Consumer Electronics Companies Favour 8K DTT for UK

The consumer electronics industry body, Intellect, have expressed their preference for the UK to change from the current 2K DVB-T transmission mode to the 8K mode, citing that 8K improves reception quality due to 8K's robustness to impulsive interference. 

The UK adopting the 2K DVB-T transmission mode was an unfortunate consequence of the government's desire for DTT to be launched as soon as possible (OnDigital launched on 15th November 1998) in order to increase competition between digital platforms, and at the time the only DVB-T receiver chips available could only receive 2K. Just 4 months after the launch of OnDigital DVB-T receivers enabled for reception of both 2K and 8K modes were already available for other countries, but the UK had already committed to 2K and changing modes would have required replacing all the set-top boxes that had already been shipped, which would have proved unpopular with OnDigital subscribers that had paid £200 for the boxes (set-top boxes were £400 for non-subscribers).

The first disadvantage of using 2K only emerged after OnDigital was launched where the switching of high electric currents, such as by switching electric lights on/off; electric motors and car ignition systems caused impulsive interference which caused the picture to break up. In comparison, 8K is far more tolerant to impulsive interference. The impulsive interference problem has significantly improved due to 4 of the 6 DTT multiplexes changing to a more robust transmission mode (16-QAM instead of 64-QAM) as well as transmitter power increases on all 6 multiplexes, but the drawback of using this more robust transmission mode is that the multiplex capacity is reduced from 24 Mbps to 18 Mbps, which is the equivalent of 1 or 2 TV channels per multiplex.

8K Allows Far More DTT Multiplexes

A more serious drawback of the UK's decision to use the 2K mode is the number of DTT multiplexes that consumers can receive. 2K DTT must use multi-frequency networks (MFNs), and the number of multiplexes that can be received is limited by the distance between two areas that use the same frequency (due to co-channel interference), called the frequency-reuse distance, and in the UK those within DTT coverage areas can receive 6 DTT multiplexes. 8K, on other hand, can use single-frequency networks (SFNs) where one transmission frequency can be used, for example, across the whole country. Theoretically, using 8K SFNs then there can be one DTT multiplex for each available channel, and as can be seen in the figure of UHF TV channels below, there are currently 46 TV channels (current TV channels are both the green and red channels -- the red channels are earmarked to be released, probably auctioned-off, after digital switchover), so, theoretically we could receive 46 DTT multiplexes. However, frequency planning isn't as simple as that, and there would no doubt be interference problems (such as causing interference in neighbouring countries) that would limit the number of possible SFN multiplexes to a significantly lower number than 46 multiplexes. Overall though, the fact remains that it is highly likely that if the UK had used 8K instead of 2K then the number of DTT multiplexes that we would be able to receive would be significantly higher than the current 6 multiplexes that we can receive today, and the implications of this would be that we could have had far more channels than we currently do get, and that the current trend of lowering the TV channel bit rates to squeeze in more channels in the limited space on DTT would have been unnecessary, or at least not as much of a problem as it is becoming (for example with the addition of 2 new TV channels on the horizon, which will have a knock-on effect on the existing TV channels' bit rates).

One drawback of changing to 8K mode is that there are still old DTT receivers (such as the oldest OnDigital boxes that are still in use) that are not enabled to receive 8K transmissions. Ofcom's TV market quarterly-update estimates the number of OnDigital set-top boxes to be 350,000 (12 months beforehand the figure was 431,000), and a percentage of these OnDigital boxes will not be capable of receiving 8K transmissions. If a change to 8K does occur, then presumably would be phased-in to coincide with each region's analogue TV signals being switched-off, which isn't due to start until 2008, by which time there should be very few 2K-only receivers left in the market.

So, assuming that the UK does change to 8K mode, then it looks like digital switchover might redeem what was a highly short-sighted, politically-motivated decision.

Unfortunately, there doesn't look like there is anything to redeem the highly short-sighted, politically-motivated (and BBC-influenced, due to their heavy investment in DAB from 1995 onwards) decision to press ahead with DAB digital radio in the 1990s despite the technology already being 10 years old and not being up to the job, and it is looking increasingly likely that the UK will be stuck with the dreadful DAB system for possibly decades to come. So, as TV moves towards the high-definition age, radio (in the UK at least) moves from FM to the significantly lower-quality DAB system.

Bookmark with:
Digg	del.icio.us	Reddit	Facebook
Google	Stumbleupon	Slashdot