Finite-SNR Diversity-Multiplexing-Delay Tradeoff in Half-Duplex Hybrid ARQ Relay Channels

International audienceIn this paper, we consider a delay-limited hybrid automatic repeat request (HARQ) protocol that makes use of incremental redundancy over the three-node decode-and-forward (DF) relay fading channel where one source cooperates with a relay to transmit information to the destination. We provide an estimate of the diversity-multiplexing tradeoff (DMT) at finite signal to noise ratio (SNR) based on tight bounds on outage probabilities for two channel models. The results for the long term quasi-static channel highlight the distributed diversity, ie. the cooperative space diversity, and the HARQ coding gain, achieved by soft combining the successive transmitted punctured codewords via incremental redundancy. On the other hand, the results for the short term quasi-static channel illustrate the diversity gains obtained thanks to cooperative space diversity and time diversity, along with the HARQ coding gain. Using the DMT formulation, we show that equal power partitioning between the source and the relay nodes provides close to optimal performance. Furthermore, thanks to the extension of the finite-SNR DMT to the finite-SNR diversity-multiplexing-delay tradeoff, we show that, unlike the asymptotic SNR analysis, the ARQ delay, defined as the number of retransmissions rounds, impacts the performance of the HARQ relay protocol for high effective multiplexing gain

Turbo codes and turbo algorithms

In the first part of this paper, several basic ideas that prompted the coming of turbo codes are commented on. We then present some personal points of view on the main advances obtained in past years on turbo coding and decoding such as the circular trellis termination of recursive systematic convolutional codes and double-binary turbo codes associated with Max-Log-MAP decoding. A novel evaluation method, called genieinitialised iterative processing (GIIP), is introduced to assess the error performance of iterative processing. We show that using GIIP produces a result that can be viewed as a lower bound of the maximum likelihood iterative decoding and detection performance. Finally, two wireless communication systems are presented to illustrate recent applications of the turbo principle, the first one being multiple-input/multiple-output channel iterative detection and the second one multi-carrier modulation with linear precoding

Reconfigurable Intelligent Surface Assisted Railway Communications: A survey

The number of train passengers and the demand for high data rates to handle new technologies such as video streaming and IoT technologies are continuously increasing. Therefore the exploration of millimeter waves (mmWave) band is a key technology to meet this demand. However, the high penetration loss makes mmWave very sensitive to blocking, limiting its coverage area. One promising, efficient, and low-cost solution is the reconfigurable intelligent surface (RIS). This paper reviews the state of the art of RIS for railway communications in the mmWave context. First, we present the different types of RIS and review some optimization algorithms used in the literature to find the RIS phase shift. Then, we review recent works on RIS in the railway domain and provide future directions

Utilisation des techniques MIMO pour des transmissions robustes et haut-débit en tunnels.

National audienceCe papier illustre le gain de performance potentiel apporté par l'utilisation des techniques MIMO dans le cadre des communications radio en tunnel ferroviaire. Différents schémas de transmission sont testés et évalués dans le cas de canaux faiblement puis fortement corrélés

Design of adaptive 2x2 space-time block codes for broadcasting applications

International audienceFuture broadcasting systems will call for multi-antenna (MIMO) transmission techniques. Space-time block codes (STBC) are conventionally designed according to rank-determinant criteria, efficient at high signal-to-noise ratios (SNR). However, broadcasting transmissions are protected by powerful forward error correcting (FEC) codes able to operate at low to moderate SNRs. The aim of this study is to design full-rate full-diversity STBCs with low detection complexity, optimized for a wide range of SNRs

Analyse de la convergence d'un système multi-antennes précodé itératif

Dans ce papier, nous proposons une analyse de la convergence d'un système multi-antennes précodé avec un traitement itératif conjoint en réception. Cette analyse est basée sur un diagramme EXIT et des simulations de type Monte Carlo. Le précodage linéaire utilise une matrice de Hadamard et le système multi-antennes met en oeuvre un multiplexage spatial à plusieurs antennes d'émission et de réception. On observe que le schéma d'émission/réception mis en place permet d'atteindre un gain en diversité potentiel égal au produit de la taille de la matrice de précodage par le nombre d'antennes de réception. L'analyse du diagramme EXIT met en évidence l'influence des paramètres système sur la convergence et les performances asymptotiques. Les résultats sont présentés pour une modulation de type MAQ-16 offrant ainsi une efficacité spectrale élevée

Maternal overnutrition programs epigenetic changes in the regulatory regions of hypothalamic Pomc in the offspring of rats.

Maternal overnutrition has been implicated in affecting the offspring by programming metabolic disorders such as obesity and diabetes, by mechanisms that are not clearly understood. This study aimed to determine the long-term impact of maternal high-fat (HF) diet feeding on epigenetic changes in the offspring's hypothalamic Pomc gene, coding a key factor in the control of energy balance. Further, it aimed to study the additional effects of postnatal overnutrition on epigenetic programming by maternal nutrition.Eight-week-old female Sprague-Dawley rats were fed HF diet or low-fat (LF) diet for 6 weeks before mating, and throughout gestation and lactation. At postnatal day 21, samples were collected from a third offspring and the remainder were weaned onto LF diet for 5 weeks, after which they were either fed LF or HF diet for 12 weeks, resulting in four groups of offspring differing by their maternal and postweaning diet.With maternal HF diet, offspring at weaning had rapid early weight gain, increased adiposity, and hyperleptinemia. The programmed adult offspring, subsequently fed LF diet, retained the increased body weight. Maternal HF diet combined with offspring HF diet caused more pronounced hyperphagia, fat mass, and insulin resistance. The ARC Pomc gene from programmed offspring at weaning showed hypermethylation in the enhancer (nPE1 and nPE2) regions and in the promoter sequence mediating leptin effects. Interestingly, hypermethylation at the Pomc promoter but not at the enhancer region persisted long term into adulthood in the programmed offspring. However, there were no additive effects on methylation levels in the regulatory regions of Pomc in programmed offspring fed a HF diet.Maternal overnutrition programs long-term epigenetic alterations in the offspring's hypothalamic Pomc promoter. This predisposes the offspring to metabolic disorders later in life

Etude et amélioration d'une technique de réception numérique itérative : turbo-égalisation

The aim of this thesis is to study and to improve a digital receiver which is called a turbo-equalizer and is based on the turbo principle. This system consists of several functions that treat iteratively different disturbances created by the propagation channel. A special equalizer called the Interference Canceller (IC) build with filters optimized according to the Minimum Mean Square Error (MMSE) criterion combats the InterSymbol Interference (ISI). Then a channel decoder processes the additive noise and the residual ISI. Each function generates soft information about the emitted data that are improved at each treatment. Consequently ISI is progressively cancelled during the iterations.Thanks to an analogy with the coded modulations, we can explain the influence of the interleaving scheme, which can be performed on the bits or on the symbols of modulation, on the performance of the turbo-equalization for different time selectivity characteristics of the propagation channel. In order to obtain satisfactory performance on the ionospheric channel, whose characteristics are well-known to be difficult, we study different structures and algorithms of the equalizers of the turbo-equalization. We then present the improvements of the demapping without a priori information. A mapping optimization for the demapping function with a priori information is proposed and leads to a gain in Bit Error Rate performance. Finally, we compare the turbo-equalization to three alternative techniques : a system with a turbo-decoder, the COFDM scheme and a turbo-detector with reduced-state trellis, called turbo-DDFSE.L'objectif de cette thèse est d'étudier et d'améliorer une technique de réception numérique appelée turbo-égalisation et basée sur le principe turbo. Ce système est constitué de plusieurs fonctions qui traitent itérativement les différentes perturbations apportées par le canal de propagation. L'Interférences Entre Symboles (IES) est corrigée par un égaliseur particulier appelé annuleur d'interférences construit à l'aide de filtres optimisés selon le critère de Minimum d'Erreur Quadratique Moyenne (MEQM). Le bruit et l'IES résiduelle sont ensuite traités par un décodeur de canal. Chaque fonction produit une information souple sur les données émises qui est améliorée à chaque traitement. L'IES est ainsi éliminée progressivement au cours des itérations.Grâce à une analogie avec les modulations codées, nous expliquons l'influence du schéma d'entrelacement, qui peut être réalisé au niveau des bits ou des symboles de modulation, sur les performances de la turbo-égalisation selon les caractéristiques temporelles des canaux de propagation. D'autre part, afin d'obtenir des performances satisfaisantes sur un modèle de canal ionosphérique, dont les caractéristiques de propagation sont réputées difficiles, nous étudions les différentes structures et algorithmes d'adaptation possibles pour les égaliseurs présents dans la turbo-égalisation. Puis nous présentons des améliorations de la conversion Maire-binaire sans information a priori. Une optimisation du mapping pour la conversion Maire-binaire avec information a priori de la turbo-égalisation est proposée et conduit à un gain de performances en terme de Taux d'Erreurs Binaires. Enfin nous comparons la turbo-égalisation à trois techniques alternatives : un système avec turbo-décodage, la technique multiporteuse COFDM, et un turbo-détecteur à treillis réduit

Blind CFO estimation for OFDM-IDMA system in Rayleigh fading multipath channel

International audienceWe address the problem of carrier frequency offset (CFO) in Orthogonal Frequency Division Multiplexing (OFDM) communications systems in the context of Interleaved Division Multiple Access (IDMA).We propose a technique to adapt a method of blind CFO estimation, called CFO estimation-Syndrome Function Minimization (C-SFM), to the context of a system combining IDMA and OFDM where a quasi-static Rayleigh fading multipath channel is considered. Performance in terms of Mean Squared Error (MSE) of carrier frequency offset is studied for a different number of users. In order to evaluate the robustness of the C-SFM method, we compare the performance of OFDM-IDMA system using C-SFM technique with that of a perfect synchronous system. Our results show that, for high Eb/N0, the two systems have the same performance

Influence du choix de l'égalisation sur les performances de la turbo-égalisation sur des canaux HF

Nous étudions la turbo-égalisation appliquée aux canaux HF et à la modulation MAQ-16. Une analyse approfondie des différents égaliseurs est réalisée dans le contexte du processus itératif. Nous montrons l'influence des structures et des algorithmes sur les performances de la turbo-égalisation à différents stades du processus