GPS Receiver Resampling for Weak-Signal Location

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Solution Overview

Problem

Conventional GPS receivers face challenges in acquiring satellite signals in weak-signal environments such as indoors and urban canyons, leading to difficulties in determining location coordinates due to low signal-to-noise ratios and inaccurate clock offsets, which limits their performance in emerging location-based applications.

Innovation Solution

The proposed solution involves using perfect reference PRN replica sequences that account for navigation data modulation, allowing for coherent integration across navigation symbol boundaries, and resampling techniques to align sampling rates with the true time scale, effectively enhancing signal processing gain and overcoming Doppler shifts.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If conventional GPS receivers acquire satellite signals in weak-signal environments, then location coordinates can be determined, but signal-to-noise ratio is too low to provide reliable position fixes

Engineering Contradiction:

Improvelocation determination accuracyVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The system performs preliminary actions by having reference receivers collect and store satellite signal characteristics (pseudoranges, geometric facts, observation sets) in advance at known locations. This pre-collected data is stored in a database and later used to assist the target receiver in determining its location without requiring strong live satellite signals

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

A hybrid database system acts as an intermediary between satellite signals and the GPS receiver. The database stores pre-processed satellite observation data from multiple reference receivers, allowing the target receiver to determine location by comparing its measurements against this stored reference data, effectively mediating the weak signal problem

Inventive Principle:

Principle #24Intermediary (Mediator)

2Loss of time

If GPS receiver uses extended ephemeris to reduce time to first fix, then acquisition time is reduced, but signal strength in indoor and urban canyon locations remains too weak

Engineering Contradiction:

Improvetime to first fixVSAvoidsignal strength

Core Design Contradiction:

Loss of timeVSObject-affected harmful factors

Solution Approach 1:

Reference receivers perform preliminary signal acquisition and store observation sets in advance at various locations. The target receiver retrieves pre-processed data from the database, eliminating the need to acquire weak satellite signals from scratch and reducing time to first fix while compensating for weak signal conditions through pre-collected reference data

Inventive Principle:

Principle #10Preliminary action

3Reliability

If coherent integration is extended across navigation symbol boundaries, then signal processing gain is improved, but sampling rate misalignment due to Doppler shift reduces integration effectiveness

Engineering Contradiction:

Improvesignal acquisition reliabilityVSAvoidsampling rate alignment

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The system applies resampling techniques to adjust the sampling rate of received signals, compensating for Doppler-induced frequency shifts. By changing the sampling rate parameter to match the true time scale, the system enables effective coherent integration across navigation symbol boundaries, improving signal acquisition reliability in weak-signal environments

Inventive Principle:

Principle #35Parameter changes

4Adaptability or versatility

If GPS receiver operates in cold start with no prior location knowledge, then it can be used anywhere, but acquisition of navigational data takes up to 15 minutes

Engineering Contradiction:

Improveoperational flexibilityVSAvoidacquisition time

Core Design Contradiction:

Adaptability or versatilityVSLoss of time

Solution Approach 1:

Reference receivers throughout the system perform preliminary signal acquisition and store observation sets in advance. When a receiver needs location data, it retrieves pre-processed information from the database rather than acquiring all navigational data from scratch, dramatically reducing cold start time while maintaining the ability to operate anywhere with database coverage

Inventive Principle:

Principle #10Preliminary action

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 enables GPS receivers to coherently integrate a sufficient number of PRN sequences, improving signal acquisition and location determination accuracy in weak-signal environments, allowing for reliable position fixes even in challenging conditions.

Implementation Method 1

coherently integrate a sufficient number of received PRN sequences to acquire a received satellite signal in a weak-signal environment

Methodology Applied

Scientific EffectCoherent integration:

Implementation Method 2

overcoming Doppler shifts

Methodology Applied

Scientific EffectDoppler shift: Doppler Effect

Data Source

PatentUS9207329B2Method and apparatus for determining device location

Publication Date: 2015.12.08 ETHERWHERE CORP

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.