The Cross Ambiguity Function (CAF) is often used for passive geolocation of an emitter based on the time difference of arrival (TDOA) and frequency difference of arrival (FDOA) of the received signals. CAF performance has been thoroughly investigated in regards to traditional single-input single-output (SISO) signals. Little is known about how the CAF will respond to signals from multiple-input multiple-output (MIMO) systems which utilize multiple antennas. This thesis focuses on characterizing the CAF's magnitude distribution in order to determine the probability of correctly determining the correct TDOA/FDOA bin, and the resulting impact on geolocation. The received signals are studied in the presence of additive white Gaussian noise (AWGN) as well as multi-channel propagation effects such as phase ambiguities and offsets due to multi-antenna transmission. Two and four transmit antennas using either a form of spatial multiplexing or space-time block coding are the focus of this work because they are mostly commonly found in currently deployed communication systems. The effects of these transmit schemes are studied with respect to TDOA/FDOA error and the resulting position error. The analysis is performed using a detection theory framework as opposed to estimation theory in order to empha- size the impact of MIMO transmission on determining the correct TDOA/FDOA bin. A simple method using the CAF magnitude as a decision statistic is also presented so that TDOA/FDOA errors can be detected and filtered in an attempt to improve positioning estimates. / Master of Science

<p>The waveform of a radar signal affects the resolution in velocity and distance. The ambiguity function is used as an aid for analysing narrow band radar signals simultaneously in time and frequency. An analysing tool for wide band radar signals is missing.</p><p>This thesis describes a generalised ambiguity function to be utilised for study of wide band signals. Waveforms are further synthesised with help of the developed analysing tool. The aim is to start with a certain ambiguity function and find a waveform that reproduces the same ambiguity function.</p><p>Mathematical formulas are presented and implemented in Matlab to produce the wide band ambiguity function. Functions for developing waveforms by synthesis is also implemented.</p><p>It turns out that the Hermitian functions used as base functions do not preserve the orthogonality when implemented as wide band signals. The synthesis is not fully successful. Therefore an alternative method with numerical optimisation is used in an attempt to find an optimal waveform.</p>

The waveform of a radar signal affects the resolution in velocity and distance. The ambiguity function is used as an aid for analysing narrow band radar signals simultaneously in time and frequency. An analysing tool for wide band radar signals is missing. This thesis describes a generalised ambiguity function to be utilised for study of wide band signals. Waveforms are further synthesised with help of the developed analysing tool. The aim is to start with a certain ambiguity function and find a waveform that reproduces the same ambiguity function. Mathematical formulas are presented and implemented in Matlab to produce the wide band ambiguity function. Functions for developing waveforms by synthesis is also implemented. It turns out that the Hermitian functions used as base functions do not preserve the orthogonality when implemented as wide band signals. The synthesis is not fully successful. Therefore an alternative method with numerical optimisation is used in an attempt to find an optimal waveform.

Synthetic aperture radar (SAR) was originally designed as an airborne ground-imaging radar technology. But it has long been desired to also be able to use SAR imaging systems to detect, locate, and track moving ground targets, a process called Ground Moving Target Indication (GMTI). Unfortunately, due to the nature of how SAR works, it is inherently poorly suited to the task of GMTI. SAR only focuses targets and image features that remain stationary during the data collection. A moving ground target therefore does not focus in a conventional SAR image, which complicates the process of performing GMTI with SAR systems. This thesis investigates the feasibility of performing GMTI with single-channel, unsquinted, broadside stripmap SAR despite this inherent limitation. This study focuses solely on the idealized case of direct energy returns from point targets on flat ground, where they and the airborne radar platform all move rectilinearly with constant speed. First, the various aspects of how SAR works, the signal processing used to collect the SAR data, and the backprojection image formation algorithm are explained. The effects of target motion are described and illustrated in actual and simulated SAR images. It is shown how the backprojection (BPJ) algorithm, typically used to image a stationary landscape scene, can also focus on moving targets when the target motion is known a priori. A SAR BPJ ambiguity function is also derived and presented. Next, the time-changing geometry between the airborne radar and a ground target is mathematically analyzed, and it is shown that the slant range between the radar and any ground target, moving or stationary, is a hyperbolic function of time. It is then shown that this hyperbolic range history causes the single-channel SAR GMTI problem to be underdetermined. Finally, a method is then presented for resolving the underdetermined nature of the problem. This is done by constraining a target's GMTI solution using contextual information in the SAR image. Using constraining information, a theoretical way is presented to perform limited GMTI with a single-channel SAR system by using a modified form of the BPJ imaging algorithm, and practical considerations are addressed that complicate the process. Instead of focusing on stationary pixels, this GMTI method uses the BPJ ambiguity function to search for moving targets on a straight path, such as a road, by performing matched filtering on a collection of moving pixels in a position-velocity image space. Nevertheless, it is concluded that for moving point targets, general GMTI with no path constraints is infeasible in practice with a single-channel SAR.

Synthetic aperture radar (SAR) systems are versatile, high-resolution radar imagers useful for providing detailed intelligence, surveillance, and reconnaissance, especially when atmospheric conditions are non-ideal for optical imagers. However, moving targets in SAR images are smeared. Along-track interferometry is a commonly-used method for extracting the motion parameters of moving targets but requires a dual-aperture SAR system, which may be power- size- or cost-prohibitive. This thesis presents a method of estimating target motion parameters in single-channel SAR data given geometric target motion constraints. I test this method on both simulated and actual SAR data. This estimation method includes an initial estimate, computation of the SAR ambiguity function, and application of the target motion constraints to form a focused image of the moving target. The constraints are imposed by assuming that target motion is restricted to a road. Finally, I measure its performance by investigating the error introduced in the motion estimates using both simulated and actual data.

No description available.

L’étude traite de la détection de cibles mobiles dans un contexte de radar passif bistatique utilisant les émetteursde télévision numérique TNT (DVB-T) comme émetteurs d’opportunité. Outre leur présence généralisée sur leterritoire, l’intérêt de ces émissions réside dans leur relative largeur de bande permettant une bonne précisiond’estimation. Le principal inconvénient de ce type d’approche réside dans l’éblouissement par le signal en trajetdirect, des échos de très faible intensité des cibles d’intérêt. Après un rappel du principe du radar bistatique etde la norme OFDM utilisée par les signaux TNT, une première étude donne une construction originale du signalde référence dans le cas multi-capteurs : le signal de référence est construit par un traitement d’antenne de typeCAPON où le balayage des paramètres optimaux est remplacé par la connaissance de signaux pilotes inséré dansles symboles OFDM. Ensuite le rapport se focalise sur l’estimation d’un filtre de canal multitrajet à partir dela connaissance de la modulation OFDM utilisée. Ce filtre, d’abord étudié comme réjecteur de fouillis originalavant détection par la fonction d’ambiguïté, donne des résultats semblables aux méthodes classiques de réjectionde fouillis standard. Étendu à toutes les fréquences Doppler, son module au carré est utilisé comme un nouveaudétecteur présentant un très faible niveau de clutter, surpassant ainsi la fonction d’ambiguïté. Une interprétationen terme de traitement d’antennes du nouveau détecteur ouvre la voie à des variantes haute-résolution de celui-ci.La validité du nouveau détecteur est illustrée par des résultats sur données réelles. / The study focuses on moving target detection from passive bistatic radar with DVB-T transmitters used asopportunity transmitters. In addition to their widespread geographical coverage, they allow a good estimationaccuracy due to their quite large bandpass. Nevertheless the continuous powerful direct path masks the verylow intensity echoes of targets of interest. The passive bistatic radar principle and the CP-OFDM standardused by DVB-T are briefly reminded, then, a new first study of reference signal retrieving in multiple sensorsconfiguration is given : the reference signal is built using a Capon receptor where the parameters scan is replacedby the knowledge of pilot signals inserted in the OFDM symbols. Next, the report addresses the multipath channelestimate by using the OFDM signal structure. This channel is firstly studied for clutter rejection before detectionfrom the cross ambiguity function (CAF). We obtain similar results than those of the classical rejection methods.This channel is extended to the whole Doppler shift, and its squared modulus acts as a new low clutter detectorthat outperforms classical CAF. A virtual beamforming interpretation of the channel estimation opens a new pathtowards high resolution array processing. Results given on real data illustrate the validity of this new channeldetector (CHAD).

Continuous Wave (CW) radars are preferred for their low probability of intercept by the other receivers. Frequency modulation techniques, the linear frequency modulation (LFM) technique in particular, are commonly used in CW radars to resolve the range and the radial velocity of the detected targets. The conventional method for target detection in a linear FMCW radar makes use of a mixer followed by a low-pass filter whose output is Fourier transformed to get the range and velocity information. In this thesis, an alternative target detection technique based on the use of the Ambiguity Function (AF) will be investigated in frequency modulated CW radars. Results of the AF-based technique and the conventional Fourier-based technique will be compared for different target detection scenarios.

No description available.

The goal of this thesis study is to investigate the Ambiguity Function Technique for target detection in phase-coded continuous wave radar. Also, phase shift keying techniques are examined in detail. Continuous Wave (CW) Radars, which are also known as Low Probability of Intercept (LPI) radars, emit continuous signals in time which are modulated by either frequency modulation or phase modulation techniques. Modulation of the transmitted radar signal is needed to estimate both the range and the radial velocity of the detected targets. In this thesis, Phase Shift Keying (PSK) techniques such as the Barker codes, Frank codes, P1, P2, P3, P4 codes will be employed for radar signal modulation. The use of Ambiguity Function, which is a non-linear Time- Frequency Representation (TFR), for target detection will be investigated in phasecoded CW radars for different target scenarios.