Abstract
Global navigation satellite system reflectometry (GNSS-R) has considerable potential for monitoring sea surface height with high spatiotemporal resolution at low cost. However, because of the immaturity of reflected signal processing, no commercial GNSS-R receiver can provide reliable altimetry measurements. Typically, raw intermediate-frequency data are collected and processed using a software-defined receiver (SDR), which allows full access for signal processing and testing innovative algorithms. Since high-precision code-ranging measurements from open-loop tracking are needed for GNSS-R altimetry, the sampling rate of raw IF data is usually several times that of conventional data used for navigation and positioning. Therefore, the increased data load makes processing very slow when using a computer with only a conventional central processing unit (CPU). To overcome such inefficiency, a graphics processing unit (GPU) was utilized in this study to design the GNSS-R altimetry SDR. As GPU can provide massive parallel computing performance, the correlators were implemented on it, while some procedures with low computational requirements were still implemented on the CPU. The performance of the developed SDR was evaluated by processing GNSS-R raw IF data highly sampled at 62 MHz from a coastal experiment, which has a central frequency of 1176.45 MHz. Then, code-level altimetry solutions were retrieved from BeiDou navigation satellite system (BDS) B2a and quasi-zenith satellite system (QZSS)/global positioning system (GPS) L5 signals. To optimize the SDR, different integration times and error control methods were tested. Results showed that centimeter-level GNSS-R code altimetry solutions can be achieved using QZSS geostationary orbit satellite signals in the case of real-time operation.
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Data availability
The datasets analyzed in this study are managed by the Institute of Space Science, Shandong University and can be made available by the corresponding author on request.
Abbreviations
- BDS:
-
BeiDou Navigation Satellite System
- BDS-3:
-
BeiDou global navigation satellite system
- NCIT:
-
Coherent Integration Time
- CPU:
-
Conventional central processing unit
- CUDA:
-
Compute Unified Device Architecture
- FFT:
-
Fast Fourier Transform
- GEO:
-
Geostationary Orbit
- GNSS:
-
Global Navigation Satellite System
- GNSS-R:
-
Global Navigation Satellite System Reflectometry
- GPS:
-
Global Positioning System
- GPU:
-
Graphics Processing Unit
- IF:
-
Intermediate Frequency
- IFFT:
-
Inverse Fast Fourier Transform
- IGSO:
-
Inclined Geosynchronous Satellite Orbit
- MA:
-
Moving Average
- QZSS:
-
Quasi-Zenith Satellite System
- SDR:
-
Software-Defined Receiver
- SNR:
-
Signal-to-Noise Ratio
- SSH:
-
Sea Surface Height
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Acknowledgments
This study is financially supported by the Key Research and Development Program of Shandong Province (Major Technological Innovation Project, 2021ZDSYS01), the National Natural Science Foundation of China (42192534, 41604003 and 41704017). We thank James Buxton MSc, from Liwen Bianji (Edanz) (www.liwenbianji.cn/), for editing the English text of a draft of this manuscript.
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XM, TX, and FG contributed to the conception of the study. XM, TX, FG and YH discussed and proposed the research methodology. FG, YH, XM, BN, and NW performed the experiment and collected the data. XM designed the SDR and verified the results. XM wrote the main manuscript text. All authors reviewed the manuscript.
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Meng, X., Gao, F., Xu, T. et al. Design of real-time GNSS-R software-defined receiver for coastal altimetry using GPS/BDS/QZSS signals. GPS Solut 28, 20 (2024). https://doi.org/10.1007/s10291-023-01563-w
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DOI: https://doi.org/10.1007/s10291-023-01563-w