| In recent years,with the development of wireless energy transmission technology,Wireless Powered Communication Networks(WPCN)is considered as a promising alternative to traditional wireless sensor networks.Compared with traditional wireless sensor networks,nodes in WPCN can collect energy from the environment without replacing or charging the battery manually,thus reducing the cost of manual operation.However,the unique phase cancellation problem in WPCN will seriously affect the communication performance of the network.In this paper,an effective node deployment scheme is proposed to solve the phase cancellation problem,which ensures the connectivity and reliability of the network.First of all,this paper explores the fundamental reasons for the existence of phase cancellation and constructs a communication model that can find the signal blind zone caused by phase cancellation.In WPCN,the communication between nodes is realized by backscattering modulation of the RF signal in the environment.However,due to the vector superposition of the backscattered signal and the RF signal in the environment at the receiving node,the receiving node may not be able to effectively demodulate the backscattered signal of the transmitting node due to its low-cost hardware,resulting in communication failure.Through theoretical analysis and experimental verification,it is found that the connectivity between nodes is closely related to the location of nodes.If the network topology is not properly planned in advance,the signals sent from the sending node may not be transmitted to the receiving node in a direct or multi-hop manner.According to Friis free space propagation formula and the principle of signal superposition,this paper constructs a communication model that can find the signal blind zone caused by phase cancellation,and uses it as a guide to deploy a reliable WPCN.Secondly,this paper proposes a set of two-stage deployment plans.In the first stage,in order to ensure that the information of all passive nodes in the network can be effectively used,this paper deploys a group of aggregation nodes outside the signal blind area to collect and forward the information of passive nodes.This paper proposes a greedy algorithm to provide data transmission services for all passive nodes with as few sink nodes as possible.In the second stage,on the basis of the already deployed sink nodes,this paper adds and deploys a group of relay nodes to connect the network composed of passive nodes and sink nodes.This paper proposes an algorithm based on minimum weight graph to construct a connected network with as few relay nodes as possible.Finally,this paper evaluates the performance of the proposed deployment scheme through a large number of simulation experiments.The results show that the performance of the proposed algorithm is 7 times better than that of the comparison algorithm in reducing the number of deployed sink nodes and relay nodes.In the scenario that there are 300 randomly distributed passive nodes in the network,the scheme in this paper only needs to deploy an average of 20 sink nodes and 9 relay nodes to make the network two-way connected. |
