Research And Implementation Of WLAN Seamless Handover Technology Based On TDMA

Wireless networks are widely used in the industrial field due to the advantages of low cost,flexible deployment,wide coverage and mobility support.At present,the Time Division Multiple Access(TDMA)has been applied to Wireless Local Area Net Work(WLAN)to meet the communication requirements of high real-time and high throughput in industrial scenarios,but the following problems still exist.Firstly,with the development of industrial wireless networks,a large number of mobile terminals appear in industrial scenarios,and the handover process of mobile terminals between wireless Access Points(AP)cannot ensure real-time and reliable data transmission.Secondly,TDMA time slots cannot be dynamically allocated according to changes in the time slot requirements of mobile terminals and network load in mobile scenarios,which results in the low utilization rate of time slots and poor latency jitter performance.In view of the above problems,this thesis designs a TDMA-based seamless cross-channel handover method for WLAN to solve the problems of large handover latency and low utilization rate of slot resources in industrial mobile scenarios.the main work is as follows:(1)Aiming at the problem of handover latency and time slot interference under the same channel,this thesis designs a method for seamless cross-channel handover based on the AP virtualization access technology and the SDN centralized control idea.Firstly,the SDN controller makes a handover trigger decision based on the change trend of the received signal strength(RSS)and the hysteresis margin RSS to improve the handover accuracy,Then it selects the handover target AP according to the time slot occupancy rate and the probe latency to ensure the terminal communication requirements,Next,reduces the handover latency by transferring virtual AP and pre-allocating slots,so that seamless cross-channel handover can be realized.(2)Aiming at the problem of time slot resource reallocation during the handover process,this thesis designs a dynamic time slot allocation method based on the queue length of terminals.Firstly,this method calculates the time slot requirement of terminals according to the queue length,and then selects the optimal time slot allocation method for time slot allocation based on the load status of the AP,which improves the time slot utilization rate while ensuring the latency jitter performance of the network,and is able to better adapt to changes in terminal time slot requirements and network load in mobile scenarios.(3)Through the establishment of relevant experimental platforms,the relevant performance test of the entire system is performed.The test results show that the technical scheme designed in this thesis can achieve transmission latency within 3ms,and the total throughput is not less than 30 Mbps,which has reached the expected goal.