Investigation On Beamforming Of Intelligent Reflecting Surface-assisted Simultaneous Wireless Information And Power Transfer Systems

With the application deployment of the fifth generation mobile communication network(5G)and the rapid development of the Internet of Things,a large number of low-power devices have become more widely used,thus making simultaneous wireless information and power transfer(SWIPT)technology more and more concerned.The SWIPT technology can use the same frequency band to transmit energy and information to the energy receivers and the information receivers at the same time,which solve the energy problem of low-power devices while ensuring the quality of communication.However,as the wireless frequency bands are getting higher and higher,the signal coverage will be limited due to factors such as distance or obstacles.In addition,in the application of Io T systems,the information receivers are often dense,and serious signal interference problems will also reduce the throughput of the system.In recent years,intelligent reflecting surfaces(IRS)that are expected to alleviate the above problems have received widespread attention.The IRS is a new type of application device based on metamaterials,which is low in cost,low power consumption,programmable and easy to install.The IRS can control the phase shift through the electronic control center in real time,forming a passive beamforming and passively reflecting the incident signal to the corresponding direction and position,which can effectively reduce the communication interference and enlarge the signal coverage area.The IRS-assisted SWIPT system can effectively solve the energy supply problem of a large number of low-power devices,while ensuring high-quality communication transmission.The research of dissertation mainly includes the following contents:(1)In order to ensure the balance of energy harvesting(EH)and information decoding(ID)performance in the multiple-input single-output(MISO)SWIPT system,with the assistance of a dedicatedly deployed IRS,a multi-antenna access point(AP)sends both information and energy signals to a set of receivers each for ID or EH.Under this setup,by jointly optimizing the active transmit information and energy bearmfoming at the AP and the passive phase-shifting at the IRS,we aim to maximize the minimum received energy among EH receivers,subject to the SINR of each ID receiver and the transmit power at AP.Although the SINR-constrainted maximization problem is highly non-convex,we apply semi-definite relaxation(SDR)algorithm and iterative optimization algorithm to obtain a high quality solution.The numerical result prove that our algorithm can solve the problem with high-quality.(2)Furtherly,we extended the single antenna EH receivers to multi-antenna.In the multiple-input multiple-output(MIMO)SWIPT system,we solve the problem in an alternative manner.Firstly,we fixed the IRS phase-shift and optimize the active beamforming,and then optimize the passive beamforming phase-shift one by one.With the joint alternating optimization algorithm,we obtain faster convergence speed and higher system gain.The simulation results confirm the effectiveness of our algorithm.