An FD-DEFLATE Data Compression Scheme for C/N0 Estimation in GNSS Interference Monitoring

Global Navigation Satellite System (GNSS) provides global users with high-precision positioning, navigation, and timing (PNT) service. However, due to its low signal power and public data structure, GNSS is vulnerable to threats of interference. GNSS interference can severely impact individual users, critical infrastructures, and safe-of-life applications that rely on GNSS PNT service, and a few GNSS interference incidents have occurred worldwide in the past decade, confirming the necessity of addressing this issue. Therefore, GNSS interference monitoring is crucial for ensuring GNSS-based systems’ continued performance and resilience. Analysis and monitoring of GNSS carrier-to-noise ratio C/N0 is a common method for GNSS interference monitoring. Nevertheless, monitoring GNSS interference involves processing a large amount of data, which may exceed the computing ability of local hardware. Meanwhile, authorized signals can also be utilized for monitoring GNSS interference, yet local hardware may be not accessible to authorized signals, limiting its monitoring performance. Due to local hardware burden and scenarios of authorized signals, there is a need in practical applications to transmit digital intermediate frequency signals to remote locations for GNSS interference monitoring. Effective compression algorithms are required for data compression to reduce the transmission cost and bandwidth. Existing compression methods are analyzed for GNSS data compression performance, which is not suitable for GNSS data compression due to poor compression rate or serious C/N0 loss. Based on this, an FD(Frequency Division)-DEFLATE compression scheme is proposed to achieve efficient compression performance. The proposed compression scheme transforms GNSS signals from the time domain to the frequency domain using DCT, followed by frequency division to retain crucial signal components, and compression encoder using the DEFLATE algorithm. Furthermore, hardware implementation of the FD-DEFLATE compression scheme is presented on the FPGA platform, showcasing its compression and real-time signal processing functionality. Targeting compression rate, stability of C/N0 loss, and impact of different compression parameters as evaluation metrics, the proposed compression scheme is tested with both simulation and real-world GPS L1 C/A signals. The results confirm the scheme’s effectiveness, which achieves a compression rate of approximately 9.5 and a C/N0 loss of 4.5 dBHz with real-world data. The stable C/N0 loss across different original C/N0 values further validates the scheme’s reliability for accurate signal quality assessment. Adjusting compression parameters can also control the balance between compression rate and C/N0 loss. The proposed FD-DEFLATE compression scheme offers a promising solution for efficient GNSS data compression in remote transmission of GNSS interference monitoring scenarios.