Satellite Positioning Signal Resampling for Fast Fix Acquisition
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Solution Overview
Problem
Conventional satellite-based positioning systems face challenges in achieving efficient signal processing in weak-signal environments, particularly due to navigation data modulation and clock offset uncertainties, which limit coherent integration and increase time-to-first-fix.
Innovation Solution
The use of perfect replica PRN sequences with conjugated navigation data modulation allows for coherent integration across navigation bit boundaries, combined with resampling techniques to align sampling rates and account for Doppler shifts, enabling extended coherent integration and improved signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional correlation methods are used to identify satellite signals, then the receiver can obtain position fixes, but the time-to-first-fix is at least six seconds due to waiting for sub-frame preamble identification
Solution Approach 1:
The patent applies preliminary action by pre-processing and storing navigation data from multiple satellites before actual positioning is needed. The system accumulates navigation data continuously, so when positioning is required, the receiver can immediately correlate with pre-stored data, eliminating the need to wait for sub-frame preamble identification and reducing time-to-first-fix below six seconds
Solution Approach 2:
The patent implements beforehand cushioning by maintaining a buffer of pre-received navigation data from multiple satellites. This data cushion allows the receiver to handle signal acquisition immediately when needed, providing a time margin that reduces time-to-first-fix while maintaining reliable position fixing even in challenging signal environments
2Measurement precision
If coherent integration is extended across navigation bit boundaries to improve signal-to-noise ratio, then positioning accuracy improves in weak-signal environments, but clock offset uncertainties cause integration errors
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the integration period to match the navigation bit duration. The system identifies navigation bit boundaries in the received signal and performs coherent integration exactly within those boundaries, adapting the integration parameters to the actual signal structure. This resolves the clock offset uncertainty problem by synchronizing integration windows with the transmitted navigation data structure
Solution Approach 2:
The patent implements feedback by using the identified navigation bit boundaries to control the coherent integration process. The system continuously monitors the received signal to detect navigation bit transitions, uses this feedback to adjust integration window timing, and thereby maintains accurate integration even with receiver clock offsets. This feedback mechanism ensures integration accuracy while enabling extended coherent integration for improved positioning precision
3Reliability
If the receiver waits for subsequent preamble identification to confirm satellite signal, then false identifications are avoided, but power consumption increases and time-to-first-fix is extended
Solution Approach 1:
The patent applies preliminary action by pre-correlating received signals with stored navigation data from multiple satellites before formal signal identification is required. This preliminary correlation establishes candidate satellite signals and their characteristics in advance, so when positioning is needed, the receiver can quickly confirm signals using pre-computed correlation results rather than performing full acquisition procedures, thereby reducing both time-to-first-fix and power consumption while maintaining identification accuracy
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 significantly reduces time-to-first-fix to 200 milliseconds or less, enhancing positioning accuracy and reliability in both weak-signal and strong-signal environments by effectively removing navigation data modulation and synchronizing sampling with the satellite clock.
Implementation Method 1
The GPS receiver correlates the received chips with its C/A code copy. Note that there is a constellation of GPS satellites so it would be very inefficient to correlate for each satellite
Implementation Method 2
The TOW, ephemeris, and other data transmitted by the satellite are designated as 'navigation data.' This navigation data is transmitted using a modulation overlay of navigation bits ('nav bits') on the C/A code sequences.
Implementation Method 3
The use of perfect replica PRN sequences with conjugated navigation data modulation allows for coherent integration across navigation bit boundaries, combined with resampling techniques to align sampling rates and account for Doppler shifts
Data Source
AI summary
A satellite-based positioning system (SPS) signal processing technique re-samples a received series of PRN sequences from an SPS satellite to align them with a nominal sampling rate for a corresponding series of perfect reference PRN replica sequences.