Reverse TDoA Asset Positioning for Low-Power Anchor Networks
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Solution Overview
Problem
Existing RTLS systems face inaccuracies due to objects on the line of sight affecting signal strength estimation and require costly, complex clock synchronization for accurate positioning, which is not feasible for battery-powered devices.
Innovation Solution
A low-power positioning system using Reverse TDoA method where anchors transmit messages and tags listen, eliminating the need for clock synchronization and reducing power consumption by duty cycling, allowing for accurate positioning calculations based on timing data from exchanged messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Two-Way Ranging (TWR) is used for positioning, then positioning accuracy is improved, but energy consumption increases due to multiple message transmissions
Solution Approach 1:
The patent implements duty-cycling where anchors periodically activate their transceivers at predetermined intervals instead of continuously operating. The serving anchor transmits ranging messages at specific periodic intervals, and participating anchors respond only during these active periods. This periodic operation maintains positioning functionality while significantly reducing energy consumption compared to continuous operation or multiple round-trip messaging schemes.
2Measurement precision
If Time Difference of Arrival (TDoA) is used for positioning, then positioning accuracy is improved, but device complexity and cost increase due to clock synchronization requirements
Solution Approach 1:
The patent extracts and removes the clock synchronization requirement from the TDoA positioning system. Instead of requiring synchronized clocks between anchors and tags, the system uses a one-way ranging approach where the serving anchor transmits messages at predetermined times and the tag measures arrival times using its own unsynchronized clock. The positioning calculation is performed using time differences relative to the serving anchor's transmission times, eliminating the need for complex synchronization infrastructure.
Solution Approach 2:
The patent inverts the traditional TDoA approach by having the tag measure arrival times of messages from multiple anchors and compare them to the known transmission times from the serving anchor, rather than having anchors measure departure times and compare to a common reference. This inversion allows the tag to perform positioning calculations using its own local clock without requiring synchronization with anchor clocks, thereby reducing system complexity while maintaining positioning accuracy.
3Measurement precision
If anchors are kept in active state for clock synchronization, then synchronization accuracy is improved, but power consumption increases making battery operation infeasible
Solution Approach 1:
The patent implements duty-cycling where anchors periodically activate their transceivers at predetermined intervals instead of continuously operating. The serving anchor transmits ranging messages at specific periodic intervals, and participating anchors respond only during these active periods. This periodic operation maintains positioning functionality while significantly reducing energy consumption compared to continuous operation or multiple round-trip messaging schemes.
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
Enables accurate positioning of assets with battery-powered devices, supporting high tag densities and reducing installation and operational costs by eliminating the need for wired power and complex synchronization.
Implementation Method 1
the distance the message has traveled through a given medium can be derived from the time of flight of a wireless message by multiplying the latter by the speed of flight through that medium
Data Source
AI summary
Described are various embodiments of a system and method for positioning an asset with a tag optimized for low-power infrastructure devices. In one embodiment, the method includes transmitting, by a serving anchor of a plurality of anchors having designated locations, during a ranging slot time period of the serving anchor, one or more anchor ranging messages. Sending, by one or more participating anchors in range of the serving anchor, each during the ranging slot time period, a return ranging message. Recording, by the serving anchor, a first timing data and by a tag positionally associated with the asset a second timing data. estimating, from said first timing data and said second timing data, either by the central entity alone or by a combination of the serving anchor and central entity, a position of the tag.