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Bouzegzi A.,CEA Grenoble | Ciblat P.,ENST | Jallon P.,CEA Grenoble
Signal Processing | Year: 2010

In the context of cognitive radio or military applications, it is a crucial task to distinguish blindly various OFDM based systems (e.g., Wifi, Wimax, 3GPP/LTE, DVB-T) from each others. Existing OFDM based systems differ from their subcarrier spacing used in OFDM modulation. One can thus carry out recognition algorithms based on the value of the subcarrier spacing. Standard approaches developed in the literature rely on the detection of the cyclic prefix which enables to exhibit the value of the used subcarrier spacing. Nevertheless these approaches fail when either the cyclic prefix duration is small or the channel impulse response is almost as large as the cyclic prefix. Therefore we propose four new algorithms to estimate the parameters of OFDM modulated signal (especially the subcarrier spacing) relying on (i) the normalized kurtosis, (ii) the maximum-likelihood principle, (iii) the matched filter, and (iv) the second-order cyclostationary property. We show the strong robustness of proposed algorithms to short cyclic prefix, multipath channel, time offset, and frequency offset. Comparisons between proposed algorithms and the state of art techniques are done by means of computer simulations. © 2009 Elsevier B.V. All rights reserved.

Bouzid M.C.,ENST | Bouzid M.C.,University of Science and Technology Houari Boumediene | Ait Haddadene H.,University of Science and Technology Houari Boumediene | Salhi S.,University of Canterbury
Computers and Operations Research | Year: 2016

In this paper, we propose an efficient and novel Lagrangian relaxation method which incorporates a new integer linear programming (ILP) formulation to optimally partition a giant tour in the context of a capacitated vehicle routing problem (CVRP). This approach, which we call Lagrangian split (Ls), is more versatile than the ILP which, in most cases, can be intractable using a conventional solver. An effective repair mechanism followed by a local search are also embedded into the process. The mathematical validity of the repair mechanism and its time complexity are also provided. An integration of Ls into a powerful variable neighbourhood search (VNS) is also presented. Computational experiments are conducted to demonstrate that Ls provides encouraging results when applied on benchmark instances and that the integration of Ls into a metaheuristic scheme produces good results when compared to those found by state-of-the-art methods. © 2016 Elsevier Ltd.

Huang Q.,National University of Defense Technology | Ghogho M.,University of Leeds | Wei J.,National University of Defense Technology | Ciblat P.,ENST
IEEE Transactions on Signal Processing | Year: 2010

In this paper, we investigate the timing and carrier frequency offset (CFO) synchronization problem in decode and forward cooperative systems operating over frequency selective channels. A training sequence which consists of one orthogonal frequency-division multiplexing (OFDM) block having a tile structure in the frequency domain is proposed to perform synchronization. Timing offsets are estimated using correlation-type algorithms. By inserting some null subcarriers in the proposed tile structure, we propose a computationally efficient subspace decomposition-based algorithm for CFO estimation. The issue of optimal tile length is studied both theoretically and through simulations. By judiciously designing the tile size of the pilot, the proposed algorithms are shown to have better performance, in terms of synchronization errors and bit error rate, than the time-division multiplexing-based training method and the computationally demanding space-alternating generalized expectation-maximization algorithm. © 2010 IEEE.

Ghannoum H.,Laboratory of Electronics and Computer Engineering | Roblin C.,Laboratory of Electronics and Computer Engineering | Begaud X.,ENST
Wireless Personal Communications | Year: 2010

Wireless Body Area Networks (WBANs) are becoming an increasingly important part of the wireless communication system. In such a communication system various electronic devices carried by a person on his body can be connected. In this paper, we investigate the UWB body area propagation channel. The channel characterization is based on UWB on-body channel measurements. This paper describes the measurement campaign and the basic characteristics of the body area propagation channel extracted from measurement data. © 2008 Springer Science+Business Media, LLC.

Bughin E.,Ecole Normale Superieure de Cachan | Almansa A.,ENST | Grompone Von Gioi R.,Ecole Normale Superieure de Cachan | Tendero Y.,Ecole Normale Superieure de Cachan
Proceedings - International Conference on Image Processing, ICIP | Year: 2010

We propose a new method for fast detection of planar patches in disparity maps. We first use a region growing algorithm on random seeds. This approach is similar to the one introduced in [1] for fast line segment detection in images. Then, the parameter-free criterion introduced in [2] is used to keep only the patches that are planar. The main advantage of our method is to be able to estimate the disparity map precision which is usually a critical parameter in other methods. This method is specially well suited to 3D reconstruction of urban environments from low-baseline aerial or satellite stereo pairs where a piecewise-planar model can be applied. © 2010 IEEE.

Mahmood A.,ENSTA | Belfiore J.,ENST
IEEE Transactions on Communications | Year: 2010

An efficient algorithm for bit-loading in multicarrier systems is proposed based upon an allocation rhythm/order underlying the classical optimal greedy bit-allocation procedure. An accurate complexity comparison in terms of the exact number of execution cycles over a processor is made with the classical Greedy [1] solution along with another recently proposed optimal bit-loading algorithm [2]. Simulation results verify the significant complexity advantage of our algorithm with no loss in performance. © 2010 IEEE.

Chen Q.,University of Shanghai for Science and Technology | Maitre H.,ENST | Deng Q.-P.,University of Shanghai for Science and Technology
Signal Processing: Image Communication | Year: 2012

Lossy compression is inherently contradictory with information hiding and may result in unreliable retrieval of embedded message. For most of the existing data hiding algorithms, the process of dealing with the conflict and trade-off of invisibility, capacity and robustness is done in an experimental fashion. We have developed an image and video unified data-embedding technique. The algorithm is capable of accurately retrieving hidden data after the embedded signals are subjected to JPEG/MPEG compression as long as its compression degree is above the predefined one. Embedding strategy is to integrate data hiding into the JPEG/MPEG coding structures and to combine the adjustment factor of the strength and quantity of data hiding with the control parameter of lossy compression, according to the constraint of human visual system, the demand of hiding capacity and distortion impact of lossy compression. Experimental evaluation demonstrates that the proposed algorithm allows us to hide data invisibly in an accurate retrievable way with effective and flexible trade-off mechanism in the presence of lossy compression. In addition, the scheme is robust to some common attacks including low-pass filtering, noisy interference, frame dropping and transcoding. © 2011 Elsevier B.V. All rights reserved.

Nguyen Thanh N.,Telecom ParisTech | Ciblat P.,ENST | Pham A.T.,University of Aizu | Nguyen V.-T.,University of California at Berkeley
IEEE Transactions on Wireless Communications | Year: 2015

We investigate the primary user emulation (PUE) attack, which is a serious security problem in cognitive radio (CR) networks. There exist three types of PUE attackers: 1) a selfish one, which aims at maximizing its selfish usage of channel resource; 2) a malicious one, which points for obstructing the operation of CR network; and 3) a mixed one, which is between a selfish and malicious PUE attacker. For combating a selfish PUE attacker, a channel surveillance process has to be implemented in order to determine active user's identification and so selfish PUE attacker. An extra-sensing process has to be implemented for observing new opportunities to access the channel and so for mitigating the malicious PUE attacker's effect. Relevant strategies for deploying the above processes are obtained through a game theory-based analysis and the exhibition of Nash equilibrium (NE). We show the NE strongly depends on the network demand, the availability of the spectrum resource, and the type of the attacker. © 2016 IEEE.

Cohen G.,ENST | Fachini E.,University of Rome La Sapienza | Korner J.,University of Rome La Sapienza
IEEE Transactions on Information Theory | Year: 2011

We introduce a new class of problems lying halfway between questions about graph capacity and intersection. We say that two binary sequences x and y of the same length have a skewincidence if there is a coordinate i for which x i=y i+1=1 or vice versa. We give relatively close bounds on the maximum number of binary sequences of length n any pair of which has a skewincidence. A systematic study of these problems helps to understand the mathematical difficulties to solve zero-error problems in information theory. © 2011 IEEE.

Battail G.,E.N.S.T.
International Symposium on Turbo Codes and Iterative Information Processing, ISTC | Year: 2014

Information can only be defined as an equivalence class of sequences with respect to alphabet changes and encodings, hence it is an abstract entity. However, a sequence is necessarily borne by a physical support. Information thus appears as a bridge between the abstract and the concrete. In the living world, the information borne by genomes acts on matter by instructing the assembly of objects. Physical perturbations degrade the supports, hence the sequences they bear, but the information they represent can be almost indefinitely conserved provided they are endowed with error-correcting codes as powerful as to enable their regeneration, and regenerated frequently enough. Codes made of nested components which successively originated over the ages account for the conservation of the oldest parts of the genomes. The component codes are 'soft', meaning that they result from any kind of non-mathematical constraint, e.g., physical-chemical or linguistic. The genomic information instructs the assembly of living structures by the agency of interwoven semantic feedback loops which lock themselves because the synthetized enzymes catalyse their own assembly. © 2014 IEEE.

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