Saturday, August 24, 2019


The demodulated symbols of an ARINC635 HFDL burst are shown below in terms of 180-symbol long frames. Doppler offset correction and symbol timing estimation were done manually using GNU octave.

According to the ICAO ARINC635 HFDL physical layer description (see correction here and here), 30 data symbols alternate with 15 known symbols. The data symbols are scrambled with a 120-bit long scrambling sequence which explains the 180-symbol period. This scrambling sequence is generated by an LFSR, and it can be checked that the sequences A, M1, and T are generated by LFSRs as well.

It should be easy to implement this mode in gr-digitalhf.

HFDL burst
See also DK8OK's excellent posts about ARINC635 HFDL.

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