Reasearch On Millimeter Wave Beamforming Technology And Application In Multi-user Transmission

With the rapid increase of high-speed short-range wireless communication services,higher and more flexible transmission rates are required.Millimeter wave band,with its rich frequency resources and ease of integration of more antennas,are good candidate for these requirements.Therefore,the thesis focuses on multi-antenna technologies at millimeter wave band for multi-user transmission.1)To utilize switched-beam-based beamforming in millimeter wave phased-array antenna system,the most needed channel state information is discrete AOD(Angle of Departure).The thesis analyzes several existing beam searching schemes from the perspective of information theory and points out that the beam searching process which searching for the best communication beam is essentially the channel estimating process aiming at getting the discrete AOD by using the beam states of high-gain or low-gain.Traditional searching schemes includes exhaustion searching scheme,dichotomy based hierarchical search scheme,etc.In these two schemes,the ratio between the number of discrete AOD that can be estimated and the number of training beams is no more than 1,and the overlapping state of beams is not fully used,so the efficiency in AOD estimating can be further promoted.Besides,the dichotomy based hierarchical searching schemes can only certain 2 discrete AOD in a single stage,leading to a rising complexity when estimating AOD of multiple users.In order to overcome the aforementioned two disadvantages,an improved beam searching scheme utilizing overlap of beams is designed in the LOS(Line of Sight)condition.The scheme designs training beams which overlap with each other according to gray mapping rule,so that a certain AOD can be estimated using the gain state of multiple training beams.In this scheme,the ratio between the number of discrete AOD that can be estimated and the number of training beams can reach 2K:K,which enhance the efficiency in AOD estimating and lowers the searching complexity in single user searching.Furthermore,in this scheme,the number of discrete AOD that can be curtained in a single stage reaches 2K,which means the scheme is faster when estimating AODs of multiple users.Thus,it can be seen that the designed scheme is suitable for LOS scenarios with stronger mobility and more users,and the advantage is more obvious when using greater number of antennas.2)When using analog beam generated by phased-array,the gain is smaller at a certain sidelobe or nulling with a bigger distance between it and mainlobe,which means the interference in this direction is smaller.By using this law,a multi-user transmission scheme based on digital-analog hybrid antenna is designed.Firstly,analog beam is used to separate different users and commits group-based multi-user management,which can control the interference to different user within a group by controlling the intervals of beam coverage areas.In this way,the capacity of each user can be controlled and the interference measuring process of every two users can be avoided.Secondly,digital MIMO technologies are used to transmit multiple data flows,and the transmission rate can be controlled by controlling the number of space streams.Simulation result shows that the multi-user management can provide differentiated capacity.In single space flow transmission,the degree of capacity difference and speed difference can reach as high as more than 2 times and 4 times.Besides,the space streams number control can further enhance the magnitude of the rate difference between different users.In multiple space flow transmission,the degree of capacity difference and speed difference can reach as high as more than 8 times and 15 times.