Research On High Precision Differential Positioning System For UAV

With the rapid development of drone technology,drones have become more and more important in various fields,and the application fields are becoming more and more extensive.Compared with the manned aircraft,the drone will not have the risk of casualties.It is more convenient to use,and the survivability is also improved.However,most of the current UAVs use single-point positioning in satellite navigation systems.Since the single-point positioning process is mixed with satellite,signal propagation and receiver-related errors,the positioning accuracy is generally controlled at about seven meters.This is far from meeting the market demand for high precision.The differential GPS(DGPS)system is an all-weather GPS augmentation system that can reduce or even eliminate various GPS measurement errors.According to different differential measurements,it is also possible to achieve sub-meter or even centimeter positioning,which greatly improves the positioning accuracy of GPS.Therefore,for the problem that the accuracy of the traditional positioning method of the UAV can not meet the existing requirements,this paper focuses on the carrier phase difference technology with the highest accuracy.A UAV based on carrier phase difference is designed to meet the low cost and high precision requirements of the UAV market,and it has important practical significance.First of all,because the carrier phase differential positioning equipment widely used in the market is generally expensive and large in size,it is only suitable for static positioning.In order to apply the carrier phase difference technology to the drone,we selected the low-cost and high-sensitivity U-blox M8 T chip and sensor such as inexpensive barometer or accelerometers and gyroscopes,designed the flight control board hardware installed on the Raspberry Pi,developed on the raspberry system on the Raspberry Pi,we also transplanted the most advanced open source flight control software ArduPilot on the raspbian system,enabling the open source flight control to read successfully data from each sensor and control the flight of the drone.Secondly,three differential positioning techniques are studied.The principle of carrier phase differential positioning,the positioning process and the EKF algorithm and LAMBDA algorithm used in the positioning process are analyzed in detail.Then,RTKLIB is used to design the RTK positioning solution program.After successfully solving the positioning results,we modified the GPS library file of the open source flight control system,so that the RTK positioning result replaces the single point positioning result of the U-blox module on the board.The resulte of high positioning information is input to the navigation control loop of the ArduPilot flight control.After the flight control is started,the RTK positioning data is transmitted to the ground by using the wireless data transmission module.Therefore,the combination of RTK technology and drones is realized.Finally,several experiments were carried out on the outdoor differential positioning system of the UAV,and the experimental results were analyzed by using a MATLAB program.The error analysis of the RTK program output before and after using the extended Kalman filter algorithm shows that the extended Kalman filter algorithm can effectively reduce the influence of measurement noise and system noise on the positioning result.The experimental results of analyzing the single point positioning of UAV and U-BLOX M8 T modules show that the UAV can achieve an accuracy of centimeter level under static and dynamic differential locking under short baseline conditions.This shows that using the carrier phase difference technology on the traditional drone,increasing the RTK positioning procedure can effectively improve the GPS positioning accuracy.