Abstract-In the past few years, energy conservation has been the main focus of researchers working on wireless sensor networks. One of the main technique to save energy is to deactivate periodically the radio module of sensor nodes: nodes alternate periods of activity and periods of inactivity, which is referred to as their duty-cycle. In this paper, we focus on asynchronous dutycycle mechanisms, as these mechanisms are usually simple, do not require time synchronization and support network changes. We propose an asynchronous MAC protocol based on blind rendez-vous and random wake-up. Our protocol is based on a modification of the IEEE 802.15.4 standard, where activities start at a random time within each activity cycle. Our simulations show that our protocol can achieve a good performance under various scenarios, for small duty cycles (ranging from 0.1% to 5%).
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
Industrials have been increasingly interested in sensor and actuator networks to monitor and control installations. The recent IEEE 802.15.4 standard has been developed to address vital issues of these networks, such as limited battery power and low processing capabilities. However, the standard does not meet all the requirements of industrial networks. For example, only some of the IEEE 802.15.4 nodes save energy, and the delay for the computer running the monitoring application to retrieve the sensor data or to activate an actuator is not bounded. Our research on energy-efficient MAC protocol is divided into two parts: Part A is the proposal of a flexible, synchronized tree-based MAC protocol called MaCARI and Part B deals with optimizations that can be performed within each cell. This paper focuses on Part A, that is, on the description of the MaCARI protocol. MaCARI is designed to tolerate scheduled activities such as sensor data retrieval and unscheduled activities such as complex routing. MaCARI achieves this flexibility by using a tree-based centralized mechanism. We show the benefits of MaCARI by ensuring all nodes sleep regularly and by proving that the maximum end-to-end delay is bounded.
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.
Wireless sensor networks (WSNs) are increasingly used in environmental monitoring applications. They are designed to operate for several months by featuring low activity cycles, in order to save energy. In this paper, we propose a MAC protocol for such WSNs with duty-cycles of 1%. Initially, nodes are activated randomly and independently, then they use the knowledge of previous successful frame exchanges to compute their next activation times. We study the choice of the history size, and we compare the performance of our protocol with other protocols from the literature. We show that with a limited history size of only six entries, we significantly improve the performance of existing protocols, while keeping the advantages of fully asynchronous protocols.
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