Some interesting dual-code properties of convolutional encoder for standards self-recognition

In Special Issue : Cognitive CommunicationsInternational audienceFor enhancement of the quality of digital transmissions, standards are in continual evolution, which generates compatibility problems. Cognitive radio systems permit one to solve this problem through the design of intelligent receivers. However, such receivers must be able to adapt themselves to a specific transmission context. This requires the development of new methods in order to blindly estimate error-correcting codes. Coding schemes such as turbocode, composed of convolutional codes, belong to a family of error-correcting codes in use in many standards. In most of the methods designed to identify convolutional encoders the algebraic properties are used implicitly. However usually, these dedicated properties are neither explicated, nor detailed, nor demonstrated. The study reported here investigates the algebraic properties of convolutional encoders, useful for blind recognition methods in the cognitive radio context and more specially the algebraic relationships between different forms of a convolutional code and its corresponding dual code. Moreover, some simulation results are presented to show the relevance of these properties for the blind identification of the convolutional encoder

Blind recovery of k/n rate convolutional encoders in a noisy environment

http://jwcn.eurasipjournals.com/content/2011/1/168International audienceIn order to enhance the reliability of digital transmissions, error correcting codes are used in every digital communication system. To meet the new constraints of data rate or reliability, new coding schemes are currently being developed. Therefore, digital communication systems are in perpetual evolution and it is becoming very difficult to remain compatible with all standards used. A cognitive radio system seems to provide an interesting solution to this problem: the conception of an intelligent receiver able to adapt itself to a specific transmission context. This article presents a new algorithm dedicated to the blind recognition of convolutional encoders in the general k/n rate case. After a brief recall of convolutional code and dual code properties, a new iterative method dedicated to the blind estimation of convolutional encoders in a noisy context is developed. Finally, case studies are presented to illustrate the performances of our blind identification method

Blind Recognition of Linear Space–Time Block Codes: A Likelihood-Based Approach

International audienceBlind recognition of communication parameters is a research topic of high importance for both military and civilian communication systems. Numerous studies about carrier frequency estimation, modulation recognition as well as channel identification are available in literature. This paper deals with the blind recognition of the space–time block coding (STBC) scheme used in multiple input–multiple-output (MIMO) communication systems. Assuming there is perfect synchronization at the receiver side, this paper proposes three maximum-likelihood (ML)-based approaches for STBC classification: the optimal classifier, the second-order statistic (SOS) classifier, and the code parameter (CP) classifier. While the optimal and the SOS approaches require ideal conditions, the CP classifier is well suited for the blind context where the communication parameters are unknown at the receiver side. Our simulations show that this blind classifier is more easily implemented and yields better performance than those available in literature

Classification Based on Euclidean Distance Distribution for Blind Identification of Error Correcting Codes in Noncooperative Contexts

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Reconnaissance en aveugle de codeur à base de code convolutif : Contribution à la mise en oeuvre d'un récepteur intelligent

For enhancement of the quality of digital transmissions, the standards are in continual evolution, but this generates compatibility problems. Cognitive radio systems provide a relevant solution to this problem: the design of an intelligent receiver. Such receivers must be able to blindly identify the transmitter parameters. This PhD work was focused on the blind recognition of encoders based on a convolutional code. Such codes enhance the reliability of transmissions by allowing, at the receiver side, the detection and/or correction of errors liable to occur over the data transmission. Our investigations started with a study of the algebraic theory of convolutional codes so as to get the properties essential for a blind recognition of convolutional encoders. Then, from the knowledge of only the coded data stream, methods were developed to identify a convolutional code in the case of a noiseless transmission, and then of a noisy one. An algorithm able to identify a punctured convolutional code was devised. From the knowledge of only a stream of encoded, punctured and noisy data, this algorithm permits the identification of the convolutional encoder and that of the puncturing pattern in use at the transmitter side. Then, two methods are proposed to identify a turbocode with noiseless parts of the received data stream. Finally, application of our blind identification algorithms to simulation parameters close to those used by the available standards gave good performances.Dans le but d'améliorer la qualité des transmissions numériques, les normes sont en perpétuelle évolution ce qui engendre des problèmes d'incompatibilité. Le domaine de la radio cognitive offre une solution pertinente à ce problème : la conception de récepteurs intelligents. Ces récepteurs devront être capables d'identifier en aveugle les paramètres de la norme utilisée par l'émetteur. Les travaux présentés dans ce mémoire portent sur la reconnaissance aveugle de codeur à base de code convolutif. De tels codes améliorent la fiabilité d'une transmission en permettant, côté récepteur, de détecter et/ou de corriger d'éventuelles erreurs intervenues lors de la transmission du message. Une étude sur la théorie algébrique des codes convolutifs a été conduite afin d'obtenir les propriétés indispensables à la mise en oeuvre de méthodes d'identification aveugle. Puis, à partir de la seule connaissance d'un train binaire codé, nous avons développé des méthodes permettant d'identifier un code convolutif lors d'une transmission non-bruitée, puis bruitée. Nous avons ensuite développé un algorithme dédié à l'identification en aveugle d'un code convolutif poinçonné. Cet algorithme permet, à partir de la seule connaissance d'une trame codée, poinçonnée et bruitée, d'identifier le code convolutif ainsi que le motif de poinçonnage utilisé à l'émission. Ensuite, nous proposons deux méthodes qui permettent d'identifier un turbocode lors de la réception d'une trame présentant une plage de donnée non-bruitée. Enfin, nous montrons que nos algorithmes d'identification offrent d'excellentes performances avec des paramètres de simulation proches de ceux utilisés dans les différents standards

Algebraic method for blind recovery of punctured convolutional encoders from an erroneous bitstream

International audienceTo enhance the quality of transmissions, all digital communication systems use error-correcting codes. By introducing some redundancy in the informative binary data stream, they allow one to better withstand channel impairments. The design of new coding schemes leads to a perpetual evolution of the digital communication systems and, thus, cognitive radio receivers have to be designed. Such receivers will be able to blind estimate the transmitter parameters. In this study, an algebraic method dedicated to the blind identification of punctured convolutional encoders is presented. The blind identification of such encoders is of great interest, because convolutional encoders are embedded in most digital transmission systems where the puncturing principle is used to increase the code rate to reduce the loss of the information data rate because of the redundancy introduced by the encoder. After a brief recall of the principle of puncturing codes and the construction of the equivalent punctured code, a new method dedicated to the blind identification of both the mother code and the puncturing pattern is developed when the received bits are erroneous. Finally, case studies are presented to illustrate the performances of our blind identification method

Dual Code Method for Blind Identification of Convolutional Encoder for Cognitive Radio Receiver Design

International audienceDigital communication systems are in perpetual evolution in order to respond to the new user expectations and to new applications transmissions constraints, in term of data rate or reliability. With this fast development of new communication standards, it becomes very difficult for users and also for communications devices producers, to stay compatible with all standards used and with the oncoming ones. For that reason, cognitive radio systems seem to provide an interesting solution to this problem. The conception of intelligent receiver able to adapt itself to a specific transmission context and to blindly estimate the transmitter parameters is a promising solution for the future. In such context, new coding schemes like turbocodes, Low-Density Parity-Check (LDPC) or concatenated codes are developed to increase transmission robustness without significant degradation of the data rate. It is why we have developed a method, described in this paper, dedicated to the blind identification of convolutional encoders usually used in many standards. Moreover, an analysis of the method performances is detailed

Blind Recovery of the Second Convolutional Encoder of a Turbo-Code when Its Systematic Outputs Are Punctured

International audienceTurbo-codes are error-correcting codes used in power­ful digital transmission systems to ensure a low binary error rate. This paper presents different approaches aimed at recovering a convolutional encoder in a non-cooperative context like in military interception or cognitive-radio applications. In this context, the intercepted data are the only known information. It also explains the residual inde­termination due to “equivalent” coders and it gives the link between an NRNSC encoder and its RSC equivalent form. Furthermore, it reports on a new approach developed to recover the interleaved version of the second encoder of a Turbo-code when its systematic outputs are punctured

Reconnaissance aveugle de turbocodes

National audienceUne chaîne de transmission numérique permet de véhiculer un message d'un émetteur à un récepteur. Lors d'une communication classique, dite coopérative, le récepteur connaît la norme utilisée par l'émetteur, il peut aisément effectuer les opérations inverses afin d'obtenir le message d'origine. En revanche, dans un contexte dit non-coopératif, le récepteur n'aura aucune connaissance sur la norme utilisée par l'émetteur. Afin d'obtenir le message d'origine, il devra estimer en aveugle (c-à-d avec la seule connaissance des données reçues) les paramètres de l'émetteur. Outre l'intérêt militaire, un tel récepteur permettrait d'une part de mettre à l'épreuve la sécurité des transmissions dans le domaine civil et d'autre part de rendre les chaînes de transmission beaucoup plus souples et évolutives en terme de changement de standard, puisque le récepteur s'adapterait automatiquement à la norme utilisée par l'émetteur. Parmi l'ensemble des étapes réalisées par l'émetteur, l'une d'elles, nommée codage de canal, permet de lutter contre les erreurs de transmission. On s'intéressera ici à la reconnaissance aveugle de turbocodes. Les turbocodes sont devenus depuis quelques années les codes correcteurs incontournables dans les systèmes de transmissions terrestres ou satellitaire. Ce succès est dû au fait qu'ils allient de très bonnes performances en termes de taux d'erreur binaire à une complexité numérique de décodage raisonnable. Un turbocode est une concaténation en parallèle de deux codes convolutifs séparés par un entrelaceur. Nous avons déjà proposé précédemment une méthode d'identification aveugle des paramètres d'un turbocode, avec ou sans le poinçonnage des voies systématiques du second codeur. Les méthodes de reconnaissance actuelles sont basées sur la redondance introduite par les codes. Ces méthodes peuvent être utilisées pour identifier le premier codeur, mais comment estimer les paramètres du second codeur, sachant que le poinçonnage des voies systématiques a supprimé toute la redondance? L'idée que nous proposons est d'estimer le premier codeur avec ces méthodes et d'en décoder les sorties afin de les utiliser pour identifier le second codeur et les paramètres de l'entrelaceur

Order Statistics on Minimal Euclidean Distance for Blind Linear Block Code Identification

International audienceThis article deals with the blind detection and identification of error correcting codes. More precisely, we aim at estimating the code length from a noisy bits stream in a non-cooperative context (e.g. Electronic Warfare). In this context, an eavesdropper may intercept a communication. To retrieve the sent information, one can consider identifying the channel code parameters. The method proposed here relies on a statistical analysis of a Euclidean distance matrix. It allows to estimate the code length. We address a process based on soft bits information with no a priori on the encoder used. Finally, we compare our method with a well known algorithm based on Gauss-Jordan elimination