RF collisions

Discussion in 'Wireless & RF Design' started by jarblue, Oct 5, 2011.

  1. jarblue

    Thread Starter New Member

    Dec 15, 2010
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    Say I have two rf transmitters that I would like to transmit 4 bits each to a single rf receiver on the same frequency. What is to keep the two transmissions from scrambling when they reach the receiver at the same time.
     
  2. BillO

    Well-Known Member

    Nov 24, 2008
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    136
    If you do not put in place some sort of protocol, there will be noting to stop this from happening.

    Normally, to eliminate collisions, you need transceivers at all ends. That way each sending device knows what the other is doing and they can negotiate an appropriate order for their deliveries.
     
  3. MrChips

    Moderator

    Oct 2, 2009
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    As BillO, says, you have to create a protocol. Four bits would not do it. You have to include error detection bits such as parity bits.

    When the two transmitters send their data, they have to wait for a response. Since the messages collided the receiver is unable to respond.

    Each transmitter will time-out while waiting for the response.
    Both transmitters will resend their message after waiting for a predetermined delay time. The delay time for each transmitter can be determined in a number of ways. It can be a random time or in can be based on priority. This reduces the chance that the retransmitted messages will collide again.
     
  4. jarblue

    Thread Starter New Member

    Dec 15, 2010
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    0
    What I am aiming for here is as simple of a circuit on the transmitter side as possible. Ideally it would not involve resending any thing. Basically your are saying to keep collisions from happening and to keep the circuit and transmitted signal as simple as possible (which is ideal for this case) I need to have a receiver for each individual transmitter?
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    Well, it depends on your application and how critical is reliability. If you only had two transmitters and wanted to keep things simple, I would have each transmitter send the same data twice with a time delay between data transmission. If you have the delay on the first transmitter different from the delay on the second transmitter then you are guaranteed that the messages will get through without collision.
     
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