Design and Development of an Improved Sensitivity Reconfigurable GNSS Receiver for Space-based Reflectometry

Surabhi Guruprasad

Abstract: This research paper addresses the design and development of a real-time reconfigurable Global Navigation Satellite System (GNSS) receiver for space-based reflectometry. The concept of reflectometry in space using reflected GNSS signals has been demonstrated in the recent years. While significant advancement has been made in the field of GNSS-based reflectometry (GNSS-R) over water, the focus is now shifting to terrestrial applications such as sensing soil moisture, vegetation and forest biomass. Several groundbased field experiments and airborne campaigns in the past have shown the possibilities to retrieve soil moisture using reflected GNSS signals. However, from the trends observed, there is a lack of emphasis on the need for a real-time reconfigurable GNSS-R receiver for soil moisture retrieval. The main objective of this research is to develop a reconfigurable GNSS-R receiver for soil moisture retrieval using commercial-off-the-shelf (COTS) components. Two dual polarised antennas are used to collect direct and reflected GNSS signals and are processed in real-time with hardware modules implemented in a Field Programmable Gate Array (FPGA). The developed GNSS-R receiver can successfully acquire, track and decode navigation messages from direct and reflected GNSS signals. Results from the conducted tests are presented and analyzed. A need to improve acquisition sensitivity of the prototype GNSS-R receiver is also addressed. Since reflected signals have low signal strengths, acquisition sensitivity of a GNSS-R receiver is a critical performance parameter. To improve the sensitivity of the developed GNSS-R receiver, an advanced acquisition algorithm known as the alternate half-bit method is implemented in the reconfigurable hardware. Hardware implementation of the alternate half-bit method improved the receiver sensitivity by 11 dB and signals with SNR as low as -46 dB can be detected. The next steps are to conduct tests in varying environments such as various soil, topography and vegetation types to observe its impact on the reflected signals. Such tests will also help calibrate the GNSS-R receiver after which flight campaigns will be conducted.
Published in: Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019)
September 16 - 20, 2019
Hyatt Regency Miami
Miami, Florida
Pages: 3437 - 3450
Cite this article: Guruprasad, Surabhi, "Design and Development of an Improved Sensitivity Reconfigurable GNSS Receiver for Space-based Reflectometry," Proceedings of the 32nd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2019), Miami, Florida, September 2019, pp. 3437-3450.
https://doi.org/10.33012/2019.16891
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