Research On The Handover And Admission Control In Hierarchical Wireless Networks

With the rapid development of mobile Internet, the demand for accessing to the Internet via mobile communication network by users is increasing. Various types of wireless multimedia services requiring high quality service emerge, which promotes the explosive growth of data traffic in mobile communication system. Wireless network needs to provide effective support, and it has brought great challenges to the development of mobile communication system. Statistics show that about90%of data services occur indoors, and it is important for operators to provide good indoor coverage for these high speed data services. As an indoor solution, femtocells are used to provide high quality service for indoor users and improve network capacity.Femtocells are introduced in the next generation wireless communication system, which changes the traditional network structure, called hierarchical macrocell and femtocell networks. Overlapping macrocells and femtocells are different in terms of application scenarios, coverage, network capacity, services support ability and transmission power. The macrocells and femtocells complement each other and jointly provide high quality services for wireless users. Therefore, the traditional radio resource management technologies cannot be directly applied in hierarchical networks. Radio resource management is the key to implement performance optimization of hierarchical networks. On the one hand, the overlapping coverage makes handover scenarios more complex, especially in the presence of a large number of femtocells. How to improve the user experience and reduce the frequent and unnecessary handovers is the focus of the researches of the handover algorithm in hierarchical networks. On the other hand, there is a contradiction between a variety of service requirements and the limited wireless bandwidth resources. Admission control for each service needs to be performed according to the technical characteristics of macrocells and femtocells to improve the utilization of the wireless resources, as well as guaranteeing the quality of service.In this paper, the research focuses on handover and admission control technology of the radio resource management in hierarchical networks. The following aspects have been studied:Users moving in hierarchical networks deploying multiple femtocells may experience frequent handovers in order to obtain higher transmission rate, which seriously increases the network load. Therefore, handover decision seeks to achieve a balance between user satisfaction and the network performance. Several factors influencing the decision making in the scene are analyzed, considering the bursty non real-time data service. The markov decision process model is used to formulate the handover decision problem. The data reward function denotes the amount of data transmitted via candidate networks, and the signaling cost function denotes the handover overhead. Users choose to handover the network with maximum reward. The simulation results show that the proposed handover scheme is effective and outperforms traditional polices.The network connection time is related to user’s mobility, the amount of data traffic, service arrival and available bandwidth. As a result, the network cannot obtain accurate network connection time when making admission decisions. The user motion model takes into consideration both the velocity uncertainty and the path uncertainty. User mobility prediction is based on the historical observation of the user location information. The service arriving to the femtocell is classified into four types which differ in signaling overhead on network. The partially observable markov decision process theory is utilized as the modeling tool, and the observation space and the observation function are given. Simulation results show the proposed admission control scheme effectively improves the resource utilization of the femtocell.A variety of handover services and new services exist in hierarchical networks. The resource utilization of the femtocell in the existing admission control schemes is low, and an admission control and transfer scheme is proposed based on the traditional admission control schemes. When there are idle resources in a femtocell, the services connecting to a macrocell while users are located in the coverage of the femtocell could be chosen to handover to the femtocell. The problem is formulated as a semi markov decision process optimization problem. The system energy efficiency reward function is defined. Simulation results show that the proposed energy efficiency priority admission control and transfer strategy effectively improves the resource utilization of the femtocell with the maximum reward, and decreases blocking probability and dropping probability.