Research On Efficient Access Algorithm In High-density WLAN

Over the past decade,IEEE 802.11 based Wireless Local Area Networks,are becoming the most popular wireless access technology as its flexibility,low cost and extensible and other features.It is being widely used in hospitals,factories,libraries,airports and many other places.In the high-density WLANs(Wireless Local Area Networks),the traditional AP association and handoff criteria in IEEE 802.11 standard,is based on the RSSI(Received Signal Strength Indication).It often leads to load imbalance between access points(APs),causes the waste of network resources,and even degrades the overall network performance.Thus,how to select the appropriate AP to associate and switch,is particularly important to achieve the load balancing between the APs,ensure network stability and improve network performance.The two important branches of wireless access algorithm in high-density WLANs,namely AP selection algorithm and handoff algorithm,are analyzed and researched.Specific work is as follows:Firstly,in response to the performance anomaly caused by mobile terminals with different rate and to achieve the load balancing of network,a joint AP association and bandwidth allocation optimization algorithm in multi-rate 802.11 WLANs is proposed.In order to solve the performance anomaly,the AP is classified according to the rate of its associated stations.In addition,for effectively realizing load balancing between the APs,the load situation of APs is considered as a measure of AP selection criteria.At the same time,from the user's point of view,by the different Quality of Service(QoS)of users,the bandwidth is allocated for achieving relatively fair.Thus the channel utilization and the overall network performance are effectively improved.Secondly,in order to reduce handoff delay when handoff decision,many factors are taken into account to achieve load balancing,which ensures that the user's quality of service.The two problems are solved: the one is how to choose the appropriate migration object;the second is how to judge of the best AP.According to the two problems,a dynamic AP handoff based on load-balancing algorithm is presented to maximize the AP utilization and the entire system capacity of the network,which also can achieve the global load balancing of the network.By ranking the associated stations with different priorities,it is gived priority to choose the users with low priority or with less number of candidate APs as migration objects and effectively guarantees the service quality of the high priority users.The handoff delay is reduced effectively.For the selection of target AP,the received signal strength,the AP's load and its impact on the global load,the three factors are taken into account to achieve the load balancing of overall network.Finally,the proposed algorithm is simulated by OPNET network simulation software.The simulation results show that the presented algorithm can effectively improve the aggregate throughput and channel utilization of the network,promote the realization of load balancing,and improve the performance of the network.