Stéphane Azou

Stéphane Azou
École Nationale d'Ingénieurs de Brest | ENIB · CNRS, UMR 6285 Lab-STICC

PhD

About

79
Publications
9,885
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
567
Citations
Citations since 2017
28 Research Items
232 Citations
2017201820192020202120222023010203040
2017201820192020202120222023010203040
2017201820192020202120222023010203040
2017201820192020202120222023010203040

Publications

Publications (79)
Article
Full-text available
This paper proposes a parametric network for the joint compensation of multiple linear impairments in coherent optical communication systems. The considered linear impairments include both static and time-variant effects such as in-phase/quadrature (IQ) imbalance, laser phase noise (PN), chromatic dispersion (CD), polarization mode dispersion (PMD)...
Article
Full-text available
This paper deals with robust heart rate detection intended for the in-car monitoring of people. There are two main problems associated with radar-based heart rate detection. Firstly, the signal associated with the human heart is difficult to separate from breathing harmonics in the frequency domain. Secondly, the vital signal is affected by any int...
Preprint
Full-text available
This paper proposes a parametric-based network architecture for joint channel estimation and data detection in communications systems with hardware impairments. This architecture is composed of a data-augmented layer, a custom soft thresholding function, and several linear layers modeling the effect of channel effects and hardware impairments. In t...
Preprint
Full-text available
In this paper, we focus on the joint impairments compensation and symbol detection problem in communication systems. First, we introduce a new multi-layer channel model that represents the underlying physics of multiple impairments in communication systems. This model is composed of widely linear parametric layers that describe the input-output rel...
Article
This article aims to propose new techniques to detect and distinguish humans from moving machines in indoor environments. Although many research efforts have been already dedicated to humans’ indoor detection, most of the work has been focused on counting people and crowd measurement for consumer business applications. Our objective is to develop a...
Preprint
This paper proposes a new estimation and compensation approach to mitigate several linear and widely linear effects in coherent optical systems using digital signal processing (DSP) algorithms. Compared to most of the available strategies that employ local estimation and/or compensation algorithms, this approach performs a global impairments estima...
Preprint
This paper proposes a new estimation and compensation approach to mitigate several linear and widely linear effects in coherent optical systems using digital signal processing (DSP) algorithms. Compared to most of the available strategies that employ local estimation and/or compensation algorithms, this approach performs a global impairments estima...
Article
This article proposes a new estimation and compensation approach to mitigate several linear and widely linear effects in coherent optical systems using digital signal processing (DSP) algorithms. Compared to most of the available strategies that employ local estimation and/or compensation algorithms, this approach performs a global impairments esti...
Conference Paper
Digital predistortion has recently spurred interest in photonics. In this paper, the authors perform a sensitivity analysis of three digital predistortion algorithms and demonstrate an increase in performance and, in some cases, robustness to uncertainties.
Article
Full-text available
Non‐linearities introduced by power amplifiers in communication systems have been a subject of interest for industry and academia for a long time. On one hand, the search for increased range intrinsically incites operators to boost input power. On the other hand, this leads to stronger non‐linear phenomena in amplifiers, which in turn increase the...
Article
Full-text available
Digital predistortion is topic of significant interest in telecommunications – both in the wireless radio field and, more recently, in photonics. In the present letter, the authors undertake a sensitivity analysis of various digital predistortion algorithms. Using recent metamodeling techniques designed for efficient stochastic analysis, the author...
Article
To enhance the error performance of impulse radio UWB transceivers, we introduce in this manuscript a novel modulation scheme based on exploiting the symmetry properties of transmitted waveforms. Parity Modulation utilizes odd versus even pulses to represent binary data, while the detector relies on a time reverser and non-coherent cross correlator...
Article
Full-text available
50 days' free access to the article. Anyone clicking on this link before October 24 https://authors.elsevier.com/c/1ZgXg6wPve~wi The inherent nonlinear effects associated to Semiconductor Optical Amplifiers (SOAs) may translate into a transmission performance loss for non-constant envelope modulation formats. However, a variety of linearization s...
Article
Full-text available
Presents corrections to the paper, “Sparse preamble design for polarization division multiplexed COOFDM/ OQAM channel estimation,” (Nhan, N.-Q., et al), J. Lightw. Technol., vol. 36, no. 13, pp. 2737– 2745, Jul. 2018.
Article
Full-text available
A phaser-based processing technique was adopted in an UWB over fiber system employing SOA. The target is to simultaneously reduce the ASE noise impact and nonlinear effects inherent to optical amplification. Experimental results prove the effectiveness of chirping in terms of cross correlation and bit error rate.
Article
Full-text available
In this paper, we consider the polarization division multiplexed (PDM) coherent optical - orthogonal frequency division multiplexing/offset-quadrature amplitude modulation (CO-OFDM/OQAM) system. The problem of channel estimation for this system is investigated. Firstly, we introduce the sparse preamble channel estimation method for PDM CO-OFDM/OQAM...
Article
Full-text available
The linearization performance of various digital baseband pre-distortion schemes is evaluated in this paper for a coherent optical OFDM (CO-OFDM) transmitter employing a semiconductor optical amplifier (SOA). In particular, the benefits of using a parallel two-box (PTB) behavioral model, combining a static nonlinear function with a memory polynomia...
Article
Full-text available
n this study, we adopt a phaser-based processing to enhance the performance of impulse radio over fiber system utilizing SOA. The amplifier has been placed at a distance in the optical link, so as to extend the coverage area of proposed transceiver. Operating in the linear or saturation region for SOA, adds ASE noise or strong nonlinearities acting...
Conference Paper
Full-text available
Semiconductor Optical Amplifiers are known to be prone to nonlinear effects in the saturated regime. This is particularly true if the signals to be amplified have a non-constant envelope and a high Peak-to-Average Power Ratio (PAPR). The benefits of envelope-tracking is investigated here for linearizing a Coherent-Optical OFDM (CO-OFDM) transmitter...
Article
Full-text available
In this paper, we investigate the usage of SOA for reach extension of an impulse r adio over fiber system. Operating in the saturated regime translates into strong nonlinearities and spectral distortions, which drops the power efficiency of the propagated pulses. After studying the SOA response versus operating conditions, we have enhanced the syst...
Article
Full-text available
A simple pulse shape randomization scheme is considered in this paper for improving the performance of ultra wide band (UWB) communication systems using On Off Keying (OOK) or pulse position modulation (PPM) formats. The advantage of the proposed scheme, which can be either employed for impulse radio (IR) or for carrier-based systems, is first theo...
Conference Paper
In this communication we use macro-modeling and signal processing techniques in order to compensate the nonlinear effects of a semiconductor optical amplifier (SOA) that is used in a CO-OFDM (coherent optical and orthogonal frequency-division multiplexing) optical transmitter. Two solutions are examined in detail: a peak-to-average power ratio (PAP...
Article
Full-text available
The joint use of peak-to-average power ratio (PAPR) reduction and linearization via digital predistortion is investigated in this letter, with the view to improve the performances of coherent optical OFDM systems employing a semiconductor optical amplifier. The PAPR reduction is performed via Wang’s nonlinear companding transform, which has been re...
Poster
Full-text available
We investigate the reach extension issue of a 2 Gbps Impulse Radio Ultra Wideband (IR-UWB) over fiber link based on OOK modulation according to two complementary approaches: a simple randomized OOK scheme is firstly adopted for spectral line reduction, and then the benefits of using an inline amplification via Semiconductor Optical Amplifier (SOA)...
Conference Paper
Full-text available
The power efficiency of a 2 Gbps OOK-based Impulse Radio-over-Fiber (RoF) system based on 5th-derivative Gaussian and Abraha's pulse is studied in this paper, with the aim of optimizing the Mach-Zehnder Modulator (MZM) setup. The best peak-to-peak (p-p) voltage is computed for several fiber lengths up to 40 Km. It is shown that adapting the p-p vol...
Article
Full-text available
Coherent-Optical OFDM systems are known to be sensitive to large peak-to-average power ratio (PAPR) at the transmitter output, due to nonlinear properties of some components involved in the transmission link. In this paper, we investigate the impact of an amplification of such signals via a semiconductor optical amplifier (SOA), considering some re...
Article
Full-text available
In this paper, we develop a statistical characterization of the multipath interference in an Impulse Radio (IR)-UWB system, considering the standardized IEEE 802.15.4a channel model. In such systems, the chip length has to be carefully tuned as all the propagation paths located beyond this limit can cause interframe/intersymbol interferences (IFI/I...
Article
Wang's nonlinear companding scheme is investigated here for the first time for CO-OFDM transmissions. As a result of an optimal predistortion function design, we demonstrate a 3 dB BER advantage for a system employing a Semiconductor Optical Amplifier (SOA).
Conference Paper
Full-text available
We consider the problem of implementing an algorithm for the extraction of leading eigenvectors of a small Hermitian matrix on field-programmable gate array (FPGA). The evolution of FPGAs can now handle increasingly bandwidth problems or larger in size. Jacobi algorithms are usually implemented in FPGA for real matrix size not exceeding 20*20. The...
Article
Full-text available
Timing synchronization is a major issue for any communication system since it is essential to ensure its stable operation and reliable performance. In this paper, we compare two low-complexity synchronization algorithms for impulse radio ultra-wideband (IR-UWB) system, employing orthogonal pulse shape modulation (PSM). The two widely adopted modula...
Article
Timing synchronization is a critical as well a challenging issue in ultra-wideband impulse radio (UWB-IR) due to their particular transmission characteristics. This letter proposes a rapid synchronization algorithm which can achieve frame-level synchronization in non-data-aided (NDA) mode. Relying on a unique transmit signal pattern based on orthog...
Conference Paper
Full-text available
This paper deals with timing recovery for Impulse Radio (IR) ultra-wideband (UWB) communication systems, which is known to be a challenging task to accomplish. We focus on blind estimation approaches, with the aim of being able to operate with minimal constraints on the signal format (no use of pilot symbols). We consider also the blind timing esti...
Article
Full-text available
Ultra wideband (UWB) radio has emerged as an attractive candidate for short-range wireless communications in recent years due to its unique features. However, implementation of UWB radios in order to utilize these features is coupled with some pronounced design challenges. To achieve precise timing synchronization is one of the most crucial task am...
Conference Paper
Full-text available
Synchronization is a key performance-limiting factor in any communication system and a challenging task to accomplish. In this paper, an energy detection based non data-aided (NDA) algorithm for orthogonal pulse shape modulated (PSM) impulse radio ultra wideband (IR-UWB) system is proposed. Relying on unique signal structure, simple overlap-add ope...
Article
Full-text available
In this correspondence, we focus on blind estimation of the chip duration of time-hopping signals by introducing a cost function based on time-of-arrival (ToA) folding over multiple observation sets. An optimization algorithm that takes advantage of the highly oscillatory behavior in the nearby of the global minimum is proposed and a performance bo...
Article
Full-text available
In this paper, an optimal approach based on B-splines functions is presented for the design of ultra wideband (UWB) pulses which satisfy simultaneously the following 3 criteria : compatibility with the spectral mask authorised in USA or in Europe, spectral efficiency and orthogonality of generated pulses. The first property allows UWB systems to co...
Article
Full-text available
Indoor propagation channel appears differently to ultra-wideband (UWB) systems than it does to narrowband systems. UWB signals have very high temporal resolution ability and this implies a frequency-selective channel with rich multipath in practice. To capture the signal energy spread over a multipath environment, a Rake receiver consisting of mult...
Article
Full-text available
The underwater positioning applications with ultra- short baseline (USBL) are based on geographical loc ating of transponders emitting deterministic waveform from a receiving antenna composed of several acoustic transducers. In addition to be robust against noise and multi-path, the transmitted signal should have low cross- correlation properties...
Conference Paper
Full-text available
The underwater positioning applications with ultra-short base line (USBL) antenna have expanded significantly over last decades. Their principles are based on the geographical positioning of transponders emitting deterministic waveform such as Costas arrays from a receiving antenna composed of several acoustic transducers. Recovering from the trans...
Article
Full-text available
A large amount of modulation recognition algorithms has been reported in literature for Single-Input Single-Output (SISO) communications. But, to our knowledge, none of them have dealt with Multiple-Input Multiple-Output (MIMO) commu- nications. The issue addressed in this paper is the modulation recognition forMIMO communications under the assumpt...
Article
Full-text available
The blind recognition of communication parameters is an important research topic in both commercial and civilian systems. In this paper, we investigate the blind recognition of the modulation. Currently most part of the existing algorithms assumes that the transmitter uses a single-antenna. This study extends the problem for multiple-antennas (MIMO...
Article
The study of time series with the aim of trying to characterize the underlying dynamical system (or data generating process) is a field of study of great interest in chaos-based communications, namely spread spectrum communications with chaotic spreading code. In order to perform any kind of analysis upon a data series, first, the phase space with...
Article
Full-text available
A closed-form state estimator for some polynomial nonlinear systems is derived in this paper. Exploiting full Taylor series expansion we first give exact matrix expressions to compute mean and covariance of any random variable distribution that has been transformed through a polynomial function. An original discrete-time Kalman filtering implementa...
Article
Full-text available
This paper adresses the problem of symbol estima- tion in the case of a spread spectrum based system where the receiver has only the information about the nonlinear function used to generate the spreading sequence. We propose two methods to achieve this, first based on the already considered DUAL form and a correlator second based one. For the DUAL...
Conference Paper
Full-text available
The aim of the present paper is to increase the reliability of a Kalman filter-based DS-SS receiver by considering in the state space models the multipath coefficients and associated delays. The objective being to operate at very low SNRs in shallow water (to achieve furtive transmissions) and with the need of a limited computational cost, the impl...
Conference Paper
Full-text available
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 a...
Article
Full-text available
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 whic...
Article
Full-text available
In this article, a new compression method is investigated using a particular chaotic modulation type. The symbolic approach presented associates to every informational sequence a trajectory in the state space of the chaotic generator. We are also introducing a new type of chaotic generator adapted to the probability distribution of the informationa...
Article
Full-text available
It has been recently pointed out than the Kalman filter is a powerful tool for the synchronization of chaos, which remains a major difficulty in the development of efficient chaos based digital communication systems, capable of operating over nonstationnary channels. The input signal power fluctuations, which often causes large errors in synchroniz...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
Recent theoretical results show that use of chaotic dynamics can significantly increase privacy of digital communication signals. The purpose of this paper is to report sea trial results of a chaotic spread spectrum system. Due to its ability to simultaneously sharing the same frequency band for various users (through Code Division Multiple Access)...
Conference Paper
Full-text available
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.
Article
Full-text available
Chaotic digital transmissions have recently emerged as a way to improve the security and privacy of digital transmissions. In this paper, we propose a new approach to estimate the transmitted symbols on the receiver side. This approach, that we call "Symbolic Matching", consists in matching vectors built from the received signal with a symbolic mod...
Conference Paper
Full-text available
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 with number theoretic transf...
Article
Full-text available
The development of digital communications creates new challenges for spectrum surveillance. Similarly, modem signal processing techniques and increasing available computational power make communication discretion ever more difficult. In this paper, we present recent methods based on time-frequency analysis and on statistical analysis of fluctuation...
Conference Paper
Full-text available
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 condition...
Conference Paper
Full-text available
In the context of spectrum surveillance (non cooperative context), a robust synchronization procedure is presented, in order to estimate the period symbol and timing offset of a direct sequence spread spectrum signal. Experimental results are given to illustrate the performances of the algorithm.