Wu Wenqi

High dynamic carrier phase tracking based on adaptive Kalman filtering

The typical GNSS carrier phase tracking loop with fixed parameters is easy to lose lock under high dynamic situation. In this paper the design of two kinds of carrier tracking method is presented. Firstly, the structure of Kalman-based-PLL is introduced. And then a new adaptive method is proposed after analyzing the relationship of carrier phase tracking error and state error covariance characteristics of Kalman-based-PLL. Simulation results show that the adaptive Kalman-based-PLL can track high dynamic carrier phase with 100g/s jerk and the carrier phase tracking error standard deviation is less than 0.011 cycles.

A New Online-Identification Algorithm for Odometer's Scale Factor

A identification in a nonlinear stochastic system - strapdown inertial navigation system is addressed. A new online-identification algorithm of odometers scale factor is proposed. From zero velocity update (ZUPT), the velocity errors in inertial navigation system propagate in the Schuler loops, and based the slow-varying property of velocity errors, the algorithm identifies the odometers scale factor using the changes of velocity during a short time. A tracking differentiator and a fadeout memory LMS algorithm is adopted in the identification to make the algorithm more practicable. The algorithm can track the odometers scale factor varying with time, and therefore be suitable for navigation case in which a vehicle runs a long time and roads vary a lot. Simulation indicates that this new algorithm can identify the odometers scale factor fast with small errors, so as to improve the accuracy of navigation.

Quadrature control of Hemispherical Resonator Gyro based on FPGA

The quadrature drift mechanism of the Hemispherical Resonator Gyro is analyzed and its equation is deduced in order to suppress the quadrature drift. The resonators two vibration modes which have different frequencies and damping decay rates cause the quadrature drift. Furthermore, the drift caused by different damping decay rates can usually be reduced by calibration, but the drift caused by different frequencies only can be suppressed by the quadrature control loop. The phase error of the 0-degree and 45-degree vibration signals are employed to eliminate frequencies split with quadrature control loop. And the FPGA digital control loop is introduced. Experiments show that the quadrature drift can be suppressed effectively by using the method mentioned before.

Base motion isolation algorithm for rate biased RLG north finder with disturbances

A base motion isolation algorithm is proposed for a rate biased RLG (Ring Laser Gyro) north finder subjected to vehicle disturbances. A single-axis rotation modulation scheme is used. Furthermore, the angular increment of the rotation of the turn table is utilized to compute the outputs of the third virtual gyroscope, by which the north finder consist of two gyroscopes and three accelerometers are translated into a Strapdown Inertial Navigation System (SINS) consist of three gyroscopes (two real and one virtual) and three accelerometers. Therefore, the north-finding problem is translated into an initial alignment problem based on a Kalman filter. The experiments results show that the new algorithm can effectively avoid the influences of vehicle disturbances. The 20min north finding accuracy of azimuth angle is better than 1′ when the weather is gusty, the vehicle is rocking and the motor is running on.

The mathematical model and simulation of north-finder based on rate biased RLG

In this paper, the basic principles of north-finder based on rate biased ring laser gyroscope (RLG), the mathematical model and the least square (LS) arithmetic are introduced. The measurement error of RLG (scale factor instability, bias instability, and random angle walk) and the angle measurement error of the platform are the major errors of the north-finder. Simulation analysis is performed to get their influence to the precision of the north-finder. Finally, an experiment is performed to test the mathematical model and the LS arithmetic.

Adaptive filter design for low-cost MEMS-IMU/GPS integrated navigation

It is essential to consider the affect of circumstance and stability of apparatus when designing a practical filter for low-cost MEMS-IMU/GPS integrated navigation. Innovation adaptive estimation (IAE) can adjust noise variance covariance online. On the other hand, IAE is more sensitive to observation outliers. Based on the orthogonal property of innovation sequence, the paper present the improved adaptive filter which inspect innovation orthogonal property and assign weight to innovation with outliers. The algorithm is embedded into MEMS-IMU/GPS tightly integrated navigation filter. Experiment shows that modified algorithm can restrain observation outliers efficiently, that improve the robustness of integrated system.

The study of north-finder based on rate biased RLG

Rated biased RLG is used in the north-finder based on a continuous rotation platform. Along with the rotating platform, the input axis of RLG relative to the earth rotation rate vector periodically changes. In this way, the measurement error of RLG is modulated in every direction. The cross-correlation analysis method is used for getting the azimuth angle. Considering the periodicity of gyro outputs, a digital filter is designed to decrease the influence of quantization error of RLG and some other wideband error sources. Experiment results show that the “cross-correlation analysis + filter” method can markedly increase the precision of the north-finder.