On The Study Of Coverage And Capacity Of Heterogeneous Networks With CoMP

The fifth generation(5G)mobile networks are expected to accommodate the 1000x improvement of mobile data rate through three main technical as-pects:network densification,spectral efficiency(SE)enhancement,and spec-trum extension.As a dominant theme,network densification is to densely de-ploy diverse smallcell base stations(SBSs)coexisting with conventional macro-cell base stations(MBSs),given rise to the heterogeneous networks(HetNets).However,the HetNet architecture introduces complex coordination and inter-ference managements.Coordinated multi-point(CoMP)transmission is ex-pected to coordinate heterogeneous BSs and mitigate co-tier and cross-tier in-terference in HetNets.Providing secure wireless transmission is one of the top priorities of 5G and HetNets.Physical layer security with CoMP is proven to be capable of providing secure transmission from the view of information-theoretic security.In this thesis,we study the coverage and capacity performance,includ-ing the secure coverage and secrecy capacity,of HetNets with CoMP.Based on stochastic geometry and game theory frameworks,several tractable models for analyzing the proposed CoMP strategies are presented to evaluate the cover-age and capacity improvement in HetNets in terms of coverage probability,SE,area SE(ASE),average data rate,secrecy outage probability and secrecy rate.Detailed contributions are summarized as follows.(1)To analyze and optimize the SE of nonuniform HetNets with CoMP,we propose a novel capacity-and trust-aware BS cooperation strategy,consid-ering the limited BS capacity and the existence of untrusted SBSs in practi-cal scenarios.By modeling the distribution of MBSs and all(normal and un-trusted)SBSs as independent homogeneous Poisson Point Process(HPPP)and Gauss-Poisson process(GPP),and with repulsive distance among MBSs and SBSs,expressions for SE and ASE are analytically derived with the charac-terization of the statistics of aggregate signal strength(ASS)and interference strength(AIS).In addition,the optimal density of normal SBSs in maximizing the SE and ASE is proved to exist and analytically obtained.Finally,simulation results are provided to validate the theoretical analysis and effectiveness of the proposed CoMP strategies.(2)To analyze the coverage probability and capacity of cache-enabled and energy harvesting-powered HetNets with CoMP,we propose a novel BS coor-dination strategy among MBSs and SBSs based on the knowledge of the energy states and the cached contents of SBSs,along with the awareness of the avail-ability of channel resources and the average received signal strength(RSS)of the corresponding link.MBSs and the SBSs are coordinated to provide high data rate and further improve the network coverage.Stochastic geometry is ap-plied to characterize the statistics of the cell load of MBSs and SBSs,as well as the ASS and AIS.Average MU capacity for the BS coordination strategy is obtained.The coverage probability is also derived with Gamma approximation for the distribution of ASS and AIS.Analytical results reveal that the average MU capacity and coverage probability can be maximized with optimal cache size,energy harvesting rate and cooperative RSS threshold.Finally,extensive numerical and simulation results are provided.(3)To analyze the SE and traffic offloading of HetNets with CoMP,con-sidering the impact of heterogeneous BS heights,we propose a MU-centric co-operative SBS clustering strategy based on the information of the cached con-tents,the transmission distance(between the elevated BSs and MUs)and the cell load of SBSs.The MUs failed to be offloaded to the cooperative SBS clusters are associated with the nearest MBSs.Incorporating nonline-of-sight(NLoS)and line-of-sight(LoS),and leveraging modified COST 231 model to evaluate the impact of BS height on the path loss parameters,explicit expres-sions for the average SE and offloading probability are derived.Extensive sim-ulations are conducted to validate the theoretical analysis and demonstrate the impact of the network parameters.(4)Finally,to analyze and optimize the secure coverage and secrecy rate of HetNets with CoMP,we first propose a dynamic point selection(DPS)-based secure BS association scheme in a two-tier HetNet.With stochastic geometry framework,closed-form expression for the secrecy outage probability(SOP)is derived.To further enhance the secrecy rate,we propose a CoMP-based cooper-ative jamming strategy,where multi-antenna BS transmits information signals along with artificial noise(AN)to disturb the eavesdropper,and multiple jam-mers are coordinated to assist the legitimate link for better secure transmission with some payoffs.A single-leader multi-follower Stackelberg game between the BS and the assisting jammers is formulated to maximize the achievable se-crecy rate at BS and payoffs at jammers.Stackelberg equilibriums,including optimal fraction of transmit power for AN,optimal transmit power and ask-ing prices of assisting jammers,are proved to exist and analytically derived.Numerical results validate the derived results and reveal that the proposed co-operative jamming strategy can significantly improve the secrecy performance and meanwhile save more energy for information signals,which is meaningful for future wireless communication.Overall,leveraging CoMP in HetNets,we propose several MU-centric BS coordination and cooperative strategies with the consideration of heterogeneous network status.To evaluate the performance of the proposed strategies,we theoretical analyze the coverage probability,SE,ASE,average MU capacity,and SOP with stochastic geometry.Moreover,the achievable secrecy rate has been maximized with game theory.The study and analysis in this thesis can provide theoretical insights for the deployment and implementation of CoMP in HetNets.