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LAUNCHXL-CC2640R2: Is it possible to use "3 tof initiators to 1 tof responder at the same time"

Stanley Tsao
Intellectual 330 points
Part Number: LAUNCHXL-CC2640R2


Hi,

TI TOF protocol uses 1 tof initiator and 1 tof responder. In this case, only the distance between each other can be calculated.

Is it possible to find out the position (x, y) of a responder using 3 initiators?

My understanding is that the 3 initiators should be synchronous with each other, using the same sync word and same frequency "at the same time", since the responder can only send one sync word on one frequency at one time, but it seems hard to achieve that?

Any comment on this case?

Thanks,

Stanley

  • 0
    TI__Guru 56335 points
    In order to increase the number of the data, you can use tof_passive project.

    Using 3 initiator with 1 responder will just confused the responder.

    For more information, please take a look at our software user's guide.
    dev.ti.com/.../index.html
  • 0 in reply to Christin Lee
    Intellectual 330 points

    Hi Christin,

    From the TI introduction below, my understanding is that ToF algorithm needs one master and one slave to transmit the same sync words on the same frequency at the same time. For the case of Trilateration, three locators and one target node are needed. Does it mean 3 ToF initiators and 1 ToF responder are needed, then how does the 4 ToF devices use the same sync words on the same frequency at the same time? According to your reply, "Using 3 initiator with 1 responder will just confused the responder.", it seems that Trilateration can NOT be done by current TI ToF algorithm. 

    Could you provide more information on how TI ToF completes Trilateration?

    Trilateration is where you know the distance between a reference node and a target node. This means that the possible locations seen by one locator constitute a circle, so typically three locators are needed to find a single common intersect point. (Assuming a 2D scenario)

    Time of Flight gives you the distance from the receiver to the transmitter.

    ../_images/trilateration.png

    Thanks,

    Stanley

  • 0 in reply to Stanley Tsao
    TI__Guru 56335 points
    You can implement ToF passive. As you can see in the user's guide that the ToF passive also listens to the sync word and can determine the distance.

    Let's say that you place Passive and Master with 3 meters between each other. And what you want to measure are the distance between
    1. (responder and initiator)
    2. (responder and passive)

    The initiator will start radio time when it sends out packet and stop the timer when it receives packet from responder. So
    the distance = (tick values )*( tick_to_meter radio) /2

    The passive will start radio time when it receive packet from initiator and stop the timer when it receives packet from responder.
    So the distance = (tick values) *( tick_to_meter radio ) - ((distance(master, responder)-distance(master, passive));

    You will need a central node to process all the data since passive won't know what the distance between initiator and responder is.
    Please take a look at the software user's guide for passive device operation.

    In summary, the trilateration can be achieved by 2 ToF passive + 1 ToF initiator + 1 ToF responder.
  • 0 in reply to Christin Lee
    Intellectual 330 points

    Hi Christin,

    Thanks for the explanation.

    About this description "the trilateration can be achieved by 2 ToF passive + 1 ToF initiator + 1 ToF responder."

    Is my understanding below correct?

    Thanks,

    Stanley

  • 0 in reply to Christin Lee
    Intellectual 330 points

    Hi Christin,

    Initiator and responder use ble connection mode (rather than advertising mode) to tx/rx sync words, is my understanding correct?
    If connection mode is used, then one initiator can only connect to one responder, right?
    And once the responder moves out of range, disconnects with initiator, it has to connect to other initiator but the other initiator may already connect to other responder, thus the moving responder may be untrackable since there might be no idle initiator to be connected to.

    How does TI ToF application overcome this situation?

    Thanks,
    Stanley

  • 0 in reply to Stanley Tsao
    TI__Guru 56335 points
    It's not in connection. TI ToF is a proprietary solution.
    All the information can be found here:
    dev.ti.com/.../index.html
    And one initiator only works with one responder.
    The sync words should only be shared with devices inside the same network, that being said others won't understand the packet and will not know what to send back.

    Please take a look at the documentation.
  • 0 in reply to Christin Lee
    Intellectual 330 points
    Hi Christin,

    I did study the TI ToF guide.
    There are advertising and connection modes in ble. Since you said that TI ToF is not in connection, does it mean advertising mode is used but with TI proprietary packet format such that only TI ToF initiator/responder can decode the packet?

    And for 1-to-1 connection, does it mean that I can not deploy two initiators and one responder at the same time? I'm wondering if two initiators can talk to the same one responder (tx/rx sync words) at the same time?

    Thanks,
    Stanley
  • 0 in reply to Stanley Tsao
    TI__Guru 56335 points

    ToF is just using BLE PHY but it's not BLE protocal.

    You can't use more than one initiator during the same time, as stated earlier, this will confuse the responder.
    And you will not be able to determine the distance too due to you won't be able to know that the responder sends the packet back because it receives initiator A's or initiator B's packet.

    If you want to use two initiator at different time slot, then it's ok. However, in this case, you can just use one passive and one initiator. So distances between initiator and responder/ passive and responder can be found after one burst instead of 2.