Research On Optimization Methods Of Full-Duplex Communication Using Intelligent Omnidirectional Surface

With the development of the 6th generation wireless communication technology,omnidirectional intelligent surface has attracted extensive attention.The omnidirectional intelligent surface,also known as simultaneous transmitting and reflecting reconfigurable intelligent surface(STAR-RIS),is introduced based on reconfigurable intelligent surface(RIS).STAR-RIS consists of a large number of reconfigurable components.By jointly adjusting the phases and amplitudes of all components,the phases of different propagation paths can be aligned,thereby enhancing the signal energy,and improving the transmission performance.Further,STAR-RIS can simultaneously adjust the phases of the signals which are reflected at its surface and which are penetrated through the surface,thus achieving a larger coverage than RIS.Full duplex communications have received a lot of attentions due to their ability to double the spectrum utilization,which enables multiple users exchange information simultaneously within the same timefrequency resource block.However,full duplex communications on the same time-frequency resource face numerous problems.One is the interference between users caused by its closeness,and the other is the selfinterference of the Base Station.Since STAR-RIS can enhance useful signals and weaken interference signals by adjusting the amplitudes and phases of the signals on different paths,and its advantage compares to traditional RIS in terms of flexibility and coverage,this thesis proposed an optimized scheme for transmission interference suppression of full duplex base stations in conjunction with STAR-RIS to deal with the inter-user interference in full duplex communications.Further,this thesis proposed an optimized scheme of full duplex communications by combining dual STAR-RISs to deal with the self-interference in full duplex communications.For orthogonal frequency division multiplexing(OFDM)full duplex communication systems assisted by STAR-RIS,this thesis proposed a scheme which deploying a STAR-RIS between uplink users and downlink users.With the assumption of perfect channel state information in a singleinput single-output(SISO)communication system,the proposed scheme can suppress inter-user interference.A model for optimizing the mean square error of signals received on multicarrier by setting the transmission and reflection coefficients of the STAR-RIS is established with a given transmission power.The optimal transmission and reflection coefficient matrix settings of the STAR-RIS are obtained through alternate optimization algorithm.Theoretical analysis and simulation results have verified that the proposed inter-user interference suppression scheme can significantly reduce the mean square error of the received signals.Compared with traditional schemes of deploying RIS,simulation results have verified that the proposed scheme outperforms the traditional schemes.For a full duplex SISO communication system assisted by STAR-RIS,this thesis proposed an interference suppression scheme of deploying two STAR-RISs in a communication system with the assumption of perfect channel state information.One STAR-RIS is deployed near the base station to eliminate the self-interference of the base station,and the other STARRIS is deployed between uplink users and downlink users to suppress interuser interference.A model is established to optimize the mean square error of the received signals by setting the transmission and reflection coefficients of the two STAR-RISs under a given transmission power.The reflection coefficients of the STAR-RIS near the base station are obtained based on the algorithm proposed in this thesis.The reflection signals of the STAR-RIS near the base station are used to eliminate the self-interference signals from the base station.The optimal reflection and transmission coefficient matrix settings of the two STAR-RISs are obtained through alternate optimization algorithms.Theoretical analysis and simulation results have verified that the interference suppression scheme can effectively suppress the self-interference of the base station and significantly reduce the mean square error of the received signals.Compared with traditional schemes of deploying RIS near the base station,the simulation results verify that the proposed scheme is superior to the traditional schemes.