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Sync word detection

Sarath Nair
Prodigy 230 points

Other Parts Discussed in Thread: CC1101

Hi

I would like to know how the CC1101 or any transceiver in general for that matter, detects the sync word of a packet. Are there standard sync words being used by wireless protocols in the sub-1GHz frequency range?

I am aware of the PQT method of lessening the detection of false sync words but would be glad to know the actual mechanism used to detect these sync words. The application in use is a packet sniffer, so definitely we would not be knowing before hand the sync word used by the transmitter. Would be glad if anyone could help me out.

Thank you

Sarath Nair

  • 0
    TI__Guru*** 130875 points

    Hi Sarath,

    Basically the sync word is something known by both radios.  This is so that when a sync word is recieved it can be compared to the expected value. 

    You can set various conditions for sync word detection as indicated on page 43 of the datasheet.  I would recommend having a look at the sync word qualifier section. 

    I hope this would help.  You can also set conditions where a certain signal strength also needs to be met.

    Cheers,
    Yoda

  • 0 in reply to Lisa TI
    Prodigy 230 points

    Dear Yoda

    Thank you for your reply. I had gone through what you suggested earlier and found the different ways of detecting the signal strength using RSSI and Carrier sense. You had mentioned that sync word will be known by both radios. But I fail to understand how the packet sniffer, as I had mention earlier was the application, will get to know the sync word that the transmitter would use. This packet sniffer would have to deal with various nodes in a network and am not quite sure how it can figure out the sync words used by different transmittes. I somehow dont get my head to wrap around this concept.

    Thank you for your support.

    Sarath

  • 0 in reply to Sarath Nair
    TI__Mastermind 21125 points

    Sarath,

    Do make a general packet sniffer without knowing what to listen for seems like quite a challenge. The TI transceivers and SoCs can be set up to finction in a wide variety of ways and support different protocols and standards . You will need to know the basics of the network in order to manage to sniff this and the frame format of the radio signal (including SYNC word configuration) is one of those things you need to know.

    Kjetil.

  • 0 in reply to Kjetil
    Prodigy 230 points

    Thank you very much sir.

    As a last query, I would also like to know if the modulation technique used by the transmitter could be found out by noting the LQI value? Or do you have any ideas to detect the modulation a transmitter in the network uses?

    Thank you very much once again.

    Sarath

  • 0 in reply to Sarath Nair
    TI__Mastermind 21125 points

    No. Modulation, frequency used and data rate are the things you need to know.
    Making a general sniffer without knowing any of these is not a task i would have even considered trying to do.

    Kjetil