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Ce travail est consacré à la conception, l'analyse et l'optimisation des codes correcteurs d'effacements de niveau applicatif (AL-FEC). Nous nous intéressons à une famille des codes LDPC généralisés (GLDPC), nommés les codes GLDPC-Staircase, qui sont composé d'un code LDPC-Staircase code de base ainsi que des codes Reed-Solomon (RS) (codes externes). Dans la première partie de cette thèse, nous commençons par montrer que les codes RS ayant une construction basée sur la matrice "quasi" Hankel sont les codes MDS les plus appropriés pour obtenir la structure des codes GLDPC-Staircase. Ensuite, nous proposons un nouveau type de décodage à ces codes, baptisé décodage hybride (IT/RS/ML), pour atteindre les capacités de correction du décodage par maximum de vraisemblance (ML) avec de faible complexité. Afin d'étudier l'impact de la structure des codes GLDPC-Staircase sur le décodage, nous proposons une autre construction : ils diffèrent sur la nature des symboles de redondance LDPC générés. Puis, pour prédire le seuil de décodage et les écarts par rapport à la limite de Shannon des codes GLDPC-Staircase, nous élaborons une analyse asymptotique en fonction de la technique d'évolution de densité (DE), les technique EXIT (Extrinsic Information Transfer) et la théorème d'air. Finalement, en se basant sur l'analyse à taille finie et l'analyse asymptotique, nous réglons les importants paramètres internes de ces codes pour obtenir la configuration optimale sous le décodage hybride (IT/RS/ML). La deuxième partie de la thèse est consacrée à l'étude des codes GLDPC-Staircase dans diverses situations. Tout d'abord, nous montrons que ces codes ont des performances asymptotiquement très proches des limites théoriques de Shannon. En plus, à taille fini, ils permettent d'atteindre d'excellentes capacités de correction d'effacements (i.e., très proches de celle des codes MDS idéal) peu importe la taille des objets : très faible overhead de décodage, faible plancher d'erreur, et une zone ``waterfull'' raide. Nous montrons aussi que ces codes surpassent les codes Raptor, les codes LDPC-Staircase, et un autre code GLDPC avec une construction differente. Finallement, nous proposons une méthodologie générale pour régler le problème de l'impact de l'ordonnancement des paquets sur les performance des codes GLDPC-Staircase sur un grand nombre des canaux à effacements (avec perte en rafale ou pas). Cette étude montre le meilleur ordonnancement de paquets. Tous les résultats mentionnés ci-dessus montrent que les codes GLDPC-Staircase peuvent considérés comme des codes FEC de niveau applicatif (AL-FEC) universelle. / This work is dedicated to the design, analysis and optimization of Application-Level Forward Erasure Correction (AL-FEC) codes. In particular, we explore a class of Gen- eralized LDPC (GLDPC) codes, named GLDPC-Staircase codes, involving the LDPC- Staircase code (base code) as well as Reed-Solomon (RS) codes (outer codes). In the first part of this thesis, we start by showing that RS codes having “quasi” Han- kel matrix-based construction are the most suitable MDS codes to obtain the structure of GLDPC-Staircase codes. Then, we propose a new decoding type, so-called hybrid (IT/RS/ML) decoding, for these codes to achieve Maximum Likelihood (ML) correction capabilities with a lower complexity. To investigate the impact of the structure of GLDPC- Staircase codes on decoding, we propose another construction: they differ on the nature of generated LDPC repair symbols. Afterwards, to predict the capacity approaching GLDPC- Staircase codes, we derive an asymptotic analysis based on DE, EXIT functions, and area theorem. Eventually, based on finite length analysis and asymptotic analysis, we tune important internal parameters of GLDPC-Staircase codes to obtain the best configuration under hybrid (IT/RS/ML) decoding. The second part of the thesis benchmarks GLDPC-Staircase codes in various situations. First, we show that these codes are asymptotically quite close to Shannon limit performance and achieve finite length excellent erasure correction capabilities very close to that of ideal MDS codes no matter the objects size: very small decoding overhead, low error floor, and steep waterfall region. Second, we show that these codes outperform Raptor codes, LDPC- Staircase codes, other construction of GLDPC codes, and have correction capabilities close to that of RaptorQ codes. Last but not least, we propose a general-methodology to address the problem of the impact of packet scheduling on GLDPC-Staircase codes for a large set of loss channels (with burst loss or not). This study shows the best packet scheduling. All the aforementioned results make GLDPC-Staircase codes an ubiquitous Application-Level FEC (AL-FEC) solution.

The objective of this dissertation is to investigate incremental redundancy low-density parity-check (IR-LDPC) codes for hybrid forward error correction / automatic repeat request (HybridARQ) schemes. Powerful capacity-approaching IR-LDPC codes are one of the key functional elements in high-throughput HybridARQ schemes and provide a flexible rate-compatible structure, which is necessary for low-complexity HybridARQ schemes. This dissertation first studies the design and performance evaluation of IR-LDPC codes, which have good error rate performance at short block lengths. The subset codes of the IR-LDPC codes are compared to conventional random punctured codes and multiple dedicated codes. As a system model for this work, an adaptive LDPC coded system is presented. This adaptive system can confront the nature of time-varying channels and approach the capacity of the system with the aid of LDPC codes. This system shows remarkable throughput improvement over a conventional punctured system and, for systems that use multiple dedicated codes, provides comparable performance with low-complexity at every target error rate. This dissertation also focuses on IR-LDPC codes with a wider operating code range because the previous IR-LDPC codes exhibited performance limitation related to the maximum achievable code rate. For this reason, this research proposes a new way to increase the maximum code rate of the IR-LDPC codes, which provides throughput improvement at high throughput regions over conventional random punctured codes. Also presented is an adaptive code selection algorithm using threshold parameters. This algorithm reduces the number of the unnecessary traffic channels in HybridARQ schemes. This dissertation also examines how to improve throughput performance in HybridARQ schemes with low-complexity by exploiting irregular repeat accumulate (IRA) codes. The proposed adaptive transmission method with adaptive puncturing patterns of IRA codes shows higher throughput performance in all of operating code ranges than does any other single mode in HybridARQ schemes.

As the success of P2P file sharing systems such as BitTorrent and eMule, P2P has become a promising technology to provide video streaming services over the Internet. The P2P technology is shown to be capable of significantly reducing the transmission overhead of video server. However, due to the dynamic nature of peers, a P2P streaming system suffers from bursty packet loss caused by peer departures. Furthermore, as the packet being forwarded peer by peer, the situation becomes worse and worse. This problem is recognized as packet loss accumulation problem. To overcome bursty packet loss and eliminate packet loss accumulation problems caused by peer departures in P2P streaming systems, a multi-source structure combining with a distributed FEC scheme for P2P streaming systems is proposed. In the proposed structure, each peer connects to multiple parents according to the pre-specified FEC packets ensemble and each parent forwards partial streaming packets to the peer. If one or few parents fail, other parents can still provide most of remaining part of streaming packets that can be used to recover the missing packets by using packet level FEC scheme. To evaluate the performance of P2P streaming systems using the proposed multi-source structure, we first propose a Continuous-Time Markov Chain to model the arrival/departure behavior of parents in P2P systems. Based on the Markov Chain, we further derived equations to calculate packet loss probabilities for both single-source and multi-source P2P systems. The mathematical analyses show how the packet loss accumulation occurs in P2P systems and how the proposed multi-source structure eliminates packet loss accumulation problem. In addition, simulations are conducted using NS2 to evaluate the proposed multi-source structure. Simulation results verify that the proposed multi-source structure combining with an appropriate FEC protection is capable of overcoming burst packet loss and eliminating packet loss accumulation problems. The simulation results also show that the proposed multi-source structure performs better than the single-source and the PROMISE/CollectCast P2P systems in terms of packet loss, end-to-end delay, and PSNR. A prototype system is implemented to conduct a real experiment over the Internet to validate the effectiveness of the proposed scheme.

La thèse s'intéresse au problème de la gestion de la fiabilité dans les réseaux par satellite basés sur la norme de diffusion DVB-S, pour des applications multipoints. En raison de possibles fluctuations des conditions de propagation, le service offert par le lien satellite n'est pas garanti. Le cas échéant, il doit être complété par un service de niveau transport, contraint à limiter l'utilisation de la voie de retour en raison du nombre potentiellement élevé de récepteurs. La première problématique étudiée concerne les concepts à envisager pour concevoir une architecture protocolaire appropriée. L'architecture prévoit de reconsidérer l'utilisation des contrôles d'intégrité des données, et de renforcer la fiabilité sur les en-têtes des différentes couches protocolaires. Ce mécanisme est appelé Multi Protocol Header Protection. La réalisation de ces concepts est également étudiée. Elle est proposée dans le cadre de la méthode Ultra Lightweight Encapsulation permettant la livraison de datagrammes IP par les réseaux DVB. L'exploitation de l'architecture pour deux services de fiabilité est ensuite discutée au niveau des protocoles de transport. Le premier service, appelé fiabilité binaire non contrôlée, peut être offert pour des applications tolérantes aux erreurs binaires. Des simulations démontrent l'intérêt de l'architecture pour ce service. Pour un service de fiabilité totale, l'élaboration d'un procédé de fiabilisation adapté à l'architecture est étudiée. Le procédé fait intervenir un algorithme de décodage FEC adapté. L'évaluation globale de l'approche estime que pour un service identique, 5 à 30 fois moins de données peuvent être économisées comparativement à une architecture conventionnelle.

<p>A forward error correction technique known as convolutional coding with Viterbi decoding was explored in this final thesis. This Viterbi project is part of the baseband Error control project at electrical engineering department, Linköping University.</p><p>In this project, the basic Viterbi decoder behavior model was built and simulated. The convolutional encoder, puncturing, 3 bit soft decision, BPSK and AWGN channel were implemented in MATLAB code. The BER was tested to evaluate the decoding performance.</p><p>The main issue of this thesis is to implement the RTL level model of Viterbi decoder. With the testing results of behavior model, with minimizing the data path, register size and butterflies in the design, we try to achieve a low silicon cost design. The RTL Viterbi decoder model includes the Branch Metric block, the Add-Compare-Select block, the trace-back block, the decoding block and next state block. With all done, we further understand about the Viterbi decoding algorithm and the DSP implementation methods.</p>

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Masters Research - Masters of Engineering / Mobile telephony, wireless networks and wireless telemetry systems have gone from simple single-input single-output wireless architectures with low data transmission rates to complex systems employing multiple antennas and forward error correction algorithms capable of high data transmission rates over wireless channels. Claude Shannon provided the fundamental capacity limits for a communications system and it can be shown that the capacity for a single-input single-output systems is limited in it’s capability to provide for modern wireless applications. The introduction of multiple-input multiple-output systems employing multiple antenna elements and orthogonal coding structures proved beneficial and could provide the capacities required for modern wireless applications. This thesis begins with an introduction and overview of space-time coding and the codes of Tarokh, Jafarkhani and Alamouti. Further, this thesis provides an introduction and overview to the family of forward error correction codes known as low-density parity-check (LDPC) codes. LDPC codes, when employed over Gaussian channels, provide near-Shannon limit performance and the question is posed as to their suitability for a wireless multiple-input multiple-output system employing multiple antennas and space-time coding. This question is answered by the use and demonstration of LDPC codes as outer codes to a MIMO system employing space-time block codes and a modified maximum-likelihood decoder. By modifying the space-time block-code decoder to provide a soft-information output, iterative decoders such as the sum-product algorithm can be employed to provide significant performance gains over a Rayleigh flat-fading channel. Further the use of design tools such as EXIT charts can then be used to design codes. The key to allowing the use of EXIT charts is the observation that a MIMO system employing orthogonal transmissions in a Rayleigh flat-fading channel is the equivalent to a SISO channel employing Nakagami-m fading coefficients. The seemingly complex MIMO system can now be analyzed in the form of a simpler SISO equivalent allowing the use of techniques such as EXIT charts to be employed in order to design codes with known and predictable performance haracteristics. This thesis demonstrates this technique and shows by example the performance gains that can be achieved for MIMO systems and opens some further questions for future research.

Masters Research - Masters of Engineering / Mobile telephony, wireless networks and wireless telemetry systems have gone from simple single-input single-output wireless architectures with low data transmission rates to complex systems employing multiple antennas and forward error correction algorithms capable of high data transmission rates over wireless channels. Claude Shannon provided the fundamental capacity limits for a communications system and it can be shown that the capacity for a single-input single-output systems is limited in it’s capability to provide for modern wireless applications. The introduction of multiple-input multiple-output systems employing multiple antenna elements and orthogonal coding structures proved beneficial and could provide the capacities required for modern wireless applications. This thesis begins with an introduction and overview of space-time coding and the codes of Tarokh, Jafarkhani and Alamouti. Further, this thesis provides an introduction and overview to the family of forward error correction codes known as low-density parity-check (LDPC) codes. LDPC codes, when employed over Gaussian channels, provide near-Shannon limit performance and the question is posed as to their suitability for a wireless multiple-input multiple-output system employing multiple antennas and space-time coding. This question is answered by the use and demonstration of LDPC codes as outer codes to a MIMO system employing space-time block codes and a modified maximum-likelihood decoder. By modifying the space-time block-code decoder to provide a soft-information output, iterative decoders such as the sum-product algorithm can be employed to provide significant performance gains over a Rayleigh flat-fading channel. Further the use of design tools such as EXIT charts can then be used to design codes. The key to allowing the use of EXIT charts is the observation that a MIMO system employing orthogonal transmissions in a Rayleigh flat-fading channel is the equivalent to a SISO channel employing Nakagami-m fading coefficients. The seemingly complex MIMO system can now be analyzed in the form of a simpler SISO equivalent allowing the use of techniques such as EXIT charts to be employed in order to design codes with known and predictable performance haracteristics. This thesis demonstrates this technique and shows by example the performance gains that can be achieved for MIMO systems and opens some further questions for future research.

A forward error correction technique known as convolutional coding with Viterbi decoding was explored in this final thesis. This Viterbi project is part of the baseband Error control project at electrical engineering department, Linköping University. In this project, the basic Viterbi decoder behavior model was built and simulated. The convolutional encoder, puncturing, 3 bit soft decision, BPSK and AWGN channel were implemented in MATLAB code. The BER was tested to evaluate the decoding performance. The main issue of this thesis is to implement the RTL level model of Viterbi decoder. With the testing results of behavior model, with minimizing the data path, register size and butterflies in the design, we try to achieve a low silicon cost design. The RTL Viterbi decoder model includes the Branch Metric block, the Add-Compare-Select block, the trace-back block, the decoding block and next state block. With all done, we further understand about the Viterbi decoding algorithm and the DSP implementation methods.