Estimation efficace des paramètres de signaux d'usagers radio-mobile par traitement avec antenne-réseau

Cette thèse aborde le problème d’estimation des paramètres de signaux d’usagers radio-mobile par traitement avec antenne-réseau. On adopte une approche de traitement théorique rigoureuse au problème en tentant de pallier aux limitations et désavantages des méthodes d’estimation existantes en ce domaine. Les chapitres principaux ont été rédigés en couvrant uniquement les aspects théoriques en lien aux contributions principales, tout en présentant une revue de littérature adéquate sur les sujets concernés. La thèse présente essentiellement trois volets distincts en lien à chacune des contributions en question. Suite à une revue des notions de base, on montre d’abord comment une méthode d’estimation exploitant des statistiques d’ordre supérieur a pu être développée à partir de l’amélioration d’un algorithme existant en ce domaine. On présente ensuite le cheminement qui a conduit à l’élaboration d’une technique d’estimation non linéaire exploitant les propriétés statistiques spécifiques des enveloppes complexes reçues, et ne possédant pas les limitations des algorithmes du second et quatrième ordre. Finalement, on présente le développement relatif à un algorithme d’estimation exploitant le caractère cyclostationnaire intrinsèque des signaux de communication dans un environnement asynchrone naturel. On montre comment un tel algorithme parvient à estimer la matrice de canal des signaux incidents indépendamment du caractère de corrélation spatiotemporel du bruit, et permettant de ce fait même une pleine exploitation du degré de liberté du réseau. La procédure d’estimation consiste en la résolution d’un problème de diagonalisation conjointe impliquant des matrices cibles issues d’une opération différentielle entre des matrices d’autocorrélation obtenues uniquement à partir de statistiques d’ordre deux. Pour chacune des contributions, des résultats de simulations sont présentés afin de confirmer l’efficacité des méthodes proposées.This thesis addresses the problem of parameter estimation of radio signals from mobile users using an antenna array. A rigorous theoretical approach to the problem is adopted in an attempt to overcome the limitations and disadvantages of existing estimation methods in this field. The main chapters have been written covering only the theoretical aspects related to the main contributions of the thesis, while at the same time providing an appropriate literature review on the considered topics. The thesis is divided into three main parts related to the aforesaid contributions. Following a review of the basics concepts in antenna array processing techniques for signal parameter estimation, we first present an improved version of an existing estimation algorithm expoiting higher-order statistics of the received signals. Subsequently, we show how a nonlinear estimation technique exploiting the specific statistical distributions of the received complex envelopes at the array can be developed in order to overcome the limitations of second and fourth-order algorithms. Finally, we present the development of an estimation algorithm exploiting the cyclostationary nature of communication signals in a natural asynchronous environment. We show how such an algorithm is able to estimate the channel matrix of the received signals independently of the spatial or temporal correlation structure of the noise, thereby enabling a full exploitation of the array’s degree of freedom. The estimation process is carried out by solving a joint diagonalization problem involving target matrices computed by a differential operation between autocorrelation matrices obtained by the sole use of second-order statistics. Various simulation experiments are presented for each contribution as a means of supporting and evidencing the effectiveness of the proposed methods

Full-duplex wireless communications: challenges, solutions and future research directions

The family of conventional half-duplex (HD) wireless systems relied on transmitting and receiving in different time-slots or frequency sub-bands. Hence the wireless research community aspires to conceive full-duplex (FD) operation for supporting concurrent transmission and reception in a single time/frequency channel, which would improve the attainable spectral efficiency by a factor of two. The main challenge encountered in implementing an FD wireless device is the large power difference between the self-interference (SI) imposed by the device’s own transmissions and the signal of interest received from a remote source. In this survey, we present a comprehensive list of the potential FD techniques and highlight their pros and cons. We classify the SI cancellation techniques into three categories, namely passive suppression, analog cancellation and digital cancellation, with the advantages and disadvantages of each technique compared. Specifically, we analyse the main impairments (e.g. phase noise, power amplifier nonlinearity as well as in-phase and quadrature-phase (I/Q) imbalance, etc.) that degrading the SI cancellation. We then discuss the FD based Media Access Control (MAC)-layer protocol design for the sake of addressing some of the critical issues, such as the problem of hidden terminals, the resultant end-to-end delay and the high packet loss ratio (PLR) due to network congestion. After elaborating on a variety of physical/MAC-layer techniques, we discuss potential solutions conceived for meeting the challenges imposed by the aforementioned techniques. Furthermore, we also discuss a range of critical issues related to the implementation, performance enhancement and optimization of FD systems, including important topics such as hybrid FD/HD scheme, optimal relay selection and optimal power allocation, etc. Finally, a variety of new directions and open problems associated with FD technology are pointed out. Our hope is that this treatise will stimulate future research efforts in the emerging field of FD communication

Analysis and design of parallel algorithms

The present state of electronic technology is such that factors affecting computation speed have almost been minimised; switching for instance is almost instantaneous. Electronic components are so good, in fact, that the time taken for a logic signal to travel between two points is now a significant factor of instruction times. Clearly, with the actual physical size of components being very small and the high circuit density, there is little scope for improving computation speech significantly by such means as even denser circuitry or still faster electronic components. Thus, development of faster computers will require a new approach that depends on the imaginative use of existing knowledge. One such approach is to increase computation speed through parallelism. Obviously, a parallel computer with p identical processors is potentially p times as fast as a single computer, although this limit can rarely be achieved

Resource allocation for cooperative broadcasting in W-CDMA networks

Imperial Users onl

Distributed speed control for multi-three-phase motors with enhanced power sharing capabilities

This thesis describes the last three years work and the results achieved after several stages of design and experimental validation. The main result is the development of a novel sharing current controller for multi-three-phase electrical machines. The proposed regulator, called "speed-drooped" or simply "droop" controller, allows the current transient triggered by a step change within the rotating reference frame to be controlled. Since multi-three-phase systems appear to be very good candidates for future Integrated Modular Motor Drives and next transportation system challenges, the work has been set up with modularity and redundancy for next future motor drives. During the preliminary stages, the mathematical models of the droop controller have been derived and validated on a multi-drive rig with two three-phase induction motors on the same shaft at the University of Nottingham. After, while developing a new general purpose control platform for power electronics able to control up to three three-phase systems, the Vector Space Decomposition for de-coupling the mutual interactions within multi-three-phase electric motors has been studied. Thanks to it, the inductance matrix of a triple-star two poles synchronous generator at the University of Trieste, Italy, has been diagonalised. Finally, the proposed current controller has been experimentally validated on a nine-phase synchronous generator and compared with the state of the art current sharing techniques. Furthermore, a post-fault compensation strategy has been formulated and validated by means of simulation work. If compared to the state-of-the-art current sharing techniques, the "droop" regulator capability of controlling current sharing transients while keeping constant speed of the shaft has been proven and successfully demonstrated by means of Matlab/Simulink simulations and experiments on both rigs

The University Defence Research Collaboration In Signal Processing

This chapter describes the development of algorithms for automatic detection of anomalies from multi-dimensional, undersampled and incomplete datasets. The challenge in this work is to identify and classify behaviours as normal or abnormal, safe or threatening, from an irregular and often heterogeneous sensor network. Many defence and civilian applications can be modelled as complex networks of interconnected nodes with unknown or uncertain spatio-temporal relations. The behavior of such heterogeneous networks can exhibit dynamic properties, reflecting evolution in both network structure (new nodes appearing and existing nodes disappearing), as well as inter-node relations. The UDRC work has addressed not only the detection of anomalies, but also the identification of their nature and their statistical characteristics. Normal patterns and changes in behavior have been incorporated to provide an acceptable balance between true positive rate, false positive rate, performance and computational cost. Data quality measures have been used to ensure the models of normality are not corrupted by unreliable and ambiguous data. The context for the activity of each node in complex networks offers an even more efficient anomaly detection mechanism. This has allowed the development of efficient approaches which not only detect anomalies but which also go on to classify their behaviour

Performance investigation of spatial modulation systems under realistic channel models

In order to fulfil the explosive demand for convenient wireless data access, novel wireless technologies such as the multiple-input-multiple-output (MIMO) have widely been used to improve the link reliability and capacity of wireless communication systems. In recent years, a new MIMO technology named the spatial modulation (SM) has attracted signi cant research interest due to its reported enhancement on the system performance with the reasonable system complexity. Before a new technology comes into real use, it is necessary to comprehensively evaluate its performance under different scenarios. In this thesis, we investigate the performance of SM systems under some important realistic scenarios for future wireless communications, such as the vehicle-to-vehicle (V2V), the high-speed train (HST), and the massive MIMO scenarios. Firstly, the bit error rate (BER) performance of SM systems under a novel threedimensional (3D) geometry based stochastic model (GBSM) for V2V MIMO channels is investigated by both theoretical analysis and system simulations. The impacts of vehicle tra c density (VTD), Doppler effect, and 3D feature on the BER performance of SM systems are thoroughly studied. In addition, other MIMO technologies, such as the vertical Bell Labs layered space-time (V-BLAST), the Alamouti scheme are compared with SM under different simulation settings. Secondly, the BER performance of SM systems is studied under a non-stationary wideband HST GBSM considering the non-ideal channel estimation case. The timevarying behaviour of the channel and its impact on the performance of SM systems are comprehensively investigated. The accurate theoretical BER expression of SM systems under a non-stationary wideband HST channels with non-ideal channel estimation is derived. A novel statistic property named stationary interval in terms of the space-time correlation function (STCF) is introduced in order to clearly explain all theoretical and simulation results. Thirdly, the performance of SM systems is evaluated under a Kroneck-based massive MIMO channel model. As a massive MIMO system employs large numbers of antennas, antenna elements are distributed over a wide range. Thus, different antenna elements may observe different sets of clusters. How this phenomenon affects the performance of SM systems is investigated by considering a survival probability of clusters, which abstracts the birth-death process of each cluster in the channel model. Moreover, the performance of SM systems is also compared with that of other MIMO technologies under the massive MIMO channel model. In summary, all research works in this thesis have considered realistic MIMO channel models, which are meaningful for the test, performance evaluation, and implementation of SM technology for future advanced wireless communications systems

Distributed speed control for multi-three-phase motors with enhanced power sharing capabilities

This thesis describes the last three years work and the results achieved after several stages of design and experimental validation. The main result is the development of a novel sharing current controller for multi-three-phase electrical machines. The proposed regulator, called "speed-drooped" or simply "droop" controller, allows the current transient triggered by a step change within the rotating reference frame to be controlled. Since multi-three-phase systems appear to be very good candidates for future Integrated Modular Motor Drives and next transportation system challenges, the work has been set up with modularity and redundancy for next future motor drives. During the preliminary stages, the mathematical models of the droop controller have been derived and validated on a multi-drive rig with two three-phase induction motors on the same shaft at the University of Nottingham. After, while developing a new general purpose control platform for power electronics able to control up to three three-phase systems, the Vector Space Decomposition for de-coupling the mutual interactions within multi-three-phase electric motors has been studied. Thanks to it, the inductance matrix of a triple-star two poles synchronous generator at the University of Trieste, Italy, has been diagonalised. Finally, the proposed current controller has been experimentally validated on a nine-phase synchronous generator and compared with the state of the art current sharing techniques. Furthermore, a post-fault compensation strategy has been formulated and validated by means of simulation work. If compared to the state-of-the-art current sharing techniques, the "droop" regulator capability of controlling current sharing transients while keeping constant speed of the shaft has been proven and successfully demonstrated by means of Matlab/Simulink simulations and experiments on both rigs