Coverage And Average Rate Analysis Of Stochastic Geometry-based Heterogeneous Cellular Networks Over Complex Fading Channels

The future wireless network not only exhibits notable heterogeneity but also plays more irregularity due to the deployment of various nodes including kinds of base stations(BSs)and users.Modeling and analysis of heterogeneous cellular networks(HetNets)based on stochastic geometry have been recently attracted much attention in the research community.The stochastic geometry-based HetNet captures the topological randomness in the wireless cellular network geometry,offers analytical flexibility,avoids complex and time-consumed system design and simulation,and provides accurate network performance evaluation.However,the HetNet system incorporates different spatial positions of nodes,lots of BS association rules,and complex fading channels,which makes the theoretical analysis face a big challenge.Therefore,this thesis pays much attention to the coverage probability of stochastic geometry-based HetNets differing in terms of the location models of nodes(a user-centric wireless network model:clustered users distributed around theirs BSs,a Poisson network model:positions of users and BSs are independent and uniform),complex and general fading channels,and BS association schemes.The main contents and contributions in this dissertation are summarized as follows.1.In the downlink user-centric wireless network,this thesis firstly focuses on a comprehensive fading environment including that(1)all signals experience a large-scale fading scenario,and(2)the desired signal undergoes the?-? shadowed fading with integer fading parameters and the interfering signals experience an arbitrary fading channel.Then,under a general BS association rule(denoted by GR for notational simplicity)impacted by the lognormal shadowing,a convergent and tractable expression for the probability density function(PDF)of serving distance based on the Gaussian-Hermit quadrature(GHQ)is obtained.By applying the tools of stochastic geometry,closed-form expressions for the downlink coverage probability of a one-tier user-centric wireless network in the comprehensive fading scenario are successfully derived and verified through simulation.In terms of the independence assumption between the network model and fading channels,the theoretical analysis of coverage probability as for the interfering channel is avoided and it is replaced by numerical calculations.Numerical results demonstrate that the ?-?shadowed fading with high parameter values is more conducive to improve the coverage probability in the user-centric wireless network.Besides,compared with a one-tier HetNet which utilizes the Poisson point process(PPP)to model the user locations,the user-centric wireless network improves the coverage probability.This insight indicates that if the clustered users exist in the HetNet,then the BS should be deployed at the cluster center to enhance the coverage probability.2.To characterize multiple independent types of shadowing in the 5th Generation mobile communication system(5G)and explore the influence of the large-scale shadowing on network performances,we firstly provide the PDF of the double shadowed fading and its approximate expressions based on the GHQ.Secondly,under the closest BS association rule(denoted by CR for notational simplicity)and the GR,we respectively obtain closed-form expressions for the coverage probability of a downlink one-tier Poisson network with double shadowed fading.Particularly,the derived expression under the GR provides an accurate and lower boundary for the coverage probability of the research point 1.Simulation results show that the double shadowed fading circumstance with rich clusters and mild fluctuations collectively provides high coverage probability.Also,using the CR can avoid the ping-pong effects compared to the GR.What is more,the convergence of coverage probability is validated when the locations of users or BSs are respectively modeled by modified Thomas cluster processes.Opposite to the research point 1,the network with clustered BSs does not increase the coverage probability when the users exhibit a uniform feature.3.For the extremely complex and general fluctuating Beckmann(FB)fading channel,we firstly use the Gamma distribution and the second-order moment matching approach to approximate it.Secondly,we propose a modified Erlang(ME)distribution for the application of the performance analysis in stochastic geometry-based HetNets and reducing the approximate error when the shape parameter of the Erlang distribution is a non-integer.Finally,by utilizing the ME-based approximation as well as the Rician approximation,we derive the approximate expressions for the coverage probability and average rate in a downlink L-tier HetNet with FB fading for the desired link and an arbitrary fading for all interfering links.The provided ME distribution keeps the exponential,generalizes the Erlang distribution to containing non-integer shape parameters,and prominently decreases the approximate error concerning the FB fading and the Gamma distribution with non-integer parameters.Numerical results indicate that the FB fading with rich clusters,severity fluctuation of the line-of-sight component and the larger power imbalance for one component promotes the coverage probability and average rate.Overall,this thesis focuses on the complex fading models concerning the comprehensive fading,double shadowed fading and FB fading,provides accurate and low computational complexity closed-form expressions for the coverage probability.For the first time,the derived coverage probability avoids high order differential calculations,removes complicated integrals,and extends the interfering fading model to an arbitrary distribution.The study and analysis in this thesis can provide system design insights and practical application value for the BS deployment in the HetNet.