Kingswood Warren in the newsIt seems that the journalists from CNet Crave have been visiting my department to have a look at my colleagues' prototype system for doubling the capacity of a DVB-T multiplex (the technology used by Freeview) to try and make terrestrial HDTV practical. The technology makes use of the fact that you can transmit two independent signals on the same frequency if you polarise them 90° apart - something that's been known for about a century, but hasn't been practical until recently, with the development of MIMO techniques.
They are currently squeezing three HD transmissions and one Standard Definition TV channel into a single multiplex, the HD channels at a bitrate of 15Mb/s - plenty for the most recent version of Dirac (although as far as I know nobody's proposing that codec for transmission) and h.264 codecs ought to be looking pretty good at that bitrate by the time any hypothetical MIMO technology could be deployed country-wide. (The current BBC HD trial service started broadcasting using h.264 at 19Mb/s back in 2006, and at that time it really needed a bit more than that, in my opinion. It is in the nature of video codec implementations to improve with time, however, as their creators find ways to make better use of the data-reducing tools that the codec standards provide.)
No technology is ideal, and this one would require everyone to upgrade their aerials again, as well as their set-top boxes, but to get HD into the very limited bandwidth available terrestrially requires compromises, and this technology is a very interesting option.
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