[pt] Este trabalho é um estudo sobre o desempenho das principais versões do protocolo TCP e de sua variação denominada STP na transmissão via satélite. Devido à grande distância da terra aos satélites geoestacionários, a transmissão via satélite se caracteriza por um grande atraso de propagação e maior ocorrência de erros em comparação com a transmissão ótica. Estes problemas causam sério impacto no desempenho do TCP pois eventuais perdas de pacote implicam em retransmissão e demorada reinicialização do protocolo. Neste estudo, abordamos especificamente o efeito dos erros no canal como fonte de perdas de pacote, considerando modelos de erros estatisticamente independentes e erros em surto. Este tipo de erro ocorre geralmente pela utilização de códigos convolucionais associados ao decodificador de Viterbi. Através de simulação em computador usando o software Matlab, foram inicialmente caracterizadas as seqüências de erros geradas por alguns codificadores convolucionais típicos. Em seguida, o efeito destas seqüências foi introduzida em simulações de uma aplicação FTP/TCP em canal satélite, comparado-se a vazão obtida com as diferentes versões do TCP. / [en] This work is a study on the performance of the main versions of protocol TCP and of its variation STP satellite transmission. Due to great distance of the land to the geostationary satellites, the satellite transmission is characterizes for a great delay of propagation and greater occurrence of errors in comparison with the optics transmission. These problems cause serious impact in the performance of the TCP therefore eventual losses of package imply in retransmission and delayed reset of the protocol. In this study, we specifically approach the effect of the errors in the canal as source of losses of package, considering models of statistically independent errors and burst errors. This type of error generally occurs for the use of convolutional code associates with Viterbi decoder. Through simulation in computer using Matlab software, we initially had been characterized the sequences of errors generated for some typical convolutional codes. After that, the effect of these sequences was introduced in simulation of an application FTP/TCP in canal satellite, compared it outflow gotten with the different versions of the TCP, using ns-2.

This dissertation examines multi-antenna transceiver design over flat-fading wireless channels. Bit Interleaved Coded Modulation (BICM) and MultiLevel Coded Modulation (MLCM) transmitter structures are considered, as well as the used of an optional spatial precoder under slow and quasi-static fading conditions. At the receiver, MultiStage Decoder (MSD) and Iterative Detection and Decoding (IDD) strategies are applied. Precoder, mapper and subcode designs are optimized for different receiver structures over the different antenna and fading scenarios. Under slow and quasi-static channel conditions, fade resistant multi-antenna transmission is achieved through a combination of linear spatial precoding and non-linear multi-dimensional mapping. A time-varying random unitary precoder is proposed, with significant performance gains over spatial interleaving. The fade resistant properties of multidimensional random mapping are also analyzed. For MLCM architectures, a group random labelling strategy is proposed for large antenna systems. The use of complexity constrained receivers in BICM and MLCM transmissions is explored. Two multi-antenna detectors are proposed based on a group detection strategy, whose complexity can be adjusted through the group size parameter. These detectors show performance gains over the the Minimum Mean Squared Error (MMSE)detector in spatially multiplexed systems having an excess number of transmitter antennas. A class of irregular convolutional codes is proposed for use in BICM transmissions. An irregular convolutional code is formed by encoding fractions of bits with different puncture patterns and mother codes of different memory. The code profile is designed with the aid of extrinsic information transfer charts, based on the channel and mapping function characteristics. In multi-antenna applications, these codes outperform convolutional turbo codes under independent and quasi-static fading conditions. For finite length transmissions, MLCM-MSD performance is affected by the mapping function. Labelling schemes such as set partitioning and multidimensional random labelling generate a large spread of subcode rates. A class of generalized Low Density Parity Check (LDPC) codes is proposed, to improve low-rate subcode performance. For MLCM-MSD transmissions, the proposed generalized LDPC codes outperform conventional LDPC code construction over a wide range of channels and design rates.

Orientador: Jaime Portugheis / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-06T08:08:11Z (GMT). No. of bitstreams: 1 Sharma_Manish_M.pdf: 1001397 bytes, checksum: 04250e6b88e19bb784d3b68313ace258 (MD5) Previous issue date: 2006 / Resumo: Nesta dissertação abordamos o problema de como construir codificadores bit-geometricamente uniformes (BGU) para a utilização como codificadores internos em sistemas com concatenação serial de códigos. A utilização destes codificadores implica na facilidade de determinação de parâmetros necessários para a análise do desempenho dos sistemas. Há um grande controle sobre estes parâmetros no projeto destes codificadores utilizando o método descrito neste trabalho, o que sugere que bons codificadores e conseqüentemente bons sistemas podem ser obtidos desta maneira. Além disso, os códigos gerados por estes codificadores possuem a propriedade de uniformidade de erro de bit, o que facilita bastante sua análise / Abstract: This thesis approaches the problem of building bit-geometrically uniform (BGU) encoders to be used as inner encoders in systems with serially concatenated codes. By using this type of encoders, certain parameters that are used to analyze the system's performance are easily determined. There is a great control over these parameters when building encoders using the method described in this work, suggesting that good encoders and subsequently good systems can be obtained. Besides, the codes generated by these encoders posses the uniform bit error property, that greatly facilitates their analysis / Mestrado / Engenharia de Telecomunicações / Mestre em Engenharia Elétrica

Adaptive modulation is widely employed to improve spectral e ciency. To date, square signal constellations have been used for adaptive modulation. In this disser- tation, triangular constellations are considered for this purpose. Triangle quadrature amplitude modulation (TQAM) for both power-of-two and non-power-of-two mod- ulation orders is examined. A technique for TQAM mapping is presented which is better than existing approaches. A new type of TQAM called semi-regular TQAM (S-TQAM) is introduced. Bit error rate expressions for TQAM are derived, and the detection complexity of S-TQAM is compared with that of regular TQAM (R-TQAM) and irregular TQAM (I-TQAM). The performance of S-TQAM over additive white Gaussian noise and Rayleigh fading channels is compared with that of R-TQAM and I-TQAM. The construction of ternary convolutional codes (TCCs) for ternary phase shift keying (TPSK) modulation is considered. Tables of non-recursive non-systematic TCCs with maximum free distance are given for rates 1=2, 1=3 and 1=4. The conver- sion from binary data to ternary symbols is investigated. The performance of TCCs with binary to ternary conversion using TPSK is compared with the best BCCs using binary phase shift keying (BPSK). / Graduate

No description available.

Os Wireless sensor networks (WSNs) evoluíram a partir da idéia de que sensores sem fio podem ser utilizados para coletar informações de ambientes nas mais diversas situações. Os primeiros trabalhos sobre WSNs foram desenvolvidos pelo Defense Advanced Research Projects Agency (DARPA)1, com o conceito de Smart Dust baseados em microelectromechanical systems (MEMS), dispositivos com capacidades de detectar luminosidade, temperatura, vibração, magnetismo ou elementos químicos, com processamento embarcado e capaz de transmitir dados via wireless. Atualmente tecnologias emergentes têm aproveitado a possibilidade de comunicação com a World Wide Web para ampliar o rol de aplicações desta tecnologia, dentre elas a Internet das Coisas (Internet of Things) IoT. Esta pesquisa estuda a implementação de um novo algoritmo e protocolo que possibilita o encaminhamento dos dados coletados nos microsensores em cenários de redes ad hoc com os sensores distribuídos aleatoriamente, em uma área adversa. Apesar de terem sido desenvolvidos vários dispositivos de hardware pela comunidade de pesquisa sobre WSN, existe um esforço liderado pela Internet Engineering Task Force (IETF)2, na implementação e padronização de protocolos que atendam a estes mecanismos, com limitações de recursos em energia e processamento. Este trabalho propõe a implementação de novos algoritmos de encaminhamento de pacotes utilizando o conceito de códigos convolucionais. Os resultados obtidos por meio de extensivas simulações mostram ganhos em termos da redução de latência e do consumo de energia em relação ao protocolo AODV. A complexidade de implementação é extremamente baixa e compatível com os poucos recursos de hardware dos elementos que usualmente compõem uma rede de sensores sem fio (WSN). Na seção de trabalhos futuros é indicado um extenso conjunto de aplicações em que os conceitos desenvolvidos podem ser aplicados. / Wireless sensor networks (WSNs) have evolved from the idea that small wireless sensors can be used to collect information from the physical environment in a large number of situations. Early work in WSNs were developed by Defense Advanced Research Projects Agency (DARPA)1, so called Smart Dust, based on microelectromechanical systems (MEMS), devices able to detect light, temperature, vibration, magnetism or chemicals, with embedded processing and capable of transmitting wireless data. Currently emerging technologies have taken advantage of the possibility of communication with the World Wide Web to expand to all applications of this technology, among them the Internet of Things IoT. This research, studies to implement a new algorithm and protocol that allows routing of data collected in micro sensors in ad hoc networks scenarios with randomly distributed sensors in adverse areas. Although they were developed several hardware devices by the research community on WSN, there is an effort led by Internet Engineering Task Force (IETF)2, in the implementation and standardization of protocols that meet these mechanisms, with limited energy and processing resources. This work proposes the implementation of new packets forwarding algorithms using the concept of convolutional codes. The results obtained by means of extensive simulations show gains in terms of latency and energy consumption reduction compared to the AODV protocol. The implementation complexity is extremely low and compatible with the few hardware resources usually available in the elements of a wireless sensor network (WSN). In the future works section a large set of applications for which the developed concepts can be applied is indicated.

Os Wireless sensor networks (WSNs) evoluíram a partir da idéia de que sensores sem fio podem ser utilizados para coletar informações de ambientes nas mais diversas situações. Os primeiros trabalhos sobre WSNs foram desenvolvidos pelo Defense Advanced Research Projects Agency (DARPA)1, com o conceito de Smart Dust baseados em microelectromechanical systems (MEMS), dispositivos com capacidades de detectar luminosidade, temperatura, vibração, magnetismo ou elementos químicos, com processamento embarcado e capaz de transmitir dados via wireless. Atualmente tecnologias emergentes têm aproveitado a possibilidade de comunicação com a World Wide Web para ampliar o rol de aplicações desta tecnologia, dentre elas a Internet das Coisas (Internet of Things) IoT. Esta pesquisa estuda a implementação de um novo algoritmo e protocolo que possibilita o encaminhamento dos dados coletados nos microsensores em cenários de redes ad hoc com os sensores distribuídos aleatoriamente, em uma área adversa. Apesar de terem sido desenvolvidos vários dispositivos de hardware pela comunidade de pesquisa sobre WSN, existe um esforço liderado pela Internet Engineering Task Force (IETF)2, na implementação e padronização de protocolos que atendam a estes mecanismos, com limitações de recursos em energia e processamento. Este trabalho propõe a implementação de novos algoritmos de encaminhamento de pacotes utilizando o conceito de códigos convolucionais. Os resultados obtidos por meio de extensivas simulações mostram ganhos em termos da redução de latência e do consumo de energia em relação ao protocolo AODV. A complexidade de implementação é extremamente baixa e compatível com os poucos recursos de hardware dos elementos que usualmente compõem uma rede de sensores sem fio (WSN). Na seção de trabalhos futuros é indicado um extenso conjunto de aplicações em que os conceitos desenvolvidos podem ser aplicados. / Wireless sensor networks (WSNs) have evolved from the idea that small wireless sensors can be used to collect information from the physical environment in a large number of situations. Early work in WSNs were developed by Defense Advanced Research Projects Agency (DARPA)1, so called Smart Dust, based on microelectromechanical systems (MEMS), devices able to detect light, temperature, vibration, magnetism or chemicals, with embedded processing and capable of transmitting wireless data. Currently emerging technologies have taken advantage of the possibility of communication with the World Wide Web to expand to all applications of this technology, among them the Internet of Things IoT. This research, studies to implement a new algorithm and protocol that allows routing of data collected in micro sensors in ad hoc networks scenarios with randomly distributed sensors in adverse areas. Although they were developed several hardware devices by the research community on WSN, there is an effort led by Internet Engineering Task Force (IETF)2, in the implementation and standardization of protocols that meet these mechanisms, with limited energy and processing resources. This work proposes the implementation of new packets forwarding algorithms using the concept of convolutional codes. The results obtained by means of extensive simulations show gains in terms of latency and energy consumption reduction compared to the AODV protocol. The implementation complexity is extremely low and compatible with the few hardware resources usually available in the elements of a wireless sensor network (WSN). In the future works section a large set of applications for which the developed concepts can be applied is indicated.

We introduced nested search methods to design (n, k) block codes for arbitrary channels by optimizing an appropriate metric spectrum in each iteration. For a given k, the methods start with a good high rate code, say k/(k + 1), and successively design lower rate codes up to rate k/2^k corresponding to a Hadamard code. Using a full search for small binary codes we found that optimal or near-optimal codes of increasing length can be obtained in a nested manner by utilizing Hadamard matrix columns. The codes can be linear if the Hadamard matrix is linear and non-linear otherwise. The design methodology was extended to the generic complex codes by utilizing columns of newly derived or existing unitary codes. The inherent nested nature of the codes make them ideal for progressive transmission. Extensive comparisons to metric bounds and to previously designed codes show the optimality or near-optimality of the new codes, designed for the fading and the additive white Gaussian noise channel (AWGN). It was also shown that linear codes can be optimal or at least meeting the metric bounds; one example is the systematic pilot-based code of rate k/(k + 1) which was proved to meet the lower bound on the maximum cross-correlation. Further, the method was generalized such that good codes for arbitrary channels can be designed given the corresponding metric or the pairwise error probability. In synchronous multiple-access schemes it is common to use unitary block codes to transmit the multiple users’ information, especially in the downlink. In this work we suggest the use of newly designed non-unitary block codes, resulting in increased throughput efficiency, while the performance is shown not to be substantially sacrificed. The non-unitary codes are again developed through suitable nested searches. In addition, new multiple-access codes are introduced that optimize certain criteria, such as the sum-rate capacity. Finally, the introduction of the asymptotically optimum convolutional codes for a given constraint length, reduces dramatically the search size for good convolutional codes of a certain asymptotic performance, and the consequences to coded code-division multiple access (CDMA) system design are highlighted.

Orientador : Reginaldo Palazzo Junior / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-04T00:27:05Z (GMT). No. of bitstreams: 1 Almeida_AntonioCarlosAidode_D.pdf: 2149041 bytes, checksum: 427f77a8e0ec2774c7b152dd209ba9fa (MD5) Previous issue date: 2004 / Resumo: A decoerencia é um dos maiores desafios obstrutivos da computação quantica. Os codigos corretores de erros quanticos tem sido desenvolvidos com o intuito de enfrentar este desafio. Uma estrutura de grupos e uma classe associada de codigos, a classe dos codigos estabilizadores, tem-se mostrado uteis na produção de codigos e no entendimento da estrutura de classes de codigos. Todos os codigos estabilizadores descobertos ate o momentos são codigos de bloco. Nesta tese, construiremos uma classe de codigos convolucional quanticos concatenados. Introduziremos o conceito de memoria convolucional quantica e algumas tecnicas simples para produzir bons codigos convolucionais quanticos a partir de classes de codigos concolucionais classicos / Abstract: Decoherence is one of the major challenges facing the field of quantum computation. The field of quantum error correction has developed to meet this challenge. A group-theoretical structure and associated class of quantum codes, the stabilizer codes, has proved particularly fruitful in producing codes and in understanding the structure of both specified codes and class of codes. All stabilizer codes discovered so far are block codes. In this thesis we will construct a class of concatenated quantum convolutional codes. We will introduce the concept of quantum convolutional memory and some simple techniques to produce good quantum convolutional codes from classes of classical convolutional codes / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

[pt] Este trabalho propõe um receptor multiusuário híbrido para utilização em um sistema DS/CDMA com modulação M-PSK e codificação convolucional. O receptor proposto é composto por um receptor decorrelator ao final do qual é realizada uma decodificação convolucional por grupos. Resultados de desempenho obtidos por simulações para grupos de dois usuários são apresentados e comparados com o desempenho do receptor convencional, formado por um banco de filtros casados, e com o desempenho do receptor decorrelator já proposto na literatura. / [en] This work proposes a hybrid multiuser receiver for a DS/CDMA system employing M-PSK modulation and convolutional coding. The proposed receiver is composed by a decorrelator receiver followed by a group convolutional decoder. Perfomance results obtained by simulation for groups of two users are presented and compared to the performance of a conventional receiver, composed of a bank of matched filters, and to the decorrelator receiver itself.