20/06/2011

BT Whitespace spectrum trials "encouraging"

Spectrum is a valuable commodity and in the UK it's pretty well all allocated (well there are certain bands that are hopefully going to be auctioned soon). It's either been taken up by (mainly) the MOD, commercial TV/radio, mobile and even some space for public use like the 2.4GHz band which is used by WiFi.

The lower the frequency of the radio wave, the better propogation characteristics it has (i.e. it travels further in air and penetrates buildings well) so even though higher frequencies can carry more data, it can be hard to get the signal to users without building very dense radio networks so the signals don't have to travel very far.

Current analogue TV uses the 800MHz band which obviously has very good propogation characteristics as pretty well anyone in the UK can receive an analogue TV signal. During 2012 all analogue transmitters will be turned off and everything migrated to digital.

Therefore there's a lot of interest in using these lower frequency bands for wireless broadband for remote areas as a single big transmitter can be dumped into the middle of the remote area and it connected back to civilisation, but everyone in the area will be able to get a signal from it - i.e. they'll be able to get a broadband connection.

This is a very attractive proposition, except for the fact that frequencies in the range of 400 - 800MHz are currently being used or have planned use which slightly scuppers its use for broadband.

BT are trialing a system known as white space transmission and it's really quite clever. The transmitting and receiving systems listen to the relevant bands that they want to use and only pick sub-bands that aren't already being used. Since modern radio equipment can be very selective and use specific frequencies, there's actually a lot of white space spectrum around (older radio systems were noisy and though bands were allocated, there are always gap-bands in between so that the real radio bands wouldn't "bleed" into each other causing interference - those gap bands contain valauable - now usable - spectrum). Also not all areas use all the sub-bands. The trials are being conducted on the (very) remote Scottish Island of Bute, so even if BT get things wrong, there's not going to be a lot of people to upset, but the trials are going well and BT is going extend to coverage to another 12 users July.

If the trials are successful this could offer a glimmer of hope in getting broadband to rural communities who are not going to be covered by BT or other operators fibre (or even 3G) roll-outs.
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