Digital Television in Australia


So what's this DVB-T then?

DVB-T is the digital broadcast standard that has been chosen for use in Australia. 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 COFDM modulation.

Oh great, another acronym. What on earth is COFDM?

COFDM stands for Coded Orthogonal Frequency Division Multiplex. You're really glad you asked aren't you?

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 summarise the features of COFDM which make it useful to the Australian 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 "multipath" 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 "multipath" 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 boffins have given this feature an acronym. SFN or Single Frequency Networks.

What's so good about SFN?

In the Australian 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 A Good Thing. Trust me.

What about the rest of the DVB family?

This is another advantage of DVB-T, but this one may or may not be realised. The DVB Family of standards are all closely related. If they are used across the various transmission types as appropriate it makes an intergrated "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.

Note: I am making no attempt to compare DVB-T with the US-based ATSC standard. DVB-T has been chosen for Australia and this siteis about Australia. So no angry e-mails about "forgotten" advantages of ATSC please - though the author admits he feels DVB-T is vastly superior.:)

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