Improving Detection Performance of Ionospheric Disturbances due to Earthquake by Optimization of Sequential Measurement Combination

Energy generated from earthquake (EQ) is transferred to the ionosphere and results in co-seismic ionospheric disturbances (CID). CID can be observed in the ionospheric combination using L1, L2 frequency carrier phase. As ionospheric trend due to normal conditions such as elevation angle of satellites is generally larger than disturbances, a proper measure is required to extract disturbance signals. Derivative, or sequential combination, is a simple and effective way to remove the normal trend in the ionospheric delay. When using derivative, however, disturbance signals can often be obscured by noise due to its small amplitude. In order to reduce the noise while preserving the time rate of data, and thus to improve signal-to-noise ratio (SNR), we designed a new derivative method using optimization under a couple of assumptions. With simulation data, it is found that N, the number of epochs used for sequential combination, turned out to be the best when N=160 with maximum SNR. Finally, the proposed algorithm’s SNR was compared to that of the previous study which also used derivative method. 120~260% improvements were observed for the proposed method compared to the conventional method

Multi-Thread Based Design of Navigation Algorithm Module in Multi Radio Integrated Navigation System M&S Software

A multi-thread based navigation algorithm module is designed in a multi radio integrated navigation system modeling and simulation software in order to efficiently use resources in the software platform of the modeling and simulation software. By adopting the multi-thread architecture, features of navigation algorithms and concurrency of the algorisms can be easily included in the navigation algorithm module. In order to show the usefulness of the multi thread based navigation algorithm module design, a navigation algorithm module in the multi-radio integrated navigation system for GPS, KNSS, Loran-C, eLoran and DME/VOR is implemented in C++ under the Windows operating system. The implementation results show that the thread based design can be useful in the development of multi radio integrated navigation systems

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

Performance Evaluation of Multi Radio Integrated Navigation System under Navigation Warfare in M&S Software

In this paper, a modelling and simulation software is designed in order to evaluate the performance of a multi radio integrated navigation system and the performance evaluation results are presented. The modelling and simulation software is divided into navigation algorithm module, navigation environment generation module, and graphic user interface module with performance evaluation algorithm. In order to show the validity of the design, the modelling and simulation software for GPS, KNSS, Loran-C, eLoran, and DME/VOR is implemented in C++ under Windows OS environment. Accuracy, integrity, continuity and availability are evaluated for the multi radio integrated navigation system in the modelling and simulation software. The performance evaluation results show that the designed modelling and simulation software can be effectively used for the performance evaluation of multi radio integrated navigation systems

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

Multi-Radio Integrated Navigation System M&S Software Design for GNSS Backup under Navigation Warfare

To avoid degradation of navigation performance in the navigation warfare environment, the multi-radio integrated navigation system can be used, in which all available radio navigation systems are integrated to back up Global Navigation Satellite System (GNSS) when the GNSS is not available. Before real-time multi-radio integrated navigation systems are deployed, time and cost can be saved when the modeling and simulation (M&S) software is used in the performance evaluation. When the multi-radio integrated navigation system M&S is comprised of independent function modules, it is easy to modify and/or to replace the function modules. In this paper, the M&S software design method was proposed for multi-radio integrated navigation systems as a GNSS backup under the navigation warfare. The M&S software in the proposed design method consists of a message broker and function modules. All the messages were transferred through the message broker in order to be exchanged between the function modules. The function modules in the M&S software were independently operated due to the message broker. A message broker-based M&S software was designed for a multi-radio integrated navigation system. In order to show the feasibility of the proposed design method, the M&S software was implemented for Global Positioning System (GPS), Korean Navigation Satellite System (KNSS), enhanced Long range navigation (eLoran), Loran-C, and Distance Measuring Equipment/Very high-frequency Omnidirectional Radio range (DME/VOR). The usefulness of the proposed design method was shown by checking the accuracy and availability of the GPS only navigation and the multi-radio integrated navigation system under the attack of jamming to GPS

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.N

Spoofing Attack Results Determination in Code Domain Using a Spoofing Process Equation

When a user receiver is tracking an authentic signal, a spoofing signal can be transmitted to the user antenna. The question is under what conditions does the tracking point of the receiver move from the authentic signal to the spoofing signal? In this study, we develop a spoofing process equation (SPE) that can be used to calculate the tracking point of the delay lock loop (DLL) at regular chip intervals for the entire spoofing process. The condition for a successful spoofing signal is analyzed using the SPE. To derive the SPE, parameters, such as the signal strength, sweep velocity, loop filter order, and DLL bandwidth are considered. The success or failure of a spoofing attack is determined for a specific spoofing signal using the SPE. In addition, a correlation between each parameter for a successful spoofing attack could be obtained through the SPE. The simulation results show that the SPE performance is largely consistent with that of general DLL methods, even though the computational load of SPE is very low

Improving Detection Performance of Ionospheric Disturbances due to Earthquake by Optimization of Sequential Measurement Combination

International audienceEnergy generated from earthquake (EQ) is transferred to the ionosphere and results in co - sei s mic ionospheric disturbances ( CI D). C ID can be observed in the ionospheric combination using L1, L2 frequency carrier phase. As ionospheric trend due to normal conditions such as elevatio n angle of satellites is generally larger than disturbances, a proper measure is required to extract disturba n ce s ignals . Derivative , or sequential combination, is a simple and effective way to remove the normal trend in the ionospheric delay. W hen using derivative, however, disturbance s ignals can often be obscured by no ise due to its small amplitude. In order to reduce the noise while preserving the time rate of data, and thus to improve signal - to - noise ratio (SNR) , we designed a new derivative method using optimization under a couple of assumptions . W ith simulation data , it is found that N, the number of epochs used for sequential combination , turne d out to be the best when N=16 0 with maximum SNR. Finally, t he proposed algorithm’s SNR was compared to that of the previous study which also used derivative method. 1 20 ~260 % improvement s w ere observed for the proposed method compared to the conventional metho