Restrictions imposed for simultaneous high data rate telemetry and varying modulation index commanding

Specifications for the Air Force Satellite Control Network (AFSCN) identify limitations for the total modulation index and telemetry data rates permitted. This paper investigates the limitations on Space-ground link subsystem (SGLS) telemetry and command performance due to varying combinations of command modulation index and telemetry data rates. The downlink SGLS signal investigated in this paper includes the telemetry data and the commanding echo data. Ranging data is not included since the ranging modulation index is small and does not interfere with the telemetry data to any significant degree. Analysis of the downlink signal will be presented to show the limitations of the command modulation index and the telemetry data rate. Current specifications for the satellite Space/ground interface allow a telemetry data rate of 256 kilobits per sec (kbps) for any combination of downlink ranging, commanding, and telemetry modulation indices given the total modulation index is less than or equal to 3.0 radians (rad). It was found that the total modulation index is much more restrictive than the 3.0 rad specification and is dependent on the telemetry data rate