COMMAND RANGING & TELEMETRY UNIT CORTEX
Is.Rev.
Date:
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Page 96
The frame synchronizer synchronizes the frame in accordance with the SYN, CTL, LTS and Bit Slip parameters
provided to it:
Figure 45: Frame Synchronization Process
3.3.8.2.
PSK Ambiguity Solving
PSK ambiguity solving is performed by the frame synchronizer during the SEARCH phase (and
only during this
phase
). If the comparison between the expected synchronization word and a given window on the received
NRZL data stream is not successful, a second comparison is made after inversion of the telemetry data. If this
second comparison is successful (to within n bits), the signal inversion is confirmed and the frame synchronizer
switches to the CHECK phase.
S
L
S: SEARCH
C: CHECK
L: LOCK
SW 7,F incorrect
NT
SW 0,8
correct
SW 2,A
correct
SW 1,9
correct
SW 3,B
incorrect
SW 4,C
incorrect
SW 6,E
incorrect
SW 5,D
incorrect
NT
NT
NT
(1)
(1)
(2)
(3)
(3)
(3)
T
NT
T
Scenario: CTL = 2, LTS = 3
SW: Synchronisation Word
NT : frame not transmitted
T : frame transmitted
Received telemetry:
Frames 0 to 2: SW correct
Frames 3 to 7: SW incorrect
Frames 8 to A: SW correct
Frames B to F: SW incorrect
Dotted lines: alternate scenario (different frame contents)
(1): return to search mode if SW incorrect
(2): stay in lock mode while SWs are correct
(3): return to lock mode if SW correct
NT
NT
T
T
T
T
F
F
F
C
C
NT
T
F: FLYWHEEL
