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Position and time information provided by the satellite navigation system is important in many application fields. However, the satellite navigation signal is vulnerable to interference signals due to the low navigation signal strength. This interference signal for the satellite navigation signal is being advanced to the spoofing signal, which can adjust the position and time information of the satellite navigation receiver, beyond simple jamming signal. To ensure the safe use of satellite navigation signals in the future, it is necessary to prepare for attacks by such spoofing signals. It is possible to reduce the damage to users of satellite navigation by early detection of the spoofing signals. For spoofing signals, the detection method should be applied according to the attack method, and various detection methods should be applied because the impact of the attacker on the receiver may vary depending on the attack method and attack item. In this study, we propose a method to detect the spoofing signal when the signal is induced based on the satellite navigation correction data and measurement value. The proposed detection method is advantageous in that it can be applied to a receiver directly because the spoofing signal can be detected without being equipped with additional hardware in a conventional receiver. Additionally, this method can be applied to a mobile receiver as well as a fixed receiver. It is expected that the proposed technique will increase the usefulness and reliability of the satellite navigation system.

BACKGROUND: To investigate the imaging findings and visibility of breast invasive lobular carcinoma (ILC) on diffusion-weighted imaging (DWI) and compare quantitative apparent diffusion coefficient (ADC) metrics of ILC and invasive carcinoma of no special type (NST) using a histogram analysis. METHODS: We performed an observational retrospective study of 629 consecutive women with pathologically proven ILC and invasive ductal carcinoma of NST, who underwent 3-T MRI including DWI, between January 2017 and August 2020. RESULTS: After propensity score matching, 71 women were allocated to each group. On DWI, 9 (12.7%) lesions of ILC and 4 (5.6%) invasive carcinomas of the NST were not visualized. For the tumor visibility on DWI, tumor size, tumor ADC value, and background diffusion grade were significantly associated with the visibility score in both groups (all P0.05). The mean ADC (1.226×10(−3) vs. 1.052×10(−3) mm(2)/s, P

Knee contact forces and knee stiffness are biomechanical factors worth considering for walking in knee osteoarthritis patients. However, it is challenging to acquire these factors in real time; thus, making it difficult to use them in robotic rehabilitation and assistive systems. This study investigated whether trained deep neural networks (DNNs) can capture the biomechanical factors only using kinematics during gait, which is possible to measure via sensors in real time. A public dataset of walking on the ground was analyzed through biomechanical analysis to train and test DNNs. Using the training dataset, several DNN topologies were explored via Bayesian optimization to tune the hyperparameters. After optimization, DNNs were trained to estimate the biomechanical factors in a supervised manner. The trained DNNs were then evaluated using two new datasets, which were not used in the training process. The trained DNNs estimated the biomechanical factors with a high level of accuracy in both types of test datasets. Results confirmed that DNNs can estimate the biomechanical factors based on only kinematics during gait.

As the strength of global navigation satellite system (GNSS) signals is very low, they are vulnerable to interference and susceptible to attacks motivated by economic, military, and security reasons. These threats are gradually increasing. The most common attack is jamming, in which a strong signal is used to make a receiver miss the GNSS signal. As attacks become more sophisticated, they are expected to evolve to spoofing interference, in which the receiver is deceived. Spoofing interference is a larger threat because the receiver cannot recognize that they are being targeted by an attacker. For this reason, it is becoming more important to monitor GNSS signals so that they can be evaluated in terms of reliability. In this paper, we analyze spoofing detection methods with respect to the navigation solution, measurements, and navigation messages obtained by a receiver. We propose an advanced detection method for overcoming the limitations of each individual detection algorithm. The proposed methods enhance the performance of spoofing detection and reduce the false alarm rate. This research can be applied directly to GNSS signal monitoring systems and will be helpful for enhancing the stability of satellite navigation systems.

Purpose To evaluate the relationships between female hormone levels and background parenchymal enhancement (BPE) or apparent diffusion coefficient (ADC) values of breast parenchyma, as well as the effects of BPE and ADC values on cancer visibility. Methods This prospective study was performed in 164 consecutive premenopausal patients who were diagnosed with invasive breast cancer from November 2016 to December 2018. Two radiologists analyzed the qualitative, quantitative BPE and ADC values of normal contralateral breast parenchyma. We also analyzed the cancer visibility using a three-point scale (0: no visibility, 1: slight visibility, 2: excellent visibility). Results The progesterone level was significantly correlated with qualitative BPE grade and quantitative values of the BPE, as well as with the mean ADC. On contrast enhanced image (CEI), the visibility score was significantly associated with tumor size, qualitative and quantitative BPE. On diffusion weighted image (DWI), tumor size was significantly associated with the visibility score, whereas the ADC value was not. Of four lesions with a score of 0 on CEI, three had a score of 2 and one a score of 1 on DWI. Regarding the visibility score on DWI, tumor size and histologic type were significantly different among the three groups. Conclusions Qualitative or quantitative BPE of breast parenchyma was positively correlated with the progesterone level and the mean ADC was negatively correlated. The cancer visibility was affected by BPE on CEI, but not by ADC on DWI. Small-sized cancer and invasive lobular cancer could be the causes of false-negative diagnoses on DWI.

As GNSS(Global Navigation Satellite System) is used in various filed, many countries establish GNSS system independently. But GNSS system has the limitation of accuracy and stability in stand-alone mode, because this system has error elements which are ionospheric delay, tropospheric delay, orbit ephemeris error, satellite clock error, and etc. For overcome of accuracy limitation, the DGPS(Differential GPS) and RTK(Real-Time Kinematic) systems are proposed. These systems perform relative positioning using the reference and user receivers. ETRI(Electronics and Telecommunications Research Institute) is developing precision navigation system in point of extension of GNSS usage. The precision navigation system is for providing the precision navigation solution to common users. If this technology is developed, GNSS system can be used in the fields which require precision positioning and control. In this paper, we introduce the precision navigation system and perform design and algorithm verification.

GNSS (Global Navigation Satellite System) Ground Station monitors navigation satellite signal, analyzes navigation result, and uploads correction information to satellite. GNSS Ground Station is considered as a main object for constructing GNSS infra-structure and applied in various fields. ETRI (Electronics and Telecommunications Research Institute) is developing Monitoring and Control subsystem, which is subsystem of GNSS Ground Station. Monitoring and Control subsystem acquires GPS and Galileo satellite signal and provides signal monitoring data to GNSS control center. In this paper, the configurations of GNSS Ground Station and Monitoring and Control subsystem are introduced and the preliminary design of Monitoring and Control subsystem is performed. Monitoring and Control subsystem consists of data acquisition module, data formatting and archiving module, data error correction module, navigation solution determination module, independent quality monitoring module, and system operation and maintenance module. The design process uses UML (Unified Modeling Language) method which is a standard for developing software and consists of use-case modeling, domain design, software structure design, and user interface structure design. The preliminary design of Monitoring and Control subsystem enhances operation capability of GNSS Ground Station and is used as basic material for detail design of Monitoring and Control subsystem.

Galileo is the Europe`s global navigation satellite system corresponding to the GPS. The GIOVE-A test experiment has been finished and the second test satellite GIOVE-B will be launched soon. The integration of GPS and Galileo lead an increase of visible satellite number. We can obtain an improved navigation performance in signal blocked area such as urban or forest. GPS and Galileo have each time-coordinate system and use the different error model to calculate the navigation solution. In this paper, we studied on GPS and Galileo channel error model and time-coordinate system. Using this result, we implement the integrated navigation algorithm. In simulation, we analyzed the navigation error caused by time and coordinate disagreement and verified performance of integrated navigation algorithm in terms of visible satellite number, DOP(Dilution of Pression) and position error.

Visibility of the satellite navigation is related to a environmental condition of a receiver. Obstacles like buildings and trees in urban areas can block signals and have effects on accuracy and reliability of positioning. This paper presents a method of creating 3D analysis model of urban canyon of Seoul using three-Dimensional digital map. Analysis techniques of visible satellites with Ray-Polygon Collision Detection and validation of algorithm through field tests are discussed. We have compared and analyzed the visibility of GPS and Galileo with respect to separate and simultaneous tracking in view of DOP (Dilution of Precision) using the 3D GIS digital map.

GNSS(Global Navigation Satellite System) is used in various fields. Because the strength of GNSS signal is very weak on Earth surface, GNSS signal is easy to be disturbed by interference. For increasing the GNSS signal stability and availability, various mitigation methods and analysis of interference are studied. As these situation, it is necessary the standard platform to assist the interference mitigation studies and analyze receiver properties and interference effect. ETRI(Electronics and Telecommunications Research Institute) is developing GNSS Interference Signal Verification Platform. This platform generates interference signal and measures the receiver properties influenced by interference. Using the measurement result and signal propagation model, this platform analyzes the effect of interference. GNSS Interference Signal Verification Platform consists of GNSS Interference Signal Generation Equipment, GNSS Interference Signal Measurement Equipment, and GNSS Interference Propagation Model. This paper introduces GNSS Interference Signal Verification and describes the generation signal types which are jamming and spoofing interference. Finally we make the interference signal generation scenario for GNSS Interference Signal Generation Equipment. This scenario reflects the purpose and usage of GNSS Interference Signal Verification Platform.

The GNSS(Global Navigation Satellite System) is used widely and generally these days. The satellite navigation system provides navigation service globally and doesn"t need an extra cost to use. Thus this system is portrayed as public service. But this system has a weak point. The satellite signal strength is very weak on the ground so this system is vulnerable against interference signal. When the GNSS interference signal is induced, the receiver cannot operate normally. The interference is presented by jamming or spoofing about GNSS signal. The effect of the interference can be done in various field from car navigation to national infrastructure like mobile communication, power plant, etc. ETRI(Electronics and Telecommunications Research Institute) developed GPS Jamming monitoring system for monitoring interference of GNSS signal. The developed GPS Jamming monitoring system has the functions which are jamming & spoofing detection and jamming location with direction finders. Among the technologies of GPS Jamming monitoring system, this paper describes spoofing detection module. This module monitors GPS signal and detects the spoofing signal with measurement and message of receiver. ETRI performed the functional test of developed spoofing detection module through the spoofing signal generation equipment. In this test, we confirm that the spoofing signal is induced in GPS receiver and verify the performance of spoofing detection.

As the field of GNSS application is stretched, the stability of GNSS is concerned. GNSS is connected with the social infrastructure and economic problem. GNSS is used in communication system, military weapon, power station, satellite system, and so on. The information of position and time which is provided by GNSS is related with economy and military capabilities. Thus the threat of GNSS attack will increase in the future. For dealing with this request, ETRI is developing GNSS interference detection system. In this paper, we introduce the GNSS interference detection system and specially focus on the spoofing detection module. The algorithm for detecting the spoofing signal is implemented on the GNSS interference detection system. The result of implemented system is verified by the system test. The functions of spoofing detection module are verified by the spoofing environment which is generated by test-bed.

A multi-mission GEO satellite, COMS has three payloads including Ka-band communications, GOCI, and MI. COMS SGCS is the only system for monitor and control of the satellite in orbit. In order to fulfill the mission operations of the three payloads and spacecraft bus, COMS SGCS performs the following functions such as reception and processing of telemetry data via S-band link, planning and transmission of telecommand, tracking and ranging of the satellite, control and monitoring of SGCS equipment, analysis and simulation of the satellite, processing and analysis of flight dynamics data, and mission scheduling and reporting. By the proper functional allocations, COMS SGCS is divided into five subsystems such as TTC, ROS, MPS, FDS, and CSS. COMS SGCS is linked with MSC, KOSC, and IDACS for satellite related data exchange. The software in the COMS SGCS is designed using the object-oriented methodology and implemented using Microsoft C# .NET environment on Intel microprocessor based computers. The hardware in the COMS SGCS includes 13-m S-band mono-pulse Cassegrain antenna and RF/BB equipment. In this paper, development of the COMS SGCS is described with respect to system functional allocations, software and hardware design, system implementation, and system test.

The modeling of satellite multi-body dynamic is quite complicate process. In developing satellite simulator, it’s proper to use multi-body dynamics in modeling satellite attitude dynamics. We will introduce the attitude dynamic module that is able to cover various satellites and operational phases. This approach may improve portability of satellite modeling. The generalization of multi-body attitude dynamics model can be used to analyze orbit and attitude dynamic of satellite. It is very useful for various satellites system and applying to other system with several parameters change.

Satellite system has lots of fault causes. For some communications satellite systems, fault management and data preservation are required to exchange data continuously and provide broadcasting service. In this paper, we have proposed fault management of satellite system using penalty method, data buffer and recovery manager. The penalty manager imposes penalty according to fault degree and manages fault quantitatively. Data Buffer has the function to store data in fault situation and prevent data damage. Recovery manager performs system monitoring and to operates recovery process in fault situation. Proposed method is fundamental concept of the architectural characteristics and enhances satellite fault management performance. This capability permits the satellite to detect and correct some of its own failures autonomously. Also, the effect of penalty method and data buffer on fault management design has been discussed.

In this paper, a method of station keeping strategy using relative orbital motion and numerical optimization technique is presented for geostationary spacecraft. Relative position vector with respect to an ideal geostationary orbit is generated using high precision orbit propagation, and compressed in terms of polynomial and trigonometric function. Then this relative orbit model is combined with optimization scheme to propose a very efficient and flexible method of station keeping planning. Proper selection of objective and constraint functions for optimization can yield a variety of station keeping methods improved over the classical ones. Nonlinear simulation results have been shown to support such concept.