Multiple Access with Collision Avoidance for Wireless

[2] Furthermore, it is the foundation of many other MAC protocols used in wireless sensor networks (WSN).

After successful reception, node B replies with an acknowledgement frame (ACK).

[1] To sum up, a successful data transfer (A to B) consists of the following sequence of frames: MACAW is a non-persistent slotted protocol, meaning that after the medium has been busy, for example after a CTS message, the station waits a random time after the start of a time slot before sending an RTS.

If for example nodes A, B and C have data fragments to send after a busy period, they will have the same chance to access the medium since they are in transmission range of each other.

Node D assumes that its RTS was not successful because of collision and hence proceeds to back off (using an exponential backoff algorithm).

Other nodes overhearing an RRTS defer for two time slots, long enough to hear if a successful RTS–CTS exchange occurs.

To summarize, a transfer may in this case consist of the following sequence of frames between node D and C: Additional back-off algorithms have been developed and researched to improve performance.

[5][6][7][8][9] The basic principle is based on the use of sequencing techniques where each node in the wireless network maintains a counter which limits the number attempts to less than or equal to the sequence number or use wireless channel states to control the access probabilities so that a node with a good channel state has a higher probability of contention success.