Research On Beamforming Technology Of Integrated Sensing And Communication For Nonorthogonal Multiple Access Networks

In recent years,with the rapid development of society and the gradual emergence of intelligent platforms such as autonomous driving and unmanned aerial vehicles,the system’s requirements for wireless communication and radar functions have gradually increased,and wireless spectrum resources have become increasingly scarce and precious.In this context,the integrated sensing and communication(ISAC)(also called integrated radar and communication)has gradually attracted the attention from academia and industry.The integrated system has the advantages of hardware and spectrum sharing,high equipment integration and small size,which can fully reduce the operational complexity of the entire system and save valuable spectrum resources.With the global deployment of 5G,as one of the traditional radar bands,the millimeter wave frequency band(frequency range of 30 GHz to 300GHz)has great potential in realizing the ISAC.However,because of the short wavelength of millimeter wave,the large spatial attenuation and the multi-user interference(MUI)of communication equipments,in order to ensure the transmission quality of signals in the millimeter-wave frequency band,this thesis introduces beamforming and NonOrthogonal Multiple Access(NOMA)technology to solve the above problems.Firstly,the principles of beamforming technologies and system application scenarios are introduced,and then this thesis presents the multiple-input multiple-output(MIMO)-based integrated system and introduces three beamforming technologies for different scenarios respectively,including communication-centric,radar-centric and joint design.We study the performance of beamforming technologies in traditional ISAC systems and it is found that when the number of users is too large,the radar performance will be greatly affected under the premise of satisfying the communication quality of service.To solve the above issue,the NOMA-based ISAC system is studied in this thesis.Then,the beamforming technology is investigated for the NOMA-ISAC system focusing on communication quality.An optimization problem is formaulated to to maximize the sum rate of the communication users,while constraining the radar beam and satisfying the quality requirements of the communication users.For the non-convex condition in the optimization problem,the semidefinite relaxation(SDR)method and the successive convex approximation(SCA)method are used to deal with it.On this basis,a SCA algorithm based on penalty terms is proposed.Finally,the beamforming technology for radar-centric NOMA-ISAC systems is studied.A beamforming method with the radar loss function as the target is formulated,and compared with traditional MIMO system in terms of the radar beam pattern and target estimation performance.In addtion,we also consider the optimization problem with the Cramer-Cao bound(CRB)as the objective function.Simulation results show that in the communication-centric scenario,when the channel correlation is high,the introduction of the Successive Interference Cancellation(SIC)technology in the NOMA mechanism will provide the system with additional degrees of freedom(Do F)and effectively improve the communication quality.Compared to the traditional integrated system,the additional Do Fs can effectively solve the radar beam problem and improve the radar performance on the premise of satisfying the communication quality.In the radar-centric scenario,compared with the traditional MIMO system,the radar performance of the NOMA-ISAC system is slightly inferior,but it can greatly improve the system communication performance in scenarios with insufficient spatial Do Fs.The different beamforming schemes proposed in this thesis for different scenarios can effectively improve the performance of the integrated system.