abstract: Memory systems are becoming increasingly error-prone, and thus guaranteeing their reliability is a major challenge. In this dissertation, new techniques to improve the reliability of both 2D and 3D dynamic random access memory (DRAM) systems are presented. The proposed schemes have higher reliability than current systems but with lower power, better performance and lower hardware cost. First, a low overhead solution that improves the reliability of commodity DRAM systems with no change in the existing memory architecture is presented. Specifically, five erasure and error correction (E-ECC) schemes are proposed that provide at least Chipkill-Correct protection for x4 (Schemes 1, 2 and 3), x8 (Scheme 4) and x16 (Scheme 5) DRAM systems. All schemes have superior error correction performance due to the use of strong symbol-based codes. In addition, the use of erasure codes extends the lifetime of the 2D DRAM systems. Next, two error correction schemes are presented for 3D DRAM memory systems. The first scheme is a rate-adaptive, two-tiered error correction scheme (RATT-ECC) that provides strong reliability (10^10x) reduction in raw FIT rate) for an HBM-like 3D DRAM system that services CPU applications. The rate-adaptive feature of RATT-ECC enables permanent bank failures to be handled through sparing. It can also be used to significantly reduce the refresh power consumption without decreasing the reliability and timing performance. The second scheme is a two-tiered error correction scheme (Config-ECC) that supports different sized accesses in GPU applications with strong reliability. It addresses the mismatch between data access size and fixed sized ECC scheme by designing a product code based flexible scheme. Config-ECC is built around a core unit designed for 32B access with a simple extension to support 64B and 128B accesses. Compared to fixed 32B and 64B ECC schemes, Config-ECC reduces the failure in time (FIT) rate by 200x and 20x, respectively. It also reduces the memory energy by 17% (in the dynamic mode) and 21% (in the static mode) compared to a state-of-the-art fixed 64B ECC scheme. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

O objetivo desta tese é introduzir uma nova metodologia para a cinética bidimensional multi- grupo de difusão de nêutrons em reatores nucleares. A metodologia apresentada usa uma aproximação polinomial em um domínio homogêneo retangular com condições de contornos não homogêneas. Como ela consiste em uma série de Taylor truncada, sua estimativa de erro varia de acordo com o tamanho do retângulo. Os coeficientes são obtidos principalmente pelas suas relações com o termo independente, que _e determinado pela equação diferencial. Estas relações são obtidas apenas pelas condições de contorno, e é demonstrado serem linearmente independentes. Um esquema numérico é feito para assegurar uma rápida convergência. Estes procedimentos feitos para um retângulo homogêneo são feitos para construir soluções para problemas de autovalor e dependentes do tempo de geometria ortogonal global com parâmetros seccionalmente constantes pelo método iterativo SOR. O autovalor dominante e sua autofunção são obtidos pelo método da potência no problema de autovalor. A solução para casos dependentes do tempo usam o método de Euler modificado na variável tempo. Quatro casos-teste clássicos são considerados para ilustração. / The objective of this thesis is to introduce a new methodology for two{dimensional multi{ group neutron diffusion kinetics in a reactor core. The presented methodology uses a polyno- mial approximation in a rectangular homogeneous domain with non{homogeneous boundary conditions. As it consists on a truncated Taylor series, its error estimates varies with the size of the rectangle. The coefficients are obtained mainly by their relations with the independent term, which is determined by the differential equation. These relations are obtained by the boundary conditions only, and these relations are proven linear independent. A numerical scheme is made to assure faster convergence. The procedures done for one homogeneous rectangle are used to construct the solution of global orthogonal geometry with step{wise constant parameters steady state and time dependent problems by the iterative SOR algo- rithm. The dominant eigenvalue and its eigenfunction are obtained by the power method in the eigenvalue problem. The solution for the time dependent cases uses the modi ed Euler method in the time variable. Four classic test cases are considered for illustration.

A necessidade de suportar serviços multimídia impulsiona o desenvolvimento das redes sem fio. Com isso, torna-se importante fornecer confiabilidade na transmissão de dados em um ambiente sujeito a variações espaciais, temporais e de freqüência, causadas por fenômenos físicos que, geralmente, causam erros nos dados transmitidos. Esses erros são basicamente de dois tipos: erros em rajada e erros aleatórios (Additive White Gaussian Noise - AWGN). Simular o comportamento dos canais sem fio afetados por erros é objeto de pesquisa há diversos anos. Entretanto, grande parte das pesquisas não considera a aplicação dos dois tipos de erros simultaneamente, o que pode gerar imprecisões nos resultados das simulações. Sendo assim, este trabalho propõe um injetor capaz de gerar tanto seqüências de erros em rajada quanto AWGN, além de propor um modelo de erros híbrido que considera a injeção de ambos os tipos de erros para simular o comportamento de um canal sem fio. O injetor de erros proposto é empregado em um estudo de caso referente à análise de desempenho do mecanismo de codificação de canal em redes que seguem o padrão IEEE 802.16, tanto nomádicas (fixas) quanto móveis. É avaliada a capacidade de correção dos codificadores Forward Error Correction (FEC), de emprego obrigatório de acordo com o referido padrão. Além disso, estuda-se o impacto causado pela aplicação de técnicas que consistem na adição de diversidade temporal à transmissão, em cenários cuja ocorrência dos erros é em rajada, e em cenários cujos erros são modelados de acordo com seqüências AWGN. Finalmente, realiza-se um estudo teórico sobre a vazão que pode ser atingida nos cenários nomádicos e móveis, além de uma discussão sobre os avanços tecnológicos trazidos pela multiplexação de canal baseada em Orthogonal Frequency Division Multiple Access (OFDMA), empregado em redes IEEE 802.16 móveis. / The demand for providing multimedia services is increasing the development of wireless networks. Therefore, an important issue is to guarantee correct transmissions over channels that are affected by time and frequency variant conditions caused by physical impairments that lead to the occurrence of errors during the transmission. These errors are basically of two types: burst errors and random errors, typically modeled as Additive White Gaussian Noise (AWGN). Simulating the behavior of wireless channels affected by physical impairments has been subject of several investigations in the past years. Nevertheless, part of the current researches does not consider the occurrence of both errors at the same time. This approach may lead to imprecisions on the results obtained through simulations. This work proposea an error sequence generator which is able of generating both burst and AWGN error models. Moreover, the proposed model can generate hybrid errors sequences composed of both error types simultaneously. The proposed error sequence generator is applied to a case study that aims to evaluate the performance of the channel encoder of nomadic (fixed) and mobile IEEE 802.16 networks. In this context, we evaluate the error correction capability of FEC encoders which are mandatory according to IEEE 802.16 standard. Furthermore, we study the impact caused by the application of time diversity techniques on the transmission, considering scenarios affected by burst errors and AWGN. We also present a study about the theoretical throughput that can be reached by nomadic and mobile technologies. Finally, we discuss the technological advances brought by Orthogonal Frequency Division Multiple Access (OFDMA) channel multiplexing technique, which is employed in IEEE 802.16 mobile networks.

Orientador: Renato Baldini Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-17T02:17:07Z (GMT). No. of bitstreams: 1 Goncalves_MariaLeopoldinaMartinsNevesSeixas_M.pdf: 2201748 bytes, checksum: 3f3d1f237a11eabcf9d6c393f0ca0cce (MD5) Previous issue date: 2010 / Resumo: Esta dissertação aborda o estudo de códigos corretores de erro baseados em matrizes quaternárias esparsas, aplicadas em sistemas de transmissão OFDM. Os códigos LDPC (Low Density Parity Check) constituem uma importante família de códigos gerados a partir de matrizes de verificação esparsas e são considerados como uma das classes de códigos que apresentam melhor desempenho em sistemas de comunicação digital. Os códigos LDPC desenvolvidos sobre o anel Z4 são o grande foco deste trabalho e para efeito de comparação de desempenho é utilizado como referência o padrão proposto pelo SBTVD (Sistema Brasileiro de Televisão Digital). No sistema de TV Digital, o receptor deve ser robusto a vários tipos de canal. Para uma recepção fixa o canal pode ser influenciado pelo ruído AWGN (Aditive White Gaussian Noise), já para uma recepção móvel o sinal pode sofrer várias reflexões e refrações, o que é caracterizado pelas interferências do desvanecimento plano e/ou seletivo. Para minimizar este problema é proposto a utilização da técnica de transmissão OFDM (Orthogonal Frequency Division Multiplexing), devido às suas vantagens com canais seletivos em frequência, como é comumente observado nos canais dos sistemas de comunicações móveis digitais. A decodificação dos códigos é feita utilizando uma adaptação (generalização) do algoritmo SISO (Soft Input Soft Output) proposto por P. Farrell e J. Moreira [39], [5]. É feita uma análise comparativa dos códigos do ponto de vista do desempenho, através de simulação de códigos de diferentes comprimentos para cada um dos três canais descritos acima. Os códigos LDPC definidos sobre Z4 apresentam bom desempenho e demonstram ser bons candidatos a sua utilização em conjunto com sistemas OFDM / Abstract: This dissertation addresses the study of error correcting codes based on sparse non-binary matrices. The LDPC (Low Density Parity Check) codes constitute a efficient family of codes generated by sparse parity check matrices and it is considered as one of the classes of codes that presents the best performance in digital communications systems. LDPC codes over the ring of integers modulo-4 (Z4) are the main focus of this work. The standard proposed by SBTVD (Brazilian Digital Television System) is used as reference for performance comparisons. It is proposed the substitution of the inner code in the channel encoding at the transmitter, for a LDPC code. On Digital TV system, the receiver must be robust to some kinds of interferences. For a fixed channel, the receiving end is basically influenced by the AWGN (Additive White Gaussian Noise). For mobile channels, the signal suffers reflections and refractions, which can be characterized as flat and frequency-selective fading. To minimize those interferences it is proposed the associated use of the OFDM (Orthogonal Frequency Division Multiplexing) technique. The decoding process is based on a generalization of the SISO (Soft Input Soft Output) algorithm proposed by P. Farrell and J. Moreira [39], [5]. A comparative analysis of the LDPC codes is made based on BER performance and on computational complexity. Finally, the simulation results for different codes lengths are presented, highlighted the significantive improvement in performance for LDPC codes / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Orientador: Jaime Portugheis / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-15T19:30:44Z (GMT). No. of bitstreams: 1 Andrade_Alexandrede_D.pdf: 5191552 bytes, checksum: ae675c28ea93ab3a91655042f4cd13d1 (MD5) Previous issue date: 2010 / Resumo: Esta tese aborda métodos de estimação probabilística em sistemas de comunicações usando a teoria de grafos-fatores e seu algoritmo genérico soma-produto. Estas ferramentas são atualmente reconhecidas como um ambiente ideal para derivar vários esquemas de decodificação/ estimação, e também integrar modelos de componentes típicos num sistema de comunicação para melhor desempenho do processo de recepção. Mais genericamente, são adequadas para projetos de receptores unificados. Além disso, vários esquemas de decodificação conjunta fonte/canal podem ser contextualizados neste ambiente. Partimos de uma revisão geral da teoria grafos-fatores e do algoritmo soma-produto de forma abrangente e inserindo os fundamentos matemáticos relacionados. Na sequência aplicamos estes conceitos a sistemas de comunicações. Focamos em sistemas de grafos com ciclos, que são de grande interesse e que resultam na versão iterativa do algoritmo somaproduto, onde cronogramas de execução devem ser arbitrados eficientemente. Descrevemos a decodificação turbo seguindo esquemas de grafos-fatores normais e causais, a forma mais apropriada para a descrição e análise de cronogramas. A partir desta formulação, estudamos o caso da decodificação turbo na sua variante não-bloco, com entrelaçadores periódicos e decodificação contínua/causal. Apresentamos um cronograma completo do algoritmo soma-produto para este caso, mostrando vantagens práticas em relação ao proposto na literatura, sobretudo em relação a sua implementação. Na última parte da tese, apresentamos um estudo da aplicação de grafos-fatores no problema de decodificação iterativa conjunta fonte/canal. Partimos de um modelo genérico de fonte com memória, discreta no tempo e contínua em amplitude, consideramos quantização vetorial e tratamos o problema da decodificação iterativa conjunta integrando modelos destes componentes com o resto do sistema. Alguns resultados de simulações computacionais para os esquemas propostos são apresentados / Abstract: The present thesis deals with probabilistic inference methods for communication systems described by the unifying framework of factor graphs and the general elimination algorithm, the so called sum-product algorithm. These exceedingly general tools are understood as a state of the art environment to build many decoding schemes, and to model typical components for a joint efficient inference at reception. More generally, is a suitable framework to unified receiver designs. Additionally, some joint source channel decoding schemes can also be proper modeled under this context. We start with a review of this framework and related mathematical topics. Thereafter, we particularize to cases of interest, like typical communication systems. This framework gives powerful insights into the structures of multivariate constrained systems and shows how distributed probabilistic inferences can be performed, as shown for typical communication systems with a standard channel encoder. Systems represented by fator graphs with cycles are the most relevant. For the iterative version of the sum-product algorithm, a calculation schedule has to be efficiently chosen. We review the turbo decoding scheme for the classical turbo code using a normal and causal factor graph realization, providing an environment for scheduling descriptions. Then, we approach the non-block turbo decoding version (stream-oriented turbo codes), where general periodic and causal interleavers can be used and continuous decoding schemes are required. We present a full decoding sum-product schedule for this case, with pratical improvements over the usual non-graphical decoding scheme. In the last part of this thesis, we address the joint source channel decoding problem using the factor-graph framework. Starting from a general source model, linear discrete time series, we consider straight vectorial quantization. Instead of trying to remove redundancy, we go in the direction of building decoding schemes that explore this redundancy from source model and quantizer map.We analyse cases when iterative decoding can be performed taking these elements into account in a proper way. Some simulation on the proposed schemes are presented / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

Orientadores: Reginaldo Palazzo Junior, Carlile Campos Lavor / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-11T22:44:54Z (GMT). No. of bitstreams: 1 LaGuardia_GiulianoGadioli_D.pdf: 1126065 bytes, checksum: c3ad65915db4e87e1752adbbbbef2841 (MD5) Previous issue date: 2008 / Resumo: Como principais contribuições desta tese, apresentamos novos métodos de construção que geram novas famílias de códigos quânticos CSS. As construções são baseadas em códigos cíclicos (clássicos) BCH, Reed-Solomon, Reed-Muller, Resíduos quadráticos e também nos códigos derivados do produto tensorial de dois códigos Reed-Solomon. Os principais códigos quânticos construídos neste trabalho, em termos de parâmetros, são os derivados dos códigos BCH clássicos. Além disso, estudamos as condições necessárias para analisar as situações nas quais os códigos cíclicos quânticos (clássicos) são códigos MDS (do inglês, Maximum- Distance-Separable codes). Apresentamos, também, novas conexões entre a teoria de matróides e a teoria dos códigos quânticos CSS, que acreditamos serem as primeiras conexões entre tais teorias. Mais especificamente, demonstramos que a função enumeradora de pesos de um código quântico CSS é uma avaliação do polinômio de Tutte da soma direta dos matróides originados a partir dos códigos clássicos utilizados na construção CSS. / Abstract: This thesis proposes, as the main contributions, constructions method of new families of quantum CSS codes. These constructions are based on classical cyclic codes of the types BCH, Reed-Solomon, Reed-Muller, Quadratic Residue and also are based on product codes of classical Reed-Solomon codes. The main family of quantum codes constructed in this work, i. e., quantum codes having better parameters, are the ones derived from classical BCH codes. Moreover, we present some new conditions in which quantum CSS cyclic codes are quantumMDS codes. In addition, we provide the elements to connect matroid theory and quantum coding theory. More specifically, we show that the weight enumerator of a CSS quantum code is equivalent to evaluating the Tutte polynomial of the direct sum of the matroid associated to the classical codes used in the CSS construction. / Doutorado / Telecomunicações e Telemática / Doutor em Engenharia Elétrica

In spread spectrum systems employing parity bit selected spreading sequences, parity bits generated from a linear block encoder are used to select a spreading code from a set of mutually orthogonal spreading sequences. In this thesis, turbo receivers for SS-PB systems are proposed and investigated. In the transmitter, data bits are rst convolutionally encoded before being fed into SS-PB modulator. In fact, the parity bit spreading code selection technique acts as an inner encoder in this system without allocating any transmit energy to the additional redundancy provided by this technique. The receiver implements a turbo processing by iteratively exchanging the soft information on coded bits between a SISO detector and a SISO decoder. In this system, detection is performed by incorporating the extrinsic information provided by the decoder in the last iteration into the received signal to calculate the likelihood of each detected bit in terms of LLR which is used as the input for a SISO decoder. In addition, SISO detectors are proposed for MC-CDMA and MIMO-CDMA systems that employ parity bit selected and permutation spreading. In the case of multiuser scenario, a turbo SISO multiuser detector is introduced for SS-PB systems for both synchronous and asynchronous channels. In such systems, MAI is estimated from the extrinsic information provided by the SISO channel decoder in the previous iteration. SISO multiuser detectors are also proposed for the case of multiple users in MC-CDMA and MIMO-CDMA systems when parity bit selected and permutation spreading are used. Simulations performed for all the proposed turbo receivers show a signi cant reduction in BER in AWGN and fading channels over multiple iterations.

Physical layer network coding (PNC) was proposed under the two-way relay hannel (TWRC) scenario, where two sources exchange information aided by a relay. PNC allows the two sources to transmit to the relay simultaneously, where superimposed signals at the relay can be mapped to network-coded symbols and then be broadcast to both sources instead of being treated as interference. Concurrent transmissions using PNC achieve a higher spectrum efficiency compared to time division and network coding solutions. Existing research mainly focused on the symmetric PNC designs, where the same channel coding and modulation configurations are applied by both sources. When the channel conditions of the two source-relay links are asymmetric or unequal amount of data are exchanged, heterogeneous modulation PNC designs are necessary. In additional, the design and optimization of multi-hop PNC, where multiple relays forming a multi-hop path between the two sources, remains an open issue. The above issues motivate the study of this dissertation. This dissertation investigates the design of heterogeneous modulation physical layer network coding (HePNC), the integration of channel error control coding into HePNC, the combination of HePNC with hierarchical modulation, and the design and generalization of multi-hop PNC. The contributions of this dissertation are four-fold. First, under the asymmetric TWRC scenario, where the channel conditions of the two source-relay links are asymmetric, we designed a HePNC protocol, including the optimization of the adaptive mapping functions and the bit-symbol labeling, to minimize the end-to-end BER. In addition, we developed an analytical framework to derive the BER of HePNC. HePNC can substantially enhance the throughput compared to the existing symmetric PNC under the asymmetric TWRC scenario. Second, we investigated channel coded HePNC and integrated the channel error control coding into HePNC in a link-to-link coding, where the relay tries to decode the superimposed codewords in the multi-access stage. A full-state sum-product decoding algorithm is proposed at the relay based on the repeat-accumulate codes to guarantee reliable end-to-end communication. Third, we proposed hierarchical modulation PNC (H-PNC) under asymmetric TWRC, where additional data exchange between the relay and the source with the relatively better channel condition is achieved in addition to that between the two end sources, benefiting from superimposing the additional data flow on the PNC transmission. When the relay also has the data exchange requirement with the source with a better source-relay channel, H-PNC outperforms HePNC and PNC in terms of the system sum throughput. Fourth, we designed and generalized multi-hop PNC, where multiple relays located in a linear topology are scheduled to support the data exchange between two end sources. The impact of error propagation and mutual interference among the nodes are addressed and optimized. The proposed designs outperform the existing ones in terms of end-to-end BER and end-to-end throughout. / Graduate

Orientador: Jaime Portugheis / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-18T15:49:19Z (GMT). No. of bitstreams: 1 PujaicoRivera_Fernando_M.pdf: 2105653 bytes, checksum: f62384ffbf5226353eba3406ba7735b8 (MD5) Previous issue date: 2011 / Resumo: Desde que Gallager introduziu o algoritmo de decodificação Bit-Flipping (BF) com decisão abrupta para códigos Low Density Parity Check (LDPC), outras duas variantes foram propostas por Sipser e Spielman para os códigos conhecidos como "Expander Codes". Posteriormente, uma versão da decodificação BF por decisão suave conhecida como decodificação Modified Weighted BF (MWBF), foi investigada. Esta tese propõe versões modificadas dos algoritmos de Sipser e Spielman. Resultados de simulações para códigos Low Density Generator Matrix (LDGM) sistemáticos, com comprimento longo mostraram um melhor desempenho da versão proposta. Adicionalmente, para um comprimento médio dos códigos LDGM, resultados de simulações mostraram um desempenho similar à decodificação MWBF com a vantagem de não ser necessário o uso de operações em ponto flutuante / Abstract: Since Gallager introduced Bit-Flipping (BF) decoding with hard-decision for Low-Density Parity- Check Codes (LDPC), other two variants were proposed by Sipser and Spielman for expander codes. Later, a soft-decision version of BF decoding, known as Modified Weighted BF (MWBF) decoding, was investigated. This thesis proposes modified versions of Sipser and Spielman algorithms. Simulation results for long systematic Low-Density Generator Matrix (LDGM) codes show a better performance of the proposed versions. Moreover, for moderate length systematic LDGM codes, simulation results show performance similar to that of MWBF decoding with the advantage of not requiring floating-point operations / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

This thesis focuses on the development and analysis of efficient simulation and inference techniques for Markovian pure jump processes with a view towards applications in dense communication networks. These techniques are especially relevant for modeling networks of smart devices —tiny, abundant microprocessors with integrated sensors and wireless communication abilities— that form highly complex and diverse communication networks. During 2010, the number of devices connected to the Internet exceeded the number of people on Earth: over 12.5 billion devices. By 2015, Cisco’s Internet Business Solutions Group predicts that this number will exceed 25 billion. The first part of this work proposes novel numerical methods to estimate, in an efficient and accurate way, observables from realizations of Markovian jump processes. In particular, hybrid Monte Carlo type methods are developed that combine the exact and approximate simulation algorithms to exploit their respective advantages. These methods are tailored to keep a global computational error below a prescribed global error tolerance and within a given statistical confidence level. Indeed, the computational work of these methods is similar to the one of an exact method, but with a smaller constant. Finally, the methods are extended to systems with a disparity of time scales. The second part develops novel inference methods to estimate the parameters of Markovian pure jump process. First, an indirect inference approach is presented, which is based on upscaled representations and does not require sampling. This method is simpler than dealing directly with the likelihood of the process, which, in general, cannot be expressed in closed form and whose maximization requires computationally intensive sampling techniques. Second, a forward-reverse Monte Carlo Expectation-Maximization algorithm is provided to approximate a local maximum or saddle point of the likelihood function of the parameters given a set of observations. The third part is devoted to applications in communication networks where also mean field or fluid approximations techniques, to substantially reduce the computational work of simulating large communication networks are explored. These methods aim to capture the global behaviour of systems with large state spaces by using an aggregate approximation, which is often described by means of a non-linear dynamical system.