Sanghoon Jeon

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.

Enhanced SBAS Integration Method Using Combination of Multiple SBAS Corrections

In this paper, we propose a new way of improving DGNSS service using combination of multiple SBAS information. Because SBAS uses Geostationary Earth Orbit (GEO) satellites, it has very large coverage but it can be unavailable in urban canyon because of visibility problem. R. Chen solved this problem by creating Virtual Reference Stations (VRS) using the SBAS signal [1]. VRS converts SBAS signal to RTCM signals corresponding its location, and broadcast the converted RTCM signals over the wireless internet. This method can solve the visibility problem cost effectively. Furthermore it can solve DGNSS coverage problem by creating just a transmitter instead of a reference station. Developing above method, this paper proposes the methods that integrate two or more SBAS signals into one RTCM signal and broadcast it. In Korea, MSAS signal is available even though it is not officially certified for Korean users. As a Korean own SBAS-like system, there is the internet-based KWTB (Korean WADGPS Test Bed) which we developed and released at ION GNSS 2006. As a result, virtually two different SBAS corrections are available in Korea. In this paper, we propose the integration methods for these two independent SBAS corrections and present the test results using the actual measurements from the two systems. We present the detailed algorithm for these two methods and analyze the features and performances of them. To verify the proposed methods, we conduct the experiment using the logged SBAS corrections from the two systems and the RINEX data logged at Dokdo monitoring station in Korea. The preliminary test results showed the improved performance compared to the results from two independent systems, which shows the potential of our proposed methods. In the future, the newly developed SBASs will be available and the places which can access the multiple SBAS signals will increase. At that time, the integration or combination methods of two or more SBASs will become more important. Our proposed methods can be one of the useful solutions for that. As an additional research, we need to extend this research to the system level integration such as the concept of the decentralized WADGPS.

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.

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.

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.

GPS Satellite State Vector Determination in ECI Coordinate System using the Civil Navigation Message

A closed form of an algorithm to determine a Global Positioning System (GPS) satellites position, velocity and acceleration is proposed, and an Earth Centred Earth Fixed (ECEF) to Earth Centred Inertial (ECI) transformation result using the Civil Navigation (CNAV) message is presented in this paper. To obtain the closed form of the GPS satellite velocity and acceleration determination algorithm using the CNAV, we analytically differentiated the IS-GPS-200F position determination function. The calculated data are transformed from the International Terrestrial Reference Frame (ITRF) to the Geocentric Celestial Reference Frame (GCRF) using an equinox-based transform algorithm that is defined in the IAU-2000 resolution system using the Earth Orientation Parameter (EOP) data. To verify the correctness of the proposed velocity and acceleration determination algorithm, the analytical results are compared to the numerical result. The equinox-based transformation result is compared to simple rotation about the z-axis, which does not use the EOP. The results show that by using the proposed algorithm and the equinox-based transformation together, the user can obtain more accurate navigation data in the ECI frame.

Development of Galileo E5 Signal Receiving Software for AltBoc Signal Modulation

This paper contains the signal receiving algorithm for Galileo E5 AltBOC signal and the development of Galileo E5 signal receiving software. The software runs the process from signal acquisition to extracting measurement data to get navigation solution. It uses logged IF data file as an input. In signal acquisition stage, 1ms and delayed 1ms data are used for reducing correlation ross from secondary code and navigation bit conversion. Signal tracking stage is made of two stages which are coarse tracking and fine tracking. It is for taking advantage of AltBOC characteristic and resolving ambiguity problem due to BOC modulation. The functions of software are verified by signal processing using logged IF data from commercial GNSS simulator.