Improving the QoS performance of EDCF in IEEE 802.11e wireless LANs

The IETF is currently specifying QoS on the Internet, but providing QoS at the IP layer is sub-optimal without lower layers' support. With the growing popularity and acceptance of IEEE 802.11 wireless LANs, it is essential to focus on QoS enhancement at the MAC layer of the 802.11 standard. The EDCF, proposed by the IEEE 802.11e, is a contention-based MAC protocol supporting service differentiation through different interframe spaces, contention window limits, and persistence factors for different traffic priority classes. In this paper, we propose a retransmission scheme, known as age-dependent backoff (ADB), to alleviate the delay and jitter of real-time packets by adjusting the persistence factors dynamically based on the ages of the real-time packets in the transmission queues and the lifetimes of the real-time packets. Simulation results indicate that using ADB in EDCF is efficient with low delay, jitter and drop rate for real-time traffic in a wide range of traffic loads.