Frame Synchronizer Configuration Details - Safran CORTEX RTR NeXt Series User Manual

6.12

Frame Synchronizer configuration details

The technique used to identify the telemetry frames is the always the same: it consists of finding the synchronization
word which marks the beginning of the frame in the NRZL signal output by the bit synchronizer and in reacting correctly
to a loss of lock. This process is illustrated by next figure:
 SEARCH phase (S) :
In this mode, the frame synchronizer compares the signal bit by bit, until it matches the expected synchronization
word to within n bits where « n » is a programmable error factor, referred to as the synchronization threshold
(Allowed Errors). The synchronization threshold can vary from 0 to 64 (inclusive).
A programmable mask can also be applied to the synchronization word to ignore corrupted bits in the
synchronization word resulting from a spacecraft failure.
WARNING: A logical "1" in the mask correspond to a bit ignore. This means that for this bit
in the Sync Word, whatever the bit received, it is not compared to defined value in the Sync
Word.
 CHECK phase (C) :
Before moving onto the LOCK mode, the frame synchronizer will check « i » consecutive occurrences of the
synchronization word (to within n errors). The content of the telemetry block between two synchronization words is
not checked. During this phase, any occurrence of an incorrect synchronization word returns the frame
synchronizer to the SEARCH mode. « i » is programmable between 0 and 15 (inclusive) and referred as the CTL
(Check-To-Lock) threshold. To go from SEARCH to LOCK, the frame synchronizer must receive i+1 correct
synchronization words except when i = 0 (in that case, the frame synchronizer will transmit frames starting from the
frame containing the first occurrence of a correct synchronization word).
© Safran Data Systems – IMP000074 e14r1
Radio Telemetry Receiver
User's Manual
Figure 3: frame synchronizer state machine
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Ref. D104004
Is.Rev 07
Previous Ref.: DTU000567
Date: 21/06/2021
Safran Data Systems
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