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CC2530 measure Time of flight

Abhishek Trivedi
Prodigy 170 points
Other Parts Discussed in Thread: SIMPLICITI

Hi,

I want to measure the time between the transmission and reception of a packet in CC2530.

Can anybody tell me how to do it programmatically?

Would really appreciate it.

Thanks.

Abhishek.

  • 0
    TI__Mastermind 19350 points

    It would seem that measuring time of flight would require unbelievably accurate clock synchronization on the devices involved in the measurement. Therefore, do any of the links that I included at the bottom of this thread help:

    http://e2e.ti.com/support/low_power_rf/f/158/p/124454/446386.aspx#446386

     

  • 0 in reply to Dirty Harry
    Prodigy 170 points

    Hey Harry,

    Thanks for the response.

    what if i measure the time of flight in the same device. Like I capture the timer when it sends the data and again capture the timer when it receives the ACK that the message has been received by the the other device. Can I do this?

    Abhishek.

  • 0 in reply to Abhishek Trivedi
    Prodigy 170 points

    Hi Harry,

    I started a timer, captured the value in the end device before sending a message to a router  and when I got the ACK from the router that the message has been received by setting the txOptions = AF_MSG_ACK_REQUEST, I stopped the timer in the same end device and captured the value again  

    And then i take the difference between the two values.

    The problem is that , when I take the end device farther from the router , the difference in the timer value doesnt change , I cannot see any variations when I take the end device away from the router.

    Can you tell me what can be the problem?

    Thanks

    Abhishek.

    Note: The difference in the timer value for several readings for the same position of router is not constant.

  • 0 in reply to Abhishek Trivedi
    TI__Mastermind 19350 points

    APS Ack happens an eternity after the message is sent and MAC Ack received. Although the round-trip time of an 802.15.4 transaction is still not close to time of flight, it is something. But regardless, the access to the Timer2 time stamps is buried in the MAC library and not accessible to you ... I'm surprised that you didn't learn all of this in the links that are referred to in the post that I suggested above. Anyway - maybe you would be better off to use the SimpliciTI for your time of flight experimentations, since you have full access to all source code - no libraries in there.

     

  • 0 in reply to Dirty Harry
    Prodigy 170 points

    Hey Harry,

    Thanks for replying. I learnt all of that, that is why I was looking for a different approach to measure TOF, because I didnt want to get in the complications of synchronization of two different devices. That is why I just thought of using the same device. Thanks for letting me know that TOF is not even close to what I was doing. Maybe I'll just stick to LQI values to find the distance. 

    What do you think should I use RSSI or LQI values for accurate distance measurement between two devices?

    Thanks.

    Abhishek.

  • 0 in reply to Abhishek Trivedi
    TI__Mastermind 19350 points

    Customer after customer has shown that you cannot accurately and reliably measure distance with LQI or RSSI in the 2.4 GHz space with an 802.15.4 radio. The only successful locationing systems are built by sending one or both of the aforementioned measurements to a powerful number crunching machine that runs complicated hueristics to make a best guess of the location.

     

  • 0 in reply to Abhishek Trivedi
    Prodigy 40 points

    Hei Abhishek.

    Sorry to intrude in this discussion, but I wonder if you could evolve in your application.

    I'm starting a similar development and have many questions about which "distance calculation approach" should I use.

    You ended up using using the RSSI? If yes, have you used the Kalman Filter?

    I would be very grateful if you could pass me any information.

    Thanks in advance.

    Cristiano

  • 0 in reply to Cristiano Tenuta
    TI__Mastermind 19555 points

    This is very interesting topic, and the only possibility to be close to ToA/F with a IEEE 802.15.4 radio will be to utilize the SFD (Start of Frame Delimiter) signal in hardware with a timer. This can be used for symbol timing, and synchronization. However, like DH says it can end up with complex algorithms.

    Kalman filtering is a great algorithm to use for RSSI analysis.

    RSSI BASED TRACKING ALGORITHMS

    Enjoy,
    LPRF Rocks the World

  • 0 in reply to Morten Braathen
    Prodigy 40 points

    If tunned well, Kalman filtering is the best application for RSSI filtering (no noise, no delay) but nevertheless one signal is not enough for RTLS (since RSSI is not reliable under all circumstances). That's why I think that we have to force the multinode RSSI measurement and multinode locating algorithms.

    LPRF Rocks was shared a very interesting paper above which summarizes the possible solutions.

    Regards,

    Onur