A CSMA-based MAC protocol for WLANs with automatic synchronization capability to provide hard quality of service guarantees

The carrier sensing multiple access with collision avoidance (CSMA/CA) protocol is a widely-adopted MAC protocol in the current wireless networks, but the quality of service (QoS) cannot be guaranteed due to random access. Investigations reveal that the collision avoidance mechanism which relies on the binary exponential backoff scheme is the root cause of QoS issue. Therefore, this paper first proposes a CSMA with automatic synchronization (CSMA/AS) MAC protocol to mitigate the collision problem caused by random access. By CSMA/AS, all the stations can be synchronized and then served in a round-robin fashion without contention collisions. Even if a new station joins, the wireless network can also quickly converge and go back to the synchronized state. The simulation results show that the proposed CSMA/AS protocol can fully mitigate the issues caused by random access, such as the severe contention collisions and large delay variation. In addition, this paper demonstrates how to provide hard QoS guarantees, such as fairness, rate guarantee, and delay guarantee, which cannot be achieved by the existing CSMA-based protocols. Because CSMA/CA does not rely on any additional control message, the implementation complexity of CSMA/AS is similar to that of legacy CSMA/CA protocols.