Safran RTR-NeXt User Interface Manual page 126

4.7.9.12 GMSK.
In GMSK mode, three demodulators are available.
GMSK is naturally differentially encoded hence phase ambiguity is solved by construction.
Note : . By precoding the GMSK signal at the transmitter, the inherent differential encoding can be removed, and so the
BER can be halved. Mathematically the equation of pre-coder GMSK is expressed as:
Where D(k) is the input NRZ bit stream
The precoded GMSK is defined in CCSDS 413.0-G (Green Book May 2003).
If at the transmit side, the GMSK is not precoded, then Differential has to be selected.
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Radio Telemetry Receiver
Graphical User Interface Manual
A(k) = (-1)^k*D(k)*D(k-1)

{+/-1}.
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Ref. D130486
Is.Rev 03
Customer Ref.: -
Date: 21/06/2021
Safran Data Systems
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Page 126