Shunting Wang

An integer ambiguity resolution method for the global positioning system (GPS)-based land vehicle attitude determination

During attitude determination using a global positioning system (GPS), cycle slips occur due to the loss of lock and noise disturbance. Therefore, the integer ambiguity needs re-computation to isolate the error in carrier phase. This paper presents a fast method for integer ambiguity resolution for land vehicle application. After the cycle slips are detected, the velocity vector is utilized to obtain the rough baseline vector. The obtained baseline vector is substituted into carrier phase observation equations to solve the float ambiguity solution which can be used as a constraint to accelerate the integer ambiguity search procedure at next epochs. The probability of correct integer estimation in the expanded search space is analyzed. Experimental results demonstrate that the proposed method gives a fast approach to obtain new fixed ambiguities while the regular method takes longer time and sometimes results in incorrect solutions.

A motion-based integer ambiguity resolution method for attitude determination using the global positioning system (GPS)

Loss of the satellite signal and noise disturbance will cause cycle slips to occur in the carrier phase observation of the attitude determination system using the global positioning system (GPS), especially in the dynamic situation. Therefore, in order to reject the error by cycle slips, the integer ambiguity should be re-computed. A motion model-based Kalman predictor is used for the ambiguity re-computation in dynamic applications. This method utilizes the correct observation of the last step to predict the current ambiguities. With the baseline length as a constraint to reject invalid values, we can solve the current integer ambiguity and the attitude angles, by substituting the obtained ambiguities into the constrained LAMBDA method. Experimental results demonstrate that the proposed method is more efficient in the dynamic situation, which takes less time to obtain new fixed ambiguities with a higher mean success rate.

Rapid alignment method of INS with large initial azimuth uncertainty under complex dynamic disturbances

For the rapid alignment of the ship-borne weapon INS with large initial azimuth attitude error under complex environment disturbances, a nonlinear error propagation model augmented by sensor errors and disturbance sources was proposed. Velocity plus angular rate matching method was applied in the implementation of the alignment. Simulation results show that comparing with the conventional solutions, this method can accomplish the transfer alignment of a mooring ships weapon INS with large heading error rapidly and accurately. Meanwhile, it has strong adaptability to the sea condition and can improve the precision of the alignment under complex environment disturbances.

A Fast Integer Ambiguity Repair Method for the Land Vehicle Attitude Determination Using GPS

The integer ambiguity needs re-computation when cycle slips occur in the carrier phase signal during attitude determination using global positioning system (GPS). This paper presents a new method for fast integer ambiguity repair for land vehicle application. The velocity vector is utilized to obtain the baseline vector when cycle slips occur. And then observation equations are solved with the obtained baseline vector for the float ambiguity solution which can be used as a constraint condition to accelerate the integer ambiguity search procedure at next epochs. Experimental results demonstrate that the proposed method gives a fast approach to obtain new fixed ambiguities while the regular method takes longer time and sometimes results in incorrect solutions.

A Mismatch Diagnostic Method for TERCOM-Based Underwater Gravity-Aided Navigation

Gravity matching algorithm is the pivotal technique in gravity-aided navigation, which is the main method in the application of underwater autonomous vehicle. TERCOM algorithm is one of the classical matching algorithms in this research field. Due to the characteristic of inertial navigation system (INS) location error, an affine or a rigid transformation relationship between actual vehicle trajectory and INS-indicated trajectory is assumed to be existed. In order to improve the accuracy of TERCOM algorithm, a mismatch diagnostic method based on the restricted spatial order constraints (RSOC) algorithm from image registration is assisted. RSOC strategy integrates spatial order constraints and decision criteria restrictions to screen outliers in a matched sequence. It is obtained that the mismatch diagnostic method can select the mismatched points accurately. Therefore, the matching algorithm with mismatch detection mechanism has better performance. The reliability and accuracy of the method are verified via simulation tests.

A High-Spin Rate Measurement Method for Projectiles Using a Magnetoresistive Sensor Based on Time-Frequency Domain Analysis

Traditional artillery guidance can significantly improve the attack accuracy and overall combat efficiency of projectiles, which makes it more adaptable to the information warfare of the future. Obviously, the accurate measurement of artillery spin rate, which has long been regarded as a daunting task, is the basis of precise guidance and control. Magnetoresistive (MR) sensors can be applied to spin rate measurement, especially in the high-spin and high-g projectile launch environment. In this paper, based on the theory of a MR sensor measuring spin rate, the mathematical relationship model between the frequency of MR sensor output and projectile spin rate was established through a fundamental derivation. By analyzing the characteristics of MR sensor output whose frequency varies with time, this paper proposed the Chirp z-Transform (CZT) time-frequency (TF) domain analysis method based on the rolling window of a Blackman window function (BCZT) which can accurately extract the projectile spin rate. To put it into practice, BCZT was applied to measure the spin rate of 155 mm artillery projectile. After extracting the spin rate, the impact that launch rotational angular velocity and aspect angle have on the extraction accuracy of the spin rate was analyzed. Simulation results show that the BCZT TF domain analysis method can effectively and accurately measure the projectile spin rate, especially in a high-spin and high-g projectile launch environment.

Absolute velocity damping algorithm with varying damping ratio for inertial navigation systems based on Kalman filter

The navigation information of an inertial navigation system (INS) is contaminated by period oscillating errors of which the amplitudes are invariant or increasing with time. A velocity damping algorithm based on Kalman filter is proposed to attenuate the oscillating errors in this paper. The differences between external velocity measurements, e.g. GPS or odometer velocity measurements, and INS velocity outputs are applied as control signals to add damping to the system. To find the optimal feedback gains for the control signals, an imaginary system model is developed according to the criterion that the estimation error vector of the states by Kalman filter is identical to the error vector of INS. Thus the elements in the gain matrix of Kalman filter are exactly the optimal gains to be determined. The horizontal velocity damping mechanization is first introduced; followed by the more complex one, i.e. absolute velocity damping mechanization. Simulations are presented in two sections respectively to illustrate the effectiveness of the above two mechanizations. The proposed method breeds a time-variant damping ratio, endowing the system with sound transient and steady-state performance. Finally, the performance of absolute velocity damping algorithm is verified on a dual-axis-rotation strapdown INS with GPS serving as the source of reference velocity.

Cooperative navigation for multiple autonomous underwater vehicles with time delayed measurements

Dealing with time delayed measurements is a key problem of cooperative navigation for multiple autonomous underwater vehicles (MAUVs). In this work, in order to solve the invalidation of location due to the time delayed measurements, an algorithm which based on the augmented extended Kalman filter (AEKF) is proposed. The algorithm expands the variable dimension of slave AUV according to the time delayed measurements, and infers the fundamental equations of AEKF. Compared to the traditional EKF method, simulation results prove that AEKF has higher positioning accuracy.

On-line self-calibration for inertial platform system with a single totally free axis

An on-line self-calibration method for estimating the error coefficients of an inertial platform system is proposed to avoid the troublesome process of dismounting the system from the carriers, such as vessels and missiles. This method belongs to the type of continuous self-calibration method according to which we implement the calibration scheme by making the platform revolve through a specified rotation trajectory at a given angular rate. Our method distinguishes from the existed continuous self-calibration methods in three aspects. First, the gyros applied in this paper are assumed to be dynamically tuned gyros which have two sensitive axes rather than a single one. Second, the process of revolving is realized by assigning instructional angular speed to the gyros not revolved by rotating the gimbals directly, which implies that the platform system operates under an autonomous navigation state throughout the calibration process, relaxing the requirement of switching the operating mode of the system. Third, the gyros are assumed to have a rotational limit of ±60° on outer gimbal and inner gimbal axes. A modified dynamic model is established to adapt to the changes mentioned previously. The observation model is based on the output model of accelerometers. Then the EKF is applied to estimate the coefficients since the model is nonlinear. The simulation results substantiate the effectiveness of the method.

Rapid alignment method of INS with large initial azimuth error under uncertain flexure disturbances

A new nonlinear initial alignment method was proposed for the rapid alignment of the ship-borne weapon INS with large initial azimuth attitude error under uncertain flexure deformation disturbances. Considering the flexure deformation of certain axis has the severest affection to the angular rate measurement, velocity and partial angular rate were used as the measurements in this method, in which the pitch rate is subtracted from the angular rate measurement. Simulation results show that comparing with the conventional solution, which compensates the flexure deformation by augmenting its model into the alignment filter, the proposed alignment method can accomplish the transfer alignment of a mooring ships weapon INS with large heading error rapidly and accurately, and it is more reliable in the situation of flexure deformation uncertainty.