A research study submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Advanced Technologies

Research Studies Project Report (M. Eng.) - Asian Institute of Technology, 1997

An option being considered by current and prospective Mobile Satellite Service (MSS) operators is the use of Low Earth Orbit (LEO) satellites to provide global personal communications. The scarcity of free spectrum, together with the bandwidth typically required, means that any new MSS system must consider sharing spectrum with other systems and services. Spectrum sharing must be based on defined interference criteria being satisfied. Before any new system can be constructed, it is necessary to demonstrate that it can be coordinated with existing systems and will not present an unacceptable level of interference. It is therefore necessary to perform a detailed interference analysis as an essential step in the engineering design. The significant difference between LEO systems and the traditional geostationary (GEO) systems is that, unlike the case of GEO system, the relative geometry between a satellite and an earth station or among the satellites themselves is not fixed. This time-dependent geometry greatly increases the complexity of the interference analysis. This research study presents a model applicable to the interference analysis among LEO/LEO and LEO/GEO systems. The analysis of interference is based on the calculation of the carrier-to-interference ratio. It has been seen that spectrum sharing is an important issue in the consideration of LEO systems, especially as the analysis shows the potential for interference caused by LEO systems and into LEO systems. This analysis can be useful in system design, ensuring that a system will not cause interference and not suffer from interference.