Sharing the Skies
(Part I)

While the big issues at this year’s conference revolve around spectrum for third generation cellular systems, broadcasting satellite plans and the move to establish a new global positioning service, there are nonetheless a number of significant but less high-profile issues. Some of these are likely to be contentious and generate vigorous debate, while others are important because they represent the first step towards the establishment of new kinds of services.

The plethora of new mobile satellite (MSS) services seeking frequency bands for operation is prompting consideration of sharing other bands currently used by aeronautical and maritime navigation systems. While WRC-97 approved new operational parameters relating to the new Global Maritime Distress and Safety System, the conference decided not to allow expansion of mobile satellite services into the bands currently allocated exclusively for aeronautical and maritime navigation systems, noting concerns from the civil aviation and maritime communities. Instead, a compromise was reached – Resolution 220 – requesting that further studies be undertaken to determine the possibility of safe sharing between radionavigation systems, including the Global Navigation Satellite System currently based on US GPS and Russia’s Glonass, and Mobile-Satellite Services.

With initial studies seeming to cast doubt on the feasibility of safe sharing between navigation and mobile satellite services in the band 1 559-1 567 MHz, most countries seem to be supporting the maintenance of an exclusive allocation to radionavigation services, and the suppression of Resolution 220. Extension of MSS into the bands 1 675-1 710 MHz has received a mixed response, with some countries supporting the findings of the Conference Preparatory Meeting Report that the band could represent a suitable candidate for MSS, and others opposing the move because of a possible risk to regional meteorological services.

The growing demand for radiocommunication-based services is exerting greater pressure on important scientific applications such as radioastronomy and other passive services, as radiotransmission signals from cellular phones, pagers, satellite systems and more increasingly affects the attempts to monitor radio activity originating outside the Earth’s atmosphere. The biggest problems are in the areas of passive monitoring, used, for example, by the world’s largest radiotelescopes to detect extremely weak celestial sources of radio activity.

From the point of view of passive space research, the signal strength from a cellular phone is huge – so high, in fact, that making a standard cellular phone call from the surface of the moon would register on a radiotelescope as the third most powerful source of radio activity in the universe. With unwanted emissions from other services threatening to blot out incoming cosmic signals and close the "spectral pinhole" through which astronomers and others learn about our world and the universe around us, radio astronomers are actively seeking better protection for vital research.

While the Radio Regulations provide for bands dedicated for Earth Exploration (passive), Space Research (passive) and the Radioastronomy Service, groups like the Inter-Union Commission on Frequency Allocation for Radio Astronomy & Space Science (IUCAF) are seeking the right to a "quasi quiet zone" in bands above 30 GHz, as well as a primary passive allocation worldwide in the band 18.6-18.8 GHz, and more effective protection from interference. At the same time, WRC-97 raised concerns about frequency sharing with the mobile satellite service in bands 1 610.6-1 613.8 MHz and 1 660-1 660.5 MHz, directing studies on the amount of tolerable interference associated with propagation variations through WRC-97 Resolution 125. The current tolerated level of interference in 10% of the total available time will be reviewed at WRC-2000.

With commercial interest in high-frequency bands being spurred by the development of new applications such as specialized radar services, as well as studies initiated by WRC-97 on the sharing of bands above 30 GHz by high altitude platform stations, the fixed service, and feeder links for the fixed satellite service, scientists may well have to fight hard to keep their tiny window on the universe clear and open.

(Continued in Part II and Part III)