Hyoungmin So

Implementation of a Vector-based Tracking Loop Receiver in a Pseudolite Navigation System

We propose a vector tracking loop (VTL) algorithm for an asynchronous pseudolite navigation system. It was implemented in a software receiver and experiments in an indoor navigation system were conducted. Test results show that the VTL successfully tracks signals against the near–far problem, one of the major limitations in pseudolite navigation systems, and could improve positioning availability by extending pseudolite navigation coverage.

The development of modularized post processing GPS software receiving platform

Modularized GPS software defined radio (SDR) software platform has many advantages of applying and modifying algorithm. Hardware based GPS receiver uses many hardware parts (such as RF front, correlators, CPU and others) that process tracked signal and navigation data to calculate user position, while SDR uses software modules, which run on general purpose CPU platform, to implement same function. SDR needs not change hardware part and it is not limited by hardware capability when new processing algorithm is required. The weakness of SDR is that software correlation takes lots of processing time. However, in these days the evolution of MPU and DSP, and the size minimization of general purpose CPU increase the competitiveness of SDR against the hardware GPS receiver. This paper presents a study of modulization of GPS SDR software platform and development of the GNSS SDR software platform using MATLAB Simulinktrade. We focus on especially post processing SDR platform which is usually adapted in research area. The main functions of SDR are GPS signal acquisition, signal tracking, decoding navigation data and calculating stand alone user position from stored data that was intermediate frequency (IF) down converted and sampled. Each module of SDR platform is categorized by function for applicability. The developed SDR software platform was tested using stored data that IF down converted and sampled. The test results present that the SDR software platform calculates user position properly.

A Pseudolite-Based Positioning System for Legacy GNSS Receivers

The ephemeris data format of legacy GPS receivers is improper for positioning stationary pseudolites on the ground. Therefore, to utilize pseudolites for navigation, GPS receivers must be modified so that they can handle the modified data formats of the pseudolites. Because of this problem, the practical use of pseudolites has so far been limited. This paper proposes a pseudolite-based positioning system that can be used with unmodified legacy GPS receivers. In the proposed system, pseudolites transmit simulated GPS signals. The signals use standard GPS ephemeris data format and contain ephemeris data of simulated GPS satellites, not those of pseudolites. The use of the standard format enables the GPS receiver to process pseudolite signals without any modification. However, the position output of the GPS receiver is not the correct position in this system, because there are additional signal delays from each pseudolite to the receiver. A post-calculation process was added to obtain the correct receiver position using GPS receiver output. This re-estimation is possible because it is based on known information about the simulated signals, pseudolites, and positioning process of the GPS receiver. Simulations using generated data and live GPS data are conducted for various geometries to verify the proposed system. The test results show that the proposed system provides the desired user position using pseudolite signals without requiring any modifications to the legacy GPS receiver. In this initial study, a pseudolite-only indoor system was assumed. However, it can be expanded to a GPS-pseudolite system outdoors.

Modified High-Resolution Correlator Technique for Short-Delayed Multipath Mitigation

Multipath is one of the main error sources in global navigation satellite system (GNSS) positioning. The high-resolution correlator (HRC) is a multipath mitigation technique well known for its outstanding performance for mid-delayed multipath, but still has a remaining error for the short-delayed multipath. This paper proposes a modified HRC scheme that can remove or reduce the error for short-delayed multipath signals. It estimates the HRC tracking error and augments the conventional HRC with the estimates. The method was implemented with a software receiver and the test results show short-delayed multipath-induced errors were reduced to about one third of those from the conventional HRC.

The Development of Modularized Post Processing GPS Software Receiving Platform using MATLAB Simulink

Modularized GPS software defined radio (SDR) software platform has many advantages of applying and modifying algorithm. Hardware based GPS receiver uses many hardware parts (such as RF front, correlators, CPU and others) that process tracked signal and navigation data to calculate user position, while SDR uses software modules, which run on general purpose CPU platform, to implement same function. SDR needs not change hardware part and it is not limited by hardware capability when new processing algorithm is required. The weakness of SDR is that software correlation takes lots of processing time. However, in these days the evolution of MPU and DSP, and the size minimization of general purpose CPU increase the competitiveness of SDR against the hardware GPS receiver. This paper presents a study of modulization of GPS SDR software platform and development of the GNSS SDR software platform using MATLAB Simulinktrade. We focus on especially post processing SDR platform which is usually adapted in research area. The main functions of SDR are GPS signal acquisition, signal tracking, decoding navigation data and calculating stand alone user position from stored data that was intermediate frequency (IF) down converted and sampled. Each module of SDR platform is categorized by function for applicability. The developed SDR software platform was tested using stored data that IF down converted and sampled. The test results present that the SDR software platform calculates user position properly.

Performance Analysis of Pseudolite Tropospheric Delay Models Using Radiosonde Meteorological Data

When pseudolite navigation system is applied to wide area, the tropospheric delay is the main error factor. In this study, we experimentally compared and analyzed the performance of the conventional pseudolite tropospheric delay models. The integration method using radiosonde meteorological data was suggested to derive the reference value for the comparison and analysis. Flight tests were carried out to analyze the performance of the tropospheric delay models according to the elevation angle and distance conditions between the user receiver and the pseudolite. As the results of this study, we provided the basis for the choice of tropospheric delay model appropriate to the relative location characteristics of the pseudolite and the user.

On-line Detection of Tracking Loss in Aviation GPS Receivers Using Frequency-Lock Loops

For high-precision real-time kinematics (RTK) and safety-of-life Global Navigation Satellite Systems (GNSS), it is critical to track the carrier reliably without interruptions. We develop hardware-oriented robust on-line cycle slip and loss detection logic for a single-frequency stand-alone aviation receiver. The moving average statistics of time-differenced frequency-lock loop (FLL) are shown to provide a robust and fixed detection threshold for cycle loss detection. A Monte-Carlo simulation shows that the detection performance remains robust when aviation dynamics from minimum operational performance standard (MOPS) are added to a simulated strong scintillation.

Performance Analysis of WADGPS System for Improving Positioning Accuracy

ABSTRACT The Wide Area Differential Global Positioning System (WADGPS) that uses a number of Global Navigation Satellite System (GNSS) reference stations are implemented with various types and provide services as it can service a wide range of areas relatively. This paper discusses a constellation design of reference stations and performance analysis of the WADGPS. It presented performance results of static and dynamic users when wide area correction algorithm was applied using eight reference stations. Keywords: GNSS, WADGPS, DGPS, SBAS been implemented and serviced as shown in the Wide Area Augmentation System in the U.S. and European Geostationary Navigation Overlay Service in Europe. In South Korea, Korean SBAS implementation project has been under way under the sponsorship of the Ministry of Land, Infrastructure, and Transport.Along with them, there is a project called Exploitation of DGPS for Guidance Enhancement (EDGE) in the U.S. (Carlo 2015). The EDGE is a WADGPS using reference stations that have a long baseline. It employed four DGPS reference stations and has been known to achieve the performance goal (3 m) of correction accuracy of user receivers. Other than above examples, there are other technical study examples such as Wide Area GPS Enhancement and Talon NAMATH that are broadcasted at the GPS P (Y) code.This paper discussed the performance analysis results about WADGPS for the purpose of improvements on GPS positioning accuracy. The target system consists of eight reference stations and one master station. Real-time user correction performance was verified.This paper is organized as follows. In Section 2, configuration of the implemented system is discussed. In Section 3, performance results of post-processing of collected data are presented in order to verify the performance of GPS observation data at the implemented reference station. In Section 4, correction performance of

Pseudolite Antenna Calibration Algorithm using a Multi-Antenna Receiver

The need for position information in indoor environments has been growing lately. Several indoor navigation systems have been studied. Among them, pseudolite-based indoor positioning systems are one of the best systems to obtain precise position measurements. However, the installation of such systems is very difficult because the calibration of pseudolite antenna position is complicated. For precise calibration, the use of carrier phase measurements is necessary, and whenever carrier phase measurements are considered, problems with cycle ambiguity appear. In this paper, a new approach to calibrate the positions of pseudolite antennas is proposed. By using a multi-antenna, the ambiguity can be eliminated, epoch by epoch, for every single carrier phase measurement. Moreover, the number of calibration points can be reduced down to 3 by use of measurements collected at unknown positions. Using the proposed methods, the process of the collection of carrier phase measurements becomes considerably simple and convenient. Simulation results are presented to verify the proposed algorithms.

Spatial Decorrelation of SBAS Satellite Error Corrections in the Korean Peninsular

The characteristics of the SBAS satellite orbit and clock corrections are highly affected by the narrow network size in the Korean peninsula, which is expected to have an important role in the future dual frequency SBAS. The correlation between satellite corrections can be analyzed in terms of the spatial decorrelation effect which should be analyzed to keep the service area as wide as possible. In this paper, the characteristics of satellite error corrections for the potential Korean dual frequency SBAS were analyzed, and an optimal filter design approach is proposed to maximize the service area.