Research On Energy Efficiency In Wireless Information And Energy Transfer Network

With the development of mobile communication technology,the fifth-generation mobile communication technology(5G)system has provided higher transmission rate and better service quality.In the future of the Internet of Everything era,the amount growth of small mobile devices will be explosive,and reducing the system consumption to achieve high energy efficiency communication is particularly important.In order to improve energy efficiency,reducing energy consumption while ensuring user service quality needs the optimization of system resources allocation.Under the existing network,resource allocation schemes represented by beamforming and other technologies can improve the efficiency of information transmission,but many electromagnetic wave resources are not fully utilized due to the negative effects such as interference.At the same time,small mobile devices often work in a passive environment,without appropriate energy supply,the equipment can not continue to work.The one-time use of devices caused huge waste,while the workload of large-scale recycling is also huge.Therefore,in order to better realize green communication,it is not only necessary to carry out reasonable network deployment and optimize hardware to reduce emissions,but also necessary to combine some new technologies to improve the utilization of resources.Wireless information and energy transfer technology,as a new transmission mode,can utilize the energy and information in the wireless electromagnetic wave more fully.It provides users with high rate of information transmission as well as providing energy,which ensures the system communication and prolongs the lifetime of the network.The transmission has gradually become a fundamental technology in modern communication.According to the dual needs of users’ information and energy,wireless information and energy transfer technology can make more effective use of system resources by utilizing the advantages of wireless information transmission and wireless energy transfer.But it also brings about the difference in the allocation of system resources in the two transmission processes.The increase of transmission power will certainly meet the demand for information transmission and energy transfer,however which will bring a lot of energy waste.In this case,the core research of wireless information and energy system is the trade-off between information transmission and energy transfer.And the problem can be solved effectively by optimizing the energy efficiency of the system,that is increasing the amount of information that can be transmitted per unit of energy.Therefore,based on the actual wireless information and energy transfer scenarios and service requirements,this paper studies how to improve the energy efficiency of the system and solve the tradeoff problem of information and energy by means of jointly optimization of beamforming,receiver strategy design and other resource allocation methods at the transmitting and receiving ends.The main research contents are as follows:Firstly,we study energy-efficient transmission design in the downlink wireless information and energy transfer networks.We put forward a novel transmission scheme where beamforming is divided by time switching into two parts,energy beamforming and information beamforming,and users receive by hybrid time switching and power splitting correspondingly.An optimization problem is established to maximize energy efficiency.According to the definition of system energy efficiency,it can be improved by increasing the total information transmission of all users or reducing the total energy consumption of the system.When the total amount of information transmitted by the system is fixed,the problem of maximizing energy efficiency can be transformed into the problem of minimizing energy consumption while meeting the rated information transmission requirements.Then,through equivalent transformation,the minimum energy consumption problem is decomposed into two sub-problems,and the sub-problems are proved to be optimal at the same time,and the optimal energy efficiency of the system is obtained.Furthermore,in order to solve the problem of high computational complexity in the process of optimal algorithm,a low-complexity suboptimal transmission schemes based on zero-forced beamforming technology is proposed.Simulation results show that the proposed strategy can effectively improve the energy efficiency of the system.Secondly,we focus on energy-efficient transmission design in the downlink wireless energy transfer and uplink wireless information transmission networks.A novel transmission scheme is proposed to maximize energy efficiency by jointly optimization of antenna number,channel estimation duration,energy precoding of source nodes,energy transmission power,energy transmission duration,and information transmission duration at passive nodes.According to the practical network application scenario,this paper considers that with the increase of the antennas number,the power consumption of source nodes increases greatly,which has a great impact on the energy efficiency of the system.A scalable energy consumption model is proposed to make the analysis of the circuit consumption of the source node more close to the actual system consumption,and then the calculation of energy efficiency is more accurate.In this paper,the maximal energy efficiency of the system is established as the objective function under the condition of ensuring system information transmission and sufficient energy supply of each node.In the solving part,a distributed iterative algorithm based fractional programming and Lagrange dual function is proposed to solve the optimization problem.Simulation results show that the proposed strategy can effectively improve the energy efficiency of the system.Finally,we study energy-efficient transmission design in the uplink wireless information and energy transfer networks.This paper proposes a new high energy-efficient wireless information and energy transfer design by jointly optimization of power control and relay selection while meeting the information transmission threshold and energy transfer threshold of the system.In order to more accord with the actual network application scenario,this paper considers the nonlinear model of energy harvesting.Meanwhile,to reduce the node operation cost,switching between single relay forwarding transmission and direct transmission is adopted.The maximal energy efficiency optimization problem is established as a non-convex optimization fractional structure problem,and then it is transformed equivalently into a subtraction convex problem to solve.In the process of solving,a distributed iterative method is proposed by using the Lagrange dual function.The closed-form solutions of the transmitting power,the energy harvesting time factor,the information transmission time factor and the relay selection strategy are given.Simulation results show that the proposed strategy can effectively improve the energy efficiency of the system.