[amsat-bb] Re: Can D-Star work on VO-52?

Edward Cole kl7uw at acsalaska.net
Mon Feb 26 23:09:02 PST 2007

GMSK: <from wikipedia>

Gaussian minimum shift keying or GMSK is a kind 
of continuous phase 
keying. The baseband 
is generated by starting with a 
0/1 and a bit-clock giving a 
for each 
<http://en.wikipedia.org/wiki//wiki/Bit>bit. This 
is the type of modulation used in 
System for Mobile Communications (GSM) - although 
that system includes 
encoding of the bitstream, which makes the 
overall modulation behave like a kind of 
continuous phase 
Phase Shift Keying with constant 

The baseband 
is generated by first transforming the zero/one 
encoded bits into -1/+1 encoded bits. This -1/+1 
signal is then 
in such a way that the "boxcar" shaped +1/-1 
are transformed into 
signals. The baseband signal is then modulated 
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 
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 
advanced decoder techniques (including 
algorithm decoders), high density codings can be 
decoded efficiently. Currently the highest density coding being used is 5-GMSK.

GMSK has high 
efficiency, but it needs higher 
level than for instance 
phase-shift keying 
to reliably 
the same amount of <http://en.wikipedia.org/wiki//wiki/Data>data.

<Don't ask me what it means>

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 at hotmail.com

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