Beamforming In Intelligent Reflecting Surface Aided Wireless Communication Systems

The sixth-generation mobile communication(6G)is moving towards the communication mode with higher frequency bands and larger bandwidth,but it is faced with the challenges that the high-frequency band channel environment is poor,the development of antenna scale is limited,and the energy consumption burden is increasing.Intelligent reflecting surface(IRS)has the unique advantages of low cost,low power consumption,and intelligent control of wireless channels.It provides a new idea to solve the above challenges and therefore becomes one of the potential key technologies of 6G.IRS-aided wireless communication systems are widely used,so it is critical of the IRS beamforming technology to display the IRSs in terms of potential to improve the system performance.However,different scenarios have different characteristics and requirements,and how to carry out the IRS beamforming in response to the special challenges and different goals is a hot and difficult problem.This paper studies IRS beamforming for different scenarios with different challenges,such as maritime wireless communication systems,orthogonal frequency division multiplexing(OFDM)multi-carrier communication systems,and integrated sensing and communication in millimeter wave communication systems.Specifically,firstly,aiming at the challenge of short data transmission in maritime wireless communication systems,a hybrid distributed transmission mode assisted by multiple passive IRSs and conventional active relays is proposed,and a joint design scheme of mode selection,power control,and beamforming is designed to effectively improve the coverage under the same energy supply.Secondly,in view of the challenges that the independent multi-carrier regulation is difficult for IRSs,and the overhead of cascaded channel state information(CSI)estimation under multiple carriers and multiple reflecting elements is extremely high in IRS-aided OFDM communication systems,a location-sensing-based beamforming scheme without cascaded channel estimation is proposed,which can effectively reduce the system channel estimation overhead while ensuring communication performance.Finally,the application of IRSs in the integrated sensing and communication of millimeter wave communication systems is explored.Aiming at the challenge that the sensing and communication performances are difficult to balance due to the sensing echo interference from the communication beam direction,a feedback-based integrated sensing and communication beam training scheme without channel estimation is proposed,which can effectively restrain the sensing echo interference to balance the sensing and communication performances as needed.To this end,in this paper,IRS beamforming technologies that face special challenges in different scenarios are studied as follows:1.Beamforming in IRS-aided active relay communication systemsTo solve the challenge of short transmission distance in maritime wireless communication systems,this dissertation proposes a new efficient transmission and joint beamforming scheme combining distributed active relays and passive IRSs to extend the maritime coverage area.Specifically,the dissertation first models a novel IRS-aided maritime relay communication system,analyzes the impacts of the relay operation mode,transmit power,and beamforming design of base station(BS)and IRSs on the system performance,and proposes a joint mode selection,power control,BS transmit beamforming,and IRS reflecting beamforming scheme to minimize the total transmit power while ensuring the system communication performance.Simulation results show that,compared to the conventional active relay scheme,the proposed IRS-aided active relay hybrid transmission mode and beamforming scheme can effectively extend maritime communication coverage under the same energy supply.Moreover,by analyzing the system performance of the proposed scheme under different system configurations,the internal relationships between the operation mode,the number of relay nodes,and the system performance are summarized.2.Location-sensing-based beamforming in IRS-aided OFDM communication systemsTo solve the challenge of the high overhead of cascaded CSI acquisition in IRS-aided OFDM multi-carrier communication systems,this dissertation proposes a location-sensingbased beamforming scheme without cascaded channel estimation to reduce the channel estimation overhead while ensuring the system communication performance.Specifically.the dissertation models a multi-IRS-aided OFDM communication system,and designs a three-phase data transmission protocol including a location-information-assisted IRS reflecting beam training phase,an equivalent channel estimation phase,and a data transmission phase.The effective channel angle information can be obtained by exploring the essential relationship between location information and ch annel estimation,a locationsensing-based beamforming scheme is proposed to maximize the system communication rate,where a bisection-based IRS reflecting beam training method,an equivalent channel estimation method,and an optimal design method of BS transmit beams are proposed for three phases,respectively,and the expressions of BS transmit beams and IRS reflecting beams are provided.Finally,the advantages and disadvantages of the proposed locationsensing-based beamforming scheme and the influences of different parameters on the system performance under the proposed scheme are explored.Simulation results verify that the proposed location-sensing-based beamforming scheme can efficiently obtain the BS transmit beams and IRS reflecting beams without cascaded channel estimation.Under the same system multi-carrier reachable rate,the proposed scheme can equivalently reduce the channel estimation cost by 40%.3,Beamforming for integrated sensing and communication in IRS-aided mm Wave communication systemsTo solve the challenge that the sensing performance and communication performance are difficult to balance in IRS-aided integrated sensing and communication systems due to the sensing echo interference from the communication beam direction,this dissertation proposes a feedback-based integrated sensing and communication beam training scheme without channel estimation to restrain the interference and balance the sensing and communication performances as needed.Specifically,the dissertation models an IRS-aided millimeter wave blind-zone integrated sensing and communication system,proposes a complex sensing echo signal model including the echo signal from the communication user,improves the joint sensing and communication performances by limiting the echo interference from the communication beam direction,and provides the expressions of communication performance and sensing performance.Considering a practical scenario where the CSI is unknown,a feedback-based integrated sensing and communication beam training scheme is proposed to fully utilize the IRS beamforming gain,limit the echo interference,and balance the sensing and communication performances as needed.The update schemes about BS transmit beams and IRS reflecting beams are designed jointly based on the particle swarm optimization idea,and the impact of the echo interference constraint on the joint sensing and communication performances is studied.Simulation results show that the proposed scheme can obtain the BS transmit beams and IRS reflecting beams without channel estimation,and effectively balance the sensing performance and communication performance by limiting the echo interference signal strength from the communication beam direction.In view of the special challenges faced by IRS-aided maritime wireless communication systems,OFDM multi-carrier communication systems,and the integrated sensing and communication scenario in millimeter wave communication systems,this paper researches the key technologies of IRS beamforming in different scenarios,and relevant research results can provide the theoretical support for IRS large-scale commercial use in the future.