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1
Mattingley-Scott, Mark Alistair. « A code division multiple spread spectrum local area network ». Thesis, Durham University, 1989. http://etheses.dur.ac.uk/1451/.
Texte intégral
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Fan, Pingzhi. « Code design and analysis for multiple access communications ». Thesis, University of Hull, 1994. http://hydra.hull.ac.uk/resources/hull:5864.
Texte intégralRésumé :
This thesis explores various coding aspects of multiple access communications, mainly for spread spectrum multiaccess(SSMA) communications and collaborative coding multiaccess(CCMA) communications. Both the SSMA and CCMA techniques permit efficient simultaneous transmission by several users sharing a common channel, without subdivision in time or frequency. The general principle behind these two multiaccess schemes is that one can find sets of signals (codes) which can be combined together to form a composite signal; on reception, the individual signals in the set can each be recovered from the composite signal. For the CCMA scheme, the isolation between users is based on the code structure; for the SSMA scheme, on the other hand, the isolation between users is based on the autocorrelation functions(ACFs) and crosscorrelation functions (CCFs) of the code sequences. It is clear that, in either case, the code design is the key to the system design. For the CCMA system with a multiaccess binary adder channel, a class of superimposed codes is analyzed. It is proved that every constant weight code of weight w and maximal correlation λ corresponds to a subclass of disjunctive codes of order T < w/λ. Results related to the decomposition of the disjunctive codes in the noiseless and noisy cases are derived. Decoding algorithms for both the noiseless and the noisy cases are proposed. For the CCMA system operating over a multiaccess Q-ary adder channel, a class of cyclic uniquely decodable codes is proposed and analyzed by employing cyclic codes with symbols from an arbitrary finite integer rings. A very low complexity decoding procedure is presented. For a synchronous SSMA system, a new approach employing orthogonal complementary sets is presented; the properties of such orthogonal complementary sets are studied in detail. Recursive formulas for constructing orthogonal complementary sets are given. Methods for synthesizing new orthogonal complementary sets from known ones with the same dimensions are also discussed. For an asynchronous SSMA system, several new spreading codes are presented and studied: 1. A new class of polyphase codes with two-valued periodic ACF and CCF properties is derived. It is proved that, for a given prime length L > 3, the out-of-phase ACFs and CCFs of the codes are constant and equal to √L. In addition, all codes of the same length are mutually orthogonal. 2. Maximal length sequences (m-sequences) over Gaussian integers, suitable for use with QAM modulation, are considered. Two sub-classes of m-sequences with quasi-perfect periodic autocorrelations are obtained. The CCFs between the decimated m-sequences are studied. By applying a simple operation, it is shown that some m-sequences over rational and Gaussian integers can be transformed into perfect sequences with impulsive ACFs. 3. Frank codes and Chu codes have perfect periodic ACFs and optimum periodic CCFs. In addition, it is shown that they also have very favourable nonperiodic ACFs; some new results concerning the behaviour of the nonperiodic ACFs are derived. Further, it is proved that the sets of combined Frank/Chu codes, which contain a larger number of codes than either of the two constituent sets, also have very good periodic CCFs. Based on Frank codes and Chu codes, two interesting classes of real-valued codes with good correlation properties are defined. It is shown that these codes have periodic complementary properties and good periodic and nonperiodic ACF/CCFs. Finally, a hybrid CCMA/SSMA coding scheme is proposed. This new hybrid coding scheme provides a very flexible and powerful multiple accessing capability and allows simple and efficient decoding. Given an SSMA system with K users and a CCMA system with N users, where at most T users are active at any time, then the hybrid system will have K . N users with at most T.K users active at any time. The hybrid CCMA/SSMA coding scheme is superior to the individual CCMA system or SSMA system in terms of information rate, number of users, decoding complexity and external interference rejection capability.
3
Zhao, Qian Effros Michelle. « Network source coding : theory and code design for broadcast and multiple access networks / ». Diss., Pasadena, Calif. : California Institute of Technology, 2003. http://resolver.caltech.edu/CaltechETD:etd-05302003-125004.
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Shaar, A. A. « A study of code-division multiple-access with reference to fibre-optic local-area networks ». Thesis, University of Kent, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.353184.
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Souissi, Slim. « Adaptive error control through packet combining in code division multiple access systems ». Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/13381.
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Geslin, Serge. « Influence of laser diode nonlinearities on fibre optic systems supporting direct-sequence code division multiple access signals ». Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269411.
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Baker, Dirk A. « Space-time block coding with imperfect channel estimates ». Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=1843.
Texte intégralRésumé :
Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains iv, 74 p. : ill. Includes abstract. Includes bibliographical references (p. 73-74).
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Manchiraju, Dinakar. « Evaluation of pseudorandom sequences used in third generation spread spectrum systems ». Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1081801327.
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Green, Crystal D. « Perceptions of Usefulness : Using the Holland Code Theory, Multiple Intelligences Theory, and Role Model Identification to Determine a Career Niche in the Fashion Industry for First-quarter Fashion Students ». Kent State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=kent1271450339.
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Sathananthan, K. « Broadband wireless communications : issues of OFDM and multi-code CDMA ». Monash University, School of Computer Science and Software Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/9401.
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Bolas, Eduardo J. « Coding-spreading tradeoff in CDMA systems ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02sep%5FBolas.pdf.
Texte intégralRésumé :
Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2002.Thesis advisor(s): Tri T. Ha, Jan E. Tighe, Jovan E. Lebaric. Includes bibliographical references (p. 85). Also available online.
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CASLINI, MANUELA. « Alessitimia e regolazione emotiva nella psicoterapia di pazienti con DCA : Analisi empirica dell’Attività Referenziale di un campione in trattamento ». Bachelor's thesis, Milano Bicocca, 2012. http://hdl.handle.net/10281/51532.
Texte intégralRésumé :
Abstract
Background
Alexythimia represents an important deficit in patients with ED and it is a responsible factor for the poor response to treatment. The difficulties found by patients in psychotherapeutic treatments come from their peculiar cognitive, emotional, behavioural and personological attitude generated by their metapsycological specific nature and reflected in a language which is often factitious and nameless for the person’s experience: examining the language can be a fundamental element to detect this pathology and its possible treatments. Considering as theoretical references the theories on alexithymia, on the Emotional Regulation and on the Bucci’s Multiple Code, this study aims at evaluating the effectiveness of psychotherapy and at observing changes in emotional expression during 61 psychotherapy sessions undergone by a series of 8 ED patients.
Methods
The effectiveness of psychotherapy has been evaluated in terms of symptomatological improvements, attitudes relating to diet, weight, physical condition, ability in emotional reading and characteristic psychological features through three repeated administrations of a set of psychometric scales (Toronto Alexithymia Scale-20, Eating Disorder Inventory-2, Body Uneasiness Test, Symptom Checklist-90-R, Multidimensional Perfectionism Scale, Worry Domain Questionnaire, Parental Bonding Instrument, Dissociative Experience Scale, Working Alliance Inventory).
Changes in the expression of emotional contents in the psychotherapeutic process have been studied through the application of computerized RA measures – I-DAAP (Italian Discourse Attribute Analyses Program); the time trend of narrative pattern in the sequence of sessions has been tested with Spearman’s correlation coefficient.
Results
The results support the efficacy of psychotherapy in terms of some key aspects – dissociative moments, impulsivity, body dissatisfaction – whereas, language indicators underline the problem of emotional states elaboration: a defensive rational attitude inactivates the emergence of dissociated emotional patterns and defenses of intellectualization set limits to the patient’s narration caused by the fear of falling into a state of emotional oppression. This narrative pattern, apparently little functional compared to an evolutionary project, is effective for the immediate reduction in the psychic distress that the subject needs to satisfy.
Conclusions
The knowledge of a psychotherapeutic process prototypical trend helps in managing actions, in adjusting the setting, in understanding defenses and moments of possible emotional connection with respect to dissociated emotional schemes. Future work will have to evaluate if and how improving emotional communication could be seen as the main focus of treatment.
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Sharma, Manish. « Receptores iterativos para canais de acesso múltiplo ruidosos com N frequências e T usuários ». [s.n.], 2010. http://repositorio.unicamp.br/jspui/handle/REPOSIP/260834.
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Orientador: Jaime PortugheisTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-17T00:51:09Z (GMT). No. of bitstreams: 1 Sharma_Manish_D.pdf: 1122815 bytes, checksum: ac184067a2eeb2f29617e0a5da608708 (MD5) Previous issue date: 2010
Resumo: O objetivo deste trabalho é analisar o desempenho da recepção e detecção conjunta e iterativa para canais de acesso múltiplo. A análise se concentrou em torno de um canal ruidoso com N frequências compartilhado por T usuários. Encontramos valores para a capacidade do canal para detecção conjunta e individual. Embora a eficiência espectral do sistema seja relativamente baixa, a combinação deste fator com uma grande faixa de frequências permite altas taxas de transmissão com baixa relação sinal ruído. O receptor foi modelado como um grafo de fatores e foi analisado através de curvas EXIT, que também são utilizadas para otimizar os códigos corretores de erro dos usuários. Propomos alguns sistemas baseados nesta técnica e simulamos a sua probabilidade de erro de bit. Os resultados indicam que é possível transmitir informação com taxas próximas da capacidade do canal. Tanto o grafo do receptor como as análises subsequentes podem ser aplicadas para outros canais de acesso múltiplo, especialmente para sistemas com N símbolos de transmissão ortogonais.
Abstract: The aim of this work is to analyze the performance of iterative joint reception and detection for multi-user channels. The analysis is centered around an N-frequency MFSK noisy channel shared by T users. Channel capacity values are obtained for joint and single user detection. Although the system's spectral efficiency is low, high rates at low signal to noise ratio are achievable by using a wide-bandwidth channel. The receiver is modeled as a factor graph and analyzed by its EXIT charts, which were also used to analyze the users' error correcting codes. Some systems are proposed and simulated to obtain the bit error probability. Results indicate that it is possible to transmit information with rates close to channel capacity. The proposed receiver and the performed analysis can be applied to other types of multiple access channels, in particular for systems with N orthogonal transmission symbols.
Doutorado
Telecomunicações e Telemática
Doutor em Engenharia Elétrica
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Radway, Nora E. « SHYNESS IN THE CLASSROOM : A STUDY IN NONVERBAL COMMUNICATION CODES ». UKnowledge, 2019. https://uknowledge.uky.edu/comm_etds/79.
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This study examined the experiences of shy, introverted, and apprehensive students in the college classroom. This study was framed by multiple goals theory to discover how these students use nonverbal communication to achieve their task, identity, and relational goals in the classroom. Shy, introverted, and apprehensive students face challenges in the classroom especially when asked to verbally participate or give presentations that their more outgoing classmates may not face. Participants (N = 16) participated in focus groups where they discussed their experiences, perceptions, and feelings about participation in their college courses. Results showed that these students do experience apprehension in communication situations, often avoiding participation when possible, and that they do use nonverbal communication to meet their task, identity, and relational goals in the classroom. Implications for theory and for both students and instructors, limitations, and future directions for research are discussed.
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Karban, Ugur. « Three-dimensional Flow Solutions For Non-lifting Flows Using Fast Multipole Boundary Element Method ». Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615042/index.pdf.
Texte intégralRésumé :
Driving aim of this study was to develop a solver which is accurate enough to be used in analysis and fast enough to be used in optimization purposes. As a first step, a three-dimensional potential flow solver is developed using Fast Multipole Boundary Element (FMBEM) for calculating the pressure distributions in non-lifting flows.
It is a steady state solver which uses planar triangular unstructured mesh. After the geometry is introduced, the program creates a prescribed wake surface attached to the trailing edge(s), obtains a solution using panel elements on which the doublet and source strengths vary linearly. The reason for using FMBEM instead of classical BEM is the availability of solutions of systems having DOFs up to several millions within a few hours using a standard computer which is impossible to accomplish with classical BEM. Solutions obtained for different test cases are compared with the analytical solution (if applicable), the experimental data or the results obtained by JavaFoil.
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D'ARMA, ALESSIA. « Come potenziare la Teoria della Mente (ToM) nella Sclerosi Multipla ? Dalla letteratura allo sviluppo di un intervento innovativo culturale ». Doctoral thesis, Università Cattolica del Sacro Cuore, 2021. http://hdl.handle.net/10280/96257.
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La Teoria della Mente (ToM), la capacità cognitiva di riuscire a rappresentare ed interpretare gli stati mentali propri e altrui al fine di prevederne in comportamento, risulta essere deficitaria nella Sclerosi Multipla (SM), patologia cronica neurodegenerativa. La messa a punto e l’implementazione di un training di potenziamento di questa abilità sociale in questi pazienti è di rilevante importanza in quanto la ToM è strettamente connessa alla loro qualità della vita. Dato che ad oggi non esistono training di potenziamento della ToM nella SM, obiettivo primario della tesi è stata l’indagine relativa ai training di cognizione sociale attualmente esistenti in altre patologie croniche dell’età adulta. E’ stata effettuata una revisione sistematica ed una meta-analisi dei training attualmente esistenti per i soggetti con schizofrenia dato che questi soggetti presentano caratteristiche demografiche simili ai soggetti con SM. Si è quindi progettato un training di potenziamento della ToM da proporre ad un sample di soggetti con SM; prima di valutarne l’efficacia è stato condotto uno studio di accettabilità del suddetto training, al fine di superare potenziali barriere per la sua fattibilità. Si è infine proceduto all’esecuzione del terzo lavoro scientifico, ovvero la valutazione dell’efficacia del suddetto training sulla ToM in soggetti affetti da SM.Theory of Mind (ToM) is the ability of recognition and mental states' attribution to predict future behaviors. ToM deficit is well recognized in MS; hence, ToM training in this population is relevant because ToM is strictly connected with quality of life of people with multiple sclerosis (pwMS). To our knowledge, there is no training established for the treatment in this population. For this reason, we proposed to investigate the efficacy of social cognition training in other adults with chronic disease. We conducted a systematic review and a meta-analysis of SC training in schizophrenia, given that these subjects present demographic characteristics similar to pwMS. Hence, we design a rehabilitation ToM training for pwMS; before evaluating its efficacy, we conducted an acceptability study to overcome potential barriers for its feasibility. Lastly, we implement this novel rehabilitation training testing its efficacy on ToM in pwMS.
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Robert, Gwezheneg. « Codes de Gabidulin en caractéristique nulle : application au codage espace-temps ». Thesis, Rennes 1, 2015. http://www.theses.fr/2015REN1S083/document.
Texte intégralRésumé :
Les codes espace-temps sont des codes correcteurs dédiés aux transmissions MIMO. Mathématiquement, un code espace-temps est un ensemble fini de matrices complexes. Ses performances dépendent de plusieurs critères, dont la distance minimale en métrique rang. Les codes de Gabidulin sont des codes dans cette métrique, connus pour leur optimalité et pour l'existence d'algorithmes de décodage efficaces. C'est pourquoi ils sont utilisés pour concevoir des codes espace-temps. La principale difficulté est alors de construire des matrices complexes à partir de matrices binaires. Les travaux présentés dans ce documents consistent à généraliser les codes de Gabidulin à des corps de nombres, en particulier des extensions cyclique. Nous verrons qu'ils ont les mêmes propriétés que leurs analogues sur les corps finis. Nous étudierons plusieurs modèles d'erreurs et d'effacements et présenterons un algorithme qui permettra de retrouver l'information transmise avec une complexité quadratique. En calculant dans des corps infinis, nous serons confrontés au problème de la taille des éléments, qui augmente exponentiellement au gré des calculs. Pour éviter ce désagrément, nous verrons qu'il est possible de réduire le code afin de calculer dans un corps fini. Enfin, nous proposerons une famille de codes espace-temps dont la construction est basée sur les codes de Gabidulin généralisés. Nous verrons que leurs performances sont similaires à celles des codes existants, et qu'ils disposent d'une structure supplémentaireSpace-time codes are error correcting codes dedicated to MIMO transmissions. Mathematically, a space-time code is a finite family of complex matrices. Its preformances rely on several parameters, including its minimal rank distance. Gabidulin codes are codes in this metric, famous for their optimality and thanks to efficient decoding algorithms. That's why they are used to design space-time codes. The main difficulty is to design complex matrices from binary matrices. The aim of the works collected here is to generalize Gabidulin codes to number fields, especially cyclique extesnions. We see that they have the same properties than Gabidulin codes over finite fields. We study several errors and erasures models and introduce a quadratic algorithm to recover transmitted information. When computing in finite fields, we are faced with the growing size problem. Indeed, the size of the coefficients grows exponentielly along the algorithm. To avoid this problem, it is possible to reduce the code, in order to compute in a finite field. Finally, we design a family of space-time codes, based on generalised Gabidulin codes. We see that our codes have performances similar to those of existing codes, and that they have additional structure
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Smith, Jacques. « Constructing low cost core-satellite portfolios with multiple risk constraints : practical applications to Robo advising in South Africa using active, passive and smart-beta strategies ». Master's thesis, Faculty of Commerce, 2020. http://hdl.handle.net/11427/32985.
Texte intégralRésumé :
Risk and tracking error budgeting was originally adopted by large institutional investors, including pension funds, plan sponsors, foundations, and endowments. More recently, risk and tracking error budgeting have gained popularity among financial advisors, multi-managers, fund of funds managers, high net worth individuals as well as retail investors. These techniques contribute to the portfolio optimisation process by limiting the extent to which a portfolio can deviate from its benchmark with regards to risk and tracking error. This is an ambitious paper that attempts to determine the optimal strategy to practically implement risk and tracking error budgeting as a portfolio optimisation technique in South Africa. This study attempts to bridge the gap between active, passive, and smart-beta investment management styles by introducing a low-cost portfolio construction technique, for core-satellite portfolio management, which contributes to the risk and tracking error budgeting process. Core-satellite portfolios are designed to expose the portfolio to a low-cost primary “core” consisting of passive and enhanced index funds, thus systematic risk “beta”, limiting the tracking error of the portfolio. The secondary “satellite” component is allocated to active and smart-beta managers to exploit expected excess return “alpha”. The primary aim of this research is to construct a rule-based product range of core-satellite portfolios called “replica portfolios”. The product range builds on the foundation of the Association for Savings & Investments South Africa (ASISA) framework. The study identifies three “target portfolios” from ASISA's framework, namely (1) High Risk: SA General Equity, (2) Medium Risk: SA Multi-Asset High Equity and (3) Low Risk: SA Multi-Asset Low Equity. Through this framework, active managers from each category are shortlisted using a Sharpe and Information Ratio filter. A secondary filtering technique, namely Returns Based Style Analysis (RBSA) is used to determine the style, R-squared and alpha-generating ability of active managers versus the passive asset classes and style indices they seek to replicate. Applying Euler's theorem for homogenous functions, we decompose the risk of the coresatellite portfolio into the risk contributed by each of its components. The primary mandate of the core-satellite portfolios in the product range is to allocate risk and tracking error efficiently across several investment management styles and asset classes in order to maximise returns while remaining within the specified risk parameters. iii The results highlighted that active managers, after fees, predominantly failed to outperform their benchmarks and passive building blocks, as identified through RBSA over the sample period (October 2009 – September 2019). However, only a small number of active managers generated superior risk-adjusted returns and were included in the core-satellite range of products. This study recommends to investors that they exploit the “hot-hands effect” by investing in specialised, benchmark agnostic active managers who consistently produce superior risk-adjusted returns. By blending active, passive and smart-beta strategies, investors are exposed to less total risk, less risk per holding and a lower tracking error. The three coresatellite portfolios developed in this study generated absolute and risk-adjusted returns that are more significant than their active and passive counterparts. Fee arbitrage was derived through the range of core-satellite products, resulting in tangible alpha over the sample period. The study encourages investors to use smart-beta strategies alongside active and passive funds since it improves Sharpe and Information ratios while enhancing the original portfolio's characteristics.
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Ouertani, Rym. « Algorithmes de décodage pour les systèmes multi-antennes à complexité réduite ». Phd thesis, Télécom ParisTech, 2009. http://pastel.archives-ouvertes.fr/pastel-00718214.
Texte intégralRésumé :
Durant ces dernières années, un grand intérêt a été accordé aux systèmes de communication sans fil ayant plusieurs antennes en émission et en réception. Les codes espace-temps permettent d'exploiter tous les degrés de liberté de tels systèmes. Toutefois, le décodage de ces codes présente une grande complexité qui croit en fonction du nombre d'antennes déployées et de la taille de la constellation utilisée. Nous proposons un nouveau décodeur, appelé SB-Stack (Spherical Bound-Stack decoder) basé sur un algorithme de recherche dans l'arbre. Ce décodeur combine la stratégie de recherche du décodeur séquentiel Stack (dit également décodeur à pile) et la région de recherche du décodeur par sphères. Nous montrons que ce décodeur présente une complexité moindre par rapport à tous les décodeurs existants tout en offrant des performances optimales. Une version paramétrée de ce décodeur est aussi proposée, offrant une multitude de performances allant du ZF-DFE au ML avec des complexités croissantes, ainsi plusieurs compromis performances-complexités sont obtenus. Comme pour tous les systèmes de communication, les codes espace-temps pour les systèmes à antennes multiples peuvent être concaténés avec des codes correcteurs d'erreurs. Généralement, ces derniers sont décodés par des décodeurs à entrées et sorties souples. Ainsi, nous avons besoin de sorties souples fournies par le décodeur espace-temps qui seront utilisées comme entrées par les premiers décodeurs. Nous proposons alors une version modifiée du décodeur SB-Stack délivrant des sorties souples sous forme de taux de vraisemblance logarithmiques (Log-Likelihood Ratio - LLR). Pour la mise en oeuvre pratique des décodeurs, il est important d'avoir une complexité faible mais avoir également une complexité constante est indispensable dans certaines applications. Nous proposons alors un décodeur adaptatif qui permet de sélectionner, parmi plusieurs algorithmes de décodage, celui qui est le plus adéquat selon la qualité du canal de transmission et la qualité de service souhaitée. Nous présentons une implémentation pratique du décodage adaptatif utilisant le décodeur SB-Stack paramétré. Le décodage des codes espace-temps peut être amélioré en le précédant par une phase de pré-traitement. En sortie de cette phase, la matrice du canal équivalente est mieux conditionnée ce qui permet de réduire la complexité d'un décodeur optimal et d'améliorer les performances d'un décodeur sous-optimal. Nous présentons et nous étudions alors les performances d'une chaine complète de décodage utilisant diverses techniques de pré-traitement combinées avec les décodeurs espace-temps étudiés précédemment.
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Bautista, Martín Miguel Ángel. « Learning error-correcting representations for multi-class problems ». Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/396124.
Texte intégralRésumé :
Real life is full of multi-class decision tasks. In the Pattern Recognition field, several method- ologies have been proposed to deal with binary problems obtaining satisfying results in terms of performance. However, the extension of very powerful binary classifiers to the multi-class case is a complex task. The Error-Correcting Output Codes framework has demonstrated to be a very powerful tool to combine binary classifiers to tackle multi-class problems. However, most of the combinations of binary classifiers in the ECOC framework overlook the underlay- ing structure of the multi-class problem. In addition, is still unclear how the Error-Correction of an ECOC design is distributed among the different classes.
In this dissertation, we are interested in tackling critic problems of the ECOC framework, such as the definition of the number of classifiers to tackle a multi-class problem, how to adapt the ECOC coding to multi-class data and how to distribute error-correction among different pairs of categories.
In order to deal with this issues, this dissertation describes several proposals. 1) We define a new representation for ECOC coding matrices that expresses the pair-wise codeword separability and allows for a deeper understanding of how error-correction is distributed among classes. 2) We study the effect of using a logarithmic number of binary classifiers to treat the multi-class problem in order to obtain very efficient models. 3) In order to search for very compact ECOC coding matrices that take into account the distribution of multi-class data we use Genetic Algorithms that take into account the constraints of the ECOC framework. 4) We propose a discrete factorization algorithm that finds an ECOC configuration that allocates the error-correcting capabilities to those classes that are more prone to errors. The proposed methodologies are evaluated on different real and synthetic data sets: UCI Machine Learning Repository, handwriting symbols, traffic signs from a Mobile Mapping System, and Human Pose Recovery. The results of this thesis show that significant perfor- mance improvements are obtained on traditional coding ECOC designs when the proposed ECOC coding designs are taken into account.En la vida cotidiana las tareas de decisión multi-clase surgen constantemente. En el campo de Reconocimiento de Patrones muchos métodos de clasificación binaria han sido propuestos obteniendo resultados altamente satisfactorios en términos de rendimiento. Sin embargo, la extensión de estos sofisticados clasificadores binarios al contexto multi-clase es una tarea compleja. En este ámbito, las estrategias de Códigos Correctores de Errores (CCEs) han demostrado ser una herramienta muy potente para tratar la combinación de clasificadores binarios. No obstante, la mayoría de arquitecturas de combinación de clasificadores binarios negligen la estructura del problema multi-clase. Sin embargo, el análisis de la distribución de corrección de errores entre clases es aún un problema abierto. En esta tesis doctoral, nos centramos en tratar problemas críticos de los códigos correctores de errores; la definición del número de clasificadores necesarios para tratar un problema multi-clase arbitrario; la adaptación de los problemas binarios al problema multi-clase y cómo distribuir la corrección de errores entre clases. Para dar respuesta a estas cuestiones, en esta tesis doctoral describimos varias propuestas. 1) Definimos una nueva representación para CCEs que expresa la separabilidad entre pares de códigos y nos permite una mejor comprensión de cómo se distribuye la corrección de errores entre distintas clases. 2) Estudiamos el efecto de usar un número logarítmico de clasificadores binarios para tratar el problema multi-clase con el objetivo de obtener modelos muy eficientes. 3) Con el objetivo de encontrar modelos muy eficientes que tienen en cuenta la estructura del problema multi-clase utilizamos algoritmos genéticos que tienen en cuenta las restricciones de los ECCs. 4) Pro- ponemos un algoritmo de factorización de matrices discreta que encuentra ECCs con una configuración que distribuye corrección de error a aquellas categorías que son más propensas a tener errores. Las metodologías propuestas son evaluadas en distintos problemas reales y sintéticos como por ejemplo: Repositorio UCI de Aprendizaje Automático, reconocimiento de símbolos escritos, clasificación de señales de tráfico y reconocimiento de la pose humana. Los resultados obtenidos en esta tesis muestran mejoras significativas en rendimiento comparados con los diseños tradiciones de ECCs cuando las distintas propuestas se tienen en cuenta.
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Teng, Sin Yong. « Intelligent Energy-Savings and Process Improvement Strategies in Energy-Intensive Industries ». Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-433427.
Texte intégralRésumé :
S tím, jak se neustále vyvíjejí nové technologie pro energeticky náročná průmyslová odvětví, stávající zařízení postupně zaostávají v efektivitě a produktivitě. Tvrdá konkurence na trhu a legislativa v oblasti životního prostředí nutí tato tradiční zařízení k ukončení provozu a k odstavení. Zlepšování procesu a projekty modernizace jsou zásadní v udržování provozních výkonů těchto zařízení. Současné přístupy pro zlepšování procesů jsou hlavně: integrace procesů, optimalizace procesů a intenzifikace procesů. Obecně se v těchto oblastech využívá matematické optimalizace, zkušeností řešitele a provozní heuristiky. Tyto přístupy slouží jako základ pro zlepšování procesů. Avšak, jejich výkon lze dále zlepšit pomocí moderní výpočtové inteligence. Účelem této práce je tudíž aplikace pokročilých technik umělé inteligence a strojového učení za účelem zlepšování procesů v energeticky náročných průmyslových procesech. V této práci je využit přístup, který řeší tento problém simulací průmyslových systémů a přispívá následujícím: (i)Aplikace techniky strojového učení, která zahrnuje jednorázové učení a neuro-evoluci pro modelování a optimalizaci jednotlivých jednotek na základě dat. (ii) Aplikace redukce dimenze (např. Analýza hlavních komponent, autoendkodér) pro vícekriteriální optimalizaci procesu s více jednotkami. (iii) Návrh nového nástroje pro analýzu problematických částí systému za účelem jejich odstranění (bottleneck tree analysis – BOTA). Bylo také navrženo rozšíření nástroje, které umožňuje řešit vícerozměrné problémy pomocí přístupu založeného na datech. (iv) Prokázání účinnosti simulací Monte-Carlo, neuronové sítě a rozhodovacích stromů pro rozhodování při integraci nové technologie procesu do stávajících procesů. (v) Porovnání techniky HTM (Hierarchical Temporal Memory) a duální optimalizace s několika prediktivními nástroji pro podporu managementu provozu v reálném čase. (vi) Implementace umělé neuronové sítě v rámci rozhraní pro konvenční procesní graf (P-graf). (vii) Zdůraznění budoucnosti umělé inteligence a procesního inženýrství v biosystémech prostřednictvím komerčně založeného paradigmatu multi-omics.
22
Zhao, Qian. « Network source coding : theory and code design for broadcast and multiple access networks ». Thesis, 2003. https://thesis.library.caltech.edu/2289/1/Zhao_Qian_thesis.pdf.
Texte intégralRésumé :
In the information age, network systems and applications have been growing rapidly to provide us with more versatile and high bit rate services. However, the limited bandwidth restricts the amount of information that can be sent through the networks. Thus efficient data representation or source coding is imperative for future network development. Distinct from the traditional source coding strategy, network source codes take advantage of the network topology and are able to maximally compress data before transmission.
In this thesis, I present a variety of source coding techniques for use in network environments and demonstrate the benefits of network source codes over traditional source codes from both theoretical and practical perspectives.
First, I address source coding for broadcast systems. The results I obtain include derivation of the theoretical limits of broadcast system source codes, algorithm design for optimal broadcast system vector quantizers, implementation of the optimal code, and experimental results.
Then, I focus on multiple access systems which are the dual systems of broadcast systems. I present the properties of multiple access source codes and generalize traditional entropy code design algorithms to attain the corresponding optimal multiple access source codes for arbitrary joint source statistics. I further introduce a family of polynomial complexity code design algorithms that approximates the optimal solutions. Application to universal coding for multiple access networks when the joint source statistics are unknown a priori is briefly discussed. Finally, I demonstrate algorithmic performance by showing experimental results on a variety of data sets.
Finally, in seeking a simple lossy source coding method for general networks, I apply entropy constrained dithered quantization in network source code design and present the coding results for multi-resolution source codes and multiple access source codes. Multi-resolution and multiple access dithered quantizers are low complexity codes that achieve performance very close to the theoretical rate-distortion bound.
23
« New adaptive transmission schemes for MC-CDMA systems ». 1999. http://library.cuhk.edu.hk/record=b5889950.
Texte intégralRésumé :
by Yin-Man Lee.Thesis (M.Phil.)--Chinese University of Hong Kong, 1999.
Includes bibliographical references (leaves 82-[87]).
Abstracts in English and Chinese.
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Overview of MC-CDMA --- p.1
Chapter 1.2 --- System Model --- p.3
Chapter 1.3 --- Receiver Optimization --- p.7
Chapter 1.4 --- Transmitter Optimization --- p.9
Chapter 1.5 --- Nonlinearly Constrained Optimization --- p.10
Chapter 1.6 --- Outline of Thesis --- p.11
Chapter 2 --- Centralized Transmitter Optimization for MC-CDMA Systems --- p.13
Chapter 2.1 --- Introduction --- p.13
Chapter 2.2 --- Problem Development --- p.15
Chapter 2.3 --- Lagrangian Optimization Approaches --- p.16
Chapter 2.3.1 --- Penalty Function Method --- p.17
Chapter 2.3.2 --- Barrier Function Method --- p.19
Chapter 2.3.3 --- Powell's Method and Augmented Lagrangian Method --- p.21
Chapter 2.4 --- Optimal FDMA System --- p.23
Chapter 2.5 --- Modified Centralized Optimization Schemes --- p.25
Chapter 2.6 --- Performance --- p.27
Chapter 2.6.1 --- Typical Behavior --- p.27
Chapter 2.6.2 --- Average Performance --- p.32
Chapter 2.7 --- Summary --- p.38
Chapter 3 --- Decentralized Transmitter Optimization for MC-CDMA Sys- tems --- p.39
Chapter 3.1 --- Introduction --- p.39
Chapter 3.2 --- System Model --- p.41
Chapter 3.3 --- Optimization --- p.42
Chapter 3.3.1 --- Receiver Optimization --- p.43
Chapter 3.3.2 --- Single-user Transmitter Optimization --- p.44
Chapter 3.3.3 --- Decentralized Transmission Scheme --- p.45
Chapter 3.3.4 --- Multirate Transmission with Decentralized Transmission Scheme --- p.47
Chapter 3.4 --- Performance --- p.48
Chapter 3.5 --- Summary --- p.57
Chapter 4 --- Performance Evaluation of Various Adaptive Transmission Schemes --- p.59
Chapter 4.1 --- Introduction --- p.59
Chapter 4.2 --- Comparison of Different Adaptive Transmission Schemes --- p.61
Chapter 4.3 --- Adaptive Transmission Schemes with K > M --- p.64
Chapter 4.4 --- Modified Adaptive Transmission Scheme with Graceful Degrada- tion in the SNR --- p.68
Chapter 4.5 --- Summary --- p.71
Chapter 5 --- Conclusions and Future Work --- p.73
Chapter 5.1 --- Conclusions --- p.73
Chapter 5.2 --- Future Work --- p.75
A The Hungarian Method for Optimal Frequency Assignment --- p.76
Bibliography --- p.82
24
Jaing, Ching-Huey, et 江慶慧. « New Power Control Method for Code Division Multiple Access based on Neural Network and Fuzzy Theory ». Thesis, 2003. http://ndltd.ncl.edu.tw/handle/17633249963034933318.
Texte intégralRésumé :
碩士樹德科技大學
電腦與通訊研究所
91
This thesis introduces a new application of neuro-fuzzy control theory to the power control in a multirate direct-sequence code-division multiple-access (DS-CDMA) cellular radio system. Emerging multimedia services in cellular radio systems introduce a variable transmission rate, meanwhile, the propagation channel of a radio system exhibits severe signal shadowing and multipath fading, which results in wide variation of signal-to-interference ratio (SIR) at the receiver. To tackle this problem, the combined control of power and transmission rate is used to maintain the desired link quality and thus achieve higher capacity and offers a user with multiple data rate simultaneously. In order to mitigate the channel variation effect precisely, a new application of neuro-fuzzy theory to the power control strategy is introduced in this thesis. Combining the approximate value in the fuzzy inference, and the detailed adjustment of the on-line learning in the neural networks, the output value can decrease the quantity the target value. Therefore, the system can predict the tendency in the signal fading and compensate the effect in the loop delay. The simulation results indicate that the neuro-fuzzy power control provides higher average transmission rate, lower probability of unsuccessful transmission, and less outage probability than the previous mechanisms.
25
« Coherent optical code division multiple access based on superstructure fiber bragg grating encoders and decoders ». 2003. http://library.cuhk.edu.hk/record=b5891483.
Texte intégralRésumé :
Li Xin.Thesis (M.Phil.)--Chinese University of Hong Kong, 2003.
Includes bibliographical references (leaves 81-86).
Abstracts in English and Chinese.
COHERENT OPTICAL CODE DIVISION MULTIPLE ACCESS BASED ON SUPERSTRUCTURE FIBER BRAGG GRATING ENCODERS AND DECODERS --- p.1
ACKNOWLEDGEMENT --- p.2
ABSTRACT --- p.III
摘要 --- p.V
CONTENTS --- p.VI
LIST OF FIGURES --- p.1
Chapter CHAPTER 1 --- INTRODUCTION --- p.3
Chapter 1.1 --- Overview of OCDMA --- p.3
Chapter 1.2 --- Classification of OCDMA Schemes --- p.6
Chapter 1.3 --- Introduction of Coherent OCDMA Schemes --- p.9
Chapter 1.4 --- Introduction of superstructure Fiber Bragg Gratings and Other Encoding and Decoding Components --- p.10
Chapter 1.5 --- Outline of the Thesis --- p.13
Chapter CHAPTER 2 --- COUPLED MODE THEORY AND SUPERSTRUCTURE FIBER BRAGG GRATING SIMULATION MODEL --- p.16
Chapter 2.1 --- Fiber Bragg Grating Model Based on Coupled Mode Theory --- p.16
Chapter 2.1.1 --- Introduction of FBG and the Coupled Mode Theory --- p.16
Chapter 2.1.2 --- FBG Model Based on CMT --- p.18
Chapter 2.1.3 --- FBG Model When there are Phase Discontinuities Between Different Parts --- p.20
Chapter 2.2 --- Properties of Fiber Bragg Gratings --- p.22
Chapter 2.3 --- Simulation Model of superstructure Fiber Bragg Gratings --- p.27
Chapter 2.4 --- Summary --- p.31
Chapter CHAPTER 3 --- COHERENT OCDMA CODING SCHEME BASED ON THE SUPERSTRUCTURE FIBER BRAGG GRATING ENCODER/DECODER --- p.33
Chapter 3.1 --- Introduction and Theoretical Derivation of the Coding Scheme --- p.33
Chapter 3.1.1 --- Introduction of the Coding Scheme --- p.33
Chapter 3.1.2 --- Derivation of SSFBG Encoder --- p.34
Chapter 3.1.3 --- Encoding for the SSFBG --- p.39
Chapter 3.2 --- Introduction of the Simulation Model and the Research on It …… --- p.44
Chapter 3.3 --- Summary --- p.47
Chapter CHAPTER 4 --- RESEARCH ON THE SIMULATED COHERENT OCDMA SYSTEM IN IDEAL CASE --- p.48
Chapter 4.1 --- Introduction of the ideal case and factors that affect the system performance --- p.48
Chapter 4.2 --- Effects by Refractive Index Modulation of the SSFBG Encoder --- p.49
Chapter 4.3 --- Effects by Code Type --- p.54
Chapter 4.4 --- Effect by the Code Length --- p.57
Chapter 4.5 --- Summary --- p.60
Chapter CHAPTER 5 --- RESEARCH ON THE SIMULATED COHERENT OCDMA SYSTEM IN PRACTICAL ENVIRONMENT --- p.62
Chapter 5.1 --- Introduction --- p.62
Chapter 5.2 --- Comparison of System Performance in Synchronous and Asynchronous Cases --- p.63
Chapter 5.3 --- Discussion on the System Performance When Users are In Different Power Levels --- p.65
Chapter 5.4 --- Analysis of Channel Noise In the Coherent OCDMA System --- p.68
Chapter 5.5 --- Summary --- p.70
Chapter CHAPTER 6 --- CONCLUSIONS AND FUTURE WORK --- p.72
Chapter 6.1 --- Conclusions --- p.72
Chapter 6.2 --- Future Work --- p.75
APPENDIX A PROOF OF SSFBG THEORETICAL MODEL APPROXIMATION --- p.77
"APPENDIX B RANDOM SEQUENCE, M-SEQUENCE AND WALSH SEQUENCE" --- p.80
REFERENCES --- p.81
26
« Coding schemes for multicode CDMA systems ». 2003. http://library.cuhk.edu.hk/record=b5891482.
Texte intégralRésumé :
Zhao Fei.Thesis (M.Phil.)--Chinese University of Hong Kong, 2003.
Includes bibliographical references (leaves 87-89).
Abstracts in English and Chinese.
Chapter 1. --- Introduction --- p.1
Chapter 1.1 --- Multirate Scheme --- p.2
Chapter 1.1.1 --- VSF Scheme --- p.3
Chapter 1.1.2 --- Multicode Scheme --- p.5
Chapter 1.2 --- Multicode CDMA System --- p.7
Chapter 1.2.1 --- System Model --- p.7
Chapter 1.2.2 --- Envelope Variation of Multicode Signal --- p.9
Chapter 1.2.3 --- Drawback of Multicode Scheme --- p.11
Chapter 1.3 --- Organization of the Thesis --- p.13
Chapter 2. --- Related Work on Minimization of PAP of Multicode CDMA --- p.15
Chapter 2.1 --- Constant Amplitude Coding --- p.16
Chapter 2.2 --- Multidimensional Multicode Scheme --- p.22
Chapter 2.3 --- Precoding for Multicode Scheme --- p.25
Chapter 2.4 --- Summary --- p.26
Chapter 3. --- Multicode CDMA System with Constant Amplitude Transmission --- p.27
Chapter 3.1 --- System Model --- p.28
Chapter 3.2 --- Selection of Hadamard Code Sequences --- p.31
Chapter 3.3 --- The Optimal Receiver for the Multicode System --- p.37
Chapter 3.3.1 --- The Maximum-Likelihood Sequence Detector --- p.38
Chapter 3.3.2 --- Maximum A Posteriori Probability Detector --- p.41
Chapter 4. --- Multicode CDMA System Combined with Error-Correcting Codes --- p.45
Chapter 4.1 --- Hamming Codes --- p.46
Chapter 4.2 --- Gallager's Codes --- p.48
Chapter 4.2.1 --- Encoding of Gallager's Codes --- p.48
Chapter 4.2.2 --- Multicode Scheme combined with Gallager's Code --- p.52
Chapter 4.2.3 --- Iterative Decoding of the Multicode Scheme --- p.55
Chapter 4.3 --- Zigzag Codes --- p.59
Chapter 4.4 --- Simulation Results and Discussion --- p.62
Chapter 5. --- Multicode CDMA System with Bounded PAP Transmission --- p.68
Chapter 5.1 --- Quantized Multicode Scheme --- p.69
Chapter 5.1.1 --- System Model --- p.69
Chapter 5.1.2 --- Interference of Code Channels --- p.71
Chapter 5.2 --- Parallel Multicode Scheme --- p.74
Chapter 5.2.1 --- System Model --- p.74
Chapter 5.2.2 --- Selection of Hadamard Code Sequences --- p.75
Chapter 6. --- Conclusions and Future Work --- p.82
Chapter 6.1 --- Conclusions --- p.82
Chapter 6.2 --- Future Work --- p.84
Bibliography --- p.87
27
Bejide, Emmanuel Oluremi. « Combined turbo coding and interference rejection for DS-CDMA ». Thesis, 2004. http://hdl.handle.net/10413/3978.
Texte intégralRésumé :
This dissertation presents interference cancellation techniques for both the Forward Error
Correction (FEC) coded and the uncoded Direct Sequence Code Division Multiple
Access (DS-CDMA) systems. Analytical models are also developed for the adaptive and
the non-adaptive Parallel Interference Cancellation (PlC) receivers. Results that are
obtained from the computer simulations of the PlC receiver types confirm the accuracy of
the analytical models that are developed. Results show that the Least Mean Square
(LMS) algorithm based adaptive PlC receivers have bit error rate performances that are
better than those of the non-adaptive PlC receivers.
In the second part of this dissertation, a novel iterative multiuser detector for the Turbo
coded DS-CDMA system is developed. The performance of the proposed receiver in the
multirate CDMA system is also investigated. The developed receiver is found to have an
error rate performance that is very close to the single user limit after a few numbers of
iterations. The receiver is also resilient against the near-far effect. A methodology is also
presented on the use of the Gaussian approximation method in the convergence analysis
of iterative interference cancellation receivers for turbo coded DS-CDMA systems.Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2004.
28
Cheung, Peter Koon Pong. « Blind linear multiuser detection for DS-CDMA wireless networks ». Phd thesis, 1999. http://hdl.handle.net/1885/144946.
Texte intégral
29
Garg, Gagan. « Analysis Of A Sieving Heuristic For The Number Field Sieve And Design Of Low-Correlation CDMA Sequences ». Thesis, 2009. http://hdl.handle.net/2005/1026.
Texte intégralRésumé :
In this thesis, we investigate in detail, certain important problems in cryptography and coding theory.
In the first part of this thesis, we discuss the number field sieve and compare the two ways in which the sieving step is implemented -one method using the line sieve and the other using the lattice sieve. We discuss why the lattice sieve performs better than the line sieve in the presence of large primes -this has not been attempted before.
In the second part of this thesis, we design low-correlation CDMA sequences over the Quadrature Amplitude Modulation (QAM) alphabet. The sequences proposed in this thesis have the lowest value of the maximum correlation parameter as compared to any other family in the literature.
In the third part of this thesis, we design large families of optimal two-dimensional optical orthogonal codes for optical CDMA. The size of these codes is larger than any other code in the literature.
30
Byers, Geoffrey James. « Concatenated space-time codes in Rayleigh fading channels ». Thesis, 2002. http://hdl.handle.net/10413/4050.
Texte intégralRésumé :
The rapid growth of wireless subscribers and services as well as the increased use of internet
services, suggest that wireless internet access will increase rapidly over the next few years.
This will require the provision of high data rate wireless communication services. However
the problem of a limited and expensive radio spectrum coupled with the problem of the
wireless fading channel makes it difficult to provide these services. For these reasons, the
research area of high data rate, bandwidth efficient and reliable wireless communications
is currently receiving much attention.
Concatenated codes are a class of forward error correction codes which consist of two or
more constituent codes. These codes achieve reliable communications very close to the
Shannon limit provided that sufficient diversity, such as temporal or spatial diversity, is
available. Space-time trellis codes (STTCs) merge channel coding and transmit antenna
diversity to improve system capacity and performance. The main focus of this dissertation
is on STTCs and concatenated STTCs in quasi-static and rapid Rayleigh fading channels.
Analytical bounds are useful in determining the behaviour of a code at high SNRs where
it becomes difficult to generate simulation results. A novel method is proposed to analyse
the performance of STTCs and the accuracy of this analysis is compared to simulation
results where it is shown to closely approximate system performance.
The field of concatenated STTCs has already received much attention and has shown
improved performance over conventional STTCs. It was recently shown that double concatenated
convolutional codes in AWGN channels outperform simple concatenated codes.
Motivated by this, two double concatenated STTC structures are proposed and their performance is compared to that of a simple concatenated STTCs. It is shown that double
concatenated STTCs outperform simple concatenated STTCs in rapid Rayleigh fading
channels. An analytical model for this system in rapid fading is developed which combines
the proposed analytical method for STTCs with existing analytical techniques for
concatenated convolutional codes.
The final part of this dissertation considers a direct-sequencejslow-frequency-hopped (DSj
SFH) code division multiple access (CDMA) system with turbo coding and multiple transmit
antennas. The system model is modified to include a more realistic, time correlated
Rayleigh fading channel and the use of side information is incorporated to improve the
performance of the turbo decoder. Simulation results are presented for this system and it
is shown that the use of transmit antenna diversity and side information can be used to improve system performance.Thesis (M.Sc.Eng.)-University of Natal, Durban, 2002.
31
Anderson, Kevin. « Practical multiuser detection algorithms for CDMA ». Thesis, 1999. https://vuir.vu.edu.au/18140/.
Texte intégralRésumé :
The aim of this thesis is to investigate practical multiuser demodulation algorithms for mobile
communications systems that are based on code division multiple access (CDMA) technologies. These
include the adaptive receiver and the interference canceller. The overall complexity of implementing them
is examined. The effects of the proposed algorithms on reducing of multiple access interference (MAI)
and their resistance to the Near Far Effect (NFE) will be explored.
32
Singh, Navin Runjit. « Multiuser demodulation for DS-CDMA systems in fading channels ». Thesis, 2000. http://hdl.handle.net/10413/5534.
Texte intégralRésumé :
The problems of optimal as well as suboptimal detection for CDMA
transmissions over an additive white Gaussian noise (AWGN) channel, have
been the focus of study in the recent past. However, CDMA transmissions
are frequently made over channels which exhibit fading and/or dispersion;
hence receivers need to be designed which take into account this behaviour.
In spite of the major research effort invested in multiuser demodulation
techniques, several practical as well as theoretical open problems still exist.
Some of them are considered in more detail in this thesis. The aim of the
thesis is to develop multiuser demodulation algorithms for mobile
communication systems in frequency-selective fading channels, and to
analyze their implementation complexity. The emphasis is restricted to the
uplink of an asynchronous DS-CDMA system where the users transmit in an
uncoordinated manner and are received by one centralized receiver.
The original work that is undertaken for the MScEng study is the evaluation
of a multiuser receiver structure for a frequency-selective fading channel,
where there exists a steady specular path and two fading paths.
Furthermore, the effect of using selection diversity is investigated by
examining the bit error rate, asymptotic multi user efficiency and near-far
resistance of the proposed detector structure. These results are confirmed
both analytically and by simulation in the thesis. An investigation is also
conducted into the application of neural networks to the problem of
multiuser detection in code division multiple access systems. The neural
network will be used as a classifier in an adaptive receiver which
incorporates an extended Kalman filter for joint amplitude and delay
estimation. Finally, some open problems for future research will be pointed
out in the thesis.
Keywords: AWGN channel , DS-CDMA system, frequency-selective,
multi user demodulation, asymptotic multiuser efficiency, near-far resistance,
neural network, Kalman filter.Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
33
« Multiple trellis coded 16 QAM ». Chinese University of Hong Kong, 1994. http://library.cuhk.edu.hk/record=b5888189.
Texte intégralRésumé :
by Kingsley, King-chi, Kwan.Thesis (M.Phil.)--Chinese University of Hong Kong, 1994.
Includes bibliographical references (leaves 85-88).
Tables of Contents
Lists of Figures & Tables
Acknowledgments
Abstract
Chapter Chapter 1 --- Introduction
Chapter 1.1 --- Digital Communication System --- p.P. 1
Chapter 1.2 --- Channel Coding --- p.P. 1
Chapter 1.3 --- Convolution Encoder --- p.P. 4
Chapter 1.4 --- Additive White Gaussian Noise (AWGN) Channel --- p.P. 7
Chapter 1.5 --- Trellis Diagram --- p.P. 8
Chapter 1.6 --- Error Event and Free Distance --- p.P. 8
Chapter 1.7 --- Euclidean Distance --- p.P. 10
Chapter 1.8 --- Organization of the Thesis --- p.P. 11
Chapter Chapter 2 --- QAM and MTCM
Chapter 2.1 --- Introduction --- p.P. 13
Chapter 2.2 --- M-ary Quadrature Amplitude Modulation (QAM)
Chapter 2.2.1 --- M-ary Digital Modulation --- p.P. 13
Chapter 2.2.2 --- Quadrature Amplitude Modulation (QAM) --- p.P. 14
Chapter 2.2.3 --- Probability of Bit Error of M-ary QAM --- p.P. 16
Chapter 2.3 --- Trellis Coded Modulation (TCM) --- p.P. 17
Chapter 2.4 --- Multiple Trellis Coded Modulation (MTCM) --- p.P. 19
Chapter Chapter 3 --- Set Partitioning of Signal Sets
Chapter 3.1 --- Introduction --- p.P. 21
Chapter 3.2 --- Traditional Set Partitioning Methods
Chapter 3.2.1 --- Ungerboeck's Set Partitioning Method --- p.P. 21
Chapter 3.22 --- Set Partitioning by M.K. Simon and D. Divsalvar --- p.P. 23
Chapter 3.3 --- The new Set Partitioning Method
Chapter 3.3.1 --- Nomenclature of the Signal Points in the Signal Constellations --- p.P. 24
Chapter 3.3.2 --- Generation of the Signal Sets --- p.P. 26
Chapter 3.3.3 --- Partitioning of the Signal Sets
Chapter 3.3.3.1 --- Input Constraints of the Partitioning Method --- p.P. 30
Chapter 3.3.3.2 --- The Set Partitioning Method --- p.P. 30
Chapter 3.3.4 --- Distance Properties of the Partitioned Signal Sets --- p.P. 36
Chapter 3.3.5 --- The Selection Scheme --- p.P. 39
Chapter 3.3.6 --- Assignment of Signal Subsets into Trellis --- p.P. 42
Chapter Chapter 4 --- Performance Evaluation
Chapter 4.1 --- Introduction --- p.P. 46
Chapter 4.2 --- Upper Bound of Error Probability
Chapter 4.2.1 --- Probability of Symbol Error --- p.P. 46
Chapter 4.2.1.1 --- Upper Bound on Probability of Symbol Error --- p.P. 48
Chapter 4.2.1.2 --- Computation of the Transfer Function --- p.P. 49
Chapter 4.2.2 --- Probability of Bit Error --- p.P. 51
Chapter 4.3 --- Computation of the Free Distance --- p.P. 53
Chapter Chapter 5 --- Results Presentation and Discussions
Chapter 5.1 --- Introduction --- p.P. 58
Chapter 5.2 --- Results Presentations
Chapter 5.2.1 --- Normalized Square Free Euclidean Distance --- p.P. 58
Chapter 5.2.2 --- Error Probability --- p.P. 71
Chapter 5.3 --- Discussions --- p.P. 77
Chapter Chapter 6 --- Conclusions --- p.P. 83
Bibliography --- p.P. 85
Chapter Appendix A - --- Flowchart of the Program --- p.P. 89
Chapter Appendix B - --- Tabulated Results of d2free --- p.P. 104
34
Paluncic, Filip. « Multiple insertion/deletion correcting and detecting codes : structural analysis, constructions and applications ». Thesis, 2012. http://hdl.handle.net/10210/5366.
Texte intégralRésumé :
D.Ing.This thesis is dedicated to an analysis of fundamental topics and issues related to deterministic insertion/deletion correcting and detecting codes. The most important contributions in this respect are the construction of a multiple insertion/deletion correcting code for run-length limited sequences and the construction and applications of multiple deletion (insertion) detecting codes. It is shown how run-length constraints and higher order moments can be combined to create a code which is simultaneously multiple insertion/deletion error correcting and runlength constrained. A systematic form of this code is presented, whereby any arbitrary run-length constrained sequence can be made into a multiple insertion/deletion correcting codeword by adding a prefix. This prefix is appended to the run-length constrained sequence in such a way that the resulting codeword is itself run-length constrained. Furthermore, it is shown that, despite the run-length constraints, the resulting code is guaranteed to have a better asymptotic rate than the Helberg code, the only other known non-trivial deterministic multiple insertion/deletion correcting code. We consider insertion/deletion detecting codes and present a multiple deletion (insertion) detecting code. It is shown that this code, which is systematic, is optimal in the sense that there exists no other systematic multiple deletion (insertion) detecting code with a better rate. Furthermore, we present a number of applications of such codes. In addition, further related topics of interest are considered. Firstly, jitter as a fundamental cause of insertion/deletion errors is investigated and as a result a counterpart to the signal-to-noise ratio in the amplitude domain is proposed for the time domain. Secondly, motivated by the correspondence of Levenshtein and Varshamov-Tenengol’ts codes, we investigate the insertion/deletion correcting capability of the single asymmetric error correcting Constantin-Rao codes within a wider framework of asymmetric error correcting and insertion/deletion correcting code structure correspondences. Finally, we propose a generalisation of Tenengol’ts’ construction for multiple non-binary insertion/deletion correction.
35
Gor, Leon. « Complexity reduction in multiple input multiple output algorithms ». 2007. http://eprints.vu.edu.au/1409/1/gor.pdf.
Texte intégralRésumé :
Wireless communication devices are currently enjoying increasing popularity and widespread use. The constantly growing number of users, however, results in the shortage of the available spectrum. Various techniques have been proposed to increase the spectrum efficiency of wireless systems to solve the problem. Multiple Input Multiple Output (MIMO) is one solution that employs multiple antennas at the transmitter and receiver. The MIMO algorithms are usually highly complex and computationally intensive. This results in increased power consumption and reduced battery lifespan. This thesis investigates the complexity – performance trade-off of two MIMO algorithms. Space Time Block Coding (STBC) is a MIMO-based algorithm, which efficiently exploits spatial and temporal diversity. Recently, it has been specified in a number of 3G standards. However, not much attention has been paid to the implementation issues of this algorithm. One such issue, clipping of the Analog to Digital Converter (ADC) at the receiver, is described in the first part of the thesis (chapter 3). A small amount of clipping in an ADC can improve dynamic range and reduce the power consumption. However, the increased clipping distortion of the signal, can adversely affect the overall performance of the system. It will be shown in this dissertation that STBC are more sensitive to clipping, compared to the uncoded single antenna systems. Two receiver structures are considered: Direct Conversion (DC) structure, where the ADCs impose a square clipping function, and a Log-Polar structure, where ADC induces a circular clipping function. Log-Polar receivers were found to be clipping insensitive for the given target Symbol Error Rate (SER) of 1*10-3. This makes Log-Polar receivers an obvious choice for the system designers. The second part of the thesis (chapter 4) addresses the complexity problem associated with the QR decomposition algorithm, which is frequently used as a faster alternative to channel inversion in a MIMO scheme. Channel tracking can be employed with QR equalization in order to reduce the pilot overhead of a MIMO system in a non-stationary environment. QR decomposition is part of the QR equalization method and has to be performed in every instance that the channel estimate is obtained. The high rate of the QR decomposition, a computationally intensive technique, results in a high computational complexity per symbol. Some novel modifications are proposed to address this problem. Reducing the repetition rate of QR decompositions and tracking R (the upper triangular matrix) directly, while holding unitary matrix Q fixed, can significantly reduce complexity per symbol at the expense of some introduced error. Additional modification of the CORDIC algorithm (a square root- and division-free algorithm used to perform QR decomposition) results in more than 80% of computational complexity savings. Further, Minimum Mean Squared Error (MMSE) detection is applied to Least Mean Squared (LMS) based R tracking and channel tracking algorithms and then compared in complexity and performance to the Recursive Least Squares Decision Feedback Equalizer (RLS-DFE) tracking system in [1]. The R tracking scheme is shown to achieve more accurate channel estimates compared to the channel tracking scenario, but this advantage does not translate into better Bit Error Rate (BER) results due to errors on the first layer of the detector. Both LMS strategies have an inferior BER performance compared to the DFE RLS-based system of [1], and surprisingly the LMS schemes show no significant complexity improvement.
36
Gor, Leon. « Complexity reduction in multiple input multiple output algorithms ». Thesis, 2007. https://vuir.vu.edu.au/1409/.
Texte intégralRésumé :
Wireless communication devices are currently enjoying increasing popularity and widespread use. The constantly growing number of users, however, results in the shortage of the available spectrum. Various techniques have been proposed to increase the spectrum efficiency of wireless systems to solve the problem. Multiple Input Multiple Output (MIMO) is one solution that employs multiple antennas at the transmitter and receiver. The MIMO algorithms are usually highly complex and computationally intensive. This results in increased power consumption and reduced battery lifespan. This thesis investigates the complexity – performance trade-off of two MIMO algorithms. Space Time Block Coding (STBC) is a MIMO-based algorithm, which efficiently exploits spatial and temporal diversity. Recently, it has been specified in a number of 3G standards. However, not much attention has been paid to the implementation issues of this algorithm. One such issue, clipping of the Analog to Digital Converter (ADC) at the receiver, is described in the first part of the thesis (chapter 3). A small amount of clipping in an ADC can improve dynamic range and reduce the power consumption. However, the increased clipping distortion of the signal, can adversely affect the overall performance of the system. It will be shown in this dissertation that STBC are more sensitive to clipping, compared to the uncoded single antenna systems. Two receiver structures are considered: Direct Conversion (DC) structure, where the ADCs impose a square clipping function, and a Log-Polar structure, where ADC induces a circular clipping function. Log-Polar receivers were found to be clipping insensitive for the given target Symbol Error Rate (SER) of 1*10-3. This makes Log-Polar receivers an obvious choice for the system designers. The second part of the thesis (chapter 4) addresses the complexity problem associated with the QR decomposition algorithm, which is frequently used as a faster alternative to channel inversion in a MIMO scheme. Channel tracking can be employed with QR equalization in order to reduce the pilot overhead of a MIMO system in a non-stationary environment. QR decomposition is part of the QR equalization method and has to be performed in every instance that the channel estimate is obtained. The high rate of the QR decomposition, a computationally intensive technique, results in a high computational complexity per symbol. Some novel modifications are proposed to address this problem. Reducing the repetition rate of QR decompositions and tracking R (the upper triangular matrix) directly, while holding unitary matrix Q fixed, can significantly reduce complexity per symbol at the expense of some introduced error. Additional modification of the CORDIC algorithm (a square root- and division-free algorithm used to perform QR decomposition) results in more than 80% of computational complexity savings. Further, Minimum Mean Squared Error (MMSE) detection is applied to Least Mean Squared (LMS) based R tracking and channel tracking algorithms and then compared in complexity and performance to the Recursive Least Squares Decision Feedback Equalizer (RLS-DFE) tracking system in [1]. The R tracking scheme is shown to achieve more accurate channel estimates compared to the channel tracking scenario, but this advantage does not translate into better Bit Error Rate (BER) results due to errors on the first layer of the detector. Both LMS strategies have an inferior BER performance compared to the DFE RLS-based system of [1], and surprisingly the LMS schemes show no significant complexity improvement.
37
Ganesan, T. « Source And Channel Coding Techniques for The MIMO Reverse-link Channel ». Thesis, 2014. http://etd.iisc.ernet.in/handle/2005/2694.
Texte intégralRésumé :
In wireless communication systems, the use of multiple antennas, also known as Multiple-Input Multiple-Output(MIMO) communications, is now a widely accepted and important technology for improving their reliability and throughput performance. However, in order to achieve the performance gains predicted by the theory, the transmitter and receiver need to have accurate and up-to-date Channel State Information(CSI) to overcome the vagaries of the fading environment. Traditionally, the CSI is obtained at the receiver by sending a known training sequence in the forward-link direction. This CSI has to be conveyed to the transmitter via a low-rate, low latency and noisy feedback channel in the reverse-link direction. This thesis addresses three key challenges in sending the CSI to the transmitter of a MIMO communication system over the reverse-link channel, and provides novel solutions to them.
The first issue is that the available CSI at the receiver has to be quantized to a finite number of bits, sent over a noisy feedback channel, reconstructed at the transmitter, and used by the transmitter for precoding its data symbols. In particular, the CSI quantization technique has to be resilient to errors introduced by the noisy reverse-link channel, and it is of interest to design computationally simple, linear filters to mitigate these errors. The second issue addressed is the design of low latency and low decoding complexity error correction codes to provide protection against fading conditions and noise in the reverse-link channel. The third issue is to improve the resilience of the reverse-link channel to fading.
The solution to the first problem is obtained by proposing two classes of receive filtering techniques, where the output of the source decoder is passed through a filter designed to reduce the overall distortion including the effect of the channel noise. This work combines the high resolution quantization theory and the optimal Minimum Mean Square Error(MMSE) filtering formulation to analyze, and optimize, the total end-to-end distortion. As a result, analytical expressions for the linear receive filters are obtained that minimize the total end-to-end distortion, given the quantization scheme and source(channel state) distribution. The solution to the second problem is obtained by proposing a new family of error correction codes, termed trellis coded block codes, where a trellis code and block code are concatenated in order to provide good coding gain as well as low latency and low complexity decoding. This code construction is made possible due to the existence of a uniform partitioning of linear block codes. The solution to the third problem is obtained by proposing three novel transmit precoding methods that are applicable to time-division-duplex systems, where the channel reciprocity can be exploited in designing the precoding scheme. The proposed precoding methods convert the Rayleigh fading MIMO channel into parallel Additive White Gaussian Noise(AWGN) channels with fixed gain, while satisfying an average transmit power constraint. Moreover, the receiver does not need to have knowledge of the CSI in order to decode the received data. These precoding methods are also extended to Rayleigh fading multi-user MIMO channels.
Finally, all the above methods are applied to the problem of designing a low-rate, low-latency code for the noisy and fading reverse-link channel that is used for sending the CSI. Simulation results are provided to demonstrate the improvement in the forward-link data rate due to the proposed methods. Note that, although the three solutions are presented in the context of CSI feedback in MIMO communications, their development is fairly general in nature, and, consequently, the solutions are potentially applicable in other communication systems also.
38
Natarajan, Lakshmi Prasad. « Low-Complexity Decoding and Construction of Space-Time Block Codes ». Thesis, 2013. http://etd.iisc.ernet.in/2005/3372.
Texte intégralRésumé :
Space-Time Block Coding is an efficient communication technique used in multiple-input multiple-output wireless systems. The complexity with which a Space-Time Block Code (STBC) can be decoded is important from an implementation point of view since it directly affects the receiver complexity and speed. In this thesis, we address the problem of designing low complexity decoding techniques for STBCs, and constructing STBCs that achieve high rate and full-diversity with these decoders. This thesis is divided into two parts; the first is concerned with the optimal decoder, viz. the maximum-likelihood (ML) decoder, and the second with non-ML decoders.
An STBC is said to be multigroup ML decodable if the information symbols encoded by it can be partitioned into several groups such that each symbol group can be ML decoded independently of the others, and thereby admitting low complexity ML decoding. In this thesis, we first give a new framework for constructing low ML decoding complexity STBCs using codes over the Klein group, and show that almost all known low ML decoding complexity STBCs can be obtained by this method. Using this framework we then construct new full-diversity STBCs that have the least known ML decoding complexity for a large set of choices of number of transmit antennas and rate. We then introduce the notion of Asymptotically-Good (AG) multigroup ML decodable codes, which are families of multigroup ML decodable codes whose rate increases linearly with the number of transmit antennas. We give constructions for full-diversity AG multigroup ML decodable codes for each number of groups g > 1. For g > 2, these are the first instances of g-group ML decodable codes that are AG or have rate more than 1. For g = 2 and identical delay, the new codes match the known families of AG codes in terms of rate. In the final section of the first part we show that the upper triangular matrix R encountered during the sphere-decoding of STBCs can be rank-deficient, thus leading to higher sphere-decoding complexity, even when the rate is less than the minimum of the number of transmit antennas and the number receive antennas. We show that all known AG multigroup ML decodable codes suffer from such rank-deficiency, and we explicitly derive the sphere-decoding complexities of most known AG multigroup ML decodable codes.
In the second part of this thesis we first study a low complexity non-ML decoder introduced by Guo and Xia called Partial Interference Cancellation (PIC) decoder. We give a new full-diversity criterion for PIC decoding of STBCs which is equivalent to the criterion of Guo and Xia, and is easier to check. We then show that Distributed STBCs (DSTBCs) used in wireless relay networks can be full-diversity PIC decoded, and we give a full-diversity criterion for the same. We then construct full-diversity PIC decodable STBCs and DSTBCs which give higher rate and better error performance than known multigroup ML decodable codes for similar decoding complexity, and which include other known full-diversity PIC decodable codes as special cases. Finally, inspired by a low complexity essentially-ML decoder given by Sirianunpiboon et al. for the two and three antenna Perfect codes, we introduce a new non-ML decoder called Adaptive Conditional Zero-Forcing (ACZF) decoder which includes the technique of Sirianunpiboon et al. as a special case. We give a full-diversity criterion for ACZF decoding, and show that the Perfect codes for two, three and four antennas, the Threaded Algebraic Space-Time code, and the 4 antenna rate 2 code of Srinath and Rajan satisfy this criterion. Simulation results show that the proposed decoder performs identical to ML decoding for these five codes. These STBCs along with ACZF decoding have the best error performance with least complexity among all known STBCs for four or less transmit antennas.
39
Rajan, G. Susinder. « Low Decoding Complexity Space-Time Block Codes For Point To Point MIMO Systems And Relay Networks ». Thesis, 2008. http://hdl.handle.net/2005/742.
Texte intégralRésumé :
It is well known that communication using multiple antennas provides high data rate and reliability. Coding across space and time is necessary to fully exploit the gains offered by multiple input multiple output (MIMO) systems. One such popular method of coding for MIMO systems is space-time block coding. In applications where the terminals do not have enough physical space to mount multiple antennas, relaying or cooperation between multiple single antenna terminals can help achieve spatial diversity in such scenarios as well. Relaying techniques can also help improve the range and reliability of communication. Recently it has been shown that certain space-time block codes (STBCs) can be employed in a distributed fashion in single antenna relay networks to extract the same benefits as in point to point MIMO systems. Such STBCs are called distributed STBCs. However an important practical issue with STBCs and DSTBCs is its associated high maximum likelihood (ML) decoding complexity. The central theme of this thesis is to systematically construct STBCs and DSTBCs applicable for various scenarios such that are amenable for low decoding complexity.
The first part of this thesis provides constructions of high rate STBCs from crossed product algebras that are minimum mean squared error (MMSE) optimal, i.e., achieves the least symbol error rate under MMSE reception. Moreover several previous constructions of MMSE optimal STBCs are found to be special cases of the constructions in this thesis.
It is well known that STBCs from orthogonal designs offer single symbol ML decoding along with full diversity but the rate of orthogonal designs fall exponentially with the number of transmit antennas. Thus it is evident that there exists a tradeoff between rate and ML decoding complexity of full diversity STBCs. In the second part of the thesis, a definition of rate of a STBC is proposed and the problem of optimal tradeoff between rate and ML decoding complexity is posed. An algebraic framework based on extended Clifford algebras is introduced to study the optimal tradeoff for a class of multi-symbol ML decodable STBCs called ‘Clifford unitary weight (CUW) STBCs’ which include orthogonal designs as a special case. Code constructions optimally meeting this tradeoff are also obtained using extended Clifford algebras. All CUW-STBCs achieve full diversity as well.
The third part of this thesis focusses on constructing DSTBCs with low ML decoding complexity for two hop, amplify and forward based relay networks under various scenarios. The symbol synchronous, coherent case is first considered and conditions for a DSTBC to be multi-group ML decodable are first obtained. Then three new classes of four-group ML decodable full diversity DSTBCs are systematically constructed for arbitrary number of relays. Next the symbol synchronous non-coherent case is considered and full diversity, four group decodable distributed differential STBCs (DDSTBCs) are constructed for power of two number of relays. These DDSTBCs have the best error performance compared to all previous works along with low ML decoding complexity. For the symbol asynchronous, coherent case, a transmission scheme based on orthogonal frequency division multiplexing (OFDM) is proposed to mitigate the effects of timing errors at the relay nodes and sufficient conditions for a DSTBC to be applicable in this new transmission scheme are given. Many of the existing DSTBCs including the ones in this thesis are found to satisfy these sufficient conditions. As a further extension, differential encoding is combined with the proposed transmission scheme to arrive at a new transmission scheme that can achieve full diversity in symbol asynchronous, non-coherent relay networks with no knowledge of the timing errors at the relay nodes. The DDSTBCs in this thesis are proposed for application in the proposed transmission scheme for symbol asynchronous, non-coherent relay networks. As a parallel to the non-coherent schemes based on differential encoding, we also propose non-coherent schemes for symbol synchronous and symbol asynchronous relay networks that are based on training. This training based transmission scheme leverages existing coherent DSTBCs for non-coherent communication in relay networks. Simulations show that this training scheme when used along with the coherent DSTBCs in this thesis outperform the best known DDSTBCs in the literature.
Finally, in the last part of the thesis, connections between multi-group ML decodable unitary weight (UW) STBCs and groups with real elements are established for the first time. Using this connection, we translate the necessary and sufficient conditions for multi-group ML decoding of UW-STBCs entirely in group theoretic terms. We discuss various examples of multi-group decodable UW-STBCs together with their associated groups and list the real elements involved. These examples include orthogonal designs, quasi-orthogonal designs among many others.