Research On Performance Analysis For 3D-Based Heterogeneous Ultra-Dense Network

With the development of science and technology,a lot of wireless terminals emerge in wireless networks,on which higher throughput requirements will be imposed accordingly.Meanwhile,it is hard to deal with such a trend for the existing wireless network.To cope with this issue,academia and industry propose several wireless techniques that can efficiently promote the network throughput,such as massive MIMO,co-frequency co-time full duplex(CCFD),non-orthogonal multiple access(NOMA),heterogeneous ultra-dense network(HetUDN),etc.The HetUDN is a important technique to significantly enhance the spectral efficiency of the cell-edge of the MC and the network throughput,and it can be easily realized by densely deploying small cells(SCs)in the existing network that is composed of macro cells(MCs).This dissertation mainly focuses on the deployment of HetUDN and its correspond-ing performance.The main research scenario is the central business district(CBD)with many skyscrapers,in which the base stations(BSs)and wireless terminals are randomly distributed.Based on this,in stead of the traditional 2D network model,a 3D network model is proposed to model the CBD scenario.Therefore,this dissertation mainly concen-trates on a 3D-based HetUDN.In addition,the mathematics foundation of this dissertation comes from stochastic geometry(SG),and several point processes(PPs)are adopted to capture the randomness and irregularity of the distribution of BSs.The main contents and contributions are as follows.Firstly,we analyze the cell average spectral efficiency(CSE)of a 2D-based two-tier HetUDN from the perspective of a typical cell(TC),and then obtain the area spectral efficiency(ASE)and energy efficiency(EE).Likewise,the expressions of the above-mentioned three performance metrics are also obtained for a 3D-based HetUDN.Numer-ical results show that the spectral efficiency of the entire system can be significantly pro-moted by densely deploying SCs in MCs,while the energy consuming is also increasing.Based on this,we jointly optimize the ASE and EE.To be specific,the firefly algorithm(FA)is adopted to search for the optimal network configuration that makes a balance be-tween the ASE and EE.In two-tier HetUDN,we suppose that macro base stations(MBSs)and small base stations(SBSs)follow two independent homogeneous Poisson point pro-cesses(HPPPs)and that the transmission power of the MBS is larger than that of the SBS.If the maximum averaged receive-signal-strength(Max-RSS)association scheme is adopted,then a majority of users will associate with the MBS tier,which is undoubtedly a huge burden for the MBS tier,but only a minority of users associate with the SBS tier.Ad-ditionally,if we adopt the maximum averaged bias-receive-signal-strength(Max-BRSS)association scheme,then a fraction of uses that associate with MCs under the Max-RSS association scheme will prefer to associate with SCs.Consequently,the load balance of the entire two-tier HetUDN is relized by transfering the load of MCs to SCs.Therefore,the Max-BRSS association schme is usually employed by the two-tier HetUDN.Secondly,we foucus on a 3D-based homogeneous ultra-dense network(HomUDN),and obtain its signal-to-interference ratio meta distribution(SIRMD)and rate meta distri-bution(RMD).In addition,we propose a mean SIR method to describe the effects of the path-loss exponent on the signal-to-interference ratio coverage probability(SIRCP),mean local delay(MLD),and rate coverage probability(RCP)of the HomUDN.Numerical re-sults show that these three performance metrics are increasing as the path-loss exponent increases.Thirdly,we investigate the SMD and RMD of a 3D-based two-tier HetUDN,where MBSs and SBSs are referred to as two independent HPPPs and the Max-BRSS association scheme is adopted.In additon,due to the offloaded users(OUs)(that are offloaded from the MC to the SC)suffering strong interference from the MC(assuming that SBSs work in underlay model),we propose a frequency band partitioning scheme,and then a fraction of bandwidth is occupied only by the OUs.Numerical results show that the performance of the entire two-tier HetUDN can be improved,if a proper fraction of bandwidth is employed by the OUs.Finally,we investigate the SMD and RMD of a 3D-based two-tier HetUDN with a non-uniform SBS deployment.In stead of an HPPP,SBSs follow a Poisson hole process(PHP),and the MBS is distribted in the central of each holes.Numerical results show that the proposed two-tier HetUDN with a non-uniform SBS deployment(i.e.,non-HPPP)outperforms the two-tier HetUDN with a uniform SBS deployment(i.e.,HPPP)in terms of the network performance.Obviously,the proposed two-tier HetUDN with a non-uniform SBS deployment is more reasonable to model the BSs of the real wireless networks.Since the spectral efficiency of the hole area is high,so that there is no need to deploy SBSs.However,the spectral efficiency of the cell-edge of the MC is low,so that it is necessary to densely deploy SBSs in this area to improve the spectral efficiency.