DVB-T is the digital broadcast standard that has been chosen for use in several countries. It comes from the "Digital Video Broadcasting" family of standards. This family covers things like Satellite and Cable broadcasting, but in our case we're interested in terrestrial broadcasting, the "over the air" broadcasting most people will be familiar with. DVB-T's main feature is that it uses on COFDM modulation.

COFDM stands for Coded Orthogonal Frequency Division Multiplex. It's probably beyond the scope of this site to describe how COFDM works (and to be quite honest - it's probably beyond me too). Instead, I'll summarize the features of COFDM which make it useful to the European television environment. Those of you who are more technically minded might like to look at the June 1998 issue of the IEEE Communications Magazine.

COFDM uses many closely spaced carriers to transmit a signal. This gives it two important properties. Firstly, it's fairly resistant to ghosting-style interference (technically called "multi-path" interference which as far as technical expressions go, is pretty non-technical).

Secondly, if there is another nearby transmitter transmitting the same COFDM signal on the same frequency, this will not be much different to "multi-path" interference. Since we've already established that COFDM is pretty good at dealing with this, we find ourselves with a very handy feature on our hands.

We can transmit the same signal on the same frequency from different sites and get away with it. The interference from the two signals will have minimal effect.

The trusty experts have given this feature an acronym. SFN or Single Frequency Networks. In the European context it generally means all "repeaters" and "translators" within the one viewing area can operate on the same frequency. This makes for much more efficient use of spectrum and will free up a lot of the stuff for future use.

This is another advantage of DVB-T, but this one may or may not be realized. The DVB Family of standards are all closely related. If they are used across the various transmission types as appropriate it makes an integrated "Set Top Unit" look very viable. It's not unlikely the subscription television industry will eventually want to reap the benefits of Digital Television and offer it to their customers.

It is at that point they will have to decide what system they will use on their cable or their microwave transmissions. With DVB-T in place they have that extra bit of incentive to choose DVB and potentially make life easier for people.