62 research outputs found

    Simple Low-Density Parity Check (LDPC) Staircase Forward Error Correction (FEC) Scheme for FECFRAME, RFC 6816

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    This document describes a fully specified simple Forward Error Correction (FEC) scheme for Low-Density Parity Check (LDPC) Staircase codes that can be used to protect media streams along the lines defined by FECFRAME. These codes have many interesting properties: they are systematic codes, they perform close to ideal codes in many use-cases, and they also feature very high encoding and decoding throughputs. LDPC-Staircase codes are therefore a good solution to protect a single high bitrate source flow or to protect globally several mid-rate flows within a single FECFRAME instance. They are also a good solution whenever the processing load of a software encoder or decoder must be kept to a minimum

    RS + LDPC-Staircase Codes for the Erasure Channel: Standards, Usage and Performance

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    Application-Level Forward Erasure Correction (AL-FEC) codes are a key element of telecommunication systems. They are used to recover from packet losses when retransmission are not feasible and to optimize the large scale distribution of contents. In this paper we introduce Reed-Solomon/LDPCStaircase codes, two complementary AL-FEC codes that have recently been recognized as superior to Raptor codes in the context of the 3GPP-eMBMS call for technology [1]. After a brief introduction to the codes, we explain how to design high performance codecs which is a key aspect when targeting embedded systems with limited CPU/battery capacity. Finally we present the performances of these codes in terms of erasure correction capabilities and encoding/decoding speed, taking advantage of the 3GPP-eMBMS results where they have been ranked first

    Erasure Codes with a Banded Structure for Hybrid Iterative-ML Decoding

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    This paper presents new FEC codes for the erasure channel, LDPC-Band, that have been designed so as to optimize a hybrid iterative-Maximum Likelihood (ML) decoding. Indeed, these codes feature simultaneously a sparse parity check matrix, which allows an efficient use of iterative LDPC decoding, and a generator matrix with a band structure, which allows fast ML decoding on the erasure channel. The combination of these two decoding algorithms leads to erasure codes achieving a very good trade-off between complexity and erasure correction capability.Comment: 5 page

    Analysis and evaluation of adaptive LDPC AL-FEC codes for content download services

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    This paper proposes the use of adaptive low density parity check (LDPC) application layer-forward error correction (AL-FEC) codes for content download services over erasure channels. In adaptive LDPC codes, clients inform the content download server of the losses they are experiencing. Using this information, the server makes forward error correction (FEC) parity symbols available to the client at an optimum code rate. This paper presents an analytical model of the proposed adaptive LDPC codes. The model is validated through measurements realized with an application prototype. In addition, results show the performance of these codes in different scenarios, compared to the performance of nonadaptive AL-FEC, optimum LDPC AL-FEC codes, and an almost ideal rateless code. Adaptive LDPC AL-FEC codes achieve download times similar to almost ideal rateless codes with less coding complexity, at the expense of an interaction channel between server and clients.De Fez Lava, I.; Fraile Gil, F.; Belda Ortega, R.; Guerri Cebollada, JC. (2012). Analysis and evaluation of adaptive LDPC AL-FEC codes for content download services. IEEE Transactions on Multimedia. 60(3):641-650. doi:10.1109/TMM.2012.2190392S64165060

    A protection scheme for multimedia packet streams in bursty packet loss networks based on small block low-density parity-check codes

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    This paper proposes an enhanced forward error correction (FEC) scheme based on small block low-density parity-check (LDPC) codes to protect real-time packetized multimedia streams in bursty channels. The use of LDPC codes is typically addressed for channels where losses are uniformly distributed (memoryless channels) and for large information blocks. This work suggests the use of this type of FEC codes at the application layer, in bursty channels (e.g., Internet protocol (IP)-based networks) and for real-time scenarios that require low transmission latency. To fulfil these constraints, the appropriate configuration parameters of an LDPC scheme have been determined using small blocks of information and adapting the FEC code to be capable of recovering packet losses in bursty environments. This purpose is achieved in two steps. The first step is performed by an algorithm that estimates the recovery capability of a given LDPC code in a burst packet loss network. The second step is the optimization of the code: an algorithm optimizes the parity matrix structure in terms of recovery capability against the specific behavior of the channel with memory. Experimental results have been obtained in a simulated transmission channel to show that the optimized LDPC matrices generate a more robust protection scheme against bursty packet losses for small information blocks

    Performance evaluation of AL-FEC LDPC codes for push content applications in wireless unidirectional environments

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    The final publication is available at Springer via http://dx.doi.org/10.1007/s11042-011-0841-yFEC (Forward Error Correction) mechanisms improve IP content transmission reliability through the recovery of packets lost in transmission. Opposite to ARQ (Automatic Repeat Request), FEC mechanisms are especially suited to unidirectional environments or to multicast environments where multiple receivers perceived different channel losses, thus making difficult the implementation of mechanisms based on feedback information. Among the different types of FEC codes, this paper presents a thorough performance evaluation of LDPC (Low Density Parity Check) codes, based on an implementation developed by the authors, according to the specifications defined by RFC 5170 for the usage of LDPC codes by push content applications based on the FLUTE protocol. LDPC codes provide a good trade-off between performance and complexity, hence, they are appropriate for mobile applications. Contributions of this paper include tests conducted with commercial mobile phones connected to the push content download server over a Wi-Fi network. The evaluation highlights the advantages of using packet level FEC encoding in file transmission over unidirectional networks and provides with a comparison between two kinds of LDPC structures: Staircase and Triangle. This is accomplished by calculating the inefficiency ratio of these LDPC structures in different environments. Results show that the implemented LDPC codes can provide inefficiency ratios close to one when the different coding parameters (as the code rate or the number of blocks) are configured to an optimal value that depends on the packet loss rate. © 2011 Springer Science+Business Media, LLC.This work was supported in part by the Ministry of Industry, Tourism and Trade of the Government of Spain, under project "Redes Hibridas para la Provision de Servicios Turisticos" (TSI-020302-2010-165).De Fez Lava, I.; Fraile Gil, F.; Belda Ortega, R.; Guerri Cebollada, JC. (2012). Performance evaluation of AL-FEC LDPC codes for push content applications in wireless unidirectional environments. Multimedia Tools and Applications. 60(3):669-688. https://doi.org/10.1007/s11042-011-0841-yS6696886033GPP TS 22.146 (2006) Multimedia broadcast/multicast service; stage 1 (release 6), V6.7.03GPP TS 25.346 (2007) Introduction of the Multimedia Broadcast Multicast Service (MBMS) in the Radio Access Network (RAN); Stage 2 (Release8), V8.0.0Bai H, Atiquzzaman M (2003) Error modeling schemes for fading channels in wireless communications: a survey. IEEE Comm Surv Tutorials 5(2)Cunche M, Roca V (2008) Optimizing the error recovery capabilities of LDPC-staircase codes featuring a Gaussian elimination decoding scheme. Proc. of the 10th IEEE International Workshop on Signal Processing for Space Communications (SPSC), Rhodes Island, GreeceCunche M, Roca V (2008) Improving the decoding of LDPC codes for the packet erasure channel with a hybrid Zyablov iterative decoding/Gaussian elimination scheme. INRIA Research Report RR-6473Cunche M, Savin V, Roca V (2010) Analysis of quasi-cyclic LDPC codes under ML decoding over the erasure channel. IEEE International Symposium on Information Theory and its Applications (ISITA), Taichung, TaiwanFaria G, Henriksson J, Stare E, Talmola P (2006) DVB-H: digital broadcast services to handheld devices. Proc IEEE 94(1):194–209Fraile F, de Fez I, Guerri JC (2011) Evaluation of a background push download service for personal multimedia devices. IEEE International Conference on Consumer Electronics, Las Vegas, USAGallager R G (1962), Low density parity check codes. IEEE Trans Inform Theor 8(1)Gil A, Fraile F, Ramos M, de Fez I, Guerri JC (2010) Personalized multimedia touristic services for mobile hybrid broadband/broadcast. IEEE Trans Consum Electron 56(1):129–211Handley M, Jacobson V (1998) SDP: session description protocol. IEFT RFC 2327IEEE (2007) Std. 802.11, wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specificationsIEEE (2009) Std. 802.16, air interface for broadband wireless systemsLacan J, Roca V, Peltotalo J, Peltotalo S (2009) Reed-Solomon Forward Error Correction (FEC) schemes. IETF RFC 5510Luby M (2002) LT codes. Proc. IEEE Symposium on Foundations of Computer Science (FOCS), Vancouver, CanadaLuby M, Shokrollahi A, Watson M and Stockhammer T (2007) Raptor forward error correction scheme for object delivery. IETF RFC 5053Luby M, Watson M, Vicisano L (2009) Layered Coding Transport (LCT) building block. IEFT RFC 5651Luby M, Watson M, Vicisano L (2010) Asynchronous Layered Coding (ALC) protocol instantiation. IEFT RFC 5775MacKay D, Neal R (1995) Good codes based on very sparse matrices. In 5th IAM Conference: Cryptography and Coding, LNCS No. 1025Paila T, Luby M, Lehtonen R, Roca V, Walsh R (2004) FLUTE—file delivery over unidirectional transport. IETF RFC 3926Park S, Miller K (1990) Random number generators: good ones are hard to find. Commun ACM 33(1):87–88INRIA Planète Research Team (2006) LDPC large block FEC codec distribution, http://planete-bcast.inrialpes.fr/article.php3?id_article=16Roca V, Neumann C (2004) Design, evaluation and comparison of four large block FEC codecs, LDPC, LDGM, LDGM staircase and LDGM triangle, plus a Reed-Solomon small block FEC codec. INRIA Research Report RR-5225Roca V, Neumann C, Furodet D (2008) Low Density Parity Check (LDPC) Staircase and Triangle Forward Error Correction (FEC) schemes. IETF RFC 5170Shokrollahi A (2006) Raptor codes. IEEE Transactions on Information Theory no. 6Watson M (2009) Basic Forward Error Correction (FEC) schemes. IETF RFC 5445Watson M, Luby M, Vicisano L (2007) Forward Error Correction (FEC) building block. IETF RFC 5052White Paper (2009) Integrated Mobile Broadcast (IMB): the power of predictive broadcasting for 3G multimedia application

    Simple Low-Density Parity Check (LDPC) Staircase Forward Error Correction (FEC) Scheme for FECFRAME

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    Internet Engineering Task Force (IETF) Request for Comments 6816This document describes a fully specified simple Forward Error Correction (FEC) scheme for Low-Density Parity Check (LDPC) Staircase codes that can be used to protect media streams along the lines defined by FECFRAME. These codes have many interesting properties: they are systematic codes, they perform close to ideal codes in many use-cases, and they also feature very high encoding and decoding throughputs. LDPC-Staircase codes are therefore a good solution to protect a single high bitrate source flow or to protect globally several mid-rate flows within a single FECFRAME instance. They are also a good solution whenever the processing load of a software encoder or decoder must be kept to a minimum

    Video over DSL with LDGM Codes for Interactive Applications

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    Digital Subscriber Line (DSL) network access is subject to error bursts, which, for interactive video, can introduce unacceptable latencies if video packets need to be re-sent. If the video packets are protected against errors with Forward Error Correction (FEC), calculation of the application-layer channel codes themselves may also introduce additional latency. This paper proposes Low-Density Generator Matrix (LDGM) codes rather than other popular codes because they are more suitable for interactive video streaming, not only for their computational simplicity but also for their licensing advantage. The paper demonstrates that a reduction of up to 4 dB in video distortion is achievable with LDGM Application Layer (AL) FEC. In addition, an extension to the LDGM scheme is demonstrated, which works by rearranging the columns of the parity check matrix so as to make it even more resilient to burst errors. Telemedicine and video conferencing are typical target applications

    Optimization of protection techniques based on FEC codes for the transmission of multimedia packetized streams

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    Esta tesis presenta dos modelos novedosos de arquitecturas basadas en esquemas FEC con el fin de proteger flujos de paquetes con contenido multimedial, para comunicaciones en tiempo real y en canales donde las pérdidas se producen en ráfagas. El objetivo de estos diseños ha sido maximizar la eficiencia de los códigos FEC considerados. Por un lado, el primer modelo busca alcanzar un menor coste computacional para los códigos de Reed- Solomon, ya que su conocida capacidad de recuperación para todo tipo de canales necesita un coste computacional elevado. Por otro lado, en el caso de los códigos LDPC, se ha perseguido aumentar la capacidad de recuperación de estos códigos operando en canales con errores en ráfagas, teniendo en cuenta que los códigos LDPC no están directamente diseñados para este tipo de entorno. El modelo aplicado a los códigos de Reed-Solomon se denomina inter-packet symbol approach. Este esquema consiste en una estructura alternativa que asocia los bits de los símbolos del código en distintos paquetes. Esta característica permite aprovechar de forma mejor la capacidad de recuperación de los códigos de Reed-Solomon frente a pérdidas de paquetes en ráfagas. Las prestaciones de este esquema han sido estudiadas en términos de tiempo de codificación/decodificación versus capacidad de recuperación y han sido comparados con otros esquemas propuestos en literatura. El análisis teórico ha demostrado que el enfoque propuesto permite la utilización de Campos de Galois de menor dimensión con respecto a otras soluciones. Esto se traduce en una disminución del tiempo de codificación/decodificación requerido, mientras que mantiene una capacidad de recuperación comparable. Aunque la utilización de los códigos LDPC está típicamente orientada hacía canales con errores uniformemente distribuidos (canales sin memoria) y para bloques de información largos, esta tesis surgiere el uso de este tipo de códigos FEC a nivel de aplicación, para canales con pérdidas en ráfagas y para entornos de comunicación de tiempo real, es decir, con una latencia de transmisión muy baja. Para satisfacer estas limitaciones, la configuración apropiada de los parámetros de un código LDPC ha sido determinada usando bloques de información pequeños y adaptando el código FEC de modo que sea capaz de recuperar paquetes perdidos en canales con errores en ráfagas. Para ello, primeramente se ha diseñado un algoritmo que realiza una estimación de las capacidades de recuperación del código LDPC para un canal con pérdidas en ráfagas. Una vez caracterizado el código, se ha diseñado un segundo algoritmo que optimiza la estructura del código en términos de capacidad de recuperación para las características especificas del canal con memoria, generado una versión modificada del código LDPC, adaptada al canal con perdidas en ráfagas. Finalmente, los dos esquemas FEC propuestos, han sido evaluado experimentalmente en entornos de simulación usando canales con errores en ráfagas y se han comparado con otras soluciones y esquemas ya existentes. ABSTRACT This thesis presents two enhanced FEC-based schemes to protect real-time packetized multimedia streams in bursty channels. The objective of these novel architectures has been the optimization of existing FEC codes, that is, Reed-Solomon codes and LDPC codes. On the one hand, the optimization is focused on the achievement of a lower computational cost for Reed-Solomon codes, since their well known robust recovery capability against any type of losses needs a high complexity. On the other hand, in the case of LDPC codes, the optimization is addressed to increase the recovery capabilities for a bursty channel, since they are not specifically designed for the scenario considered in this thesis. The scheme based on Reed-Solomon codes is called inter-packet symbol approach, and it consists in an alternative bit structure that allocates each symbol of a Reed- Solomon code in several media packets. This characteristic permits to exploit better the recovery capability of Reed-Solomon codes against bursty packet losses. The performance of this scheme has been studied in terms of encoding/decoding time versus recovery capability, and compared with other proposed schemes in the literature. The theoretical analysis has shown that the proposed approach allows the use of a lower size of the Galois Fields compared to other solutions. This lower size results in a decrease of the required encoding/decoding time while keeping a comparable recovery capability. Although the use of LDPC codes is typically addressed for channels where losses are uniformly distributed (memoryless channels) and for large information blocks, this thesis suggests the use of this type of FEC codes at the application layer, in bursty channels and for real-time scenario, where low transmission latency is requested. To fulfill these constraints, the appropriate configuration parameters of an LDPC scheme have been determined using small blocks of information and adapting the FEC code to be capable of recovering packet losses in bursty environments. This purpose is achieved in two steps. The first step is performed by an algorithm that estimates the recovery capability if a given LDPC code in a burst packet loss network. The second step is the optimization of the code: an algorithm optimizes the code structure in terms of recovery capability against the specific behavior of the channel with memory, generating a burst oriented version of the considered LDPC code. Finally, for both proposed FEC schemes, experimental results have been carried out in a simulated transmission channel to assess the performances of the schemes and compared to several other schemes

    Improving the Decoding of LDPC Codes for the Packet Erasure Channel with a Hybrid Zyablov Iterative Decoding/Gaussian Elimination Scheme

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    This work focuses on the decoding algorithm of the LDPC large block FEC codes for the packet erasure channel, also called AL-FEC (Application-Level Forward Error Correction). More specifically this work details the design and the performance of a hybrid decoding scheme, that starts with the Zyablov iterative decoding algorithm, a rapid but suboptimal algorithm in terms of erasure recovery capabilities, and, when required, continues with a Gaussian elimination algorithm. For practical reasons this work focuses on two LDPC codes for the erasure channel, namely LDPC-staircase and LDPC-triangle codes. Nevertheless the decoding scheme proposed can be used with other LDPC codes without any problem. The performance experiments carried out show that the erasure recovery capabilities of LDPC-triangle codes are now extremely close to that of an ideal code, even with small block sizes. This is all the more true with small code rates: whereas the Zyablov iterative decoding scheme becomes unusable as the code rate decreases, the Gaussian elimination makes the LDPC-triangle codes almost ideal. In all the tests, when carefully implemented, the LDPC-triangle codec featuring the proposed decoding scheme is fast, and in particular always significantly faster than the reference Reed-Solomon on GF(282^{8}) codec. The erasure recovery capabilities of LDPC-staircase codes are also significantly improved, even if they remain a little bit farther from an ideal code. Nevertheless, a great advantage is the fact that LDPC-staircase codes remain significantly faster than LDPC-triangle codes, which, for instance, enables their use with larger blocks. All these results make these codes extremely attractive for many situations and contradict the common belief that using Gaussian elimination is not usable because of a prohibitive processing load. Moreover the proposed approach offers an important flexibility in practice, and depending on the situation, one can either choose to favor erasure recovery capabilities or the processing time
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