Thesis (M.App.Sc.) - Carleton University, 2002. / Includes bibliographical references (p. 59-63). Also available in electronic format on the Internet.

Στην παρούσα διπλωματική εργασία εξετάζεται η εκμετάλλευση της διαφορετικότητας πολλών χρηστών και της προσαρμοστικής διαμόρφωσης στα OFDMA συστήματα. Οι αλγόριθμοι που εκμεταλλεύονται αυτά τα κέρδη δεν προσδιορίζονται από το πρότυπο WiMAX, και έτσι όλοι οι κατασκευαστές WiMAX να είναι ελεύθεροι να αναπτύξουν τις δικές τους καινοτόμες διαδικασίες. Η ιδέα είναι η ανάπτυξη αλγορίθμων για την κατανομή των υποφορέων στους χρήστες, για τον προσδιορισμό των ποσοτήτων ισχύος σε αυτούς. Η μελέτη εστιάζεται στην κάτω ζεύξη (downlink) του συστήματος OFDMA, δηλαδή στη μετάδοση δεδομένων από το σταθμό βάσης της κυψέλης στους χρήστες – δέκτες. Οι διαθέσιμοι πόροι του συστήματος είναι οι ορθογώνιοι υποφορείς και η συνολική διαθέσιμη ισχύς στο σταθμό βάσης. Οι χρήστες κάνουν εκτίμηση και ανατροφοδότηση της πληροφορίας κατάστασης του καναλιού (CSI-channel state information) σε έναν κεντρικό σταθμό βάσης, όπου υποφορείς και κατανομή ισχύος προσδιορίζονται σύμφωνα με CSI των χρηστών και τη διαδικασία κατανομής των διαθέσιμων πόρων. Μόλις οι υποφορείς για κάθε χρήστη καθοριστούν, ο σταθμός βάσης πρέπει να ενημερώνει τον κάθε χρήστη για το ποιοι υποφορείς έχουν ανατεθεί στον καθένα. Συνήθως, η κατανομή των πόρων πρέπει να γίνεται σε χρονικά διαστήματα της τάξης του χρόνου συνοχής, αν και μπορεί να γίνει πιο συχνά, αν υπάρχουν πολλοί χρήστες που ανταγωνίζονται για τους πόρους που είναι διαθέσιμοι. Στην παρούσα διπλωματική εργασία εξετάζονται διαφορετικά σενάρια κατανομής των πόρων που περιλαμβάνουν αλγορίθμους για την ανάθεση των υποφορέων και το διαμοιρασμό των κατάλληλων ποσοτήτων ισχύος στους υποφορείς. Ανάλογα με το στόχο και τις ανάγκες των χρηστών του συστήματος, καθώς και με το ποσό της διαθέσιμης πληροφορίας καναλιού στο σταθμό βάσης, χρησιμοποιούνται διαφορετικοί αλγόριθμοι. Η κατανομή των διαθέσιμων πόρων συνήθως διατυπώνεται ως πρόβλημα βελτιστοποίησης με περιορισμούς, είτε (1) ελαχιστοποίηση της συνολικής εκπεμπόμενης ισχύoς με περιορισμό στο ρυθμό μετάδοσης δεδομένων στο χρήστη είτε (2) μεγιστοποίηση του συνολικού ρυθμού μετάδοσης δεδομένων με περιορισμό στην συνολική εκπεμπόμενη ισχύ. Ο αλγόριθμος με περιορισμό αναλογίας των ρυθμών μετάδοσης (Proportional Rate Constraints algorithm - PRC) έχει ως στόχο τη μεγιστοποίηση της συνολικής διεκπεραίωσης με τον περιορισμό ότι ο ρυθμός μετάδοσης δεδομένων σε κάθε χρήστη είναι ανάλογος με ένα σύνολο από προκαθορισμένες παραμέτρους του συστήματος. Ενώ ο στόχος του αλγόριθμου μέγιστου ολικού ρυθμού μετάδοσης (MSR- maximum sum rate algorithm), είναι η μεγιστοποίηση του συνόλου των ρυθμών μετάδοσης όλων των χρηστών, λαμβάνοντας υπόψη έναν περιορισμό της συνολικής εκπεμπόμενης ισχύoς. / In this diploma thesis, multiuser diversity and adaptive modulation in OFDMA systems is considered. Algorithms that take advantage of these gains are not specified by the WiMAX standard, and all WiMAX developer are free to develop their own innovative procedures. The idea is to develop algorithms for determining which users to schedule, how to allocate subcarriers to them, and how to determine the appropriate power levels for each user on each subcarrier. The downlink of a single-cell system is considered in the downlink transmission. The available resources to be distributed among the users of the OFDMA system comprise the subcarriers over which the signals of the users are transmitted and the available power that is allocated among subcarriers. Users estimate and feedback the channel state information (CSI) to a centralized base station, where subcarrier and power allocation are determined according to users’ CSI and the resource-allocation procedure. Once the subcarriers for each user have been determined, the base station must inform each user which subcarriers have been allocated to it. Typically, the resource allocation must be performed on the order of the channel coherence time, although it may be performed more frequently if a lot of users are competing for resources. In this diploma thesis, different resource allocation strategies for the downlink of an OFDMA system are compared. Each algorithm has a different objective. The resource allocation is usually formulated as a constrained optimization problem, to either (1) minimize the total transmit power with a constraint on the user data rate or (2) maximize the total data rate with a constraint on total transmit power. The proportional rate constraints (PRC) algorithm is to maximize the sum throughput, with the additional constraint that each user’s data rate is proportional to a set of predetermined system parameters. While the objective of the maximum sum rate (MSR) algorithm, is to maximize the sum rate of all users, given a total transmit power constraint.

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: In this thesis, the investigation into the optimization of low speed communication protocols for narrow band networks will be presented. The main focus will be on analysing commonly used low speed communication protocols and investigate an alternative to these protocols to provide an optimized low speed narrow band network that provides better performance at high and low channel utilization. A study of existing low speed communication networks within the field of water supply has been used to identify the most appropriate protocols to be included in the analysis. The analysis of each protocol discussed includes the development of a simulation and theoretical model, with parameters based on those obtained from implemented communication networks focusing on the parameters used within the Namib water supply scheme of NamWater in Namibia. Of the currently implemented contention protocols, the non-persistent Carrier Sense Multiple Access (CSMA) protocol is implemented the most. Current models used for modelling these protocols make use of various assumptions. These models have been expanded to provide a more accurate representation of the non-persistent CSMA model. The Round Robin Polling (RRP) protocol is another well known protocol used within the telemetry industry and has also been modelled as an alternative to the non-persistent CSMA model. The Adaptive Tree Walk (ATW) protocol has been identified as the limited contention protocol to be modelled as a possible alternative to the conventional methods used. A new model has been developed for modelling this protocol by making use of the same strategies and tools used in the modelling of the non-persistent CSMA and RRP protocols. The Simulation modelling has been developed by making use of DESMO-J, an Object Orientated Simulation API based in Java, developed by the Faculty of Informatics at the University of Hamburg. DESMO-J has been chosen as an alternative to the more traditional simulation languages due to its complete documentation, support structures, ease of use and flexibility. All theoretical models have been implemented in Matlab. / AFRIKAANSE OPSOMMING: In hierdie tesis sal die ondersoek na die optimering van laespoed protokolle vir kommunikasie oor nouband netwerke voorgelê word. Die hoof fokus is op die analise van algemene laespoed kommunikasie protokolle en die ondersoek van alternatiewe wat ’n meer optimale laespoed nouband netwerk sal lewer deur beter werkverigting by lae en hoë kanaalverkeer. ’n Studie van praktiese laespoed nouband netwerke in die veld van waterverspreiding word gebruik om die mees algemene protokolle te identifiseer wat in die analise ingesluit moet word. Die analise van die protokolle sluit in teoretiese en simulasie modelle, met parameters soos geidentifiseer uit die studie van ‘n praktiese netwerk, naamlik die Namib waterverspreidingskema van NamWater in Namibië. Die ’Non-persistent Carrier Sense Multiple Access’ en ’Round Robin Polling’ protokolle is geidentifiseer as dié wat meeste geimplementeer word. Die werkverigting van die protokolle is geanaliseer deur gebruik te maak van teoretiese en simulasie modeleringstegnieke. Huidige modelle van die CSMA protokol is gebaseer op sekere aannames. Hierdie aannames word aangepas en verbeter vir implementering van die teoretiese model. Die model word ook verder uitgebrei om beter resultate te lewer oor ’n groter parameterstel. Die ’Adaptive Tree Walk’ protokol is geidentifiseer as ’n moontlike optimale protokol en word gemodeleer en vergelyk teen die CSMA en RRP protokolle se werkverigting. Die simulasiemodelle is ontwikkel deur gebruik te maak van die DESMO-J sagteware, soos ontwikkel as ’n Java program-koppelvlak deur die Universiteit van Hamburg se Fakulteit van Informatika. DESMO-J is gekies as ’n alternatief vir die meer tradisionele simuleringstale omrede goeie dokumentasie, maklike gebruik en buigbaarheid. Alle teoretiese modelering is uitgevoer in Matlab.

Le travail de recherche présenté dans cette thèse est basé sur l’étude du protocole de communication par satellite appelé « Enhanced Spread Spectrum Aloha » (E-SSA) et créé par l’Agence Spatiale Européenne (ESA) en 2009. Il s’agit d’une technique qui permet à un terminal d’envoyer des messages courts par satellite de manière totalement asynchrone. L’intérêt est de maximiser l’efficacité spectrale tout en gardant une complexité minimale du terminal grâce aux techniques d’étalement de spectre et d’annulation d’interférences (SIC). Alors qu’au départ le protocole E-SSA avait pour but d’apporter un support physique pour des applications destinées à des terminaux mobiles en bande S, les développements se sont récemment étendus à une gamme de terminaux fixes dans des bandes de fréquence différentes (C, Ku ou Ka). À partir de ces deux modèles d’utilisation de l’E-SSA, ce travail de recherche se concentre sur la mise en place de solutions techniques permettant d’augmenter significativement la capacité globale du système. Cela est possible à travers une optimisation des différents paramètres du protocole et la conception d’algorithmes de gestion des puissances des terminaux. / The work presented in this thesis focuses on the satellite communication protocol named “Enhanced Spread Spectrum Aloha” (E-SSA) and developed in 2009 by the European Space Agency (ESA). The E-SSA structure, based on fully asynchronous random access, perfectly copes with low-duty cycle bursty transmissions adapted to satellite messaging. High performance in terms of spectral efficiency is possible by exploiting iterative successive interference cancellation (SIC) while keeping minimal complexity at the terminal side. If the first exploitation of the protocol concerned mobile applications in S-band, it has been extended to fleets of fixed terminals in other frequency bandwidths (C, Ku or Ka). Starting from these two scenarios, this thesis proposes different innovations to further boost the E-SSA global system capacity. These technical solutions particularly include a fine optimization of protocol parameters and new power control algorithms.

abstract: Distributed inference has applications in a wide range of fields such as source localization, target detection, environment monitoring, and healthcare. In this dissertation, distributed inference schemes which use bounded transmit power are considered. The performance of the proposed schemes are studied for a variety of inference problems. In the first part of the dissertation, a distributed detection scheme where the sensors transmit with constant modulus signals over a Gaussian multiple access channel is considered. The deflection coefficient of the proposed scheme is shown to depend on the characteristic function of the sensing noise, and the error exponent for the system is derived using large deviation theory. Optimization of the deflection coefficient and error exponent are considered with respect to a transmission phase parameter for a variety of sensing noise distributions including impulsive ones. The proposed scheme is also favorably compared with existing amplify-and-forward (AF) and detect-and-forward (DF) schemes. The effect of fading is shown to be detrimental to the detection performance and simulations are provided to corroborate the analytical results. The second part of the dissertation studies a distributed inference scheme which uses bounded transmission functions over a Gaussian multiple access channel. The conditions on the transmission functions under which consistent estimation and reliable detection are possible is characterized. For the distributed estimation problem, an estimation scheme that uses bounded transmission functions is proved to be strongly consistent provided that the variance of the noise samples are bounded and that the transmission function is one-to-one. The proposed estimation scheme is compared with the amplify and forward technique and its robustness to impulsive sensing noise distributions is highlighted. It is also shown that bounded transmissions suffer from inconsistent estimates if the sensing noise variance goes to infinity. For the distributed detection problem, similar results are obtained by studying the deflection coefficient. Simulations corroborate our analytical results. In the third part of this dissertation, the problem of estimating the average of samples distributed at the nodes of a sensor network is considered. A distributed average consensus algorithm in which every sensor transmits with bounded peak power is proposed. In the presence of communication noise, it is shown that the nodes reach consensus asymptotically to a finite random variable whose expectation is the desired sample average of the initial observations with a variance that depends on the step size of the algorithm and the variance of the communication noise. The asymptotic performance is characterized by deriving the asymptotic covariance matrix using results from stochastic approximation theory. It is shown that using bounded transmissions results in slower convergence compared to the linear consensus algorithm based on the Laplacian heuristic. Simulations corroborate our analytical findings. Finally, a robust distributed average consensus algorithm in which every sensor performs a nonlinear processing at the receiver is proposed. It is shown that non-linearity at the receiver nodes makes the algorithm robust to a wide range of channel noise distributions including the impulsive ones. It is shown that the nodes reach consensus asymptotically and similar results are obtained as in the case of transmit non-linearity. Simulations corroborate our analytical findings and highlight the robustness of the proposed algorithm. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

Orientador: Renato da Rocha Lopes / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-25T22:46:18Z (GMT). No. of bitstreams: 1 Gomes_MarcoAurelioCazarotto_D.pdf: 1053505 bytes, checksum: d53cf702c634d7c73f9e121a123bc2ba (MD5) Previous issue date: 2014 / Resumo: Este trabalho está dividido em duas partes. Na primeira, propomos um método para melhorar a estimação de informações sobre descasamentos de impedância em redes de cabos coaxiais. Esses descasamentos geram micro-reflexões, que por sua vez geram distorções na rede. Informações sobre a localização dos descasamentos podem ajudar as equipes de manutenção a localizá-los e repará-los. Atualmente a informação é estimada no padrão DOCSIS de manutenção preventiva, e baseia-se apenas nos coeficientes do equalizador que já são conhecidos pelo sistema. Assim, o método não exige qualquer alteração ao sistema. Iremos demonstrar que, em contraste com a abordagem atual DOCSIS, o nosso método fornece uma estimativa mais fina, e permite a estimativa de informação mesmo quando mais de uma micro-reflexão está presente. Na segunda parte propomos soluções para dois problemas relacionados ao canal gaussiano. No primeiro momento estamos interessados no problema do ponto de vista do primeiro usuário de um canal de múltiplo acesso (MAC, do inglês Multiple Access Channel), onde vamos tratar o sinal do segundo usuário como ruído na detecção. Esta estratégia é conhecida como cancelamento de interferência (SIC, do inglês Successive Interference Cancellation). O primeiro usuário utiliza um código Low Density Parity Check (LDPC). Na detecção, o LDPC assume que o ruído é gaussiano (AWGN, do inglês additive white Gaussian noise). Com isso, vamos propor duas estratégias (shaping e transformada de Fourier) para modificar a distribuição do segundo usuário, de forma que esta se aproxime de uma distribuição gaussiana. Vamos comprovar que as duas estratégias têm melhor desempenho comparadas à estratégia envolvendo modulação com distribuição discreta uniforme. Em um segundo momento propomos um sistema simples que se aproxima da capacidade do AWGN. Para isso, vamos explorar um paralelo entre o AWGN e o MAC. Em nossa proposta, o que no MAC eram usuários agora são níveis paralelos e independentes de um código multinível, onde cada nível usa uma entrada binária e um código que se aproxima da capacidade, resultando em um sistema com codificação simples que opera perto de capacidade. Na decodificação novamente vamos usar SIC. Como resultado, o receptor é constituído por uma série de receptores binários simples. Vamos mostrar que o sistema proposto funciona a uma pequena distância em relação à capacidade do AWGN, e que esta distância pode ser atribuída apenas à distância do próprio código / Abstract: This work is divided into two parts. At first, we propose a method for improving the estimation of impedance mismatch information in coaxial cable networks. These impedance mismatch generate micro-reflections, which distorts the network. Information about the location of mismatches can help maintenance team to locate to them and repair them. Currently, the information is estimated in the DOCSIS preventive maintenance, and is based only on the coefficients of the equalizer are already known by the system. Thus, the method does not require any change into the system. We will show that, in contrast with the current DOCSIS approach, our method provides a finer estimate, and allows the estimation of information even when more than one micro-reflection is present. In the second part we propose solutions to two problems related to the Gaussian channel. At first we are interested in the problem from the point of view of the first user of a multiple access channel (MAC), where we treat the user as the second signal in noise in the detection. This strategy is known as successive interference cancellation (SIC). The first user uses a Low Density Parity Check code (LDPC). In detection , the LDPC assumes that the noise is Gaussian (AWGN). With this, we propose two strategies (shaping and Fourier transform) to modify the distribution of the second user, so that it approaches a Gaussian distribution. We will show that both strategies outperform the strategy involving modulation compared with discrete uniform distribution. In second user, we propose a simple system that approaches the capacity of the AWGN. For this, we explore a parallel between the AWGN and MAC. In our proposal, which were in the MAC users, now are parallel and independent levels of a multilevel code, where each level uses a binary input and a code approaches the capacity, resulting in a simple coding system that operates close to capacity. We will use SIC for decoding again. As a result, the receiver is constituted by a simple binary receivers series. We will show that the proposed system works at a small distance from the capacity of AWGN, and this distance can be assigned only the gap of the code / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

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The telecommunications technology has been developed tremendously as there has been an ever-increasing demand for more speed and reliability. The enormous increase in the number of smart phones and other data consuming devices, combined with the development of enhanced multimedia applications has resulted in a dramatic increase in the volume of mobile data traffic. In order to accommodate the growing needs, it is required to utilise the spectrum efficiently. The design of radio access technology plays an important role in the aspect of system performance. These radio access technologies are typically characterised by the multiple-access techniques used. Non-Orthogonal Multiple Access (NOMA) is a multiple access scheme proposed for 5G and it utilises the power domain which was not sufficiently utilised in the previous systems.        This thesis work is mainly focused on the performance analysis of the NOMA technique in mobile media (images). This analysis is achieved by transmitting a high definition image at various power levels to two users who are located at two different distances from the base station. The images are transmitted through suitable noise channels. An analysis is done on how NOMA copes with the users having poor channel conditions. The performance is analysed by comparing the output images at both the receivers based on the structural similarity index and bit error rate parameters.

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