Theoretical Research Of High Efficient Ultra-Dense Cellular Networks

With the fast-growing data traffic and the explosive increase of mobile devices,the operator has proposed to deploy ultra-dense heterogenous cellular networks to meet the incremental traffic demand of users and to improve the network capacity.Under the constraints of limited spectral and energy resources,operators pay more attention to the network spectral,energy and economic efficiency during and before the operation.To further enhance the network capacity and fully utilize the radio frequency,resear chers have considered to incorporate device-to-device(D2D)communications into cellular networks,which can alleviate the traffic burden of base stations.Therefore,how to design an efficient wireless network from the system-level perspective based on the analysis of theoretical model as well as the parameters optimization has become a key challenge of future research direction.We first introduce the research background and significance of the ultra-dense heterogenous cellular networks,and we present the technologies of ultra-dense small cell cellular networks and D2 D communications.Regarding to the problem of traffic offloading in the ultra-dense cellular networks,we discuss the applications and implementations of the D2 D assisted offloading in cellular networks.Then,we illustrate the network economic efficiency and the network energy efficiency in the sequel,which are usually used to evaluate the performance of wireless network.Next,we study an economic aspect of traffic offloading via content sharing among multiple devices and propose an incentive framework for D2 D assisted offloading.Leveraging the tools from stochastic geometry,we model the distributions of base stations,users and D2 D transmitters as independent two-dimensional Poisson point processes.Furthermore,we analytically characterize the impact of different-tier interferences on the performance of cellular link and D2 D link,and the relationship between the shared content popularity and the residual cellular users' density is obtained.In addition,we derive the expected minimum transmit powers of a typical base station and D2 D transmitter.The closed-form expressions of the network economic efficiency with underlay and overlay modes of D2 D communications are obtained.To well capture the economic interactions between the operator and the D2 D transmitter,we model the optimization of the network economic efficiency as a two-stage Stackelberg game,and the results show that the network economic efficiency can be maximized by optimizing the incentives and the bandwidth allocation parameters.Finally,from the point of network energy efficiency,we model and analyze the wireless-powered D2D-assisted offloading in cellular networks,where the D2 D transmitters can harvest the radio frequency energy from nearby BSs and utilize the harvested energy to share popular contents with nearby users.Stochastic geometry is used to characterize the intrinsic relationship between the wireless power transfer and the wireless information transmission.Based on the proposed model,we derive the average transmit power at a typical D2 D transmitter,the expected minimum transmit power at a typical base station,the D2 D user's outage probability and the cellular downlink user's outage probability.We also investigate the energy efficiency of the entire network from the system-level perspective.Our results show that the network energy efficiency can be maximized by optimizing the fraction of time allocated for wireless power transfer and it can be further improved by using massive antenna arrays at each base station and by sharing more popular contents between devices.