Research On The Mobility Management Strategies In Heterogeneous Networks

With the development of the wireless communication technology, various radio access technologies are emerging and the existing technologies are developed to a higher level. The heterogeneity of wireless networks is more and more prominent. Heterogeneous networks composed by cellular mobile communication systems, short-range wireless access systems, WLAN, WiMAX and other wireless access technology, can provide users with more colorful services by cooperation. With the development of the conventional cellular technology, low power base stations such as femto cell, home eNodeB and relay node are deployed within the coverage of macro cells to form the overlapping heterogeneous system. With that deployment, the enhanced hotspots coverage, improved cell capacity and extended cell rang can be achieved.In the complicated heterogeneous environment, with the development of services, higher requirements of mobility management will be put forward by users. Therefore, a rational mobility management strategy must be developed to ensure the seamless mobility. Heterogeneous network mobility management has become a key technology in the future development of communication technology.The main works of the paper include the following aspects:In order to support the seamless mobility between heterogeneous networks, appropriate network interworking architectures must be developed. Therefore, the interworking architectures proposed by the academia and the standardization organizations, as well as the mobile service levels achieved by the respective architectuers, are analysed. The conclusion is that the tighter coupling between networks, the higher level of mobility can be achieved, but more changes to the existing networks are needed.Unlike horizontal handover between homogeneous networks, vertical handover between heterogeneous networks can be caused not only by the weakness of the signal, but also by the changes of the service needs and the network status. Therefore, various vertical handoff algorithms are classified and compared according to the difference of the handover decision factors. As can be seen, the algorithms based on the different decision-making factors can enhance certain aspects of the system performance and some algorithms using multi-attribute decision models to synthesize several decision factors can achieve the optimization of the comprehensive performance, but this will increase the algorithm complexity.In the group moving scenes, many users need to hand off to other networks at the same time. If users make decisions to choose the target networks alone, it may cause the congestion of some networks. In order to solve the problem of incomplete decision information, a network-side central-controlled algorithm is proposed. Firstly, the number of users accessed by each network is determined based on the principle of load balance. Then each user’s target network can be decided with the Hungarian algorithm. Simulation results show that the algorithm can maximize the user satisfaction under the premise of network load balance, and the complexity of the algorithm is low.For the heterogeneous networks inside the cellular systems, local cells coexist with macro cells. As the coverage of the local cell is small, it is likely to cause the frequent handover for the high-speed users when passing the local cells and waste the system resourse. Meanwhile, in the CRE regions, since the received signal from the macro cell is stronger than that from the local cell, the users will be subject to serious interference from the macro cell. To solve the above two problems, a base station selection strategy taking account of the the user moving speed and a carrier selection strategy considering the fairness between users are proposed. The simulation results show that the algorithm can reduce unnecessary handover of the high-speed users and improve the throughputs of the CRE region users and the high-speed users.