International Telemetering Conference Proceedings / October 13-16, 1986 / Riviera Hotel, Las Vegas, Nevada / Predetection recording of spread-spectrum (SS) signals such as GPS transmissions is a desirable objective for both users and developers of equipment designed to receive such signals. (GPS user-equipment development is a lengthy process during which signal simulators are only partially useful.) Upon playback, GPS signals are used by the same or modified receivers so that acquisition, processing, detection and tracking loops can be altered to optimize the receiver parameters. Development of predetect SS signal recording systems is difficult to achieve in practice. Such systems not only must be of suitable phase linearity to preserve the signal content to be extracted but sometimes must also preserve the exact signal-to-noise ratio (SNR) characteristics of the recorded signals. Existing conventional test equipment is unsuitable for deriving value judgments of the quality of a predetect recording system’s output because the SS signal has a negative SNR. This paper reveals that it is possible to use, for this purpose, tape recorders now available on many test ranges in combination with auxiliary equipment similar to that designed for the U.S. Navy’s TRIDENT Program (recording C/A-code data from in-flight missile translators). The basic techniques are described in some detail to enable potential users to understand the necessary equipment concepts and evaluate the author’s approach in terms of their own applications.

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Le but de cette thèse est l'étude et la mise en oeuvre d'un système de localisation sous-marine compact et simple à mettre en place pour une utilisation en zones portuaires, côtières et environnements peu profonds. Nous proposons un système SBL (Small Distance Baseline) avec un nombre réduit de transducteurs (une balise d'émission et deux hydrophones). La configuration géométrique du système étant contraignante (hydrophones proches) la précision du positionnement obtenue par les méthodes classiques est faible. Nous proposons une nouvelle méthode de localisation améliorant la précision. La balise à localiser émet un signal à étalement de spectre. La différence de distance entre les trajets des signaux des hydrophones est mesurée par corrélation. Nous proposons deux boucles de poursuites pour l'estimation conjointe de la fréquence Doppler et du délai entre les signaux reçus. Ces techniques de poursuite basées sur un filtre de Kalman sont implémentées en boucle fermée et ouverte. Les observations TDOA (Time Difference Of Arrival) conduisent à utiliser une technique de localisation hyperbolique. Nous proposons une représentation statistique qui exploite la géométrie de notre système de mesure pour déterminer une zone de localisation probable autour de chaque hyperbole. En utilisant des positions de bateau successives, on construit une densité de probabilité dont le maximum définit la position de la balise. On montre sur données synthétiquesque pour un bruit de mesure réaliste, il est possible de déterminer la position de la balise avec une précision submétrique. Les expérimentations réelles confirment la faisabilité du système et la précision obtenue est dans ce cas métrique. / The purpose of that thesis work is the research and implementation of a compact and simple underwater localization system that aim to be used in ports, coastal areas and other low-depth environments. Our system is SBL (Small Distance Baseline), with a small number of transceivers (only one emitter and two hydrophones). Due to the system's geometric configuration not being optimal (both hydrophones are close to one another), the precision obtained using classical approaches is poor. We therefore propose a new localization approach that will improve it. The emitter we wish to localize emit a spread spectrum signal. The time difference of arrival (TDOA) between the two hydrophones is then determined using correlations methods. We propose in our work two tracking loops that will estimate both the delay and the doppler frequency between the signals. Using a Kalman filter , those methods are implemented respectively in open and close loop. From each TDOA measurement, we can calculatea hyperbolic area of possible emitter location. We thus use a statistical model which takes into account the local geometry of our measurements system in order to create a probable localization area around each hyperbole. By using the measurements at several different boat positions, we create a probability density whose maximum will be centered around the emitter's position. We show that, on simulated data, it is possible to localize the beacon with a precision beneath a meter with a realistic noise level. Experimental work and real data collection confirm that the method can in that context achieve the same result with a precision of a few meters.

This thesis deals with a method of spectrum-spreading of the data signals transmitted in the radio channel. There exist three different ways of spreading application, they uses pseudorandom sequences and also orthogonal sequences. In these systems we can find various kinds of modulations, one of them (Quadrature Phase Shift Keying) is shown at the end of the thesis. Spectrum spreading orthogonal multiplex OFDM is based on this method. The thesis wants to present the principle of the spectrum spreading method and the description of systems, transmitters and receivers that are using this method.