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Physical-layer securityBloch, Matthieu 05 May 2008 (has links)
As wireless networks continue to flourish worldwide and play an increasingly prominent role, it has become crucial to provide effective solutions to the inherent security issues associated with a wireless transmission medium. Unlike traditional solutions, which usually handle security at the application layer, the primary concern of this thesis is to analyze and develop solutions based on coding techniques at the physical layer.
First, an information-theoretically secure communication protocol for quasi-static fading channels was developed and its performance with respect to theoretical limits was analyzed. A key element of the protocol is a reconciliation scheme for secret-key agreement based on low-density parity-check codes, which is specifically designed to operate on non-binary random variables and offers high reconciliation efficiency.
Second, the fundamental trade-offs between cooperation and security were analyzed by investigating the transmission of confidential messages to cooperative relays. This information-theoretic study highlighted the importance of jamming as a means to increase secrecy and confirmed the importance of carefully chosen relaying strategies.
Third, other applications of physical-layer security were investigated. Specifically, the use of secret-key agreement techniques for alternative cryptographic purposes was analyzed, and a framework for the design of practical information-theoretic commitment protocols over noisy channels was proposed.
Finally, the benefit of using physical-layer coding techniques beyond the physical layer was illustrated by studying security issues in client-server networks. A coding scheme exploiting packet losses at the network layer was proposed to ensure reliable communication between clients and servers and security against colluding attackers.
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Implementação de técnicas robustas de codificação e modulação para o sistema ISDB-TB LDMOliveira, George Henrique Maranhão Garcia de 06 February 2017 (has links)
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Previous issue date: 2017-02-06 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Fundo Mackenzie de Pesquisa / This work presents the characteristics of the ISDB-TB, adopted in Brazil as part of
Digital TV Brazilian System (SBTVD) and the challenges and needed adaptations for
the next digital TV generations. It also shows the historic of SDR, physical layer LDM,
NUC modulations and error correction code LDPC technologies. Their advantages are
demonstrated in terms of eficient use of spectrum, robustness and increase of transmission
rate. A digital communication system with this technologies was proposed, allowing the
compatibility with the ISDB-TB system. The focus of this work are the stages of coding
and modulation in the LDM lower layer, enabling better performance of this technique in
the ISDB-TB system. This implementation was performed with the software GNU Radio
Companion and the use of the C ++ language. / Este trabalho apresenta as características do ISDB-TB, adotado no Brasil como parte
do Sistema Brasileiro de TV Digital (SBTVD) e os desafios e adaptações necessárias para
as próximas gerações da TV digital. O trabalho também mostra o histórico das tecnologias
SDR, camada física LDM, modulações NUC e código corretor de erro LDPC. Suas
vantagens de utilização são demonstradas em termos de sua eficiência espectral, robustez
e do aumento da taxa de dados transmitida. Um sistema de comunicação digital unindo
estas tecnologias é proposto, permitindo a compatibilidade com o sistema ISDB-TB. O
foco deste trabalho são as etapas de codificação e modulação da camada inferior do LDM,
permitindo maior desempenho desta técnica no sistema ISDB-TB. Esta implementação
foi realizada com o software GNU Radio Companion e o uso da linguagem C++.
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Improvement for LDPC Coded OFDM Communication System over Power LineDan, Wu January 2013 (has links)
Power line communication has been around in past decades and gained renewed attention thanks to the demand of high-speed Internet access. With the significant advantages of existing infrastructure and accessibility to even remote areas, power grid has become one of the promising competitors for multi-media transmission in household. However, the power line was not oriented for data transmission providing a rather hash environment. To overcome the difficulties, advanced modulation and channel coding schemes should be employed. In the thesis low density parity check code (LDPC) is employed to reduce the loss caused by various kinds of effects in the channel especially the noise since its performance approaches to Shannon capacity limit. Moreover, OFDM multi-carrier transmission technique is involved which could decrease the inter-symbol interference and frequency selective fading. Nevertheless, LDPC decoding process was designed specifically for the common Gaussian white noise condition, combined with OFDM modulation the system still could not provide satisfying and practicable performance so improvements are needed for the system. The main works of the thesis are as follows. Set up an environment of power line transmission investigating and simulating the channel characteristics; employ multi-path channel model and Class‐A noise model for further developing the improvement algorithms to deal with the selective fading and impulse noise. Two algorithms proposed here are from different perspectives: the first one is modifying initial posterior information for LDPC decoding and the second one aims at suppressing the impulse noise after demodulation. Finally, a few simulations are performed to reveal the effectiveness of proposed methods. As a result, the improved scheme shows a great superiority improving the performance by no less than 5dB compared to traditional system.
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Reconnaissance de codes correcteurs / Blind reconstruction of error-correcting codesTixier, Audrey 14 October 2015 (has links)
Dans cette thèse, nous nous intéressons au problème de la reconnaissance de code. Ce problème se produit principalement lorsqu'une communication est observée dans un milieu non-coopératif. Une liste de mots bruités issus d'un code inconnu est obtenue, l'objectif est alors de retrouver l'information contenue dans ces mots bruités. Pour cela, le code utilisé est reconstruit afin de décoder les mots observés. Nous considérons ici trois instances de ce problème et proposons pour chacune d'elle une nouvelle méthode. Dans la première, nous supposons que le code utilisé est un turbo-code et nous proposons une méthode pour reconstruire la permutation interne (les autres éléments du turbo-codeur pouvant être facilement reconstruits grâce aux méthodes existantes). Cette permutation est reconstruite pas à pas en recherchant l'indice le plus probable à chaque instant. Plus précisément, la probabilité de chaque indice est déterminée avec l'aide de l'algorithme de décodage BCJR. Dans la seconde, nous traitons le problème de la reconnaissance des codes LDPC en suggérant une nouvelle méthode pour retrouver une liste d'équations de parité de petits poids. Celle-ci généralise et améliore les méthodes existantes. Finalement, avec la dernière méthode, nous reconstruisons un code convolutif entrelacé. Cette méthode fait appel à la précédente pour retrouver une liste d'équations de parité satisfaites par le code entrelacé. Puis, en introduisant une représentation sous forme de graphe de l'intersection de ces équations de parité, nous retrouvons simultanément l'entrelaceur et le code convolutif. / In this PhD, we focus on the code reconstruction problem. This problem mainly arises in a non-cooperative context when a communication consisting of noisy codewords stemming from an unknown code is observed and its content has to be retrieved by recovering the code that is used for communicating and decoding with it the noisy codewords. We consider here three possible scenarios and suggest an original method for each case. In the first one, we assume that the code that is used is a turbo-code and we propose a method for reconstructing the associated interleaver (the other components of the turbo-code can be easily recovered by the existing methods). The interleaver is reconstructed step by step by searching for the most probable index at each time and by computing the relevant probabilities with the help of the BCJR decoding algorithm. In the second one, we tackle the problem of reconstructing LDPC codes by suggesting a new method for finding a list of parity-check equations of small weight that generalizes and improves upon all existing methods. Finally, in the last scenario we reconstruct an unknown interleaved convolutional code. In this method we used the previous one to find a list of parity-check equations for this code. Then, by introducing a graph representing how these parity-check equations intersect we recover at the same time the interleaver and the convolutional code.
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Circular Trellis based Low Density Parity Check CodesAnitei, Irina 19 December 2008 (has links)
No description available.
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Investigation on Digital Fountain Codes over Erasure Channels and Additive White Gaussian Noise ChannelsHuang, Weizheng 25 July 2012 (has links)
No description available.
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An LDPC error control strategy for low earth orbit satellite communication link applicationsOlivier, Francois Jacobus 12 1900 (has links)
Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Low earth orbit (LEO) satellite communication presents a unique environment
which inherently di ers from most other communication channels.
Due to the varying orbital patterns of LEO satellites the link exhibits varying
link margins. Limited communication time windows need to be optimised to
maximise the volumetric data throughput.
Large coding gains can be obtained by the implementation of forward error
correction codes. This thesis presents a means for optimising the data
throughput of LEO satellite communication through the implementation of a
mission speci c error control strategy. Low density parity check (LDPC) codes
are versatile and present good error performances at many di erent code rates
and block lengths. With power limitations on the space segment and remote
ground stations, hardware utilisation e ciency must be optimised to reduce
power consumption. In response to this requirement, this thesis evaluates
various algorithms for LDPC decoders.
An iterative LDPC decoder, implementing an approximation algorithm,
is presented as a low complexity solution with good error performance. The
proposed solution provides a very good balance between required hardware
complexity and coding performance. It was found that many parameters of
the decoders and codes can be altered to allow the implementation of these
codes in systems with varying memory and processing capabilities. / AFRIKAANSE OPSOMMING: Kommunikasiekanale van satelliete met lae wentelbane, bied 'n unieke omgewing
wat inherent verskil van meeste ander kommunikasiekanale. As gevolg
van veranderende wentelbaanpatrone, vertoon die kanaal 'n wisselende foutgedrag.
Kommunikasievensters is beperk en moet geoptimeer word om die totale
deurset van die stelsel te maksimeer.
Groot koderingswinste kan verkry word deur die implementering van foutkorreksie
kodes. Hierdie tesis voorsien 'n metode om die datadeurset van
satelliete met lae wentelbaan te optimeer, deur middel van implementering
van 'n missie-spesi eke foutbeheer strategie. Lae digtheid pariteit toetskodes
(LDPC) is veelsydige kodes, bied goeie foutbeheer en is doeltre end vir verskillende
kodekoerse en bloklengtes. Met drywingsbeperkinge op die ruimtesegment
en afgesonderde grondstasies, moet hardeware komponente doeltreffend
gebruik word om drywingsverbruik te verminder. Ten einde aan hierdie
ontwerpsvereiste te voldoen, evalueer hierdie tesis verskeie LDPC dekodeerderalgoritmes.
Deur 'n iteratiewe LDPC dekodeerder met 'n benaderingsalgoritme te implementeer,
word 'n oplossing van lae kompleksiteit aangebied, maar wat steeds
goeie foutkorreksie eienskappe toon. Die voorgestelde oplossing bied 'n baie
goeie balans tussen benodigde hardeware kompleksiteit en koderingsprestasie.
Daar is gevind dat heelwat parameters van die dekodeerders en kodes aangepas
kan word, ten einde implementering in stelsels met 'n wye verskeidenheid van
geheuespasie en verwerkingsvermoëns moontlik te maak.
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Implementation of a protocol and channel coding strategy for use in ground-satellite applicationsWiid, Riaan 03 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A collaboration between the Katholieke Universiteit van Leuven (KUL) and
Stellenbosch University (SU), resulted in the development of a satellite based
platform for use in agricultural sensing applications. This will primarily serve
as a test platform for a digitally beam-steerable antenna array (SAA) that was
developed by KUL. SU developed all flight - and ground station based hardware
and software, enabling ground to flight communications and interfacing with
the KUL SAA. Although most components had already been completed at the
start of this M:Sc:Eng: project, final systems integration was still unfinished.
Modules necessary for communication were also outstanding. This project
implemented an automatic repeat and request (ARQ) strategy for reliable file
transfer across the wireless link. Channel coding has also been implemented
on a field programmable gate array (FPGA). This layer includes an advanced
forward error correction (FEC) scheme i.e. a low-density parity-check (LDPC),
which outperforms traditional FEC techniques. A flexible architecture for
channel coding has been designed that allows speed and complexity trade-offs
on the FPGA. All components have successfully been implemented, tested and
integrated. Simulations of LDPC on the FPGA have been shown to provide
excellent error correcting performance. The prototype has been completed and
recently successfully demonstrated at KUL. Data has been reliably transferred
between the satellite platform and a ground station, during this event. / AFRIKAANSE OPSOMMING: Tydens ’n samewerkingsooreenkoms tussen die Katholieke Universiteit van
Leuven (KUL) en die Universiteit van Stellenbosch (US) is ’n satelliet stelsel
ontwikkel vir sensor-netwerk toepassings in die landbou bedryf. Hierdie stelsel
sal hoofsaaklik dien as ’n toetsmedium vir ’n digitaal stuurbare antenna
(SAA) wat deur KUL ontwikkel is. Die US het alle hardeware en sagteware
komponente ontwikkel om kommunikasie d.m.v die SAA tussen die satelliet en
’n grondstasie te bewerkstellig. Sedert die begin van hierdie M:Sc:Ing: projek
was die meeste komponente alreeds ontwikkel en geïmplementeer, maar
finale stelselsintegrasie moes nog voltooi word. Modules wat kommunikasie
sou bewerkstellig was ook nog uistaande. Hierdie projek het ’n ARQ protokol
geïmplementeer wat data betroubaar tussen die satelliet en ’n grondstasie
kon oordra. Kanaalkodering is ook op ’n veld programmeerbare hekskikking
(FPGA) geïmplementeer. ’n Gevorderde foutkorrigeringstelsel, naamlik ’n lae
digtheids pariteit toetskode (LDPC), wat tradisionele foutkorrigeringstelsels
se doeltreffendheid oortref, word op hierdie FPGA geïmplementeer. ’n Kanaalkoderingsargitektuur
is ook ontwikkel om die verwerkingspoed van data
en die hoeveelheid FPGA logika wat gebruik word, teenoor mekaar op te weeg.
Alle komponente is suksesvol geïmplementeer, getoets en geïntegreer met die
hele stelsel. Simulasies van LDPC op die FPGA het uistekende foutkorrigeringsresultate
gelewer. ’n Werkende prototipe is onlangs voltooi en suksesvol
gedemonstreer by KUL. Betroubare data oordrag tussen die satelliet en die
grondstasie is tydens hierdie demonstrasie bevestig.
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JPEG 2000 and parity bit replenishment for remote video browsingDevaux, François-Olivier 19 September 2008 (has links)
This thesis is devoted to the study of a compression and transmission framework for video. It exploits the JPEG 2000 standard and the coding with side information principles to enable an efficient interactive browsing of video sequences. During the last decade, we have witnessed an explosion of digital visual information as well as a significant diversification of visualization devices. In terms of viewing experience, many applications now enable users to interact with the content stored on a distant server. Pausing video sequences to observe details by zooming and panning or, at the opposite, browsing low resolutions of high quality HD videos are becoming common tasks. The video distribution framework envisioned in this thesis targets such devices and applications.
Based on the conditional replenishment framework, the proposed system combines two complementary coding methods. The first one is JPEG 2000, a scalable and very efficient compression algorithm. The second method is based on the coding with side information paradigm. This technique is relatively novel in a video context, and has been adapted to the particular scalable image representation adopted in this work. Interestingly, it has been improved by integrating an image source model and by exploiting the temporal correlation inherent to the sequence.
A particularity of this work is the emphasis on the system scalability as well as on the server complexity. The proposed browsing architecture can scale to handle large volumes of content and serve a possibly very large number of heterogeneous users. This is achieved by defining a scheduler that adapts its decisions to the channel conditions and to user requirements expressed in terms of computational capabilities and spatio-temporal interest.
This scheduling is carried out in real-time at low computational cost and in a post-compression way, without re-encoding the sequences.
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Large Scale Content Delivery applied to Files and VideosNeumann, Christoph 14 December 2005 (has links) (PDF)
Le multicast fiable est certainement la solution la plus efficace pour la distribution de contenu via un<br />tres grand nombre (potentiellement des millions) de recepteurs. Dans cette perspective les protocoles<br />ALC et FLUTE, standardises via l'IETF (RMT WG), ont ete adoptes dans 3GPP/MBMS et dans le<br />DVB-H IP-Datacast dans les contextes des reseaux cellulaires 3G.<br />Ce travail se concentre sur le multicast fiable et a comme requis principal le passage l'echelle massif<br />en terme de nombre de clients. Cette these se base sur les solutions proposees via l'IETF RMT WG.<br />Ces protocoles de multicast fiable sont construit autour de plusieurs briques de base que nous avons<br />etudie en detail:<br />* La brique Forward Error Correction (FEC) :<br />Nous examinons la classe de codes grands blocs Low Density Parity Check (LDPC). Nous concevons<br />des derivees de ces codes, et les analysons en detail. Nous en concluons que les codes<br />LDPC et leur implementation ont des performances tres prometteuses, surtout si ils sont utilisees<br />avec des fichiers de taille importante.<br />* La brique controle de congestion :<br />Nous examinons le comportement dans la phase de demarrage de trois protocoles de controle de<br />congestion RLC, FLID-SL, WEBRC. Nous demontrons que la phase de demarrage a un grand<br />impact sur les performances de telechargement.<br />Cette these a aussi plusieurs contributions au niveau applicatif:<br />* Extensions de FLUTE :<br />Nous proposons un mecanisme permettant d'agreger plusieurs fichiers dans le protocole FLUTE.<br />Ceci ameliore les performance de transmission.<br />* Streaming video :<br />Nous proposons SVSoA, une solution de streaming base sur ALC. Cette approche beneficie de<br />tout les avantages de ALC en terme de passage a l'echelle, controle de congestion et corrections<br />d'erreurs.<br /><br />Mots cles : Multicast fiable, FLUTE, ALC, codes correcteur d'erreurs, Forward Error Correction<br />(FEC), Low Density Parity Check (LDPC) Codes, diffusion de contenu
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