39 research outputs found

    Woven Graph Codes: Asymptotic Performances and Examples

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    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 ss-partite, ss-uniform hypergraphs, where ss 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 Rwg=1/3R_{\rm wg}=1/3 woven graph code with dfree=32d_{\rm free}=32 based on Heawood's bipartite graph and containing n=7n=7 constituent rate Rc=2/3R^{c}=2/3 convolutional codes with overall constraint lengths νc=5\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 νc\nu^{c} is presented.Comment: Submitted to IEEE Trans. Inform. Theor

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

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    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

    Woven convolutional graph codes with large free distances

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    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

    Codes on Graphs and More

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    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

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

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    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

    Domain specific high performance reconfigurable architecture for a communication platform

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    Geometry and Topology in Memory and Navigation

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    Okinawa Institute of Science and Technology Graduate UniversityDoctor of PhilosophyGeometry and topology offer rich mathematical worlds and perspectives with which to study and improve our understanding of cognitive function. Here I present the following examples: (1) a functional role for inhibitory diversity in associative memories with graph- ical relationships; (2) improved memory capacity in an associative memory model with setwise connectivity, with implications for glial and dendritic function; (3) safe and effi- cient group navigation among conspecifics using purely local geometric information; and (4) enhancing geometric and topological methods to probe the relations between neural activity and behaviour. In each work, tools and insights from geometry and topology are used in essential ways to gain improved insights or performance. This thesis contributes to our knowledge of the potential computational affordances of biological mechanisms (such as inhibition and setwise connectivity), while also demonstrating new geometric and topological methods and perspectives with which to deepen our understanding of cognitive tasks and their neural representations.doctoral thesi

    A novel concept of non-metallic orthopedic implants for load-bearing applications

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    Metallic implants have remained the state of the art for skeletal reconstruction for over a hundred years. However, the excessive stiffness of metallic implants can lead to unphysiological direct bone healing and bone resorption in both humans and animals. Fiber reinforced composites (FRC) were proposed as alternative to metals in the “less rigid fixation” concept and were successfully approved in animal models and in clinical trials in humans as early as in 1970th and 1980th. However, the use of FRC implants is still limited due to such drawbacks as the lack of contourability, which is desirable in many applications, and high manufacturing costs. The present dissertation addresses the limitations of FRC implants and suggests a novel concept of non-metallic load-bearing implants. The research further develops the “less rigid fixation” concept and complements it with the application of modern additive manufacturing and composite technologies, such as 3D printing and tailored fiber placement (TFP). The novel concept assumes that the design of the implants does not simply copy the existing conventional metallic counterparts but is initially aimed at the specified fabrication methods to reduce the costs and improve the tailorability and scalability for different clinical conditions and patients. The concept allows application of both biostable and bioresorbable polymeric materials, can be implemented in various designs and can be combined with bioactive agents to stimulate bone growth and decrease the rate of complications related to infections. The dissertation includes four multidisciplinary studies in which the concept was described, and the basic aspects of that were investigated. Two different clinical problems, frequently occurred in veterinary practice, were addressed. Two prototype designs, an FRC fracture fixation plate, made by TFP and intended for the treatment of antebrachial fractures in toy-breed dogs, and a 3D-printed bioresorbable bioactive tibial tuberosity advancement implant for the treatment of cranial cruciate ligament disease in large dogs, were proposed based on the findings of the research. It is expected that the novel implants can improve the ossification and decrease the complications rate in animals. In addition, the present research serves as the first step towards the anticipated implementation of the novel concept in implants for humans.Uudenlainen konsepti metallittomiksi ortopedisiksi implanteiksi kuormaa kantaviin sovelluksiin Luuston korjauksessa on yli sadan vuoden ajan käytetty pääosin metallisia implantteja. Niiden jäykkyys voi kuitenkin johtaa epäfysiologiseen suoraan luunmuodostukseen ja luun resorptioon sekä ihmisillä että eläimillä. Kuitulujitettuja komposiittimateriaaleja (fiber reinforced composite, FRC) on 1970- ja 1980-luvuilta lähtien onnistuneesti kokeiltu eläinkokeissa ja kliinisissä kokeissa vähemmän jäykkänä vaihtoehtona metalleille. FRC-implanttien käyttö on toistaiseksi ollut rajallista, sillä valmistuksen jälkeen ne eivät ole muovattavissa, mikä olisi suotava ominaisuus monessa käytännön sovellutuksessa, ja niiden valmistus on kallista. Tässä väitöskirjassa paneudutaan FRC-implanttien puutteisiin ja ehdotetaan uudenlaista konseptia metallittomiksi kuormaa kantaviksi implanteiksi. Tutkimuksessa kehitettiin vähemmän jäykkää luufiksaatiota moderneilla 3D-tulostus- ja räätälöity kuitusijoitus (tailored fiber placement, TFP) -tekniikoilla. Implantit on varta vasten valituille valmistustekniikoille suunniteltu, eivätkä pelkkiä kopioita metallisista vastineistaan. Tarkoituksena on vähentää valmistuksen kustannuksia ja parantaa implanttien muokattavuutta erilaisia kliinisiä tilanteita ja potilaita varten. Konsepti mahdollistaa sekä biohajoavien että biohajoamattomien implanttien valmistuksen eri muodoissa, ja siihen voidaan yhdistää bioaktiivisia yhdisteitä stimuloimaan luun kasvua ja vähentämään infektioista johtuvia komplikaatioita. Väitöskirjan neljässä poikkitieteellisessä osatyössä konsepti kuvaillaan ja sen perusominaisuuksia tutkitaan. Implanttiprototyypit kehitettiin kahteen yleiseen eläinlääketieteelliseen kliiniseen ongelmaan: TFP-tekniikalla valmistettu FRCfiksaatiolevy radiuksen ja ulnan murtumien hoitoon pienikokoisilla koirilla, ja isojen koirien polven eturistisidevaurioiden hoitoon tarkoitettu 3D-tulostettu bioaktiivinen ja bioresorboituva implantti sääriluun kyhmyn eteenpäin siirtämiseksi. Oletuksena on, että implantit parantavat luutumista ja vähentävät komplikaatioriskiä eläimillä. Lisäksi tämä tutkimus on ensimmäinen askel tämän uudenlaisen konseptin käyttöön ihmisillä
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