Wireless Location Anchor Synchronization to Reduce Multipath Errors
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Solution Overview
Problem
Existing Real Time Locating Systems (RTLS) face inaccuracies in synchronization due to multipath propagation errors, especially when using wireless channels, which affect the Time Difference Of Arrival (TDOA) calculations, and require additional hardware complexity and processing load.
Innovation Solution
A method for determining an instantaneous phase difference between the time bases of location anchors using broadcast messages exchanged between anchors, eliminating the need for reference tags and minimizing multipath errors by calculating synchronization based on measured TDOA values, allowing precise distance and position determination of location tags without additional measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wireless channel is used for synchronization instead of wired connection, then installation cost and complexity are reduced, but synchronization accuracy deteriorates due to multipath propagation errors
Solution Approach 1:
The patent introduces a location server as an intermediary that processes TOA stamps from multiple location anchors to calculate synchronization corrections. The server acts as a mediator that aggregates data from multiple sources and performs complex calculations to eliminate multipath errors, enabling wireless synchronization while maintaining accuracy through centralized processing.
Solution Approach 2:
The system implements feedback mechanisms where location anchors continuously exchange TOA stamps with the location server, which then calculates synchronization corrections and feeds them back to the anchors. This closed-loop feedback process enables continuous refinement of synchronization accuracy despite the presence of multipath propagation in the wireless channel.
2Ease of operation
If reference tags are used for wireless synchronization, then synchronization can be achieved without wired connections, but device complexity and hardware requirements increase
Solution Approach 1:
The patent makes location anchors multi-functional by enabling them to both transmit and receive TOA stamps for synchronization purposes, rather than requiring separate reference tags. The same location anchors that perform location determination also participate in synchronization, reducing hardware complexity while maintaining wireless synchronization capability.
Solution Approach 2:
Instead of using dedicated reference tags, the system creates virtual reference functions by having location anchors generate and exchange TOA stamps that replicate the synchronization function. The TOA stamps serve as copies of timing information that enable synchronization without requiring physical reference tag hardware at every location.
3Measurement precision
If additional measurements are performed to correct multipath errors, then synchronization accuracy improves, but processing load and airtime increase
Solution Approach 1:
The patent performs preliminary calculations at the location server by processing TOA stamps from multiple location anchors to pre-compute synchronization corrections before they are needed for location determination. This advance processing eliminates the need for additional measurements during the actual location fixing process, improving overall system efficiency.
Solution Approach 2:
The system merges the synchronization function with the location determination function by using the same TOA stamp exchanges for both purposes. The location server combines synchronization calculations with location calculations in a unified processing approach, eliminating redundant measurements and reducing overall processing load compared to separate synchronization and location processes.
Data Source
AI summary
A method for determining an instantaneous phase difference between time bases of at least two location anchors for a desired point in time (t), each of the location anchors having transmitting and receiving access to a joint broadcast transmission medium and a respective time base for measuring time, wherein a first of the location anchors broadcasts a first broadcast message at least twice; the first location anchor and at least a second of the location anchors receive the first broadcast messages; the second location anchor broadcasting a second broadcast message at least twice; and the second location anchor and at least the first location anchor receive the second broadcast messages. The location server calculates the instantaneous phase difference from a determined first and second clock model functions and from a time elapsed between a reference point in time and the desired point in time t.