Current satellite architectures for delivering interactive IP services and broadband connectivity are based on the layered principles of the OSI reference model. There is no denying that the traditional research approach focusing on layer-specific problems faced by satellite architectures within the well-defined bounds of the layered model has been rather fruitful. Wireless-friendly adaptations of major protocols exist today, and state-of-the-art coding and modulation techniques have taken physical layers close to their theoretical performance limits. However, a number of critical issues such as end-to-end fulfillment of service-level agreements, seamless mobility or scalable support for reliable multicast have not yet found optimal solutions by means of independent layer tuning, due to the unique characteristics of satellite links. The modular approach blurs the dynamics of layers interaction with the wireless medium, hindering the overall system performance with redundancy, inefficient resource handling and suboptimal performances. Recent research has thus started to address these problems in a holistic way, by stressing the potential benefits of authorizing information exchanges across layers beyond the scope of the reference model. Multi-layers feedback and the resulting system adaptivity offer multiple possibilities for attuning the protocol stack as a whole, allowing for overall optimization and better integration of satellite links in the increasingly heterogeneous network environment. Cross-layer design has emerged as a promising research area in the satellite and wireless communications fields, characterized by a multi-disciplinary approach involving information theory, network protocol design, optimization techniques, stochastic modeling and advanced signal processing. Since recent crosslayer proposals have started tackling successfully some complex problems that layered architectures do not address properly, next-generation standards and protocols are starting to integrate crosslayer principles de facto. This thesis addresses the error control problem for satellite links from the perspective of cross-layer design. At the crossroads of QoS-related constraints, devices complexity and efficient spectrum use, error control is indeed a key aspect of wireless communications — particularly crucial in the satellite context — where cross-layer enhancements can play an important role. After a thorough introduction to cross-layer design, the first part of this work focuses specifically on the error control strategy of early DVB satellites, where redundancies between the channel decoder and the adaptation layers are set to light in order to propose a joint bandwidth-efficient error control policy. The focus then moves to second-generation DVB satellites and the definition of the novel, IPcentric and cross-layer friendly GSE encapsulation protocol, where results from the aforementioned study were successfully applied. Finally, a whole new cross-layer framework called HERACLES is introduced, offering efficient and overhead-free error correction capabilities for almost any layer of a protocol stack and being patented at the moment of writing these words. The results of the overall work show the strengths of an integrated approach to error control, and open the way for innovative cross-layer mechanisms to be deployed in next-generation communications networks.

In this paper, we introduce a new approach for the acquisition of weak GNSS signals. For the GPS L1 signal, we utilize the replication property of the C/A code within each data bit to introduce a block averaging pre-processing (BAP) approach for improving receiver robustness against undesired signals. A large number of weighted signal blocks is coherently accumulated and synchronously averaged to obtain a single block with improved signal power. We present several properties of the proposed GNSS signals enhancement technique and we analyze its robustness against noise and different classes of interferers. Thus, we develop a software defined acquisition procedure using the efficient FFT correlation approach. We propose two acquisition algorithms based on the BAP approach. The first scheme implements the parallel code phase search in finding the 2-D spectrum peak using circular cross-correlations. In the second scheme, we exploit the BAP for a fast acquisition performing the frequency estimation prior to the 1-D code-phase search.

In this paper, a way of improving the positioning performance of the GNSS system through hybridization with distances derived from GSM power measurements was proposed. The GNSS/GSM Fusion algorithm was an APF (Auxiliary Particle Filter) algorithm with UKF (Unscented Kalman Filter) proposal and Rao-Blackwellisation allowing tight hybridization of GPS and GSM measurements. Scenario 1 and 2 showed an improvement in terms of accuracy and availability thanks to the use of GSM received powers in addition to GPS pseudoranges in a realistic scenario. Several perspectives can be given: First, the automatic estimation of hyperparameters: PF algorithms can be used to perform joint estimation of some global parameters (as for instance observation and evolution noises variances). This would give the fusion algorithm a better adaptability to local situations. Finally, the use of “multiple models” formulation can be envisaged: ability of PF algorithms to select automatically the most adapted model among a bank of available evolution and observation models. This would allow the algorithm to deal better with multipath effects.

This paper deals with the detection of mechanical load faults in induction motors during speed transients. The detection strategy is based on stator current analysis. Mechanical load faults generally lead to load torque oscillations at specific frequencies related to the mechanical rotor speed. The torque oscillations produce a characteristic sinusoidal phase modulation of the stator current. Speed transients result in time-varying supply frequencies that prevent the use of classical, Fourier transform-based spectral estimation. This paper proposes the use of a time-frequency distribution, the Wigner Distribution, for stator current analysis. Fault indicators are extracted from the distribution for on-line condition monitoring. The proposed methods are implemented on a low-cost digital signal processor. Experimental results in a steady-state and during transients with load torque oscillations and load imbalance are presented.

For GNSS civil aviation applications, it is necessary to be able to guarantee the required level of performance specified by ICAO during a given phase of flight. The use of several GNSS components such as various signals, constellations or augmentation systems, sometimes redundant, helps monitoring the system robustness against several sources of perturbations like ionosphere or jammers for instance. In case of perturbation preventing one of the needed components to meet the phase of flight required performance, it is necessary to be able to switch to another available component in order to try to maintain if possible the level of performance in terms of continuity, integrity, availability and accuracy. But, to this end, future combined receivers must be capable of detecting the largest number of degradations that should lead to the loss of one GNSS component. Among the perturbations, one can note atmospheric disturbances, multipath, cycle slips, interferences. It is consequently necessary to identify and test degradation detection means that will enable if possible the receiver to maintain the level of performance requirement during an aircraft flight. Because of the interests in civil aviation and the restrictive requirements associated, it is interesting to focus on the degradation detection during LPV phases of flight. The interference is among the most feared events in civil aviation use of GNSS. Detection, estimation and removal remain an open issue and may affect pseudoranges measurements accuracy as well as integrity, continuity and even availability of those measurements. In literature, many different interference detection algorithms have been proposed at the front-end level of the receiver. For instance making chi-square tests at the ADC level, as in nominal conditions, the ADC bins distribution is Gaussian. Other non exhaustive means are to study the design of the receiver antenna or to make a spectral selectivity using filters. However, detection within tracking loops is not widely studied to our knowledge that is why it is an interesting investigation way that may complete other detection means, as proposed in [Bastide, 2001]. The goal of this paper is to estimate the performance of detection algorithm of Carrier Waves and Narrow Bands interferences. The main results are missed detection probability and the non-detected tracking error induced by interferences. Indeed, those types of interferences may affect powerful GPS L1 C/A or Galileo E1 code spectrum lines and may produce Misleading Information. It is consequently important to study the effects of such interferences on different spectrum lines and with different settings, varying the amplitude and for Narrow Bands, the bandwidth of this perturbation. The detection algorithms used are based on multi correlator receiver outputs to detect the I and Q correlation distortions due to interferences. The paper starts with the presentation of the detection technique. Performance analysis is then conducted taking into account required continuity during LPV phase of flight, to determine a threshold on the interference detection criteria (FFT of the correlator outputs). Interference missed detection probability is then estimated and finally the algorithm integrity performances are discussed. To comply with actual conditions, as the receiver is supposed onboard a flying aircraft, tests were conducted under multipath conditions modelled with the DLR Aeronautical Channel, taking into account the ground reflection and fuselage echoes during LPV. In addition, simulations were performed under all kinds of dynamics, complying with DO 229 d specifications and interim Galileo MOPS. The results indicate these techniques are good detection means under actual conditions, and do not require a too large number of calculations. The inclusion of the proposed algorithms before Receiver Autonomous Integrity Monitoring algorithms and combined integrity results are discussed. Further studies should provide results on the accuracy of interference estimation and repair algorithms.

In contrast with ground applications the GNSS constellations are not optimized for space applications. Moreover, the different types of mission, i.e. Low Earth Orbit (LEO), Medium Earth Orbit (MEO), Geosynchronous Earth Orbit (GEO), have all specific requirements. Our motivation is to define an «Ubiquitous GNSS receiver (UGNSS)», i.e. a single receiver able to cope with all types of mission. The analyze of the different types of mission shows that the UGNSS receiver should deal with both GPS and GALILEO signals as well as other future GNSS systems. It should also be able to have fast synchronization and robust tracking with extremely wide Doppler range(LEO mission)or be able to cope with very weak signals (GEO mission).In order to fulfill those requirements, we define the specifications of a reconfigurable decoder that allows to allocate the hardware resources to the type of processing required by the mission. In this paper we consider the algorithm which aims to acquire GNSS signals. This algorithm is based on two IP cores which perform a 8 points FFT and a 2048 points FFT. These two cores are configured to achieve GNSS signal acquisition in any space mission, by taking into account the signal structure (BPSK(1)or BOC(1,1))and the signal features(C/No ratio, Doppler span and Doppler rate).

In high frequency bands (Ka and above), multimedia satellite communication systems may suffer from deep fading caused by atmospheric phenomena. Unfortunately, those deep atmospheric losses can no longer be overcome by a static link margin. Fade Mitigation Techniques (FMT) are then used to counteract those fades by enabling link adaptation according to propagation conditions. Without sacrificing bit error rate, FMT provide high average spectral efficiency by transmitting at high speeds under favorable channels conditions and by reducing throughput as the channel degrades. This capacity variation causes some difficulties to define resource management mechanisms, in particular the Connection Admission Control (CAC). Indeed a CAC function, which only uses current capacity information, may lead to intolerable dropping of admitted connection, and thus breaches the QoS guarantees made upon connection acceptance. This thesis focuses, then, on CAC mechanisms suitable for satellite systems with varying capacity. In those kinds of systems, CAC functions should estimate the possible evolution of the capacity. Therefore connections will only be admitted if the CAC function supposes the required capacity to be available for a long period of time. This kind of CAC is called as adaptive CAC. This work deals with the variation of the capacity by analyzing the different climatic phenomena and their prediction. The current study made on attenuation spatio-temporal models and their prediction showed their unsuitability for an adaptive CAC function. In fact, either they act over a very short period of time, typically some seconds, or they are too complex to be used within the context of a real system. Therefore, a simplified approach is argued in this study. It consists in separating the configuration where the Gateway/NCC is facing atmospheric impairments from the one where some user terminals face directly rain cells. For the admission policy, one could use one of the two CAC defined in this document, according to the way the system capacity varies in comparison with the connections duration : an optimistic CAC and a pessimistic CAC. This latter supposes the variation of the channel quality to be faster than connections duration. Therefore, the system capacity, on which connection admission decisions are based, corresponds to the case when the deepest fades occur. The optimistic policy is defined in the favorable case when channel quality varies slowly w.r.t to connections duration. The system capacity is, then, supposed to remain constant during connections lifetime. Thus, connection admission decision is made upon the current system capacity and the actual transmission condition faced by any of the user terminals.

The aim of this paper was to propose a way of improving the positioning performance of the GPS system through hybridization with distance measurements derived from GSM power measurements. Both GPS and GSM measurements were generated using simulation models. The algorithm chosen to perform the hybridization is a particle filter. Simulations showed that while accuracy can only be slightly improved, a position solution can be obtained even when the GPS system is not available, thus considerably improving availability.

The trajectory of Space Vehicles (SVs) derives due to external perturbations, such as the variation in the gravitation fields (earth, moon and sun) or the solar pressure effect. The station keeping of SVs is the operation that keeps the satellites in a predefined window. This operation implies that the SV position is known. Actual positioning systems for SVs are mainly based on ground equipment, that means heavy infrastructures. Autonomous positioning and navigation systems using Global Navigation Satellite System (GNSS) can then represent a great reduction in platform design and operating costs. This paper presents the configurations for Low Earth Orbit (LEO) and Geosynchronous Earth Orbit (GEO) missions. These configurations have been modeled from real mission parameters with the help of a dedicated software.

Header Compression techniques are now widely used in wireless and satellite communications. The main drawback of these techniques is to weaken the transmission against bit error or packet losses. Indeed, a corrupted or missing header can lead to a non-decompression of consecutive packets and then to a disconnection until the reception of a non-compressed packet. The parameters of the header compression system should then be carefully determined. In this paper, we first review the main header compression protocols standardized for a unidirectional link. This analysis allows us to build a simple generic header compression model depending on few parameters characterizing a header compression protocol. The evaluation of this model in cases corresponding to particular applications allows us to draw some first lessons for the use of header compression in Satellite communications.