Carrier Phase Filtering for GNSS-R Height Precision
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current GNSS-R systems face challenges in obtaining centimeter-level height measurements due to low signal-to-noise ratio, large signal amplitude fluctuations, and frequency shifts caused by the Doppler effect, leading to cycle slips and noise in phase measurements during open-loop carrier signal tracking.
Innovation Solution
The implementation of simultaneous cycle slip and noise filtering (SCANF) using a Kalman filter, which estimates the carrier-to-noise ratio (C/N0) to correct cycle slips and noise in phase measurements, effectively mitigating errors caused by signal fading and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If open-loop carrier signal tracking is used to obtain phase measurements, then centimeter-level height measurements can be achieved, but cycle slips and noise occur due to low signal-to-noise ratio and signal amplitude fluctuations
Solution Approach 1:
The system performs preliminary action by estimating the carrier-to-noise ratio (C/N0) before phase measurement processing. This preliminary C/N0 estimation is used to predict potential cycle slips and noise occurrences, allowing the system to prepare appropriate filtering and correction measures in advance, thereby improving the reliability of phase measurements while maintaining centimeter-level precision
Solution Approach 2:
The system implements feedback by using the estimated C/N0 values to continuously adjust and refine phase measurements. The C/N0 estimation feeds back into the measurement processing chain, enabling real-time identification and correction of cycle slips and noise, thus resolving the contradiction between achieving high precision and maintaining reliability under low signal-to-noise conditions
2Measurement precision
If carrier phase measurements are used for centimeter-level height determination, then measurement precision improves, but noise and cycle slips increase due to Doppler effect and signal fading
Solution Approach 1:
The system performs preliminary C/N0 estimation to predict the impact of Doppler effect and signal fading before they corrupt the phase measurements. This advance preparation allows the system to apply appropriate filtering and correction techniques, maintaining centimeter-level precision while mitigating noise and cycle slips caused by these harmful factors
Solution Approach 2:
The system converts the harmful effect of signal fading and Doppler-induced noise into a benefit by using the C/N0 estimation to identify and correct cycle slips. The very conditions that cause measurement degradation provide information about where corrections are needed, allowing the system to improve precision by leveraging the patterns in the noise and fading
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
SCANF significantly reduces cycle slips and noise in phase measurements, enabling more accurate centimeter-level height determinations and improving the precision of remote sensing applications such as sea level and sea ice monitoring.
Implementation Method 1
The processor applies a filter to the estimated phase to produce an estimated filtered phase. The filter is adapted to filter the estimated phase using the estimated carrier-to-noise ratio to reduce cycle slips and noise in the estimated filtered phase.
Implementation Method 2
The processor applies a filter to the estimated phase to produce an estimated filtered phase. The filter is adapted to filter the estimated phase using the estimated carrier-to-noise ratio to reduce cycle slips and noise in the estimated filtered phase.
Data Source
AI summary
DLOS and reflected signal components of an RF carrier signal are received. The reflected component is reflected from a point on the surface of the earth. The DLOS and reflected components are converted to digital DLOS IF and reflected IF signals, respectively. Modeled parameters are generated using the digital DLOS IF signal and locations of one or more antennas, the transmitter, and the point. A reference signal is generated based on the modeled parameters. The reference signal is correlated with the digital reflected IF signal to produce in-phase and quadrature-phase correlation results. A C/N0 and an estimated phase (EP) are calculated for the digital reflected IF signal from the correlation results. A KF is applied to the EP to produce an estimated filter phase (EFP). The KF is adapted to filter the EP using the estimated C/N0 to reduce cycle slips and noise in the EFP.