Research On User Access Method Of Millimeter Wave MIMO System

In order to meet the blasting-type wireless communication data transmission requirements,the development of the spectrum of the millimeter wave(mmWave)frequency band will become an effective way to solve the bottleneck of low transmission rate and limited spectrum resources.At present,the millimeter-wave multiple-input multiple-output(MIMO)system has become the focus of academic and industry attention.On the one hand,it can meet the needs of wider transmission bandwidth and higher spectral efficiency.On the other hand,in order to overcome the severe propagation loss in the millimeter wave band,millimeter-wave MIMO systems require directional multi-beam technology for signal transmission.This move makes the control layer process more complicated,which may lead to the failure of the traditional omnidirectional transmission cell access scheme,so it is necessary to redesign the access scheme of the millimeter wave MIMO system.This paper only discusses the cell search process in the initial access of the millimeter wave MIMO system.The high-pointing characteristics of beam transmission in millimeter-wave communication inevitably bring about two challenges of coverage and delay.In order to overcome the low coverage and high training overhead of the traditional millimeter wave MIMO system initial access,this paper proposes a cell access scheme based on out-of-band information for millimeter wave MIMO system.This solution is a heterogeneous network model consisting of a Sub-6GHz system and a millimeter wave MIMO system.The research content can be divided into two parts.The first part,the community search problem.According to the characteristics of the millimeter wave channel,the problem detected by the base station(BS)is expressed as Hypothesis Testing Problem(HTP),and then the detector is solved by the Test of Generalized Likelihood Ratio(GLRT)detector.The second part,the multi-beam search process.First,the broadcast information covered by the whole cell in the Sub-6 GHz system is used to quickly determine the approximate range of the user equipment(UE).The millimeter wave is then subjected to beam space scanning based on the known range,so that the beam of the BS and the UE are aligned.The analysis of the simulation results shows that the scheme can reduce the system overhead and improve the access probability.In order to further improve the user access probability of the millimeter wave system,it can be realized by improving the estimation accuracy of Angle of Arrival(AoA)and Angle of Departure(AoD).Therefore,this paper proposes based on out-of-band information.Beamforming design.The scheme mainly uses the out-of-band information provided by the low frequency band as the angular range of the initial beamforming vector,and minimizes the Cramer Rao Lower Bound(CRLB)of AoA and AoD by using the maximum likelihood estimation criterion.Solving the convex optimization problem,the beamforming vector with the best estimation accuracy is obtained.The simulation results show that compared with the traditional beamforming design scheme,the estimation accuracy,beam gain and system capacity of the scheme are significantly improved.