Safran CORTEX CRT Quantum - Downlink Tones Processing; Tone Acquisition; Phase-Locked Loop; Doppler Compensation (ESA, ESA-Like, Hybrid Ranging and USB Standards)

COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Ref. DTU 100042
Is.Rev. 5.17
Date: Dec.
03, 2021Sept. 30, 2021
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Page 153
3.6.3. Downlink Tones Processing
3.6.3.1. Tone Acquisition
3.6.3.1.1. Phase-Locked Loop
Major tone acquisition for all standards as well as minor tones acquisition and demodulation for the INMARSAT
and LMCO standards, is performed by a 2nd-order digital PLL. The loop bandwidth (2Bn) is programmable
between 0.1 and 8 Hz. The RAU features automatic loop bandwidth adjustment at tone acquisition for fast
acquisition in case of high Doppler rate.
3.6.3.1.2. Doppler Compensation (ESA, ESA-like, Hybrid Ranging and USB Standards)
Since satellite range measurement is not instantaneous, the major challenge consists in being able to accurately
track the satellite all along the ranging sequence (taking care of zero-crossing on the tone phases) and to
compensate the phase measurements on the minor tones for the satellite motion prior resolving the ambiguity.
This compensation is of paramount importance in the case of LEO satellites where using raw phase data for the
minor tones would make the ambiguity solving impossible.
Doppler compensation is at two levels:
 Doppler compensation during minor tone integration.
 Correction of the phase measurements on the minor tones so that all minor tone phases are related to
a single time reference corresponding to the time-stamp in the ranging transaction response message
(first phase measurement on the major tone).