| Millimeter wave(mmWave)with a huge spectrum resources has been proposed as an important communication band of 5th Generation mobile communication technology(5G).However,the disadvantageous propagation characteristics of mm Wave,including high path loss and the weak diffraction ability,make millimeter wave communication challenging.In order to establish the links in mm Wave systems,it is necessary to form high directional beams with beamforming(BF)technology.In practical systems,the directional beam require fine alignment,which is achieved through a set of operations known as beam management.In general,beam management is consist of two processes.including initial access and beam tracking.In the traditional beam management scheme,beam training is required to obtain channel state and for various system operations.Nevertheless,the high directional beams lead to serious training overhead and delay.Moreover,the high mobility application scenarios of mm Wave will exacerbate this problem.Recently,out-of-band information is utilized to assist the beam management in mm Wave systems.Out-of-band information refers to the information that not obtained from the mm Wave communication system,including the channel information of other bands and the sensor information.Obviously,the acquisition of out-of-band information does not occupy communication resources.Therefore,the overhead of beam management can be significantly reduced with the assistance of out-of-band,which has very important research significance and application value.This dissertation mainly study on the problem of mm Wave beam tracking with the assistance of out-of-band information.In the beam tracking process,the movement of user equipment(UE)will cause rapid changes in channel state.Thus,frequent beam training and updating are required to maintain the link,which brings a lot of system overhead.On the other hand,the sensors on the intelligent terminal can provide the realtime spatial information,including the position and the attitude.Spatial information provides the accurate motion state of the terminal.It can be utilized to estimate the channel state and significantly reduce the system overhead in beam tracking.Therefore,this dissertation focuses on the problem of spatial information aided mmWave beam tracking in the scenarios with mobile UE.The key to this problem is how the motion of UE affects the channel state.Specifically,the main research results and contributions of this dissertation can be summarized in the following three parts.(1)Study the change law of mmWave channel states when the UE rotates and the attitude information aided beam tracking algorithm.Firstly,the function of spatial information in the tracking is determined by the motion state of UE.Specifically,the motion of UE can be decomposed into displacement and rotation,which are indicated by the position and attitude,respectively.This dissertation studies the change law of mm Wave channel when the UE is rotating.Based on the geometric channel model of mm Wave,we establish the relationship between the attitude of UE and the channel matrix.Then,we propose a single-end compensation scheme during the rotation of UE.In this scheme,only the transceiver at the UE is updated after the rotation,while the one at base station(BS)remains unchanged.We also prove that the spectral efficiency performance loss compared to that of joint transmitter and receiver design is generally trivial.Finally,under the digital beamforming(DBF)architecture and hybrid beamforming(HBF)architecture,we propose the attitude information aided beam tracking algorithms based on the single-end compensation scheme.(2)Study the problem of attitude information aided beam tracking based on codebook and the design of codebook.In practical systems,the transceivers are generally designed based on the codebook.The main reason is that it can reduce the overhead and delay of BF compared to the method without codebook.This dissertation studies on the beam tracking based on the codebook during the rotation of UE.Firstly,we propose a beam switching algorithm with the assistance of attitude information.Affected by the estimation error of attitude,the switching may be earlier or later,which leads to beam misalignment.As a result,there is a trade-off in the codebook design problem:wider beams can reduce the probability of misalignment but suffer more from insufficient power;narrower beams provide higher gain but are more sensitive to the error.Then we derive the closed-form expression of the optimal beamwidth that maximizes the average transmission rate.To further prevent misalignment in the tracking,we consider the codebook with overlapping beams,then derive the optimal overlap ratio and beamwidth.(3)Study the spatial information aided beam tracking when there are displacement and rotation of the UE simultaneously.In this kind of scenario,both the position and attitude information are required to assist the beam tracking.Firstly,based on the geometric channel model of mm Wave,we establish the channel evolution model with the position and attitude information under the line-of-sight(LOS)condition.The evolution model is actually a recurrence relation of channel states.Based on the model,the real-time channel state can be calculated with the spatial information.We also consider the measurement error of spatial information and modify the model.Then,a spatial information assisted beam tracking algorithm is-proposed,where the beam training is utilized as a measurement of channel states and improve the accuracy of beam tracking.Finally,a novel training beam design is proposed to mitigate the non-linearity of measurement function and improve the tracking accuracy. |
