Implementation of adaptive modulation as a fade countermeasure

Miodrag Filip*, Enric Vilar

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Three key problem areas associated with implementation of the concept of adaptive modulation as a fade countermeasure in a practical VSAT system are addressed in this paper. First, the heart of such a system, an adaptive modem, is described; such a device should be able to support a number of different modulation schemes, independently for modulation and demodulation. It is shown how an adaptive modulator can be built around a VLSI numerically controlled oscillator and that an adaptive demodulator is feasible once the universal carrier tracking loop is implemented with use of digital signal processing. As regards system operation, a data transfer scenario is described which highlights that it is important to expand the set of commands and responses of the data link control protocol in order to cater for the new abilities of the system. Finally, the article describes a computer simulation of system performance evaluation under dynamic rain fading propagation conditions and applied to a Ka band link. The results confirm earlier theoretical work and show great advantage over systems using fixed modulation schemes and fixed link propagation budget margins.

Original languageEnglish
Pages (from-to)181-191
Number of pages11
JournalInternational Journal of Satellite Communications
Issue number2
Publication statusPublished - 1 Mar 1994


  • Adaptive modulation
  • Direct digital
  • Fade countermeasures
  • Satellite communications
  • signal synthesis
  • VSAT


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