Base Station Ranging for GNSS Positioning in Obstructed Environments
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Solution Overview
Problem
GNSS receivers, such as those on small rovers like golf carts, face accuracy degradation due to signal obstructions from trees and man-made structures, as they often receive fewer than the required four satellite signals, leading to inaccurate position determination.
Innovation Solution
A fixed base station broadcasts an RF signal modulated with a pseudo-random code, synchronized with GPS time, to serve as an additional ranging signal for rovers, enhancing position determination even with fewer satellite signals, and provides information to help rovers acquire and track weak satellite signals, improving accuracy by separating height and clock errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a rover uses traditional GNSS receivers to determine position, then the system is simple and cost-effective, but position determination accuracy degrades when signal obstructions block satellite signals
Solution Approach 1:
The patent introduces a base station as an intermediary ranging transmitter that broadcasts RF signals modulated with pseudo-random codes. This base station serves as a terrestrial mediator that provides alternative ranging signals when satellite signals are blocked by trees or structures, enabling the rover to maintain position determination accuracy without requiring line-of-sight to satellites.
Solution Approach 2:
The base station performs multiple functions: it acts as a ranging transmitter providing satellite-like signals, serves as a timing reference synchronized with GPS time, and can operate in various frequency bands including unlicensed ISM bands. This multi-functionality allows a single terrestrial installation to support multiple rovers in diverse environmental conditions.
2Measurement precision
If a rover receives fewer than four satellite signals due to obstructions, then the system remains simple, but position determination becomes inaccurate
Solution Approach 1:
The base station creates artificial copies of satellite ranging signals by broadcasting RF signals modulated with pseudo-random codes that have the same chip rate and structure as GPS satellite signals. These copied signals appear to the rover as additional ranging sources, allowing it to calculate position accurately even when fewer than four actual satellite signals are available.
Solution Approach 2:
The base station signals are synchronized with GPS time, maintaining the same temporal parameters as satellite signals. The rover processes these signals using the same receiver algorithms, effectively changing the physical state of the signal source from natural satellite emission to terrestrial transmission while preserving the essential ranging parameters needed for accurate position determination.
3Measurement precision
If existing solutions use complex integrated navigation systems with Kalman filters and multiple modules, then position accuracy improves, but system complexity and cost increase
Solution Approach 1:
The patent employs a simple base station design that can be implemented using inexpensive components and unlicensed frequency bands. Rather than requiring complex integrated navigation systems with multiple sensors and sophisticated algorithms, the solution uses a straightforward RF signal transmission and reception system that provides sufficient accuracy for the application.
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 solution enhances position determination accuracy for rovers by providing a terrestrial ranging source, improving geometry and reducing errors in height and clock parameter estimation, especially useful in applications requiring precise height determination like earth excavation and road paving, while being cost-effective and easier to implement than existing systems.
Implementation Method 1
a fixed base station, which has a known position, broadcasts to the rovers an RF signal that is modulated with a pseudo-random code
Implementation Method 2
Each rover receives the ranging signal from the base station and aligns its code generator and carrier phase with that signal
Implementation Method 3
If a rover can receive useful signals from only two satellites, the base station can calculate its range to the rover by comparing the timing of its transmission with the timing of a return signal from the rover
Implementation Method 4
if the rover receives usable information from only a single satellite, a somewhat less accurate estimate of the rover's position can be obtained by ascertaining the intersection of a sphere centered on the satellite with a radius equal to the calculated range between the rover and the satellite
Data Source
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AI summary
A system, for enhancing location estimates by movable rovers that use receivers for processing ranging signals from orbiting satellites, including a fixed base station that serves as a ranging signal source for the rovers' receivers. The base station may also determine and transmit the azimuthal angles of the respective rovers. The rovers use this information, along with a calculated or transmitted ranges to the base station to calculate the ranging system times at the locations of the rovers. Further, the rovers may use the information along with signals from satellites in view to determine position.