Analysis And Research On Energy Haversting Wireless Sensor Network Nodes With Energy Backup

In recent years,with the wide application of Internet of Things,Cloud Computing and other technologies in Wireless Sensor Network(WSN),WSNs is considered that has the potential to change the world.However,the lifetime and network performance of WSNs are always constrained by the energy constraints of sensor nodes.In order to solve the problem of energy constraints of traditional WSNs,Energy Harvesting Wireless Sensor Network(EH-WSN)came into being with the development of energy harvesting technology and energy conversion technology.In EH-WSN,sensor nodes can convert external environmental energy into electrical energy for nodes to communicaiton.However,the randomness and stability of external energy harvesting will make the sensor nodes unable to ensure stable data transmission.Therefore,the simple power supply mode of energy harvesting can not make the wireless sensor networks realize uninterrupted long-term or permanent communication.Based on the above background,this paper studies the energy management and data transmission strategy of Energy Harvesting Wireless Sensor Network with reliable backup energy.The main contents include the following three aspects:(1)A scheme of hybrid power supply for wireless sensor nodes with replaceable battery as standby energy and external energy harvesting is proposed in this paper.On the energy harvesting(EH)wireless sensor network node,the battery is used as a substitute for the energy buffer.When the energy in the battery is exhausted,another new fully charged battery is connected immediately.The new battery not only brings new energy,but also can receive the energy obtained from the outside when the battery energy is dissatisfied.This not only makes use of the energy obtained from the outside,but also avoids the impact of energy depletion on the system.Firstly,the Markov random fluid queue is used to model the system,and then the stationary density of the system horizontal process is derived according to the model.According to the derivation process of the stationary density,two important performance indexes,the average replacement time of the battery and the risk coefficient of the system replacing the battery,are further obtained.Finally,the numerical implementation and simulation verification of the theoretical results are given.(2)A scheme of hybrid power supply for EH key nodes by connecting to the power grid as standby energy and external energy harvesting is proposed in this paper.For the scenario of high energy consumption of EH key nodes and convenient access to the power grid,the power grid will supply energy to the system at a constant energy rate after access.If EH node is continuously tconnected to the power grid,it will lead to serious energy waste.The access of power grid is often controlled by the energy level in the energy buffer.Specifically,wecanset the upper reminder value and the lower reminder value respectively.When unconnected to the power grid and the energy buffer level touching the lower reminder value,it’s time to connect to the power grid.On the contrary,when connected to the power grid and the energy buffer level touching the lower reminder value,it’s time to disconnect the power grid.Firstly,the stationary probability density function and stationary distribution function of energy level in the buffer are obtained by using the method of expanding the state space.The average time of single access to the power grid and the time of non access to the power grid are obtained through the Laplace-StieltjesTransform of two First Passage Times at the first arrival time,and they are converted into the dimensionless average time of single access to the power grid,so as to obtain the influence of the upper reminder value on the access to the power grid.Finally,the numerical realization of stationary density function and stationary distribution function is given,and the correctness of the theoretical results is verified by the numerical simulation results of stationary distribution function.(3)The energy supplement data transmission strategy of Energy Harvesting Wireless Sensor nodes with reliable energy backup is studied.The goal is to use the minimum energy consumption to transmit the specified amount of data in a limited time in the wireless channel.A new stochastic system model for point-to-point data transmission of EH wireless sensor nodes with backup power supply is proposed.In this model,a delay limited data transmission is considered,and the data task should be completed within the specified time limit.Two stochastic processes are used to model the energy collection process and channel fading process respectively.On this basis,the dynamics of transmitter energy level and the evolution of residual data task process are characterized.The control problem is modeled as a Markov decision process(MDP)to obtain the best energy supplement strategy required by Reliable Energy Backup(REB)and the minimum expected energy consumption provided by REB.When the energy supply of EH wireless sensor nodes is only provided by REB,using the concept of supermode,it is proved that the optimal energy replenishment strategy is a monotonic increasing function of the remaining transmission time and the remaining amount of data tasks.The optimized energy supplement strategy proposed in this paper is to minimize the total expected energy consumption provided by the backup power supply and ensure that the data task is completed within the limitedtime,so as to ensure the timeliness of data communication.