[Discuss-gnuradio] NRZI decoding

[irene159]

Hi,
I am trying to get a better understanding of different receiver blocks. 
In the ais-tools-gnuradio-1.0.2 (http://funwithelectronics.com/sdr/ais.php)
source code (aisrcv-usrp.py), once symbols are mapped to bits after
demodulation and symbol clock recovery the signal is sent to the following
blocks:
gr.diff_decoder_bb() and ais.invert10_bb()
I suppose gr.diff_decoder_bb() is a differential decoder and
ais.invert10_bb() only inverts bits (a 0 becomes a 1 and inversely). Am I
wrong?
I have done some documentation research on AIS and the signal is NRZI
encoded before modulation. I don’t understand how these blocks perform NRZI
decoding. Can someone please give me a brief explanation?
Thanks,
Irene


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