Link Availability Aware Routing Metric For Wireless Mesh Networks

International audienceThis paper investigates the design of effective routing metrics in the purpose of network resources optimization and the satisfaction of users QoS requirements. Using several real experiments, we point out the shortcoming of the Expected Transmission Count (ETX) metric for eventual optimizations towards a more efficient routing. Experiments were carried out into an heterogeneous IEEE 802.11n based network running with OLSR routing protocol and have shown that ETX presents several shortcoming resulting in inaccurate estimation of the link quality and then of the routing decision. This paper presents improvements of the ETX metric based on link availibility for accurately finding high-throughput paths in multihop wireless mesh networks

Experimental Performance Analysis of Routing Metrics in Wireless Mesh Networks

International audienceThis paper provides a description of a wireless mesh network testbed setup and a measurement-based performance evaluation of the Optimized Link State Routing (OLSR) protocol [7] under three different routing metrics. The considered metrics include hop-count, ETX and ETT. The network performances are evaluated in an indoor testbed formed by heterogeneous MIMO devices. A part of our tests was about the impact of 802.11n features on the network performances showing the importance of lower layers consideration. Our measurements point out the shortcoming of each metric and eventual optimizations towards a more efficient routing. Experimental results show that OLSRETT outperforms OLSR-ETX and OLSR-hopcount significantly in terms of packet loss, end-to-end delay, and efficiency

Towards an Optimized Traffic-Aware Routing in Wireless Mesh Networks

International audienceIn this paper we study through simulations the impact of PHY/MAC protocols on higher layers. In a comparative way, we investigate the effectiveness of some protocols when they coexist on a wireless mesh network environment. Results show that PHY/MAC parameters have an important impact on routing performances. Based on these results, we propose two tra c-aware routing metrics based on link availability. The information about the link availability/occupancy is picked up from lower layers using a cross-layer approach. The rst metric is load-sensitive and aims to balance the tra c load according to the availability of a link to support additional ows. The second metric reproduces better the capacity of a link since it is based on its residual bandwidth. Using several real experiments, we have shown that our proposals can accurately determine better paths in terms of throughput and delay. Our experiments are carried out into an heterogeneous IEEE 802.11n based network running with OLSR routing protocol

Impact des interférences dans un réseau sans fil multi-sauts

National audienceCe papier introduit le problème des interférences dans les réseaux sans fil multi-sauts. Nous nous adressons à deux types d'interférences : intra-flux et inter-flux et nous discutons de leur impact sur l'estimation des ressources disponibles notamment la bande passant

Towards robust and optimized routing mechanisms in a wireless metropolitan and collaborative network

Les réseaux sans fil maillés offrent une infrastructure pour interconnecter les stations d’accès de réseaux de différentes technologies. Ils disposent d’une topologie maillée où tous les routeurs sont connectés de proche en proche sans hiérarchie centrale. Le routage des données, dans ce type de réseaux, doit être réalisé tout en optimisant les ressources du réseau et en respectant au mieux les exigences de QoS des utilisateurs. Dans cette thèse, nous proposons un routage orienté qualité de service dans un réseau sans fil métropolitain grâce à une approche de type cross-layer. Nous avons commencé par étudier l’impact des couches PHY et MAC sur le routage afin d’en déduire la meilleure combinaison protocolaire pour un réseau sans fil maillé. Nous avons, par la suite, orienté notre travail sur l’étude du comportement du protocole de routage OLSR sous différentes métriques de routage. Les résultats de cette étude ont confirmé les limites des métriques existantes à reproduire la qualité réelle des liens et ont soulevé plusieurs points d’optimisation sur lesquels nous avons focalisé. Nous avons donc proposé de nouvelles métriques qui renseignent sur la qualité des liens, en se basant sur les caractéristiques PHY et MAC des liens réseaux, notamment la disponibilité du lien, le taux de perte, la bande passante résiduelle, etc. L’acquisition de ces paramètres des couches basses se fait à l’aide d’un mécanisme de cross-layer. Ces métriques permettent d’appréhender les interférences inter-flux et d’éviter de créer des goulots d’étranglement en équilibrant les charges sur les différents liens. En se basant sur le modèle de graphe de conflit et le calcul des cliques maximales, nous avons proposé une méthode d’estimation de la bande passante résiduelle qui permet de considérer, en plus, les interférences intra-flux. Finalement, nous avons proposé un protocole de routage qui supporte cette métrique et nous avons étudié ses performances par simulation en comparaison avec d’autres métriques et protocoles de routage existants. Les résultats obtenus ont révélé l’aptitude de notre protocole à supporter le passage à l’échelle du réseau ainsi que sa capacité à choisir les routes offrant le plus de débit et le moins de délai, permettant ainsi, une meilleure livraison du trafic de données.Wireless Mesh Networks provide infrastructure to interconnect access stations in networks of different technologies. They have a mesh topology where all the routers are connected with no central hierarchy. Routing in WMNs must be carried out while optimizing network resources and respecting the best user QoS requirements. In this thesis, we propose a QoS-oriented routing in a metropolitan wireless network using a cross-layer approach. We first studied the impact of the PHY and MAC layers on routing to deduce the best combination protocol for a wireless mesh network. We have subsequently focused our work on studying the behavior of the OLSR routing protocol with different routing metrics. The results of this study confirmed the limits of existing metrics to reproduce the real link quality and raised a number of optimization points on which we focused. We have, therefore, proposed new metrics that provide information about link quality, based on PHY and MAC characteristics, including the link availability, the loss rate, the available bandwidth, etc. These low layers parameters are acquired using a cross-layer mechanism. These metrics allow to apprehend inter-flow interferences and avoid bottleneck formation by balancing traffic load on the links. Based on the conflict graph model and calculation of maximal cliques, we proposed a method to estimate the available bandwidth of a path which considers, in addition, intra-flow interferences. Finally, we proposed a routing protocol that supports this metric and we studied by simulation its performances compared to different existing routing metrics and protocols. The results revealed the ability of our protocol to support the network scalability as well as its ability to choose routes with high throughput and limited delay, thus, better delivery of data traffic

Inter-flow and intra-flow interference mitigation routing in wireless mesh networks

International audienceIn this paper, we address the problem of QoS support in an heterogeneous multi-rate wireless mesh network. We propose a new routing metric that provides information about link quality, based on PHY and MAC characteristics, including the link availability, the loss rate and the available bandwidth. This metric allows to apprehend inter-flow interferences and avoid bottleneck formation by balancing traffic load on the links. Based on the conflict graph model and calculation of maximal cliques, we define a method to estimate the available bandwidth of a path which considers, in addition, intra-flow interferences. Finally, we propose a routing protocol that supports this metric and we study by simulation its performances compared to different existing routing metrics and protocols. The results revealed the ability of our protocol (LARM) to support the network scalability as well as its ability to choose routes with high throughput and limited delay, thus, better delivery of data traffic

Dynamic Slotted Network Coding Protocol

International audienceNetwork Coding (NC) is a technique that enhances the performance of wireless networks by increasing the throughput and decreasing the delay. The basic idea is to exploit the mixing of signals that occurs naturally when end nodes transmit at the same time. The main challenge stands for a medium access scheduling allowing synchronized coordination between the nodes involved in that coded transmission. Most of the proposed Medium Access Control (MAC) protocols are based either on the CSMA/CA or the TDMA scheduling. The CSMA/CA based protocols suffer from synchronization issues, while the TDMA based protocols suffer from the delay due to their static design. This paper introduces a new NC MAC protocol called Dynamic Slotted Network Coding Protocol (DSNCP) based on a time scheduling to avoid the synchronization issue and uses a new design that makes the data slot assignments dynamic in order to reduce the delay. Simulation results show a significant performance gain of the proposed DSNCP compared to CSMA/CA and static TDMA protocols in terms of throughput and delay. In some scenarios, the throughput gain of the DSNCP could reach 130% and 100% compared to TDMA and CSMA/CA, respectively, and the delay gain could reach 80% and 40% compared to TDMA and CSMA/CA, respectively

A new Taxonomy of Physical-Layer Network Coding techniques in Two Way Relay Channel model with single antenna

International audiencePhysical-layer network coding (PNC) can effectively improve wireless networks by extracting superimposed signals and transforming collision’s dilemma into an advantage. The proposition of higher layer methods (such as Data Link and Network Layer) explicitly designed for PNC can better enhance wireless network performances. Since the field of PNC is very vast and has several applications, the researchers of the higher layers find it very difficult to propose a suitable PNC system for their research, which has led to the scarcity of research works of this type. This article proposes a new classification method designed to help researchers choose the optimal method that suits their system. This paper is a complete guide for researchers of higher layers to discover the PNC field and improve wireless network performances

Distributed Physical-layer Network Coding MAC Protocol

International audiencePhysical-layer Network Coding (PNC) was first proposed for a Two-Way Relay Channel (TWRC) to improve the spectrum efficiency since it allows nodes to transmit simultaneously via a relay node. This technique requires multiple nodes to transmit their packets with accurate synchronization. Therefore, in many works of literature, centralized scheduling with perfect synchronization has been assumed to be employed on top of PNC. Such assumptions are not applicable in general random access multi-hop wireless networks. Therefore, this paper proposes a distributed MAC protocol that supports PNC in static multi-hop wireless networks. The proposed MAC protocol is based on the Carrier Sense Multiple Access (CSMA) strategy, where RTS/CTS frames are used to detect PNC opportunities and to offer the appropriate scheduling of the involved transmissions that should occur simultaneously. This packet exchange process is coordinated by the relay node and was designed to guarantee compatibility with other conventional relaying schemes with specific concerns for the hidden node issues. Our solution was practically tested on a real testbed with different static wireless topologies and several physical settings. With numerical results, we investigate the effectiveness of PNC in distributed wireless multi-hop networks. Compared to the conventional CSMA/CA and the PNC opportunistic (PNCOPP) MAC protocols, the proposed protocol's performances are advantageous in various scenarios, especially in large networks

Physical-layer Network Coding: A Heterogeneous Software-Defined-Radio based Implementation

International audienceCollisions in multi-hop wireless networks downgrade the system's performance and affect its reliability. Therefore, most of the existing solutions aim to avoid or reduce the interference cases. Counter to all previous works, the newly proposed technique called Physical-layer Network Coding (PNC) transforms the collision's dilemma into an advantage in such a manner that multiple transmissions occur simultaneously and end nodes can extract the superimposed signals. Although there have been many theoretical studies on PNC efficiency, there have been few experiments with pure and heterogeneous PNC schematics. This paper presents the first heterogeneous PNC Software Defined Radio based implementation with a brief discussion of the main challenging related issues. Obtained results proved the efficacy of the proposed solution in indoor environment and serve as a proof for the practicability of PNC in heterogeneous real-time applications