Rack-Mount RDMS
TM
Telemetry Receiver
163
Quasonix, Inc.
11 Appendix C
– Phase Noise Compensation
11.1 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 248, shows all of the possible paths the phase trajectory can take over a period of
seven bits. Figure 249 shows the two unique paths, based on whether the second bit is a 1 or 0.
Figure 248: Ideal PCM/FM Phase Tree (h = 0.7)