Design And Implementation Of Clock Synchronization For Distributed Multi-user MIMO System Based On USRP Platform

The distributed Multiple Users Multiple Input Multiple Output(MU-MIMO)system combines multiple geographically adjacent base stations,which can effectively eliminate inter-cell interference through beamforming technology and fully exploit the spatial freedom,thus greatly improving the spectrum efficiency and system throughput.The above advantages make the distributed MU-MIMO system become one of the core technologies of the fifth generation mobile communication and the new generation wireless LAN.However,in the distributed MU-MIMO system,since the clock oscillators among the distributed base stations are independent,there are serious frequency offsets and phase offsets between the transmitting antennas of different base stations,resulting in severe inter-user interference,which greatly reduces the spectrum efficiency and system throughput.Therefore,it is of great significance to study clock synchronization between base stations for distributed MU-MIMO systems.This paper proposes a synchronization algorithm based on the master-slave architecture for the clock synchronization of distributed MU-MIMO systems.The key idea of the master-slave architecture is to select one base station in the system as the master base station and other base stations as slave base stations.By measuring the relative frequency offset from the slave base stations to the master base station,adjust the work clock from the base station so that all the base stations work at the same clock frequency.Based on this architecture,this paper proposes a Zadoff Chu(ZC)sequence of time and frequency synchronization algorithm and designs its pilot structure.Due to the excellent correlation characteristics of the ZC sequence itself,this algorithm can complete the time-frequency offset estimation of the master-slave base station with higher accuracy,less extra bandwidth resources and lower algorithm complexity than the traditional synchronization algorithm.In addition,in order to verify the feasibility of the proposed master-slave synchronization scheme,this paper uses the Universal Software Radio Peripheral(USRP)to design a hardware implementation platform for distributed MU-MIMO.In addition,based on the hardware platform,this paper leverage Lab VIEW to implement the clock synchronization,beamforming,modulation and demodulation algorithms in distributed MU-MIMO.Finally,based on the platform,this paper performed a lot of field tests,analyzed and evaluated the performance of synchronization accuracy,constellation diagram,bit error rate and so on.The test results show that the master-slave synchronization algorithm proposed in this paper can effectively address the clock synchronization problem of the distributed MU-MIMO system,thereby greatly improving the system throughput.