OFDM Geo-Location via Branched Preamble Correlation
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Solution Overview
Problem
Existing wireless location systems using IEEE 802.11 technology face limitations in accurately determining the geo-location of wireless devices due to restricted receive sensitivity, which affects the range and accuracy of geo-location, especially in environments with significant RF obstruction losses.
Innovation Solution
The method involves transmitting a ranging signal and receiving an OFDM response signal, with processing circuitry that determines an expected bit sequence, detects the presence of an OFDM waveform, cross-correlates received samples, and estimates the carrier frequency offset using a branched preamble detector, allowing for geo-location determination based on the time of transmission and reception of the signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional receive processing is used, then the system operates with standard complexity, but the receive sensitivity is restricted and geo-location range is limited
Solution Approach 1:
The patent segments the receive processing into multiple parallel branches, each handling a specific carrier frequency offset range. This segmentation allows the system to process signals with different frequency offsets independently, improving receive sensitivity without overwhelming the processor with a single complex operation.
Solution Approach 2:
The patent implements partial correlation by processing only a portion of the OFDM signal (the preamble portion) rather than the entire signal. This partial action approach maintains improved receive sensitivity while reducing the overall computational complexity of the correlation operation.
2Length of stationary object
If the measuring station attempts to detect weak signals with negative signal-to-noise ratios, then the geo-location range increases, but the complexity of signal detection and processing increases
Solution Approach 1:
The patent replaces traditional mechanical signal detection methods with signal processing techniques including Fast Fourier Transform (FFT) for frequency domain analysis and correlation processing. This substitution enables the detection of weak signals with negative signal-to-noise ratios by transforming the detection problem into the frequency domain where signal characteristics can be more effectively extracted.
Solution Approach 2:
The patent uses a local copy of the expected signal waveform (preamble sequence) to correlate with the received signal. This copying approach allows the receiver to compare the received signal against a known reference, enabling detection of weak signals by identifying correlations even when the received signal is buried in noise.
3Measurement precision
If multiple measuring devices are used for simultaneous TOA and TOD measurements, then the geo-location accuracy improves, but the system complexity and coordination requirements increase
Solution Approach 1:
The patent implements feedback mechanisms where each measuring device receives information about the measurements taken by other devices in the network. This feedback allows devices to coordinate their measurements and adjust their operation to achieve consistent and accurate geo-location results across the distributed system.
Solution Approach 2:
The patent designs the measuring devices to perform multiple functions: they can act as both transmitters (for TOD measurement) and receivers (for TOA measurement), and each device can process signals from multiple other devices. This multi-functionality reduces the need for specialized dedicated hardware and simplifies the overall system architecture.
Data Source
AI summary
A method and wireless device are disclosed that increase the range of active geo-location from the measuring station as compared with known solutions by increasing the effective receive sensitivity of the measuring station by transmitting a predetermined ranging packet and correlating the raw received bit stream of the response packet with one or more predetermined bit streams. In one embodiment, the disclosed method and system may be applied to the reception of IEEE 802.11 orthogonal frequency division multiplexed (OFDM) acknowledgments (ACK) and clear-to-send (CTS) packets in response to OFDM data null and OFDM request-to-send (RTS) packets respectively, in the 2.4 GHz and 5 GHz bands.