An Adaptive Transmission Timing Control Scheme for IEEE 802.11 WLAN

TXOP (Transmission Opportunity) and CW (Contention Window) can be look on as the most typical transmission timing control parameters in WLAN MAC layer, which have great influence on the system performance. In this paper, we firstly propose a TXOP adaption, according to the theory that there always have an optimal TXOP in specific services model. Basing on the transmitting queue length in the AP, the TXOP length can be adjust adaptively to match the variation of the traffic. Through TXOP Adaption, the user and service type with high priority can be scheduled in time, which can shorten the end-to-end time delay of MAC, compared with static TXOP scheme, and enhance the QoS (Quality of Service) guarantee ability for WLAN. Secondly, a CW Adaption is put forward, according to the direct proportional relation between the CW size and the scale of concurrent users. And by consideration of both virtual collision rate and channel occupancy rate, the CW size can be chosen adaptively, which can realize the optimization of the prediction throughput, thus benefit to both the utilization of channel in few users scenario and the throughput of WLAN in multi-users scenario.