Analysis of Doppler Frequency and Doppler Frequency Rate Characteristics for Vehicular GNSS Receivers in Urban Environments

The rapid development of autonomous driving technologies has stimulated extensive research aimed at improving the accuracy and reliability of Global Navigation Satellite Systems (GNSS) in urban environments. Achieving precise positioning and reliable tracking in these complex settings poses significant challenges, necessitating the development of advanced baseband algorithms. These algorithms must address key issues such as tracking sensitivity, accuracy, and dynamic performance under the diverse and often unpredictable conditions characteristic of urban landscapes. GNSS signals in urban environments are inherently weak and subject to considerable variability. Although prior studies have highlighted the vulnerability and fluctuations of these signals, comprehensive analyses of their dynamic characteristics—particularly with regard to Doppler frequency and Doppler frequency rate—are still limited. These parameters are crucial for GNSS receiver design, as they directly impact the effectiveness of baseband tracking strategies. This study investigates the dynamic characteristics of GNSS signals encountered by vehicular receivers in urban environments, combining theoretical modeling with real-world experimentation. Doppler frequency and Doppler frequency rate are first derived theoretically, considering the kinematics of GNSS satellites and the motion of the vehicle-mounted receiver. The analysis further incorporates the effects of signal obstructions and reflections, which introduce additional variations in these parameters as the vehicle moves through urban settings. Subsequently, field tests were conducted in urban environments, and the measured values were compared with the theoretical values. Through a detailed examination of the Doppler characteristics of GNSS signals in urban environments, this study derives theoretical ranges for the variation of Doppler frequency and rate experienced by vehicular receivers. These findings fill a gap in the existing literature and provide valuable insights that are expected to guide the development of more robust and reliable GNSS tracking strategies, essential for enhancing the performance of autonomous systems in urban environments.