Research On Energy Efficient Decoupled Uplink/Downlink Access In Heterogeneous Cellular Networks

With the rapid development of Internet and Internet of Things(IoT),the data traffic of wireless communication systems is explosively growing.Under limited spectrum resources,hetgeneous cellular network(Hetnet)has been proposed as an effective way to improve network capacity.Based on infrustructures deployed by traditional homogeneous cellular networks,HetNets additionally deploy low-power and low-cost equipment on hot or blind traffic areas to achieve better services.Although the low-power small base stations(BSs)lower the average energy consumption of BSs,the increasing small BSs increase the energy consumption of the whole network.Especially in the 5th generation communication system,with denser BS deployment,energy efficient HetNets design has arose great attention in both industry and academia.In this paper,we focus on the access architecture design of HetNet,and theoretically analyze and develop a new energy efficient HetNet access architecture,named uplink(UL)and downlink(DL)decoupled access(DUDA)architecture.In conventional cellular networks,a user accesses to a same BS in both UL and DL transmissions.This BS is usually the geographically nearest BS,which also dlivers the strongest received signal.However,the conventional access scheme is no longer effective in HetNets.On one hand,BSs in different tiers of HetNets have different transmit power,and thus the geographically nearst BS may not be the one with the strongest received signal strength.On the other hand,user equipment with limited power may prefers to access the geographically nearest BS for energy saving.Due to different access cretirias of UL and DL transmissions,analysis for DUDA mode has drawn great concerns.Based on existing research,this paper comprehensively analyzs DUDA mode,in terms of application scenarios,challenges,exsiting problems and possible solutions.Through using stochastic geometry and queuing theory tools,we respectively analyze the network performance benefits brought by DUDA mode,the universality for different scenarios,the energy efficient design for DUDA mode,etc.The main work and achievements of this thesis are as follows.1)We theoretically analyze the performance benefits of HetNets brought by DUDA mode.Compared with conventional access mode,DUDA mode intuitively improves the UL performance.However,there exists additional cost,such as signal synchronization,authentication and handover.By using stochastic geometry,we theoretically model DUDA mode and evaluate the performance gain compared with conventional access mode.The results show that DUDA mode bring performance benefits including load balance,improved spectrum efficiency and energy efficiency,and fairness of user services,which laid solid foundation for practical application of DUDA mode.2)DUDA mode can be effectively applied in multiple network scenarios.This paper analyses two typical user distributions,including uniform distribution and clustering distribution in hot traffic areas respectively by Poisson point process and Poisson cluster process.The results show that both the two user distributions can improve network performance.Although the clustering distributed user scenario introduces certain difficulty of our modelling,the analysis reveals the applicability of DUDA mode.3)We theoretically analyze energy-efficient sleep strategy for DUDA mode.Although DUDA mode can improve the energy efficiency of HetNets,the application of sleep strategy may further brings higher energy efficiency.Through using stochastic geometry theory,we model the sleep strategy for a two-tier HetNet.The results show that conventional sleep strategy designed for conventional coupled UL/DL access mode can not be applied to DUDA mode,which may leads to excessive turn off,lower the quality of user services and decrease the actual system energy efficiency.According to the characteristics of DUDA mode,we design a novel sleep strategy,which can effectively save energy and garantee high-quality services.4)We design energy efficient DUDA sleep strategy considering dynamic user arrivals.According to queuing theory,we model the sleep process of DUDA mode.We explore the tradeoff between the energy saving and tolerable access delay by specifying appropriate sleep window size,which provides insights for DUDA sleep design with dynamic user traffic.