Daniel Roviras

A generalized methodology for bit-error-rate prediction in correlation-based communication schemes using chaos

The aim of this paper is to present a new and accurate approach to compute the bit-error-rate (BER) performance of coherent and non-coherent chaos-based communication systems. The approach explores the dynamical properties of chaotic sequences and takes into account that the bit energy is varying from one transmitted bit to another. Compared with other widely used approaches in the literature, the proposed methodology gives accurate results even for low spreading factors.

A Methodology for Bit Error Rate Prediction in Chaos-based Communication Systems

This paper is devoted to the derivation of an exact analytical expression of the bit error rate for chaos-based DS-CDMA systems. For the studied transmission system, we suppose that synchronization is achieved perfectly, coherent reception is considered, and an Additive White Gaussian Noise channel (AWGN) is assumed. In the first part of the paper, performance of a mono-user system with different chaotic sequences is evaluated and compared in terms of the error probability. This comparison is realized thanks to the probability density function of the bit energy of a chaotic sequence. The bit error rate can be easily derived by numerical integration. In some particular cases, for certain chaotic sequences with known probability density function of bit energy, we propose an analytical expression of the bit error. In the second part of the paper, the performance of a chaos-based DS-CDMA system is evaluated in the multi-user case. A general conclusion is that probability density function of chaos bit energy, for a given spreading factor, can give a clear idea about how to choose a “good” chaotic sequence for improving the performance of the chaos-based CDMA system.

Performance Analysis in the Downlink of Asynchronous OFDM/FBMC Based Multi-Cellular Networks

This paper provides a theoretical performance evaluation of the downlink of asynchronous orthogonal frequency division multiplexing (OFDM) and filter bank based multicarrier (FBMC) cellular radio communication systems. An accurate derivation, for the interference caused by the timing synchronization errors in the neighboring cells, is developed. The multipath effects on the interfering and desired signal are also considered. Based on computing the moment generating functions of the interference power, exact expressions are derived for average error rates of OFDM and FBMC systems considering the frequency correlation fading in the case of block subcarrier assignment scheme.

Robust synchronization for asynchronous multi-user chaos-based DS-CDMA

In this paper we propose two systems for achieving synchronization in asynchronous multi-user chaos-based DS-CDMA. For the first system, synchronization process is realized thanks to a binary code used as an additive pilot sequence to the spreaded signal. Gold sequences are used as pilot signals for the different users to accomplish the synchronization. For the second synchronization system, the synchronization is made through a binary code used as a multiplicative pilot signal for the spreaded data sequence. These synchronization processes are evaluated under the assumption of an additive white Gaussian noise channel together with multi-user interferences. In this paper we will focus on the initial synchronization phase (code acquisition) and we assume that the system can achieve correctly the code tracking after this first synchronization phase. The code acquisition for the two systems is evaluated in terms of the probability of detection and probability of false alarm.

Spectral efficiency comparison of OFDM/FBMC for uplink cognitive radio networks

Cognitive radio (CR) is proposed to automatically detect and exploit unused spectrum while avoiding harmful interference to the incumbent system. In this paper, we emphasize the channel capacity comparison of a CR network using two types of multicarrier communications: conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) and Filter Bank based MultiCarrier (FBMC) modulations. We use a resource allocation algorithm in which subcarrier assignment and power allocation are carried out sequentially. By taking the impact of Inter-Cell Interference (ICI) resulting from timing offset into account, the maximization of total information rates is formulated under an uplink scenario with pathloss and Rayleigh fading, subject to maximum power constraint as well as mutual interference constraint between primary user (PU) and secondary user (SU). Final simulation results show that FBMC can achieve higher channel capacity than OFDM because of the low spectral leakage of its prototype filter.

Adaptive predistortions based on neural networks associated with Levenberg-Marquardt algorithm for satellite down links

This paper presents adaptive predistortion techniques based on a feed-forward neural network (NN) to linearize power amplifiers such as those used in satellite communications. Indeed, it presents the suitable NN structures which give the best performances for three satellite down links. The first link is a stationary memoryless travelling wave tube amplifier (TWTA), the second one is a nonstationary memoryless TWT amplifier while the third is an amplifier with memory modeled by a memoryless amplifier followed by a linear filter. Equally important, it puts forward the studies concerning the application of different NN training algorithms in order to determine the most prefermant for adaptive predistortions. This comparison examined through computer simulation for 64 carriers and 16-QAM OFDM system, with a Salehs TWT amplifier, is based on some quality measure (mean square error), the required training time to reach a particular quality level, and computation complexity. The chosen adaptive predistortions (NN structures associated with an adaptive algorithm) have a low complexity, fast convergence, and best performance.

Adaptive MLSE receiver over rapidly fading channels

Abstract This paper develops an adaptive maximum likelihood sequence estimator (MLSE) for rapidly fading channels corrupted by additive white Gaussian noise. This estimator is based on an explicit incorporation of the time-varying characteristics in channel modelling. When the multipath is caused by a few strong reflectors, the channel is shown to be poly-periodically time varying. The channel impulse response is then approximated by a linear combination of a finite set of complex exponential functions whose frequencies are termed Doppler frequencies. This modelling is well motivated in aeronautical radio communications and cellular telephony. During the training period, a cyclic statistics-based approach is developed to estimate the Doppler frequencies. An eigenvector approach as well as a maximum likelihood method are proposed to estimate the coefficients of linear expansion. After this initialization, the channel parameters are updated using a modified version of the LMS algorithm. Computer simulations are carried out to evaluate the proposed receiver performance. The new approach exhibits a large saving in computational complexity and offers superior performance over conventional adaptive MLSE in rapidly fading environment.

Inter-cell interference analysis for OFDM/FBMC systems

Multicarrier communication technologies are promising candidates for 4G wireless access systems. In this paper, we focus on the downlink of multicellular networks and we investigate the influence of the inter-cell interference in an unsynchronized frequency division duplex (FDD) context with a frequency resuse of 1. We compare the conventional orthogonal frequency division multiplexing with cyclic prefix modulation (CP-OFDM) and the filter bank based multi-carrier modulation (FBMC). Two tables modeling the mean interference power are given and show that, in FBMC case, the interference is more localized than in OFDM case. Finaly, these tables are used to evaluate performance in terms of average capacity in FBMC multi-cell networks compared to CP-OFDM ones.

On the Use of Filter Bank Based Multicarrier Modulation for Professional Mobile Radio

Our main emphasis is on the use of enhanced OFDM and filter bank based multicarrier (FB-MC) waveforms for utilizing effectively the available fragmented spectrum in heterogeneous radio environments. Special attention is on the broadband-narrowband coexistence scenario of the Professional Mobile Radio (PMR) evolution. The target here is to provide broadband data services in coexistence with narrowband legacy services of the TETRA family. The core idea is a multi-mode radio platform, based on variable filter bank processing, which is able to perform modulation/detection functions simultaneously for different signal formats with adjustable center frequencies, bandwidths and subchannel spacings.

Theoretical performance for asynchronous multi-user chaos-based communication systems on fading channels

In this paper, we present a study of the bit error rate (BER) performance of chaos-based DS-CDMA system over an m-distributed fading channel. In this system, the perfect synchronization between receiver and transmitter is assumed. The transmitted bit energy after spreading by chaotic signal is not considered as constant in order to evaluate with precision the BER for such system. The performance of chaos-based DS-CDMA system is examined first in mono-user case. An approximation of the received bit energy by a known distribution leads to an accurate analytical BER expression. This BER computation approach is generalized for asynchronous multi-user case. The performance of DS-CDMA system using Gold sequence is compared and discussed to chaos-based DS-CDMA system. A perfect match between simulations and analytical BER expressions confirms the exactitude of our approach.