Overheard ACK With Token Passing: An Optimization to 802.11 MAC Protocol

Distributed Coordination Function (DCF) is defined in IEEE 802.11 standard, which is widely used in practice. Despite of its wide use, it has several limitations. Because of the idle and collision times, it suffers from poor channel utilization. Besides, the control packets, particularly, Acknowledgement (ACK), consume non-trivial amount of bandwidth. Though the number of control bits in an ACK frame is small, the added overheads like the preamble, packet header etc. make the situation worse. In this paper, we propose a scheme called Overheard ACK where the explicit ACK frame has been eliminated by using the leverage of packet overhearing. Also, by incorporating explicit and implicit token-passing, this protocol attempts to schedule transmissions without having to use random access, dramatically reducing the idle time and collision time. Simulation results using NS2 confirm that this protocol significantly outperforms the conventional 802.11 DCF.