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Browse Prior Art Database

LITTLE LOW EARTH ORBIT (LITTLE LEO) COMMUNICATIONS SYSTEM

IP.com Disclosure Number: IPCOM000009644D
Original Publication Date: 2000-Jan-01
Included in the Prior Art Database: 2002-Sep-06
Document File: 1 page(s) / 62K

Publishing Venue

Motorola

Related People

Allen L. Davidson: AUTHOR [+2]

Abstract

Low earth orbit satellite systems for low-speed data communications have been proposed - the so- called "Little LEO" systems. Data transmissions on the uplink consist of short (< 500 ms) bursts of data sent in time slots. Each burst is sent on a frequency which is randomly picked from a bank of available frequencies.

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0 M MOTOROLA Technical Developments

LllTLE LOW EARTH ORBIT (LITTLE LEO) COMMUNICATIONS SYSTEM

by Allen L. Davidson and Michael L. Needham

  Low earth orbit satellite systems for low-speed data communications have been proposed - the so- called "Little LEO" systems. Data transmissions on the uplink consist of short (< 500 ms) bursts of data sent in time slots. Each burst is sent on a frequency which is randomly picked from a bank of available frequencies.

  The Little LEOs have proposed that their sys- tems could share spectrum with existing land- mobile voice communication systems for the uplink, with little or no interference to the existing systems. To prevent such interference, the Little LEOs have proposed a scheme whereby the satellite would scan the available channels, then indicate an "OK to send" status to ground units for those channels found to be idle.

  However, there is a problem with "Doppler smearing" of signals from earth to a Little LEO satellite, which has a proposed footprint as big as the continental United States. That is, earth signals originating from in front of the satellite's directional path would be shifted higher in frequency (because the satellite is approaching them at a high speed), while those originating from behind would appear lowered in frequency. So, when the Little LEOs try

to share frequencies with existing land-mobile ser- vices, the whole spectrum may appear to be occu- pied, even when it may not be. The spaces between the assi...