# Re: Can D-Star work on VO-52?

• Subject: [amsat-bb] Re: Can D-Star work on VO-52?
• From: Edward Cole <kl7uw@xxxxxxxxxxxxx>
• Date: Mon, 26 Feb 2007 22:09:02 -0900

```GMSK: <from wikipedia>

Gaussian minimum shift keying or GMSK is a kind
of continuous phase
<http://en.wikipedia.org/wiki//wiki/Frequency-shift_keying>frequency-shift
keying. The baseband
<http://en.wikipedia.org/wiki//wiki/Modulation>modulation
is generated by starting with a
<http://en.wikipedia.org/wiki//wiki/Bitstream>bitstream
0/1 and a bit-clock giving a
<http://en.wikipedia.org/wiki//w/index.php?title=Timeslice&action=edit>timeslice
for each
<http://en.wikipedia.org/wiki//wiki/Bit>bit. This
is the type of modulation used in
<http://en.wikipedia.org/wiki//wiki/Global_System_for_Mobile_Communications>Global
System for Mobile Communications (GSM) - although
that system includes
<http://en.wikipedia.org/wiki//wiki/Differential_encoding>differential
encoding of the bitstream, which makes the
overall modulation behave like a kind of
continuous phase
<http://en.wikipedia.org/wiki//wiki/Binary_Phase_Shift_Keying>Binary
Phase Shift Keying with constant
<http://en.wikipedia.org/wiki//wiki/Envelope_detector>envelope.

The baseband
<http://en.wikipedia.org/wiki//wiki/Signal_%28information_theory%29>signal
is generated by first transforming the zero/one
encoded bits into -1/+1 encoded bits. This -1/+1
signal is then
<http://en.wikipedia.org/wiki//wiki/Electronic_filter>filtered
in such a way that the "boxcar" shaped +1/-1
<http://en.wikipedia.org/wiki//wiki/Pulse>pulses
are transformed into
<http://en.wikipedia.org/wiki//wiki/Normal_distribution>Gaussian-shaped
signals. The baseband signal is then modulated
using
<http://en.wikipedia.org/wiki//wiki/Frequency_modulation>frequency
modulation, producing a complete GMSK signal. If
the Gaussian shapes do not overlap, then the
modulation form is called 1-GMSK. If the slots
overlap 50% (½), the modulation is called 2-GMSK, and so on.

The more the bits overlap, the more significant
<http://en.wikipedia.org/wiki//wiki/Intersymbol_interference>intersymbol
interference (ISI) from adjacent bits will be,
and for 4-GMSK and up, the ISI seen at any
particular point in time is stronger than the
signal from the bit currently being decoded. By
looking at greater parts of the signal using
<http://en.wikipedia.org/wiki//wiki/Viterbi_algorithm>Viterbi
algorithm decoders), high density codings can be
decoded efficiently. Currently the highest density coding being used is 5-GMSK.

GMSK has high
<http://en.wikipedia.org/wiki//wiki/Spectral_efficiency>spectral
efficiency, but it needs higher
<http://en.wikipedia.org/wiki//wiki/Electrical_power>power
level than for instance
phase-shift keying
(<http://en.wikipedia.org/wiki//wiki/QPSK>QPSK)
to reliably
<http://en.wikipedia.org/wiki//wiki/Communicate>communicate
the same amount of <http://en.wikipedia.org/wiki//wiki/Data>data.

<Don't ask me what it means>

73,
Ed - KL7UW
======================================
BP40IQ   50-MHz - 10-GHz   www.kl7uw.com
144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
DUBUS Magazine USA Rep dubususa@hotmail.com
======================================
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