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Optimal RX / ACK timeouts and maximal retries

mx_de
Prodigy 220 points
Other Parts Discussed in Thread: CC2510

Hi All,

  I am developing a RF communication protocol using CC1111 and CC430, but I have a question, does anyone of you know how to calculate optimal timeout for ACKs before re-sending the packet and also after sending the ACK how long should the receiver wait to receive the next packet before re-sending the ACK? right now I have it both at 500 Milliseconds (configurable). And also number of retries before aborting the procedure, right now I have maximum 5 retries. I really don't know if there are any standards or if it needs to be compliant with any government regulation as it will be distributed in the future to customers. That is why I come to you, to see if you can shed any light, I've been looking on the Web, but haven't found anything.

  Any help which would point me in the right direction would be appreciated.

 Thanks,

   mx_de

  • 0
    Expert 2056 points

    I'd like to know, too.  For the CC2510, there's a variable sReplyDelayScalar which gets set with some radio settings.  It's used in NWK_REPLY_DELAY.

    void MRFI_ReplyDelay()
    {
      bspIState_t s;
      uint16_t    milliseconds = sReplyDelayScalar;

    ...

                                          processing time on peer
                                          |   round trip
                                          |   |      max number of replays
                                          |   |      |             number of backoff opportunities
                                          |   |      |             |         average number of backoffs
                                          |   |      |             |         |                                    */
    #define   PLATFORM_FACTOR_CONSTANT   (2 + 2*(MAX_HOPS*(MRFI_CCA_RETRIES*(8*MRFI_BACKOFF_PERIOD_USECS)/1000)))

    ...

        /* processing on the peer + the Tx/Rx time plus more */
        sReplyDelayScalar = PLATFORM_FACTOR_CONSTANT + (((bits/dataRate)+5)/10);

  • 0
    TI__Mastermind 36395 points

    mx_de

    For Sub1GHz radios like the CC1111 and CC430x the most important parameters are which regulatory requirements will your final system have to pass. If you plan on shipping stuff in Europe you have to comply with ETSI regulation and here in the US it would be the FCC regulation. In Europe there is an note in the requirements that your transmitter has to perform a "Clear channel Assessment" before transmitting. Where the US based FCC does not have that requirements. Here in the US you have to perform frequency hopping to enable higher output power that 0dBm.

    That being said, generally there is a lot of work going on right now in figuring out what the best low power wireless MAC is, here is a link to a good paper. 

    http://www.sics.se/~adam/dunkels11contikimac.pdf

    Regards,
    /TA