Beamforming Design In Cooperative Millimeter Wave Networks

Facing the dilemma of increasingly crowded spectrum,5G communication introduces the millimeter wave(mm Wave)frequencies to realize higher-data-rate by exploring unoccupied bandwidth.Benefiting from the advantages of short wavelength of mm Wave,the massive multiple-input multiple-output(MIMO)technology provides sufficient beamforming gain to compensate for the pathloss of mm Wave and it also shows a great performance advantage in improving the spectral efficiency(SE).The beamforming technique is very critical in mm Wave communication systems,and its algorithm design also plays a crucial role in improving system performance.In addition to the enhancement of SE performance,the quality of service(Qo S)for users is also a major concern of future communication systems.On the other hand,with the strong centralized processing capability,cooperative networks can realize jointly beamforming design,eliminate multi-user interference,and collaborative power control,which finds new possibilities for the improvement of Qo S.It is worth mentioning that,as a novel cooperative network,cell-free(CF)networks are very attractive in terms of balancing Qo S for all users and flexible deployment.Therefore,it is imperative to seek and explore the beamforming design and algorithm for cooperative mm Wave networks.In this thesis,for the cooperative mm Wave networks,aiming at improving the SE performance,improving the energy efficiency(EE)performance,and enhancing the Qo S for users,three beamforming design algorithms are proposed,and numerical simulation results are provided.The main work and contributions of this thesis can be summarized in the following three points:Firstly,this thesis considers the traditional cooperative mm Wave MIMO communication system and proposes a joint design of user association and beamforming scheme for the user association problem.While selecting and accessing the best base station for users,the efficient beamforming design algorithm is proposed to maximize the SE performance,also known as the sum-rate performance.In addition,the computational complexity analysis and the performance verification based on the MATLAB simulation are provided.Secondly,this thesis discusses the hybrid beamforming design in the novel cooperative mm Wave networks.For the sum-rate maximization problem,the hybrid beamforming antenna array architectures are considered and an efficient iterative algorithm is proposed to design the hybrid beamformer,which is based on the fully connected architecture.Furthermore,the proposed algorithm is extended to the fixed subarray and dynamic subarray architectures,and some improvements to the analog beamforming algorithm are made.Detailed simulation results illustrate the performance advantages of the proposed algorithm and the impact of the dynamic subarray architecture on EE performance.Finally,this thesis introduces low-energy reconfigurable intelligent surface(RIS)as an auxiliary communication device in the novel cooperative network to further improve SE performance.With the consideration of centralized processing capability and local optimization constraints,this thesis proposes a partially distributed beamforming design algorithm to tackle the problem of heavy signaling overhead caused by frequent information exchange between access points(APs).Simulation results verify the effectiveness of the proposed algorithm and the improvement of system performance by RIS.In summary,this thesis proposes three beamforming design algorithms for cooperative networks to illustrate the effects of user association,antenna array architecture,and RIS on system performance.Results have shown that both cooperative mm Wave networks and cell-free networks can suppress multi-user interference,achieve better SE performance,and have great development potential in future communication systems.