Cognitive radio allows spectrum sharing

In the event of a disaster, the emergency services have to be able to trust communication networks. But what happens if the network is overloaded or even off the air as a result of the disaster?

Soon it will be possible to borrow free space in other frequency bands or to organise an ad hoc communication network on the spot thanks to ‘cognitive radio’. This means that the scarce space available will be put to better use.

While special emergency channels are allocated to prevent the emergency services from being too dependent on the public network, these channels often have a limited bandwidth. This means that if emergency services also want to communicate via video in the future, or want to send data on a patient to the hospital, more bandwidth will be needed.

Cognitive radio can identify and use all transmitting and receiving possibilities in the vicinity. It is even possible to construct an ad hoc network without the basic infrastructure being present. Mobile users in the area will jointly form the nodes of a temporary network. The information flow will jump from node to node.

This will require a new approach to the radio spectrum: instead of the current highly channelled approach, cognitive radio borrows bandwidth in other bands, without disturbing the users of these bands.

Qiwei Zhang, PhD student at the University of Twente (UT), the Netherlands, has been developing techniques for finding available spectrum.

Because cognitive radio must be highly flexible and capitalises on local circumstances, it requires a lot of calculating power.

According to Zhang, the reconfigurable processor ‘Montium’ that was developed at the UT is suitable for this because, amongst other things, this chip has a limited energy consumption.

Zhang has also developed algorithms to adapt the transmitting signal to the local conditions and to prevent interference with other users.

Cognitive radio is not restricted to applications in emergency situations. This approach will work at any spot where wireless network jams occur.

The challenges are not only technical. Due to the totally different approach, a lot will also have to change in the legislation.

Zhang carried out his doctoral research at the UT’s Centre for Telematics and Information Technology (CTIT). The project was a part of the Ad-Hoc Adaptive Freeband project of the national Freeband program.

University of Twente