Research On Handover Algorithm In Macrocell-femtocell Hierarchical Networks

In the Macrocell-Femtocell hierarchical networks,although the Femtocell can compensate the blind spots coverage of the edge area in Macrocells and increase the system capacity of hot area,it also introduces the problem of frequent handover due to the small coverage of Femtocell and thus it is of great significance to study the handover technique.In order to solve the problems that the existing research of handover algorithm does not fully consider the UE speed and is of high complexity for network selection as well as unable to dynamically adjust the threshold for resource reservation,two improved handover algorithms are proposed in this thesis.Firstly,aiming at the problems that the existing handover algorithm does not focus on the UE speed and has high complexity for the network selection and has the unbalanced cell load,this thesis proposes an improved handover algorithm based on objective optimization function.The proposed algorithm mainly includes two parts: 1.According to the factors of RSS,UE speed and the type of users,the proposed algorithm filters the users with handover request and then deeply analyzes the users’ speed by using the fuzzy logic algorithm to process the speed value,speed direction and the distance between the user and the base station,which could reduce the unnecessary handover numbers.2.In the network selection algorithm,the target cell is selected through the proposed objective optimization function which contains the parameters of network performance,network load and the handover cost,of which the network performance is obtained through the TOPSIS algorithm by processing the RSS,time delay,mobility support and energy consumption.Theoretical analysis shows that the complexity of this algorithm is relatively lower compared to the algorithms directly using the network performance parameters,besides,the simulation results show that the algorithm can reduce the unnecessary handover probability and blocking rate and also achieve the load balancing of each network.Secondly,as for the problems that the traditional algorithm is not suitable for hierarchical network scenarios and the resource utilization is relatively low due to the small handover calls,an improved handover algorithm based on dynamic delay and dynamic resource reservation is proposed in this thesis.The main idea of the algorithm is structured as follows: 1.According to the problem of asymmetric transmission power of base station,the method of using RSS of Femtocell is put forward to judge the transmit power which can reduce the access threshold,furthermore,the speed-based delay function and RSS continuous judgment method are proposed to reduce the number of unnecessary handover.2.The handover algorithm based on dynamic resource reservation is improved to achieve that the resource reservation threshold can be dynamically adjusted with the change of call number.Meanwhile,the access probability of new call is also optimized,so the new call can access to the reserved resource with the access probability while the reserved resource is idle.Simulation results show that the proposed algorithm can reduce the number of handover times,the blocking rate and the drop rate,and also improve the resource utilization rate meanwhile.