Thermal Characterization and Thermal Management in Processor-Based Systems

The register file is one of the hottest devices in processor-based systems. Leakage reduction techniques and DTM mechanisms require a thermal characterization of the hardware. This paper presents a thermal model to analyze the temperature evolution in the shared register files found on VLIW systems. The use of this model allows the analysis of several factors that have an strong impact on the heat transfer. The results obtained can be used in the design of temperature-aware compilers and place&route tools

Impact of intra-flow network coding on the relay channel performance: an analytical study

International audienceOne of the most powerful ways to achieve trans- mission reliability over wireless links is to employ efficient coding techniques. This paper investigates the performance of a transmission over a relay channel where information is protected by two layers of coding. In the first layer, transmission reliability is ensured by fountain coding at the source. The second layer incorporates network coding at the relay node. Thus, fountain coded packets are re-encoded at the relay in order to increase packet diversity and reduce energy consumption. Performance of the transmission is measured by the total number of trans- missions needed until the message is successfully decoded at the destination. We show through both analytical derivations and simulations that adding network coding capabilities at the relay optimizes system resource consumption. When the source uses a random linear fountain code, the proposed two-layer encoding becomes more powerful as it reduces the transmission rate over the direct link between the source and the destination

On the Flooding Overhead of Fountain Codes in Wireless Sensor Networks

This paper concentrates on the proper use of fountain codes for the transmission of sporadic data in a wireless sensor network (WSN). Fountain codes offer great perspectives for the self-organization of WSNs: they self adapt to the channel error rate without any control data. When deploying fountain codes on a WSN, two problems arise. First, the size of the data transmitted by a sensor is small in comparison to the size considered traditionally with fountain codes. The analysis of the decoding overhead for fountain codes is often done for large data. Second, the communications are done in an hop-by-hop fashion. It implies that the destination of the data can not acknowledge instantaneously its reception to the source. Therefore, the transmissions of useless packets for the destination can not be prevented. The impact of this flooding traffic is analyzed. It depends on the data size and on number of hops between the source and the destination. The context of our study is a line network, i.e. a cascade of erasure channels. The flooding traffic has been evaluated as well through realistic simulations for three different relaying strategies where packets are lost due to both small scale fading and collisions for an unslotted IEEE 802.15.4 medium access layer.Cet article propose l'optimisation de l'usage d'un code fontaine pour une transmission sporadique de données dans les réseaux de capteur. Dans ce contexte, ces codes présentent un avantage relatif à l'auto-organisation du réseau: son taux de transmission de données est variable et s'adapte intrinsèquement à la qualité du canal radio sans qu'il n'y ait besoin de paquets de contrôle supplémentaires. Cependant, pour pouvoir utiliser les codes fontaines dans les réseaux de capteurs, il est nécessaire de prendre en compte les contraintes suivantes : premièrement, le surcoût lié au décodage n'est plus négligeable lorsque la taille des données devient petite et deuxièmement, il existe un débordement du flux des paquets codés relatif à la transmission en mode multi-sauts de l'acquittement. En effet, si l'acquittement mets plus de temps à atteindre la source relativement à la vitesse de relayage des paquets codés par la source, certains relais ainsi que la source émettent un nombre de paquets inutiles au décodage avant d'arrêter la transmission. C'est principalement le cas pour une transmission en cascade multi-sauts pour laquelle le nombre de relais est élevé. Dans cet article, nous étudions ce surcoût qui varie avec la quantité de paquets à transmettre et le nombre de sauts entre la source et le destinataire. Ce surcoût de transmission est analysé pour plusieurs stratégies de relayage, tout d'abord analytiquement puis par simulation pour un protocole Zigbee IEEE 802.15.4

Exploring Temperature-Aware Design of Memory Architectures in VLIW Systems

This paper presents a thermal model to analyze the temperature evolution in the shared register files found on VLIW systems. The use of this model allows the analysis of several factors that have an strong impact on the heat transfer: layout topology, placement and memory accesses. Finally, some relevant conclusions are obtained after analyzing the thermal behavior of several multimedia applications

Exploitation de la diversité par relayage dans les réseaux de capteurs sans fils

International audienceIl est reconnu que la diversité permet de fiabiliser la transmission de données. Dans cet article, nous proposons d'exploiter la diversité dans un réseau de capteurs utilisant les codes fontaine LT avec différentes techniques de relayage. Contrairement à une transmission traditionnelle, chaque capteur participe activement à la transmission des informations. Les algorithmes de relayage que nous proposons sont basés sur une opération XOR entre les paquets codés reçus par le relai. Nous montrons que ces algorithmes apportent un gain de performance tout en conservant une complexité algorithmique basse pour convenir aux ressources limitées des capteurs

Towards increasing packet diversity for relaying LT Fountain Codes in Wireless Sensor Networks

Diversity is a powerful means to increase the transmission performance of wireless communications. For the case of fountain codes relaying, it has been shown previously that introducing diversity is also beneficial since it counteracts transmission losses on the channel. Instead of simply hop-by-hop forwarding information, each sensor node diversifies the information flow using XOR combinations of stored packets. This approach has been shown to be efficient for random linear fountain codes. However, random linear codes exhibit high decoding complexity. In this paper, we propose diversity increased relaying strategies for the more realistic Luby Transform code in order to maintain high transmission performance with low decoding computational complexity in a linear network. Results are provided herein for a linear network assuming uniform imperfect channel states

Energy Efficient Authentication Strategies for Network Coding

International audienceRecent advances in information theory and networking, e.g. aggregation, network coding or rateless codes, have significantly modified data dissemination in wireless networks. These new paradigms create new threats for security such as pollution attacks and denial of services (DoS). These attacks exploit the difficulty to authenticate data in such contexts. The particular case of xor network coding is considered herein. We investigate different strategies based on message authentication codes algorithms (MACs) to thwart these attacks. Yet, classical MAC designs are not compatible with the linear combination of network coding. Fortunately, MACs based on universal hash functions (UHFs) match nicely the needs of network coding: some of these functions are linear h(x1⊕x2)=h(x1)⊕h(x2). To demonstrate their efficiency, we consider the case of wireless sensor networks (WSNs). Although these functions can drastically reduce the energy consumption of authentication (up to 68% gain over the classical designs is observed), they increase the threat of DoS. Indeed, an adversary can disrupt all communications by polluting few messages. To overcome this problem, a group testing algorithm is introduced for authentication resulting in a complexity linear in the number of attacks. The energy consumption is analyzed for cross-point and butterfly network topologies with respect to the possible attack scenarios. The results highlight the trade-offs between energy efficiency, authentication and the effective throughput for the different MAC modes

Thermal Characterization and Thermal Management in Processor-Based Systems

The register file is one of the hottest devices in processor- based systems. Leakage reduction techniques and DTM mechanisms re- quire a thermal characterization of the hardware. This paper presents a thermal model to analyze the temperature evolution in the shared reg- ister files found on VLIW systems. The use of this model allows the analysis of several factors that have an strong impact on the heat trans- fer. The results obtained can be used in the design of temperature-aware compilers and place&route tools

Fountain codes for exploiting diversity in wireless sensor networks

Important sujet de recherche dans les télécommunications contemporaines, les réseaux de capteurs sont des réseaux sans fil constitués de plusieurs nœuds pouvant communiquer entre eux. Chaque capteur est autonome et possède une durée de vie limitée, liée à la taille de sa batterie. Dans ce contexte, l’énergie est une ressource critique qui peut être économisée en minimisant le nombre de paquets émis. De part la nature du médium radio, les données transmises subissent des pertes du canal. La fiabilisation de données dans ce contexte n’est pas simple et devient d’autant plus problématique lorsque la taille de réseau augmente. C’est dans ce contexte que s’inscrit cette thèse qui vise à fournir une technique de fiabilisation des transmissions dans un réseau de capteur. Pour cela, nous proposons de mettre en oeuvre un mécanisme de transmission qui exploite le code fontaine. Ce code est sans rendement et les symboles de redondance sont générés à la volée. Il permet de fiabiliser la transmission avec l’utilisation d’un canal de retour limité. Le code fontaine permet d’alléger le mécanisme de contrôle des transmissions tout en assurant un lien complètement fiable, ce qui permet de réduire la latence et la consommation énergétique d’une transmission. Afin d’optimiser la performance globale du réseau, nous étudions également dans cette thèse le cas où les nœuds sont autorisés à coopérer pour le relayage multi-sauts de paquets destinés à des nœuds distants. Nous montrons dans cette thèse que la technique de codage réseau permet d’introduire de la diversité d’information et ainsi d’améliorer la performance globale de transmissions multi-sauts mono-chemin. Ce résultat a été étendu à la transmission coopérative pour laquelle nous avons à la fois pu exploiter la diversité d’information et la diversité spatiale.This thesis is dedicated to the deployment of fountain codes and network coding in a wireless sensor network (WSN). A WSN is composed of sensor nodes with restricted capacities : memory, energy and computational power. The nodes are usually randomly scattered across the monitored area and the environment may vary. In the presence of fading, outage and node failures, fountain codes are a promising solution to guaranty reliability and improve transmission robustness. The benefits of fountain codes are explored based on an event-driven WSNet simulator considering realistic implementation based on standard IEEE802.15.4. Fountain codes are rateless and capable of adapting their rate to the channel on the fly using a limited feedback channel. In this thesis, we highlight the benefits brought by fountain code in terms of energy consumption and transmission delay. In addition to the traditional transmission with fountain code, we propose in this thesis to study the network coding transmission scheme where nodes are allowed to process the information before forwarding it to their neighbors. By this means, we can say that packet diversity is exploited as each individual packet is unique and contains different representations of binary data. Redundancy is thus optimized since repetitions are avoided and replaced with diversified information. This can further lead to an overall improved performance in cooperative communication where nodes are allowed to assist in relaying packets from the source the destination. We highlight in this thesis the benefits of fountain code combined to network coding and show that it leads to a reduction in transmission delay and energy consumption. The latter is vital to the life duration of any wireless sensor network