Wireless sensor networks find their way in logistics, in product quality control and even in the Great Barrier Reef where they monitor the quality of water. But how do hundreds of sensors communicate without consuming too much battery power? Lodewijk van Hoesel of the Centre for
Telematics and Information Technology (CTIT) of the University of Twente lets sensors 'speak' to their neighbours without the need of a central director.
Wireless sensor networks are hot. In any application in which wires use to cause problems, autonomous and wireless sensors can be positioned. An example of a project Van Hoesel is involved with, is monitoring the water quality in the fragile ecology of the Great Barrier Reef without the need of an 'intrusive' infrastructure. But also for climate control in buildings and for monitoring industrial processes, wireless sensor networks have been introduced. The sensors exchange information and form 'multi hop' connections. Because they sometimes stay in place for years, the use of battery power must be kept to a minimum.
The sensors don't just constantly transmit their data to a central server; that would cost far too much energy. Communication is expensive in terms of energy consumption, therefore intelligence is added locally to each sensor node: the sensors know when to transmit their data and when to pass data through, coming from neighbouring sensors. For this, they have to be 'on speaking terms', as Van Hoesel calls it. In this way, the network itself can carry out complex tasks.
He therefore designed a so-called Medium Access (MAC) protocol, based on self organization of the network. The sensors keep an eye on their neighbours and autonomously decide whether to start transmitting or not. This also holds for the neighbours next-door to the closest neighbours: in this way, Van Hoesel avoids conflicts in the network and keeps energy use to a minimum.
This approach can be further improved by introducing passive sensors in the network: they provide data but they don't actively participate in the multi hop communication. Passive sensors use less energy and thus extend the lifetime of the network as a whole. As wireless networks in general can be vulnerable to attacks from the outside, Van Hoesel presents adequate countermeasures.
Lodewijk van Hoesel, who defended his PhD thesis 'Sensors on speaking terms' on June 21 is also the cofounder -together with Paul Havinga and Stefan Dulman- of Ambient Systems, a company specialized in wireless sensor networks. The young company recently was awarded the Dutch ICTRegie Award and the Van den Kroonenberg Award, an award of the University of Twente for young entrepreneurs. Ambient Systems started cooperation with the Australian Institute of Marine Science for monitoring the water quality around the Great Barrier Reef using
wireless sensor networks. More info: www.ambient-systems.net