Michel Misson

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.

Cluster-tree based energy efficient protocol for wireless sensor networks

Wireless sensor networks are conceived to monitor a certain application or physical phenomena and are supposed to function for several years without any human intervention for maintenance. Thus, the main issue in sensor networks is often to extend the lifetime of the network by reducing energy consumption. When the network topology does not change very often, a clustering technique can be used to manage the network activity. Some applications have high priority traffic that needs to be transfered with bounded end-to-end delay. The IEEE 802.15.4 standard defines a MAC protocol that saves energy by putting nodes periodically in sleep mode. The ZigBee protocol defines a hierarchical addressing mechanism by creating cluster-tree based on regrouping the star topology of the IEEE 802.15.4 standard. In this paper, we show how these two standards fail to guarantee quality of service and energy saving at the same time. We propose a time segmentation approach that saves energy, enables quality of service in terms of guaranteed access to the medium and improves the overall performance of the network. This time segmentation is achieved by synchronizing nodes activity using a tree-based beacon diffusion. The tree-based topology is inspired from the cluster-tree proposed by ZigBee. Our solution guarantees end-to-end delay for high priority traffic. The efficiency of our solution is proven by simulation and implementation.

Radio Proximity Detection in a WSN to Localize Mobile Entities within a Confined Area

To localize mobile entities within a confined area, a wired infrastructure is neither scalable nor cost-effective. An alternative solution consists in deploying a Wireless Sensor Network (WSN), made of energy-autonomous devices. In an environment where GPS is inoperative, we propose that the position of a mobile is given relatively to a set of tag nodes deployed in the zone of activity and signaling their position. In a symmetrical way, each mobile node is announced periodically thus allowing a mutual detection of radio proximity (tag-mobile or mobile-mobile). During the contact the nodes are able to share and store the information required by the localization application. This information is then largely scattered by using the mobility of nodes to carry data up to the application collection points. Then arises the question about the choice of the medium access method and its performances for the proximity detection in a cell covered by a tag node. IEEE 802.15.4 unslotted CSMA/CA being largely used in low power WSN, we study its performances according to the density of the mobiles and the load of the cell.

Automatic discovery of topologies and addressing for Linear wireless sensors networks

Wireless sensor networks are a collection of sensor nodes that collaborate to sense a specific event in a given environment. When sensors monitor a structure organized linearly (e.g., pipelines, rivers, railways), they are organized in Linear WSN (LWSN, constituted by connected portions of lines), with different properties than a uniformly deployed WSN. The distributed address allocation in the ZigBee cluster-tree suffers from limitations in LWSN: the number of children is limited, as well as the maximum number of children routers, and the maximum tree depth. Stochastic address assignment, also available in ZigBee, has a high cost in exchanged messages and requires an expensive (in terms of messages and memory) routing process. This paper proposes an automatic discovery of topologies for linear wireless sensor networks combined with an efficient addressing mechanism. We show that our proposition avoids the waste of addresses while keeping the number of messages exchanged proportional to the number of nodes in the network.

Cross-layering in an Industrial Wireless Sensor Network: Case Study of OCARI

Wireless sensor networks are adapted to monitoring applications. Specific solutions have to be developed for industrial environments in order to deal with the harsh radio conditions and the QoS (quality of service) requirements of industrial applications. In this paper, we present the main protocols used in the OCARI project, and we describe their use of cross-layering techniques. We show how it enables us to improve the performance of the network. For each protocol, we give a performance evaluation of its main characteristic.

Overview on Multi-Channel Communications in Wireless Sensor Networks

In this paper, we focus on multi-channel MAC protocols specifically designed for Wireless Sensor Networks (WSNs). The use of multiple channels helps overcome interferences and thus enhance the overall network performance. In order to establish channel and slot allocation to enable simultaneous transmissions, many protocols have been proposed in the literature. Some of them are based on a TDMA approach which offers a more deterministic behavior but requires a strict synchronization, while others are based on CSMA/CA which is an asynchronous medium access algorithm that suffers from collisions due to its probabilistic behavior. Different classifications have been proposed in previous survey papers depending on the periodicity of channel switching, on whether they are centralized or distributed, synchronized or asynchronous, etc. In this paper, we present a survey of the different techniques used in WSNs and that are applicable on the IEEE 802.15.4 standard. We detail some of the most popular protocols and discuss their advantages and weaknesses. We conclude the paper with an open discussion concerning future research directions.

Node Coloring and Color Conflict Detection in Wireless Sensor Networks

In wireless sensor networks, energy efficiency is mainly achieved by making nodes sleep. In this paper, we present the combination of SERENA, a new node activity scheduling algorithm based on node coloring, with TDMA/CA, a collision avoidance MAC protocol. We show that the combination of these two protocols enables substantial bandwidth and energy benefits for both general and data gathering applications. As a first contribution, we prove that the three-hop node coloring problem is NP-complete. As a second contribution, the overhead induced by SERENA during network coloring is reduced, making possible the use of these protocols even in dense networks with limited bandwidth. The third contribution of this paper is to show that applying any slot assignment algorithmwith spatial reuse based on node neighborhood without taking into account link quality can lead to poor performances because of collisions. The use of good quality links will prevent this phenomenon. The fourth contribution consists of optimizing end-to-end delays for data gathering applications, by means of cross-layering with the application. However, color conflicts resulting from topology changes, mobility and late node arrivals can give rise to collisions. As a fifth contribution, we show how the MAC layer can detect color conflicts, and cope with them at the cost of a slightly reduced throughput. Then, we discuss the tradeoffbetween requesting SERENA to solve the color conflicts and dealing with them at the MAC layer, our third contribution. The combination of SERENA and TDMA/CA is evaluated through simulations on realistic topologies.

Hybrid Multi-Channel MAC Protocol for Wireless Sensor Networks: Interference Rate Evaluation

This paper evaluates a channel allocation algorithm of a Hybrid Multi-Channel MAC protocol, HMC-MAC, that tries to improve communication performance in Wireless Sensor Networks (WSNs). We also analyze different techniques that are used in multi-channel MAC protocols proposed for WSNs. These protocols often use either a schedule-based or a contention based MAC protocol to communicate with each others. HMC-MAC takes advantage of the synchronous activity of TDMA to achieve collision free communications, of the flexibility offered by CSMA/CA to offer a scalable network, and of the parallel transmissions over different channels provided by FDMA to enhance the overall throughput. HMC-MAC assumes that sensor nodes are equipped with one half-duplex radio interface. We define a new method for channel allocation that enables nodes to choose the most convenient channel in its three-hop neighborhood in order to minimize interference as much possible. Simulation results demonstrate that HMC-MAC provides smaller interference rate and outperforms other mechanisms.

Using LLC type 1 and LLC type 3 services to communicate through a hybrid network with mobile devices

A hybrid LAN topology including wired end systems and movable or moving end systems in an industrial environment is presented. The hybrid topology is built with a MAP backbone and infrared star subnets. LLC type 1 and LLC type 3 primitives are combined to allow the different kinds of stations to communicate according to an LLC type 3 service. The use of the connectionless mode with acknowledgment greatly improves the security of communications. Data exchange between two mobile devices is described in more detail, and an implementation approach is provided.<<ETX>>

Channel allocation evaluation for a multi-channel MAC protocol

In recent years, the use of multi-channel MAC protocols in the Wireless Sensor Networks has attracted the attention of many researchers. In this paper, we analyze the different techniques that are used in multi-channel MAC protocols proposed for WSNs. These protocols often use either a centralized or a distributed manner to select and allocate channels. We present HMC-MAC, a Hybrid Multi-Channel MAC protocol that takes advantage of the synchronous activity of TDMA to achieve collision free communications, of the flexibility offered by CSMA/CA to offer a scalable network, and of the parallel transmissions over different channels provided by FDMA to enhance the overall throughput. It is based on a decentralized method for channel allocation that enables nodes to choose the most convenient channel in its 3-hop neighborhood. The method used to evaluate this channel allocation scheme is based on the number of conflicts generated by the use of the same channel in a three-hop neighborhood. We present simulation results using NS-2 that show the efficiency of the proposed channel allocation method.