Institute of Electrical & Electronic Engineers
CSMA/CA is a slotted random access protocol that is widely used in indoor wireless systems such as the IEEE 802.11 and Zigbee. It is also used in wired systems such as HomePlug. In CSMA/CA, each node assigns itself a random backoff counter value uniformly polled from the range [0, CW - 1] when it has a new frame to be transmitted. This backoff value represents the number of idle slots it must wait before transmitting. At the start of each slot, the node will sense the state of the channel. If the channel is sensed idle, the node will decrement its counter. If the channel is sensed busy, the counter is suspended.