by Gerald E. Oberst Jr.

Although the next ITU world radiocommunication conference is not scheduled until 2000, the Conference Preparatory Meeting or "CPM" for WRC-2000 is going on late this month. One of the hottest topics at the meeting will be how to deal with non-geostationary (NGSO) satellites. This topic has taken thousands of hours of effort by industry experts, and the outstanding regulatory issues are not yet resolved.

The CPM prepares a background report that is used at each radio conference. As such, it is a lightning rod for the issues on the WRC-2000 agenda. A draft of this report has already been prepared, and the second meeting of the CPM in Geneva from November 15 to 26 will consider the document. One of the seven chapters of the report concerns how NGSO satellites can operate in the same frequencies as geostationary (GSO) fixed and broadcasting satellite service (FSS and BSS) systems.

The last WRC in 1997 set provisional power limits for NGSO operations, but called on the ITU to conduct technical, operational and regulatory studies on co-frequency NGSO and GSO operations. The big debate now is whether these power limits are appropriate, and to fine-tune the technical regulations.

Why are these questions so complicated? GSO and NGSO satellite networks operate in very different ways. For GSO networks, the communication links that must be protected are fixed between the satellite and earth stations concerned, so the coordination models are static. By contrast, a NGSO constellation of satellites is constantly in motion. These networks are based on a large number of small satellites moving in different orbital planes, not fixed relative to the earth as are GSO FSS and BSS satellites. Therefore, the NGSO link path is constantly moving and the coordination parameters are dynamic.

The resulting regulatory conflicts are obvious for co-frequency operation. On the one hand, there is a need to protect the enormous investment already made and continuing into the future for GSO satellite networks. On the other hand, there is the need to set the NGSO power limits so that the resulting increase in the complexity, mass and cost of the small NGSO satellites does not price them out of the market.

An early issue arose over the number of NGSO networks that would operate. Each network adds to the interference potential of NGSO operations overall. To protect GSO systems, the power limits must apply to the sum of emissions from all NGSO satellites. Thus, the total amount of interference potential has to be divided over the universe of NGSO systems. If you assume that only one network will be implemented, then the power limits could be higher, but no subsequent networks could be launched. If you assume that a large number of NGSO networks will be implemented, then each network can have only a small proportion of the total interference potential, which could translate to limits so low that no single system could operate. After almost endless discussion, the current approach is to assume that 3.5 networks will ever fly, at least in the Ku-band, and to base the power limits available for each single system on that assumption.

By the end of the summer, many other highly technical issues had been resolved, based on intensive work and many compromises. Among the most important were power limits that protect smaller GSO FSS receive earth station antennas with diameters between 60 and 120 centimeters. One issue that is not yet resolved, at presstime, is how to protect larger GSO FSS earth station antennas, with diameters of 3 meters and 10 meters. These larger antennas are more susceptible to interference from the swirling NGSO networks. Administrations have supplied data on about 400 large antennas worldwide, mainly in the Ku-band, that are at risk.

Efforts to resolve these issues doggedly continue. The Europeans who are the main proponents of the co-frequency NGSO operations conducted workshops in September in Brussels and the FCC is pursuing its own rulemaking activities.

Along the way, an enormous amount of regulatory time and attention has been devoted to this effort. The draft CPM report on this topic is an engineer’s dream (or nightmare), with numerous equations, charts and tables. More than 400 papers have been submitted to date to the joint task group, JTG 4-9-11, that was set up by the ITU to conduct the studies, and we hear that at least another 400 papers were submitted in other committees on the same questions. The ITU collected parameters for more than 800 GSO links into a database to use in the study process. The costs of all these efforts could probably finance an entire satellite network, and still, the work is not done.

The weary experts that have dedicated two years and more to these NGSO issues for co-frequency operation with GSO satellites have achieved much, but the regulatory problems of these operations remain on the ITU agenda. The satellite industry already spends much time and fortune on contesting for spectrum with the terrestrial industry. It seems a shame that new conflicts have arisen between the satellite technologies themselves, distracting untold numbers of regulators and experts from the task of providing services and networks.

Gerry Oberst is a partner in the Brussels office of the Hogan & Hartson law firm. His email address is [email protected].