Research On Vertical Handoff Strategy Of Indoor VLC Heterogeneous Network

With the rapid growth in the number of mobile communication users,RF spectrum resources are constantly compressed.Therefore,it is urgent to develop a new communication method to overcome the current shortage of spectrum resources.Visible light communication has become a research hotspot of wireless communication because of its extensive spectrum resources without authorization.Since most of visible light propagation depends on line-ofsight propagation,its coverage is small,and when it encounters an object occlusion,the signal will be attenuated sharply.Therefore,combining the advantages of RF to build visible light communication-based heterogeneous network becomes one of the solutions to increase the coverage and throughput of the whole network.In a heterogeneous network,mobile users are bound to face the problem of network handover,and the vertical handover strategy becomes an important factor affecting the user’s network experience.Therefore,this paper studies the Vertical Handoff Strategy of visible light communication-based heterogeneous networks.The main work and research results are as follows:1.Dynamic timer vertical handoff strategy based on prediction algorithm.The proposed strategy of adjusting the timer threshold according to the predicted interrupt time interval is as follows:if the predicted interrupt time interval is short,it can be considered that the terminal moves more frequently in the network boundary area.In this case,we can appropriately increase the timer threshold to avoid unnecessary vertical handoff and reduce the impact of the ping-pong effect.If the predicted interruption time interval is long,it can be considered that the terminal rarely reaches the network boundary.Hence,we can appropriately reduce the timer threshold to increase the network connection time and improve the data throughput of heterogeneous systems.The performance of the Vertical Handoff Strategy under 10 paths,50 paths,and 100 paths is simulated respectively.The simulation results show that the proposed algorithm can still maintain good performance when the walking path becomes longer.And three-terminal mobile scenarios are set:the enduser walks randomly in the room,the end-user walks randomly in the boundary area of the visible light network,and the end-user crosses the visible light center.In these motion scenarios,the proposed algorithm also performs well in the average data rate and switching times.2.Dynamic timer vertical handoff strategy based on fuzzy logic.The proposed vertical handoff strategy is divided into two steps:the first step is to make a handoff decision.The second step is to use the fuzzy logic system to calculate the timer threshold.The handover decider determines whether to perform handover through the relationship among three parameters:the size of the unsent message,the vertical handover delay,and the predicted interruption time interval.The fuzzy logic system has two inputs:the occurrence probability of "occlusion interruption" and the switching failure probability,and take timer threshold as output.The membership functions of input parameters and output parameters and fuzzy reasoning rules are designed respectively to obtain the timer threshold.The simulation results show that the proposed vertical handover strategy can adjust the timer threshold to the most appropriate state according to the network conditions,eventually greatly reduce the average transmission delay,Improve the user’s network experience.