Due to manufacturing and environmental reasons, a GPS receiver's actual and manufacturer specified sampling frequency may differ significantly. Accurate knowledge of the sampling frequency is fundamental for high sensitivity and high accuracy receiver signal processing.Additionally, applications such as pre-correlation signal quality monitoring employing periodic averaging and dithered sampling techniques to enhance the signal-tonoise ratio (SNR) and sampling resolution depend on the accuracy of the sampling frequency. A refined mathematical model of software-correlator based receiver processing in the presence of clock error is established in the paper, and a novel inline method is presented to estimate the accurate sampling frequency. The method is a solely software-based technique requiring no additional hardware other than the GPS receiver RF front end output samples. Neither a priori knowledge of the specific frequency plan of the RF front end circuit nor complex receiver output data fitting are needed. The impact of the sampling frequency error on the performance of receiver signal processing and pre-correlation periodic averaging, and the performance of the frequency calibration method are evaluated using simulated signals as well as live GPS signals collected by GPS data acquisition equipments manufactured by different vendors. Several experimental measurements are presented to support the evaluation including the receiver observables and navigation solutions, as well as the pre-correlation time domain waveforms and eye patterns, Power Spectrum Density (PSD) envelopes, amplitude probability density histograms, correlation function and S-curve bias after periodic averaging. Our simulation results show that the method can calibrate the sampling frequency with an accuracy resolution down to 10 -9 of the true sampling frequency online, and the pre-correlation SNR can be potentially improved by 39dB using periodic averaging.

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Background The higher professional identity of general practitioners (GPs) helps to promote the establishment of hierarchical diagnosis and treatment in China. However, previous studies focus on the investigation of specialists. As the main provider of residents’ health services, GPs are the basis of primary health care services in China. This study aims to investigate the professional identity of GPs and its influencing factors. Methods A cross-sectional online questionnaire survey was conducted from December 2021 to January 2022, and subjects were selected by two-stage stratified random sampling. A self-administered questionnaire was used to collect data from 2,200 GPs (99.1% response rate) in Chongqing, a municipality in western China. Practicing identity was measured by the Practicing Identity Scale, psychological capital was measured by the Psychological Capital Questionnaire (PCQ-24), and patients were measured by the Perceptual Patient Slowness Questionnaire. Through the construction of a multiple linear regression model to analyze correlation, the related factors of GPs’ professional identity are discussed. Results The total score of professional identity of GPs was 65, with an average score of 53.59 (SD = 6.42). The scores of self-efficacy, hope, optimism, and resilience in psychological capital were 26.87 ± 5.70, 26.47 ± 5.74, 26.97 ± 5.55, and 26.86 ± 5.59, respectively. The score of perceived patients was 34.19 ± 7.59. Average monthly income, management responsibility, work tenure, self-efficacy, hope, resilience, and patient’s contempt are related to practice identity (P < 0.05). Conclusions GPs in Chongqing, a municipality directly under the central government in western China have high professional identity and strong psychology.