environmental monitoring or coastal defense. Due to its ability of simultaneously sharing the same frequency band for various users and the poor propagation conditions usually encountered in shallow water environment, the Code Division Multiple Access (CDMA) is a promising scheme for UAN. Recent results show that a standard CDMA direct-sequence spread spectrum approach is not sufficient to ensure Low Probabilities of Detection (LPD) and/or Interception (LPI), that is an unauthorized observer may notice that a communication signal is present. For many applications, this drawback is not acceptable. In this paper, the application of chaos to transmission of information is under investigation to achieve an LPI/LPD objective in an UAN context. Performance results of two receivers are shown for a single user through a realistic simulation scenario. An experiment at sea will be conducted by GESMA soon to confirm these first results. I

Design of a chaos-based spread-spectrum communication system using dual Unscented Kalman Filters

Abstract- It has been demonstrated recently than use of chaotic spreading codes can significantly increase transmission privacy for direct-sequence spread spectrum systems. In this note, we consider the problem of receiver synchronization as a dual estimation of the clean state and the underlying model parameters from the observed noisy chaotic signal. An efficient implementation of the demodulator is investigated owing to the Unscented Kalman Filter, a recent alternative to the Extended Kalman Filter, providing superior performance at an equivalent computational complexity. Numerical simulations show the performance of this novel demodulator against noise for a single user on Gaussian channels. I

Sea trial results of a chaotic direct-sequence spread spectrum underwater communication system

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Performance analysis of a spreading sequence estimator for spread spectrum transmissions

Direct sequence spread spectrum transmissions (DS-SS) are now widely used for secure communications, as well as for multiple access. They have many interesting properties, including low probability of interception. Indeed, DS-SS transmitters use a periodical pseudo-random sequence to modulate the baseband signal before transmission. A receiver which does not know the sequence cannot demodulate the signal. In this paper, we propose a new method which can estimate the spreading sequence in a non cooperative context. The method is based on eigenanalysis techniques. The received signal is divided into windows, from which a covariance matrix is computed. We show that the sequence can be reconstructed from the two first eigenvectors of this matrix, and that useful information, such as desynchronisation time, can be extracted from the eigenvalues. The main achievement of the present paper is a performance analysis of the proposed spreading sequence estimation procedure. An analytical approach is first considered owing to matrix perturbation theory and Wishart matrix properties. Then, complementary Monte Carlo simulations are performed to show the effectiveness of the proposed method

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A robust synchronization procedure for blind estimation of th

Linear Predictive Speech Coding using Fermat Number Transform

Abstract- This paper is about the reduction of the computational complexity of a speech codec. A Linear Predictive Coding procedure is developed to allow its implementation with Number Theoretic Transforms. The use of Fermat Number Transform can reduce, in a significant way, the cost of Linear Predictive algorithm implantation on Digital Signal Processor

FAST PITCH MODELLING FOR CS-ACELP CODER USING FERMAT NUMBER TRANFORMS

This paper presents a double improvements to reduce the speech coding complexity of the pitch prediction in a Code-Excited Linear Prediction (CELP) coder. First, the pitch analysis structure is modified. A new fast Pitch Modelling by linear-Filtering (PMF) procedure will determine the adaptive and stochastic codebook contributions of the excitation signal. Afterwards, an e�cient implementation of the PMF � CELP coding is proposed by using Number Theoretic Transforms which can significantly reduce the algorithm computation complexity. 1

Design of a variable rate algorithm for CS-ACELP coder

Abstract- This paper is about the reduction of the computational complexity of the CS-ACELP codec, described in ITU recommendation G.729, and used for the transmission of voice over IP. A Voice Activity Detection module is proposed to replace the G.729 Annex B algorithm. The new procedure was developed to allow its implementation wit

A complete receiver solution for a chaotic direct sequence spread spectrum communication system

Abstract — This paper is devoted to receiver design in a Chaotic Direct-Sequence Spread Spectrum (CD3S) digital communication system. The demodulation is achieved through chaos synchronization in an efficient manner thanks to dual Unscented Kalman Filtering. The problem of carrier phase recovery, frequently neglected in chaos-based communication systems, is addressed either through Costas loop prior to demodulation or by dual estimation of the code, symbol and phase in baseband. The input signal power fluctuations, which often causes large errors in synchronizing chaotic waveforms, is also taken into account. Numerical simulations are provided to show the significance of the proposed receiver for both Additive White Gaussian Noise (AWGN) channel and a nonstationary channel. I