Gaussian minimum shift keying modulator [for satellite communication]

Modern satellite systems must transmit ever increasingly large amounts of digital data. A number of techniques are available to do this: (1) higher transmit and receive frequencies, (2) better management of existing frequencies, (3) the use of efficient source encoding techniques and 4) the use of spectrally efficient modulation techniques. A relatively new satellite communication scheme, Gaussian Minimum Shift Keying (GMSK), addresses many of these techniques. GMSK's main attributes are constant envelope, spectral efficiency, error rate performance and self-synchronizing capability. GMSK is an especially desirable modulation technique where satellite adjacent channel interference could be a significant problem. However, GMSK requires greater on-board digital processing which, due to advances in IC processing, has become available only recently. This paper describes the prototype implementation and test of a GMSK modulator.