As preparations for the launch of HD on Freeview begin, Justin Mitchell from BBC research and innovation offers up some detail on the DVB-T2 trials.

DVB-T2 is a new coding specification and an extension of the DVBT transmission standard currently used in the UK.

Using a transmitter in Guildford, Surrey - and utilising facilities provided by National Grid Wireless and Arqiva - the very first DTT signals using DVB-T2 were pumped out last Friday (27 June).

DVB-T2 is expected to deliver an increase of at least 30% in the capacity of a DTT multiplex.

Following a reorganisation of the current channels on the multiplexes - and an upgrade of multiplex B - this will allow four HD channels to be shoehorned onto Freeview by 2012.

If consumer equipment is ready in time, Ofcom believes that the Granada region will be first part of the UK to get HD channels on Freeview. This will happen towards the end of 2009.

Here Justin Mitchell, the leader of the DVB-T2 modem development team at the BBC, explains how the DVB-T2 tests will work.

What are you doing?

“We've built ourselves a hardware modulator which is compliant to the standard and we've put the signal on air. What we're doing now, for ourselves, is building the equivalent demodulator and we'll take that out in a van and try and receive signals around Guildford to see if the predicted coverage matches our expectations. If it doesn't match-up we'll capture the signal and go back try and figure out why.”

What signals are you transmitting?

“We can pump out a pre-coded one-hour long loop of HD or we can transmit a pseudo random sequence which is pretty useful as then we know exactly what was transmitted.”

Why are you doing it?

“The point of this is three-fold. The validation of DVB-T2 is the first thing. T2 contains a lot of new techniques in signal processing. And we want to be sure that they all work. There are quite a lot optional ones so if some of them were found not to deliver we'd get some feel about whether to use them in the UK or not.

“Then we need to establish the set of parameters that the UK is going to use. The T2 specification contains a lot of options and it would be unrealistic to expect a manufacturer to include them all. We need to tie that down.

“The other thing, in order to get the [initial] launch next year, we need to give the manufacturers all the help they can get. Having a signal on air that is free to use is a big help to them. If they need help they can contact us.”

Can it go wrong?

“Some elements of the standard might not deliver what we'd expect in which case we would choose not to use them in the UK. The T2 standard hasn't been built anywhere in hardware yet. There could be a nasty surprise!”

What are your benchmarks?

“It's all a bit new. We want to establish that the coverage is similar to DVB-T. Or to put it another way, we want to establish how much bit rate or capacity we can get that has a similar reach to DVB-T.

“DVB-T carries either 18 or 24 megabits per second, depending on which multiplex you're on. Our expectation at the moment is that T2 will carry 36 or 40 megabits per second.”

What is the timetable?

“We're currently working on our demodulator and we're hoping to have that complete in a couple of months. The first place we're likely to show the results is at IBC in September. We'll show an end-to-end chain on the DVB stand.”

“After that the receiver manufacturers are going to want to tie us down to a profile. We're going to want to have a pretty good idea of what that is going to be by the end of the year.”

Can anyone else test the signal?

“The signal is on air and anyone is welcome to use it. That was the intention. Anyone making a receiver can receive the signal as well and try out their products. They might well want to try it in a real reception environment.”