COMMAND RANGING & TELEMETRY UNIT CORTEX
Is.Rev.
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Page 38
3.3.2.
IF Carrier Acquisition
3.3.2.1.
Acquisition Algorithms
3.3.2.1.1. FFT
– Wide Spectrum
Based on spectrum analysis with aliasing. This algorithm is fast and rather robust to noise. In case of low signal
to noise ratio, the acquisition performance depends on the demodulation scheme.
3.3.2.1.2. FFT
– Narrow Spectrum
Based on spectrum analysis. This algorithm is robust to noise and Doppler rate. Very low bit rates require higher
FFT resolution; hence acquisition is slower and proportional to the acquisition range and loop bandwidth.
3.3.2.1.3. Scanning Sweep
The software sweeps the acquisition range by regular steps and selects the most significant signals. Acquisition
time is directly proportional to the acquisition range, the symbol rate and the loop bandwidth.
3.3.2.1.4. Highest Spectrum Line
Based on spectrum analysis. Selection of the highest spectrum line rising out of the noise. Used for acquiring a
remnant IF carrier, PM modulated by a sub-carrier or a PCM signal, with a modulating index such that the side
lobes are lower than the carrier.
Highest
signal
Center frequency
Noise + Margin
Threshold
Frequency
|A| (dB)
Ex: Video Signal
Peak-to-peak acquisition range
