GPS Receiver Time-to-First-Fix Reduction via Counter-Based Bit Boundary Calculation
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Solution Overview
Problem
Conventional GPS receivers face a long time-to-first-fix (TTFF) when re-powered after being off, as they need to perform a lengthy bit synchronization process to determine navigation data bit boundaries due to inaccurate local time from the real-time clock.
Innovation Solution
A GPS system with a clock module providing counter values at multiple time points, allowing a system module to calculate an estimated time value based on these counter values, enabling rapid re-acquisition of GPS signals without the need for conventional synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional GPS receiver uses a real-time clock (RTC) to provide local time after being powered off, then the receiver can maintain time information, but the local time from the RTC is not accurate enough to determine the boundary of navigation data bit, requiring a lengthy bit synchronization process
Solution Approach 1:
The system performs preliminary actions by continuously counting clock cycles during the powered-off state using a simple counter driven by a low-cost crystal oscillator. When re-powered, this pre-collected counter data is immediately used to calculate the bit boundary without requiring the lengthy conventional synchronization process, thus resolving the contradiction between maintaining time information and avoiding long TTFF.
Solution Approach 2:
The invention replaces the expensive battery-powered real-time clock with a simple counter driven by a low-cost crystal oscillator. The counter uses minimal power and can be easily re-initialized, providing adequate time-tracking functionality for the specific purpose of determining bit boundaries without the complexity and power requirements of a full RTC system.
2Measurement precision
If the GPS receiver performs the conventional bit synchronization process to determine the boundary of navigation data bit, then accurate bit boundary detection is achieved, but the process takes a relatively long time
Solution Approach 1:
The invention substitutes the mechanical/search-based conventional bit synchronization process with a calculated approach. Instead of performing lengthy signal processing and correlation operations to search for bit boundaries, the system uses a mathematical calculation based on the counter value and stored parameters to directly determine the bit boundary position, achieving both accuracy and speed.
Solution Approach 2:
The system uses its own internal counter and stored parameters from previous operations to self-determine the bit boundary without requiring external synchronization signals or lengthy processing. The receiver serves itself by using its pre-collected timing data to rapidly re-acquire the signal after power cycling.
3Reliability
If a battery-powered clock module is used to maintain accurate time during power-off periods, then time accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The invention replaces the expensive, complex, and power-hungry battery-powered clock module with a simple counter driven by a low-cost crystal oscillator. This simplified approach provides adequate time-tracking functionality for determining bit boundaries without the complexity and ongoing power requirements of a full real-time clock system.
Solution Approach 2:
The simple counter serves multiple functions: it tracks time during power-off periods, provides timing reference for bit boundary calculation, and can be easily re-initialized. This multi-functional use of a simple component replaces the need for a dedicated, complex clock module.
Data Source
AI summary
A global positioning system (GPS) system includes a clock module for providing multiple counter values at multiple time points. The GPS system also includes a system module coupled to the clock module. The system module is capable of obtaining a time value for each time point according to a set of signals from a signal source. The system module is further capable of calculating a set of parameters based on the counter values and the time value for each time point, and determining an estimated time value based on the parameters and a present counter value from the clock module.