Energy Efficient For Dense Dis- Tributed Hetergeneous Net- Works

With the rapid development of the mobile internet and the massive popularity of mobile intelligent terminal, the number of users and data traffic of mobile communication network will show a large scale growth. The overlay heterogeneous networks (HetNets) are seen as a promising way to deal with the contradiction between the blowout type growth of wireless network capacity requirements and the limited spectrum resources. Heterogeneous networks cost-effectively solve the coverage and capacity problems of the current wireless network. At the same time, all base stations which are densely deployed in the heterogeneous networks also bring the corresponding challenges to the energy and the environment. Due to the great attention on energy and the environment around the world, green communications gets exten-sive attention. Considering that the energy consumption of the mobile communications net-work is mainly from the part of the base stations, this paper conducts the research on the sleep mode of the base stations aiming at the heterogeneous networks scenario.First of all, this paper studies the technical characteristics of the heterogeneous cellular networks, studies the deployment strategy of the low-power base station of the heterogeneous networks and in different deployment strategies how to reduce the interference between macro base station (MBS) and the base station with the low power consumption. The main study is based on three deployment strategies of multicarrier, carrier aggregation and co-channel deployment and focuses on the cell selection and inter cell interference coordina-tion (ICIC) technology for the co-channel deployment. In order to reduce the adverse effects of uplink and downlink coverage imbalance, interference and other problems caused by the great difference in signal transmission power between MBS and low-power base station, when user select the serving cell, cell range expansion (CRE) technology and ICIC technolo-gy should be used to control the interference. With the heterogeneous cellular network as the background, we have studied the existing typical sleep algorithms of base station and ana-lyzed their advantages and disadvantages. This paper have studied the base station sleep technology from the two aspects of centralized sleep algorithm for pico base stations (PBSs) and the hybrid base station sleep algorithm based on the virtual cell for femto base stations (FBSs) to lay the foundation for the follow-up study.Then, we propose a two-stage centralized dynamic sleep algorithm for PBS in heteroge-neous cellular networks. On the basis of modeling the heterogeneous networks, using the dif-ferent data traffic distribution in time and space, we design a utility function of PBS about the traffic load and the interference from other base stations of the PBS. The first-stage algorithm considers both the load conditions of MBS and PBS as well as energy-saving performance and complexity of the algorithm. The algorithm close the PBSs with lower value of utility function as much as possible, and focus the data traffic on the PBSs with higher value of the utility function in a iterative way; The second-stage algorithm makes up for the first-stage algorithm which tries to switch off the PBSs which are still open under the coverage of the MBSs with very low load. In order to analyze the performance of the algorithm, the proposed algorithm and progressive switch off algorithm for PBS which also belongs to the centralized algorithm are compared. The results show that with respect to the progressive switch off al-gorithm, the two-stage base station switching off algorithm presented in this paper has signif-icant performance gain in energy saving.Finally, a hybrid base station sleeping algorithm is proposed in virtual cell-based dense het-erogeneous cellular networks. In the dense-deployed FBSs heterogeneous networks, consid- ering the complexity of base station sleep algorithm, we design a hybrid cluster-based dy-namic base station sleeping algorithm. The goal of the algorithm is not only to close more FBSs, more importantly, it is to improve the energy efficiency of the whole network. Firstly, FBSs are clustered around the chosen FBS leader according to the distance between them, and in the initial time of algorithm, each cluster simultaneously and independently applies the centralized algorithm to try to switch off the FBSs in the cluster. Clusters are divided into two categories, the clusters with more than one member try to switch off FBSs with low energy efficiency as much as possible based on whether the access subscribers of the FBS can trans-fer to other FBSs in the cluster and whether the total energy efficiency would improve; the clusters with only a single FBS need to monitor the FBS for a period of time. If there is no user calling, it can be switched off. The simulation results show that the proposed algorithm not only reduced the algorithm complexity, but also improved the network energy efficiency greatly while ensure the network communication service quality.