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CC430 How does the frequency offset estimation work when there are multiple transmitters?

Bob Chou
Intellectual 530 points

Hi there,

Now I'm working on CC430 and doing single transmitter--multiple receivers experiments, which tested the FREQOFF_EST working fine on all the receivers. But I am curious about how would the carrier frequency offset estimation work when I have multiple transmitters transmitting simultaneously. For example when I assign them to different channels(FDMA) or scheduling the transmissions in a time sequence(TDMA)? Would the register react that fast and store the estimation for each channel? How would it work?

Thanks in advance!~

  • 0
    TI__Guru**** 317180 points
    The receiver can only receive from one transmitter at a given time. And only one transmitter should transmit in a channel at a given time. The frequency offset estimation is done on each received packet. If you want to store the estimate you have to read out the estimate for each packet and store it in a data structure. The FREQOFF_EST register is overwritten for each received packet.

    What are you planning to use the estimate for?
  • 0 in reply to TER
    Intellectual 530 points

    Thanks TER,

    With the estimate I want to evaluate the performance of the RF crystal on each chip, like how stable they are oscillating and the errors in PLL. I want to let the estimate help me analyze them and I guess it contains those information. Would you think that is possible?

  • 0 in reply to Bob Chou
    TI__Guru**** 317180 points
    Remember that the estimate will the frequency offset between the Tx and Rx side. You can risk that both the Tx and Rx side have the same offset so the frequency offset you read is zero but the RF frequency could still have a large offset compared to the programmed frequency.

    As long as you are aware of this you can use the offset to keep track of if it changes over time etc. If you have a communication between Tx1 and Rx1 and Rx2, Rx1 and Rx2 can send the estimate back to tx1. Then the next time tx1 sends to Rx1 the tx frequency could be adjusted according to the offset between tx1 and rx1 and the same when it sends to rx2.
  • 0 in reply to TER
    Intellectual 530 points

    Thank you so much TER, that inspired me a lot!

    One thing I'm not clear is that could I physically adjust the RF frequency from its origin? Because I want not only compensating it when TXing or RXing with a specific one but also adjusting all the RF frequency to the same synchronized level. To do that I may have to make all the XT2 reference frequency in the frequency synthesizer to be the same?

  • 0 in reply to Bob Chou
    TI__Guru**** 317180 points
    Please look at section 25.3.3.3.1 in www.ti.com/.../slau259e.pdf

    If you have found that the offset between tx1 and rx1 is offset1 you can set FSCTRL0.FREQOFF = offset1. For the next link equal to offset2 etc.