Search

Network 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 significant proportion of elderly population suffers from age-related health issues and different chronic diseases which leads to a progressive decline in physical and cognitive skills which prevents them to live independently in their home and to perform basic Activities of Daily Living (ADL). In this context, the integration of information and communication technologies (ICT) has resulted in a rapid emergence of pervasive healthcare systems such as Health Smart Homes which aim to monitor and evaluate the person’s health condition and their behavior in performing ADL and to avoid, as long as possible, the delays of recourse to healthcare institutions (e.g. nursing homes and hospitals). In this research, we propose a predictive model for detecting behavioural and health-related changes in a patient who is monitored continuously in an assisted living environment. We focus on keeping track of the evolution of the dependency level and detecting the loss of autonomy for elderly person using a Hidden Markov Model based approach. We were interested in including blood pressure in this predictive process as it is considered the primary risk factor for cardiovascular disease, stroke, kidney failure and many other diseases. Our simulation was applied on a empirical dataset that concerned 3046 old persons monitored over 9 years. The results show that our model accurately evaluates person’s dependency, follows its evolution of autonomy over the time and thus predicts moments of important changes.

International audience; In 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.

International audience; In 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.

National audience; Ce 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 passante

International audience; This 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.

International audience; Current routing mechanisms proposed for adhoc networks still feasibly applied in Wireless Mesh Networks given their similarities. Many researchers have conducted numerous simulations for comparing the performances of these routing protocols under various conditions and constraints. Most made comparisons are not aware of PHY/MAC layers and their impact on routing performances. In this paper we study through simulations the impact of PHY/MAC protocols on higher layers. The considered protocols include three propagation models, ie., FreeSpace, TwoRayGround and Shadowing, three different PHY/MAC protocols specified IEEE 802.11 standards namely, 802.11b, 802.11s and 802.11n, and finally three routing protocols, ie., AODV, OLSR and HWMP. In a comparative way, we investigate the effectiveness of these protocols when they coexist on a wireless mesh network environment. Our results show that the routing strategy can significantly impact the network performance only if it is strongly linked to the characteristics of the lower layers.

Wireless sensor networks are often deployed in hardly accessible or hazardous fields. Their main goal is to monitor the target field and transmit surveillance data to a sink. Therefore, connectivity of the sensor network and the coverage ratio of the monitored area are the most relevant concerns to reach these goals. In this paper, we propose to use several mobile robots to assist sensor networks redeployment in order to enhance the network connectivity and the coverage ratio of the monitored area. We model the sensor network as an islets-based topology and we propose to use robots to detect and heal connectivity and coverage holes availing the sensors redundancy. Preliminary simulations showed that our new scheme can significantly enhance the connectivity ratio of the initial network and improve the coverage ratio by using few numbers of robots.

International audience; This paper presents two novel metrics, Link Occupancy aware routing Metric (LOM) and Residual Link Capacity based routing metric with Interference Consideration (RLCIC), for accurately finding high-throughput paths in multihop wireless mesh networks. The first metric is load-sensitive and aims to balance the traffic load according to the availability of a link to support additional flows. The second metric reproduces better the capacity of a link since it is based on its residual bandwidth. It captures accurately the available path bandwidth information when considering both the intra-flow and the interflow interferences. Using several real experiments carried out into an heterogeneous IEEE 802.11n based network running with OLSR routing protocol, we have shown that our first proposal can accurately determine better paths in terms of throughput and delay, thereby significantly outperforming the other existing metrics. The consistency of the second metric RLCIC is proved formally based on notions of graph theory.

International audience; This 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.