Frédérique Jacquet

Medium access control for a tree-based wireless sensor network: Synchronization management

Energy efficiency is a primordial issue in the wireless sensor networks. This is achieved by deactivating nodes when possible. In this paper we describe the MAC protocol MaCARI that synchronizes nodes in order to schedule active and inactive periods. MaCARI divides time into three periods: a synchronization period, a scheduled activities period where communications are constrained by a tree and an unscheduled activities period where nodes can communicate whenever in range. With this synchronization, nodes are able to save energy during specific time intervals. Therefore, we focus on the synchronization period and apply an optimization to reduce its duration. We validate this approach by simulations under different tree topologies.

A method for increasing throughput based on packet striping

This paper presents a method based on packet striping aimed at increasing throughput and quality of service. Striping is a method for improving network performance by splitting traffic over multiple physical links. Striping algorithms have to deal with the different characteristics of the links. A multilink system is described, it provides a basis for exploring and testing several striping schemes. We propose a new striping algorithm which tends to keep the order of packets and limits the effects of different delays on channels. This is done not by a synchronization at the receiver side but by detecting which packets are expected to be late regarding to the others. These packets are sent in advance so that an in-order delivery is aimed for. This algorithm is efficient even when there are high error rates like it can be encountered in wireless networks. A modeling of the multilink system provides different simulation results which allow the interest of our striping algorithm to be verified.

Using a token approach for the MAC layer of linear sensor networks: Impact of the node position on the packet delivery

Wireless sensor networks (WSNs) consist of a large number of sensor nodes which communicate via wireless links for monitoring applications. In several applications, such as the monitoring of pipelines or roads, the network topology is linear. This type of WSN is called linear sensor network (LSN). Our goal is to improve the behavior of a MAC protocol for LSNs, by using a token approach. As usual, the possession of the token grants the node permission to transmit on the medium during a given amount of time. The payload of the token is used to propagate network parameters such as delay between tokens, sleep and wakeup calendar. In this paper, we study the behavior of this MAC protocol and we evaluate the impact of the node position on the packet delivery for two types of LSNs.

Striping over wireless links: effects on transmission delays

Striping is a method for increasing network performance by splitting the traffic over multiple physical links. We propose a striping configuration adapted for wireless and mobile communications which tends to cope with limited bandwidth, high error rates and intermittent connectivity. We show how the order in which the packets are sent can heavily affect the transmission delays if lost packets are detected and sent back quickly or not. We present a new striping algorithm which leads to short delays between two consecutive packets. We analyzed and compared the effects of possible packet striping methods on the transmission delay.

Striping scheme for wireless communication systems

Using a communication system composed of multiple links, with different characteristics and throughputs, not only increases the global transmission throughput but also considerably improves the reliability of the system. However, to be fully efficient such a system requires particular schemes, called striping schemes, to split traffic over the links. The allocation of the successive packets towards one or other link can heavily affect delays before retransmission of any lost packets, and finally modifies the final throughput obtained. This paper considers wireless communications with particularly unreliable performances. It proposes an analysis of the effects of possible packets striping methods and presents some simulation results which allow some parameters of our striping algorithm to be optimized. The delays obtained with our method is then compared to those obtained with other schemes.

Study of a Wireless Medium Access Method inspired from PCF for industrial applications

Infrastructure-based wireless local area networks (WLAN) shows us a lot of advantages for industrial applications because they allow mobile entities and a priori fixed supervisor entities to communicate but, for this moment, the standard 802.11 does not provide any management of quality of service (QoS) facilities. For these reasons in our project, we implement a new mechanism for access method (pseudo-PCF) inspired from the PCF option. Firstly, in this paper we study the characteristics of this new mechanism and we compare with DCF mechanism. In the second and the third part we study the influence of the charge in a cell and the additional traffic on the transmission time between the mobiles

Using a Token Approach for the MAC Layer of Linear Sensor Networks

Wireless Sensor Networks (WSNs) consist of a large number of sensor nodes deployed in a wide area for monitoring applications. For some of these applications, as pipeline or road monitoring, wireless sensor nodes have to be deployed in a linear manner. We refer to these WSNs as Linear Sensor Networks (LSNs). Due to specificity of LSNs, MAC protocol designed for WSNs, as contention or TDMA based protocols, are often not suitable. Furthermore, wireless node deployment can provide a certain form of redundancy to prevent link or node failures. In this paper, we propose a token based MAC protocol for linear sensor networks in order to improve the network performance. We evaluate the effect of the redundancy on the number of packets delivered to the sink. We show that the redundancy induces a significant improvement both on the delivered traffic and on the FIFO queue size of the nodes.

Multicast Strategies for Robots Moving within the Coverage of A WLAN

The are many advantages of Infrastructure based wireless local area networks (WLAN) for industrial applications because they allow mobile entities and a priori fixed supervisor entities to communicate. If mobiles are to cooperate they have to share common information thanks to multicast protocols. The standard mechanisms are not performed in a short enough time to allow efficient cooperation. This paper addresses the need for a fast multicast mechanism dedicated to mobiles moving within a same WLAN. This mechanism makes the access points (AP) play the part of a mirror and of an exchange master. Its performances are evaluated thanks to network simulator (NS2) in function of the number of cooperating mobiles moving within the same cell.

Mechanism for multi-domain marking in DiffServ architecture

In a DiffServ domain, several marking mechanisms for packets have been proposed. They make it possible to downgrade or to remove the packets from flows which are not in conformity with the traffic contract. However, all these mechanisms are adapted to operate in intra-domain rather than in multi-domain marking. We propose a mechanism called multi-domain marker (MDM) for flows crossing one or more DiffServ domains in order to reduce the impact of losses on packets which have significant semantic value. The marking is carried out at the entrance to the DiffServ domain and at the exit where the initial priority of the downgraded packets is restored. Simulation results show a reduction in the losses of significant packets. We compare this mechanism to already existing mechanisms by measurements of QoS parameters (delay, jitter, packet losses) of the various real-time flows.