Optimized O-ACK: An adaptive wireless MAC protocol for multiple access points

In wireless LANs, MAC protocols perform one of the most important tasks: efficiently sharing the limited bandwidth among the contending stations. In IEEE 802.11, Distributed Coordination Function (DCF) is used as a default MAC protocol. Despite its wide acceptance, it has two major downsides: i) Channel idle time and ii) Collision overheads. Besides, the use of the explicit ack frames incurs extra overhead due to the preamble, packet headers etc. This paper presents an optimized version of the Overheard-ACK (O-ACK) protocol (presented in [2]) which incorporates piggybacking, packet overhearing and token based scheduling to significantly reduce the overheads. The previous version of O-ACK creates chains of transmissions, where consecutive transmissions are separated by SIFS interval, which increases the throughput. But on the downside, as two adjacent transmissions are separated by only SIFS idle time, a newly arrived station cannot start transmission. Our current version of O-ACK ensures higher throughput and fairness in multiple AP scenario by continuously adapting the chain creation process based on the surrounding environment. Our NS-2 based simulation results confirm that this protocol significantly outperforms the DCF protocol.