Continuous Descrambling - Safran CORTEX CRT Quantum User Manual

3.3.16.4.Continuous Descrambling

The continuous descrambling mode is a non-CCSDS descrambling method. In this configuration, the
descrambling is performed before the frame sync. It is only available in a TMU with Viterbi and custom LFSR
scrambling licenses. The corresponding scrambling is also implemented in the Telemetry Simulation.
The received bits are passed to the LFSR. The LFSR generates the descrambling bit based on the polynomial.
Then the received bit is XORed with the descrambling bit. For a polynomial of degree p, it takes p received bits
for the descrambler to be synchronized. The LFSR is never reset during the reception. Hence, the sync word is
also descrambled.
The following figure shows an example of the continuous scrambling and descrambling operations for the
polynomial used in G3RUH encoding:
17 12
�� = �� + �� + 1
© Safran Data Systems
COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Figure 50 Continuous Scrambling and Descrambling
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Ref. DTU 100042
Is.Rev. 5.17
Date: Dec.
03, 2021Sept. 30, 2021
Page 108