GPS Receiver Frequency Estimation Using Temperature Sensor Hysteresis Bounds
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Solution Overview
Problem
Navigation satellite receivers face challenges in accurately acquiring GPS signals due to frequency uncertainty caused by temperature variations in crystal oscillators, which affects the precision of location determination and increases the time to first fix.
Innovation Solution
A method that uses a temperature sensor closely coupled with the crystal oscillator to estimate frequency variations, providing outer bounds of frequency drift over temperature ranges, and updates these bounds based on the oscillator's behavior, allowing for a weighted average frequency estimate to be used in the GPS receiver, thereby reducing the impact of hysteresis effects and improving initial frequency accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a crystal oscillator is used to generate the local clock signal, then the receiver can operate with simple circuitry, but frequency accuracy deteriorates due to temperature variations
Solution Approach 1:
A temperature sensor is introduced as an intermediary element to measure the temperature of the crystal oscillator. The temperature measurement is then used to calculate frequency compensation values, which adjust the local clock signal to compensate for temperature-induced frequency drift. This mediator approach allows the system to maintain frequency accuracy without changing the simple crystal oscillator circuitry.
Solution Approach 2:
The system dynamically changes the frequency parameter of the local clock signal based on temperature measurements. By calculating frequency compensation values from temperature data and applying these compensations to adjust the clock frequency, the system adapts to temperature variations and maintains accurate frequency tracking throughout the operating temperature range.
2Measurement precision
If temperature compensation is implemented, then frequency accuracy improves, but device complexity increases
Solution Approach 1:
The patent replaces complex hardware-based temperature compensation circuits with a software-based compensation algorithm. Instead of using additional analog circuits to actively compensate for temperature effects, the system uses a processor to calculate compensation values based on temperature sensor readings and applies these corrections digitally to the frequency measurements and signal processing operations.
Solution Approach 2:
The system performs self-compensation by using its own temperature sensor to monitor its operating conditions and automatically adjusting its frequency measurements and processing parameters. The receiver uses its internal temperature data to correct its own frequency errors, eliminating the need for external compensation mechanisms or complex additional hardware.
3Reliability
If the frequency search window is widened to account for frequency drift, then signal acquisition reliability improves, but acquisition time increases
Solution Approach 1:
The system performs preliminary temperature measurement and frequency compensation calculation before the signal acquisition process begins. By pre-determining the expected frequency offset based on temperature conditions, the system can set an appropriately narrow frequency search window that is centered on the expected frequency, thereby reducing the search time while maintaining reliable acquisition.
Solution Approach 2:
The frequency search window is made dynamic rather than fixed. The system adjusts the search window parameters based on real-time temperature measurements and the current operating conditions. This dynamic adjustment allows the search window to be optimized for each specific acquisition scenario, balancing reliability and acquisition time based on actual temperature-driven frequency variations.
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
This approach reduces the average time to first fix by providing a more accurate initial frequency estimate, enhancing the GPS receiver's ability to acquire signals quickly and maintain accuracy over temperature changes and aging of the oscillator.
Implementation Method 1
A temperature sensor is closely coupled with the crystal of the GPS receiver crystal oscillator or TCXO and during GPS tracking mode, when the error in the oscillator signal is known with precision, outer bounds of TCXO frequency at given temperatures are maintained.
Implementation Method 2
These crystal oscillator or TCXO output signals, even with temperature compensation, are subject to variations due to changes in temperature... The oscillator signal variation in frequency in response to temperature change is complex and not necessarily uniform.
Data Source
AI summary
A method and apparatus for estimating oscillator signal variation due to temperature and for providing an estimated frequency to a GPS receiver in order to assist the GPS receiver to acquire the signals quickly is disclosed. A temperature sensor is closely thermally coupled with the crystal oscillator in the GPS receiver and during GPS tracking mode, when the error in the oscillator signal is known with precision, outer bounds of TCXO frequency at given temperatures are maintained, which may correspond to rising and falling temperature conditions. During acquisition mode, an estimated frequency value is provided to the GPS receiver based on a determined average of these bounds. Optionally, an uncertainty factor associated with the frequency estimated may also be provided. The two bounds take into account the hysteresis effects of the oscillator signal drift due to temperature so that a more accurate initial frequency estimate can be provided to the GPS receiver, thus reducing its average time to first fix.