![]() A standard RDSS relies on an elevation library. Compared with other navigation satellite systems, the BeiDou system has the radio determination satellite service (RDSS) capability as well as the radio navigation satellite service (RNSS) capability. To achieve better anti-spoofing performance, more features of navigation system should be explored and utilized.įortunately, the BeiDou system has such features. ![]() The methods mentioned above have room for improvement. Techniques with additional sensors, such as multiple antennas, power measuring equipment, and inertial navigation systems (INSs) are usually robust, but the expense increases greatly when precise sensors are added. However, these methods are not practical as they require changes to the current system. Spread spectrum security code (SSSC) and navigation message authentication (NMA) can recognize spoofing signals by encrypting a civil signal. Receiver autonomous integrity monitoring (RAIM) can inspect the measurements consistency, therefore, it can exclude one or two spoofing signals, but a great number of spoofing signals will invalidate the method. They may falsely judge multipath signals as spoofing ones because multipath signals may also distort the correlation peak. Signal quality monitoring methods detect spoofing signals from correlation peak distortion. There have been many pieces of research on anti-spoofing. Spoofing mitigation ensures that a user can obtain a correct navigation solution under spoofing attacks. Spoofing detection detects a spoofing attack and determines whether the navigation solution is reliable. Anti-spoofing ability can be divided into two categories: spoofing detection and spoofing mitigation. Therefore, anti-spoofing is of great significance in modern navigation applications. Spoofing signals usually lead to erroneous time delay measurements, ultimately misleading the positioning and timing results of the user.Ĭonventional receivers usually do not consider the impact of spoofing attacks that may result in terrible consequences. On the other hand, although military signals are encrypted, a spoofing device can still spoof a military user by replaying the authentic signals and adding delays. Because the structure of civilian navigation signal is open to the public, a spoofing device can easily generate signals that can suppress authentic signals, thus, misleading a victim receiver to track spoofing signals. Spoofing attacks are key issue in navigation security. Meanwhile, the Seni-SH-LSTM model takes about 2 h per day to forecast.With the development of the global navigation satellite system (GNSS), satellite navigation security issues have become increasingly significant. For the multi-day global ionospheric TEC prediction, Semi-SH-LSTM model can improve the RMS of residual by 10.5% and 8.5%, and the residual proportion less than 1 TECU by 3.9% and 3.2% respectively. Experimental results indicate that compared with the Semi-SH and combined Semi-SH and AR models, the RMS of prediction residual of the single-day global ionospheric TEC based on Semi-SH-LSTM model is improved by 12.6% and 13.1%, respectively, and the corresponding proportion of residual less than 1 TECU is improved by 4.9% and 4.6% respectively. The spherical harmonic function coefficient products of the Center for Orbit Determination in Europe (CODE) are performed in this study, and the validity of the Semi-SH-LSTM model is verified by using two experimental schemes as single- and multi-day prediction. It uses quadratic polynomial and semiparametric kernel estimation methods to fit the trend and periodic terms of SH coefficients and finally uses LSTM in compensation prediction for the fitting residuals. However, the estimation of window width parameter in the Semi-SH model can bring some estimation bias, this study takes the advantage of the favorable adaptability of Long-Short Term Memory Networks (LSTM) in non-stationary time series forecasting, and proposes a global ionospheric total electron content (TEC) short-term forecast model by combing Semi-SH and LSTM models, referred to as Semi-SH-LSTM model, which is suitable for short-term forecast of 1-5 days.This model calculates the global ionospheric TEC through predicting spherical harmonic (SH) coefficients. Semiparametric Spherical Harmonic (Semi-SH) model can reduce the ionospheric forecast model errors and the systematic errors caused by residual period.
0 Comments
Leave a Reply. |