A satellite selection criterion incorporating the effect of elevation angle in GPS positioning

When positioning by global positioning systems, geometric dilution of precision is generally used as a satellite selection criterion. While it takes account of only geometric effects, there are other factors causing positioning error, such as ionospheric delay, tropospheric delay, and multipath. In this paper, a new criterion for satellite selection, which considers the effect of these errors, is proposed and the effectiveness of the proposed criterion is shown.     

The stability analysis of the adaptive fading extended Kalman filter using the innovation covariance

The well-known conventional Kalman filter gives the optimal solution but to do so, it requires an accurate system model and exact stochastic information. However, in a number of practical situations, the system model and the stochastic information are incomplete. The Kalman filter with incomplete information may be degraded or even diverged. To solve this problem, a new adaptive fading filter using a forgetting factor has recently been proposed by Kim and co-authors. This paper analyzes the stability of the adaptive fading extended Kalman filter (AFEKF), which is a nonlinear filter form of the adaptive fading filter. The stability analysis of the AFEKF is based on the analysis result of Reif and co-authors for the EKF. From the analysis results, this paper shows the upper bounded condition of the error covariance for the filter stability and the bounded value of the estimation error. Keywords: Adaptive Kalman filter, forgetting factor, nonlinear filter, stability analysis. Recommended by Editorial Board member Huanshui Zhang under the direction of Editor Young Il Lee. Kwang-Hoon Kim received the Ph.D. degree in the School of Electrical Engineering and Computer Science at Seoul National University in 2006. His research interests include Kalman Filtering, GNSS/INS integration system, and GNSS signal processing algorithm. Gyu-In Jee received the Ph.D. degree in Systems Engineering from Case Western Reserve University in 1989. His research interests include Indoor GPS positioning, Software GPS receiver, GPS/Galileo baseband FPGA design, and IEEE 802.16e based wireless location system. Chan-Gook Park received the Ph.D. degree in Control and Instrumenta-tion Engineering from Seoul National University in 1993. His research interests include INS/GPS integration system, inertial sensor calibration, navigation and control for micro aerial vehicles, and estimation theory. Jang-Gyu Lee received the Ph.D. degree from the University of Pittsburgh in 1977. He is currently a Professor at the School of Electrical Engineering and Computer Science at Seoul National University. His research interests include micro inertial sensors, inertial navigation systems, GPS, and filtering theory.     

Position determination using the DTV segment sync signal

As a supplement to the Global Positioning System (GPS) in an urban center and indoor environment, the digital television (DTV) segment sync signal can be employed to obtain a mobile user’s position. Two DTV receivers and a counter are integrated to measure the time difference of arrival (TDOA) for a pair of received signals from a transmitter and its corresponding repeater (DTVR). Using the measurements from a transmitter and its multiple corresponding DTVR pairs, the mobile user position can be estimated using the recursive least square method. An experiment done in Seoul using two low-grade high resolution digital television (HDTV) receivers and a two-channel universal counter demonstrates that the mean value of the mobile user position measurement is accurate to 42.58 meters circular error probability (CEP).     

Adaptive vector-tracking loop for low-quality GPS signals

Recently, several researchers have studied a vector-tracking loop to improve tracking performance for Global Positioning System receivers. The advantage of the vector-tracking loop is that noise is reduced in all of the tracking channels. In addition, the vector-tracking loop can operate successfully when the independent scalar tracking loop approach fails. However, the vector-tracking loop is vulnerable to low-quality signals because all tracking channels are dependent on each other. To solve this problem, this paper proposes an adaptive vector-tracking loop based on a linear local filter and an adaptive navigation filter. The covariance rescaling method is used to lessen the effect of low-quality signals. The proposed adaptive vector-tracking loop shows a better tracking performance compared to the conventional vector-tracking loop that is used when satellite signals are low quality.     

Spoofing Signal Generation Based on Manipulation of Code Delay and Doppler Frequency of Authentic GPS Signal

We propose an efficient spoofing signal generation method that uses the processing results of a global positioning system (GPS) receiver for authentic GPS signals. Conventional methods of generating spoofing signals use expensive GPS simulators because the structures of the spoofing signals must be almost identical to those of the GPS signals. Simulators require GPS ephemeris at a specific time and target position. Subsequently, a complicated process is used to generate navigation data using the ephemeris and model error sources such as the satellite clock bias and ionospheric delay. In contrast, the proposed method can generate spoofing signals for the desired target position without requiring GPS simulators; it does so by adjusting the signal processing results of the receiver. Using the navigation results of the receiver, such as position and velocity, the pseudorange delay and spoofing Doppler frequency between the estimated position of the receiver and the target spoofing position are obtained; these are then applied to shift the signal-tracking results of the receiver to create a new signal for the target spoofing position. Our experimental results indicate that the proposed algorithm can effectively generate spoofing signals with characteristics highly similar to those of authentic GPS signals. In addition, we confirmed that the spoofing signals generated by the proposed method are difficult to be detected using conventional spoofing detection techniques.