WRC 2000 feature article

	World Radiocommunication Conference 2000
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Eye in the Sky

Over the years, the WRC has earned a reputation as a gruelling event peppered with contentious issues that regularly keep delegates in the conference halls well after midnight. This year’s event promises to be no different, with vigorous debate expected on proposals for a re-planning of the broadcast satellite service and a push for additional spectrum for IMT-2000-based third generation cellular systems.

Another issue expected to generate some heat on the conference floor is the bid by the European Union for spectrum to support a new satellite positioning system to add to the two current systems, Russia’s GLONASS (Global Navigation Satellite System) and the US Global Positioning System (GPS). The proposed new system, known as Galileo, would spread the capacity to provide increasingly important position and navigation services. The challenge for Europe’s CEPT (European Conference of Postal and Telecommunications Administrations) which has tabled the proposal will be to secure the vital spectrum needed to ensure the system’s viability and effective operation.

The Story So Far

The proposal to launch a new European satellite positioning system has been taken up by the European Union in the light of two factors: the world’s increasing reliance on satellite services such as positioning and precision timing for a wide range of industries, from computing and communications to manufacturing and assets monitoring and the need to move to next generation radionavigation-satellite systems.

The issue will be dealt with by the conference under Agenda Item 1.15 - Radionavigation Satellite Service (RNSS) – and involves a proposal by CEPT for new allocations for space-to-Earth service in the bands 1 151-1 215 MHz, 1 260-1 300 MHz and 5 010-5 030 MHz, with priority given to existing aeronautical services in the 1 151-1 215 MHz band and provisional system power limits (pfd or power flux density limits) imposed in the band 1 260-1 300 MHz until further studies on possible interference with existing systems are complete.

CEPT’s position is to push for a new primary allocation for the Galileo space-to-space segment, and, in order to protect the new system from interference which could hinder its operation and accuracy, to phase out fixed service applications like microwave links from the band 1 559-1 610MHz over a 15-year period.

The proposed Galileo system is said to comprise a constellation of between 21-37 medium-earth orbit (MEO) satellites and between 3-9 conventional geostationary satellites, and will integrate the existing European Geostationary Navigation Overlay Service (EGNOS). System cost is estimated at around EUR2 billion in the construction period to 2008, with ongoing operational costs of between EUR97-141 million annually. The system is tentatively scheduled to go into operation in 2008.

While the EU has been keen to promote partnership development of the project with both existing satellite positioning operators, only Russia has so far expressed interest in participating in the project. Partners participation aims at not only at providing the project with access to considerable expertise in space systems development, but also at helping with access to much-needed radio frequency spectrum, through shared availability of the allocations used by current systems.

Positioning to Win

While Europe’s plan to set up a new, global positioning system would seem to be relatively straightforward, securing the necessary spectrum for the project already proved a sticking point at the last WRC in 1997. At that event, moves to agree on allocations in new bands were blocked on the ground that the proposal for the GPS and Galileo systems to share some of the same frequency bands would effectively jeopardize smooth and reliable functioning of the GPS system. Concerns were also expressed about the shared use of bands currently allocated for aeronautical navigation, which it was said could also pose safety risks.

The 1997 conference decided to order studies to be undertaken by experts of the Radiocommunication Sector, with the results of that research to be presented at WRC-2000. Technical studies on the feasibility of sharing between the GPS and planned Galileo systems fell to the Sector’s Study Group 8, with preliminary results generally favourable to coexistence of the two systems provided certain criteria like power limits are observed.

Should the European delegation be unable to garner the support it needs to secure new frequencies for Galileo, it would face three options: continue to use existing systems; try to identify new, regional candidate bands and convince EU Member States to re-farm spectrum for Galileo by reallocating services currently in those bands to other parts of the spectrum; or accept a delay until the next WRC in 2003.

The first option has been ruled out categorically in the EU’s 1999 Consultation Paper on the issue and re-farming is considered a costly, if not virtually impossible course given that some European nations have sold suitable spectrum to private companies, and would have to try to buy it back. Tough negotiations can therefore be expected. n

GPS and GLONASS Explained

GPS

Controlled by the US Department of Defense, the GPS system comprises 24 NAVSTAR MEO (medium Earth orbit – about 19 300 kilometres from the planet’s surface) rotating in six orbital planes and spaced at a distance of 60° apart, each of which circumnavigates the Earth once every 12 hours. The satellites in the system are fitted with four highly accurate atomic clocks, and calculate their position relative to the Earth’s surface by sending radio signals to receiving dishes, which themselves determine their distance from the sending satellite by measuring the precise time taken for the message to arrive. By taking measurements from 3-4 satellites the system triangulates the signals to deliver a positioning reading which can be accurate to within 22 meters horizontally, 27 metres vertically, and with a time frame accuracy of 200 nanoseconds. However, this level of accuracy – the Precise Positioning Service – is only available to selected military and government agencies. Ordinary users have only access to the Standard Positioning Service, which uses Selective Availability to deliberately degrade the precision of the measurement. The SPS service delivers accuracy of 100 metres horizontally, 156 metres vertically, and a time frame of 340 nanoseconds. The PPS service uses the band 1 227.60MHz, while the SPS services is located in the band 1 575.42MHz.

GLONASS

Like GPS, Russia’s GLONASS system was originally developed for military applications but is now available to civilian users, albeit in a cut-down, less precise version. The system is managed by the Russian Space Forces, and comprises 24 MEO satellites arranged in three orbital planes separated by a distance of 120° , orbiting 19,100km above the Earth. Each satellite complete an entire orbit once every 11 hours 15 minutes, with satellite spacing designed so that five satellites are in view of a ground-based user at any one time. Cesium atomic clocks on board each unit synchronize with a hydrogen atomic clock called the Central Synchronizer, located at Mendeleevo, near Moscow. Like GPS, the GLONASS system can generate both high precision and standard precision signals, with the standard signal delivering positioning data with an accuracy within 57-7- metres horizontally, within 70 metres vertically.

Positioning data is calculated from at least four satellites, using triangulation methods similar to those used by GPS. The system uses the 1 602MHz band to transmit its standard signal.