Method And Implementation Of Multi-GNSS Real-Time Relative Positioning

At present,the prospect of GNSS application in the real-time positioning is particularly wide,and the era of multi-systems and multi-frequencies bring users an advantageous condition of positioning.In the field of real-time positioning,relative positioning emerges advantages of widely-used,high-efficiency and good precision.At the view of navigation users,the length between reference station and user determine the result and precision of positioning.For short-baseline positioning which is less than 20km,effect of clock errors,ionosphere delay,troposphere delay,satellite orbit errors and DCB can be validly eliminated,and in the condition of correct-fixed of ambiguity,the positioning precision of static station and dynamic station can reach or exceed the level of centimeter.For the long-baseline positioning from tens to hundreds kilometer,effect of clock errors and DCB can still be canceled out,while delay of ionosphere and troposphere can hardly be eliminated due to the huge space difference between reference station and user.Generally,these effects can be vanished using model-correction,parameters-estimate and observation combinations,and then the positioning precision can reach the level of dm or cm.For the very long-baseline positioning,the elimination of errors is quite similar with long baseline.However,due to the pretty long distance between reference station and user,the number of common satellites is extremely small,making high positioning more impossible especially for the kinematic rover.This paper works on the method of Multi-GNSS real-time relative positioning,and main innovations and conclusions are summarized as follows:(1)Aiming at the AR in real-time short baseline relative positioning,a new strategy using average value to initialize ambiguity in the beginning of a few of epochs is proposed.The short baseline positioning examination indicate that,the initial time to fix ambiguity is lower than 30 epochs,and then the accuracy of static and kinematic positioning is in the level of millimeter and centimeter respectively.(2)Using average LC ambiguity and constrained ionosphere 2 strategies to solve ambiguity in long-baseline positioning.In the condition of long baseline,the ionosphere delay had to be eliminated using ionosphere-free combination if it cannot be efficiently corrected,halving the quantity of observation.However,it adds more difficulty to the long-baseline users which has only a few common satellites sharing with reference station.Thus,for the user having enough observations,this propose average LC ambiguity strategy;for the user having insufficient observations receiving single-frequency signal,this paper presents constrained ionosphere strategy based on ionosphere product.After the convergence of ambiguity,the positioning accuracies applying these 2 strategies can both reach the level of centimeter.(3)Researching on cycle slip detection strategy using GF combination + average based MW combination.GF combination of phase observation is available for the detection of small slip,but some certain proportion between two frequency would make it unreliable.In this situation,MW combination can cover the shortage of GF combination,although MW combination is seriously affected by noise of pseudo-range.Therefore,applying average based MW combination will lower the influence of this noise and boost reliability and success rate of the detection of cycle slip.(4)Researching on the posterior fixed weight and resolving of IFB of phase observations in Multi-GNSS relative positioning.Along with the accomplishment of our country's BDS and other GNSSs(GPS of USA,GLONASS of Russia,Galileo of EU),it is worth to research on the method to achieve high precision Multi-GNSS positioning.In this paper,the difference between IFB proportion coefficients of reference and test stations is parameterized and resolved as random walk model,to eliminate IFB errors;CEV of Helmert is adopted to posterior fix weight of Multi-GNSS observations.(5)Developing a Multi-GNSS relative positioning software from the bottom,facing real-time and post users.This software references part of data formats and data stream routines from RTKLIB,controlling GNSS resolution by config file.Main functions of this software are summarized as follows:read and decode of stream,read and save of GNSS data,SPP and static/kinematic relative positioning.