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RTOS/CC1310: Related issues with the rfListenBeforeTalk example

user4959119
Expert 2215 points
Part Number: CC1310


Tool/software: TI-RTOS

Hi Team，

In a star network, the signal strength sent by the node will vary due to various factors. If the LSB function is used, how to ensure that all nodes can correctly perform carrier sensing.In other words, how do you determine the minimum security value for RSSI_THRESHOLD_DBM?

  • 0
    TI__Guru 58425 points
    HI Xi,

    I'm not sure what you mean by "security value" but as for RSSI threshold you would need to set this with the operation environment in mind. Try to consider what the noise floor in the environment is and at what signal strength you expect to receive at (at least).
  • 0 in reply to IUsedToBeARealPerson (M-W)
    Expert 2215 points
    The meaning of the security value is: If the threshold is too high, the far-distance node will think that the channel is idle and there is a possibility of conflict, how to avoid this situation.
  • 0 in reply to user4959119
    TI__Guru 58425 points

    Hi X,

    Do you mean that if you set the threshold to low (read as higher number RSSI) the nodes far away would mistake an active channel for idle? This is really something you would need to handle depending on the use case, ideally each node should take the noise floor around it into consideration as this put a hard limit on how low you can set it. 

    In the end, as you are using RSSI, you are limited to what each device can actually "hear". If two sensors are to far away from each other, they might not be able to sens each other when performing TX. The only thing you could try to avoid such a situation is to actually control when the nodes send data, trying to make it more spread out and deterministic. 

  • 0 in reply to IUsedToBeARealPerson (M-W)
    Expert 2215 points

    Yes，I happen to run into this problem. If my two nodes receive broadcasts at the same time and send them at the same time, the probability of failure is relatively large. It seems that CSMA is not perfect. How to increase the dispersion of their transmission time? I think of this way:

    RF_cmdNop.startTrigger.triggerType = TRIG_ABSTIME;
    RF_cmdNop.startTime = RF_getCurrentTime() + rand();

  • 0 in reply to user4959119
    TI__Guru**** 317180 points
    The example is just an example of how to make LBT from a software perspective.

    An example on how to make a more robust algorithm could be found in 9.2.2 in www.etsi.org/.../en_30022001v020401o.pdf
  • 0 in reply to TER
    Expert 2215 points
    Ok，can you help me answer this question? The employees have not responded for a long time.
    RTOS/CC1310: Time synchronization over the air