In the last post we talked about the Oxford Flood Network and that we would provide Internet connectivity to the sensors in Hogacre Eco-Park through a TV Whitespace (TVWS) link. Well, this link has now been successfully established and we are very excited as we can now start collecting data from the sensors. The performance that we obtained for a single channel occupation is quite impressive: 13Mbps in download and 3Mbps in upload from the client station site (we used speedtest.net to assess the performance over a Virgin ADSL broadband connection).
With the Oxford Flood Network we are making use of spectrum that was freed up by the Digital Switchover to provide internet connectivity to sensors. You might ask why we decided to use TVWS instead of other access technologies. Well, unfortunately there is no ADSL nor fibre in the areas where the sensors will operate; also, even assuming cellular radio coverage availability, setting up the network could have proved to be more challenging. Therefore, using TVWS is not only exciting from a R&D point of view, but it also makes lots of sense for this scenario as the excellent propagation characteristics of frequencies in the TV band solve the connectivity problem in an elegant way.
While establishing the TVWS link Nominet and LoveHz have worked out some best practices for setting up a TVWS network. Line-of-sight between stations is not essential at those frequencies, but the best channel to operate on has to be carefully selected amongst the ones which actually present the lowest noise on both radio locations. In fact, although the White Space Database (WSDB) has generally a good picture of the RF environment in every location of the UK, in practice unexpected transmissions or high noise floor can make signal reception impossible. This last point seems to support the need for sensing technologies in both radios, such that a hybrid solution combining database and sensing can provide the optimal operational performance.
Accessing TVWS frequencies for transmission needs to be carefully coordinated in order to avoid interference with other services operating in this band, such as Digital TV broadcasts and wireless microphones. In the past months we have developed a database for TVWS (i.e. a WSDB) which can be interrogated by devices in order to get the list of available channels and maximum power for any UK location. At this moment the database is operating as part of a pilot with Ofcom, so the learning can be used to define the regulatory operational framework for TVWS. At the same time we are also collaborating with WS radio manufacturers and one of them provided the radios that we are using in the Oxford Flood Network project.
Now the link is up and running we will soon be able to talk about the data collection for the Oxford Flood Network, so watch this space.