A Public, High-fidelity GNSS Signal Catalog
Emily Batista University of New South Wales (UNSW), Australia; Chris Phillips, Jamie Stevens, CSIRO Australia; Craig Benson UNSW, Australia
In recent times both the number of Global Navigation Satellite Systems, and the range of signals each delivers has increased dramatically. Global or regional navigation satellite systems include the original GPS and Glonass, plus the newer Galileo, Beidou and IRNSS systems. Furthermore augmentation systems such as WAAS, EGNOS, MSAS and more recently QZSS have enhanced the performance of GNSSs through a range of signals that are sometimes unique. These new signals are also based on different spreading waveforms compared to the conventional Direct Sequence Spread Spectrum signals used in GPS. A key feature is the increasing prevalence of Binary Offset Coding (BOC). The implications of BOC are still the topic of active research, both to mitigate problems and to exploit opportunities.
High fidelity observations of GNSS signals can be made by large dishes such as those used for radio astronomy. The large antenna gathers a strong signal, and those same dishes have very low noise receivers, providing a very good signal-to-noise ratio on signals that would otherwise be buried well under the noise floor. Furthermore those large dishes have high quality heterodynes, digitisers and clocks. These high fidelity observations are then typically recorded for later analysis and distribution. Such later, off-line analysis and processing is ideal for research purposes since the exactly the same signal can be processed many times to provide a fair comparison between processing techniques.
The benefits of high fidelity signal observations include intuitive study of the signal for instruction and education and the ability to clearly observe subtle effects in the received signal structure, such as between sidebands in BOC signals due to the dispersive propagation delay. Furthermore experimental processing techniques can be rapidly developed and debugged because the signal and partially processed results can be clearly observed due to the high signal to noise ratio.
Although high fidelity recordings have been used in previous studies, the data is generally not publically available. There are however several benefits inherent in a common and public signal catalog of high fidelity recordings. These include simplified verification of published works that are based on such a library, easier and more reliable comparison between published works, eliminating variations due to use of different signal recordings, access to GNSS signals for researchers lacking in infrastructure and financial resources.
The body of this work details the parameters of and public access to a library of high fidelity GNSS recordings, including GPS, Beidou, Galileo, QZSS. The recordings comprise of both 8-bit recordings of 16MHz bandwidth and 2-bit recordings of 64MHz bandwidth. This is followed by illustrative analysis in both the frequency and time domains to both confirm the signal fidelity and to highlight the educational benefit for students of GNSS.
The initial, publically available catalog comprises 97 minutes of very high SNR recordings taken simultaneously in both the 8-bit 16MHz bandwidth and 2-bit 64MHz bandwidth formats. There are 29 minutes of Beidou recordings covering the full range of Beidou downlink signals, 22 minutes of GPS spanning L1, L2 and L5 from a GPS Block IIF satellite, 15 minutes recorded from Galileo and 31 minutes of QZSS including the experimental and unique LEX signal. In addition tools to load the file formats in Matlab are described and included in the catalog.