Key Technologies Research And Verification Of Channel Calibration In Massive MIMO

With the rapid growth of mobile communication services,comes unprecedented high requirements for the fifth generation mobile communication systems on spectrum efficiency and system capacity.Massive MIMO technology has the advantages on higher spectrum efficiency,higher capacity and lower energy consumption,and it is attracting more and more attention as the key to the next-generation wireless communication system.The time-division duplex is the main transmission mode of the massive MIMO system,that exploits the uplink channel and downlink channel reciprocity,the base station uses the uplink channel estimation to carry out the downlink beamforming to achieve the purpose of simultaneous communication with the multi-user.However,the actual uplink and downlink channels do not meet with the channel reciprocity,therefore,the system must be reciprocal error compensated for each channel.In this paper,the key technology of channel calibration in massive MIMO system is studied.Based on the zero-forcing beamforming,the channel calibration algorithm is deduced and implemented by FPGA hardware platform.The main contents are as follows:Firstly,the influence of channel calibration and channel characteristics is analyzed.Based on the time-division duplex LTE link and the pratical design requirements,the corresponding frame structure is designed,and the ZC sequence is selected as the calibration sequence according to the calibration sequence requirement characteristic.The results show that the amplitude error and the phase error of the antenna are close to zero after calibration,and the purpose of calibration is achieved.Then,based on the simulation link,the whole system is implemented on FPGA.By dividing the system according to modular function we design our system implementation framework.Then the channel calibration module is introduced in detail,and the channel calibration verification scheme and the scheme flow are given.Finally,the channel calibration algorithm is tested based on a massive MIMO prototype platform,which includes functional test and performance test;the experimental results show that the system transceiver module meets the requirements in function.In performance,the modulus error is less than 0.01,and the phase error is less than 5o,meeting the requirements of massive MIMO system.The massive MIMO channel calibration method,as a prerequisite for beamforming technology,has been successfully verified on the platform,which provides a solid foundation for the application of massive MIMO key technology,and a guarantee for the fifth generation mobile communication.It has significances in engineering reference and in theory.