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Tunis, Tunisia

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. Source

Barbouchi M.,National Agronomic Institute of Tunisia INAT | Barbouchi M.,COSIM Laboratory | Abdelfattah R.,COSIM Laboratory | Abdelfattah R.,Telecom Bretagne | And 4 more authors.
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing | Year: 2015

The phenomenon of soil salinization in semi-arid regions is getting amplified and accentuated by both anthropogenic practices and climate change. Land salinization mapping and monitoring using conventional strategies are insufficient and difficult. Our work aims to study the potential of synthetic aperture radar (SAR) for mapping and monitoring of the spatio-temporal dynamics of soil salinity using interferometry. Our contribution in this paper consists of a statistical relationship that we establish between field salinity measurement and InSAR coherence based on an empirical analysis. For experimental validation, two sites were selected: 1) the region of Mahdia (central Tunisia) and 2) the plain of Tadla (central Morocco). Both sites underwent three ground campaigns simultaneously with three Radarsat-2 SAR image acquisitions. The results show that it is possible to estimate the temporal change in soil electrical conductivity (EC) from SAR images through the InSAR technique. It has been shown that the radar signal is more sensitive to soil salinity in HH polarization using a small incidence angle. However, for the HV polarization, a large angle of incidence is more suitable. This is, under considering the minimal influence of roughness and moisture surfaces, for a given InSAR coherence. © 2008-2012 IEEE. Source

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. Source

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. Source

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. Source

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