Civilian services of Global Navigation Satellite System are threatened by spoofing attacks since it is hard to determine the authenticity of a navigation signal with a detailed structure open to the public. Signal authentication effectively protects the security of the signal by attaching unforgeable information to one or several elements of the signal. Receivers can verify the authenticity of the signal by extracting and validating this information. Developing good signal authentication schemes requires understanding possible spoofing modes, signal element specialty, and performance evaluation methods. This paper is an overview of navigation signal authentication, where the theories and reported approaches are described in detail. A design/performance matrix that demonstrates the advantages and defects of the signal element and its authentication design is summarized. Recommendations are proposed to improve the robustness, security, efficiency, and implementation hardness for future designs of navigation signal authentication.

Low Earth Orbit (LEO) is of great benefit for the positioning performance of Global Navigation Satellite System (GNSS). To realize the system of LEO-augmented GNSS, three methods to integrate communication and navigation signal for LEO communication system with the least influence on the communication performance are analyzed. The analysis adopts the parameters of IRIDIUM signal as restrictions. This paper gives quantitative comparison of these methods considering CN0(carrier noise power spectral density rate) margin, pseudorange accuracy, Doppler accuracy, and communication loss. For method 1, a low-power navigation signal is added to the communication signal. For method 2, the navigation signal is launched in one or more frames. For method 3, the navigation signal is launched in the frequency band separated to the communication signal. The result shows that the pseudorange accuracy of method 2 is far below method 1 and method 3. However, the difference of Doppler accuracy among the three methods can be emitted. Detailed analysis shows that method 1 is practicable when the communication and navigation signal power rate is 15 dB. It achieves the balance of pseudorange accuracy and bit error rate (BER) performance under this condition. Comprehensive comparison of these methods is given in the last. The result shows that the CN0 margin of the navigation signal for method 3 can be 13.04 dB higher than method 1, based on the accuracy threshold considered in this paper. Methods 1 and 3 have the advantage of high accuracy and high CN0 margin respectively. However, method 3 causes high communication capacity loss. Considering that the main disadvantage of GNSS signals is low CN0, method 3 is a good choice for the LEO-augmented GNSS system. Methods 1 and 3 can be combined to realize both high accuracy and high CN0 margin if possible.

In satellite navigation system using spot beam to build inter-satellite link (ISL) for Autonomous Navigation, each satellite has less number of transceivers than its visible satellites, which poses the natural problem of how to assign these transceivers to point other satellites effectively in order to meet the both crosslink ranging and data exchange requirements of Autonomous Navigation. This paper provides a topology model applicable for both requirements. Based the topology model, this paper presents a link assignment algorithm which is designed to maximize the quantity of crosslink ranging information periodically and to improve the communication performance of inter-satellite network simultaneously. Although some communication performance loss is inevitable to perform link assignment for crosslink ranging, the simulation results show that the algorithm gives better communication performance than mesh-link link assignment which is adopted in Iridium system in up to 80 percent of each satellite period.

Spoofing interference poses a significant challenge to the Global Navigation Satellite System (GNSS). To effectively combat intermediate spoofing signals, this paper presents an enhanced spoofing detection method based on abnormal energy of the quadrature (Q) channel correlators. The detailed principle of this detection method is introduced based on the received signal model under spoofing attack. The normalization parameter used in this method was the estimation of the noise floor. The performance of the proposed Q energy detector is validated through simulations, the Texas Spoofing Test Battery dataset and field tests. The results demonstrate that the proposed detector significantly enhances detection performance compared to signal quality monitoring methods, particularly in overpowered scenarios and dynamic scenarios. By increasing the detection probability in the presence of spoofing signals and decreasing the false alarm probability in the absence of spoofing signals, the proposed detector can better meet the requirements of practical applications.

The Global Position System (GPS) satellites of Block IIR-M and later versions can turn on the signal power enhancement if needed. In recent years, this power enhancement has been triggered several times when the U.S force was involved in local conflicts, which was observed by the monitoring receivers at International GNSS Service (IGS)/international GNSS Monitoring and Assessment System (iGMAS) stations or the high-gain antennas at monitoring ground stations. The specific power enhancement magnitudes with these two observation methods are different. The observations of L1/L2 P(Y) power with a high-gain antenna are accurate, while the observations at IGS/iGMAS stations contain biases. This paper analyses the reasons for the observation biases with monitoring receivers at IGS/iGMAS stations and proposes a method verifying the accurate relation between the observed carrier-to-noise ratio (C/N₀) data and the real power enhancement magnitudes. When the power enhancement event happens, the observed L1/L2 P(Y) C/N₀ data at IGS/iGMAS stations can be corrected using the model proposed in this paper. In the analysis, this paper concludes that the power of L1P(Y) increases by about 4.3–5.3 dB and the power of L2P(Y) by about 4.6–5.2 dB in power enhancement events, which matches the designed capability of GPS satellites as well. The results are also verified by the data of high-gain antennas.

Antenna arrays with adaptive filtering can protect the integrity and functionality of global navigation satellite system (GNSS) receivers against interference. However, a major problem with existing adaptive array processing algorithms is that they cause phase distortions and introduce bias errors into the carrier phase measurement, limiting high-precision applications. In this paper, a robust phase compensation technique is proposed to reduce the phase distortion. First, a phase bias detection method is developed to trigger the phase compensation technique. Then, the phase bias is estimated using a robust estimation method and compensated for in the GNSS receiver. The proposed technique operates in real time and causes no processing delay, while requiring only a minor modification to existing GNSS receivers. This technique is applied to the power inversion adaptive antenna, and can also be extended to a wide variety of adaptive antennas. The simulation experiments verify the applicability of the proposed technique and also confirm its superiority over existing techniques.