Space-time Adaptive Processing (STAP) is a two-dimensional filtering technique for antenna array with multiple spatial channels. The name "space-time" describes the coupling of these spatial channels with pulse-Doppler waveforms. Applications for STAP includes ground moving target indicator (GMTI) for airborne radar systems. Today, there are strong interests to develop STAP algorithms for operations in “sample starved” environments, where intense environmental interference can reduce STAP capacity to detect and track ground targets. Careful applications of STAP can effectively overcome these conditions by suppressing these interferences and maximize the signal to interference plus noise ratio (SINR). The Multi-stage Wiener filter (MWF) and principal component signal dependent (PC-SD) algorithm are two such methods that can suppress these interference through truncation of the signal subspace. This thesis makes contribution in several ways. First it details the importance of rank compression and sample compression for effective STAP operations in “sample starved” environments. Second, it shows how MWF and PC-SD could operate in this type of environment. Third it details how a “soft stop” technique like diagonal loading (DL) could improve STAP performance in target detection for MWF and PC-SD. Fourth, this thesis contrasts the performance of several existing “hard stop” techniques in rank compression and introduces a new one using a-priori knowledge.

As the size of an adaptive antenna array grows, the system is able to resist interference signals of increasing bandwidth. This is a result of the transmit pattern gain increasing, which raises the target's return power, and a greater number of degrees of freedom. However, once the interference signal decorrelates completely from one channel to the next, increasing array size will cease to improve detection capability. The use of tapped delay-line processing to improve correlation between channels has been studied for smaller arrays with single element antennas, but previous analyses have not considereded larger systems that are partitioned into subarrays. This thesis quantifies the effect that subarrays have on performance, as measured by the interference bandwidth that can be handled, and explains how tapped delay-line processing can maintain the ability to detect targets in an environment with high bandwidth interference. The analysis begins by deriving equations to estimate the half-power bandwidth of an array with no taps. Then we find that a single delay with optimal spacing is sufficient to completely restore performance if the interference angle is known exactly. However, in practice, the tap spacing will never be optimal because this angle will not be known exactly, so further consideration is given to this non-ideal case and possible solutions for arbitrary interference scenarios are presented. Simulations indicate that systems with multiple taps have more tolerance to increasing interference bandwidth and unknown directions of arrival. Finally, the tradeoffs between ideal and practical configurations are explained and suggestions are given for the design of real-world systems.

With the developing radar technology, radars have been started to be used in the airborne platforms due to the need of fast, accurate and reliable information about the enemies. The most important and tactically needed information is the movements in an observation area. The detection of a ground moving target buried in a dense clutter environment from a moving air platform is a very challenging problem even today. The geometry of the operation, the course of the flight and structure of the clutter are the most effective parameters of this problem. There are some &ldquo / Ground Moving Target Indication&rdquo / (GMTI) techniques that have been studied for the last twenty years to overcome this problem. In this thesis, the simulation of some of these techniques in a realistic environment and the comparison of their performances are discussed. In this work, a GMTI simulator is developed to generate the environment containing the clutter and the noise signals, to locate and simulate the targets in this environment and to apply the GMTI techniques on the raw data generated by the simulator. The generation of the clutter signals including the internal clutter motion (ICM) for different types of clutter distributions is one of the most important parts of this thesis. The GMTI techniques being investigated throughout this thesis are &ldquo / Displaced Phase Center Antenna&rdquo / (DPCA), &ldquo / Along-Track Interferometry&rdquo / (ATI), &ldquo / Adaptive DPCA&rdquo / , &ldquo / Pre-Doppler Sigma-Delta STAP&rdquo / and &ldquo / Post-Doppler Sigma-Delta STAP&rdquo / techniques. These techniques are compared according to their clutter suppression and target detection performances under different environmental conditions.

Ground Moving Target Indicator (GMTI) is a well-known and widely used signal processing method in airborne and spaceborne radars. In airborne radar and GMTI literature, many radar designs and signal processing techniques have been developed to increase the detection and estimation performance under heavy interference conditions. The motion of the aircraft on which the radar is mounted, high altitudes and ranges, targets with low radar cross sections and slowly moving targets complicates the problem of localization and observation of moving targets on a huge area of interest. In order to overcome these problems, engineers developed more complex radar hardwares with many receiver channels and signal processing algorithms. Multi-channel receivers provide adaptive digital beam-forming and adaptive Doppler processing capabilities. However, designing a cost efficient and light multi-channel receiver and a signal processing unit, which can handle a huge amount of received data from multi channels, is a difficult task to accomplish. Therefore, this thesis aims to propose non-adaptive antenna beams to reduce the number of channels to two in GMTI processing. This reduction yields a simplification both in receiver structure and signal processing unit. The measure of excellence of these propositions will be the ability to detect slowly moving targets with nearly optimum performance.

Une des finalités du traitement d’antenne est la détection et la localisation de cibles en milieu bruité. Dans la plupart des cas pratiques, comme par exemple le RADAR ou le SONAR actif, il faut estimer dans un premier temps les propriétés statistiques du bruit, et plus précisément sa matrice de covariance ; on dispose à cette fin de données secondaires supposées identiquement distribuées. Dans ce contexte, les hypothèses suivantes sont généralement formulées : bruit gaussien, données secondaires ne contenant que du bruit, et bien sûr matériels fonctionnant parfaitement. Il est toutefois connu aujourd’hui que le bruit en RADAR est de nature impulsive et que l’hypothèse Gaussienne est parfois mal adaptée. C’est pourquoi, depuis quelques années, le bruit et en particulier le fouillis de sol est modélisé par des processus elliptiques, et principalement des Spherically Invariant Random Vectors (SIRV). Dans ce nouveau cadre, la Sample Covariance Matrix (SCM) estimant classiquement la matrice de covariance du bruit entraîne des pertes de performances très importantes des détecteurs / estimateurs. Dans ce contexte non-gaussien, d’autres estimateurs de la matrice de covariance mieux adaptés à cette statistique du bruit ont été développés : la Matrice du Point Fixe (MPF) et les M-estimateurs.Parallèlement, dans un cadre où le bruit se décompose sous la forme d’une somme d’un fouillis rang faible et d’un bruit blanc, la matrice de covariance totale est structurée sous la forme rang faible plus identité. Cette information peut être utilisée dans le processus d'estimation afin de réduire le nombre de données nécessaires. De plus, il aussi est possible d'utiliser le projecteur orthogonal au sous espace fouillis à la place de la matrice de covariance ce qui nécessite moins de données secondaires et d’être aussi plus robuste aux données aberrantes. On calcule classiquement ce projecteur à partir d'un estimateur de la matrice de covariance. Néanmoins l'état de l'art ne présente pas d'estimateurs à la fois être robustes aux distributions hétérogènes, et rendant compte de la structure rang faible des données. C'est pourquoi ces travaux se focalisent sur le développement de nouveaux estimateurs (de covariance et de sous espace), directement adaptés au contexte considéré. Les contributions de cette thèse s'orientent donc autour de trois axes :- Nous présenterons tout d'abord un modèle statistique précis : celui de sources hétérogènes ayant une covariance rang faible noyées dans un bruit blanc gaussien. Ce modèle et est, par exemple, fortement justifié pour des applications de type radar. Il à cependant peu été étudié pour la problématique d'estimation de matrice de covariance. Nous dériverons donc l'expression du maximum de vraisemblance de la matrice de covariance pour ce contexte. Cette expression n'étant pas une forme close, nous développerons différents algorithmes pour tenter de l'atteindre efficacement.- Nous développons de nouveaux estimateurs directs de projecteur sur le sous espace fouillis, ne nécessitant pas un estimé de la matrice de covariance intermédiaire, adaptés au contexte considéré.- Nous étudierons les performances des estimateurs proposés et de l'état de l'art sur une application de Space Time Adaptative Processing (STAP) pour radar aéroporté, au travers de simulations et de données réelles. / One purpose of array processing is the detection and location of a target in a noisy environment. In most cases (as RADAR or active SONAR), statistical properties of the noise, especially its covariance matrix, have to be estimated using i.i.d. samples. Within this context, several hypotheses are usually made: Gaussian distribution, training data containing only noise, perfect hardware. Nevertheless, it is well known that a Gaussian distribution doesn’t provide a good empirical fit to RADAR clutter data. That’s why noise is now modeled by elliptical process, mainly Spherically Invariant Random Vectors (SIRV). In this new context, the use of the SCM (Sample Covariance Matrix), a classical estimate of the covariance matrix, leads to a loss of performances of detectors/estimators. More efficient estimators have been developed, such as the Fixed Point Estimator and M-estimators.If the noise is modeled as a low-rank clutter plus white Gaussian noise, the total covariance matrix is structured as low rank plus identity. This information can be used in the estimation process to reduce the number of samples required to reach acceptable performance. Moreover, it is possible to estimate the basis vectors of the clutter-plus-noise orthogonal subspace rather than the total covariance matrix of the clutter, which requires less data and is more robust to outliers. The orthogonal projection to the clutter plus noise subspace is usually calculated from an estimatd of the covariance matrix. Nevertheless, the state of art does not provide estimators that are both robust to various distributions and low rank structured.In this Thesis, we therefore develop new estimators that are fitting the considered context, to fill this gap. The contributions are following three axes :- We present a precise statistical model : low rank heterogeneous sources embedded in a white Gaussian noise.We express the maximum likelihood estimator for this context.Since this estimator has no closed form, we develop several algorithms to reach it effitiently.- For the considered context, we develop direct clutter subspace estimators that are not requiring an intermediate Covariance Matrix estimate.- We study the performances of the proposed methods on a Space Time Adaptive Processing for airborne radar application. Tests are performed on both synthetic and real data.

[pt] Processamento em arranjos de sensores é uma área com vasta aplicação, tanto civil quanto militar, por exemplo em sonar, radar, sismologia e comunicações sem fio. Por meio de processamento espacial e espácio-temporal é possível melhorar suas funcionalidades e explorar novas possibilidades. Esta área vem atraindo cada vez mais a atenção e os esfor¸cos da comunidade científica, especialmente agora, em que antenas phased-array se estabeleceram como uma tecnologia comercial e madura. Neste contexto, nós tratamos o problema de processamento com posto reduzido em processamento espacial (beamforming) e espácio-temporal de sinais radar e a nova área de radares com função dual de radar e comunicações (dualfunction radar-communications, DFRC), que pode ser resumida na incorporação de mensagens de comunicações nas transmissıes radar como uma tarefa secundária. Nesta tese, nós investigamos a aplicação de um novo esquema de reduções de posto baseado em interpolação e decimação em duas áreas distintas: processamento espacial e processamento espácio-temporal de sinais radar. Este algoritmo para redução de posto nunca havia sido testado nestes ambientes antes e apresentou resultados bastante expressivos. Nós também propomos simplificações para reduzir a complexidade computacional do algoritmo em bemforming. Quanto ao tópico de DFRC, nós propomos dois métodos originais para incorporar modulação de amplitude/fase aos lóbulos laterais do diagrama de irradiação do radar de forma robusta. Os métodos propostos são muito mais simples do que o estado-da-arte e apresentam desempenho superior em termos de robustez e aplicabilidade em operações de tempo-real. Nós ainda provemos várias outras análises, comparações e contribuições a esta nova área. / [en] Array processing is an area with many civilian and military applications, e.g. sonar, radar, seismology and wireless communications. By means of space and space-time processing it is possible to enhance their features and explore new possibilities. This area has been attracting increasingly more attention and gathering more efforts of the science community, especially now, that phased array antennas are established as a commercial and mature technology. Within this context, we address the problem of reduced rank processing in space and space-time radar signal processing and the new area of dual-function radar-communications (DFRC), which may be summarized as embedding communication messages into radar emissions as a secondary task for the radar. In this thesis, we investigate the application of a new joint interpolation and decimation rank reducing scheme in two different areas: beamforming and space-time radar processing. This rank reducing algorithm was never tested within these contexts before and shows impressive results. We also propose simplifications for decreasing the computational complexity of the algorithm in beamforming. In the topic of DFRC, we propose two original robust radar-embedded sidelobe phase/amplitude modulation methods which have simple closed form equations. The proposed methods are much simpler than the state of the art and have superior performance in terms of robustness and real-time applicability.

Abstract in English, Xhosa and Afrikaans / In South Africa, the number of households owning private cars has increased from 22.9% in 2003 to 28.5% in 2013. The City of Tshwane Metropolitan Municipality (City of Tshwane) in South Africa had the largest increase in population that was using private cars between 2003 and 2013 of approximately 11.3%; hence, a need was identified to shift from private cars to sustainable modes of transport. The purpose of this study was to develop guidelines for sustainable urban transport. Geographical location was used for quota sampling to ensure that all seven regions of the Tshwane municipal area would be represented. The sample size of the study comprised 418 participants. The primary data were gathered in Tshwane during the month of August 2017 using a structured questionnaire. The Likert scale was employed to ascertain the public's attitudes towards sustainable urban transport. Descriptive statistics, exploratory factor analysis and inferential statistics were used to analyse the data. The results revealed that the private car is the most frequently used mode of transport in the City of Tshwane. The results further indicated that the majority of the residents of the City of Tshwane had a negative attitude towards sustainable transport modes, which was attributed to safety, reliability and convenience concerns. Regions 4 and 6 differed statistically and significantly from region 5 regarding their opinions on the safety and comfort of private cars. In order to promote sustainable transportation, it is recommended that the City of Tshwane implement transport initiatives that can improve the service quality and safety features of sustainable transport modes. Each region of the City of Tshwane made specific recommendations that were based on the results of the study. The findings of this study provide insights that can be useful to the city planners to secure sustainable urban transportation for the City of Tshwane. Future research could investigate the feasibility of public bicycle rental programmes in the City of Tshwane. / EMzantsi Afrika, inani lamakhaya aneenqwelo mafutha landile ukusukela kuma-22.9% ngonyaka wama-2003 ukuya kuma-28.5% ngowama-2013. Umasipala Wesixeko Esimbaxa saseTshwane (Isixeko saseTshwane) eMzantsi Afrika ube nelona nani lamakhaya asebenzisa iimoto zabucala elande ngaphezu kwabo bonke abanye ooMasipala phakathi kowama-2003 nama-2013, landa ngesithuba se-11.3%. Le nto idale isidingo sokushenxa kwisimbo sokusebenzisa iimoto zabucala, ukuze kusetyenziwe ezinye iindlela zokuhamba eziya kuhlala zihleli. Injongo yesi sifundo kukuvelisa isikhokelo seendlela zokuhamba eziya kuhlala zihleli kwimimandla yasezidolophini. Ekukhetheni abathathi nxaxheba, kwasetyenziswa indawo abahlala kuyo abantu, ukuqinisekisa ukuba zosixhenxe iingingqi zomasipala waseTshwane zinabameli. Ubukhulu besampulu yaba ngabathathi nxaxheba abangama-418. Iinkcukacha zolwazi ezingundoqo zaqokelelwa eTshwane ngenyanga yeThupha kowama-2017, kwaye kwasetyenziswa uluhlu lwemibuzo ecwangcisiweyo. Kwasetyenziswa isikali esaziwa ngokuba yiLikert scale ekufumaniseni izimvo zoluntu jikelele ngeendlela zokuhamba eziya kuhlala zihleli kwimimandla yasezidolophini. Iinkcukacha zolwazi (idata) zahlelwa ngokusebenzisa indlela yamanani okucacisa iipatheni zezimvo zoluntu (descriptive statistics), indlela yokufumana iimpawu eziphambili kulwazi olufunyenweyo (exploratory factor analysis) nendlela yokungqinisisa izimvo ebezifudula zikho ngaphambi kophando (inferential statistics). Iziphumo zophando zadiza ukuba ukusebenzisa imoto yabucala yeyona ndlela yokuhamba esetyenziswa kakhulu kwisixeko saseTshwane. Ezi ziphumo zaphinda zabonisa ukuba uninzi lwabahlali besixeko saseTshwane abazithandi iindlela zokuhamba zikawonkewonke ngenxa yokungabikho kokhuseleko, ukuthembeka nokuba luncedo. Ingingqi yesi-4 neyesi-6 zahlukana kakhulu nengingqi yesi-5 ngokwamanani, malunga nezimvo ezingokhuseleko nokuhlala ntofontofo kwiimoto zabucala. Ukuze kukhuthazwe iindlela zokuhamba zikawonkewonke eziya kuhlala zihleli kucetyiswa ukuba Isixeko saseTshwane senze amalinge okuthutha abantu anokuphucula ukunikezelwa kwenkonzo yothutho, iphucule nokhuseleko. Ingingqi nganye yesixeko saseTshwane yenza iingcebiso ezathi zafakwa kwiziphumo zesifundo. Okufunyaniswe kwesi sifundo kunika iimbono ezinokuba luncedo kubacebi nabalungiseleli besixeko ekuveliseni iindlela zothutho eziya kuhlala zihleli kwisixeko saseTshwane. Uphando oluzayo lusenokuphanda ngokusetyenziswa kweenkqubo zokuqeshisa ngeebhayisikili kwisixeko sase Tshwane. / Die aantal huishoudings in Suid-Afrika wat private motors besit, neem van 22.9% in 2003 tot 28.5% in 2013 toe. In die Stad Tshwane- Metropolitaanse Munisipaliteit (Stad Tshwane) in Suid-Afrika toon die aantal inwoners wat private motors tussen 2003 en 2013 gebruik, die grootste toename van nagenoeg 11.3%. Daar word op grond hiervan ’n behoefte geïdentifiseer om van die gebruik van private motors weg te beweeg na volhoubare vervoerwyses. Die doel van hierdie studie is om riglyne vir volhoubare stedelike vervoer te ontwikkel. Geografiese ligging is vir die kwotasteekproefneming gebruik om te verseker dat al sewe streke van die Tshwane- munisipale gebied verteenwoordig word. Vir die steekproef wat vir die studie geneem word, word 418 deelnemers gebruik. Die primêre data word met behulp van ’n gestruktureerde vraelys in die loop van Augustus 2017 in Tshwane ingesamel. Die publiek se houdings jeens volhoubare stedelike vervoer word aan die hand van die Likert-skaal vasgestel. Beskrywende statistiek, verkennendefaktor-ontleding en inferensiële statistiek word gebruik om die data te ontleed. Dit blyk uit die resultate dat die private motor die vervoerwyse is wat die gereeldste in die Stad Tshwane gebruik word. In die resultate word verder aangedui dat die meerderheid inwoners van die Stad Tshwane ’n negatiewe houding teenoor volhoubare vervoerwyses het, wat toegeskryf word aan kwessies van veiligheid, betroubaarheid en gerief. Streek 4 en 6 verskil statisties aansienlik van streek 5 betreffende hul menings oor die veiligheid en gemak van private motors. Om volhoubare vervoer te bevorder, word aanbeveel dat die Stad Tshwane vervoerinisiatiewe implementeer wat die diensgehalte en veiligheidskenmerke van volhoubare vervoerwyses kan verbeter. Elke streek van die Stad Tshwane het vorendag gekom met spesifieke voorstelle wat by die resultate ingesluit is. Die bevindinge van hierdie studie bied insigte wat bruikbaar vir stadsbeplanners kan wees om volhoubare stedelike vervoer in die Stad Tshwane moontlik te maak. Die uitvoerbaarheid van openbare fietshuurprogramme in die Stad Tshwane kan in toekomstige navorsing ondersoek word. / Transport Economics, Logistics and Tourism / M. Com. (Transport Economics)