On The Basic Theory And Key Technologies Of Buffer-aided Wireless Powered Communication Networks

With the rapid development of mobile networks and smart terminals,the explosive growth of mobile data has posed enormous challenges to wireless communication technologies.On one hand,the key issue of wireless communication research is how to design an efficient wireless transmission scheme to significantly improve the spectral efficiency and energy efficiency.On the other hand,with the increasing maturity of energy-constrained networks such as the Internet of things,the number of wireless devices is growing rapidly,which results in the cost of power-ing large-scale mobile devices or frequently replacing battery will increase dramatically.In the energy-constrained network,how to obtain a sustainable energy supply and achieve efficient wireless information transmission has become one of the most important issues in the field of wireless communication.Buffer-aided wireless transmission technologies have attracted con-siderable attention due to their ability to significantly improve the energy sustainability and re-duce power consumption.Benefiting from the great potential of buffers in wireless communica-tion networks,this thesis takes wireless powered communication networks(WPCN)as the basic research object,and integrates the data buffer and energy storage into wireless energy transfer technique to improve the system performance and prolong the lifetime of energy-constrained networks.We conduct in-depth research on the buffer-aided WPCN from three aspects:system model,transmission scheme design,and performance analysis.Firstly,a buffer-aided two-way wireless powered relay network is investigated.we explore the impact of the data buffer and energy storage on the achievable rate region of the system.The system model is modeled to maximize the achievable rate region by jointly considering the power and rate allocation under constraints of the data queue and energy queue causality,the average power,and the peak power.By transforming the original non-convex problem into a convex one,we present an optimal transmission design.To fulfill delay-sensitive transmission requirements,a delay-aware adaptive transmission scheduling scheme is proposed to guarantee the average delivery delay.Our analysis discloses that,the average achievable rate region of the two-way wireless powered relay network can be improved when fully considering the potentials by deploying data buffer and energy storage at the relay,and there exists an inherent tradeoff among the achievable sum rate,the delivery delay,and the power consumption.Secondly,we study the energy efficiency issue of a buffer-aided wireless powered cooper-ative non-orthogonal multiple access network.We aim at minimizing the power consumption of the system subject to the given target of users.Based on the conventional time switching re-laying(TSR)and power splitting relaying(PSR)protocols without buffering,we first derive the minimum power consumption for TSR and PSR,respectively.Considering the scenario where the relay is equipped with the data buffer and energy storage,an energy-efficient buffer-aided adaptive transmission scheme is proposed to minimize the average power consumption of the system.The analysis results show that,compared with conventional TSR and PSR protocols,benefiting from the advantages of the data buffer and energy storage,the proposed energy-efficiency buffer-aided adaptive transmission scheme can significantly improve the energy effi-ciency of the system,and reveals the tradeoff between the average power consumption and the average queuing delay.Thirdly,the effects of the finite data buffer and energy storage on the transmission perfor-mance of the wireless powered communication network are investigated.For the limited data buffer and energy storage size,there might be data loss due to either data buffer overflow or en-ergy storage depletion.We propose a buffer-aided adaptive transmission scheme,in which the energy beamforming vector design,the power allocation,the rate control,the time allocation,and the transmission mode selection are jointly optimized to maximize the average transmis-sion of users subject to data loss ratio requirements.In addition,in order to effectively meet the fair access requirements,a weighted max-min fair access scheme is proposed to ensure that the access rate of all users is max-min fair.Finally,we study the data gathering and wireless energy transfer problem in rechargeable wireless sensor networks with a mobile sink.We aim at maximizing the network utility by designing an efficient routing,the transmission power control scheme,the energy beamforming,and the traveling speed control scheme.To reduce the computing load of the mobile sink,we propose a distributed speed control and routing algorithm to obtain the near-optimal solution for data gathering.Moreover,our analysis unveils that,there exists an inherent tradeoff between the average data queue size and the network utility,and it is shown that the proposed adaptive transmission scheme can achieve the near-optimal network utility if a certain queueing delay is tolerable.In summary,this thesis conducts an in-depth study on the buffer-aided wireless powered communication networks,and explores the impact of the data buffer and energy storage on user scheduling,power allocation,and energy transmission,and reveals the tradeoff between the transmission rate,energy consumption,and transmission delay.