Several future operators of the mobile handheld telephone (P‐service) satellite communications systems are gearing up for system implementation to compete for the mobile handheld telephone market of the future. While these companies are proceeding with system realization, they are also looking for partners to finance these huge satellite projects. Potential partners or bulk users are administrations of national communication systems and operators of national communication satellites. These future partners ask themselves which P‐service satellite communication system they should choose. There is not an easy answer because P‐service satellite systems come in many varieties. There are the low altitude earth orbiting satellites (LEOs), the medium altitude earth orbiting satellites (MEOs), and the geosynchronous altitude earth orbiting satellites (GEOs). Each system has a different type of satellite repeater: digital regenerative, transparent digital, and the bent‐pipe. And each satellite system uses its own modulation/multiple access system. The fact that satellites circle the earth at different altitudes has an impact on speech quality, and, because systems vary in satellite as well as constellation complexity, there are different price tags attached. All systems display ingenious features and will eventually work. Mobile users will decide which system will best serve their purposes. This article attempts to compare six P‐service satellite systems and find a method for system selection. By use of self‐established system criteria, it is possible to arrive at a P‐service system selection. By weighing the system criteria, the sensitivity of system selection can be tested. The results or the selection of a particular system should not be considered a recommendation; rather, the process of selection should be used as a possible guideline.

No abstract

No abstract

Ύϊΐ€ mcNtn has been successfully used as a calibrated source of RF emissions in determining the gain-to-noise-temj^rature ratios (G/T^s) of medium size €-band antennas. This method to determining G/T has recently been applied to K^-band antennas as well, and the results have agreed well with independent measurements of gain and temperature. However, because of the fact that the moon's angular diameter may extend beyond the main lobe of lobe antenna, a gain correction factor has to be applied. This factor requires accurate knowledge of the gain pattern for its determination, but once such knowledge has been obtained by pattern measurement, the G/T can be calculated with reasonable accuracy.

At present a major effort is under way to define the most efficient modulation/multiple access system in mobile satellite communication. Where the emphasis is on digital voice modulation, the proposed multiple access methods almost always imply frequency division multiple access (FDMA). This analysis presents a comparison between FDMA and code division multiple access (CDMA), for the operation of both multiple access methods in the mobile satellite communication environment. The mobile satellites under consideration use multiple‐beam or scan‐beam antennas and employ frequency reuse of the allocated L‐band frequency spectrum. As CDMA is better at absorbing Doppler and multipath effects, and permits higher rate coding, in general (practical considerations aside) it appears to be the more capable system.