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Conference Paper

Fast Acquisition Unit for GPS-GALILEO Receivers in Space Environment

Authors: Calmettes Vincent, Dion Arnaud, Boutillon Emmanuel and Liegon Emmanuel

In Proc. Institute of Navigation - ION, San Diego, USA, January 28-30, 2008.

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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).

Signal and image processing / Localization and navigation and Space communication systems

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PhD Thesis

Contrôle d’Admission des Connexions pour les Systèmes de Télécommunication par Satellite avec des Liaisons Physiques Adaptatives

Author: Tra Ferdinand

Dedended in January 2008

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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.

Networking / Space communication systems

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Conference Paper

Improving Vehicles Positioning Using Wireless Telecommunication Media and GNSS Hybridization

Authors: Bonacci David and Paimblanc Philippe

In Proc. IEEE International Workshop on Intelligent Transportation, Hamburg, Germany, March 18-19, 2008.

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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.

Signal and image processing and Digital communications / Localization and navigation

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Reconfigurable GPS-Galileo Receiver for Satellite Based Applications

Authors: Dion Arnaud, Calmettes Vincent and Boutillon Emmanuel

In Proc. Institute Of Navigation, Global Navigation Satellite Systems Meeting (ION GNSS), Fort Worth, USA, September 27-28, 2007.

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.

Signal and image processing / Localization and navigation

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Lost Sample Recovering of ECG Signals in e-Health Applications

Authors: Prietro-Guerrero Alfonso, Mailhes Corinne and Castanié Francis

in Proc. IEEE Int. Conf. on Eng. Medicine Biol. Soc. (EMBC), Lyon, France, pp. 31-34, August 23-27, 2007.

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This paper shows the interest of an interpolation method based on parametric modeling to retrieve missing samples in ECG signals. This problem occurs more and more with the emergence of telemedicine applications. The different links (fixed access network (PSTN), mobile access network (GSM/GPRS and future UMTS) or satellite interfacing (DVB- RCS technology)) involved in e-health applications are liable to induce errors on the transmitted data. These errors/losses can occur anytime and anywhere (according to the channel availability, memory overflows, protocols, etc) during a transmission process. Therefore the recovering of missing samples for biomedical signals is of great interest. The method used in this paper is based on a left-sided and right-sided autoregressive model, i.e., the interpolation algorithm uses the samples before and after the sequence of missing samples. An objective measure is used to assess the method performance. Results show that this interpolation method represents a really suitable technique to ECG signal reconstruction in a possible corrupted transmission.

Signal and image processing / Space communication systems

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PhD Thesis

Techniques avancées de traitement du signal GPS pour les services LBS

Author: El Natour Hanna

Defended in July 2007

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In the past, in order for GPS (Global Positioning System) to work accurately, the presence of an unobstructed LOS (Line-Of-Sight) signal was necessary. Weak signals were not suitable for use because they may have large associated noise and other errors. The expansion of GPS to LBS (Location-Based Services) and other navigation applications all over the world, such as the E-911 and the E-112 mandates in the United States and Europe respectively, changed the paradigm. Consequently a dramatic increase in the need for more and more performant positioning techniques is expected, especially in urban and indoor environments. These rising localization requirements pose a particularly difficult challenge for GPS receivers design. The thesis objective is to evaluate and enhance existing GPS signal acquisition techniques for positioning goals in harsh environments, in the context of AGPS (Assisted GPS). The AGPS system assumes that the GPS receiver is connected to or introduced in a mobile phone. This allows for the transfer of AD (Assistance Data) to the GPS receiver via the GSM (Global System for Mobile communications) cellular network. Amongst others, the AD provides the GPS receiver with the list of visible satellites and estimates of their Dopplers and code delays, thus reducing the search window of these parameters. This work consists in exploring different GPS signal acquisition to reduce the acquisition time or TTFF (Time To First Fix), without affecting the receiver sensitivity. This is done after a prior study of the GPS radio channel. The study starts out with a revue of the GPS system and the GPS transmitted and received signal structure. The acquisition process is then described in details: the classical acquisition is first described in order to proceed afterwards with the impact of the propagation environment on this stage of the signal processing. For this purpose, harsh environments (urban and indoor) are modelled and analysed. This analysis enables to study the problems which encounter the radio frequency signal propagation through such environments. Note that the urban channel is studied using an existing statistical model developed by Alexander Steingass and Andreas Lehner at the DLR (German Aerospace Center) [Steingass et al., 2005]. On the other hand, an indoor channel model was developed by the ESA (European Space Agency) in the frame of a project entitled “Navigation signal measurement campaign for critical environments” and presented in [Pérez-Fontán et al, 2004]. But this model considers a time invariant statistical channel. Consequently, we developed an Indoor model which rather considers a time variant channel, by taking into account temporal variations of some channel parameters, like the transfer function delay and phase. The initial values are however based on the statistical distributions provided by the ESA model. The channels are analysed is terms of multipaths, cross-correlations and signal masking. The multipaths replicas are particularly disturbing in urban environments while the cross-correlations and masking effects are more disturbing in indoor environments. These phenomena may induce errors in the final solution calculated by the receiver. In order to avoid this error, one solution consists in increasing the signal observation duration in order to enhance the signal to noise ratio. But this generally implies longer acquisition time, thus affecting the receiver performance, commercially speaking. Indeed, the time requirements are as important as sensitivity requirements for GPS users. However, these two requirements are not generally compatible with each other. Consequently, an ideal solution consists in reducing the acquisition time without greatly affecting the receiver sensitivity. Accordingly, such advanced methods for acquisition signal processing are described next. Most of these methods aim at reducing the total acquisition time, rather than enhancing the receiver sensitivity. This means however that longer signal blocks can be processed (thus enhancing sensitivity) without affecting the global processing duration. At first, each of these methods is evaluated through the description of its advantages and drawbacks. A performance evaluation of these algorithms, using signals generated with a Spirent STR4500, ensues as a final step of this study.

Signal and image processing and Digital communications / Localization and navigation

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Journal Paper

Improving Subband Spectral Estimation Using Modified AR Model

Authors: Bonacci David and Mailhes Corinne

Signal Processing Elsevier, vol. 87, n° 5, pp. 937-949, May, 2007.

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It has already been shown that spectral estimation can be improved when applied to subband outputs of an adapted filterbank rather than to the original fullband signal. In the present paper, this procedure is applied jointly to a novel predictive autoregressive (AR) model. The model exploits time-shifting and is therefore referred to as time-shift AR (TSAR) model. Estimators are proposed for the unknown TS-AR parameters and the spectrum of the observed signal. The TS-AR model yields improved spectrum estimation by taking advantage of the correlation between subseries that arises after decimation. Simulation results on signals with continuous and line spectra that demonstrate the performance of the proposed method are provided.

Signal and image processing / Other

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Conference Paper

Signed Binary Digit Representation to Simplify 3D-EZW

Authors: Christophe Emmanuel, Duhamel Pierre and Mailhes Corinne

In Proc. IEEE Int. Conf. Acoust., Speech and Signal Processing (ICASSP), Honolulu, Hawaii, USA, April 18-23, 2007.

Zerotree based coders have shown a good ability to be successfully adapted to 3D image coding. This paper focuses on the adaptation of EZW for the compression of hyperspectral images with reduced complexity. The subordinate pass is removed so that the location of significant coefficients does not need to be kept in memory. To compensate the quality loss due to this removal, a signed binary digit representation is used to increase the efficiency of zerotrees. Contextual arithmetic coding with very limited contexts is also used. Finally, we show that this simplified version of 3D-EZW performs almost as well as the original one.

Signal and image processing / Space communication systems

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Journal Paper

Adaptation of Zero-Trees Using Signed Binary Digit Representations for 3D Image Coding

Authors: Christophe Emmanuel, Duhamel Pierre and Mailhes Corinne

EURASIP International Journal of Image and Video Processing, n° 054679, February, 2007 (open access).

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Zerotrees of wavelet coefficients have shown a good adaptability for the compression of three-dimensional images. EZW, the original algorithm using zerotree, shows good performance and was successfully adapted to 3D image compression. This paper focuses on the adaptation of EZW for the compression of hyperspectral images. The subordinate pass is suppressed to remove the necessity to keep the significant pixels in memory. To compensate the loss due to this removal, signed binary digit representations are used to increase the efficiency of zerotrees. Contextual arithmetic coding with very limited contexts is also used. Finally, we show that this simplified version of 3D-EZW performs almost as well as the original one.

Signal and image processing / Earth observation

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Conference Paper

Compliance of Single Frequency Ionospheric Delay Estimation and Cycle Slip Detection with Civil Aviation Requirements

Authors: Ouzeau Christophe, Macabiau Christophe, Roturier Benoît and Escher Anne-Christine

In Procc. National Technical Meeting of The Institute of Navigation, San Diego, USA, January 22-24, 2007

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Ionosphere is a dispersive medium that can strongly affect GPS and GALILEO signals. Ionospheric delay affecting the GPS and GALILEO single frequency pseudorange measurements is the largest source of ranging error. In addition, this perturbation is difficult to model and thus difficult to predict. Nominal dual frequency measurements provide a good estimation of ionospheric delay. In addition, the combination of GPS and GALILEO navigation signals at the receiver level is expected to provide important improvements for civil aviation. It could, potentially with augmentations, provide better accuracy and availability of ionospheric correction measurements. Indeed, GPS users will be able to combine GPS L1 and L5 frequencies, and future GALILEO signals will bring their contribution as some of them will be transmitted at the same frequencies as the GPS signals. However, if affected by radio frequency interference, a receiver can lose one or more frequencies leading to the use of only one frequency to estimate ionospheric code delay. Therefore, it is felt by the authors as an important task to investigate the performance of techniques trying to sustain multi-frequency performance when a multi-constellation receiver installed in an aircraft loses dual frequency capability, during critical phases of flight. After a loss of several frequencies leading to a single frequency degraded mode, a receiver can use code and carrier phase pseudoranges made on only one carrier frequency to estimate the ionospheric delay. To achieve this estimation, the receiver can use the difference between code and carrier phase measurements. Indeed, this quantity can be modelled as twice the ionospheric delay plus noise, multipath, and the carrier phase ambiguity. The ionospheric delay can then be extracted from this, provided the ambiguity is properly removed. This can be achieved after convergence of a Kalman Filter for example, but then cycle slips need to be monitored. The probability of a cycle slip to occur is low but not negligible for civil aviation purposes. Several causes of cycle slips may be identified. For instance multipath, dynamics, signal blockage and ionospheric scintillation may be sources of this type of rupture in carrier phase measurements. Cycle slips may have random magnitudes. Those ones have to be detected and corrected with a performance compliant with civil aviation requirements for integrity, continuity, accuracy and availability. This problem of cycle slip detection is a priority before analyzing the accuracy of the single frequency iono corrected pseudorange. We propose to follow the methodology exposed below to assess the performance of potential algorithms of detection (and estimation) of cycle slips. First, the cycle slip detection and correction ability will be defined by the smallest cycle slip detectable with a required probability of missed detection. This smallest detectable cycle slip implies a bias on position error depending on geometry. Therefore, availability of protection against cycle slips compatible with APV 1 and APV 2 for instance, depends on geometry and must be computed at every second. The main goal of this paper is to know exactly the impact of the capability of cycle slip detection algorithms on the availability of reliable single frequency iono corrected pseudoranges.

Signal and image processing / Aeronautical communication systems and Localization and navigation

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ICASSP 2020

Conference talk of Barbara Pilastre, TeSA PhD, at ICASSP 2020

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Activity Report

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Pau Closas, Northeastern Univ Boston, in TeSA

TeSA welcomes him with a research fellowship for July!