AIS Transceiver Issue (GMSK Modulation)

Hi,

I am working on AIS Transceiver , for that I am getting help from " ship tracking using AIS Signal MATLAB Example " and File from MATLAB File Exchange " AIS Decoder by Mike Donovan " . The issue is that I have finalized my receiver with proper demodulation and decoding and it's working fine. For testing I am using capture data provided by above resources and its decoding 100% correctly.

Now I am working on AIS transmitter in which I have take one packet from MATLAB example capture data , get its Packet Bits and on this packet I perform gmsk modulation with same setting (BT,sps,span) and made a modulated signal.

The issue is that I am not getting the same packet signal from which I get packet bits. The captured packet have smooth transistion like sine way, while the shape of modulated signal from comm.gmskmodulator don't have this structure and due to this discrepancy my demodulatoion chain failed to decode data. I guess there is some post processing on capture signal but i am not getting it. I am attaching zoom in pictures of both modulated signal and capture signal real plots for reference.

[Hamza]

@Mike Donovan can you please help in this query?

[Hamza]

@Walter Roberson can you help me with this query?

[Walter Roberson]

@Hamza

Sorry, I do not have any experience with that topic.