The Scheduling Problem in Satellite Communications Systems

In satellite communications systems, the assignment of communications channels to users is a separate function from that of satellite acquisition and the establishment of actual communications circuits. A discussion of this scheduling problem is presented with emphasis on system analysis and mathematical formulation. The system factors pertinent to the scheduling problem are classified into three categories: 1) Satellite availability, e.g., coverage characteristics of the satellite-trunk configuration 2) Communications requirements, e.g., trunk priorities 3) Quality of communications, e.g., satellite-trunk compatibility. As a result of this approach, several computational procedures have been developed for schedule generation. A preliminary evaluation of the various methods in relation to total system performance indicates general criteria for selecting a scheduling method based on system characteristics. This paper also discusses a simulation study designed to evaluate a linear programming algorithm for scheduling specific configurations of medium-altitude communications satellites and trunks. The simulation was programmed in FORTRAN and run on the IBM 7090 computer. The scheduling algorithm selected maximizes total weighted systems communications time. For each configuration, the generated satellite-trunk schedules were evaluated in terms of system performance relative to total communications capability and its distribution in time.