Session B5: Receiver Design, Signal Processing, and Antennas

Analysis of Doppler Frequency and Doppler Frequency Rate Characteristics for Vehicular GNSS Receivers in Urban Environments
Zhihang Qu, Yong Li, Wenhui Yang, and Daifang Huang, University of Electronics Science and Technology of China
Location: Beacon B

The rapid advancements in autonomous driving have driven extensive research on improving the accuracy and reliability of GNSS in urban environments. To enable the GNSS receiver to achieve a precise solution and robust tracking capability in such environments, the design of a suitable GNSS baseband algorithm becomes a challenge work. Such kind of algorithms should be taken into account of issues like tracking sensitivity, accuracy, and dynamic performance in the design.
It is known that the GNSS signals in urban environments exhibit the characteristics of dynamic weak signals. While existing studies have documented the weakness and considerable fluctuations of these signals, a comprehensive analysis of the dynamic features of Doppler frequency and Doppler frequency rate is still lacking. It is well known now the characteristics of Doppler frequency and Doppler frequency rate are essential for GNSS receiver design and crucial for developing effective baseband tracking strategies.
This study investigates the dynamic characteristics of GNSS signals for vehicular receivers in urban environments, employing both theoretical analysis and real-world testing. Initially, the theoretical ranges of Doppler frequency and Doppler frequency rate are computed upon the kinematics of GNSS satellites and the motion of the vehicle-mounted receiver. The analysis further considers the impact of signal obstructions and reflections, which introduce additional variations in Doppler frequency and Doppler frequency rate as the vehicle moves in urban environments.
Given the weak signal characteristics of GNSS in urban areas, the Doppler frequency and Doppler frequency rate data derived from methodologies associated with the u-blox F9P receiver may exhibit potential inaccuracies, limiting their utility as benchmarks. From the perspective of GNSS baseband signal processing, it is preferable to directly extract these dynamic parameters from the received signals. This paper proposes a time-frequency analysis method that combines partial matched filtering with the Fractional Fourier Transform (FrFT) to extract Doppler frequency and Doppler frequency rate parameters from the pilot channel of the BeiDou B1C band.
Furthermore, due to the concentration of energy at specific rotation angles in the FrFT domain, the proposed method can extract the aforementioned parameters from the received signals and achieve more accurate results compared to traditional methods. To demonstrate the method, intermediate frequency (IF) signals were collected in real-world environments using a signal collection device based on the MAX2771 commercial RF front-end. A u-blox F9P receiver was used solely for comparative reference in the experiments. The Doppler frequency was extracted directly from the F9P receiver's data packets, while the Doppler frequency rate was computed by differentiating consecutive Doppler measurements across time epochs.
In summary, this paper provides a detailed analysis of the Doppler characteristics of GNSS signals in urban environments and theoretically derives the ranges of Doppler frequency and Doppler frequency rate variation for signals received by vehicular receivers in such settings. Moreover, it introduces an innovative method for directly extracting these two dynamic parameters—Doppler frequency and Doppler frequency rate—from GNSS signals. This study provides an insight view into the dynamic behavior of GNSS signals within urban environments, filling a gap in existing research. It can potentially help for advancing the design of robust and reliable GNSS receiver acquisition and tracking strategies to deal with the challenges in urban environments.