GNSS Code-Free Signal Processing for Deep-Fading Carrier-Phase Estimation
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Solution Overview
Problem
GNSS receivers face challenges in accurately tracking Global Navigation Satellite System signals under challenging reception conditions, particularly due to multipath and deep fading, which can lead to inaccurate position calculations and loss of signal lock.
Innovation Solution
A method and apparatus for processing GNSS signals that decouples real-time signal-tracking estimates from positioning calculations by generating code-free samples, storing a sequence of these samples, and analyzing them to estimate signal characteristics such as carrier phase, using techniques like Kalman smoothing and neural networks to improve robustness and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional phase locked loop tracking is used, then real-time signal tracking is achieved, but the carrier phase estimates are coupled to the tracking loop and cannot utilize additional information from past and future samples
Solution Approach 1:
The patent segments the carrier phase estimation process into two independent parts: real-time tracking loop estimates and post-processing estimates. The tracking loop handles real-time feedback control while the post-processing module analyzes past and future samples to generate improved carrier phase estimates. This segmentation allows each module to optimize for its specific function without interfering with the other.
Solution Approach 2:
The patent introduces code-free samples as an intermediary data structure that bridges the tracking loop and positioning calculations. These samples contain carrier information with the spreading code removed, enabling analysis of signal characteristics without the constraints of real-time tracking feedback, thus serving as a mediator between real-time tracking and post-processing estimation.
2Reliability
If receiver sensitivity is increased to detect weak LoS signals, then the likelihood of detecting LoS signal improves, but the receiver becomes more vulnerable to multipath and deep fading
Solution Approach 1:
The patent performs preliminary action by storing a sequence of code-free samples before final carrier phase estimation. This allows the system to analyze signal characteristics over an extended duration, identifying true LoS signals before they are corrupted by multipath or deep fading, and enabling the receiver to maintain robustness even when sensitivity is increased.
Solution Approach 2:
The patent implements feedback mechanisms where the post-processing module uses the analysis of past and future samples to generate improved carrier phase estimates that feed back into the positioning calculations. This feedback loop allows the system to compensate for multipath and deep fading effects by utilizing historical and predictive information about signal characteristics.
3Reliability
If deep fading occurs with rapid receiver dynamics, then signal power drops to low levels, but this increases the likelihood of cycle slips and loss of signal lock
Solution Approach 1:
The patent performs preliminary action by pre-storing sequences of code-free samples before signal processing. This allows the system to have historical data ready to analyze even when rapid dynamics cause deep fading, enabling the receiver to maintain signal lock by referencing past signal characteristics that can compensate for temporary signal power drops.
Solution Approach 2:
The patent applies beforehand cushioning by using the stored sequence of code-free samples as a buffer against deep fading and cycle slips. The analysis of these pre-stored samples provides a cushion of information that can compensate for signal power drops during rapid receiver dynamics, preventing loss of signal lock even when the receiver experiences sudden acceleration or movement.
Data Source
AI summary
A method and apparatus are provided for processing a GNSS signal received at a receiver. The method includes obtaining samples of the GNSS signal. The samples contain a carrier signal modulated by a spreading code. The method includes generating, based on the obtained samples, code-free samples. These code-free samples contain the carrier signal but the spreading code has been wiped off. The method may include storing a sequence of the code-free samples, the sequence having an associated duration. Additionally, the method comprises analysing the sequence of code-free samples to estimate one or more signal characteristics over the duration of the sequence. The signal characteristics include a carrier phase of the carrier signal.