Irfan Ali

Doppler as a new dimension for multiple access in LEO satellite systems

The problem of flow control for little LEO satellite communications systems is studied. In these systems the satellite functions as a ‘bent pipe’ transponder for messaging between small terminals and a command and data acquisition (CDA) earth station. A novel scheme for averting traffic overflow on the inbound channel (from terminal to CDA), which we call ‘Doppler-based multiple access’ (DBMA), is introduced. In DBMA the CDA specifies a subset of the visibility footprint as a region of eligibility (ROE). Only terminals located in the ROE are permitted to transmit. By varying the size and location of the ROE, effective flow control on the inbound channel is achieved. The ROEs are specified in terms of parameters of the Doppler frequency shift versus time curve observed at terminals on the outbound downlink channel (from satellite to terminal). The effectiveness and elegance of the DBMA protocol are illustrated through computer simulation.