digital television digital radio analogue spectrum planning

Transcription

1 digital television digital radio analogue spectrum planning 57

2 Chris Smith, the Minister responsible for broadcasting, recently announced the Government s plans for switching off analogue television once digital television has gained a significant following. We are investigating the ways in which we might make the transition from analogue to digital if this becomes policy. There is a legacy, which must be respected, of receivers in the UK market which can only receive a sub-set of the digital standards. SFNs providing services to a region give better coverage if we adopt a modest guard interval. MFNs which do not rely on significant guard intervals do best. MFNs need an absolute minimum of four UHF channels new applications. This is one of the Government s objectives. We have examined the effect of releasing either the lowest six channels (in Band IV) or the upper nine channels (in Band V). It is clear from our study that there is particular value in retaining the channels in be very difficult and costly to implement. In practice, we would not be able to match the analogue coverage using a clean sheet plan. We would have to make use of the existing analogue assignments, converting them to digital. We have been in close contact with the Radiocommunications Agency, SPECTRUM PLANNING of options provided the greatest per multiplex, although this configuration has a fundamental Band IV, not least because many of the high power analogue assignments use who will be responsible for technical advice to ministers, and have carefully Switch over from benefit. As the starting point, 20 limit to the overall coverage. this band, and these can easily be explained the issues to ensure that well analogue to digital scenarios were identified for MFNs need six channels per switched to provide digital services informed decisions can be taken. There are many options for an investigation in our study, including multiplex for expansion to near under internationally agreed rules. If the channels above 60 are all-digital plan. Many people assume options for national and regional complete coverage. They Following the Government released to the Government, there will that the most efficient way forward coverage for fixed, portable and provide coverage at least as announcement that it would consider be consequential changes required at is to operate all the transmitting mobile reception. The aim was to good and probably better than switching off all the analogue TV the 37 digital sites that use these stations on the same frequency refine a large number of possibilities the original analogue services. transmitters some time after the year frequencies. It should be possible to (the so-called Single Frequency and define a sub-set that will form the In general, our studies show that a 2006, we considered the options for provide adequate services using Network), but this does not fit basis of detailed planning scenarios minimum of six frequencies (8 MHz the BBC. The 80 digital stations now in frequencies released by switching off easily with the editorial desire to to be investigated. channels) per multiplex are needed to service cover fewer people than the analogue TV. This does create a offer different services in different Based on these scenarios, our provide universal digital coverage, entire analogue services. We need to chicken and egg problem, which parts of the country. For this, studies to date have produced equivalent to today s analogue find satisfactory ways of enhancing the means that switch over will have to be networks using different frequencies some interesting findings in which coverage. Based on this assumption, a digital service. a gradual process, rather than a big for each transmitter (or Multiple elements of some scenarios appear total of 36 channels are required for an There are basically two approaches bang. As frequencies are released, they Frequency Networks) are contenders. more beneficial than others. The key all-digital plan for six multiplexes to an all-digital plan for the UK. The can be re-used for digital services in In addition, many of the parameters points are: significantly fewer than the 46 used first involves the conversion of existing nearby areas. In time it will then be of the transmitted signal can be SFNs do not provide the in the current mixed analogue and analogue assignments into digital, as possible to switch off analogue varied, giving a different trade off universal coverage we first digital environment. internationally agreed, and the second is services there. between the ruggedness and anticipated, even with fairly long Therefore, it appears there may be to adopt a totally new plan. Whilst the capacity of the network. Our work guard intervals (for the type of potential for releasing a significant latter might seem attractive in terms of sought to identify which combination data rates required in UK). amount of spectrum (up to 80 MHz) for spectrum efficiency, it would, in practice, 58 APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW 59

3 We are also considering methods to planning process. Recent developments When the original UK digital plans development of a Common Prediction Coldfield and Waltham DTT within a short period of the stations optimise future digital networks to have included: were developed, a cautious approach Method which met with the agreement transmitters. These showed up a few being brought into service, and provide coverage to portable receivers. Programs for simple MFN was adopted in the planning whereby of all the planning organisations. The areas of good coverage where the remedial action has been put into place This work has revealed that a network channel allocation studies to interference to the analogue network adoption of this method by each of the prediction models had indicated a prior to a large take up of the services. infrastructure using around 130 assist in the preparation of was minimised. This resulted in planning organisations has meant that marginal service, and a number of other transmitters would provide useful, all-digital plans. different coverage for the different consistent coverage predictions can areas where coverage was poorer than Long distance propagation though not complete coverage. This can Extensions to PlanTX (one of multiplexes, varying from 81% for now be achieved. predicted. In addition to providing A key element in planning our digital be achieved using the current UK our main coverage and the BBC s services down to around We supply ONdigital with periodic valuable information to help improve services is a detailed knowledge of the variant of the DVB system, so there interference assessment tools) 64% for the lowest coverage updates of the latest coverage the prediction models, this information behaviour of long distance radio wave would be no reduction in capacity of to perform percentage-of- ONdigital multiplex. information. In order to assist our also enables informed judgements to be propagation. The signal strength from a the multiplexes. coverage calculations and to This variability in coverage has coverage planning, and to assist with made on whether proposed coverage distant station may be low for much of allow population counting. limited the potential audience for the the validation of the data supplied to improvements to the network are likely the time, but may suddenly rise by as European aspects A new program to display terrain complete package of ONdigital ONdigital, a new feature has been to be cost-effective. much as 60 db in particular types of The CEPT (European Conference of profiles, incorporating a full set services. Experience with the roll out added to our internal coverage display These investigations help to guide weather. Many of our service areas Postal and Telecommunications of high-resolution terrain data- has shown that a more aggressive facilities. It is now possible for us to the planning for future coverage are defined by interference-limited Administrations) has agreed to prepare bases and the latest version of the approach in the planning is possible to generate maps with overlays showing enhancements. For instance, contours. Early measurements were for an all-digital planning meeting to be international propagation tools provide better matching of the all the the number of multiplexes or plans international co-ordination difficulties based only on narrow band signals, held in the time frame (ITU-R Recommendation P.370). coverage areas, without causing exceeding a user-specified coverage have been encountered with the and ceased at midnight (when most of Currently, digital television frequency A revised version of our Windows- unacceptable difficulties, and this enables threshold at each geographical location. Belgians for the Sudbury transmitter, the transmitters stopped broadcasting). assignments are regulated by the based interface to the Oracle a significant amount of re-optimisation Although much of the UK 81-station and with the Dutch for the Tacolneston For this reason, we have been agreement reached in Stockholm in transmitter database is proving valuable of the network to take place. plan is acceptable to neighbouring transmitter, for which work is now undertaking long distance propagation A new plan is necessary because in maintaining an accurate basis on This work is being undertaken in countries, we have now entered a in hand to develop technical solutions. studies of digital signals for the last the parameters and methods used at which to undertake calculations. collaboration with the ITC, ntl and phase of protection for the UK services A good knowledge of the UK few years. These studies have now that time, and in subsequent years as Some fundamental research into Crown Castle International and is (both analogue and digital) as Ireland, coverage gives us an advantage in entered a new phase by looking at a the analogue television networks ways to improve terrain-based independent of any decisions about the France, Belgium, the Netherlands and international negotiations. wider range of receiving sites (instead throughout Europe developed, are not calculation methods is underway as part implementation of analogue switch off. Norway start to develop their own of only Daventry). optimised to make the best use of of the DigiPlan collaborative project One problem that arose during this plans. In this respect, a potentially DTT helicopter surveys As well as testing typical spectrum in an all-digital scenario. with Surrey University. We are process was that the coverage difficult situation has been resolved in We have developed a method for propagation over land, we are testing a Preparations for the proposed optimistic that this will ultimately lead predictions of the different planning recent discussions with Belgium. Our measuring the radiation patterns of mixed land/sea path from the Dutch planning conference are expected to to a significant improvement in the organisations varied significantly from submission of detailed calculations for transmitting antennas using a helicopter transmitter at Goes. We have also take a minimum of four years. The accuracy of our prediction models, each other. Our prediction method has Crystal Palace, including portions of as the measurement platform. established a receiving site at groundwork is being carried out jointly which in turn should assist in making always been accurate within defined measured radiation patterns, has This enables both rapid and Guilmécourt in northern France, to by the EBU and CEPT, although the more effective use of the spectrum. limits. Nevertheless, we are always demonstrated to the satisfaction of all accurate evaluation of antenna radiation monitor the potential level of official conference preparations are likely to be carried out under the auspices of the ITU. DTT ROLL-OUT AND COVERAGE EXTENSIONS striving to improve the accuracy and this is facilitated by increased computer power and availability of new parties that it is possible for the Belgian broadcasts to operate co-channel with Crystal Palace on Channels 22 and 25. patterns. Hitherto we had to rely on manufacturers works tests, and were unable to verify whether or not an interference from Crystal Palace DTT to our French neighbours. It is somewhat surprising to discover that In the period April 1999 to March 2000, terrain/clutter data bases. The installed antenna was working properly. we seem to be the only organisation in Planning tools 40 transmitting stations for digital differences between our tools and Vehicle-based survey work This year helicopter antenna Europe carrying out such studies, Our extensive set of software tools is terrestrial television were brought on those of the other planners caused Although most coverage is now surveys have been carried out at a particularly as the results are of vital being continuously developed to reflect air as a result of our planning work. difficulties when trying to reach predicted by computer, vehicle-based further 44 digital terrestrial transmitting importance to future planning. the needs of those of us engaged in the This brings the total to eighty stations, agreement on which changes to survey work continues to be valuable. stations. The value of these helicopter providing BBC services to 52 million implement. A significant amount of Targeted coverage surveys were measurements is evident in the fact that people (81% of the UK population). work was therefore put into the undertaken of the Winter Hill, Sutton faults were discovered at 17 of stations, BBC R&D ANNUAL REVIEW APRIL 1999 MARCH 2000

4 Digital Radio is now well established. With the addition of one new Digital Radio transmitting station at Zouches Farm (covering the Luton area) the total number of stations rose to 29, providing BBC Digital Radio to 33.6 million people (60% of the UK population). IF Digital Radio increases in popularity in line with expectations, we will want to expand the availability of the service around the country. We have therefore prepared a consolidation plan for an additional 15 transmitters, designed to reinforce the existing UK coverage, filling particular holes in coverage. An additional plan for ten stations to extend coverage in Scotland has also been prepared. Two additional stations at Craigkelly and Hemel Hempstead are being considered to take advantage of particular circumstances that will enable them to be built at low cost. DigitalONE, the new commercial radio multiplex, have proposed a similar network of transmitters in Scotland. If the BBC wishes to expand services to match, our existing proposals could be used to provide coverage to 75% of the population of Scotland. In this respect, it is important for the BBC to ensure that potential future sites are known and properly co-ordinated. The helicopter measurement system has been used for assessing digital radio stations. To date, 14 stations have been checked, revealing faults in some of the installations, and remedial action has been initiated. In the UK, we are using spectrum in Band III for Digital Radio. There is also a tranche of spectrum available in L-Band (between 1452 and 1492 MHz) which is being used extensively in some countries. This band was originally allocated for satellite transmissions, but there is now pressure to assign the whole band for terrestrial broadcasting. In Europe, the CEPT (responsible for co-ordinating European use of spectrum) is considering a conference to allot a greater part of L-Band for terrestrial Digital Radio. We think these frequencies may be better suited to meet the growing demands for local radio services. If agreement is reached on the need for additional spectrum, it is likely that a planning conference will be convened within a year to allot a further seven frequency blocks (multiplexes), in addition to the existing nine. As part of this process we are working with the EBU to define the technical criteria for the allotment of the L-band spectrum, and with the Radio-communications Agency to develop an appropriate UK position. The existing rules, agreed at the Wiesbaden Conference, are not ideal for the smaller areas that are anticipated for local coverage requirements. 62 APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW 63

5 Although there is now a rapid take up of our new digital services, our traditional analogue services still provide the majority of our listeners and viewers with their quality services. These services are still being improved and re-engineered to provide more editorial variety and better quality of service. have produced an up-to-date set of maps for our national Medium and Long Wave services. TELEVISION Analogue television coverage licence payers, and will seek to scrutinise all new plans for major building developments. In the case of one wind farm, our assessment revealed that up to 100 people could be affected. Fortunately, we were licensing body. With the recent introduction of digital television services, it has been necessary to recreate the maps to cover not only the updated analogue situation but also the recently introduced digital services. RADIO for supporting additional services. The continues to be important not surprisingly as it is still our main able to advise that by re-alignment of the viewers receiving antennas towards Another ancillary service that operates in the broadcasting bands is Radio Wales, the English language contract for the review was awarded to delivery mechanism. an alternative transmitter, it should be the Digital Reverse Audio Bearer service for Wales, is now on air as a Aegis, who have drawn on our Many of the most recent possible to restore the reception of (DRAB) radiated from Crystal Palace. result of our recent frequency planning considerable database information. questions have been trying to resolve those affected by the wind farm. This allows the BBC to provide a work. Although Wales is extremely difficult to serve, given the extensive use of spectrum for other services and Their initial report was published at the end of March. We will give the report careful examination to ensure that all anomalies, ensuring that we broadcast appropriate editorial content in specific regions. We have provided SERVICES ANCILLARY TO BROADCASTING reliable and continuous communication link to our Outside Broadcast operations around London. the difficult terrain, Radio Wales FM is existing BBC public services (especially coverage maps showing the recent A significant proportion of the BBC s This link has been affected by the now on-air with seven transmitters, and our national networks) are not London and South East split, and programme making facilitates, introduction of digital television. Our the network is now stereo-capable, compromised unnecessarily. advice on analogue television coverage including radio microphones and first thought was that it may have to bringing the coverage to nearly half of There has been much discussion in North Norfolk as the matter of talkback, rely on the shared use of be shut down because of the the population in Wales. recently about Medium Wave/FM regional programme anomalies in this broadcast spectrum. Because these introduction of new digital services There is continuing pressure for simulcasting and as part of the BBC s area was discussed in Parliament. services can only operate on a at Reigate. However, as a result of new broadcasters to be given the future response to the FM Spectrum We are still one of the main non-interference basis to our studies, we were able to show chance to offer new radio programmes, Review. The situation has been a little sources of assistance and advice when broadcasting, it is necessary to that this system could operate without despite a shortage of frequencies. The confused because of the lack of new buildings and wind farms are provide means by which potential causing interference. Government has decided to review the information about FM and Medium planned and erected. Whilst it is not users can quickly assess the options use of FM spectrum. We helped draw Wave coverage for our BBC Local intended that we should bid for future available for a given location. up the terms of reference for the Radio stations. This has been clarified consultancy work relating to the impact For a number of years, we have review, which aims to address the (probably for the first time!) with the of buildings on analogue television provided electronic map-overlay data spectrum efficiency of existing services production of a set of coverage maps reception, the BBC is continuing in its to facilitate such assessments in relevant in Band II, and whether there is room for all these services. Furthermore, we role as guardian of the interests of its BBC departments and in the relevant 64 APRIL 1999 MARCH 2000 BBC R&D ANNUAL REVIEW 65