Guard band reduction in open loop tdma communications

Abstract

An open loop TDMA communications system includes a transponder located on a spacecraft in quasi-synchronous earth orbit; a reference station periodically transmits a timing marker through said transponder to a plurality of geographically separated earth stations. Spacecraft position varies within controlled limits, and at any time the reference station has available to it information respecting the spacecraft's position. The reference station transmits, along with the timing marker, a spacecraft position index signal which is received at the geographically separated stations. Each of the stations detects the spacecraft position index signal, and based on its own geographic location, translates the spacecraft position index into a transmit timing adjustment. The transmit timing adjustment is employed to vary transmit timing from nominal and to thereby reduce the extent of the guard time used to ensure non-overlapping of bursts from the plurality of stations at the transponder.