Research On Power Allocation Of UAV Relay-Assisted Wireless Powered Communication Networks

The rise of the Internet of Everything concept has enabled a large number of Io T wireless devices to connect to the Internet.However,the battery life of wireless devices is usually limited due to their small battery capacity.How to improve the battery life of wireless devices has become a key issue that needs to be solved urgently.Wireless Powered Communication Networks(WPCN)with wireless energy transmission as the core can easily and stably transmit energy and collect information for wireless devices,which is expected to solve the above problems,so it has become a research hotspot in the field of Internet of Things.However,the problem of energy transmission loss makes WPCN mainly suitable for short-range communication with lower transmit power requirements.Considering the Line-of-Sight characteristics of UAV communication and the ability of relay cooperation,this thesis combines UAV relay and WPCN technology to study the power resource allocation technology of UAV relay-assisted WPCN.The main contributions of this thesis are listed as follows:Firstly,the transmission capacity of UAV relay-assisted WPCN is studied,in which UAV as a Hybrid Relay Node(HRN)first transmits energy to passive node,and then uses Amplify and Forward(AF)or Decode and Forward(DF)protocol assists passive node to transmit information to information access point.Under the constraint of the limited total power of UAV,according to different protocols,power allocation schemes to maximize the system channel capacity are proposed respectively,and the optimization problem of the power allocation of the UAV’s energy transmission power and information transmission is constructed.For the AF protocol,the constructed power allocation problem is proved to be a convex optimization problem,and an iterative algorithm for optimal power allocation is designed.For the DF protocol,a closed-form solution for optimal power allocation is derived.The simulation results show that the proposed power allocation scheme is significantly better than the traditional equal power allocation scheme in terms of channel capacity.Secondly,the transmission reliability of UAV relay-assisted WPCN is studied,in which UAV as HRN first transmits energy to passive node,and then uses DF protocol assists passive node to transmit information to information access point.An approximate closed expression for the outage probability of the system under the Rice fading channel is derived.Under the constraint of the total power of the UAV,a power allocation scheme that minimizes the outage probability of system is proposed,and the optimization problem of the power allocation of the UAV’s energy transmission power and information transmission power is constructed.Due to the high complexity of the objective function of the constructed problem,an iterative algorithm for optimal power allocation based on particle swarm optimization is designed.The simulation results show that the proposed power allocation scheme significantly reduces the system outage probability compared with the traditional equal power allocation scheme.Finally,the physical layer security of UAV relay-assisted WPCN is studied,in which UAV as HRN first transmits energy to passive node,and then uses AF protocol assists passive node to transmit information to information access point,and there are ground eavesdropping node tries to eavesdrop on the source node information forwarded by the UAV.Under the constraint of the total power of the UAV,a power allocation scheme to maximize the safety capacity of the system is proposed,and the optimization problem of the power allocation of the UAV’s energy transmission power and information transmission power is constructed.Due to the non-convexity of the constructed problem,the Taylor expansion is used for convex approximation of the problem,and a two-layer iterative power allocation algorithm is designed,and the convergence of the algorithm is guaranteed.The simulation results show that the safety capacity of the proposed power allocation scheme is significantly higher than that of the traditional equal power allocation scheme.