Research On Relative Navigation Technology Of Small UAV Formation Based On Inertial/GNSS/UWB Information Fusion

The UAV formation cooperation technology utilizes the information interaction between the multi-UAV sensors with better operability,stability,and security when performing tasks.So it has a very broad application prospect.Relative navigation information,as the key information to achieve collaborative control,is of great significance for its accuracy and reliability.This paper designs a set of relative navigation scheme based on ranging information between drones to figure out the solution of close-range relative navigation information between small UAVs.The analysis and research of carrier phase difference technology,UWB ultra-wideband communication and ranging technology,GNSS/INS tightly-coupled technology and other related technologies were carried out.The main research contents of this paper include the following aspects:Firstly,this paper studies the UWB ranging optimization algorithm for the accuracy of ranging in relative navigation.Based on the UWB ranging model,the error is compensated and calibrated using a linear fit for the antenna delay due to the communication frame from the transmit circuit to the transmit antenna.An error compensation model is established for the ranging offset caused by the relative motion between nodes.Aiming at the ranging error generated in the NLOS state,the sliding window method is used to identify,and the optimized Kalman filter algorithm is designed to realize the error correction.The experimental results show that compared with the traditional ranging algorithm,the accuracy of the optimized ranging algorithm is reduced by 70% in the LOS(empty environment)state and by 50% in the NLOS(non-line-of-sight environment)state.Secondly,aiming at the accuracy and reliability of the ambiguity resolution of differential GNSS technology in the relative navigation scheme,the related algorithm of UWB-assisted ambiguity resolution is studied.UWB's ranging information is used to constrain the objective function to quickly converge the whole-circumference ambiguity floating-point solution.The accuracy is improved by an order of magnitude,and the search efficiency of the ambiguity integer solution is improved by 6%.The search auxiliary space is established.Under the premise of minimizing the computational burden,the search scope is expanded,and the success rate of the ambiguity integer solution search is improved by 4%.In addition,an ambiguity verification method is designed,which not only overcomes the limitation of the two candidate ambiguities required for the Ratio test,but also improves the reliability of the test.Then,for the problem that the accuracy of INS/GNSS combination method does not meet the relative navigation requirements,UWB-assisted INS/GNSS relative navigation fusion algorithm is studied based on UWB ranging information and GNSS differential technology.In view of the large fluctuation of the carrier measurement noise,the estimation result is biased.The anti-difference adaptive factor is designed to optimize the unscented Kalman filter to weaken the influence of the large deviation of the observation on the filter iterative process and improve system accuracy and robustness.The simulation results show that the fusion algorithm improves the positioning accuracy of relative navigation with respect to tight-coupled INS/GNSS algorithm by at least 50%,and the absolute precision is about 10 cm,which satisfies the positioning accuracy requirements of relative navigation.At the same time,the robust adaptive factor can better correct the estimation error when the observation error is large.Finally,aiming at the mutual information needs of small UAV formation members,based on UWB sensor,the communication and ranging functions in this relative navigation scheme are studied.Based on the communication mechanism of IEEE802.15.4a,both of the data frame format of UWB ranging and communication and the data receiving and transmitting strategy are designed.In addition,a hardware verification platform for relative navigation was built,and the overall performance of the navigation and positioning and the rationality of the algorithm were verified by experiments.