Handover Performance Analysis And Research Of Heterogeneous Cellular Networks

The number of mobile devices and mobile data traffic volume have been experiencing an extremely fast growth in the previous decade,and such growth is expected to continue in the near future.In order to meet the huge wireless communications traffic demand given the limited available radio spectrum,heterogeneous cellular networks have emerged as a major way to meet the network capacity and coverage area requirements.The basic method of such networks is to deploy small cellular cells of low cost,small size,low transmit power and small coverage in the coverage of the macro cell.Heterogeneous cellular networks not only can efficiently use the limited spectrum resources,but also can increase the network capacity and coverage.Handover has an important impact on the capacity and service quality of mobile communication systems.Thus it is an important area for mobile cellular communications.Optimized handover mechanisms are especially critical for heterogeneous networks to operate at their maximum potential in terms of capacity and coverage.However,handover in heterogeneous cellular networks faces significant new challenges than in traditional macro-cell-centric networks.In the traditional homogeneous cellular network,the UEs could use the same handover parameter settings.In heterogeneous cellular networks,however,using the same set of handover parameters will result in many issues such as an increased ping-pong effect and a high handover failure probability.The goal of this thesis is to analyze the influence of handover parameters on handover performance in a heterogeneous cellular network and derive the closed-form expressions of handover as a function of various network parameters.Based on the analytical results obtained in this thesis,one can conveniently optimize the set of handover parameters according to the specific network deployment scenario to achieve the best handover performance.Main contributions of this thesis include:1.After a systemic but concise introduction of handover concept and models in heterogeneous cellular networks,various network parameters that affect the handover performance of heterogeneous cellular networks are discussed and analyzed.2.The handover performance of the UEs in a two-tier heterogeneous cellular network is analyzed,and closed-form expressions of the handover performance as a function of various network parameters are derived.These analytical results are validated via simulation.Based on these analytical results,handover parameters can be conveniently optimized to maximize the handover performance in a heterogeneous cellular network.And a method of reducing ping-pong effect is proposed,which can effectively reduce the probability of ping-pong effect under thepremise of controlling a certain probability of handover failure.3.The handover performance of heterogeneous cellular networks based on directional antennas is analyzed.Millimeter wave communication is introduced in 5G.A typical application scenario is to deploy the millimeter wave small base stations in the coverage of the macro base stations.Millimeter wave small base stations typically use directional transmission,resulting in significantly different handover scenarios than in the traditional cellular networks.A two-tier heterogeneous cellular network model of a millimeter wave small base station in the coverage area of a macro base station is introduced and modeled.The handover performance of the UEs in this scenario is analyzed,and the closed-form expressions of handover performance with directional transmission considered are obtained.Additionally,the influence of distance between base stations on handover performance is analyzed.Simulation results are also obtained to validate the analytical results for this deployment scenario.Then we can select the appropriate handover parameters to achieve the best handover performance.The influence of some of parameters of the directional antenna on the handover performance is also analyzed.