JPL's Wireless Communication Reference Website

Chapter: Network Concepts and Standards
Section: Satellite Systems


Non-geostationary Systems

Contributed by Miquele Dlodlo

As much as the GEOS system strictly belongs in the FPLMTS track and is run by a public sector international co-operative, INMARSAT, the numerous upcoming non-GEOS networks are largely proposals from the private business sector for the PCS market. The clear exception is INMARSAT P with its smaller satellites in an intermediate, inclined circular orbit (ICO). At the time of writing, none of the contenders for this market has reached the commercial stage, and as such, great expectations rest mainly on current business plans around the world. The PCS paradigm calls for wire-line quality voice and data services combined with small handheld all-purpose terminals. Up to now, no research effort has turned up a feasible realisation of a GEOS solution to these conflicting requirements mainly because of the long path which calls for high-powered transmitters. Solutions thus are being actively pursued in the 600 - 11 000 km range of satellite heights above the earth’s surface.

Description (see table)

. The wide variety of systems at lower orbits are named according to the types of orbit they follow. For instance, the highly-elliptical earth orbit (HEO), medium earth orbit (MEO), low earth orbit (LEO) and the inclined circular orbit (ICO) are typical. An apt description for all these systems would be: a satellite-based PCS intended to facilitate inter- and intra-system telecommunications throughout the world for voice, data, fax and paging communications in the commercial, rural and mobile sectors to subscribers using pocket-sized, hand-held, digital, personal communication terminals. Most are designed to inter-operate with terrestrial systems through the use of dual-mode hand-held units. Commercially, they are more or less targeted at the business traveller as well as individuals from different walks of life. The traveller may be passing through locations that are remote with respect to telecommunications facilities, working in developing nations with no existing telecommunications infrastructure, participating in rescue team work in times of disaster. System attributes differ widely according to the design philosophy of the implementors.

Advantages and Limitations.

The most compelling features of the non-geostationary DLMSC systems include the possibility of global access using low-power handheld terminals. It is clear that the proponents have mass markets in mind when using the small size, longer battery life, a wide variety of service choices as well as global access as selling points. All these are possible due to the low heights ranging between 10 354 and 695 km which reduce the path loss and delay associated with the GEOS system.



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