1、 Rep. ITU-R BT.2075 1 REPORT ITU-R BT.2075*Protection requirements for terrestrial television broadcasting services in the 620-790 MHz band against potential interference from GSO and non-GSO broadcasting-satellite systems and networks (2006) Background The band 620-790 MHz is heavily used in Region
2、s 1, 2 and 3 for the analogue terrestrial television broadcasting service (BS) in many countries. Moreover, digital BS have been developed in a number of countries in this frequency range. The simulcast transmission period is foreseen for 20-25 years to come and requires careful planning to minimize
3、 disruption of services. A satellite filing was received by the BR before WRC-03 for the use of the band 620-790 MHz in accordance with former Radio Regulation (RR) No. 5.311, this footnote was modified by WRC-03 clarifying the sharing conditions. Frequency sharing between BSS transmissions and BS i
4、n the band 620-790 MHz is stipulated by RR No. 5.311 (as modified by WRC-03), Recommendation 705, and Resolution 545 (WRC-03) of the ITU Radio Regulations. RR No. 5.311 was modified at WRC-03 and further studies, already called for by Recommendation 705, were invited to be urgently carried out on sh
5、aring criteria for the protection of terrestrial services in particular television broadcasting services from potential BSS systems operating in the band 620-790 MHz (under WRC-07 agenda item 1.11). In this regard, ITU-R has undertaken technical studies to identify the protection requirements in ter
6、ms of the maximum power flux-density (pfd) not to be exceeded at the site of the television receiving station to protect from interference from existing and planned analogue and digital terrestrial BSS in the band 620-790 MHz. This Report provides a methodology for the protection requirements for BS
7、, as well as the results of numerical applications of this methodology for terrestrial analogue and digital (fixed, portable outdoor, portable indoor and mobile) BS. It is worth noting that RRC-06 adopted Resolution 1 (RRC-06) which resolves to invite WRC-07 to take appropriate and necessary measure
8、s to effectively protect the broadcasting Plans adopted by RRC-06 and their subsequent evolution from the GSO-BSS and/or non-GSO BSS networks/systems which were not brought into use prior to 5 July 2003. It is noted the planning for the band 620-790 MHz arising from the GE-06 plan will not apply to
9、administrations beyond Region 1 and neighbouring countries. 1 Introduction This Report gives the protection requirements for terrestrial broadcasting services in the 620-790 MHz band against potential interference from broadcasting BSS (GSO, non-GSO) satellite systems. This Report focuses on potenti
10、al future GSO and non-GSO BSS systems assumed to use *The administrations of Syria, Lebanon and United Arab Emirates in conformity with the Arab States position in WRC-03, RRC-04 and in RRC-06 continue to object to any consideration of the broadcasting from non-GSO so called “HEO” satellite systems,
11、 noting that RR No. 5.311 currently does not allow such broadcasting and the need to protect fully the output Plans and their subsequent evolutions of RRC-06 and hence they are not bound by the content of this Report and will not allow any application in accordance of RR Article 23 for their territo
12、ries to be covered by any new satellite system of both GSO and non-GSO. 2 Rep. ITU-R BT.2075 digital transmissions and circular polarization and to operate with elevation angles (in the BSS coverage areas) above 60 only. Annex 1 presents information on these BSS systems which can use both GSO and no
13、n-GSO orbits, transmit signals with uniform spectral distribution, which are significantly different from typical analogue BSS emissions. It should be noted the BSS systems considered in this report do not include terrestrial re-transmission facilities. The protection requirements have been derived
14、from published information about the needs for the broadcasting service (CPM Report to WRC-97, ITU Digital Terrestrial Television Handbook, Recommendations ITU-R BT.417, ITU-R BT.419, ITU-R BT.655 and ITU-R BT.1368). However, only those broadcasting systems which are currently using frequencies in t
15、he 620-790 MHz band or which are expected to use it in the near future have been included. BSS systems currently introduced include the Russian networks, Statsionar-T and Statsionar-T2, and a proposal for a highly elliptical orbit (HEO) system using a digital modulation and circular antenna polariza
16、tion. Digital television services have already commenced operation in a number of countries in this frequency range. It is expected that digital television services will be deployed in an even higher number of countries in the near future and it is expected that analogue television services will con
17、tinue in many countries for many, possibly 20 to 25 years. Protection of the analogue services is likely to be rather more difficult than is the case for digital services. This is especially true for those countries or parts of countries where the television networks have not yet been fully develope
18、d, or in areas where the man-made noise levels are low and where the protection requirements are more stringent simply because the noise and the existing interference levels are low. In Recommendation 705 (WARC-79) in considering e) the following qualification is provided to administrations in calcu
19、lating minimum field strengths when referencing Recommendation ITU-R BT.417: a) that with terrestrial television receiving systems using current technology, the minimum field strength to be protected may in some cases be less than the values included in Recommendation ITU-R BT.417; b) that account m
20、ay have to be taken of ground reflections; c) that energy dispersal techniques may reduce the required protection ratio and should be used if shown to be effective. While Recommendation ITU-R BT.417 Annex 1 states the boundaries of the television service in rural districts having a low population de
21、nsity, where television services are to be provided for a sparsely populated region, in which better receivers and antenna installations are likely to be employed, administrations may find it desirable to establish the appropriate median field strength for which protection against interference is pl
22、anned. It should be noted that Recommendation ITU-R BT.417 was last reviewed in 1992 by the ITU-R and may not reflect the performance of todays television receivers and antennas. Recommendation ITU-R BT.417 gives values obtained from median field-strength investigations at the edge of the coverage a
23、rea and picture quality assessments for Bands I and III in rural districts of Australia, India and Italy and for Bands IV and V at both rural and urban locations in Italy and the United Kingdom. It may be noted that in Bands IV and V where man-made noise is not generally a problem, the field-strengt
24、h values quoted for rural areas may also be applied in urban areas. A key element in planning of terrestrial television services is the consideration given to the point where the television service becomes unwatchable. In some administrations the reception quality of the analogue service is matched
25、to the point where reception of the digital signal would just “fail”. In this way the gradual failure characteristic of the analogue signal is matched to the more sudden failure of the digital signal. One administration has adopted in Band V for digital planning minimum median field strength values
26、of 10 dB below the current analogue values. Rep. ITU-R BT.2075 3 Because it is certain that terrestrial analogue and digital television services will continue to be deployed over a period of very many years, it is extremely important that the possible existence of satellite-based television transmis
27、sion and reception in the same band should not in any way interfere with such deployment. In particular, it will be necessary to ensure that if satellite-based services were to become operational, they cannot claim protection of their reception as a reason to prevent the installation of new terrestr
28、ial analogue and digital television transmitters or the change of analogue or digital frequency assignments to facilitate the transition period. The satellite service could be considered to be a 100% of the time co-channel continuous interference source. In Recommendations ITU-R BT.655 and ITU-R BT.
29、1368, the values of protection ratio quoted apply to interference produced by a single source. Except where otherwise stated, the ratios apply to tropospheric, T, interference and correspond closely to a slightly annoying impairment condition. They are considered to be acceptable only if the interfe
30、rence occurs for a small percentage of the time, not precisely defined but generally considered to be between 1% and 10%. For substantially non-fading unwanted signals, it is necessary to provide a higher degree of protection and ratios appropriate to continuous, C, interference should be used. If t
31、he latter are not known, then the tropospheric, T, values increased by 10 dB can be applied. 2 Minimum field strengths for the terrestrial television broadcasting service It should be the minimum field strength value which is the starting point for the discussion. However, this is not usually the ca
32、se and the minimum median value is taken as a starting point and the resultant discussion becomes rather convoluted as a result. The reason for the shift in the starting point is partly historic and partly convenience. At the time when the concept and the relevant values were being developed (during
33、 the 1950s), it was not known how far equipment development could go and this was especially true for the band 470 to 862 MHz. Certainly the equipment available at that time could not achieve the performance which was implied by the values adopted. Since then performance has continued to improve and
34、 nowadays exceeds that expected. Consequently the real minimum field strength is now even less than that used in planning. It was a matter of convenience to relate all of the planning work to the minimum median field strength values as this: provided a fixed reference which did not depend on televis
35、ion receiver development and thus did not change with time; provided a link with any coverage measurements which were made; provided an approach which simplified the development of international plans and simplified discussions on an international basis. As a result, it has become current practice t
36、o start with the minimum median field strength values and, when necessary, “work backwards” to the minimum field strength values which are the real basis for planning. In fact, it is only very rarely that it is really necessary to do this reverse engineering and this could help to explain why it is
37、always so difficult to do it and to understand it, even though the basics seem to be very simple. It is interesting to note that adopting the minimum median field strength values as the reference and then deriving the minimum field strength values from them has the result that these minimum field st
38、rength values are somewhat higher than they would be if derived directly from the performance of modern television receivers. In other words, the protection requirements placed on other services are lower than they could reasonably be argued to be. One case where it is necessary to consider the basi
39、c numbers and their derivation is where some limiting values must be taken into account. This is particularly true for the case of areas where 4 Rep. ITU-R BT.2075 interference levels are low and listeners/viewers may be expected to use better than average receiving installations. Such areas exist i
40、n most countries, but are particularly relevant to developing countries where transmission networks may not attempt to cover the whole country and viewers are expected to make extra efforts to obtain satisfactory reception quality, for example by using high gain, low noise pre-amplifiers and low los
41、s feeder cable. However, it must not be assumed that such considerations apply only to developing countries. For example, the broadcasting coverage model applied in one administration seems to concentrate attention on the urban areas and many people living in rural areas need to install special rece
42、iving equipment in order to obtain satisfactory reception. In addition, it should be noted that the reference value for digital television reception adopted in another administration seems to include the requirement to use a low noise pre-amplifier wherever necessary. In both of these cases, the imp
43、act is to make it necessary to provide protection against interference for signal levels which are lower than those normally adopted in Europe. 3 Protection against interference Although not directly related to the derivation of minimum field strength and minimum median field strength values, it is
44、necessary to add some words about protection against interference as there is often confusion between the two topics. This is particularly true as the overall treatment in the case of protection of digital television is quite different from that adopted for protection of analogue television. In some
45、 countries the allotment planning for terrestrial television broadcasting services has not included any margin(s) for interference from any other sources other than the adjacent or co-frequency broadcasting service in the band 620-790 MHz. As a result no provisions or co-frequency coordination requi
46、rements have been included in the regulatory provisions of many administrations for sharing between broadcasting and other services where broadcasting is the Primary service. The basis for protection of a wanted signal against interference from some other signal (usually referred to as an “unwanted”
47、 signal) is basically very simple and can be considered in terms of a “protection margin”. The protection margin at the input to the receiver is given by: Protection margin = Wanted signal level Impact of interfering signal The term “impact of interfering signal” takes account of the fact that the a
48、ffect of the interfering signal is increased by the relevant protection ratio. In practice, it is usually found to be more convenient to deal with field strength values and this then necessitates taking account of the relative gain of the receiving antenna in the direction of the interfering signal.
49、 It can be assumed that the feeder cable loss and any frequency dependence either of the receiving antenna or of the feeder cable may be disregarded as they affect the wanted signal and the interfering signal equally this simplification cannot be made in all interference situations, but applies in the case under consideration here. In the case where the protection margin is positive, the wanted signal is taken to be protected against interference and is defined to be acceptable. This means that the reception and protection conditions must be clearly defined. This is why, for exampl
