Deok Won Lim

Unified approach to ultra-tightly-coupled GPS/INS integrated navigation system

A unified approach to the ultra-tightly coupled GPS/INS Integrated navigation system is proposed. It is shown that other methods of ultra-tightly coupled GPS/INS integrated navigation systems are included in the proposed framework, and some implementation issues are discussed. In order to show the validity of the proposed approach, position accuracy and anti-jamming capabilities of three methods of ultra-tightly-coupled GPS/INS integration system, included in the proposed framework, were compared. The comparisons were carried out through computer simulations and post-processing of data from a GNSS hardware simulator. The results show that the proposed approach works well and gives accurate navigation output with anti-jamming capability.

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.

Design of an Assisted GPS Receiver and its Performance Analysis

Demands on the indoor positioning capability is being increased. The assisted GPS (AGPS) needs the enhanced correlator scheme and the assistance information to acquire the weak GPS signal with strength below -150dBm within 2 ~ 3 seconds. This paper designs the AGPS receiver with an efficient digital correlator scheme that is able to reduce the squaring loss for weak signal acquisition. In order to evaluate the performance of the correlator scheme, this paper shows the success rates of signal acquisition under various environments. Finally, the performance of the designed receiver is analyzed with positioning accuracy and TTFF using assistance information from CDMA network of the cell phone

Hybrid TDOA/AOA Localization Algorithm for GPS Jammers

For a localization system, the TDOA (Time Difference of Arrival) measurement and AOA (Angle of Arrival) measurement are often used for estimating target’s positions. Although it is known that the accuracy of TDOA based localization is superior to that of AOA based one, it may have a poor vertical accuracy in bad geometrical conditions. This paper, therefore, proposes a localization algorithm in which the vertical position is estimated by AOA measurements and the horizontal one is estimated by TDOA measurement in order to achieve high 3D-location accuracy. And this algorithm is applied to a GPS jammer localization systems because it has a large value of the DOP (Dilution of Precision) when the jammer is located far away from the system. Simulation results demonstrate that the proposed hybrid TDOA/AOA location algorithm gives much higher location accuracy than TDOA or AOA only location.Abstract: For a localization system, the TDOA (Time Difference of Arrival) measurement and AOA (Angle of Arrival) measurement are often used for estimating targets positions. Although it is known that the accuracy of TDOA based localization is superior to that of AOA based one, it may have a poor vertical accuracy in bad geometrical conditions. This paper, therefore, proposes a localization algorithm in which the vertical position is estimated by AOA measurements and the horizontal one is estimated by TDOA measurement in order to achieve high 3D-location accuracy. And this algorithm is applied to a GPS jammer localization systems because it has a large value of the DOP (Dilution of Precision) when the jammer is located far away from the system. Simulation results demonstrate that the proposed hybrid TDOA/AOA location algorithm gives much higher location accuracy than TDOA or AOA only location.

A Simple and Efficient Code Discriminator for a MBOC Signal Tracking

Substantial interest has been given to algorithms that track multiplex binary offset carrier (MBOC) signals to be transmitted by Galileo and modernized GPS satellites, because such signals may cause a false lock in a receiver. In this paper, we propose a code discriminator named WDELP to resolve this problem. We derive the code-tracking error of this discriminator to determine the weights for its minimization and show the tracking performance of it.

A Model-Based Multipath Estimation Technique for GPS Receivers

Multipath remains a dominant source of ranging errors in GNSS (Global Navigation Satellite System). And it is generally considered undesirable in the context of GNSS, since the reception of multipath can make significant distortion to the shape of the correlation function. In this paper, therefore, the model of the distorted shape of the correlation function is formulated and a MBME (Model-Based Multipath Estimation) technique for GPS L1/L5 receivers is proposed in order to estimate the parameters of the indirect signal such as the amplitude and the delay. The MBME technique does not require the any hardware modifications and it can estimate the parameters for both the short and long-delay multipath. Especially, it would be the very effective technique for the short- delay multipath if the L5 signal is available. Finally, the feasibility of the proposed technique has been confirmed by simulation results.

Design of a software-based multi-channel GNSS IF signal generator

New GPS signals and Galileo signals are preparing the civil navigation system. GPS L2C signal is being broadcasted and GPS L5 and Galileo signals are being developed. Galileo system is planned to provide E1 and E5 signal for not only civil navigation but also commercial service and Safety of Life service. New GPS civil signals and Galileo signals are expected to provide much enhanced navigation performance. This paper designs a software-based multi-channel GNSS IF signal generator for simulating future navigation system. The generated signals are verified using a software-based GNSS receiver. The software-based multi-channel GNSS IF signal generator provides GPS L1 C/A, L5 signals and Galileo E1, E5 signals. The navigation message is included only in GPS L1 signal, and other signals do not include the navigation data. Therefore, generated L1 signal is validated by its navigation results; other generated signals are validated by their acquisition and tracking results using a software GNSS receiver.

Design of GPS/SBAS software receiver

Correction data of SBAS are classified to three categories such as the fast correction, the long term correction and the ionospheric correction. To retrieve and process the correction data, this paper modifies the software GPS receiver designed by CSLAB. The designed receiver can process all kinds of SBAS signals: WAAS, EGNOS, MSAS and GAGAN by just changing software. The performance of the implemented GPS/SBAS receiver is evaluated using real WAAS satellite signal and MSAS satellites signals which are available in Korea.

Relationship Between Readers' Arrangement and DOP in the TDOA Based Position Tracking System

A relationship between reader arrangement and DOP is derived from the geometry matrix of the TDOA-based position tracking system. It is shown that the minimum value of the DOP is affected by the number of readers, arrangement of readers and position of the tag. The relationship is verified through computer simulations for two cases of reader arrangement.

Dilution of Precision Relationship between Time Difference of Arrival and Time of Arrival Techniques with No Receiver Clock Bias

Dilution of Precision (DOP), as a measure of positioning accuracy, is an essential factor. Therefore, the DOP relationship between systems is very important. In this paper, the DOP relationship between TDOA and TOA in systems lacking clock bias is derived analytically and verified experimentally. Also, using those of earlier studies, the DOP relationship in each of defined systems is derived analytically.