The Research On Low-Cost Single-Frequency GNSS Real-Time Kinematic Algorithm

Under the trend of navigation and positioning technology gradually developing towards low cost and high precision,many practical engineering problems have put forward corresponding requirements for GNSS relative positioning technology.Low-cost equipment has certain challenges for data processing,because it has more gross errors,cycleslips and multipath effects.The main work and conclusions of this paper are as follows:1.Low-cost receiver data quality analysis.The differences between measurement equipment and low-cost equipment,the influence of different antennas on low-cost equipment and the data quality measurement of low-cost receivers under dynamic conditions are compared and analyzed,from the aspect of data quality and velocity accuracy.The main conclusions are as follows:a.In the aspect of data quality,it is found that there are more gross errors and multipath effects in the observation data of low-cost equipment compared with the survey-grade equipment;the influence of the antenna on the data quality of low-cost equipment is small;in the double-difference phase observation,there is a half-cycle phenomenon and it is more serious in a dynamic environment.b.In the aspect of velocity accuracy: the velocity result of low-cost equipment has the same accuracy with that of the measurement type receiver,but the former has a large noise influence in the Doppler result;in static environment,Doppler velocity result and time differenced carrier phase velocity result can reach centimeter lever and millimeter lever,respectively;in dynamic environment,Doppler velocity result and time differenced carrier phase velocity result can reach decimeter level and centimeter level,respectively.2.The gross error detection method for low-cost equipment is analysed and inproved in both post-preocess and pre-process.Improvements have been made in the threshold of the elevation angle,signal-to-noise ratio,and pseudo-range gross error detection based on prior position for low-cost equipment.In oder to deal with the possibility of undetected small cycleslips during pre-process,an improved IGGIII robust solution is used.The measured data shows that the method mentioned before can effectively improve the positioning accuracy and the fixed rate of ambiguity.3.A joint cycleslip detection method suitable for low-cost GNSS RTK is proposed.The performance of Doppler assisted detection under high sampling rate is analyzed.The results show that when the data quality is good,Doppler-assisted detection can detect small cycleslip which is on less than one cycle;but for low-cost receivers such as ublox,because of the the observations' low accuracy,the method is less sensitive to cycle slips,and only 3 weeks and more can be detected under dynamic conditions.In order to solve the problem,TDCP is used to detect the second cycle slip after the Doppler menthod applied.The experimental results show that the joint cycleslip detection method used in this paper can successfully detect small cycleslip.4.The velocity constrained GNSS RTK positioning model and algorithm is analysed.Compare the difference in low cost relative positioning accuracy in multi-epoch mode and single epoch mode under static and dynamic senarios.The performance of the single epoch relative positioning algorithm using the velocity information for constrained analysis is analyzed.The experiments show that there are a large quantity of gross errors and anomalies in the traditional single epoch mode solution,and the multi-epoch have better results when the cycle slip is well detected.The reliability of the single epoch solution is significantly improved after adopting the velocity constrains,but there is still a certain gap compared with the multi-epoch positioning result.5.An algorithm strategy for low-cost GNSS relative positioning is proposed.The measured data shows that using low-cost positioning strategy can reach a stable and reliable real-time dynamic positioning results in complicated observation eviroment under the support of network RTK or short-range RTK.The overall acuracy is at the decimeter level,and the positioning accuracy of the fixed solution is at the centimeter level.