Wi-Fi Carrier Phase Ranging for Sub-Centimeter Accuracy
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Solution Overview
Problem
Existing Wi-Fi ranging techniques, such as Fine Timing Measurement (FTM), are limited by bandwidth and signal-to-noise ratio, achieving only approximately 1-3 meters of ranging accuracy, which is insufficient for many applications requiring finer range resolution, and are adversely affected by target device movement during measurements.
Innovation Solution
Utilizing carrier phase information from Wi-Fi channel state information (CSI) to enhance round-trip time estimation through super-resolution methods, incorporating inter-subcarrier phase and absolute phase of CSI to improve range estimation accuracy, potentially achieving sub-centimeter precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Wi-Fi ranging uses traditional FTM methods, then the system is simple to implement, but the ranging accuracy is limited to 1-3 meters
Solution Approach 1:
The patent changes the measurement parameter from traditional time-based FTM to carrier phase-based measurement. By using the phase information of the Wi-Fi carrier signal, the system achieves sub-centimeter ranging accuracy (better than 1 cm) compared to the 1-3 meter accuracy of conventional FTM methods. This parameter change fundamentally improves measurement precision without requiring additional hardware infrastructure.
Solution Approach 2:
The patent replaces the mechanical timing measurement system with a signal processing-based phase measurement system. Instead of relying on timestamp exchange and time-of-flight calculations, the system uses carrier phase information from Wi-Fi CSI to determine distance, substituting a more precise electromagnetic field-based measurement approach.
2Measurement precision
If Wi-Fi ranging increases bandwidth to improve accuracy, then ranging precision improves, but the system becomes more complex and energy-consuming
Solution Approach 1:
The patent substitutes bandwidth-intensive time-based measurement with phase-based measurement that works effectively across existing Wi-Fi bandwidths. The carrier phase information is extracted from standard Wi-Fi CSI data without requiring increased transmission bandwidth, thereby avoiding the energy penalty associated with wider bandwidth operations while achieving superior ranging accuracy.
3Measurement precision
If Wi-Fi ranging uses carrier phase information, then ranging accuracy improves to less than 1 cm, but the system becomes more complex due to offset compensation requirements
Solution Approach 1:
The patent performs preliminary calibration to measure and store clock offset and carrier frequency offset parameters before actual ranging operations. By pre-characterizing these offset parameters, the system eliminates the need for complex real-time compensation calculations during ranging, reducing processing complexity while maintaining sub-centimeter accuracy.
Solution Approach 2:
The patent implements a feedback mechanism where the measured carrier phase information is used to continuously track and compensate for clock and frequency offsets. The system uses the phase measurements themselves to detect and correct drift, creating a self-correcting measurement system that maintains high accuracy without requiring external calibration references.
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
The proposed method significantly enhances ranging accuracy to less than 1 cm, independent of bandwidth, by leveraging carrier frequency precision and compensating for clock and carrier frequency offsets, suitable for various wireless communication technologies.
Implementation Method 1
obtaining Wi-Fi channel state information (CSI) parameters measured at an anchor and a target device from Wi-Fi frames transmitted between the anchor and the target device, the CSI parameters comprising, for each of the anchor and the target device, frame transmission and reception times, a carrier phase of the CSI
Implementation Method 2
compensating for clock and carrier frequency offsets, suitable for various wireless communication technologies
Data Source
AI summary
A method includes obtaining Wi-Fi channel state information (CSI) parameters measured at an anchor and a target device from Wi-Fi frames transmitted between the anchor and the target device, the CSI parameters comprising, for each of the anchor and the target device, frame transmission and reception times, a carrier phase of the CSI, a crystal offset factor, and a packet detection time error. The method also includes determining a round trip time (RTT) estimate or a relative change in the RTT estimate as a function of the CSI parameters. The method further includes estimating a range between the anchor and the target device as a function of the RTT estimate, or estimating a change in the range between the anchor and the target device as a function of the relative change in the RTT estimate.