Dong-Hwan Hwang

Position DOP Analysis for Sensor Placement in the TDOA-based Localization System

A relationship between the sensor placement and the PDOP (Position Dilution of Precision) is derived in the TDOA-based localization system. And the geometric condition of the sensor placement is analyzed in order to get a minimum PDOP based on the derived relationship. Through computer simulations, effect of the sensor placement on the PDOP is observed.

Attitude Determination GPS/INS Integrated Navigation System with FDI Algorithm for a UAV

Recently an unmanned aerial vehicle (UAV) has been widely used for military and civil applications. The role of a navigation system in the UAV is to provide navigation data to the flight control computer (FCC) for guidance and control. Since performance of the FCC is highly reliant on the navigation data, a fault in the navigation system may lead to a disastrous failure of the whole UAV. Therefore, the navigation system should possess a fault detection and isolation (FDI) algorithm. This paper proposes an attitude determination GPS/INS integrated navigation system with an FDI algorithm for a UAV. Hardware for the proposed navigation system has been developed. The developed hardware comprises a commercial inertial measurement unit (IMU) and the integrated navigation package (INP) which includes an attitude determination GPS (ADGPS) receiver and a navigation computer unit (NCU). The navigation algorithm was implemented in a real-time operating system with a multi-tasking structure. To evaluate performance of the proposed navigation system, a flight test has been performed using a small aircraft. The test results show that the proposed navigation system can give accurate navigation results even in a high dynamic environment.

INS/Vision Integrated Navigation System Considering Error Characteristics of Landmark-Based Vision Navigation

The paper investigates the geometric effect of landmarks to the navigation error in the landmark based 3D vision navigation and introduces the INS/Vision integrated navigation system considering its effect. The integrated system uses the vision navigation results taking into account the dilution of precision for landmark geometry. Also, the integrated system helps the vision navigation to consider it. An indirect filter with feedback structure is designed, in which the position and the attitude errors are measurements of the filter. Performance of the integrated system is evaluated through the computer simulations. Simulation results show that the proposed algorithm works well and that better performance can be expected when the error characteristics of vision navigation are considered.

Attitude Determination GPS/INS Integration System Design Using Triple Difference Technique

GPS attitude outputs or carrier phase observables can be effectively utilized to compensate the attitude error of the strapdown inertial navigation system. However, when the integer ambiguity is not correctly resolved and/or a cycle slip occurs, an erroneous GPS output can be obtained. If the erroneous GPS output is applied to the attitude determination GPS/INS (ADGPS/INS) integrated navigation system, the performance of the system can be degraded. This paper proposes an ADGPS/INS integration system using the triple difference carrier phase observables. The proposed integration system contains a cycle slip detection algorithm, in which the inertial information is combined. Computer simulations and flight test were performed to verify effectiveness of the proposed navigation system. Results show that the proposed system gives an accurate and reliable navigation solution even when the integer ambiguity is not correctly resolved and the cycle slip occurs.

A Deeply Coupled GPS/INS Integrated Kalman Filter Design Using a Linearized Correlator Output

GPS/INS integration systems can be classified into loosely coupled, tightly coupled, and deeply coupled method. The deeply coupled method is known to give the best performance on signal tracking and anti-jamming capability. Since the I and Q measurements, which are measurements of the GPS receiver in the deeply coupled method, are nonlinear functions of the carrier frequency, carrier phase and code phase, the function should be linearized in order to use it in the extended Kalman filter of the integration system. In this paper, a Kalman filter design using a linearized correlator output for the deeply coupled GPS/INS integration system is proposed. Before the linearization equation is derived, the I and Q measurements were expressed in position error and velocity error. The effectiveness of the Kalman filter was shown through computer simulations.

Two-Dimensional Navigation Error for Geometry of Landmark in Line-Of-Sight Measurement Based Vision Navigation System

Geometric effect of landmarks to the navigation error is investigated in the two-dimensional line-of-sight measurement based vision navigation system. DOP is derived between line-of-sight measurement error and navigation solution error. For cases of three landmarks in an area, variations of the DOP were observed through computer simulations. Vision navigation system experiments were performed for the cases. Simulation and experimental results show that navigation solution errors have similar trend to DOP values of the simulation.

The novel impact point prediction of a ballistic target with interacting multiple models

The threat of ballistic targets has increased rapidly in recent years. Therefore, it is essential to prepare the capabilities to predict their impact points in order to assign the firing battery to defense them effectively. Because the trajectory of a short-range ballistic target represents severe non-linear characteristics and consists of boost phase and ballistic phase, it is difficult to estimate the state and predict its impact point using single dynamic model in overlapping region. In this paper, the method to distinguish the trajectory phase from the measurement data and the method to estimate the state using a different extended Kalman filter (EKF) with interacting multiple models are proposed in order to fuse the state of a ballistic target in overlapping region. For effective the state fusion, it is necessary to merge each state from a different EKF in accordance with the mode probability depending on the residual error between the estimated state and measurement. A Monte Carlo simulation is used in the verification of the proposed method.

TDOA Measurement Based Taylor Series Design Method Considering Height Error for Real-Time Locating Systems

This paper proposes a Taylor-series design method which reduces the height error of the tag when readers are arranged at the same height in 3-dimensional space. The proposed method consists of two steps. Firstly, the planar position is estimated by the Taylor-series method using the TDOA measurement. Next, the height is estimated from the estimated planar position. In order to show the validity of the proposed method, computer simulations were performed for the static case and linear trajectory of the tag. Results show that the proposed method gives convergent estimated position and better height estimate than the Taylor series method.

Vision/INS Integrated Navigation System for Poor Vision Navigation Environments

In order to improve the performance of an inertial navigation system, many aiding sensors can be used. Among these aiding sensors, a vision sensor is of particular note due to its benefits in terms of weight, cost, and power consumption. This paper proposes an inertial and vision integrated navigation method for poor vision navigation environments. The proposed method uses focal plane measurements of landmarks in order to provide position, velocity and attitude outputs even when the number of landmarks on the focal plane is not enough for navigation. In order to verify the proposed method, computer simulations and van tests are carried out. The results show that the proposed method gives accurate and reliable position, velocity and attitude outputs when the number of landmarks is insufficient.

GNSS receiver rotation tracking loop design for spinning vehicles

In spinning vehicles, phase of the GNSS signal is modulated due to the rotation motion. The phase modulation results in carrier tracking error. In the conventional tracking loop, loop bandwidth has been adjusted in order to reduce the dynamics stress error. However, in the spinning vehicles, this method may not be effective when the vehicles rapidly rotate. This paper proposes a GNSS receiver tracking loop design method for spinning vehicles. In the proposed method, the influence of the rotation motion on the GNSS signal is eliminated by adding rotation tracking loop into the conventional tracking loop of the GNSS receiver. The added loop tracks rotation angle and frequency of the vehicles. The proposed method was verified through computer simulations.