Capacity Analysis Of Cognitive Heterogeneous Networks Via Stochastic Geometry

With the rapid development of wireless networks,people have higher demand of the wireless data transmission speed.Heterogeneous cellular network is the main structure of 5G,which can significantly improve the system capacity and coverage.However,how femtocells coexist with macro cell is an important question.In the heterogeneous cellular network,what kind of method is used to improve the system performance and efficiently use sub-channel resources is the key of the research.The channel access strategy of femtocell is one of the hot issues in the study.As the femtocell is deployed by the user randomly within the coverage of the macro cell and works with the technology of plug and play,may move from one location to another location,it is difficult for telecom operators to manage spectrum resources dynamically through the central control.Cognitive radio can dynamically and opportunistically use the idle spectrum through spectrum sensing,which can improve the utilization of spectrum resources.Considered the low utilization rate of the macro cellular spectrum in some periods or in some areas,cognitive radio(CR)is a promising technology.Cognitive femtocell can use the unused spectrum resources of macro cell through spectrum sensing,and thus greatly improve the system spectrum utilization.This thesis introduces two kind of spectrum sharing schemes,namely,overlay scheme and underlay scheme.In this thesis,we use the stochastic geometric tool to study the performance of cognitive heterogeneous networks in the case of perfect channel perception.In the overlay scheme,we derive the capacity performance of macro cell and femtocells under multi-channel conditions with specific interruption constraints.In the process of derivation,the randomness of the macro mobile station(MS),the femto MS and its base station distance is also considered.Therefore,the derivation result is robust to the system topology.The capacity of the single macro resource block(RB)can be improved by spatial multiplexing both under the general underlay scheme and the controlled underlay scheme.Simulation results the relationship between the transmission capacity and the radius of femtocell and the base station power in the overlay spectrum sharing scheme and the underlay spectrum sharing scheme respectively.The general underlay scheme and the controlled underlay scheme is compared in terms of capacity improvement in the single macro resource block.This thesis has some guiding significance for the research of future heterogeneous cellular network architecture.