Time filter

Source Type

Kaaniche M.,Telecom ParisTech | Pesquet-Popescu B.,Telecom ParisTech | Pesquet J.-C.,University Paris Est Creteil | Benazza-Benyahia A.,COSIM Laboratory
Proceedings - International Conference on Image Processing, ICIP | Year: 2012

Many existing works related to lossy-to-lossless image compression are based on the lifting concept. In this paper, we present a sparse optimization technique based on recent convex algorithms and applied to the prediction filters of a two-dimensional non separable lifting structure. The idea consists of designing these filters, at each resolution level, by minimizing the sum of the ℓ1-norm of the three detail subbands. Extending this optimization method in order to perform a global minimization over all resolution levels leads to a new optimization criterion taking into account linear dependencies between the generated coefficients. Simulations carried out on still images show the benefits which can be drawn from the proposed optimization techniques. © 2012 IEEE.

Zouaidi F.,COSIM Laboratory | Boujemaa H.,COSIM Laboratory | Siala M.,MEDIATRON Laboratory
3rd International Conference on Communications and Networking, ComNet 2012 | Year: 2012

In this paper, we evaluate the performance of Automatic Repeat reQuest (ARQ) protocols for MIMO (Multiple In Multiple Out) Systems using fixed and adaptive Modulation based on the instantaneous Signal to Noise Ratio (SNR). Transmit Antenna Selection (TAS) or/and Space Time Block Coding (STBC) are used. At the receiver, Maximum Ration Combining (MRC), Selection Combining (SC), Generalized SC (GSC), Minimum Selection GSC (MSGSC) and Maximum Likeliood (ML) detection are used. We also propose a combination of TAS and STBC where STBC is performed over two selected best antennas. We provide an analysis of the throughput performance of ARQ for MIMO systems using different transmitting and receiving techniques. Simulation results are also provided to confirm the accuracy of the theoretical analysis. © 2012 IEEE.

Fki S.,Telecom Bretagne | Abdelkefi F.,COSIM Laboratory | Siala M.,MEDIATRON Laboratory | Ferre G.,Laboratoire IMS
European Signal Processing Conference | Year: 2012

In this paper, we consider a downlink cooperative multicell Base stations (BSs) system where the BSs are coordinating their transmitted signals to communicate with Mobile Stations (MSs) and both BSs and MSs are equipped with multiple antennas. We model this multicell cooperative system under the presence of channel estimation errors and we consider a general framework where the power that is transmitted from the BSs to the MSs is not constrained to be uniform. We propose to perform a modified version of the classical ZF beamforming where we decouple the power control and beamforming processes and we derive its corresponding cooperative system sum-rate. In order to maximize the system sum-rate, we propose a projected gradient based iterative algorithm and we show that using our proposed algorithm as a power allocation policy leads to significantly enhance the reachable multicell cooperative system sum-rate compared to the known situation where the power of the BSs is uniformly distributed. Simulation results are given to support our claims. © 2012 EURASIP.

Nasraoui L.,COSIM Laboratory | Najjar Atallah L.,COSIM Laboratory | Siala M.,MEDIATRON Laboratory
Annales des Telecommunications/Annals of Telecommunications | Year: 2014

This paper presents a performance analysis of a recently proposed preamble-based reduced-complexity (RC) two-stage synchronization technique. The preamble, composed of two identical subsequences, is first used to determine an uncertainty interval based on Cox and Schmidl algorithm. Then, a differential correlation-based metric is carried using a new sequence obtained by element wise multiplication of the preamble subsequence and a shifted version of it. This second step is performed to fine tune the coarse time estimate, by carrying the differential correlation-based metric over the uncertainty interval of limited width around the coarse estimate, thus leading to low computational load. In this paper, we first discuss some complexity issues of the RC approach compared to previously proposed algorithms. Then, we study the effect of the training sequence class and length choices on the synchronization performance in the case of multipath channels. The impact of the uncertainty interval width on the trade-off between performance and complexity is also studied. The two-stage approach was found to provide almost equal performance to those obtained by the most efficient differential correlation-based benchmarks. However, it has a very reduced computational load, equivalent to that of sliding correlation-based approaches. © 2013 Institut Mines-Télécom and Springer-Verlag France.

Nasraoui L.,COSIM Laboratory | Atallah L.N.,COSIM Laboratory | Siala M.,MEDIATRON Laboratory
IEEE Vehicular Technology Conference | Year: 2012

In this paper, we analytically study the performance of a recently proposed efficient reduced complexity time synchronization approach for orthogonal frequency division multiplexing systems. This method uses a preamble of two identical parts and proceeds in two stages. In the first stage, the repetitive structure of the preamble is exploited to provide the coarse time estimate respecting the algorithm of Cox and Schmidl. In the second stage, a fine metric, based on differential correlation, is carried over a reduced time window centered on the coarse estimate. We here study the performance of the fine stage, assuming a successful coarse stage whereby the fine search window is centered on the correct frame start. We approximate the fine metric by a Gaussian distribution to derive a closed form expression of the frame start correct detection probability. To this end, a statistical characterization of the fine metric is achieved by its mean and variance computation. Simulations are used to validate the results of the analysis. Indeed, the evaluated rate of correct detection perfectly concords with the theoretical probability in both additive white Gaussian noise and multipath channels. © 2012 IEEE.

Hraiech Z.,University of Carthage | Siala M.,University of Carthage | Abdelkefi F.,CoSIM Laboratory
European Signal Processing Conference | Year: 2014

High mobility of terminals constitutes a hot topic that is commonly envisaged for the next Fifth Generation (5G) of mobile communication systems. The wireless propagation channel is a time-frequency variant. This aspect can dramatically damage the waveforms orthogonality that is induced in the Orthogonal frequency division multiplexing (OFDM) signal. Consequently, this results in oppressive Inter-Carrier Interference (ICI) and Inter-Symbol Interference (ISI), which leads to performance degradation in OFDM systems. To efficiently overcome these drawbacks, we developed in [1] an adequate algorithm that maximizes the received Signal to Interference plus Noise Ratio (SINR) by optimizing systematically the OFDM waveforms at the Transmitter (TX) and Receiver (RX) sides. In this paper, we go further by investigating the performance evaluation of this algorithm. We start by testing its robustness against time and frequency synchronization errors. Then, as this algorithm banks on an iterative approach to find the optimal waveforms, we study the impact of the waveform initialization on its convergence. The obtained simulation results confirm the efficiency of this algorithm and its robustness compared to the conventional OFDM schemes, which makes it an appropriate good candidate for 5G systems. © 2014 EURASIP.

Ammar-Badri H.,COSIM Laboratory | Benazza-Benyahia A.,COSIM Laboratory
European Signal Processing Conference | Year: 2013

Blotches are artifacts that contaminate old films and cause the loss of some information in the film. Their detection is required prior to any restoration. The goal of this paper is to reduce the false alarm rate of the detection. By assuming that blotches correspond to local illumination variations between the degraded frame and its surrounding ones, the novelty of the approach we propose is threefold. Firstly, an appropriate photometric parametricmodel is adopted. Secondly, a motion analysis involving a robust adaptive cross-correlationmeasure is used to locally measure the illumination variation. Thirdly, the extension to color sequences is performed. Experimental evaluation shows the efficiency of the proposed preprocessing. © 2013 EURASIP.

Nasraoui L.,COSIM Laboratory | Atallah L.N.,COSIM Laboratory | Siala M.,University of Carthage
2013 9th International Wireless Communications and Mobile Computing Conference, IWCMC 2013 | Year: 2013

This paper applies a recently proposed efficient technique that has been conducted regarding timing synchronization in OFDM systems, to the IEEE 802.11a/g standards. The time synchronization is fulfilled using the structure specificity of the short training sequence of IEEE 802.11a/g preamble. Two versions of the applied technique are considered: a singlestage brute force approach, which carries differential correlation exclusively, and a two-stage reduced complexity approach comprising coarse and fine stages. The coarse synchronization is achieved using sliding correlation, characterized by its low computational load, whereas the fine synchronization is realized by differential correlation, characterized by its high computational load and carried around the coarse time estimate. In the two stage approach, the combined use of sliding correlation and differential correlation, carried for short interval, results in an overall reduced complexity approach. Simulation results show that, applied in the IEEE 802.11a/g norm, both of the considered approaches provide accurate time synchronization in the AWGN and multipath channels. Moreover, the two-stage version has a low computational load, which makes it suitable for fast symbol timing synchronization in bursty IEEE 802.11a/g OFDM systems. © 2013 IEEE.

Chaker A.,COSIM Laboratory | Kaaniche M.,University of Paris 13 | Benazza-Benyahia A.,COSIM Laboratory
EUVIP 2014 - 5th European Workshop on Visual Information Processing | Year: 2015

Ongoing developments in stereoscopic display technologies have led to the proliferation of huge stereo image databases. Therefore, the design of an appropriate Content Based Image Retrieval (CBIR) system for stereo images is an important emerging issue. In this paper, we propose a novel retrieval method which exploits simultaneously the spatial and cross-view dependencies of the stereo images. Within each subband, the joint distribution of the resulting wavelet coefficients of the two views located at the same spatial position as well as those of the neighboring pixels, is modeled by a multivariate statistical model based on Spherically Invariant Random Vectors (SIRV). The parameters of the SIRV model are selected as relevant signatures of the stereo pair. Experimental results show the benefits which can be drawn from the proposed retrieval approach. © 2014 IEEE.

Chaker A.,COSIM Laboratory | Kaaniche M.,University of Paris 13 | Benazza-Benyahia A.,COSIM Laboratory
2014 IEEE International Conference on Image Processing, ICIP 2014 | Year: 2014

The great interest of stereo images in several applications has led to the proliferation of huge and ever growing image databases. Therefore, there is an urgent demand for an effective Content Based Image Retrieval (CBIR) system devoted to stereo images. To meet such a demand, this paper proposes new wavelet-based retrieval approaches that exploit not only the visual contents of the Stereo Image (SI) pair but also its related disparity field. The first approach takes into account implicitly the disparity information by computing features from the disparity compensated left image and the right image. The second one aims at extracting relevant features directly from the left and right views, and the disparity map. Experimental results indicate that adding disparity information allows us to improve the retrieval performances of stereo images. © 2014 IEEE.

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