WRC-2000: Results of Interest to Satellite Operators
By Jorn Christensen
The World Radiocommunication Conference, WRC-2000, was held in Istanbul, Turkey from May 8 to June 2. More than 2,500 delegates from more than 140 countries attended this conference. A WRC is held about every three years with the last WRC having decided the tentative agenda. These conferences are treaty-making conferences. Once administrations have ratified the Final Acts of the conference they are bound by the results.
Delegates have to decide between competing proposals for use of the limited radio spectrum. In most cases, new applications need to share frequencies with existing users. Therefore, the proponents of a new application must show that it does not cause interference to or constrain the development of the service(s) offered by the incumbent users of the spectrum. Such studies are usually done in Working Parties within the International Telecomunication Union (ITU) in the interval between WRCs.
To gain international recognition for new applications using the radio spectrum, the goal is to obtain the required frequency allocation at the WRC. If enough studies have been done and sharing is possible, a WRC will usually make new allocations, along with the technical conditions for the use of the newly allocated frequencies. Additional regulatory text is often required in the Radio Regulation. If enough studies have not been carried out, then the conference may make provisional frequency allocations to be confirmed by the next WRC.
Agreements are reached through consensus building, although some administrations occasionally take a reservation on certain decisions. Sometimes the divergence of opinion is too great and no decision can be taken. For example, in a certain frequency range, should preference be given to terrestrial networks or satellite networks? In these cases, a carefully worded resolution to further study the issue is agreed and the item is postponed to a future conference.
The WRC-2000 agenda contained over 20 items and agreement was reached on almost all items. While this article only addresses BSS re-planning and sharing between GSO and non-GSO systems, the complete list of WRC-2000 issues that may be of interest to satellite operators is:
- Region 1 and 3 BSS re-planning (ITU Region 1 designates Europe and Africa, ITU Region 3 designates Asia and Australia and ITU Region 2 designates North and South America.);
- Sharing between non-GSO FSS, GSO FSS and FS;
- Frequency Issues Related to the Radionavigation-Satellite Service (eg, GPS, Galileo and Glonass);
- Additional Frequencies for IMT-2000/UMTS;
- Frequencies for the Mobile-Satellite Service (MSS);
- Use of Small Diameter Antennas in the Band 13.75 to 14.0 GHz;
- Earth Stations Located onboard Vessels Operating in the C-band;
- Satellite Frequencies in the Range 37.5 to 42.5 GHz;
- Frequencies for High Altitude Platforms (HAPS);
- Regulatory Issues
Region 1 And 3 Bss Re-Planning
- New Region 1 and 3 BSS Plan increased the number of channels to 10 in Region 1 and 12 in Region 3
- New systems (modifications to plan) for more capacity than was allocated have limited lifetime of 30 years
- An administration cannot provide service to another administration without its consent
- New simplified technical criteria for coordinating new systems
Reasons For Re-Planning At Wrc-2000
The re-planning of the Region 1 and 3 Broadcasting Satellite Service (BSS) Plan was the highest priority item for the Arab, African and, to a lesser extent, the Asian countries. The WRC-2000 agenda item dealing with the Region 1 and 3 BSS Plan called for only the results of studies on the feasibility of a Region 1 and 3 BSS re-planning to be presented to WRC-2000. If re-planning was deemed to be feasible, then the actual re-planning was to be completed at the next WRC.
The Arab and African countries presented a document to WRC-2000 proposing a basis on which re-planning should be done during the present conference. This document also contained views on other agenda items of importance, especially to Europe. These other items were additional frequencies for IMT-2000, new frequencies for Radionavigation Satellite Service (RNSS and Galileo), non-geosynchronus orbit (GSO) Fixed Satellite Service (FSS)/GSO sharing (Skybridge) and high-density fixed systems.
Although the document did not explicitly say so, it was stated verbally that the Arab and African countries would withhold support on these other items unless WRC-2000 agreed to the re-planning of the Region 1 and 3 BSS Plan at this conference. The conference agreed and this in turn ensured support of the Arab and African countries on the other items. The BSS re-planning was for Regions 1 and 3 only and did not include the Region 2 BSS Plan (i.e. the frequencies used by such operators as DirecTV, Echostar, etc.).
Warc-77 Bss Plan
The Region 1 and 3 BSS Plan was originally adopted in 1977 (WARC-77 Plan for short). (The Region 2 BSS Plan was not adopted until 1983). In Region 1 there is a total of 800 MHz of spectrum allocated (40 channels in the range 11.7 to 12.5 GHz on the downlink) and in Region 3 a total of 500 MHz spectrum allocated (24 channels in the range 11.7 to 12.2 GHz on the downlink). The uplink frequencies are in the band 17.3 to 18.1 GHz. Countries outside Europe may choose feeder link frequencies in the band 14.5 to 14.8 GHz instead of the band 17.3 to 18.1 GHz, but most administrations have their feeder links in the band 17.3 to 18.1 GHz. The downlink BSS Plan for all Regions is contained in Article S.30 in the Radio Regulations and the feeder link plan in Article S.30A of the Radio Regulations.
The WARC-77 Plan assigned, on average, five channels to countries in Region 1 and four channels to countries in Region 3. The beams of the Plan cover the national territory only (excepts for a couple of multi-country beams). In the case of some countries with large territories, several beams were required to provide national service.
Wrc-97 Re-Planning Of Region 1 And 3 Bss Plan
The WARC-77 Plan was updated at WRC-97 using new technical parameters to take into account the improvements in technology, such as better G/T (figure of merit) of the receiving installation. In addition, new countries that did not exist in 1977 were assigned channels in 1997.
WRC-97 did not increase the number of channels and many Region 1 and 3 countries were not happy with the small number of channels. These countries wanted a further re-planning of the Region 1 and 3 BSS Plan to provide a minimum of around 10 analog-equivalent channels. WRC-2000 was to examine only the feasibility of providing each country with a minimum of 10 analog-equivalent channels. In the Region 1 and 3 BSS Plan, an analog channel has a nominal bandwidth of 27 MHz, but the channel spacing used in the Plan allows for bandwidths as large as 33 MHz.
Modifications/Additions To The Plan
The procedures associated with the BSS Plans allow administrations to implement regional beams using up to the full complement of channels (40 in Region 1 and 24 in Region 3), provided that such systems can be coordinated with the assignments of the Plan. Satellite operators have submitted so-called modifications/additions to the Plan, and many such systems have been coordinated and entered into the Plans.
There is great pressure on the BSS frequencies through such modifications/additions, and several hundred such systems have been filed and are being coordinated. Even though many of the filings represent “paper satellites,” there are many systems with a large enough service area and a sufficient number of channels to represent economically viable networks.
Most countries do not implement their assignments in the BSS Plan, since these assignments use beams that provide national service only, and for most countries such a service is not economically viable. Therefore, planning often sterilizes the spectrum/orbit resource, since assignments in the Plan have to be protected as if they were operating networks.
This was the reason that Europe, especially, was opposed to re-planning the Region 1 and 3 BSS Plan. Europe preferred to access the excess capacity in the Plan though the modification/addition procedures associated with the Plan. However, the developing countries feared that the developed countries would eventually exhaust the excess capacity.
The Compromise That Allowed Re-Planning
The difficult question was to decide which modifications/additions to the Plan should be taken into account in the re-planning. This was an important question, since networks not included in the planning could find that they could no longer be implemented because the re-planning may have assigned new beams and channels to administrations, and these would have priority. After long and difficult discussions it was decided that two types of systems should be taken into account.
The first type was the so-called “existing systems,” which were defined as assignments that are fully coordinated, notified, have been brought into use and for which the date of bringing into use has been confirmed by the Bureau. The second type was the so-called Part B networks, which were networks for which all required coordination had been completed. In addition, Resolution 49 information for the network had been submitted.
The original proposal from the Arab and African countries was to accept only networks falling into the first category above, but it was the acceptance of networks also falling into the second category that was the main compromise that allowed re-planning to proceed at WRC-2000.
The modifications/additions not taken into account during the re-planning will be re-examined, and the Bureau will identify, based on the new Region 1 and 3 BSS Plan, the networks with which coordination is required. This includes networks in the FSS and terrestrial fixed service (FS). The work will be carried out as specified in Resolution 533 (rev.WRC-2000).
WRC-2000 increased the number of channels assigned to each administration from five channels to 10 channels for countries in Region 1, and from four channels to 12 channels for countries in Region 3. Again, the Plan is based on beams with national coverage. Even with the increase in the number of channels, it does not make economic sense to launch a satellite with only 10 (or 12) transponders, and therefore the majority of beams in the Plan will probably never be implemented.
A BSS payload with 10 (or 12) transponders can make economic sense if it is on a satellite that is already carrying an FSS payload. However, the orbital locations for the BSS assignments are essentially the locations taken from the WARC-77 Plan, and these locations are spaced regularly at six degree intervals throughout the arc. During the planning exercises on which the final plan is based, administrations were given the opportunity to choose a different orbital location. Only a small number of administrations wisely asked that their BSS orbital location be coincident with an orbital location where they already operated or planned to operate an FSS satellite.
In a few special cases, neighboring countries combined their assignments at one orbital location for a common beam. For example, Germany, Austria, Switzerland and Lichtenstein asked for and received a common beam, and by combining their national allocation of 10 channels, all 40 channels will be available in the common beam. The combined population within this beam is about 100 million.
New Features Of Region 1 And 3 Bss Plan
The new Region 1 and 3 Plan contains several new features.
Any requirement for capacity in the Region 1 and 3 Plan, over and above what is assigned by the Plan, is now called an additional use, and such assignments have a limited lifetime. Such assignments include assignments with a larger service area, or assignments for additional channels over and above the number of assigned channels. These assignments are not included in the Plan, but entered into the “Region 1 and 3 list of additional uses” (in short, “the List”). The lifetime of assignments in “the List” is 15 years and is automatically renewable for another 15 years. The developing countries insisted on this new feature, with the intent to ensure that in the long term, the developed countries do not use all additional capacity of the Plan.
The European satellite operators agreed to the conditions above, provided that new provisions were added whereby a satellite network could be launched and operated for the 30- year period, even if all coordination could not be completed. The relevant provisions (4.1.18 to 4.1.20 of Article 4 Appendices S30/S30A) were very controversial, since they allow an administration to essentially ignore, for up to 30 years, assignments in the Plan not brought into use. These provisions were taken from the regulations that apply to FSS, where they are used to help eliminate “paper satellites.”
The new BSS provisions state that, even if coordination cannot be obtained with certain assignments in the Plan, the notifying administration of a new satellite network can insist on being included provisionally in the List. If, after four months of operation, there has been no complaint of interference from the assignments that were the basis of the disagreement, then the provisional remark is removed. Of course, if the assignments with which coordination could not be completed have not been brought into use, there will be no interference. However, the assignments with which coordination could not be obtained retain their priority, and should they be brought into use at a later date, then the new satellite network must eliminate any interference. This could mean that the new satellite must stop transmitting. The question now becomes whether the banks would finance a system to implement planned assignments that would cause interference and be interfered with as soon as the network is launched.
When identifying networks with which an additional use network must coordinate, the concept of coordination arc is used. Frequency coordination is required with any network within +/-9 degrees. This is the same concept that WRC-2000 adopted for FSS networks.
Some frequencies that are used for BSS in one region are used for FSS in another region. For example, in Region 1, the BSS frequencies span the range 11.7 to 12.5 GHz. In Region 3, however, the frequency range 12.2 to 12.5 GHz is allocated to the FSS. WRC-2000 decided that the new Regions 1 and 3 BSS Plan must protect such FSS networks for which complete APS4 data has been submitted by July 21, 2000.
When the WARC-77 Plan was adopted, it contained a provision (old RR 2674) which said that “in devising the characteristics of a space station in the broadcasting satellite service, all technical means available shall be used to reduce, to the maximum extent practicable, the radiation over the territory of other countries unless an agreement has been previously reached with such countries.”
Before WRC-95, the Bureau maintained that it did not have the information to determine if all technical means had been employed, and therefore the Bureau, in examining notices for BSS, did not examine the notice for conformity with this provision. Broadcasting is a sensitive issue, and many countries do not want certain programs to be broadcast to their territory.
Based on a proposal made by the Arab countries, WRC-95 adopted a resolution (Resolution 531), which caused the Bureau to revise its rule of procedure with respect to S23.13 (new RR 2674). In accordance with the new rule of procedure, the Bureau requires that if a modification/addition to the BSS Plan submitted after November 18, 1995, (end of WRC-95) includes the territory of another administration, then the notifying administration must obtain a separate agreement with that administration. If such agreement is not obtained then the administration is removed from the service area.
WRC-2000 incorporated the above rule of procedure into the radio regulations as S23.13B. In addition, WRC-2000 went one step further. It allows administrations included in the service area of a BSS network to ask the Bureau at any time to remove it from the service area (S23.13C). In the case of a network that has already been launched, it would mean that the service would no longer be protected in that country, but it would still be available since the satellite antenna coverage area could not be changed.
Sharing Between Non-Gso Fss, Gso Fss And Fs
- Power limits on non-GSO FSS systems agreed in both Ku- and Ka-bands. These limits consist of three single-entry epfd limits and one aggregate epfd limit. The Ku-band limits will allow Skybridge to proceed as planned.
- More work needed on methodologies to verify two of the three single-entry epfd limits
- Regulatory procedures required in case limits are exceeded by a single non-GSO FSS system
- More work needed on methodology to calculate aggregate epfd produced by all non-GSO FSS systems
For certain Ku- and Ka-frequency bands, WRC-97 adopted provisional values of equivalent power flux-density (epfd) limits on emissions from non-GSO FSS systems (such as Skybridge in the Ku-band) to enable them to share frequencies with and to protect FSS and BSS GSO networks. To protect and share frequencies with the terrestrial fixed service (FS), a per-satellite power flux-density limit for each satellite in the non-GSO FSS constellation was provisionally adopted. (This latter limit was the same as the limit that applies to satellites operating in the GSO FSS.)
Definition Of EPFD Limits
The definition of epfdup takes into account the total of the emissions from all earth stations used by the non-GSO FSS system in the direction of a GSO satellite receiver located at any point on the GSO. The limits proposed by the non-GSO community for epfdup were not contentious, and both the GSO and non-GSO communities agreed on values that will protect GSO satellite receivers.
The definition of epfddown takes into account the pfd produced by all satellites from a given non-GSO FSS system visible at any one time at a GSO earth station. The pfd produced by each satellite of the constellation is referenced to the on-axis gain of the GSO earth station. This is done by adding the gain (in dB) of the GSO earth station antenna in the direction of the satellite and then subtracting the on-axis gain (in dB) of the GSO earth station. The resulting pfd for all visible satellites of one non-GSO FSS system is added (in dB) and the sum is the “equivalent” pfd or “epfd.” (In the following “epfd” will mean “epfddown” unless otherwise specified.)
Agreeing on these epfd values was probably one of the most controversial and difficult agreements reached within the ITU in many years and was the subject of much discussion in the ITU-R between WRC-97 and WRC-2000.
In order to protect GSO received carriers, non-GSO systems are designed to produce only negligible interference into GSO networks. This is generally done by the use of GSO arc- avoidance. Skybridge, for example, uses an avoidance angle of +/-108 so that there is no main-beam to main-beam coupling between the non-GSO satellite and the GSO satellite link, no matter where on the surface of the earth the GSO receive station is located.
The residual interference from non-GSO satellites into GSO networks is time varying in nature and is modeled as a value of epfd against a percentage of time for which this value is not to be exceeded. The short term interference is the interference not to be exceeded for very small percentages of time. Short term interference into the GSO earth station is dominated by the residual radiation through the sidelobes of the non-GSO satellite in the case where the non-GSO satellite is in-line with the on-axis direction of the GSO antenna and the non-GSO satellite is illuminating an adjacent service area. The long term interference is interference which occurs for larger percentages of time approaching 100 percent or the steady state. This interference is dominated by the sum of main beam non-GSO interference into the sidelobes of the GSO earth station.
Single-Entry And Aggregate EPFD Limits
WRC-2000 adopted two types of epfd limits: single-entry and aggregate. The epfd limits that apply to one non-GSO system (comprised of many non-GSO satellites) are referred to as single entry limits. The epfd limits that apply to the total number of non-GSO systems are referred to as aggregate limits. These epfd limits are not to be exceeded and are therefore called “hard” limits. If these levels are not exceeded, then the interference into GSO networks (both FSS and BSS) is deemed to be acceptable.
WRC-2000 confirmed the agreement reached by the Conference Preparatory Meeting, CPM-99, on the values of the single entry and aggregate epfd limits for both the Ku- and Ka- bands. For the downlink, this agreement consists essentially of different types of epfd limits for non-GSO FSS systems to protect GSO links from interference from non-GSO FSS systems. Each of the different epfd limits addresses a different concern. The epfd curves give epfd values not to be exceeded for different percentages of time varying from 0 percent of the time to 100 percent of the time. The different epfd limits agreed are listed below.
The single-entry validation epfd limits are upper bound single entry-limits derived from using worst case assumption for the non-GSO FSS constellation, such as worst-case location of GSO earth station and full loading of all beams on non-GSO satellite. The ITU-R has developed a recommendation containing the functional specifications for the software to be used by the Bureau in checking compliance with these limits. These are the only epfd limits for which the Bureau will check compliance.
The single-entry operational epfd limits are for the 100 percent value only (i.e. the value never to be exceeded). They are more stringent than the 100 percent value of the validation epfd limit and restrict the maximum epfd that an operational non-GSO FSS system may transmit into operational earth stations. These limits were agreed to minimize the risk of a GSO earth station losing sync.
The ITU-R has developed several methods for measuring the epfd values from an operating non-GSO FSS system in order to determine whether the single entry operational epfd limits are exceeded. These measuring techniques have been agreed by both the GSO and non-GSO parties. In general, there is a tradeoff between accuracy and simplicity of measuring technique. It is expected that in the case of a dispute where accuracy of measurement may be an issue, the more accurate techniques will be used.
Should an administration measure a non-GSO signal above the operational limits in an operational GSO earth station, the non-GSO operator has to reduce power to a value equal to or less than the operational limit in the direction of the earth station of concern.
Single-Entry Additional Operational EPFD Limits
These limits apply for 3-meter and 10-meter GSO earth station antennas only. They were chosen as specified points of the epfd curve generated by simulation of the Skybridge system. They are intended to give the GSO operator further assurance of the actual epfd statistics of a non-GSO system in operation. These limits are more stringent than the validation limits.
It is agreed that measuring these limits is not practical (except for the 100 percent value). An administration proposing a non-GSO system would have to guarantee, at the time of submitting the filing to the ITU, that the proposed system will meet these limits. Also, the ITU-R is revising an existing recommendation (Rec. ITU-R S.1325) to enable, with the use of software modeling, the accurate prediction of the epfd levels produced by a proposed non-GSO FSS system into a GSO earth station.
The Aggregate EPFD Limits
What is important to the GSO operator is the aggregate epfd produced by all non-GSO FSS systems. These values were agreed by CPM-99 for different GSO antenna sizes. When the ITU-R examined the impact of non-GSO FSS systems on GSO networks, this examination was carried out using the aggregate epfd values. The epfd values that are generated by one non- GSO FSS system are called the single-entry epfd values.
These values were derived for different GSO antenna sizes from the aggregate curves assuming 3.5 homogeneous non-GSO FSS systems. In typical ITU fashion, this number was a compromise. The non-GSO FSS community proposed “3” as a value and the GSO community proposed “4” as a value. The ITU-R recognized that non-GSO FSS systems are likely to be inhomogeneous and therefore the aggregate epfd levels from multiple non-GSO FSS systems will not be directly related to the actual number of such systems operating co-frequency. Hence a number which is not necessarily an integer could be used to derive the single-entry interference allowance from the aggregate allowance.
Verifying Compliance With EPFD Limits
The Bureau will check compliance with single-entry validation epfd limits using agreed software. Regarding the single-entry operational epfd limits and the single-entry additional operational epfd limits, the Bureau will not check compliance with these two limits. WRC-2000 adopted a resolution (COM5/7) which, inter alia, invites the ITU-R to develop by WRC-03 methodologies that may be used by administrations to verify these limits. In the case of single-entry operational epfd limits, the methodology will rely on measurement and in the case of single-entry additional operational epfd limits, it will rely on software simulation. WRC-2000 also adopted a resolution (COM5/23), calling for the ITU-R to develop in time for consideration by WRC-03 regulatory procedures in case these limits are exceeded at an operational GSO earth station.
The Aggregate EPFD Limits
The aggregate epfd limits adopted by WRC-2000 are attached to Resolution COM5/6. This resolution calls on administrations intending to operate a non-GSO FSS system to take all possible steps to insure that the aggregate interference levels given in the tables attached to this resolution are not exceeded. The ITU-R is invited to develop a methodology for calculating the aggregate epfd produced by all non-GSO FSS systems in the range 10-30 GHz. The ITU-R is also invited to develop a recommendation on the accurate modeling of interference from non-GSO systems into GSO FSS and GSO BSS networks.
Jorn Christensen, Ph.D, P.eng, is a frequency coordination consultant based in Wiarton, Canada. he can be reached at 519/534-3345 or via e-mail at firstname.lastname@example.org.