The campaign for reusing spectrum released after complete analogue switch off in 2012 has gained a lot of prominent voices, with those looking at the technical feasibility saying that perhaps 6-8 high definition channels could be accommodated.
The BBC has been exploring a different method of squeezing more HD content out of the existing Freeview service, by using technology to double the bandwidth available.
Using MIMO (multiple input, multiple output) communication, two signals are sent from broadcasters on the same frequency, using two separate transmitters, and picked up and decoded by two separate receivers in the aerial.
It works by making the signals "spatially multiplexed". The receiver can tell which signal is which because they're sent at slightly different times. Additionally, one bitstream is sent horizontally polarised, and the other is sent vertically polarised, making it easier for the decoder to differential between the two.
The BBC has conducted a successful small-scale test. Whether it makes it out into the wild, though, is another matter. It's not going to happen before 2012, anyway, and even if a solution for getting high definition on terrestrial TV rolls out, it's going to require new receiver equipment for every person who wants to access it.
From: Sony to double BRAVIA LCD TV production for growing European demand