Mobile Positioning Frequency Stabilization
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Solution Overview
Problem
Satellite-based mobile positioning systems face challenges in reliability and accuracy due to weak GPS signal reception and temperature-dependent clock frequencies, which require complex and expensive temperature-compensated crystals, and existing solutions like U.S. Pat. No. 5,841,396 are prone to errors and instability.
Innovation Solution
A mobile communication and positioning device with a first temperature-compensated frequency source and a second frequency source independent of the first, using interpolation to detect and correct frequency differences, allowing for more accurate and reliable satellite signal demodulation even with non-temperature-compensated crystals, enhancing stability and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If temperature-compensated crystals (TCXO) are used to maintain stable clock frequency, then frequency stability is improved, but device complexity and cost increase
Solution Approach 1:
The patent divides the frequency stabilization function into two independent parts: a simple crystal oscillator that provides the base frequency and a separate temperature compensation mechanism that calculates and applies corrections. This segmentation allows the main oscillator to remain simple while the compensation is handled by additional processing circuits that analyze temperature effects and adjust frequency accordingly.
Solution Approach 2:
The patent implements feedback by continuously monitoring temperature effects on the crystal oscillator and using this information to dynamically adjust the frequency. The system measures the actual frequency drift caused by temperature changes and feeds this information back to the frequency control mechanism, which then applies compensating adjustments to maintain stable operation.
2Adaptability or versatility
If frequency multiplication is performed to match GPS signal frequency, then signal demodulation capability is improved, but measurement precision requirements increase
Solution Approach 1:
The patent introduces an intermediary frequency signal that serves as a bridge between the low-frequency crystal oscillator and the high-frequency GPS signals. This intermediary signal is generated through controlled frequency multiplication while maintaining precise frequency relationships, allowing the system to handle the large frequency ratio between the crystal oscillator and GPS signals without losing measurement precision.
Solution Approach 2:
The patent performs preliminary frequency adjustment and stabilization before the actual signal demodulation process. By pre-compensating for temperature effects and establishing a stable intermediate frequency, the system prepares the frequency reference in advance, ensuring that when the GPS signals are processed, the frequency relationships are already optimized for accurate demodulation.
3Reliability
If weak GPS signals are received, then positioning capability is maintained, but signal detection difficulty increases
Solution Approach 1:
The patent creates a synthesized copy of the expected GPS signal waveform using the stabilized frequency reference. This synthesized signal serves as a template that can be correlated with the weak received signals, enhancing the ability to detect and measure GPS signals even when they are very weak. The frequency-accurate copy allows for precise correlation processing that improves signal detection sensitivity.
Data Source
AI summary
A dual mode device (110) comprising a communications block (120) and a satellite positioning block (130), each comprising respective Base Band (BB) blocks (123, 132) and crystals or frequency sources (122, 1312). The communications crystal (122) provides a cellular clock signal (FS1) to the satellite positioning block (130), which monitors the difference in the frequencies the crystals produce (FS1, FS2), using Vernier interpolation to gain a resolution greater than one clock cycle. The positioning crystal (1312) is used independent of the cellular crystal to demodulate satellite signals. The positioning BB (132) tracks the demodulated satellite signals compensating any errors caused by the positioning crystal signals (FS2) to the demodulation, using the information resulting from the monitoring. The communications crystal is capable to network based calibration and the positioning BB can compensate for the fluctuation thus caused in the cellular clock signal (FS1).