OFDM Doppler Tracking Using CSI Without Active Target Signals
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Solution Overview
Problem
Existing methods for locating and tracking targets require the target to transmit signals or rely on active querying, necessitating precise synchronization and infrastructure, which can be intrusive and costly.
Innovation Solution
A method utilizing Doppler shifts in existing radio signals, such as Wi-Fi, to track targets without requiring the target to transmit signals, allowing for covert tracking and reducing synchronization requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the target transmits signals or active querying is used for tracking, then tracking accuracy is improved, but infrastructure complexity and cost increase
Solution Approach 1:
The target object itself serves as the signal source by reflecting existing ambient radio signals. The tracking system utilizes signals that already exist in the environment, eliminating the need for separate signal transmission infrastructure at the target. This self-service approach allows the target to be tracked passively without adding complexity to the infrastructure.
Solution Approach 2:
The system uses existing radio signals (such as Wi-Fi, broadcast signals, or other ambient electromagnetic waves) for multiple purposes: both for their original communication function and for target tracking. This multi-functionality eliminates the need for dedicated tracking infrastructure, reducing overall system complexity while maintaining tracking capability.
2Reliability
If precise synchronization infrastructure is implemented for target tracking, then tracking reliability is improved, but system cost and complexity increase
Solution Approach 1:
The patent introduces signal processing techniques (Fourier transform, channel state information analysis) as intermediaries to extract Doppler shift information from received signals. These processing methods enable reliable tracking without requiring precise hardware synchronization infrastructure, as the Doppler effect can be measured through software-based signal analysis of ambient signals.
3Measurement precision
If active signal transmission is used for tracking, then measurement precision is improved, but covert operation capability deteriorates
Solution Approach 1:
The target passively reflects existing ambient radio signals rather than actively transmitting signals. This passive reflection enables the tracking system to obtain precise Doppler shift measurements while the target remains covert, as no additional signal transmission occurs that would reveal the target's presence or location to others.
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 tracking of targets using existing signals, reducing infrastructure costs and maintaining covert operation, suitable for various settings from indoor environments to airspace.
Implementation Method 1
Tracking a target using doppler shift
Data Source
AI summary
For tracking a target, a method receives a combined signal comprising a target signal reflected by a target and a transmitter signal not reflected by the target, wherein the transmitter signal is comprised of a plurality of orthogonal frequency division multiplexing (OFDM) subcarrier signals. The method calculates a signal Fourier transform for the combined signal to obtain the complex symbols. The method estimates a sequence of channel state information. The method estimates CSI over for non-pilot OFDM subcarriers of the combined signal to obtain CSI for a sequence of M OFDM symbols. The method computes a CSI Fourier transform for the sequence of CSI for a plurality of OFDM subcarriers. The method estimates a CSI Doppler frequency by matching a Fourier transform template to the CSI Fourier transform. The method computes each of a target position and a target velocity vector for the target.