3
rd
Generation Dual Channel
Compact RDMS
TM
Telemetry Receiver-Combiner
120
Quasonix, Inc.
Figure 165: Phase Trajectory Never Forgets
12.1.1 Trellis Demodulation Summary
The basic premise of trellis demodulation is that the signal from the transmitter follows a known path through the
phase tree. When the demodulator knows this, it can use a sequence of several symbols to help make better decisions
about each individual bit. This process improves BER performance by about 3.5 to 5 dB over conventional FM
detection. However, this assumes that the transmitter is really following the "known" and "correct" phase tree, and
this assumption is NOT always true.
High phase noise can reduce the trellis detection gain because phase noise corrupts the tree. The following figures
illustrate the differences in trellis detection gain depending on the amount of phase noise introduced.
Figure 166: Trellis Detection Gain with Zero to Minimum Phase Noise