GMSK: Gaussian minimum shift keying

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GMSK Gaussian minimum shift keying
Brian Kessler EE-194SDR
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Uses

• Like most communication protocols, can be used to
  transport data of any kind voice, files,
  graphics.
• Important due to its use in the GSM mobile
  telephone system
• Has built in error correcting in the signal

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How?

• A digital data signal (1,0) is converted into a
  signal of 1 and -1 in the amplitudes.
• The new signal is sent through a filter that
  transforms it into a Gaussian signal.
• The signal is frequency modulated to finally
  produce the GMSK signal to be transported.

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Visually
The resulting Gaussian bursts
The 1/-1 signal
After FM encoding
After added together
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Overlap

• After being converted to a Gaussian signal, there
  is sometimes overlap in the bits.
• The signal is designated (n)-GMSK, where n is the
  number of overlap, with 1 being no overlap.
• This allows high density signals to be sent, as
  well a the retrieval of lost bits using Viterbi
  algorithm.

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Sources

• Wikipedia http//en.wikipedia.org/wiki/GMSK
• University of Hull
• http//www.emc.york.ac.uk/reports/linkpcp/appD.pd
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