Design And Implementtation Of Handover Methods In Software-defined WLAN System

The Software Defined Wireless Network(SDWN) is a key technology in the evolution of 5G and can provide flexible unified coordination and management of traditional closed WLAN architectures.In a densely deployed SDWN network,in order to ensure the network service quality of mobile users during roaming,the terminal needs to implement fast handover between APs,but the handover method in the existing SDWN may cause ping-pang effect and AP selectivity.To solve the above problems,based on virtualized access and network centralized programming,the thesis designed and implemented the handover method between APs and handover prototype system in SDWN.The following work was mainly completed:(1)Aiming at the problem of ping-pong effect in dense deployment environment,a triggering method based on terminal motion trend prediction is designed by using the optimized path loss model.The method accumulates the displacement difference of the terminal in the AP radius direction in real time to acquire the state information such as the moving direction and the moving speed of the terminal relative to the AP,and at the same time combines the hysteresis RSS and the dynamic adjustment of the dwell time to carry out the comprehensive setting of the handover conditions,and finally the controller decides whether to trigger the handover to avoid unnecessary handover,thereby reducing the impact of ping-pong and improving system handover performance.(2)Aiming at the problem of AP selectivity in the network,an AP selection method based on load sensing is designed.Firstly,using the virtual VAP and the global perspective of the SDN controller,real-time monitoring of network links and AP load to determine the network status;and then using libpcap open source library,Netlink technology and OpenFlow protocol in real time to obtain the network parameters such as RSS,number of associated terminals and AP bandwidth utilization,the above parameters are used to measure the status of the AP and generate a list of candidate APs.Finally,the lightest AP is selected and used as the target access point to avoid the excessive number of associated users under a single AP to balance the load among the APs.(3)In order to verify the feasibility of the above method,a prototype system for handover in SDWN was designed and implemented based on the "Basic Experimental Facility of Future"-SDWN tested of the laboratory building,and the related handover methods were tested for related functions and performance.Experimental results prove that the method can significantly reduce the number of handovers and balance the load among APs in the dense deployment environment of APs,improving the handover performance of the system,and provide user with high-bandwith,low-latency network services.The handover handover designed and implemented in the thesis lays the foundation for researching and designing the handover technology in SDWN,and it also has reference significance for other network switching modes.