With ending of the launch procedure of Iridum system, the newly developed commercial satellite communications systems have entered a new era. These new systems, which use non-geostationary orbits, can provide services like mobile telephony, paging and Internet data links, etc. It is also believed that in the next century, there will be more and more players in this area as a result of regulatory liberalization as well as new technologies. Radio frequency, which is limited, is a major natural resource for those new ocmers. As satellite communications systems keep on growing and becoming more versatile, the use of frequency, an issue that is always bothering communication enginerrrs, is becoming more serious.
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