Research On Power Control And Mobility Management In Ultra-dense Networks

With the development of the mobile Internet industry,wireless terminal devices such as smart phones and smart wearers have rapidly spread and become the necessity in people's life.It has become a daily demand to obtain various types of information by such smart terminals.Low latency,high reliability and massive connections are great challenges for future mobile communication industry.However,the shortage of spectrum resources has greatly restricted the development of mobile communications.In order to cope with these problems,3GPP proposed the concept of ultra-density networks in R10 and increased the frequency band utilization by arranging a large number of small cells to improve the communication network capacity.Whereas,with the increasing of cells' density,energy consumption also increases,and green communication is an important research topic.In addition,the reduction of base station coverage area will cause frequent base station switching for users,especially when users move quickly.Besides,mobility management is also one of the key issues under these scenarios.Due to the obvious tidal effect of communication requirements,closing some base stations can effectively reduces energy consumption without degrading the network performance.At the same time,the switching of the cell will make users switch the service base station,which will also bring considerable energy consumption.Most algorithms do not consider this issue.In this paper,the switching overhead is reasonably modeled from the perspective of switched cells.Considering the complexity of the problem,this paper solves energy optimization problems in two steps.Firstly,the centralized access method is used to optimize the switching energy consumption.Then,in the switching process,this paper analyzes the problem that the early termination problem of common dormancy algorithms and optimizes the common heuristic algorithm by taking consideration of neighbor sites' load.Simulation results show our algorithm effectively reduces the overall energy consumption of the network.A large increasing of cell density will lead to frequent handovers during user moving process,especially when the users moves at high speed.The cost of control signals will even occupy the resources of normal data transmission and the interference is extremely large at the edge of cells.To solve these problems,this paper introduces the Poisson distribution process in stochastic geometry to model the ultra-density networks.A typical skip handover strategy can cut down the handover frequency,but this method sacrifices the optimal connection and it performs bad at low speed.Different from other studies,this paper adopts a more practical Gaussian motion model and propose an advanced handover scheme with the combination of CoMP according to this model.This scheme reduces the handover frequency by skipping some cells,improves the overall network throughput performance by CoMP technology and achieves good performance both of low-speed motion and high-speed motion.Finally,this paper builds a system-level simulation platform for ultra-density networks and verifies the proposed algorithms in this paper.For the dormancy algorithm,the proposed scheme effectively reduces the energy consumption and the centralized access strategy also optimizes the switching power cost.For the mobility management algorithm,the proposed scheme effectively reduces the switching frequency and have a significant gain of overall network throughput.