Modified Cramér-Rao lower bound for TOA and symbol width estimation. An application to search and rescue signals

International audienceThis 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

Modified Cramér-Rao lower bound for TOA and symbol width estimation. An application to search and rescue signals

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

Performances de détection et de localisation des terminaux « SAR » dans le contexte de transition MEOSAR

Le système Cospas-Sarsat est un système de recherche et de sauvetage à l’échelle mondiale qui fonctionne à l’aide de satellites en orbite basse et de satellites en orbite géostationnaire. La constellation de satellites actuelle est en cours de remplacement par des satellites en orbite moyenne qui couvrent de plus grandes zones de la surface de la Terre permettant des alertes quasi instantanées. L’objectif de cette thèse est d’étudier les performances de localisation de ce nouveau système, qui a été nommé système MEOSAR (Medium Earth Orbit Search and Rescue). Nous étudions d’abord la qualité de la liaison entre la balise de détresse, le satellite, et la station de réception au sol à l’aide d’un bilan de liaison. Ensuite, nous proposons un modèle de signal basé sur des fonctions sigmoïdes afin de modéliser les transitions douces du signal de détresse. Pour ce modèle, les performances de localisation (en terme de bornes de Cramér-Rao et de la variance d’estimateurs) sont étudiées pour l’estimation de position de la balise, et pour l’estimation de différents paramètres, y compris le temps d’arrivée, la fréquence d’arrivée et la durée du symbole. Ensuite, nous étudions l’impact de l’ajout d’information a priori sur la période symbole et sur le temps de montée du signal, qui proviennent des tolérances autorisées sur les spécifications des balises de détresse. Nous étudions également l’erreur introduite par l’ajout de bruit de phase caractéristique des oscillateurs des balises, et nous considérons l’amélioration de l’estimation de position en prenant en compte les multiples émissions de la balise de détresse. Finalement, les performances de localisation du système MEOSAR sont données pour les balises de détresse de deuxième génération, qui sont en cours de développement, et qui utilisent une modulation avec étalement de spectre. ABSTRACT : Cospas-Sarsat is an international search and rescue system that operates using low-orbit satellites and geostationary satellites. The current satellite constellation is being replaced by medium Earth orbit satellites which will cover larger areas of the surface of the Earth, permitting almost instantaneous alerts. The objective of this thesis is to study the localization performance of this new system, named MEOSAR (Medium Earth Orbit Search and Rescue). We first study the quality of the link between the beacon, the satellite and the ground receiving station through a link budget. Then, we propose a signal model based on sigmoidal functions to model the smooth transitions of the distress signal. For this model, the localization performance (in terms of Cramér-Rao bounds and estimator variances) is studied for the estimation of the beacon position and for different parameters including the time of arrival, the frequency of arrival and the symbol width. Then, we study the impact of adding prior information on the symbol width and the signal rise time, which are constructed from the allowed tolerances on the beacon specifications. We also investigate the error introduced by the addition of oscillator phase noise, and we show how the position estimation can be improved by taking into account multiple emissions of the beacon. Finally, the localization performance of the MEOSAR system is studied for second generation beacons, which are being developed using spread spectrum modulation

Software Simulator and Signal Analysis for Galileo E5 band Signals

Galileo is the European Global Navigation Satellite System (GNSS) that aims at providing high availability, increased accuracy, and various location services under the civilian control. Four in-orbit validation satellites have already been launched till date and the system is estimated to be fully deployed by the year 2020. The Galileo navigation signals are transmitted at four frequency bands, which are named E5a, E5b, E6, and E1 bands. The signal of interest in this thesis is Galileo E5a band and Galileo E5b band signals. Signal acquisition and signal tracking are the main functions in a GNSS receiver. Acquisition identifies all the visible satellites and estimates the coarse values of carrier frequency and code phase estimates of the satellite signal. Tracking refines the coarse carrier frequency and code phase estimates, and keeps track of the satellite. The objective of this thesis has been to design and implement Galileo E5a and E5b signals receiver which can acquire all the visible E5a and E5b signals and which gives coarse estimate of carrier frequency and code phase. Such a receiver has been successfully designed in Matlab starting from the Matlab initial files provided by the Finnish Geodetic Institute (FGI) provided tool. In this thesis, two different software implementations are analyzed: 1) The acquisition and tracking of simulated Galileo E5a signals generated in the Matlab Simulink E1-E5 model; and 2) The acquisition of real-time Galileo E5b signals received from the satellite provided by Finnish Geodetic Institute (FGI), Masala, Finland. In the Simulink implementation, the whole E5 signal is generated and propagated through different channel profiles. The received signals are tested with acquisition and tracking and the results are compared for different channel profile and Carrier-to-Noise density ratio. Similarly, the real-time Galileo signals from four satellites now available on sky from the Galileo constellation were received and performed acquisition. In both implementations, a sharp triangular peak was observed at the rough frequency and code phase estimates, proving that the Galileo E5a/b signals can be indeed acquired correctly with the implemented simulator

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion