Research On Deep Integration Technology For GNSS Carrier Phase Quality In Complex Signal Environment

With the rise of technical fields such as autonomous driving and unmanned aerial Vehicle(UAV),the demand for high-precision positioning has entered the mass market from the professional field.Global Satellite Navigation System(GNSS)is one of the important means of outdoor positioning.The centimeter-level positioning accuracy can be achieved by using GNSS carrier phase differential positioning technology.Due to the fragility of carrier phase tracking,the continuous and reliable centimeter-level positioning accuracy can only be guaranteed in open-sky scenes with good observation conditions.Therefore,it is important to study carrier phase tracking and observation quality in complex signal environment.Traditional GNSS receiver faces many challenges and parameter design limitations of dynamic and weak signals in complex signal scenarios,while the GNSS/INS deep integration receiver has excellent dynamic performance and can effectively improve the tracking performance of the carrier loop.Based on the analysis of traditional scalar deep integration and vector deep integration structure,this paper implements a deep integrated software receiver based on scalar deep integration structure and the idea of information sharing between vector receiver channels.Based on the deep integration software receiver platform,aiming at the challenges faced by carrier baseband tracking level and observation extraction level under complex signal conditions,corresponding optimization methods are proposed to improve carrier phase quality and receiver positioning accuracy.At the carrier phase baseband tracking level,firstly,for the problem of carrier phase tracking discontinuity caused by signal weakening,a COOP tracking loop structure with deep integration assistance is proposed.The strong signal channels are used to estimate the influence of the receiver clock drift on each tracking loop,so that the carrier loop overcomes the contradiction between dynamic stress and tracking sensitivity,and improves tracking sensitivity.Secondly,aiming at the discontinuity of carrier phase tracking under the condition of frequent discontinuity of signals,a carrier phase prediction method is proposed.The phase prediction method is used to maintain the carrier phase continuity of the occluded satellite during the short occlusion time and the fast lock after the signal recovery,and the Doppler estimation of the receiver clock drift of the occluded satellite channel is optimized.At the carrier phase observation level,for the problem of half-cycle ambiguity of carrier phase measurement due to the insensitivity of carrier loop phase detector to 180 degree flip,a bit prediction method is proposed to determine half-cycle ambiguity quickly.Then,a cycle slip detection and repair method of carrier phase observation based on INS and odometer is proposed.Based on the short-term high accuracy of INS,carrier phase cycle slip is detected by using the high precision positioning results of RTK/INS/odometer.Compared with the result of the true value file,this method can improve the continuity of carrier phase observation to a certain extent.Finally,the deep integration software receiver is tested and evaluated by design experiment.Firstly,the carrier phase tracking performance is quantitatively tested based on simulation test scenarios.The results show that the tracking sensitivity of the carrier loop in this paper is 12 dB higher than that of the traditional PLL and 4 ~ 7 dB higher than that of the classical deep combination PLL in the dynamic weak signal test.In signal intermittent test,more than 90% of the test results can maintain carrier phase divergence for less than 1/4 cycles in 15 s prediction time when simulating partial satellite occlusion in static and dynamic scenarios.The effect of phase prediction method on RTK positioning in dynamic scenes is tested.The results show that the phase prediction method can effectively improve the fixed rate and positioning accuracy of RTK under intermittent satellite signals.Then,the carrier phase observation quality and RTK positioning accuracy of the deep integrated software receiver are tested and evaluated in the real vehicle environment.The test results show that the carrier phase observation continuity,RTK fixing and overall positioning effect of the deep integration software receiver are better than those of ublox receiver,which shows the effectiveness of the carrier phase optimization method proposed in this paper.