UK DTT SERVICE EXCEEDING COVERAGE PREDICTIONS
TBS (Telecommunications and Broadcasting Services) has published its findings on the newly launched UK digital terrestrial television service including results from a series of operational measurements conducted in the London and South-East area over the past ten days, in areas served by the Crystal Palace (London) and Oxford transmitters. These two transmitters were chosen because in one case (Crystal Palace) all DTT services can be received by existing aerials and, in the other case (Oxford), it was thought that most existing aerials would encounter some problems with receiving all DTT services. Tests were carried out using the Philips DTX6370 set-top box receiver for digital terrestrial services, now on sale in retail outlets, at a large variety of receiving locations across the region including residential, business and other locations.
Existing aerials performance
TBS tested the receiver at over 100 separate domestic installations with a variety of in-situ external antenna systems. These included ultra-modern installations, aerials which were installed for colour television in the 1970s, and with a number of damaged aerials.
In the vast majority of cases (90%+) existing outdoor aerial systems produced all six DTT multiplexes transmitted from the Crystal Palace transmitter, and in the other cases aerials were either severely damaged or had fallen down, also producing very poor analogue pictures. In a number of cases with sub-optimal aerials it proved possible to bring up all six multiplexes with inexpensive low-noise amplifiers costing a few pounds. This also worked very effectively in areas served by the Oxford transmitter, where some multiplexes are transmitted outside the existing aerial group.
It also proved possible to receive the Crystal Palace (London) DTT services perfectly just outside Oxford where the corresponding analogue terrestrial reception from this transmitter is very noisy, using a high-gain antenna system with a mast-head amplifier already installed for analogue reception from London. This demonstrates that long-range DTT reception is entirely feasible.
Amplifiers extend coverage
The receiver has been tested with a variety of consumer grade distribution systems and mast-head/indoor amplifiers. These all pass through DTT services without any problems and can therefore be used to extend the coverage of the multiplexes which are transmitted at lower powers well beyond their predicted coverage areas, in particular those assigned to ONdigital and SDN.
The boosting of signal strength using consumer grade equipment trips the receiver over the threshold for perfect pictures, enabling signals to be perfectly resolved, because the receiver rejects the higher-power analogue signals much more effectively than theory had predicted. This has significant commercial implications for extending the effective reach of DTT services.
A DTT box was tested connected in a daisy chain with a complex consumer distribution system containing analogue satellite, VCRs and a number of digital satellite set-top boxes. When passed through this RF daisy-chain, the DTT services were resolved by the set-top box at every point in this distribution system, even over very long cable-runs using consumer grade amplifier systems.
Indoor aerial reception
Indoor aerial reception exceeds expectations. In many parts of London perfect set-top reception is possible with small indoor aerials purchased from DIY chains for under £10. These will often produce perfect pictures when located indoors by the window or on window ledges, facing the direction of the transmitter.
In some locations where the lower coverage multiplexes cannot be received on indoor aerials unaided, these services can be received by adding a set-top amplifier costing under £10 from a DIY shop.
In one instance, which has been filmed, in a ground-floor room in a house in Fulham perfect DTT signals were received without an amplifier on a piece of cable attached to the receivers antenna input. Corresponding analogue signals were unwatchable at this ground-floor location.
Perfect portable pictures via DTT using an indoor aerial have also been demonstrated from within CNBC Europes building and were shown on its television programme, Media Report, weekend ending 22 November 1998.
It is expected that indoor aerial reception will be very widespread in a number of cities such as Belfast, Edinburgh and other parts of the UK which have special terrain characteristics in relation to the positioning of the DTT transmitter to the city served.
The system produces perfect ghost-free studio quality pictures at all served locations, including many where analogue terrestrial reception is very poor on indoor aerials. This may lead to a renaissance of indoor aerial reception in a number of localities.
Multiple Dwelling Unit Reception
There are reports of DTT reception using loft aerials and communal aerials attached to MDU (Multiple Dwelling Unit) systems in apartment buildings, condominiums, tower blocks etc, emerging via Internet newsgroups and other public sources. In a number of MDUs where the communal system has not been upgraded or does not seamlessly pass through DTT signals, a number of Internet postings indicate viewers are using set-top aerials to receive DTT delivered perfect portable pictures, bypassing the communal system.
The receiver has not been tested in large MDU buildings on communal aerial systems, although there is at least one report of DTT reception using a communal aerial system in a large MDU. As noted in the earlier TBS report, Digital Television: Can you get it? MDU buildings comprising up to seven million homes (30% UKTVHH) are a recognised problem area for all digital television platforms.
System performance exceeds theoretical predictions
Initial measurements indicate that the DTT system is performing up to 3-4dB above its theoretical performance. This has major beneficial implications for the coverage and access provided by Digital Terrestrial Television. Areas thought to be unserved are receiving DTT services perfectly, including locations for which publicly available coverage maps and predictive computer databases indicated that DTT reception is not possible. Achievable coverage by the commercial DTT services from ONdigital appears to be much better than predicted.
Areas of London and the SouthEast, which are notorious for poor analogue reception, are receiving perfect DTT services. This has significant implications for future reception of Free-To-Air services, now provided by other delivery systems, when extrapolated nationwide.Aircraft flutter and wind-loading recovery
The COFDM DTT system deals very effectively with aircraft flutter and mast-rocking problems, which spoil analogue reception in areas close to airports or under flightpaths, and in high wind conditions where aerials are mounted atop tall masts. In all observed cases these problems are virtually eliminated or the receiver automatically readjusts in about a second. (This latter mast-rocking problem is common in densely populated urban areas such as London, Birmingham and other cities where tall masts are required in order to eliminate analogue ghosting problems, and also in some rural areas.)
Plug and play tested
We tested the receivers plug and play capability. Setup takes about five minutes when the box is connected by SCART cable to a modern tv receiver, and the receiver will then autotune all the available DTT services in the locality at the push of a button on the remote control. Although billed on-screen as taking around twenty minutes, in practice this takes less than ten minutes.
When connected via an older coaxial cable the receiver connection takes a little longer. It is necessary to be able to tune in the set-top box output channel on the TV set, similar to tuning in a VCR or satellite receiver. Thereafter the digital tuning process is identical.
Enclosing the smartcard in the box enables the consumer to access available pay-tv services within minutes of telephoning the authorisation number on arrival home after purchase, and has been tested out. Full authorisation for pay-tv services takes place within about twenty minutes.
The DTT set-top box is easy to install, can be carried out by the general public, and is well documented. In-store contract information for pay-tv services is clear and can be completed rapidly.
Tuning subsequent services is straightforward by making the receiver rescan for all available channels. This facility brought in the SDN test transmissions, which commenced 16 November 1998. It has also been used to receive digital services in other locations in the UK, and to receive out-of-area DTT transmissions using an antenna fitted with a rotator in some locations.
Electronic Programme Guide
We tested the receivers Electronic Programme Guide (strictly speaking Event Service Guide). This is easy to use, provides a green on-screen overlay with now-and-next information, enabling the digital television service to continue to be viewed in the background, and has a rapid response time. Three forms of channel zapping are possible including a favourite channels menu (enabling unwanted channels to be suppressed), a programme up/down key, and the On-Screen Guide.
Channel number allocation is intuitive and provides seamless crossover from analogue terrestrial television (BBC1=1, ITV=3 etc). Free-To-Air services are listed first and only one remote control keystroke is required to select any terrestrial service. Channels can be reordered according to viewer preference.
The supplied DTT remote control can be programmed to control most major brand TVs and, uniquely, most major brand VCRs. This facility has been tested, and is very useful to reduce remote control clutter.
The receiver has an event timer, which is ideal for recording television services in conjunction with a VCR. This mirrors the functionality provided by the best analogue satellite receivers.
Teletext functions of the receiver could not be tested, as the digital teletext services provided by the BBC and Teletext Ltd have not yet started transmissions in their dedicated digital channels.
Commenting on the operational findings, Dermot Nolan, a Director of TBS said: "It is rapidly becoming apparent that the UK DTT system is operationally performing far better than expected in terms of predicted coverage, plug-and-play installation and ease of access. In particular the more widespread availability of indoor reception and the use of amplifiers to cost-effectively extend the overall DTT coverage is a big surprise. This is likely to have a profound impact on the economics of multichannel television distribution with long-term sectoral implications."
Nolan added: "Based on the UK operational experience, it now seems likely that the European DTT system will hold major commercial, strategic and technical advantages over the rival US ATSC system for DTT in world markets where a choice between the competing systems has yet to be made."
Roger Stanyard, a leading satellite communications consultant, said: "The operational results confirm widespread Internet reports that coverage of DTT is much better than expected. This gives COFDM DTT a major competitive advantage in digital multichannel television distribution economics, at the all important consumer end of the transmission chain, he explained. 'It allows easy reception of DTT signals by portable TV sets, second TV sets in the households and TV sets in blocks of flats."
Stanyard added: "The DVB-T system is suitable for High Definition Television (HDTV) transmissions as well as standard definition television services (the UK business model). In world markets where a convincing business case can be made for HDTV it is now operationally clear that DVB-T has significantly greater cost/performance benefits than ATSC."
Over the next few months it is expected that a comprehensive national picture of operational coverage attainable by UK DTT services will emerge based on direct consumer experience and transmission operator measurements. Based on sampling points in London and the South East it is now apparent that coverage will considerably exceed expectations and, in fringe areas, is greatly assisted by the addition of inexpensive amplifiers. In the UK situation, coverage is expected to improve further with the addition of one new transmitter a week until well after the Millennium.
These findings indicate that the Economically Accessible Coverage achievable by UK DTT is now likely to be up to 95% by the Millennium, an attainable coverage figure which cannot, in practice, be cost-effectively matched by other digital delivery systems.
For further information Contact Dermot Nolan, TBS, or Roger Stanyard, a leading
satellite communications consultant and former Managing Director of Interspace.
Contact TBS on +44 (0)171 286 5570 or by e-mail: firstname.lastname@example.org.
Mr. Stanyard can be reached directly on +44 (0)1962 877850