Research On Large Scale Antenna Beamforming Technology

Beamforming is a signal preprocessing technology based on antenna array.Its basic idea is to provide array response gain for signals in a specific direction while suppressing signals in other directions.Beamforming can not only increase communication coverage,improve spectrum utilization and increase system capacity,but also has strong anti-interference and anti-fading capabilities.Beamforming includes downlink beamforming and uplink beamforming.The downlink beamforming vectors designed based on Signal to Interference plus Noise Ratio(SINR)needs to be jointly optimized,while the uplink beamforming vectors designed based on SINR can be independently optimized.However,due to the duality between the uplink and downlink beamforming,this duality makes it possible to effectively solve the downlink optimization problem by considering the uplink optimization problem.In addition,in the user access stage,each user sends orthogonal pilot sequences to the base station,and the beamforming vector used by the base station to receive the pilot is a wide beam vector satisfying the coverage range.In the data transmission stage,the base station has different narrow beam vectors that are designed to be aimed at different users,but the receiver estimates channel information for data demodulation based on pilot sequences,so there is a deviation between the channel estimation value and the actual channel experienced by the data,which will lead to a phase mismatch between the pilot transmission channel and the data transmission channel,then affect the demodulation performance of the receiver.This paper introduces and uplink power minimization optimization with SINR target constraints and downlink power minimization optimization with SINR target constraints in the single-cell multi-user system.First,the feasibility of the optimization problem is analyzed,then the weak duality and strong duality of the uplink and downlink are analyzed.And iteratively solves the optimization problem where the objective function is to maximize the minimum SINR balance ratio by using the dual principle of uplink and downlink.Finally,focus on the analysis of the impact of phase mismatch on the performance of the system in a single-cell multi-user system.In order to solve the phase mismatch between the uplink pilot transmission channel and the downlink data transmission channel,on the basis of channel estimation,and under the constraint of total transmission power and the constraints of phase matching between the uplink pilot wide beam pattern and the downlink data narrow beam pattern,an optimization problem with the objective function of maximum-minimum SINR is proposed.Due to the difficulty of phase information extraction,a sub-optimal algorithm is proposed to jointly optimize the beamforming matrix and the power allocation vector.In the solution of beamforming,an extended two-layer Dinkelbach algorithm is studied and derived to solve the beamforming vector of each user.The beam forming vector and power allocated to each user can match the phases of the uplink pilot transmission channel and the downlink data transmission channel in the main angle of the channel,and can effectively reduce the bit error rate(BER)of transmission.