In 802.11, I have been studying different types of CSMA/CA. And I come across the following
DCF - Distributed Coordination Function
- Relies on the ability of computers to physically listen before they transmit
- When a node wants to send a message:
- First listens to make sure that the transmitting node has finished, then
- Waits a period of time longer
- Each frame is sent using stop
- By waiting, the listening node can detect that the sending node has finished and
- Can then begin sending its transmission
- ACK/NAK sent a short time after a frame is received,
- Message frames are sent a somewhat longer time after (ensuring that no collision will occur)
I have few questions regarding DCF and its relationship with Clear Channel Assessment (CCA) (the threshold that indicates that the channel is busy)
Is DCF implemented using Energy detection or is it using preamble detection?
does the node that wish to transmit, detect energy at its antenna and then defer transmission? Is there a certain gain threshold (CCA threshold) in dbm that nodes should compare to and how do they calculate it?
Thanks, looking forward for your discussion or references.