Research On Methods To Improve Access Efficiency In Millimeter Wave WLAN

Millimeter waves(mm Wave)have been widely used for long-distance point-to-point communications between satellites and terrestrial network.However,commercial technologies for mm Wave in Wireless Local Access Network(WLAN)and cellular networks are still at research and development stage.In the 60 GHz unlicensed band,the available spectrum bandwidth can reach 9GHz,which has great potential values.The path loss of mm Wave is severe,and the distance of omni-directional communication is limited.In order to extend the communication distance,beamforming technology has become the consensus of the industry.Beamforming technology brings two new problems: beamforming increases the complexity and delay of initial access,and beamformed links are easily interrupted by obstructions,device movement,and rotation.This thesis first summarizes and analyzes the existing initial access technologies in mm Wave network.Subsequently,for the mm Wave WLAN,this thesis simulates and analyzes the access time of 802.11 ad initial access protocol.Based on the assumption that Directional Multi-Gigabit Station's(DMG STA)distribution obeys the Poisson point process,this thesis proposes a hybrid Association Beamforming Training(A-BFT)scheme.In this scheme DMG STAs that are closer to the Access Point(AP),in the iterative access phase,use the wide beam(or sector,quasi-omni pattern)to complete the initial access.DMG STAs farther away,are in the exhaustive access phase,the initial access is completed by traversing a series of narrow beams.Compared with IEEE 802.11 ad scheme,this scheme can reduce initial access time and improve initial access efficiency.Channels of mm Wave are sparse in spatial,that is,the probability that one obstacle blocks multiple links concurrently is quite small.Therefore,the impact of bloackage on mm Wave links could be reduced effectively by dual-link or multi-link.Based on this property,an mm Wave WLAN dual-link scheme is proposed in this thesis: through the Software Defined Network(SDN),the WLAN controller coordinates the APs to realize the dual-link communication between the DMG STA and the two APs.Using Jackson's network model,this paper analyzes the delay of dual-link communication.The results show that the more severe the blockage is,the more obvious the effect of dual-links on reducing communication delays.For link interruptions caused by DMG STAs' movement,this thesis proposes a beam tracking scheme based on Kalman filter(KF)algorithm.In this scheme,the KF algorithm is used to predict the trajectory of the DMG STA by the AP and the AP determines the target beam to be tracked according to the predicted result.If the prediction fails,then AP traverses the beam cluster to find an available beam.This scheme makes the traditional beam tracking scheme target,reducing the number of beams to be tracked while preserving the reliability of beam tracking.