Research On The Spatial Spectrum And Energy Efficiency Of 5G Ultra-dense Small Cell Networks

With the mad growth of mobile users and mobile connected devices,mobile broadband data traffic has experienced unprecedented growth.Cisco predicts that there will be 11.5billion mobile devices and connections by 2019.Global monthly mobile data traffic will reach 10 times 2014,which is 24.3 exabytes.The search for a suitable,effective and practically applicable next-generation communication technology,namely B4G or fifth-generation mobile communication technology(5G),will be the key to meeting this demand.The 5G demand mainly includes three aspects,namely,the rate demand,delay demand and energy cost requirements,and the rate demand is the basis for other needs.Starting from the Shannon formula,we can increase the rate in three dimensions:(cells/km~2)dimensions,(bits/s/Hz/cell)dimensions,and(Hz)dimensions.The corresponding technologies are super dense networks,increasing available spectrum and other advanced technologies that increase spectrum efficiency,such as massive MIMO.This dissertation focuses on the challenges and unsolved problems in the deployment of ultra-dense networks.Specifically,these challenges include:1)As more and more base stations are in the same area,mobile users will“see”more interference sources,and the macro base station and small cell base stations co-channel with it.Mutual interference between each other may weaken the reception quality of mobile users;2)As mobile devices support the needs of multiple access technologies such as 2G/3G/4G/WLAN and even future 5G,it will become important to be able to use them simultaneously.This may bring about some self-interference;3)The coverage radius of the small cell is smaller than that of the macro cell,so there are more frequent cell handovers.The literature shows that the handover performance of heterogeneous networks is not as good as a pure macro cell,and mobility management needs to be redesigned.The main innovations in this dissertation are summarized as follows:Firstly,considering both non-line-of-sight(NLoS)and line-of-sight(LoS)transmissions,the transitional behaviors from noise-limited regime to dense interference-limited regime have been investigated for the fifth generation(5G)small cell networks(SCNs).Besides,we identify four performance regimes based on base station(BS)density,i.e.,(i)the noise-limited regime,(ii)the signal-dominated regime,(iii)the interference-dominated regime,and(iv)the interference-limited regime.To characterize the performance regime,we propose a unified framework analyzing the future 5G wireless networks over generalized shadowing/fading channels,in which the user association schemes based on the strongest instantaneous received power(SIRP)and the strongest average received power(SARP)can be studied,while NLoS/LoS transmissions and multi-slop path loss model are considered.Simulation results indicate that different factors,i.e.,noise,desired signal,and interference,successively and separately dominate the network performance with the increase of BS density.Hence,our results shed new light on the design and management of SCNs in urban and rural areas with different BS deployment densities.Secondly,we investigate network performance of ultra-dense heterogeneous networks(HetNets)and study the maximum energy-efficient BS deployment incorporating probabilistic NLoS and LoS transmissions.First,we develop an analytical framework with the maximum instantaneous received power(MIRP)and the maximum average received power(MARP)association schemes to model the coverage probability and related performance metrics,e.g.,the potential throughput(PT)and the energy efficiency(EE).Second,we formulate two optimization problems to achieve the maximum energy-efficient deployment solution with specific service criteria.Simulation results show that there are tradeoffs among the coverage probability,the total power consumption,and the EE.To be specific,the maximum coverage probability with ideal power consumption is superior to that with practical power consumption when the total power constraint is small and inferior to that with practical power consumption when the total power constraint becomes large.Moreover,the maximum EE is a decreasing function with respect to the coverage probability constraint.Thirdly,the control and user plane separation(CUPS)architecture becomes more appealing for higher mobility profiles as the densification of networks.Compared with the conventional architecture,CUPS architecture is envisioned to provide enhancement for networks,e.g.,reducing latency on application service,in a flexible way,while not affecting the functionality of the existing BSs.In this dissertation,we compare the performance of ultra-dense millimeter-wave networks with the conventional and the CUPS architectures.An analytical framework is proposed to study the coverage probability and handover cost,which takes the propagation characteristic of millimeter-wave networks into consideration.The proposed framework is then simplified in an ultra-dense scenario,formulating two optimization problems to achieve the minimal handover cost while guaranteeing the minimal coverage probability requirement.Numerical results show that the CUPS architecture outperforms the conventional architecture with respect to the coverage probability as well as the handover cost.Moreover,we shed light on network deployment,indicating that the optimal deployment solution for networks with the conventional architecture is adding more macrocell BSs(MBSs)into the existing networks;in contrast,the optimal solution for networks with the CUPS architecture is adding more small cell BSs(SBSs)into the existing networks.Finally,it is a great challenge to evaluate the network performance of cellular mobile communication systems.In this dissertation,we propose new spatial spectrum and energy efficiency models for Poisson-Voronoi tessellation(PVT)random cellular networks.To evaluate the user access the network,a Markov chain based wireless channel access model is first proposed for PVT random cellular networks.On that basis,the outage probability and blocking probability of PVT random cellular networks are derived,which can be computed numerically.Furthermore,taking into account the call arrival rate,the path loss exponent and the BS density in random cellular networks,spatial spectrum and energy efficiency models are proposed and analyzed for PVT random cellular networks.Numerical simulations are conducted to evaluate the network spectrum and energy efficiency in PVT random cellular networks.In summary,this dissertation focuses on the challenges and unresolved issues in the deployment of future 5G ultra-dense networks and combines a general theoretical model to demonstrate the necessity of 5G ultra-dense networks and brings them for ultra-dense deployments.The problem of declining user service quality provides an optimized deployment scheme for base stations under the guarantee of service quality,which provides certain reference and reference for future deployment of base stations.