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%).

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.

In wireless sensor networks (WSNs) applications such as environmental monitoring, it is essential to design protocols that are energy efficient and that are scalable. The main technique to reduce energy consumption is to use a duty-cycle, where nodes periodically go to sleep. However, the implementation of such a duty-cycle often requires nodes to be synchronized, which is difficult to achieve in a scalable manner. In this paper, we study the delay of blind rendezvous for unsynchronized nodes, that is the delay required for two unsynchronized nodes to be active at the same time. There are several major advantages of blind rendezvous: nodes do not need to share a prior knowledge, nodes do not need to be synchronized, and the support for network dynamicity (due to node mobility or failure) is simplified. We show through simulations that the delay to achieve a blind rendezvous is reasonable in many scenarios.