The technique of direct sequence spread spectrum (DS/SS) has been widely used in commercial mobile communication systems. The efficiency of DS/SS system is highly dependent on the accurate and fast synchronization between the incoming and locally generated PN (pseudo-noise) codes. The code synchronization is processed in two steps, acquisition (coarse alignment) and tracking (fine alignment), to bring the delay offset between the two codes. Conventionally, for code synchronization, most of techniques were proposed based on the correlation property of PN codes. Recently, the different approach, by using the adaptive LMS filtering scheme, has been proposed to reduce the hardware complexity and to improve the performance of code synchronization, especially for a long PN code. In this thesis, a new coherent adaptive code synchronization scheme is proposed, where the adaptive constrained LMS (CLMS) algorithm with the maximum tap-weight (MTW) test method is devised for code acquisition. The statistics of weight vector of the proposed CLMS scheme are derived to evaluate the performance, in terms of mean acquisition time (MAT). Analytical and simulation results verify that the proposed scheme for code acquisition outperforms the one using the conventional LMS filtering schemes, under the integer and non-integer time delay cases. Moreover, the setting of threshold value is derived for code acquisition, which is independent of the values of signal-to-noise ratio (SNR) and time delay. Next, the CLMS scheme is proposed associated with the direct delay estimation (DDE) formula for code tracking. This approach does achieve a good delay-tracking performance, which is verified via computer simulation. Simultaneously, the hardware complexity can further be reduced due to that a code-tracking loop implemented by the interpolation method is not required.

The efficiency of direct sequence spread spectrum (DS/SS) receiver is highly dependent on the accurate and fast synchronization between the incoming and locally generated PN (pseudo-noise) codes. The code synchronization is processed in two steps, acquisition (coarse alignment) and tracking (fine alignment), to estimate the delay offset between the two codes. In general, the schemes for code acquisition and tracking processes are performed, separately, and implemented with different structure. Recently, an alternative approach, with the adaptive LMS filtering scheme, has been proposed for performing both code acquisition and tracking with the identical structure, where the coherent receiver was employed. With this approach, dramatically, hardware complexity reduction could be achieved, especially, when long PN code is considered. In this thesis, a new differentially coherent code synchronization scheme, based on a differential detector followed by an adaptive constrained LMS (CLMS) filtering algorithm with maximum tap weight (MTW) test scheme, is devised for performing both code acquisition and tracking with the identical structure. With a differential detector for code synchronization, the prior knowledge of the carrier phase is not required as the non-coherent techniques. Numerical analyses and simulation results verify that the proposed scheme has better acquisition performance, in terms of mean acquisition time, than the conventional LMS filtering algorithm with MTW test and mean square error (MSE) test schemes for the integer and non-integer time delay environments. At the same time, the proposed scheme has better tracking capability, in terms of mean hold-in time and mean penalty time, over the conventional LMS filtering schemes, for the variation of signal-to-noise ratio (SNR) and delay offset (delay difference).

¡@¡@Pseudo-noise (PN) code synchronizer is an essential element of direct-sequence code division multiple access (DS-CDMA) system because data transmission is possible only after the receiver accurately synchronizes the locally generated PN code with the incoming PN code. The code synchronization is processed in two steps, acquisition and tracking, to estimate the delay offset between the two codes. Recently, the adaptive LMS filtering scheme has been proposed for performing both code acquisition and tracking with the identical structure, where the LMS algorithm is used to adjust the FIR filter taps to search for the value of delay-offset adaptively. A decision device is employed in the adaptive LMS filtering scheme as a decision variable to indicate code synchronization, hence it plays an important role for the performance of mean acquisition time (MAT). In this thesis, only code acquisition is considered. ¡@¡@In this thesis, a new decision device, referred to as the weight vector square norm (WVSN) test method, is devised associated with the adaptive LMS filtering scheme for code acquisition in DS-CDMA system. The system probabilities of the proposed scheme are derived for evaluating MAT. Numerical analyses and simulation results verify that the performance of the proposed scheme, in terms of detection probability and MAT, is superior to the conventional scheme with mean-squared error (MSE) test method, especially when the signal-to-interference-plus-noise ratio (SINR) is relatively low. ¡@¡@Furthermore, an efficient and joint-adaptation code acquisition scheme, i.e., a smart antenna coupled with the proposed adaptive LMS filtering scheme with the WVSN test method, is devised for applying to a base station, where all antenna elements are employed during PN code acquisition. This new scheme is a process of PN code acquisition and the weight coefficients of smart antenna jointly and adaptively. Numerical analyses and simulation results demonstrate that the performance of the proposed scheme with five antenna elements, in terms of the output SINR, the detection probability and the MAT, can be improved by around 7 dB, compared to the one with single antenna case.

In general, PN code synchronization consists of two steps: PN code acquisition (coarse alignment) and PN code tracking (fine alignment), to estimate the delay offset between received and locally generated codes. Recently, the schemes with a joint adaptive process of PN code acquisition and the weight coefficients of smart antenna have been proposed for improving the received signal-to-interference-plus-noise ratio (SINR) and simultaneously achieving better mean-acquisition-time (MAT) performance in direct-sequence code-division multiple access (DS-CDMA) systems. In which, the setting of the threshold plays an important role on the MAT performance. Often, the received SINR is varying, using the fixed threshold acquisition algorithms may result in undesirable performance. To improve the above problem, in this thesis, a new adaptive threshold scheme is devised in a joint adaptive code acquisition and beam-forming DS-CDMA receiver for code acquisition under a fading multipath and additive white Gaussian-noise (AWGN) channels. The basic idea of this new adaptive threshold scheme is to estimate the averaged output power of smart antenna to scale a reference threshold for each observation interval, such that it can approximately achieve a constant false alarm rate (CFAR) criteria. The system probabilities of the proposed scheme are derived for evaluating MAT under a slowly fading two-paths channels. Numerical analyses and simulation results demonstrate that the proposed adaptive threshold scheme does achieve better performance, in terms of the output SINR, the detection probability and the MAT, compared to a fixed threshold method.

Model-Based Software Engineering (MBSE) a été proposé comme une méthodologie prometteuse de développement de logiciels pour surmonter les limites de la méthodologie traditionnelle basée sur la programmation pour faire face à la complexité des systèmes embarqués. MBSE favorise l’utilisation de langages de modélisation pour décrire les systèmes d’une manière abstraite et fournit des moyens pour générer automatiquement de différents artefacts de développement, p.ex. code et documentation, à partir de modèles. Le développement d’un système complexe implique souvent de multiples intervenants qui utilisent différents outils pour modifier les artefacts de développement, le modèle et le code en particulier dans cette thèse. Les modifications apportées aux artefacts évoquent le problème de cohérence qui nécessite un processus de synchronisation pour propager les modifications apportées dans l’un artefact aux autres artefacts. Dans cette étude, le problème de la synchronisation des modèles d’architecture basés sur les éléments UML composite structure (UML-CS) et UML state machine (UML-SM) du langage de l’Unified Modeling Language (UML), et le code orienté objet est présenté. UML-CSs sont utilisés pour décrire l’architecture du logiciel basée sur les composants et UML-SMs pour les comportements discrets liés aux événements des systèmes réactifs. Le premier défi est de permettre une collaboration entre les architectes de logiciels et les programmeurs produisant de modèle et de code, en utilisant différents outils. Il soulève le problème de synchronisation où il existe de modifications simultanées des artefacts. En fait, il existe un écart de perception entre les langages à base de diagramme (langages de modélisation) et les langages textuels (langages de programmation). D’une part, les programmeurs préfèrent souvent utiliser la combinaison familière d’un langage de programmation et d’un environnement de développement intégré. D’autre part, les architectes logiciels, travaillant à des niveaux d’abstraction plus élevés, favorisent l’utilisation des modèles et préfèrent donc les langages à base de diagramme pour décrire l’architecture du système. Le deuxième défi est qu’il existe un écart d’abstraction significatif entre les éléments du modèle et les éléments du code: les éléments UML-CS et UML-SM sont au niveau d’abstraction plus élevé que les éléments du code. L’écart rend la difficulté pour les approches de synchronisation actuelles car il n’y a pas de façon facile de réflecter les modifications du code au modèle. Cette thèse propose une approche automatisée de synchronisation composée de deux principales contributions corrélées. Pour aborder le premier défi, on propose un patron méthodologique générique de synchronisation entre modèle et code. Il consiste en des définitions des fonctionnalités nécessaires et plusieurs processus qui synchronisent le modèle et le code en fonction de plusieurs scénarios définis où les développeurs utilisent différents outils pour modifier le modèle et le code. Cette contribution est indépendante de UML-CSs et UML-SMs. La deuxième contribution traite du deuxième défi et est basée sur les résultats de la première contribution. Dans la deuxième contribution, un mapping bidirectionnel est présentée pour réduire l’écart d’abstraction entre le modèle et le code. Le mapping est un ensemble de correspondances entre les éléments de modèle et ceux de code. Il est utilisé comme entrée principale du patron méthodologique générique de synchronisation entre modèle et code. Plus important, l’utilisation du mapping fournit les fonctionnalités définies dans la première contribution et facilite la synchronisation des éléments de UML-CS et UML-SM et du code. L’approche est évaluée au moyen de multiples simulations et d’une étude de cas. / Model-Based Software Engineering (MBSE) has been proposed as a promising software development methodology to overcome limitations of traditional programming-based methodology in dealing with the complexity of embedded systems. MBSE promotes the use of modeling languages for describing systems in an abstract way and provides means for automatically generating different development artifacts, e.g. code and documentation, from models. The development of a complex system often involves multiple stakeholders who use different tools to modify the development artifacts, model and code in particular in this thesis. Artifact modifications must be kept consistent: a synchronization process needs to propagate modifications made in one artifact to the other artifacts. In this study, the problem of synchronizing Unified Modeling Language (UML)-based architecture models, specified by UML composite structure (UML-CS) and UML state machine (UML-SM) elements, and object-oriented code is presented. UML-CSs are used for describing the component-based software architecture and UML-SMs for discrete event-driven behaviors of reactive systems. The first challenge is to enable a collaboration between software architects and programmers producing model and code by using different tools. This raises the synchronization problem of concurrent artifact modifications. In fact, there is a perception gap between diagram-based languages (modeling languages) and text-based languages (programming languages). On the one hand, programmers often prefer to use the more familiar combination of a programming language and an Integrated Development Environment. On the other hand, software architects, working at higher levels of abstraction, tend to favor the use of models, and therefore prefer diagram-based languages for describing the architecture of the system. The second challenge is that there is a significant abstraction gap between the model elements and the code elements: UML-CS andUML-SM elements are at higher level of abstraction than code elements. The gap makes current synchronization approaches hard to be applied since there is no easy way to reflect modifications in code back to model. This thesis proposes an automated synchronization approach that is composed of two main correlated contributions. To address the first challenge, a generic model-code synchronization methodological pattern is proposed. It consists of definitions of necessary functionalities and multiple processes that synchronize model and code based on several defined scenarios where the developers use different tools to modify model and code. This contribution is independent of UML-CSs and UML-SMs. The second contribution deals with the second challenge and is based on the results from the first contribution. In the second contribution, a bidirectional mapping is presented for reducing the abstraction gap between model and code. The mapping is a set of correspondences between model elements and code elements. It is used as main input of the generic model-code synchronization methodological pattern. More importantly, the usage of the mapping provides the functionalities defined in the first contribution and eases the synchronization of UML-CS and UML-SM elements and code. The approach is evaluated by means of multiple simulations and a case study.