Steve Taylor

A USRP-based GNSS and interference signal generator and playback system

This paper presents a low cost, portable, and flexible GNSS signal and interference signal generator based on a general purpose software radio front end, the Universal Serial Radio Peripheral (USRP) family of devices. We paired a USRP-N210 mother board with appropriate RFX daughter boards to generate all GNSS signals controlled by a personal computer. The source of the signal can be pre-recorded digital samples obtained from specific RF front end or arbitrary samples generated using MATLAB programs. An adjustable low noise signal amplifier mounted between the USRP output and the transmitting antenna was used to control the transmitted power of the signal. A spectrum analyzer was used to directly monitor the transmitted signal. The NovAtel receiver was used to verify the performance of this signal generator and playback system. The received GNSS data after transmitting via USRP-N210 and the original GNSS data before transmitting are processed by NovAtel receiver and software receiver programs respectively for performance evaluation purposes. Some comparisons had been done to demonstrate the accuracy of the playback system.

Comparative studies of high-latitude and equatorial ionospheric scintillation characteristics of GPS signals

The ionospheric scintillation phenomenon that affect the accuracy and integrity of Global Navigation Satellite System (GNSS) is mostly observed in high-latitude and equatorial regions. Scintillation events in these two regions, however, are usually influenced by different factors and thus have different characteristics. This paper makes use of real scintillation data collected at Gakona, Alaska, and Jicamarca, Peru during the current solar maximum to investigate and compare scintillation features observed at the two locations. Based on scintillation events extracted from the raw data, several statistical distributions have been established to characterize the intensity, duration and occurrence frequency of amplitude and phase scintillation. Results confirm that scintillation at low latitudes is generally more intense and longer lasting, while high-latitude scintillation is usually dominated by phase fluctuations and shorter events. The occurrence frequency of scintillation, on the other hand, are influenced by a variety of factors.

Multi-constellation and multi-frequency GNSS studies of ionospheric scintillation

Summary form only given. The recent proliferation of multi-constellation Global Navigation Satellite Systems (GNSS) is offering a great opportunity for ionosphere scintillation studies. Since 2009, our research team has established permanent and temporary portable ionosphere scintillation monitoring and data collection systems in Alaska, Ascension Island, Hong Kong, Peru, and Singapore to collect multi-constellation multi-frequency GNSS scintillation data. Raw wideband IF samples were recorded during scintillation events at these locations. Advanced GNSS receiver signal processing algorithms have been developed and applied to post-process these data with the objective to preserve GNSS signal parameters in their distorted state due to scintillation. Quantitative analysis of the impact of conventional GNSS receiver signal processing on the scintillation signal parameters will be presented, followed by approaches to correct receiver processing effect to reveal the true state of signals experiencing scintillation. ScinThe recent proliferation of multi-constellation Global Navigation Satellite Systems (GNSS) is offering a great opportunity for ionosphere scintillation studies. Since 2009, our research team has established permanent and temporary portable ionosphere scintillation monitoring and data collection systems in Alaska, Ascension Island, Hong Kong, Peru, and Singapore to collect multi-constellation multi-frequency GNSS scintillation data. Raw wideband IF samples were recorded during scintillation events at these locations. Advanced GNSS receiver signal processing algorithms have been developed and applied to post-process these data with the objective to preserve GNSS signal parameters in their distorted state due to scintillation. Quantitative analysis of the impact of conventional GNSS receiver signal processing on the scintillation signal parameters will be presented, followed by approaches to correct receiver processing effect to reveal the true state of signals experiencing scintillation. Scintillation signals parameters obtained using these approaches for GPS, Beidou, Galileo, and GLONASS from the locations listed above will be presented to highlight the differences between high latitude and equatorial regions.tillation signals parameters obtained using these approaches for GPS, Beidou, Galileo, and GLONASS from the locations listed above will be presented to highlight the differences between high latitude and equatorial regions.

L band ionosphere scintillation impact on GNSS receivers

Ionosphere scintillation is a natural interference encountered by RF signals propagating through the ionosphere. It can affect the performance of Global Navigation Satellite Systems (GNSS) signals and receivers. Since 2009, our research team has established several ionosphere scintillation monitoring and data collection system in Alaska, Singapore, and Hong Kong to collect both naturally occurring and artificially controlled L band scintillation data. As we enter the current solar maximum period, these data has provided us with a good opportunity to obtain statistical impact of high-latitude and equatorial scintillations on GNSS receivers.This paper presents the analysis results based on measurements obtained from a GNSS array in HAARP, AK and commercial receiver measurements from Singapore and Hong Kong. For the HAARP, AK setup, scintillation event triggers have been implemented to initialize RF front ends data recording systems during strong scintillations. A conservative event filter was created to allow us to extract all scintillation events with amplitude scintillation index S4 greater than 0.12 and phase standard deviation sigma phi greater than 6 degrees [3]. The low filter cutoff values are set to automatically flag both strong and weak scintillation events for further analysis. We are interested in both strong and weak scintillation because strong scintillation events have major impact on robustness of GNSS receiver operation, while the weak events are good indicators of ionosphere irregularities occurrence and plasma drift.