System and method for channel assignment in a satellite telephone system

Abstract

A system and method for making channel assignments in a low earth orbit satellite telephone system wherein Doppler effect is utilized as a parameter in channel assignment. In a first embodiment the satellites orbit in a fixed grid pattern, and in a second embodiment the satellites move in orbits that appear random relative to each other.

Description

BACKGROUND OF THE INVENTIONThe explosive growth of cellular radio during the late 1980s and early 1990s highlighted the importance of mobile telephone communications. Almost all large world wide cities in the developed world now enjoy some form of cellular communications. However, there are still some areas that are not served by cellular. In some developing nations there is not enough of a demand to install wide area cellular systems. In developed nations, there are still remote areas that have not yet been covered by the cellular system.One approach that has enjoyed considerable press is the idea of creating a satellite system that would provide telephone service the world over. The argument for such an approach is that it would provide coverage to developing countries, and also provide coverage in remote areas in developed countries. (In addition many land line phone companies have less than stellar reputations in some countries, and it is assumed that many citizens would also us...

AI Technical Summary

Benefits of technology

This invention provides a new approach to channel assignment in a LEOS system by using signal strengths adjusted by Doppler effects to calculate assignments based on actual signal strengths without relying on satellite position. This approach provides both the satellites and the earth user with a better signal.

Problems solved by technology

However, there are still some areas that are not served by cellular.

In some developing nations there is not enough of a demand to install wide area cellular systems.

In addition, the cost of cellular radio is quite high, and there is a good possibility that satellite systems would yield a lower cost to the final user.

Radio propagation is such that the available higher frequencies for such a system will not bend around the curvature of the earth, and that such systems will be generally limited to line of sight communications.

1) The very high altitude of geostationary satellites causes limited frequency reuse in the system. Since spectrum is a valuable resource, such high altitude satellites are very spectrally inefficient in that the channels could only be used once in a very large area.

2) The very high altitude of geostationary satellites implies that there is a considerable distance between the phone user and his satellite. This large distance requires large transmitter power and / or a large antenna system at both ends of the communication link. These two limitations are especially difficult for the roaming mobile telephone user.

Although these approaches are technically sound, the cost to create one of these systems is estimated to be near four billion dollars.

This results in a very expensive satellite, and also in a very expensive rocket launch cost.

In addition to the expensive and heavy satellites there is a very expensive satellite orbit control system to keep the satellites in their proper orbits.

In addition, the complete failure of any one satellite would require the moving of a back up unit to take its place in the grid.

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