GNSS Receiver Micro-Jump Detection and Correction
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Solution Overview
Problem
Global navigation satellite systems (GNSS) face disruptions due to temperature-induced frequency jumps in quartz oscillators, which can cause temporary loss of satellite tracking, especially in ultra-tightly-coupled modes of operation with Inertial Navigation Systems (INS)/GNSS, where the system is more susceptible to micro-jumps.
Innovation Solution
A navigation system with a micro jump detection and correction module that monitors carrier to noise density (C/N0) ratios to detect abrupt decreases, adjusts carrier numerically controlled oscillator (NCO) commands to search for frequency shifts across signal tracking channels, and sends corrections to a GNSS/inertial Kalman filter to maintain tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system operates in ultra-tightly-coupled (UTC) mode with narrower tracking bandwidth to achieve enhanced anti-jam performance and better tracking during high dynamic operation, then anti-jam performance and high dynamic tracking are improved, but susceptibility to quartz crystal micro-jumps increases
Solution Approach 1:
The system performs preliminary detection of micro-jump events by monitoring C/N0 ratios before they cause tracking loss. When a micro-jump is detected (abrupt decrease in C/N0), the system proactively searches for frequency shifts and adjusts carrier NCO commands in advance, preventing tracking channel release and maintaining continuous tracking in UTC mode
Solution Approach 2:
The system implements continuous feedback monitoring of C/N0 ratios across all signal tracking channels. When micro-jump events are detected through this feedback mechanism, the system automatically adjusts carrier NCO commands and searches for frequency shifts, creating a closed-loop control system that maintains tracking robustness despite the narrow bandwidth inherent in UTC operation
2Stability of the object's composition
If the system uses temperature compensated quartz oscillators that are prescreened over temperature to reject oscillators with frequency jumps larger than maximum limits, then frequency stability is improved, but the system remains vulnerable to severe micro-jumps that exceed screening thresholds
Solution Approach 1:
The system performs preliminary detection of micro-jump events by monitoring C/N0 ratios before they cause tracking loss. When a micro-jump is detected (abrupt decrease in C/N0), the system proactively searches for frequency shifts and adjusts carrier NCO commands in advance, preventing tracking channel release and maintaining continuous tracking even when oscillators exceed prescreening thresholds
Solution Approach 2:
The system prepares compensation mechanisms in advance by continuously monitoring C/N0 ratios and having the carrier NCO command offsets module ready to search for frequency shifts. This beforehand cushioning allows the system to quickly respond to micro-jumps that exceed oscillator prescreening limits, cushioning against tracking loss before it occurs
Data Source
AI summary
A navigation system comprises a GNSS receiver that receives GNSS signals on multiple tracking channels, an INS that generates inertial data, and a processor. A micro jump detection and correction module comprises an oscillator micro jump detector that monitors estimates of C/N0 in all tracking channels, and detects a micro-jump event when there is an abrupt decrease of C/N0 in all tracking channels. An offsets module defines a plurality of carrier NCO command offsets to search over signal Dopplers in all available tracking channels after the micro jump event is detected, and sends the carrier NCO command offsets to the GNSS receiver to be added to nominal carrier NCO commands. The micro jump detector selects a tracking channel with the highest C/N0 after carrier NCO command offsets are added to nominal carrier NCO commands, computes corrections for clock error estimates, and sends the corrections for the clock error estimates to a GNSS/inertial Kalman filter.