On the coordinated use of a sleep mode in wireless sensor networks : ripple rendezvous

It is widely accepted that low energy consumption is the most important requirement when designing components and systems for a wireless sensor network (WSN). The greatest energy consumer of each node within a WSN is the radio transceiver and as such, it is important that this component be used in an extremely energy e±cient manner. One method of reducing the amount of energy consumed by the radio transceiver is to turn it off and allow nodes to enter a sleep mode. The algorithms that directly control the radio transceiver are traditionally grouped into the Medium Access Control (MAC) layer of a communication protocol stack. This thesis introduces the emerging field of wireless sensor networks and outlines the requirements of a MAC protocol for such a network. Current MAC protocols are reviewed in detail with a focus on how they utilize this energy saving sleep mode as well as performance problems that they suffer from. A proposed new method of coordinating the use of this sleep mode between nodes in the network is specifed and described. The proposed new protocol is analytically compared with existing protocols as well as with some fundamental performance limits. The thesis concludes with an analysis of the results as well as some recommendations for future work

Energy efficient medium access control for wireless sensor networks

A wireless sensor network designates a system composed of numerous sensor nodes distributed over an area in order to collect information. The sensor nodes communicate wirelessly with each other in order to self-organize into a multi-hop network, collaborate in the sensing activity and forward the acquired information towards one or more users of the information. Applications of sensor networks are numerous, ranging from environmental monitoring, home and building automation to industrial control. Since sensor nodes are expected to be deployed in large numbers, they must be inexpensive. Communication between sensor nodes should be wireless in order to minimize the deployment cost. The lifetime of sensor nodes must be long for minimal maintenance cost. The most important consequence of the low cost and long lifetime requirements is the need for low power consumption. With today's technology, wireless communication hardware consumes so much power that it is not acceptable to keep the wireless communication interface constantly in operation. As a result, it is required to use a communication protocol with which sensor nodes are able to communicate keeping the communication interface turned-off most of the time. The subject of this dissertation is the design of medium access control protocols permitting to reach a very low power consumption when communicating at a low average throughput in multi-hop wireless sensor networks. In a first part, the performance of a scheduled protocol (time division multiple access, TDMA) is compared to the one of a contention protocol (non-persistent carrier sensing multiple access with preamble sampling, NP-CSMA-PS). The preamble sampling technique is a scheme that avoids constant listening to an idle medium. This thesis presents a low power contention protocol obtained through the combination of preamble sampling with non-persistent carrier sensing multiple access. The analysis of the strengths and weaknesses of TDMA and NP-CSMA-PS led us to propose a solution that exploits TDMA for the transport of frequent periodic data traffic and NP-CSMA-PS for the transport of sporadic signalling traffic required to setup the TDMA schedule. The second part of this thesis describes the WiseMAC protocol. This protocol is a further enhancement of CSMA with preamble sampling that proved to provide both a low power consumption in low traffic conditions and a high energy efficiency in high traffic conditions. It is shown that this protocol can provide either a power consumption or a latency several times lower that what is provided by previously proposed protocols. The WiseMAC protocol was initially designed for multi-hop wireless sensor networks. A comparison with power saving protocols designed specifically for the downlink of infrastructure wireless networks shows that it is also of interest in such cases. An implementation of the WiseMAC protocol has permitted to validate experimentally the proposed concepts and the presented analysis