Woven Graph Codes: Asymptotic Performances and Examples

Constructions of woven graph codes based on constituent block and convolutional codes are studied. It is shown that within the random ensemble of such codes based on $s$-partite, $s$-uniform hypergraphs, where $s$ depends only on the code rate, there exist codes satisfying the Varshamov-Gilbert (VG) and the Costello lower bound on the minimum distance and the free distance, respectively. A connection between regular bipartite graphs and tailbiting codes is shown. Some examples of woven graph codes are presented. Among them an example of a rate $R_{\rm wg}=1/3$ woven graph code with $d_{\rm free}=32$ based on Heawood's bipartite graph and containing $n=7$ constituent rate $R^{c}=2/3$ convolutional codes with overall constraint lengths $\nu^{c}=5$ is given. An encoding procedure for woven graph codes with complexity proportional to the number of constituent codes and their overall constraint length $\nu^{c}$ is presented.Comment: Submitted to IEEE Trans. Inform. Theor

Woven convolutional graph codes with large free distances

Constructions of woven graph codes based on constituent convolutional codes are studied and examples of woven convolutional graph codes are presented. The existence of codes, satisfying the Costello lower bound on the free distance, within the random ensemble of woven graph codes based on s-partite, s-uniform hypergraphs, where s depends only on the code rate, is shown. Simulation results for Viterbi decoding of woven graph codes are presented and discussed

A rate R=5/20 hypergraph-based woven convolutional code with free distance 120

A rate R=5/20 hypergraph-based woven convolu- tional code with overall constraint length 67 and constituent con- volutional codes is presented. It is based on a 3-partite, 3-uniform, 4-regular hypergraph and contains rate R=3/4 constituent convolutional codes with overall constraint length 5. Although the code construction is based on low-complexity codes, the free distance of this construction, computed with the BEAST algorithm, is dfree=120, which is remarkably large

Codes on Graphs and More

Modern communication systems strive to achieve reliable and efficient information transmission and storage with affordable complexity. Hence, efficient low-complexity channel codes providing low probabilities for erroneous receptions are needed. Interpreting codes as graphs and graphs as codes opens new perspectives for constructing such channel codes. Low-density parity-check (LDPC) codes are one of the most recent examples of codes defined on graphs, providing a better bit error probability than other block codes, given the same decoding complexity. After an introduction to coding theory, different graphical representations for channel codes are reviewed. Based on ideas from graph theory, new algorithms are introduced to iteratively search for LDPC block codes with large girth and to determine their minimum distance. In particular, new LDPC block codes of different rates and with girth up to 24 are presented. Woven convolutional codes are introduced as a generalization of graph-based codes and an asymptotic bound on their free distance, namely, the Costello lower bound, is proven. Moreover, promising examples of woven convolutional codes are given, including a rate 5/20 code with overall constraint length 67 and free distance 120. The remaining part of this dissertation focuses on basic properties of convolutional codes. First, a recurrent equation to determine a closed form expression of the exact decoding bit error probability for convolutional codes is presented. The obtained closed form expression is evaluated for various realizations of encoders, including rate 1/2 and 2/3 encoders, of as many as 16 states. Moreover, MacWilliams-type identities are revisited and a recursion for sequences of spectra of truncated as well as tailbitten convolutional codes and their duals is derived. Finally, the dissertation is concluded with exhaustive searches for convolutional codes of various rates with either optimum free distance or optimum distance profile, extending previously published results

Flax–Glass Fiber Reinforced Hybrid Composites Exposed to a Salt-Fog/Dry Cycle: A Simplified Approach to Predict Their Performance Recovery

Despite natural fibers gaining significant attention in recent decades, their limited performance and poor durability under humid environments cannot allow them to fully replace their synthetic counterparts as reinforcement for structural composites. In such a context, this paper aims to investigate how exposure to a humid/dry cycle affects the mechanical response of epoxy laminates reinforced with flax and glass fibers. In particular, the main goal is to assess the performance evolution of a glass–flax hybridized stacking sequence in comparison with the full glass and flax fiber reinforced composites. To this end, the investigated composites were first exposed to salt-fog for 15 or 30 days and then to dry conditions (i.e., 50% R.H. and 23 °C) for up to 21 days. The presence of glass fibers in the stacking sequence significantly stabilizes the mechanical performance of composites during the humid/dry cycle. Indeed, hybridization of inner flax laminae with outer glass ones, acting as a protective shield, hinders the composite degradation due to the humid phase also promoting performance recovery during the dry phase. Hence, this work showed that a tailored hybridization of natural fibers with glass fibers represents a suitable approach to extend the service-life of natural fiber reinforced composites exposed to discontinuous humid conditions, thus allowing their employment in practical indoor and outdoor applications. Finally, a simplified theoretical pseudo-second-order model that aimed to forecast the performance recovery shown by composites was proposed and experimentally validated, highlighting good agreement with the experimental data

The action of geotextiles in providing combined drainage and reinforcement to cohesive soil

PhD ThesisThis thesis describes a study into the action of geotextiles in providing combined drainage and reinforcement to cohesive soil and the identification of the interaction of different geotextiles with a cohesive soil. The study involved both experimental and analytical investigations. Fine grained cohesive soil is a complex material. The introduction of geosynthetics providing both drainage and a reinforcement function produce a marked increase in the shear strength characteristics of the clay material. A number of consolidated undrained and consolidated drained triaxial compression tests and Rowe cell consolidation tests were conducted. The objective of the tests was to identify the separate effects (improvement) on the shear strength properties of the cohesive soil (kaolin) provided by the drainage function and separately that provided by the reinforcing function of a number of geotextiles. An Electron Scanning Microscope study was used to investigate the interaction between the cohesive soil and the geosynthetic materials. The study provided qualitative information concerning the relative improvement of the physical properties of a fine grained cohesive soil when used in construction with range of geosynthetic materials. Analysis of the results of the research suggest that geotextile products could offer significant technical, practical and economic advantages when constructed with poor quality soils. The combined function of drainage and reinforcement which could be developed by some geosynthetic materials could be substantial. Combining the functions of drainage and reinforcement in a single material requires the resulting geosynthetic to have special properties. The form of a geocomposite drainage and reinforcement material with these properties is propose

New low-density parity-check codes with large girth based on hypergraphs

codes with large girth based on hypergraphs. In [Host publication title missing]. 10.1109/ISIT.2010.5513639 General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal? Take down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Download date: 17. Sep. 2016 IEEE COPYRIGHT NOTICE c©2010 IEEE. Personal use of this material is permitted. Permission fro

Searching for Voltage Graph-Based LDPC Tailbiting Codes with Large Girth

The relation between parity-check matrices of quasi-cyclic (QC) low-density parity-check (LDPC) codes and biadjacency matrices of bipartite graphs supports searching for powerful LDPC block codes. Using the principle of tailbiting, compact representations of bipartite graphs based on convolutional codes can be found. Bounds on the girth and the minimum distance of LDPC block codes constructed in such a way are discussed. Algorithms for searching iteratively for LDPC block codes with large girth and for determining their minimum distance are presented. Constructions based on all-ones matrices, Steiner Triple Systems, and QC block codes are introduced. Finally, new QC regular LDPC block codes with girth up to 24 are given.Comment: Submitted to IEEE Transactions on Information Theory in February 201

An exploratory study about Portuguese Music Festivals’ Word-of-Mouth (WOM)

Music festivals are crucial events in the Portuguese live show structure. There are hundreds per year, diverse in dimension, territory and musical genre, attracting millions of festivalgoers, who talk with their friends and family about it. Due to the social and experiential characteristics of music festivals, it is significantly important to find out how WOM is affecting their communication. There is a lack of research about which information and content constitutes Portuguese music festival’s WOM, through which channels it is spread, who is more susceptible of engaging in it, and how it can affect audiences. This dissertation aims to provide insights on this behalf. It is based on literature relating music festivals with marketing strategies, more specifically on word-of-mouth. It also analyzes the impact of content circulation on social media pages, affecting music festivals’ communication. A complementary purpose of this paper is to examine if the results vary according to type of festival and with audience demographic characteristics. Data were collected concerning six Portuguese music festivals – NOS Alive, Vodafone Paredes de Coura, NEOPOP, Festival Músicas do Mundo, EDPCOOLJAZZ and MUSA Cascais – through a web-based survey which gathered 288 respondents. The results show that information related with the lineup and useful details about the festival organization are the topics that festivalgoers search the most. What they prefer to share are visual memories from past editions, information about the lineup and content produced in real time during the event. Social media pages are their favorite channel to engage in both input and output WOM. By doing so, festivalgoers are also co-producers, acting as brand ambassadors of music festivals. The results also show that satisfied and recurrent festivalgoers are more propense of engaging in output WOM. Most of them were influenced by friends or relatives to attend the event. There were no big discrepancies between festivalgoers and non-festivalgoers’ perceptions towards the event. Other finding is that non-festivalgoers also engage in WOM. Even though advertising is the primary communication channel raising awareness about Portuguese music festivals, WOM also plays a significant role in regard to this matter.Os festivais de música desempenham um papel fundamental na estrutura dos espetáculos ao vivo em Portugal. Existem centenas destes eventos por ano, diversos em dimensão, território, e género musical, atraindo milhões de festivaleiros que partilham as experiências vividas com os seus amigos e familiares. Devido às suas características sociais e experienciais, é relevante analisar o papel do passa-a-palavra na comunicação dos festivais de música em Portugal. Pouco se sabe sobre este tema. Qual a informação e conteúdo que o constitui, através de que canais se espalha, quem é mais suscetível de se envolver nesse processo, e qual o impacto que tem nas audiências. A presente dissertação pretende fornecer conhecimentos nesse sentido. Foca também o impacto que a circulação de conteúdos tem nas redes sociais, afetando a comunicação dos festivais de música. Um propósito adicional é o de investigar se os resultados obtidos variam consoante o tipo de festival e as características demográficas dos participantes. Foram recolhidos dados relativos a seis festivais de música portugueses - NOS Alive, Vodafone Paredes de Coura, NEOPOP, Festival Músicas do Mundo, EDPCOOLJAZZ e MUSA Cascais – através de um formulário online que reuniu 288 respostas válidas. Os resultados demonstram que os festivaleiros procuram maioritariamente informação sobre o cartaz e detalhes úteis acerca da organização do festival. O que preferem partilhar são memórias visuais de edições anteriores, conteúdo produzido em tempo real e informação sobre o programa. As redes sociais são o seu meio favorito neste processo. Ao produzir e partilhar este tipo de conteúdo, os festivaleiros agem como embaixadores destes eventos. Os resultados demonstram ainda que os festivaleiros regulares e satisfeitos são os mais propensos a partilhar dados acerca do evento. A maioria foi influenciada por amigos ou familiares a frequentar o festival. Não houve grandes discrepâncias entre as perceções dos festivaleiros e dos restantes inquiridos. Os participantes que não foram aos eventos em análise, também se envolveram no passa-a-palavra. Apesar de a publicidade ter sido o principal meio de divulgação dos festivais de música em Portugal, o passa-a-palavra também se revelou importante nesse sentido

Optimisation de la transmission de phonie et vidéophonie sur les réseaux à larges bandes PMR

Cet exposé analyse les perspectives large bande des réseaux PMR, à travers l'évaluation du candidat LTE, et la proposition d'une possible évolution du codage canal, la solution brevetée des codes turbo à protection non uniforme. Une première étude dans le chapitre 2 se concentre sur l'analyse multi-couche et l'identification des problèmes clé des communications de voix et de vidéo sur un réseau LTE professionnel. Les capacités voix et vidéo sont estimées pour les liens montant et descendant de la transmission LTE, et l'efficacité spectrale de la voix en lien descendant est comparée à celle de PMR et GSM. Ce chapitre souligne certains points clé de l'évolution de LTE. S'ils étaient pas résolus par la suite, LTE se verrait perdre de sa crédibilité en tant que candidat à l'évolution de la PMR. Une telle caractéristique clé des réseaux PMR est le codage canal à protection non uniforme, qui pourrait être adapté au système LTE pour une évolution aux contraintes de la sécurité publique. Le chapitre 3 introduit cette proposition d'évolution, qui a été brevetée: les turbo codes à protection non uniforme intégrée. Nous proposons une nouvelle approche pour le codage canal à protection non uniforme à travers les codes turbo progressives hiérarchiques. Les configurations parallèles et séries sont analysées. Les mécanismes de protection non uniformes sont intégrés dans la structure de l'encodeur même à travers l'insertion progressif et hiérarchique de nouvelles données de l'utilisateur. Le turbo décodage est modifié pour exploiter de façon optimale l'insertion progressive de données dans le processus d'encodage et estimer hiérarchiquement ces données. Les propriétés des structures parallèles et séries sont analysées à l'aide d'une analogie aux codes pilotes, ainsi qu'en regardant de plus près leurs caractéristiques de poids de codage. Le taux de transmission virtuel et les représentations des graphs factor fournissent une meilleure compréhension de ces propriétés. Les gains de codage sont évalués à l'aide de simulations numériques, en supposant des canaux de transmission radio statiques et dynamiques, et en utilisant des codes de référence. Enfin, dans le chapitre 4, l'idée breveté du code turbo parallal progressif et hiérarchique (PPHTC) est évaluée sur la plateforme LTE. Une description détaillée de l'architecture des bearers de LTE est donnée, et ses conséquences sont discutées. Le nouveau codage canal est inséré et évalué sur cette plateforme, et ses performances sont comparées avec des schémas de transmission typique à LTE. L'analyse de la qualité de la voix aide à conclure sur l'efficacité de la solution proposée dans un système de transmission réel. Pourtant, même si cette dernière donne les meilleurs résultats, d'avantage d'optimisations devraient être envisagées pour obtenir des gains améliorés et mieux exploiter le potentiel du codage proposé. L'exposé se conclut dans le chapitre 5 et une courte discussion présente les futures perspectives de rechercheThis dissertation analyzes the PMR broadband perspectives, through the evaluation of the preferred candidate, LTE, and the proposal of a possible channel coding evolution, the patented solution of unequal error protection embedded turbo codes. A first study in chapter 2 focuses on the multi-layer analysis and the identification of key issues for professional-like LTE for voice and video communications. The voice and video capacities are estimated for both downlink and uplink LTE transmissions, and the downlink LTE voice system efficiency is compared with that of the PMR and Global System for Mobile Communications (GSM). This chapter helps highlighting some of the key points. If not resolved, the latter could lead to the LTE downfall as a candidate for the PMR evolution. One such key characteristic of PMR systems is the unequal error protection channel coding technique, which might be adapted to the LTE technology for its evolution to public safety requirements. Chapter 3 further introduces the proposed evolution patented ideas: the unequal error protection embedded turbo codes. We propose a new approach for the unequal error protection channel coding through the progressive hierarchical turbo codes. Both parallel and serial turbo configurations are closely studied. The unequal error protection mechanisms are embedded in the encoder s structure itself through the progressive and hierarchical insertion of new data. The turbo decoding is modified as to optimally exploit the progressive insertion of information in the encoding process and hierarchically estimate the corresponding data. Both parallel and serial configurations properties are analyzed using an analogy with a pilot code behavior, as well as a zoom on the weight error functions coefficients. The virtual code rate and factor graph interpretations also provide a better insight on the code properties. The code possible gains are highlighted through computer simulations in both static and dynamic transmission environments, by using carefully chosen benchmarks. Finally, in chapter 4, the patented idea of parallel progressive hierarchical turbo codes (PPHTC) is evaluated over the LTE platform. A detailed description is given of the voice transmission bearer architecture over LTE, and its consequences are discussed. The new channel code is inserted and evaluated over this platform and its performances compared with the existent LTE transmission schemes. The voice quality results help concluding on the efficiency of the proposed solution in a real transmission scenario. However, even though the newly presented solution gives the best results, further system optimizations should be envisaged for obtaining better gains and exploit the parallel progressive hierarchical turbo codes potential. The dissertation concludes in chapter 5 and a short discussion is given on future research perspectivesEVRY-INT (912282302) / SudocSudocFranceF