| With the development of human society,the original open outdoor environment has become more and more complicated due to the increasing number of skyscrapers in cities.When the satellite signal is propagated in the outdoor environment with skyscrapers or in the indoor environment with complicated environment,one or more reflections will occur after the signal encounters the obstruction,which will cause a very serious multipath effect,resulting in low positioning accuracy or even positioning failure of the satellite navigation system.However,people spend 80% of their time indoors,so they urgently need to obtain indoor location information.Therefore,indoor positioning technology is booming.At present,common indoor positioning technologies include pseudo-satellite,Bluetooth,Wi Fi,RFID and other solutions.Among them,the pseudo-satellite system can be deployed in any area with positioning measurement requirements and has a wide coverage.The most important point is that the pseudo-satellite system can achieve seamless indoor and outdoor positioning by combining with the satellite navigation system,which cannot be achieved by other technologies.Based on the advantages of pseudo-satellite system,this paper researches and implements the indoor positioning system of distributed pseudo-satellite.The main research includes the following points:(1)The principles of the pseudo-code,carrier generation and signal modulation at the transmitter of pseudo-satellite system,and the principle of acquisition and tracking of the user receiver are thoroughly researched.And analyze the carrier loop and code loop in the tracking phase and the original observations of the system output.The principle of the TDOA positioning algorithm adopted by the system and Chan's mathematical model are analyzed,and the problem of drifting of the system positioning results caused by the pseudo-satellite transmitter carrier phase asynchronism and the problem of near-far effect are also focused on.(2)Aiming at the problem of pseudo-satellite system positioning results drifting,a series of comparative test experiments were conducted and the experimental results were analyzed.According to the analysis,a set of carrier phase correction loops of the pseudo-satellite transmitter is designed and implemented on the FPGA + DSP hardware platform.This section introduces the carrier phase correction scheme,the pseudo-satellite signal module for processing feedback and the design of the pseudo-satellite signal remodulation module.Finally,the clock of system was constrained and analyzed to provide a good timing sequence for the pseudo-satellite indoor positioning system and ensure the stability of system timing sequence.(3)This section analyzes the causes of the near-far effect from two perspectives: the power of the signal and the correlation value of the signal.And study the interference cancellation algorithm and blind multi-user detection algorithm that based on subspace from the correlation value;For the received signal that containing impulsive noise,use the fractional low-order moments combined with M estimation to limit the impulsive noise in the signal firstly,and then complete the blind estimation of the pseudocode sequence by the enhanced projection approximate subspace tracking(Epastd)algorithm.The simulation results show that using the Epastd algorithm to estimate the processed received signal,the impact component in the estimation result is basically eliminated and the pseudo-code sequence estimation effect is very good under the condition of low noise ratio.(4)The pseudo-satellite signal generated by this system is tested and verified,and the distributed pseudo-satellite positioning system is tested statically and dynamically.After a long time of testing,it is shown that the distributed pseudo-satellite indoor positioning system designed in this paper has a positioning accuracy of centimeter level under static conditions and decimeter level under dynamic conditions. |
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