Le système d’identification automatique (AIS) est un système permettant aux navires de s’échanger certaines informations, dont leur position, par radio. L’objectif du travail réalisé est de permettre la réception des messages AIS par un satellite en orbite basse sans modifier le matériel existant équipant les navires. Il sera ainsi possible de connaître la position de tous les navires à travers le monde. Plusieurs services sont possibles, comme le contrôle maritime ou, pour les armateurs, la connaissance permanente de la position de leurs bateaux. Ce séminaire présentera le correcteur d’erreurs élaboré afin de s’affranchir du niveau élevé de bruit et les méthodes permettant de prendre en compte les propriétés des signaux AIS.

Communication satellites emerge as an attractive solution in providing broadband connectivity to a variety of users thanks to its inherent global coverage. The broadcast nature of satellites (with higher frequency bands Ku/Ka) makes them the natural choice for multicasting services, for interconnecting geographically high-speed networks, and for providing multimedia services. However, this higher frequency band imposes challenging channel conditions. To avoid such problem, upcoming broadband satellite networks have adopted the adaptive coding and modulation at the physical layer. This is the main driver of this thesis due to the crucial fact that such adaptivity makes traditional satellite system design totally inefficient. In this thesis, we focus on a different paradigm to address such new challenges, based on a joint optimization across layers of the protocol stack. The fundamental idea behind this concept is the fact that adaptivity at the physical layer should be followed at upper layers in order to achieve efficient management of the system resources, and in order to comply with the stringent QoS of new applications services. We cover several aspects related to the networking optimization; allocating resources efficiently, maximizing the throughput and assuring fairness among all the users, according to channel condition. Our efforts have been also focused on choosing the best methodology in terms of selecting; efficient mathematical tools, most suitable architecture, novel adaptive technologies at higher layers, the best approach to the cross-layer design, and truly available standardized tools.

Increasing the coherent integration for acquisition of weak GNSS signals in urban and indoor environments is limited by several challenges. Besides of the possible sign reversal of the navigation data bit every 20ms, Doppler shift increases with the integration time. Inaccurate estimate of this offset may severely reduce the correlation power and prevent the receiver from detecting the presence of low-power signals. Standard acquisition approaches are not efficient for performing long coherent integrations. Furthermore, they achieve their limitations in high dynamics, where the signal frequency cannot be considered constant over the entire period of observation. In this paper, Frequency Offset Correction (FOC) loops are explored to compensate for the Doppler shift during the correlation process, thus enhancing stand-alone receivers’ sensitivity. The estimated frequency offset during the previous coherent integrations is used in a feedback scheme for self-aiding to extend the coherent integration time. We propose a new FOC loop architecture for compensating the frequency of each sample of the input signal. State of the art frequency compensation methods correct for the frequency drift on the post-correlation output for fine acquisition. At this stage, the correlation loss is already large enough to prevent the gain from accumulating longer signal.

Coastal altimetric waveforms may be corrupted by peaks. A simple parametric model was recently introduced to model peaky altimetric waveforms. This model assumes that the received altimetric waveform is the sum of a Brown echo and a Gaussian peak. This model has provided interesting results for symmetric peaks affecting altimetric signals. However, it is not appropriate for altimetric signals corrupted by asymmetric peaks. This paper introduces a Brown with asymmetric Gaussian peak model for altimetric waveforms. The parameters of this model are estimated by a maximum likelihood estimator. The performance of the proposed model and the resulting estimation strategy are evaluated via simulations conducted on synthetic and real data.

The delineation of P and T waves is important for the medical interpretation of ECG signals. We propose a Bayesian algorithm for simultaneous detection, delineation, and estimation of P and T waves. A block Gibbs sampler exploits the strong local dependencies in ECG signals by imposing block constraints on the P and T wave locations. The proposed algorithm is evaluated on the annotated QT database and compared with two classical algorithms.

In this paper, SAR processing algorithms for automotive applications are presented and illustrated on data from non-trivial test scenes. The chosen application is parking lot detection. Laboratory results obtained with a teaching sonar experiment emphasize the resolution improvement introduced with range-Doppler SAR processing. A similar improvement is then confirmed through full scale measurements performed with an automotive radar prototype operating at 77GHz in very close range conditions, typical of parking lot detection. The collected data allows a performance comparison between different SAR processing algorithms for realistic targets.

This paper introduces a new error correction strategy using cyclic redundancy checks (CRC) for a trellis coded system in the presence of bit stuffing. The proposed receiver is designed to simultaneously demodulate, decode and correct the received message in the presence of bit stuffing. It is based on a Viterbi algorithm exploiting the conditional transitions of an appropriate extended trellis. The receiver is evaluated with automatic identification system (AIS) messages constructed with a 16 bit CRC and a Gaussian Minimum Shift Keying (GMSK) modulation. The stuffed bits are inserted after any sequence of five consecutive bits 1 as requested by the AIS recommendation. Simulation results illustrate the algorithm performance in terms of packet error rate. A gain of more than 2,5 dB is obtained when compared to the conventional GMSK receiver.

The problem of detecting T-wave alternans (TWA) in ECG signals has received considerable attention in the biomedical community. This paper introduces a Bayesian model for the T waves contained in ECG signals. A block Gibbs sampler was recently studied to estimate the parameters of this Bayesian model (including wave locations, amplitudes and shapes). This paper shows that the samples generated by this Gibbs sampler can be used efficiently for TWA detection via different statistical tests constructed from odd and even T-wave amplitude samples. The proposed algorithm is evaluated on real ECG signals subjected to synthetic TWA and compared with two classical algorithms.

Space Wire is a wormhole network standard scheduled to be used as the sole on-board network for future satellites by the ESA. As the network will be shared by real-time and non real-time traffic, network designers require a tool to check that temporal constraints are verified for all the urgent messages. Previously, we proposed a model for a best-effort worm-hole network based on Network Calculus theory. This model is based on new network element that we call the Wormhole Section. Here, we show how to combine Wormhole Section elements to compute the end-to-end service curve offered to a flow and illustrate its use on a industrial case study.