High data rate UHF satcom

Users of UHF satcom require higher data rates to support today's sophisticated C4I mission planning and execution methods that are associated with the digital battlefield of the war fighter. Unfortunately, the UHF satcom channel has characteristics which prevent the implementation of advanced modulation techniques developed in the commercial industry. As an example, the QAM modulation format of cable modems cannot be transmitted through the limiters in the UHF satellites because it does not have a constant waveform envelope. For optimum UHF satellite transponder performance, the modulation must have a constant envelope. This paper discusses modulation formats that have a constant envelope and a bits/Hertz performance much closer to Shannon's (1949) limit than the current waveforms on UHF satcom. A set of waveforms is presented which is compatible with the UHF satcom specifications and provides the desired data rate improvement without requiring additional bandwidth. These waveforms allow a doubling of the current data rates without requiring additional bandwidth. In many applications these increased data rates are available without increased transmitter power.