Synchronization of earth stations to a switching satellite using non-coherent frequency shift keying

Abstract

<p>In a space division multiple access/spacecraft switched-time division multiple access (SDMA/SS-TDMA) satellite system, precise synchronization between the satellite switching sequence and the earth stations is required. Fine synchronization can be achieved by transmitting non-coherent frequency shift keying (FSK) signals. The timing error between the satellite and the earth station time bases is defined on-board the satellite by the sync-wnidow modulation of the sync bursts (FSK) signals). A measure of the timing error, i.e. the error voltage, is obtained at the receiver and fed to the timing circuits. Depending on the value of the error voltage, the timing circuits shift the earth station time base accordingly so as to reduce the timing error. This procedure is repeated until synchronization is achieved, i.e., the timing error becomes zero.</p> <p>Two sources of noise (uplink and downlink) are considered in this synchronization loop. The noise affects the number of iterations required to achieve synchronization as well as the accuracy of the synchronization in the steady state. The study is supported by a digital computer simulation of the envelope-detected signal in the receiver.</p>