Train Trajectory Localization Using Virtual Beacons and Correlation Delay
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Solution Overview
Problem
Existing satellite positioning systems face errors due to signal interference, atmospheric conditions, and receiver noise, which hinder accurate and reliable positioning, especially in critical applications like railway navigation, requiring additional ground infrastructure for safety integrity.
Innovation Solution
A method using correlation delay measurements between satellite signals and known virtual beacons to determine the best position, eliminating bias from received power and ensuring autonomous measurement integrity without additional sensors, by converting correlation lag into spatial bias and comparing it against a predefined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional satellite positioning systems are used, then positioning can be performed without additional infrastructure, but positioning accuracy is degraded due to signal errors from satellites, atmosphere, and receiver
Solution Approach 1:
The patent introduces virtual beacons as intermediary reference points distributed along the trajectory. These virtual beacons serve as mediators between the satellite system and the receiver, providing known reference positions that enable correlation-based positioning. The virtual beacons are calculated positions along the trajectory where correlation measurements are performed, acting as intermediate reference points that improve both accuracy and reliability without requiring physical ground infrastructure.
Solution Approach 2:
The patent creates virtual copies of beacon positions along the trajectory by calculating expected correlation values at multiple predetermined positions. Instead of using a single reference point, multiple virtual beacon positions are created computationally, each with expected correlation values. The actual correlation measurements are then compared against these virtual copies to determine the receiver's position, enabling more accurate and reliable positioning through pattern matching.
2Measurement precision
If correlation power maximization is used to identify beacon position, then positioning can be performed, but bias is introduced due to variations in received signal power
Solution Approach 1:
The patent changes the measurement parameter from correlation power (amplitude-based) to correlation lag (time-delay-based). Instead of identifying the beacon position that maximizes correlation power, the system identifies the position where the correlation lag is zero or minimal. This parameter change eliminates the bias introduced by variations in received signal power, as correlation lag is independent of signal amplitude and only depends on the time delay, which is directly related to geometric position.
Solution Approach 2:
The patent inverts the traditional correlation approach by not seeking to maximize correlation power, but rather to minimize correlation lag. The conventional approach looks for the strongest signal correlation, while this patent looks for the most temporally aligned correlation. This inversion of the optimization criterion eliminates the power-dependent bias and provides a more accurate measure of geometric position.
3Reliability
If ground infrastructure is added to improve positioning reliability, then safety integrity level can be achieved, but system complexity and cost increase
Solution Approach 1:
The patent enables the satellite positioning system to self-improve its reliability by using multiple virtual beacons along the trajectory and performing correlation measurements at each. The system uses the redundancy of multiple measurement points and the consistency checking across different virtual beacons to achieve high safety integrity levels without external ground infrastructure. The trajectory knowledge and multiple virtual reference points provide self-contained error detection and validation capabilities.
Solution Approach 2:
The patent makes the virtual beacons serve multiple functions: they provide reference positions for correlation measurements, enable position determination through pattern matching, and provide redundancy for error detection. The same set of virtual beacons along the trajectory is used for both positioning and integrity verification, eliminating the need for separate ground-based reference infrastructure and achieving multi-functionality with a single system design.
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 reduces positioning errors and ensures reliable navigation by identifying the correct beacon based on spatial bias, suitable for railway applications without additional infrastructure, providing autonomous and accurate location determination.
Implementation Method 1
a satellite receiver on board the craft being adapted to receive at a time t geopositioning signals from a satellite system
Implementation Method 2
calculation of the delay, between the geostationary signal received by the satellite receiver at time t from the satellite Sk and the theoretical geostationary signal calculated as having to be received from the satellite Sk at time t at the position of the virtual beacon Bi
Implementation Method 3
a representative value of the correlation lag X(Sk, Bj) is converted into a corresponding distance, ΔSBj,Sk, called spatial bias, by multiplying this value representing the correlation lag X(Sk, Bj) by c, the speed of light in a vacuum
Data Source
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AI summary
The invention relates to a method for locating a train (4) moving on a set of tracks (V1, V2) on which virtual beacons defined by their geographic coordinates are distributed, and equipped with an onboard satellite receiver receiving geopositioning signals from satellites S1, ...; Ss for each beacon Bj, j = 1 to N and each satellite Sk, k = 1 to s: calculation of the correlation delay, X(Sk, Bj) between the geostationary signal received by the satellite receiver from Sk and the theoretical geostationary signal calculated as having to be received from Sk in Bj; a representative value of the correlation delay X(Sk,Bj) is converted into a distance, ΔSBj,Sk by multiplying this representative value by c and dividing it by the cosine elk of the elevation of Sk; it is determined MSBBj = MAXk=1 to s{ΔSBj,Sk} the MSBBj, j= 1 to N are compared to a predefined threshold MSBREF: following this comparison, if only one beacon has a maximum spatial bias MSBBj less than MSBREF, this beacon is then detected as the one at which the train is located.