Future of French DTT: VHF Band III + DVB-T2 = fewer HD channels (and a new aerial?)
My curiosity was piqued in my previous post about France’s DGMIC consultation (on the future of the DTT platform) by the possibility that it might use VHF frequencies in Band III to make up for the loss of the 700MHz band to mobile.
My first thought was: ‘wouldn’t everyone have to change their roof-top aerials’? Well, yes and no. This article on the US regulator FCC’s website is relevant. In the USA, digital TV is transmitted both on VHF channels (2-13) and on UHF ones (14-51), and while the FCC says “it is important that your antenna be able to receive both”, it says that only ‘some antennas’ only provide good reception of one or the other, implying that many antennas on the market already do both.
The same may be true in France, although I guess one of the reasons USA antennas are often hybrid is simply because that’s always been the prevailing environment. But even if it’s not, upgrades would not be out of the question – after all, French consumers are going to have to upgrade their in-home equipment anyway to DVB-T2 and MPEG-4 (if not HEVC) at some point if the whole platform is to transition to HD – as is the current plan. That would still be a pain, but the upgrades could all be engineered to happen at the same time, and subsidised if necessary.
More interesting, perhaps, are the bandwidth implications. It so happens that the European Broadcasting Union published some figures a couple years back about the use of DVB-T2 (which will have to be introduced for any wholesale migration to HD) in Band III. These suggest that at 200 MHz, an indicative bit-rate for a DVB-T2 mux would be in the range of 30-35 Mbit/s (256-QAM, FEC 2/3, 32k, PP7 Normal). This contrasts with a bit-rate of 35-40 Mbit/s at 650 MHz using similar parameters.
So use of VHF would incur an additional cost over and above any need to upgrade rooftop aerials: and that is that significantly fewer HD channels could be squeezed into a DVB-T2 mux than if using UHF frequencies.
On the other hand, the EBU paper notes that VHF Band III has some technical advantages when it comes to using mobile services instead of fixed ones. This is significant in the French context since attempts to launch a mobile broadcast platform there have never taken off – an additional reason, perhaps, for the DGMIC’s interest in VHF Band III.
(Aerial image courtesy of Daniel Christensen via Wiki Commons)