HDTV on Freeview in Granada by next year

Ofcom has published its plans for the reorganisation of Freeview multiplexes, which includes three HDTV channel slots being made available to viewers once a region has completed digital switchover, so viewers in the Granada region should be able to receive three HD channels next year, and Ofcom thinks that it will be possible to carry four HD channels by 2012.

Current organisation of Freeview multiplexes

Up to now, Freeview multiplexes have been split between being BBC and commercial multiplexes, as shown in the table below, and all of the mutiplexes provided similar coverage areas, and 73% of the population could receive Freeview -- although the signals for the 16-QAM multiplexes have always been more robust than those for the 64-QAM multiplexes, so the 16-QAM multiplexes might have provided slightly higher population coverage than the 64-QAM multiplexes.

Freeview multiplexes after reorganisation

Digital switchover will change the above situation, and multiplexes will be described as PSB (public service broadcasting) and non-PSB multiplexes. The PSB multiplexes must provide population coverage that's roughly equivalent to what analogue TV currently provides (98.5% population coverage), and this will involve a lot more transmitters being used to provide the extra coverage. The non-PSB multiplexes will only be transmitted from the same transmitters that are currently being used, but due to increases in the transmission powers coverage will increase to around 80% of the population.

HDTV to be carried on Multiplex B

In order to allow HD channels to launch, Ofcom's plans are to clear existing channels from Multiplex B, and to use that multiplex to carry HDTV channels:

The reason for putting all of the HDTV channels on one multiplex is that it will allow the capacity to be increased. HDTV channels (such as on satellite) are using the new MPEG-4 H.264 video codec, so existing Freeview set-top boxes and IDTVs (which can only decode MPEG-2 video) won't be able to receive the HDTV channels, and anyone wishing to receive HDTV channels will need to buy a new set-top box. So as people will need to buy a new set-top box anyway, Ofcom has decided to use a new technology called DVB-T2 for Multiplex B, which will allow the multiplex's capacity to increase by about 33% over and above what is possible with the current DVB-T standard. Currently, the 64-QAM Freeview multiplexes have a capacity of 24 Mbps using the DVB-T standard, so increasing the capacity by a third increases that to 32 Mbps (I put "estimated" in brackets in the table above because the DVB-T2 standard isn't even out yet, so no-one knows for certain exactly what the capacity increase will be, but it's estimated to be around 30%, and Ofcom said that it's likely to be more than that, so I've estimated that it will be able to increase the capacity by 33%).

Freesat will be far better than Freeview for HDTV

Ofcom has said that at first three HDTV channels could be carried on Multiplex B, and then by 2012 this could increase to four HD channels. This is due to the bit rates needed to provide a certain level of picture quality will reduce over time as the engineers working on H.264 become accustomed to the new codec, so they're better able to optimise it -- the bit rates required by new audio and video codecs to provide a certain level of quality always reduces significantly in the first few years from when the codec is first released.

However, it is going to be a squeeze to fit three HDTV channels into about 32 Mbps of capacity. The BBC is currently using a bit rate of 16 Mbps for the BBC HD channel on satellite, which is using the 1080i format, albeit that they're using 1440 x 1080 rather than the full 1920 x 1080 pixels that the 1080i format is specified for. But on Freeview, 32 Mbps would have to be divided between three HD channels, which is just 10.7 Mbps per channel. And then Ofcom thinks that four HD channels will be able to fit onto Multiplex B by 2012, which would reduce the HD channel bit rates to just 8 Mbps.

Because the bit rates on Freeview are much lower than those being used on satellite, the HD channels on Freeview will have to use the lower resolution 720p HDTV format. But estimates have it that 720p required about 15 - 20% lower bit rates than the full (1920x1080) 1080i format, and the BBC and others are using the slightly reduced resolution with 1440 pixels per horizontal picture line, so that difference will be smaller. Overall, it's basically inevitable that HDTV on Freeview will be at a lower quality than HDTV on satellite. And as the Freesat platform is about to launch in May, I would advise people who want to receive the best HDTV picture quality without having to pay a subscription to get Freesat rather than persevering with Freeview. More HDTV channels will launch on Freesat than on Freeview as well, because Freeview is severely capacity-constrained, whereas satellite isn't, and it has been estimated (by the outgoing Director of Future Media & Technology at the BBC, Ashley Highfield) that transmitting a TV channel on satellite is 10-times cheaper than transmitting it on DTT, which is another reason why there's likely to be more HDTV channels on Freesat in future than there will be on Freeview. Incidentally, Ashley Highfield also estimated that distributino costs on the Internet are ten times cheaper than on satellite -- or in other words 100 times cheaper than on DTT -- so eventually the platform with the most HDTV channels is likely to be the Internet.

Only BBC HD is effectively guaranteed to launch

It's effectively certain that the BBC HD channel will launch on Freeview in the Granada region next year, but Ofcom is going to auction off the remaining capacity in 'slots', so it's possible that broadcasters wanting to launch SDTV channels will outbid the likes of ITV and Channel 4, who would probably want their HD channels to be launched.

SDTV capacity -- before and after

Someone emailed me saying that he'd seen a report that capacity for existing SDTV channels would be severely reduced by Ofcom's proposed changes. However, if you look at the two tables above, the total capacity for SDTV channels at the moment is 120 Mbps, and assuming that Multiplex B will only be used for HDTV channels, there will still be 120 Mbps of capacity for SDTV channels (plus the radio stations) afterwards, so there's no change at all to the capacity for existing SDTV channels and the radio stations -- the additional 32 Mbps available for HDTV is due to the use of DVB-T2 on Multiplex B plus the move from using 16-QAM to 64-QAM on four multiplexes.

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