COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Ref. DTU 100042
Is.Rev. 5.17
Date: Dec.
03, 2021Sept. 30, 2021
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It cannot be duplicated or distributed without expressed written consent.
3.3.1.3.4.3. Propagation Factor
The trellis Propagation Factor parameter controls the contribution of previous symbols to computing the states
metrics of the detector trellis at each stage. Expected value is from 0.4 to 0.9.
In perfect conditions (no signal distortion), the optimum value that minimizes the BER for a given
is equal
to 0.9.
By reducing this factor, to 0.6 for example, the receiver becomes more robust against signal distortion (like
phase noise and mod index variation) by limiting the propagation of the memorized information in the trellis and
making more “local” decisions.
Nominal mode
In this mode, the MS-FM demodulator uses the optimal value 0.9. This mode is suitable only for
numerically modulated PCM/FM signal and reliable transmission channel (without noticeable
distortions). For analog modulator or unreliable transmission channel, this mode is not recommended
because the detector in this case is very vulnerable to signal distortion
Manual Mode
Selecting this mode, the user can define the Propagation factor in the Propagation Value field. We
recommend always using this mode with a propagation value of 0.6 regardless of the channel quality.
Using this configuration in perfect conditions, the degradation, compared to the optimal value (0.9), is
only 0.5 dB. However, the detector is much more robust against any channel imperfections.
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