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Article de conférence

Carreau : CARrier REsource Access for mUle, DTN Applied to Hybrid WSN / Satellite System

Auteurs : Raveneau Patrice, Chaput Emmanuel, Dhaou Riadh, Beylot André-Luc, Dubois Emmanuel et Gélard Patrick

In Proc. IEEE Vehicular Technology Conference (VTC 2013), Las Vegas, USA, September 2-5, 2013.

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Both WSNs (Wireless Sensor Networks) and observation satellites are able to get measurements from a geographic area. To interconnect these technologies, we propose to use a store-carry-and-forward architecture relying on the DTN (Disruption and Delay Tolerant Networking) Bundle Protocol. This architecture aims at being generic, so it is application-agnostic and suits a wide range of scenarios. WSN may collect sporadically large data volume while terrestrial stations communicating with Low Earth Orbit (LEO) satellites have to endure long link disruptions when the satellite is not in the line of sight. These sporadic growths within the WSN coupled with the large latency on satellite links require to schedule data to provide quality of service to several flows. We propose a scheduling policy based on deadline of Bundles and compare it with classical DTN solutions.

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Réseaux / Systèmes spatiaux de communication

Borne de Cramér-Rao modifiée pour le temps d’arrivée et la période symbole. Application aux signaux de recherche et de sauvetage.

Auteurs : Bissoli Nicolau Victor, Coulon Martial, Gregoire Yoan, Calmettes Thibaud et Tourneret Jean-Yves

In Proc. Groupement de Recherche en Traitement du Signal et des Images (GRETSI), September 3-6, 2013.

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This paper focuses on the performance of time of arrival estimators for distress beacon signals which are defined by pulses with smooth transitions. These signals are used in the satellite-based search and rescue Cospas-Sarsat system. We propose a signal model based on sigmoidal functions. Closed-form expressions for the modified Cramér-Rao bounds associated with the parameters of this model are derived. The obtained expressions are easy to interpret since they analytically depend on the system parameters. Simulations conducted on realistic search and rescue signals show good agreement with the theoretical results.

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Traitement du signal et des images / Localisation et navigation

Article de journal

Adaptive Processing with Signal Contaminated Training Samples

Auteurs : Besson Olivier et Bidon Stéphanie

IEEE Transactions on Signal Processing, vol. 61, pp. 4318-4329, August, 2013.

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We consider the adaptive beamforming or adaptive detection problem in the case of signal contaminated training samples, i.e., when the latter may contain a signal-like component. Since this results in a significant degradation of the signal to interference and noise ratio at the output of the adaptive filter, we investigate a scheme to jointly detect the contaminated samples and subsequently take this information into account for estimation of the disturbance covariance matrix. Towards this end, a Bayesian model is proposed, parameterized by binary variables indicating the presence/absence of signal-like components in the training samples. These variables, together with the signal amplitudes and the disturbance covariance matrix are jointly estimated using a minimum mean-square error (MMSE) approach. Two strategies are proposed to implement the MMSE estimator. First, a stochastic Markov Chain Monte Carlo method is presented based on Gibbs sampling. Then a computationally more efficient scheme based on variational Bayesian analysis is proposed. Numerical simulations attest to the improvement achieved by this method compared to conventional methods such as diagonal loading. A successful application to real radar data is also presented.

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Traitement du signal et des images / Systèmes spatiaux de communication

Robust Adaptive Beamforming Using a Bayesian Steering Vector Error Model

Auteurs : Besson Olivier et Bidon Stéphanie

Signal Processing, vol. 93, pp. 3290-3299, August, 2013.

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We propose a Bayesian approach to robust adaptive beamforming which entails considering the steering vector of interest as a random variable with some prior distribution. The latter can be tuned in a simple way to reflect how far is the actual steering vector from its presumed value. Two different priors are proposed, namely a Bingham prior distribution and a distribution that directly reveals and depends upon the angle between the true and presumed steering vector. Accordingly, a non-informative prior is assigned to the interference plus noise covariance matrix R, which can be viewed as a means to introduce diagonal loading in a Bayesian framework. The minimum mean square distance estimate of the steering vector as well as the minimum mean square error estimate of R are derived and implemented using a Gibbs sampling strategy. Numerical simulations show that the new beamformers possess a very good rate of convergence even in the presence of steering vector errors.

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Traitement du signal et des images / Systèmes spatiaux de communication

CRC-Based Detection Algorithms for AIS Signals Received by Satellite

Auteurs : Prévost Raoul, Coulon Martial, Bonacci David, Le Maitre Julia, Millerioux Jean-Pierre et Tourneret Jean-Yves

Int. J. Satell. Commun. Network., vol. 31, no. 4, pp. 157-176, July/August, 2013.

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This paper addresses the problem of demodulating signals transmitted in the automatic identification system. The main characteristics of such signals consist of two points: (i) they are modulated using a trellis-coded modulation, more precisely a Gaussian minimum shift keying modulation; and (ii) they are submitted to a bit stuffing procedure, which makes more difficult the detection of the transmitted information bits. This paper presents several demodulation algorithms developed in different contexts: mono-user and multi-user transmissions, and known/unknown phase shift. The proposed receiver uses the cyclic redundancy check (CRC) present in the automatic identification system signals for error correction and not for error detection only. By using this CRC, a particular Viterbi algorithm, on the basis of a so-called extended trellis, is developed. This trellis is defined by extended states composed of a trellis code state and a CRC state. Moreover, specific conditional transitions are defined to take into account the possible presence of stuffing bits. The algorithms proposed in the multi-user scenario present a small increase of computation complexity with respect to the mono-user algorithms. Some performance results are presented for several scenarios in the context of the automatic identification system and compared with those of existing techniques developed in similar scenarios.

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Communications numériques / Systèmes spatiaux de communication

Exact Symbol Error Probability of Hybrid/Integrated Satellite-Terrestrial Cooperative Network Outage

Auteurs : Sreng Sokchenda, Escrig Benoît et Boucheret Marie-Laure

IEEE Transactions on Wireless Communications, vol. 2, pp. 1310-1319, July, 2013.

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Communications numériques / Systèmes spatiaux de communication

A Paradox about the Analytic Signal of Laser Beams

Auteur : Lacaze Bernard

Open Optics Journal, vol. 7, n° 1, p. 1, January, 2013.

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In the signal theory framework the "analytic signal” is a particular polar representation of a signal f (t). It defines an envelope (a modulus) and a phase (an argument) and these parameters are basic in communications. In this paper, we show that amplitude demodulations generally change envelopes and reduced phases. Consequently we show that recent results in laser communications about these parameters are erroneous.

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Traitement du signal et des images / Autre

Masses of Negative Multinomial Distributions: Application to Polarimetric Image Processing

Auteurs : Chatelain Florent, Bernardoff Philippe et Tourneret Jean-Yves

Journal of Probability and Statistics, Hindawi Publishing Corporation, vol. 2013, 2013.

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This paper derives new closed-form expressions for the masses of negative multinomial distributions. These masses can be maximized to determine the maximum likelihood estimator of its unknown parameters. An application to polarimetric image processing is investigated. We study the maximum likelihood estimators of the polarization degree of polarimetric images using different combinations of images.

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Traitement du signal et des images / Observation de la Terre

Article de conférence

On the Impact of Link Layer Retransmissions on TCP for Aeronautical Communications

Auteurs : Kuhn Nicolas, Van Wambeke Nicolas , Gineste Mathieu, Gadat Benjamin, Lochin Emmanuel et Lacan Jérôme

In Proc. 5th International Conference on Personal Satellite Services (PSATS), Toulouse, France, June 27-28, 2013.

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In this article, we evaluate the impact of link layer retransmissions on the performance of TCP in the context of aeronautical communications.We present the architecture of aeronautical networks, which is manly driven by an important channel access delay, and the various retransmission strategies that can be implemented at both link and transport layers. We consider a worst case scenario to illustrate the benefits provided by the ARQ scheme at the link layer in terms of transmission delay.We evaluate the trade-off between allowing a fast data transmission and a low usage of satellite capacity by adjusting link layer parameters.

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Réseaux / Systèmes de communication aéronautiques

Physical Channel Access (PCA): Time and Frequency Access Methods Simulation in NS-2

Auteurs : Kuhn Nicolas, Mehani Olivier, Bui Huyen-Chi, Lacan Jérôme, Radzik José et Lochin Emmanuel

In Proc. 5th International Conference on Personal Satellite Services (PSATS), Toulouse, France, June 27-28, 2013.

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We present an NS-2 module, Physical Channel Access (PCA), to simulate different access methods on a link shared with Multi-Frequency Time Division Multiple Access (MF-TDMA). This technique is widely used in various network technologies, such as satellite communication. In this context, different access methods at the gateway induce different queuing delays and available capacities, which strongly impact transport layer performance. Depending on QoS requirements, design of new congestion and ow control mechanisms and/or access methods requires evaluation through simulations. PCA module emulates the delays that packets will experience using the shared link, based on descriptive parameters of lower layers characteristics. Though PCA has been developed with DVB-RCS2 considerations in mind (for which we present a use case), other MF-TDMA-based applications can easily be simulated by adapting input parameters. Moreover, the presented implementation details highlight the main methods that might need modifications to implement more specific functionality or emulate other similar access methods (e.g., OFDMA).

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Réseaux / Systèmes spatiaux de communication

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