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Compact RDMS
TM
Telemetry Receiver
41
Quasonix, Inc.
13 Appendix D – Phase Noise Compensation
13.1 Trellis Demodulation Basics
Legacy Single-Symbol Detection:
Uses basic Limiter-Discriminator operation
Frequency in this bit above nominal
→
data = 1
Frequency in this bit below nominal
→
data = 0
Makes no use of adjacent symbols for error correction
Trellis Detection:
Uses the phase tree for data detection
Uses adjacent symbols to help decide on “iffy” bits
Improves BER performance by 3.5 to 5.0 dB
The Phase Tree shown in Figure 14, shows all of the possible paths the phase trajectory can take over a period of
seven bits. Figure 15 shows the two unique paths, based on whether the second bit is a 1 or 0.
Figure 14: Ideal PCM/FM Phase Tree (h = 0.7)