Ofcom Bingo III - compatibility or improvements?

In the final part of this short series of articles on the future of the Freeview UHF frequency allocations looks at how technological improvements to digital television systems - may provide more with less

^{Published on 14th May 2012 at 19:34 by Brian Butterworth on UK Free TV}
We have seen in  Ofcom channel bingo II - introducing the bands, that in the next decades Ofcom may decide to take some frequency allocations away from Freeview and allocate them to 4G mobile broadband.

The previous article showed how the allocations could be reorganized - even if many homes might need to ensure they have wideband aerials to continue to watch the three commercial Freeview multiplexes.

However, even with these limited resources, it would be possible for additional services to be provided. There are basically two types of enhancement: changes that work with existing equipment and changes to the network that requires new consumer hardware (set top box).

We have already seen one incompatible change in the last few years - the introduction of the DVB-T2 standard, which has been used to provide the high capacity for Freeview HD.

Freeview HD, because it requires the consumer to buy new equipment to use the service, but is "backward compatible", which means the consumer has access to the new and all of the existing channels.

An example of an upgrade to the system where no new set-top hardware is required is the recent changes on the commercial multiplexes where changes have been made to the transmission parameters to increase the capacity of the broadcast ( Changes to commercial multiplex capacity - 2012 timetable ).

Another example, as pointed out in this recent report -  Technical Evolution of the DTT Platform An independent report by ZetaCast, commissioned by Ofcom, was move to using "statistical multiplying" to increase the number of TV channels carried Freeview multiplex.

However, there is always a limit to what can be done with such changes - each minor change can cause problems with some equipment. For example, the very minor change for "2k" mode to "8k" mode at digital switchover has invalided some very old Freeview boxes -  TVs and boxes that do not support the 8k-mode - ukfree.tv has details.

And the benefits often have some small flaw - statistical multiplexing usually means that at least one channel in the group could drop in quality from time to time, because all of the others have sudden high bandwidth needs.

There are limits to gains in the MPEG2 (and indeed MPEG4) encoding process that can be done by improvements because Moore's Law will deliver better computing capacity, but the limitations of the in-home receivers will always put an upper limit on this.

One incompatible improvement that is planned for 2013-15 and beyond is the upgrade from MPEG4 to what is known as HEVC ( High Efficiency Video Coding - Wikipedia, the free encyclopaedia).

Like MPEG2 and MPEG4, HEVC is a "decoding" standard. It will allow set-top boxes to be made that decode to the standard, and this will allow for future improvements to the encoder, to decrease the bits used for the same picture quality.

This should mean, if Freeview users slowly upgrade their equipment over the years to Freeview HD and then Freeview HD/HEVC, eventually the current five SD multiplexes can move first to DVB-T2 to increase their bitrates capacity and then to HEVC to provide more services in that capacity.

The report mentioned above lists 5 HD 1080-line services per DVB-T2 multiplex in 2012, 8 in 2020, 9 in 2025 and 2030, or 11, 17, 19 and 21 720-line services on a DVB-T2 multiplex.

This should be balanced against the need to upgrade the picture quality from the 1080-line HD standard to possibly Ultra-HDTV 3840x2160 and 7680x4320 pixels over the period, which may just result in the same number of television channels, but with much better pictures.

Of course, some additional distribution of television will be done using IPTV (for example, the soon-to-launch YouView) but terrestrial broadcasts will still have a large part to play because they can reach 98.5% of the UK using existing technology.

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