In this paper a low power Spreading Code Authentication (SCA) sequence with a BPSK(1) modulation at a frequency offset of +7.161 MHz is tested for authentication purposes, the Galileo E1OS is used as base signal. The tested signals comprise a Galileo constellation with 5 satellites including the Galileo OS Navigation Message Authentication (OSNMA) and a low power offset BPSK (OBPSK(7,1)) as SCA component. The signals are generated with the software based MuSNAT-Signal-Generator. The generated signals were transmitted Over-The-Air (OTA) using a Software-Defined-Radio (SDR) as pseudolite. With a real-environment-testbed the performance of the SCA in real channel conditions (fading and multipath) was tested. A new SCA evaluation scheme is proposed and was implemented. Under real channel conditions we derive experimental threshold values for the new SCA evaluation scheme which allow a robust authentication. A Security Code Estimation and Replay (SCER) spoofing attack was mimicked on the real-environment-testbed and analyzed with the SCA evaluation scheme. It was shown that the usage of an OBPSK is feasible as an authentication method and can be used in combination with the OSNMA to improve the authentication robustness against Security SCER attacks.

For the purpose of development of anti-jamming GPS receiver we have developed an anti-jamming algorithm and its Simulink implementation model. The algorithm used here is a form of Space-Time Adaptive Processing (STAP) filter which is well known as an effective way to remove wideband jamming signals. We have chosen Minimum Variance Distortionless Response (MVDR) block-adaptive beamforming algorithm for our development since it can provide relatively fast convergence speed to reach optimal weights, stable and high suppression capability on various types of jamming signals. We will show modeling results for this MVDR type adaptive beamformer and some simulation results. We also show the integrity of the demodulated satellite signals and the accuracy of resulting navigation solutions after anti-jamming operation.

The antenna arrays are known to be effective for GPS anti-jamming and the performance can be improved further if a dual-polarized antenna array is used. However, when the Minimum Variance Distortionless Response (MVDR) beamformer is used as a signal processing algorithm for the dual-polarized antenna array, the anti-jamming performance can degrade in the presence of errors in the steering vector that is a key factor of the MVDR beamformer. Therefore, in this paper, the effect of the steering vector error on the anti-jamming performance of the dual-polarized antenna array is analyzed by simulations and the result is compared to that of the single-polarized antenna array.

For a wireless communication system, the angle-of-arrival (AOA) of the signal has a variety of applications. The signal AOA is estimated utilizing various antenna array structure such as Uniform Linear Array (ULA), Uniform Rectangular Array (URA), and Uniform Circular Array (UCA). In this paper, we introduce a cascade AOA estimation algorithm based on the UCA, which is consisted of CAPON and Beamspace MUSIC. CAPON is employed to estimate approximate AOA groups including multiple AOA signals and Beamspace MUSIC is employed to estimate detailed signal AOAs in the estimated AOA groups. In addition, we provide the computer simulation results for verifying and analyzing the performance of the cascade AOA estimator based on UCA.

KRS which is subsystem of Korea Augmentation Satellite System (KASS) performs a role of collecting and monitoring GPS signals. In order to generate the accurate correction message, the site which meets the requirements should be selected and verification to meet each requirement should be accompanied. When the sites are selected, the environmental considerations are EMI, clear horizon (CH) and multipath. Of these, EMI and CH can be checked for satisfaction by instrumentation, but multipath error is difficult to predict. Therefore, multipath error analysis for the installation position of actual antenna at each KRS site should be preceded, and multipath scenario should be generated for each location to analyze the effects of the resulting system performance. In this paper, based on satellite signals collected from each KRS sites, the method for analyzing multipath error in each KRS sites is described, and the multipath error is analyzed. Also to perform an analysis of the effects on system performance due to multipath error, multipath error modeling is performed for the generation of simulation scenarios.

We determined Global Positioning System (GPS) satellite visibilities in signal-blockage simulations and then analyzed Position Dilution of Precision (PDOP) fluctuations obtained from those simulated satellite geometries. PDOP values under harsh signal-blockage simulation conditions become very high compared to those calculated with real observations. Especially when the number of observed satellites is four, which is the minimum requirement for GPS positioning, PDOP values instantaneously reached several hundreds or even several tens of thousands. It was also found that the volume of the tetrahedron composed with four satellites decreases significantly. When the correlation of the tetrahedron volume and PDOP was analyzed, we reached the following conclusions: PDOP values less than 4 can be acquired when the volume is larger than 103.2 × 10¹⁹ ㎥, and PDOP values increase beyond 50 when the volume is less than 6.0 × 10¹⁹ ㎥.

Prediction of clock behaviors is necessary to generate very high stable system time which is essential for a satellite navigation system. For the purpose, we applied the Auto-Regressive Integrated Moving Average (ARIMA) model to the prediction of two hydrogen masers' behaviors with respect to the rapid Coordinated Universal Time (UTCr). Using the packaged programming language R, we made an analysis and prediction of time series data of [UTCr - clocks]. The maximum variation width of the residuals which were obtained by the difference between the predicted and measured values, was 6.2 ns for 106 days. This variation width was just one-sixth of [UTCr-UTC (KRIS)] published by the BIPM for the same period. Since the two hydrogen masers were found to be strongly correlated, we applied the Vector Auto-Regressive Moving Average (VARMA) model for more accurate prediction. The result showed that the prediction accuarcy was improved by two times for one hydrogen maser.

Since GNSS is easily affected by jamming and/or spoofing, alternative navigation systems can be operated as backup system to prepare for outage of GNSS. Alternative navigation systems are being researched over the world, and a multi-radio integrated navigation system using alternative navigation systems such as KNSS, eLoran, Loran-C, DME, VOR has been researched in Korea. Least Square or Kalman filter can be used to estimate navigation parameters in the navigation system. A large number of measurements of the Kalman filter may lead to heavy computational load. The decentralized Kalman filter and the federated Kalman filter were proposed to handle this problem. In this paper, the decentralized Kalman filter and the federated Kalman filter are designed for the multi-radio integrated navigation system and the performance evaluation result are presented. The decentralized Kalman filter and the federated Kalman filter consists of local filters and a master filter. The navigation parameter is estimated by local filters and master filter compensates navigation parameter from the local filters. Characteristics of three Kalman filters for a linear system and nonlinear system are investigated, and the performance evaluation results of the three Kalman filters for multi-radio integrated navigation system are compared.

In this paper, the symmetric position drift of the integration approach in pedestrian dead reckoning (PDR) system with dual foot-mounted IMU is analyzed. The PDR system that uses the inertial sensor attached to the shoe is called the IA-based PDR system. Since this system is designed based on the inertial navigation system (INS), it has the same characteristics as the error of the INS, then zero-velocity update (ZUPT) is used to correct this error. However, an error that cannot be compensated perfectly by ZUPT exists, and the trend of the position error is the symmetric direction along the side of the shoe(left, right foot) with the IMU attached. The symmetric position error along the side of the shoe gradually increases with walking. In this paper, we analyze the causes of symmetric position drift and show the results. It suggests the possibility of factors other than the error factors that are generally considered in the PDR system based on the integration approach.

In this paper, Zero velocity UPdaTe (ZUPT) is implemented on the navigation system of Remotely Piloted Aircraft for GNSS denied environment. RPA's navigation system suffers from lack or loss of satellite signal while maintenance or ground test inside a hangar. Although some of the hangars install GPS repeaters for indoor tests, the anti-jamming equipment with array antenna blocks the repeater signal regarding them as hostile jamming signal. With ZUPT, an aircraft navigation system can be tested free from the divergence of navigation solution without line-of-sight satellites. The designed ZUPT aided centralized Kalman Filter is implemented on the Embedded GPS&INS and simulated with Captive Flight Test data. The simulation result shows stable navigation solution without GNSS updates.

In this paper, we analyze the delay phenomenon that can occur when controlling an unmanned aerial vehicle using a camera and describe a solution to solve the phenomenon. The group of pictures (GOP) value is changed in order to reduce the delay according to the frame data size that can occur in the moving image data transmission. The appropriate GOP values were determined through experimental data accumulation and validated through camera self-test, system integration laboratory (SIL) verification test and system integration test.

In this paper, design measure were proposed for the construction of terminal systems for airborne platforms, which are key element in the Joint Tactical Data Link System (JTDLS) complete system. The Korean perfect tactical data link (JTDLS) is a communication system to establish an independent tactical data link network and needs to develop a MIDS-LVT (Link-16) communication terminal for datalink. Once a Ground/Navy JTDLS terminal system is established around airborne platform, it will be possible to break away from reliance on NATO-based tactical data link joint operations and establish independent Korean surveillance reconnaissance real-time data sharing and tactical data link operations concepts. in this paper, the essential development elements of airborne platform mounting and operable JTDLS terminals are presented, and the concept of system design is proposed to embody them. Further, improved system performance was analyzed by applying the concepts of complex relative navigation system and Advanced TDMA protocol for the deployment of airborne tactical datalink networks.