Design And Implementation Of Transmitter For High-Precision Double Differential Ground Positioning System

Global Navigation Satellite System(GNSS)is a radio positioning system widely used in the outdoor location,and GPS is the typical representative.Once the receiver on the earth can receive a good GPS satellite signal,it can realize positioning.However,due to the impact of signal attenuation,GPS positioning accuracy is limited,which can not meet the needs of high-precision wireless location.Especially in the buildings,trees and other dense shelter or tunnel,indoor and some low-lying terrain,the satellite signal is severely attenuated or even completely blocked,resulting in inaccurate positioning or even completely unable to locate.In addition,the position of the effective navigation satellites is kept in the head region of the receiver due to the limitation of the receiver's elevation angle,resulting in the vertical positioning error being far greater than the horizontal positioning error,so the GPS can not meet the high vertical positioning accuracy requirements.Pseudolite positioning technology can effectively address the problem.The main idea of pseudolite positioning is to replace the occluded GPS satellites in certain areas with pseudolites,on the one hand to increase the number of effective satellites,on the other hand to improve the geometric structure of satellite constellation,thus expanding the application of GPS and improve positioning accuracy.In this dissertation,the design of pseudolite transmitter is studied.Under the GPS constrained scenario,the pseudolite transmitter is compatible with the existing GPS system and has the capability of locating with meter-level accuracy in the range of 200 meters with pseudorange double difference technique.In this dissertation,the signal format of a pseudolite is designed,and the basic design parameters are given.Based on the similarities and differences between the pseudosatellite and the GPS,the navigation message of the pseudolite is redesigned.In order to reduce the influence of pseudolite clock error,a pseudorange double difference model of pseudo-satellite and GPS is established based on the GPS double difference model,and the related algorithm is designed.Based on this algorithm,the performance of single pseudolite is simulated under different GPS conditions.The simulation results show that the increase of the pseudolites can not only achieve the accuracy of meters in the case of only 3 GPS satellites,but also further enhance the positioning performance in the case of more than 3 GPS satellites.The near-far effect of pseudolites and its solution are analyzed in detail.Pseudolite pulse transmission mode can reduce the interference to the weak GPS signal by shorten the signal transmission time,and realize the compatibility between the pseudolite and the GPS signal in a wider range.Based on the idea of GPS software receiver,the simulation system of pulse pseudolite combined with GPS is established.The simulation results show that the pulsed pseudolite can effectively solve the pseudolite near-far effect.The hardware and software design of the pseudolite transmitter based on Xilinx FPGA is realized,including the key baseband / IF module design and the SOPC system,and the RF circuit is also designed.