Research On Beam Cooperation In Millimeter-wave Communication Systems

Millimeter Wave(mmWave)communication system has become an extensive research in the industry due to its rich spectrum resources,high speed,and high security.The high path loss of mmWave wireless communication determines that it needs to use beamforming technology to compensate for propagation loss and improve link quality.The base station equipped with array antenna can generate multiple directional beams through beamforming technology and provide services for multiple users.It can fully utilize mmWave beam resources and effectively improve system spectrum efficiency.However,overlapped coverage is often existed between the beams.The high-gain beams exist inter-beam interference.How to reduce beam interference is an important factor affecting system performance by multi beam coordination and cooperation.Therefore,this paper focuses on the mmWave system beam collaboration technology,and from the beam selection and the beam schedule two aspects to improve the system performance.Firstly,the key technology of mmWave beamforming is studied,and the transmission characteristics of millimeter wave and the channel model describing the characteristic of millimeter wave are expounded.Based on the principle of beam generation by uniform linear antenna arrays,the bit error rate performance of adaptive beamforming and based on codebook beamforming were simulated and analyzed.When the base station is equipped with a large-scale antenna and the codebook set is large enough,the performance of the beamforming technology based on the beam codebook is close to the adaptive beamforming,and it is widely used because of its simple implementation.In a single-cell scenario,the base station selects appropriate service beams for the user through a beam selection algorithm to reduce inter-beam interference and achieve beam cooperation.Therefore,fast and accurate beam selection algorithms become the key factors that affect system performance.On the premise of analyzing and comparing the maximum energy beam selection algorithm and the interference-aware beam selection algorithm,a minimum interference beam selection algorithm is proposed in this paper.The algorithm utilizes the sparseness of the beam space and measures the beam serving capability through the beam space signal-to-noise ratio.The selected beam can provide better service and reduce the interference to other users.Simulation experiments show that thelow-complexity minimum beam selection algorithm can greatly reduce the time complexity of the algorithm and guarantee system performance,especially in the scenario with more users.For multi-cell mm Wave communication systems,the inter-beam interference is complex and consists of the same cell beam interference and adjacent cell beam interference.Therefore,beam cooperation scheduling is used to achieve beam coordination and improve system performance.The central controller performs coordinated beam scheduling according to the information fed back by the users.Each slot schedules beams with small interference to each other,and beams with severe interference are dispersed in different scheduling slots.Any base station-scheduled beam affects the inter-beam interference distribution.By establishing an interference model,a beam scheduling algorithm based on user classification is proposed.Take the user's response to different beams as a priori information of beam scheduling.And then schedule the corresponding transmission mode for different types of users through user classification.The proposed algorithm simultaneously schedules the beams of strong interferences in different time slots,and maximizes the capacity guidelines for the same time slot beam.Simulation analysis shows that the proposed beam scheduling algorithm has better performance under the same conditions.