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Original question:

Medium Access Scheme in bluetooth low energy

CC2650: Does Carrier-sense multiple access(CSMA) technique is implemented for Bluetooth?

Kainat Altaf
Prodigy 90 points
Part Number: CC2650
Other Parts Discussed in Thread: BLE-STACK

Hey!

Suppose we have multiple devices which are advertising/sending data at the same channel. How can we avoid RF collisions? Is there a CSMA/CA scheme which does the trick, or is it simple TDMA(Time-division multiple access) without any knowledge at the sending side about the channel occupancy? Where can I find more info about the Medium access techniques used in Bluetooth low energy?

  • 0
    TI__Guru 57865 points

    Hi Kainat,

    There are three advertising channels that advertising packets are transmitted on based on an advertising interval (typ 20-2000ms). There is an added advertising delay each event, which would help with collision avoidance, although best is to enter a connection as soon as possible and utilize the 37 data channels.

    With BT5, there is the addition of extended advertising, which utilizes the data channels to host the advertising payload while the advertising channels only introduce the pointer.

  • 0 in reply to J Lindh
    Prodigy 90 points

    Hi Lindh,

    What I understand from your answer is that Bluetooth 4 does not utilize CSMA. If we want to avoid collisions then we have to add time delay to every advertising event. Am I getting it right?

    My goal is to make connection-less communication on Bluetooth 4. That is why I want to avoid collision without entering into a connection.

  • 0 in reply to Kainat Altaf
    TI__Guru 57865 points

    Hi,

    The random delay is added automatically by the BLE-Stack, per the core specification. The challenge with a Broadcaster/Observer system is that there is no security and the communication in one directional meaning you have no way of knowing if your packet came through.