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Purpose of Carrier Sense in Sync Word Qualifier

Charles Gervasi
Expert 2270 points


The CC430 User's Guide contains this chart showing the options for identifying the Sync Word:

What is the purpose of the requiring the carrier strength to exceed a threshold?  Isn't a matching sync word sufficient to detect a packet?

  • 0
    TI__Genius 12480 points

    Hi,

    The sync word follows the preamble and is used for byte synchronization. Following the sync word is payload and possibly CRC. Detecting a sync word means that the radio has received a sync word, not the entire packet.

    The Carrier sense above threshold setting can be used to ensure that the received signal is strong enough so that the probability of receiving the whole frame/packet without errors is high. 

    If you want to see if a packet is received correctly the GDO pins can be setup to monitor that.

    Cheers,

    Jonas

  • 0 in reply to Firefighter
    Expert 2270 points

    Firefighter said:

    The Carrier sense above threshold setting can be used to ensure that the received signal is strong enough so that the probability of receiving the whole frame/packet without errors is high. 

    Thank you for answering. What I'm trying to understand is why you'd care about signal threshold.  If you receive the sync word at a very low signal strength, the probability of a bit error somewhere in the packet is high (simply b/c BER increases as SNR decreases).  There is still some chance, though, that you will receive the packet.  What is the advantage to ignore signals below a certain threshold? 

  • 0 in reply to Charles Gervasi
    TI__Guru* 86731 points

    There is always a chance that you will receive noise that looks like the sync word you are looking for. Waking up the MCU on "false" sync words will for example increase the current consumption on the MCU. If you know that the all your transmitters are relatively near by the receiver so that the RSSI is strong, you can use CS to gate sync search to avoid waking up on noise.

    BR

    Siri