Digital terrestrial television in the United Kingdom is made up of over fifty primarily free-to-air television channels (including all the national analogue stations) and over twenty radio channels from Freeview, Top Up TV and Setanta Sports. It is intended that digital terrestrial television will completely replace analogue terrestrial television in the United Kingdom by 2012.

Receiving digital terrestrial television in the UK
Digital terrestrial television provides many more channels than analogue television. For many viewers it offers a higher-quality picture (with many channels broadcasting in 16:9 anamorphic widescreen). A number of interactive services, including a newer version of Teletext, are also offered.
An eight-day electronic programme guide (EPG) allows viewers to see the names, descriptions and broadcast times for programmes. As this was not an original feature of digital terrestrial television (it was introduced in 2004), some receivers feature an EPG with details of the current and next programme only.
A third-party proprietary 14-day EPG is also provided by a company called 4TV, who formerly carried a 7-day service when only now and next data was normal. This is only available on boxes which support their format and pay a licence fee, generally resulting in more expensive boxes. The service is carried on Multiplex D, meaning that not all viewers can even receive the data.

Features

History
Digital terrestrial television launched in the UK on 15 November 1998 (just after digital satellite television on 1 October 1998). The technology required that the UK government license the broadcast of channels in six groups, or multiplex (usually abbreviated to 'mux') labelled 1, 2, A, B, C, and D.

Development and launch

Main article: ITV Digital ITV Digital

Main article: Freeview Freeview

Main article: Top Up TV Top Up TV
Unless noted otherwise, channels may broadcast twenty-four hours a day (though not all use all of this available time).

List of digital terrestrial channels

Logical Channel Number
ITV1 is the brand name for 12 of the 15 regional ITV Network franchises for England, Wales, southern Scotland, the Isle of Man and the Channel Islands. Each of these 12 franchises has a separate brand name used prior to local programming, see ITV1. STV is the brand name for the franchises for central and northern Scotland. UTV operates the franchise for Northern Ireland. All 15 franchises broadcast 0925-0600; GMTV operates the franchise for national breakfast television and broadcasts 0600-0925.
Five, S4C and S4C2 will move to a public service multiplex at the start of digital switchover, using the bandwidth created by switching from 16QAM to 64QAM mode, so will be transmitted from all 1,154 UK transmitters. Multiplexes A, C and D will only be transmitted from the current 80 transmitters after switchover but with higher powered signals (and in 64QAM mode). Television channels

Text and interactive services

Radio stations

The multiplexes
Operated by the BBC; broadcasts nationwide in 16QAM mode at 18 megabits/second

TV: BBC One (regional variation), BBC Two (national variation), BBC Three, CBBC Channel, BBC News 24
Radio: BBC Radio Wales (Wales only), BBC Radio Scotland (Scotland only), BBC Radio Ulster (Northern Ireland only), BBC Radio Cymru (Wales only), BBC Radio nan Gàidheal (Scotland only), BBC Radio Foyle (Northern Ireland Only)
Text/Interactive: BBCi, Multiplex 1
Operated by Digital 3&4 (an ITV/Channel 4 consortium); broadcasts nationwide in 64QAM mode at 24 megabits/second

TV: ITV (regional service), Channel 4, ITV2, ITV3, More4, E4, ITV4, Film4+1, CITV
Radio: U105 (Northern Ireland only), Heart (except Scotland), Radio Music Shop (except Scotland)
Text/Interactive: Teletext, Teletext Holidays (Wales only), Teletext Cars, Teletext on 4 Multiplex 2
Operated by SDN (owned by ITV plc); broadcasts nationwide in 64QAM mode at 24 megabits/second

TV: S4C Digidol (Wales only), Five, TeleG (Scotland only), ABC1 (except Wales), QVC, UKTV Gold*, bid tv, price-drop tv, Thomas Cook TV, UKTV Style*, British Eurosport*, Five US, Five Life, Top Up Anytime 1*, Top Up Anytime 2*, Top Up Anytime 3*, S4C2 (Wales only), Teachers' TV, Television X*, Setanta Sports 1*
Radio: BBC Radio 1, BBC Radio 2, BBC Radio 3, BBC Radio 4, Mojo (except Wales), Heat (except Wales)
Text/Interactive: Teletext Holidays (except Wales), Teletext Games Multiplex A
Operated by the BBC; broadcasts nationwide in 16QAM mode at 18 megabits/second

TV: BBC Four, CBeebies, BBC Parliament, Community Channel
Radio: BBC 1Xtra, BBC Radio Five Live, BBC Five Live Sports Extra, BBC 6 Music, BBC 7, BBC Asian Network
Text/Interactive: BBCi (301, 302, 303, 305) Multiplex B
Operated by National Grid Wireless; broadcasts nationwide in 16QAM mode at 18 megabits/second

TV: Sky Three, UKTV History, E4+1, SmileTV, Sky News, Sky Sports News
Radio: talkSPORT, Clyde 1, Premier Christian Radio, Virgin Radio
Text/Interactive: Sky Text, TVTV Digital Multiplex C
Operated by National Grid Wireless; broadcasts nationwide in 16QAM mode at 18 megabits/second
* Pay TV service

TV: The Hits, UKTV Bright Ideas, Ftn, TMF, Ideal World, Film4, ITV2+1
Radio: BBC World Service, The Hits Radio, Smash Hits, Kiss 100, Magic 105.4, Q, Oneword, 102.2 Smooth FM, Kerrang!
Text/Interactive: 4TVInteractive Multiplex D
Some of these multiplexes carry a much larger number of services than others for various reasons. Firstly, a number of services share bandwidth on a timesharing basis — so some channels turn off when others are on (for example one will never see CBeebies and BBC Four on air at the same time, as they use the same space in Multiplex B, with CBeebies broadcasting from 6am until 7pm and BBC Four from 7pm onwards; the situation is the same for CBBC and BBC Three). In addition, some multiplexes have fewer channels so as to allocate more data to fewer services, thus ensuring higher quality (for example, BBC One on Multiplex 1 is carried as a 4.4 Megabit stream, while Sky Sports News typically uses 2 Megabits per second).
On top of this, the modulation of the multiplexes can be varied to squeeze higher digital bitrates out of the same portion of the electromagnetic spectrum. This comes at the cost of making it harder to get a good signal. There are three basic modulation schemes currently in use in the UK; in order of bandwidth efficiency, they are: QPSK (only used for tests in the Oxford and London areas), 16 QAM and 64 QAM, each with a progressively higher bitrate, at the cost of progressively higher likelihood of signal degradation. Currently multiplexes 2 and A use 64 QAM (and are consequently more prone to poor reception) while the other multiplexes all currently use 16 QAM.
Furthermore, multiplexes can make use of statistical multiplexing at the MPEG video coder whereby the bitrate allocated to a channel within the multiplex can vary dynamically depending on how difficult it is to code the picture content at that precise time, and how much demand there is for bandwidth from other channels. In this way, complex pictures with lots of detail may demand a higher bitrate at one instant and this can result in the bitrate allocated to another channel in the same multiplex being reduced if the second channel is currently transmitting pictures which are easier to code, with less fine detail. The only channel on the DTT system not to use statistical multiplexing, i.e. has a constant bit rate, is BBC One. This is so the English Regions and Nations can perform a simple transmultiplex, or T-Mux, operation and insert their local version of BBC One over the London feed straight into the existing BBC Multiplex 1 without having to re-code the entire multiplex at each regional centre, requiring specialist (and costly) equipment at several locations.

Use of multiplexing technology
Better implemented compression technology has provided for two additional television stations on the National Grid Wireless multiplex using the same bandwidth, with the possibility of more to follow on this and some other multiplexes.
This technique is only suitable for the multiplexes that are identical nationwide. On Multiplex 1 where BBC One is one of 15 regional versions, and BBC Two is one of four national variants (England, Scotland, NI and BBC 2W in Wales) it has proved harder to increase the number of channels carried Any such change would, however, render obsolete all existing receivers as new decoder set-top boxes or integrated digital televisions would be required, unless they are able to be reprogrammed for additional codecs which is widely not the case. BSkyB's proposals are pending approval by OfCom, where these issues are likely to be a consideration.
The BBC, who would like to broadcast high-definition television on at least some Freeview channels, is considering an alternative method utilising spare capacity at night to allow the download of high definition programmes for later replay. The use of alternative codecs for the sake of high-definition is likely to be less of an issue, due to the fact that new televisions are required to view such services, which could include any new standard that might be agreed. In addition the BBC's Research and Development team have invented a new transmission method for delivering twice the bandwidth that can currently be delivered via each DTT frequency. An explanation is that 2 signals are sent on the same frequency in slightly different directions and at slightly different times. However the "spatial multiplexing" requires new transmitters to be built and will need a new aerial and box.

New compression technology
For full list of dates, see Digital switchover dates in the United Kingdom.
The British Government has given Ofcom and Digital UK the joint task of switching off the analogue terrestrial signals. The switchoff will occur on an ITV sub-region basis.
¹ At the switchover it is planned that Caldbeck will broadcast both England and Scotland muliplexes to better serve viewers north of the border and Sandale will cease to broadcast TV.

Mobile Television services
Wireless broadband services
Wider coverage for advanced services in remote and rural areas
More multiplexes carrying more channels
High definition services