Research And Implementation Of Indoor MIMO Pseudolite Positioning System

GNSS can provide high-precision navigation and positioning services in outdoor areas,but in indoor environments,due to signal occlusion and other problems,its positioning accuracy is poor or even completely ineffective.As an extension of GNSS,pseudolite(PL)technology can not only realize regional enhancement and increase the number of visible satellites,but also independently network to provide reliable positioning services in the indoor environment.Clock synchronization is a necessary condition for pseudolite systems to realize high-precision positioning function.Therefore,it is important to build corresponding communication links between pseudolite base stations to form a unified time reference.In order to solve the clock synchronization problem of pseudolite system,an indoor distributed pseudolite positioning system with a communication link among base stations is designed.The MIMO(Multiple Input Multiple Output)architecture pseudolite base station used in the system is studied,and the transmitter module,receiver module and clock phase correction module are designed and implemented in detail,A communication link is established between pseudolite base stations through the hardware of "transceiver",and a clock synchronization method based on single difference is designed to carry out preliminary time service and precise clock difference monitoring in the slave base station.The main work is as follows:(1)The key technologies of MIMO pseudolite system are studied,and the corresponding base station architecture and implementation scheme are designed.Aiming at the problem that traditional pseudolite networking requires multiple transmitters and a monitoring station,this paper puts forward the system structure,networking scheme,base station framework and signal system of MIMO pseudolite,studies and analyzes clock synchronization methods between base stations,and designs the hardware platform to realize the base station architecture.(2)The signal processing flow scheme of the MIMO pseudolite system base station is designed,and the main functional modules of the transceiver base station are realized.According to the characteristics of application scenarios,the layout scheme of navigation message content is designed,and the IF(Intermediate Frequency)scheme of "Beidou lower sideband and GPS upper sideband" is designed for dual-frequency signals.Considering the requirements of the clock synchronization method,the tracking loops of "second-order frequency locking auxiliary third-order phase-locked carrier loop" and "second-order delay locking code loop" are designed.The generation,broadcasting,receiving and processing of pseudolite signals are realized through FPGA,ARM and AD9361.(3)The method of clock synchronization between base stations based on single difference is proposed.Taking advantages of the characteristics of integrated transceiver of the MIMO pseudolite system,a communication link is constructed between the master and slave base station.According to the pseudorange observation values under two different ranging codes,the preliminary timing and precision clock difference monitoring are carried out respectively,and the clock phase correction module based on delay correction is used to adjust the phase of1 PPS second pulse signal in the process of clock coarse synchronization.The test results show that in the indoor environment,the preliminary timing process can achieve the timing accuracy better than 10 nanoseconds,and the clock difference monitoring accuracy better than 1nanosecond can be achieved by using high-speed ranging code.(4)The test environment of the MIMO pseudolite system is established,and the signal transceiver performance and positioning function of the base station are evaluated and analyzed.The test results of the transmitted signal show that the waveform and spectrum of the pseudolite signal broadcast by the base station have no obvious distortion,the modulation accuracy is high,and the signals between multiple channels are consistent.The test results of the received signal show that the acquisition and tracking module can meet the requirements of the method of clock synchronization.The experimental results of base station positioning show that a single MIMO pseudolite base station can achieve centimeter-level static positioning results in indoor environments,which preliminarily meets the needs of indoor positioning.