Research On QOE Guaranteed Handoff Strategy In SDN Based WLANs

In a large-scale intensive WLAN deployment environment, mobile stations (STAs) usually undergo frequent handoffs between different access points (APs) under unified control. However, the traditional handoff mechanisms can lead to long handoff delay, so it is still a challenge to ensure the user experience during the handoff phase. Based on the concept that control plane is decoupled from the data plane of software defined network (SDN) technology, this thesis focuses on how to ensure the user experience during the handoff process in WLANs. We have studied the SDN based WLAN network architecture and the handoff strategy to guarantee the user experience.This thesis proposes a SDN based WLAN network, the OpenFlow protocol is used by controller to control the data forwarding of switching devices, and we also designed a custom southbound protocol to realize wireless management functions in WLAN. Applications can be deployed on the controller to implement network management functions. Then we build the corresponding experiment network, and test the basic functions of the proposed SDN based WLAN network to verify the feasibility of the proposed scheme.On the basis of the proposed SDN based WLAN network architecture,we focus on studying the handoff strategy to guarantee the user experience.Firstly, we propose a pre-scan based controller-assisted fast handoff strategy, station can obtain the target AP in advance after fast pre-scan process, and when the handoff is triggered, station can perform the authentication and reassociation process toward the target AP directly,which can effectively reduce the handoff delay and achieve the goal of fast handoff. Secondly, since RSS may fluctuate significantly due to signal noise, which may trigger unnecessary pre-scan and result in frequent handoffs, we propose a Kalman filter based RSS filtering strategy to obtain better accurate estimate of RSS. Experiment results show that the proposed scheme can effectively reduce the handoff delay, and meet the specified time delay requirement of some time-sensitive services.