Research On The Key Technologies For Vertical Handoff In Heterogeneous Wireless Networks

In recent years, with the rapid development of wireless communicationtechnologies, a lot of new wireless access technologies are emerging. Thenext-generation wireless communication network is developing in the direction toachieve the integration of heterogeneous wireless networks. Due to the differenttechnical characteristics and types of service provided of different wireless networks,mobility management has become one of the key technologies for heterogeneouswireless networks. As the core content of the mobility management, vertical handoffmainly completes the switching of communication connection for user betweendifferent wireless networks. Therefore, the performance of vertical handoff methodbecomes the vital factor to achieve optimal allocation of resources and seamlessmobility in heterogeneous wireless networks.In this thesis, the main work is to make some analysis, improvements andsimulation base on the existing vertical handoff methods in heterogeneous wirelessnetworks, especially the channel preemption based upward vertical handoff method(referred to as CPUVH), the priority based upward vertical handoff method (referred toas PPUVH) and the time threshold based upward vertical handoff method (referred to asTTUVH), which specifically includes:1. Make some simulation and comparative analysis for the CPUVH scheme, thePPUVH scheme and the TTUVH scheme, the results show that: compared to theCPUVH scheme, the PPUVH scheme is able to effectively reduce the droppingprobability of UVH calls while maintaining high channel utilization and low blockingprobability of new calls in the cellular cell; the TTUVH scheme can effectively avoidthat the cellular channels occupied by the online voice calls with a very short duration inthe double coverage area to be preempted.2. Considering the defects of the CPUVH scheme and the shortcomings result fromthat each of the two improved schemes mentioned above only concerns with a singleaspect of the problem, combining the PPUVH scheme and the TTUVH scheme, apriority and double time threshold based channel preemption upward vertical handoff method (referred to as PTUVH) is presented, which is characterized by priority baseddefinition of channel occupancy and preemption right, double time threshold baseddefinition of channel protection right and multi-parameter based definition of channelpreemption rules. The results of simulation and comparative analysis of the new methodand the three original methods mentioned above show that: the PTUVH scheme can notonly effectively reduce the dropping probability of UVH calls but also protect the onlinevoice calls with a very short or very long duration in the double coverage area againstchannel preemption, maintain high channel utilization and low blocking probability ofnew calls in the cellular cell at the same time, significantly improve the vertical handoffperformance of the cellular and WLAN interworking system and the QoS of voiceservices and user experience.