A load adaptive IEEE 802.11e EDCA backoff scheme with enhanced service differentiation

In view of the disadvantages of IEEE 802.11e EDCA in QoS guarantee and collision avoidance, an enhanced EDCA scheme called SD-AEDCA is presented which dynamically adjusts two EDCA parameters, namely contention window (CW) and backoff time counter (BC), according to channel load conditions and QoS requirements of network services. SD-AEDCA makes improvements to EDCA backoff scheme from post-backoff, upon-collision and post-transmission phases respectively by differentiating real-time and non real-time frames. Specifically, frozen rate is calculated to estimate the channel load conditions during EDCA backoff process and then used to guide CW and BC adjustment. And the waiting time is explored deliberately to satisfy the transmission latency requirements of real-time frames. Simulation results show that SD-AEDCA improves network throughput by reducing transmission collisions and provides more satisfactory QoS to real-time services at heavy load conditions.