NAIC/AO Newsletter, November 1997
The radio spectrum is mostly used by "active" spectrum users using transmitters. A relatively small fraction of the spectrum is used by "passive" scientific users, who use only receiving systems in certain allocated spectral bands to detect natural emissions. For astronomers the radio spectrum is one of only two spectral windows available to observe the universe with ground-based receiving instruments, the other being the optical window. Astronomers study the radio emissions from stellar objects and gas clouds in our Galaxy and distant galaxies, in order to understand the past history of Earth, the Solar System, our Galaxy, and the Universe. All of these natural emissions are very weak. For example, a standard cellular phone placed on the Moon would be about the third strongest radio source observable in the Universe, and most other sources many million times weaker.
On the other hand, the remote sensing community uses both passive and active techniques for studies of the Earth's surface and the atmosphere. The ozone hole, the health of the rain forests, the distribution of natural resources, pollution, and global and local weather patterns are all areas of studies. Although the passive users operate in well-chosen spectral bands set aside for these purposes, they are struggling increasingly to keep these special spectral windows free from interference from the active users in adjacent or even distant bands. Often the scientific spectrum users find themselves on the defensive against commercial users with dramatically different operational standards and conceptions of spectrum efficiency.
The World Radiocommunication Conference-97
Use of the radio spectrum is primarily regulated by the Radiocommunication Sector of the International Telecommunication Union (ITU-R), part of the United Nations. Actual spectrum allocations are finalized at bi-annual ITU-R World Radiocommunication Conferences (WRCs). The next four-week-long WRC-97 conference will be held in Geneva from October 27 till November 21, 1997. During a WRC the spectrum is allocated on an equitable basis to all operational services. Within each allocated service band, each national government can make operational assignments of particular systems within this service. Naturally the allocation process at WRCs is affected by a political give-and-take that does not always ensure the best solution as a final outcome. The guiding notion for a WRC is that all administrations and users should go home "happy" or at least "equally unhappy".
All interested parties - governments, commercial enterprises, and international organizations - may participate in the discussions at the WRC and the numerous meetings leading up to the WRCs. However, only the national administrations are "Full Members" of the ITU and make the final decisions. All other participating non-voting entities are called "sector members" or members with a "small m". The intense participation of commercial sector members in recent years has dramatically changed the atmosphere at the ITU-R. As governments have less money to spend, the ITU has come to rely on financial contribution from the commercial sector members. In return, these entities have been granted more direct participation in the allocation processes, which may erode the objectivity of the ITU-R. The continual pressure of the commercial entities may even oblige the ITU to concede an even larger part of the decision making process in the future.
Issues at WRC-97 that concern the Passive Services
The scientific spectrum user community strongly participates in the allocation process in order to protect the existing radio windows to the Universe for current and future research. The agenda of the upcoming WRC-97 also has a number of issues that affect the spectrum for scientific users utilizing the bands in the Radio Astronomy and the Earth-Exploration (Satellite) Services.
First, the Mobile Satellite Service (MSS) needs more band space for uplinks, downlinks, feeder links, etc. Many of the over 300 MSS networks planned for geo-stationary (GSO) and non-GSO orbits require spectrum between 1000 and 3000 GHz. By the year 2000 a total of 2 x 250 MHz of spectrum will be needed. Currently only 2 x 140 MHz is available in the Americas and 2 x 100 MHz in the rest of the world. Frequency sharing is not possible for most of the proposed MSS systems and each system would therefore need its own band section. Efforts will have to be made at the WRC-97 to harmonize the MSS requirements around the world but there are only a limited number of options. There are strong concerns within the radio astronomy community, the World Meteorological Organization (WMO) and the International Civil Aviation Organization (ICAO), that for certain proposed space service band allocations the protection safeguards to protect other users are ineffective and impractical.
In addition, the existing and proposed GSO networks feel threatened by the numerous non-GSO systems operating in "low earth orbit" (LEO) below them. Simultaneous operation of existing GSO and the new non-GSO LEO systems in shared or adjacent spectrum bands require extensive coordination. Many of these coordination discussions have been carried over from previous WRCs for reconsideration.
Second, the Earth Exploration-Satellite Service needs to implement more advanced technological sensor systems for studies of various aspects of the Earth's surface and atmosphere. A number of bands are being considered for upgrading or re-allocation in order to make these systems possible.
Third, beside a number of additional spectrum items such as HF Broadcasting and Maritime and Aeronautical Services, there is also a proposal of new standards on "spurious emissions" on the WRC-97 agenda. This interference issue is critical to the science services, because of the limited protection provided by the Radio Regulations (RR) of the ITU-R.
The Protection of the Science Services within the ITU-R
As distinct operational services within the ITU, the passive Radio Astronomy and Earth Exploration Services have clearly different protection requirements than the active services. But in reality, the inter-service protection criteria within the ITU-R RR are based on an "equal for all" principle and thus the provisions for protecting the science services are still quite inadequate. Since the majority of spectrum users are (commercial) telecommunication entities, the prevailing criteria do not translate into "equal interference for all". The major problem in protecting the passive services lies in the fact that it will cost money for the active spectrum services to do so. Since protection of the more vulnerable passive services will also protect the "active services" from each other, this concept should be considered as "the cost of doing business" just as in the environmental arena. It is essential the ITU_R modernize and improve its protection standards of the passive services as it introduces and regulates these new space-based telecommunication industries.
New Standards for Unwanted Emissions
Besides the wanted signal, a transmitter also generates "unwanted" signals that are not essential for the transfer of information. Immediately outside the bandwidth of the wanted signal, there is first the "out-of-band emission" and beyond that the "spurious emission". With filters and good engineering practices, an engineer can reduce the unwanted emissions; but, there are practicable limits, both economic and technical. In practice, one cannot always make a transmitter operate within some well- defined sharp spectrum edges. In this context, WARC-92 approved Recommendation 66 which called for a study on standards for unwanted emissions to help protect the Radio Astronomy Service. ITU-R Task Group 1-3 has worked during the last three years to define these new standards on spurious emissions, which are to be incorporated into the ITU-R Radio Regulations at WRC-97.
However, the final recommendations of ITU-R Task Group 1-3 are a set of antiquated standards dating from the 1970's (as used in the USA and Canada) long before the present explosion of space-based telecommunication. They do very little to protect the RAS. After adoption of the results in the new Recommendation SM.329 into Appendix 8 of the Radio Regulations at WRC-97, these standards will be about thirty years old before they are implemented sometime in the next century. The great obstacle for progress is that globally applicable tighter standards may make some products slightly more expensive. In addition, the space services were exempted with too lenient "design goals" rather than mandatory limits.
A new Task Group 1-5 is currently considering limits on out-of-band emission and may reconsider the spurious limits for the space and other services. Considering that out-of-band emissions occur closer to the wanted signal than the spurious emissions, the spurious limits are the ultimate standard. In order to improve the interference situation for many spectrum users, it is imperative that TG 1-5 be allowed to a) consider unwanted emissions as one coherent problem and b) propose new spurious and out-of-band standards that better reflect current engineering practices. Furthermore, c) TG 1-5 and the ITU-R must earnestly address the issue of protecting the passive services from interference and d) establish some practical proposals.
In the meantime, the 42 CEPT countries will continue to maintain their own more stringent spurious standards for most services, these are 100 to 1000 times tighter than those of the ITU-R. Hopefully, these CEPT standards will become the default standards, because global manufacturing will have to adhere to the tighter of any two standards.
Passive Users Concerns Regarding the Space Service Issues
Communication technology is changing most rapidly in the space services as digital and spread spectrum techniques are being applied to provide seamless communication systems. Although many systems are global, they may service a rather select customer base. Some such systems would provide the technology to let the kids play interactive video games with their friends from the back of the car, while on a shopping or vacation trip. On the other hand, the advent of terrestrial wireless networks, global PCS systems, the advance of the unifying CEPT GSM standards around the world, and more complete coverage of the Earth with fiber cable will eventually eliminate the need to provide certain services using space-based systems.
The new systems proposed in the space services require uplinks, downlinks, feeder links and inter-satellite links to operate. These link transmissions constitute the single-most important interference threat for other spectrum users and could spell d-i-s-a-s-t-e-r for radio astronomy and remote sensing operations in adjacent or nearby bands. Already about 75 percent of the radio astronomy bands are being threatened by adjacent or nearby Space Service bands. While some space transmission systems are specifically designed to protect radio astronomy bands, others cause or will cause serious damage. Three examples may serve to explain how things can go wrong for the passive users:
1. GLONASS is a Russian global positioning system providing a service similar to the American GPS system. According to ICAO both 24-satellite systems will be part of the Global Navigation Satellite System for aviation use in the future. However, the system design of GLONASS has resulted in severe interference for passive users in the 1610.6-1613.8 MHz spectrum band. After extensive discussions with the radio astronomers and several administrations, the GLONASS system is presently being modified to eliminate unwanted emissions in the radio astronomy band and also to make spectrum available for MSS operators in the 1610-1626.5 MHz band. But this interference problem will not be eliminated until the year 2005.
2. IRIDIUM is a 66 satellite constellation designed by Motorola to provide a seamless but expensive global telecommunication system. In 1992 when IRIDIUM was presented and spectrum was allocated, Motorola made promises that radio astronomy operations in the 1610.6-1613.8 MHz band would be protected from the IRIDIUM downlink in an adjacent band. At this point in time it is evident that the IRIDIUM cannot possibly protect the RAS band except during some 4-5 hours of night-time low traffic periods. IRIDIUM carries no final stage filters to eliminate unwanted emissions into the neighboring RAS band.
Attempts at coordination between IRIDIUM and the radio astronomy community are still continuing in various countries, but at this point IRIDIUM can only admit that it will not interfere more than the present GLONASS system. This state of events cannot promote spectrum efficiency. IRIDIUM has provided no clear technical solutions for protection of the RAS operations as demanded by the ITU-R Radio Regulations. The only viable solution from the astronomy point-of-view seems to be a form of "traffic shedding" to reduce the unwanted emissions during RAS operations.
3. ASTRA-D is a direct TV broadcasting satellite operated from Luxembourg. As a broadcasting satellite, it operates in a Fixed Satellite Service band of 10.7-11.7 GHz without permission from the ITU-R. Because of inadequate ground-based system testing, a technical flaw resulted in broadcasting signals spilling over into the 10.6-10.7 GHz radio astronomy band. Because this system provides popular TV channels to a large audience, nobody dares to turn off the satellite. Instead some administrations have made arrangements for radio astronomy to operate in a shifted band to avoid the unwanted signals of ASTRA-D.
Keeping the Windows to the Universe Open
Most people would be sympathetic to the request by the scientific community to keep some spectral windows "free from interference". Some operators may oppose any special protection for scientific use of the spectrum, because it could constitute a financial burden for operators of such useful services as cellular phone or TV broadcasting systems. However, sooner or later spectrum pollution will haunt all spectrum users, because there are practical limits to increasing the number of users in the spectrum. Efforts to protect the most vulnerable passive spectrum users at this time will pay off in protection for all future spectral users.
The ITU-R will have to face up to the realization that "equal for all" does not protect the scientific users and some realistic alternatives need to be found. Besides reduction of unwanted emissions, some creative time sharing and geographical sharing schemes may provide some protection for passive users. Geographical sharing schemes will require the creation of coordination zones or quiet zones by national administrations to provide local protection of sensitive observatories. As for the threat posed by the space services, it is prudent to avoid problems by preventing them, since retro-fitting of satellites is a lengthy and costly business. An honest environmental impact statement and more extensive ground-based testing for satellite transmission systems could help to avoid mishaps in the future.
"Spectrum splintering" and having "incompatible services in adjacent bands" often prohibits spectrum-efficient operations and forces many services to accept a certain amount of interference from neighboring operators. One would hope that beginning with WRC-97, the administrations make a start towards creating broader allocations for the various services. Further spectrum splintering must be avoided at WRC-97 and some (long-term) re-arranging of spectral bands may need to be considered.
Many new spectrum management issues lie on the horizon for the scientific services. For instance, the increasing commercial use of frequency bands above 30 GHz will pose new problems. Scientific spectrum applications have been ahead of commercial applications for many years and radio astronomers still operate alone in most frequency bands above 60 GHz and all the way up to above 1000 GHz, which almost reaches the infra-red part of the spectrum. Astronomers search for interstellar molecules and atoms at these high frequencies, which provides clues about interstellar chemistry and even about life itself. ITU-R regulation of these high frequency bands should take into account the interference lessons learned at lower frequencies. Otherwise the same congestion problems that make passive operations difficult at lower frequencies will repeat themselves.
The accelerated rate of development in the telecommunication industry is critical for the Radio Astronomy and passive Earth Exploration and Earth Exploration- Satellite Services. Will the governmental spectrum management agencies around the world continue to uphold the protection of the scientific services from systems such as IRIDIUM or will commercial interests prevail? Is the expressed desire to protect the passive services fact or fiction?
Willem A. Baan is the Chairman of IUCAF, the Inter-Union Commission on the Allocation of Frequencies for Radio Astronomy and Space Science. IUCAF operates under the auspices of ICSU, the International Council of Scientific Unions and is supported by the International Astronomical Union, the International Union of Radio Scientists, and the Committee on Space Research. IUCAF is a sector member of the ITU.