Active Geo-Location Using Additive Correlation for OFDM WLAN
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Solution Overview
Problem
Existing geo-location methods for wireless devices, particularly those using IEEE 802.11 technology, face limitations in range and accuracy due to restricted receive sensitivity and interference from RF obstructions, which affect the ability to accurately determine the location of target stations.
Innovation Solution
The method employs orthogonal frequency division multiplex (OFDM) signals and additive correlation techniques to enhance the receive sensitivity of airborne measuring stations by cross-correlating received response signals with expected samples and bits, using a branched preamble correlator to account for carrier frequency offsets, and applying a rolling sum correlation to improve signal detection and location calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional TOA/TOD measurement methods are used for geo-location, then the location can be determined, but the range and accuracy are limited due to restricted receive sensitivity and RF obstruction interference
Solution Approach 1:
The patent combines multiple correlation outputs from multiple measuring devices into a rolling sum correlation value. This merging of correlation results from different devices and multiple signals enhances the overall signal detection capability and geo-location accuracy while maintaining robustness against RF obstructions.
Solution Approach 2:
The patent employs continuous correlation processing where multiple measuring devices continuously transmit signals and process correlation outputs. The rolling sum correlation accumulates correlation values over time, providing continuous and improved geo-location measurements even in the presence of intermittent RF obstructions.
2Measurement precision
If multiple measuring devices are used to determine location through simultaneous TOA/TOD measurements, then the location calculation can be performed, but the system complexity increases
Solution Approach 1:
The patent designs the measuring devices to perform multiple functions: transmitting OFDM signals, receiving response signals, performing correlation processing, and determining both TOA and TOD. This multi-functionality allows the same device structure to handle all measurement tasks, reducing overall system complexity while maintaining high location determination accuracy.
3Length of stationary object
If the measuring device transmits packets to the target device and measures TOA of response packets, then the round trip time can be calculated, but the receive sensitivity is restricted affecting the measurement range
Solution Approach 1:
The patent uses dynamic correlation processing where the correlation threshold and integration time can be adjusted based on signal strength and environmental conditions. This dynamic adaptation allows the system to maintain high receive sensitivity across varying distances, extending the effective measurement range while ensuring reliable detection.
Solution Approach 2:
The patent performs preliminary correlation processing on individual signals before combining results. By pre-processing signals to extract correlation values and then accumulating these values, the system enhances weak signals from distant targets before final location calculation, effectively extending the measurement range.
Data Source
AI summary
A method in a wireless device (WD) is described. The method is at least for determining a geo-location of a target station using round-trip times (RTTs) of a plurality of signals transmitted by the WD and a plurality of response signals received from the target station corresponding to the plurality of signals transmitted by the WD. The method includes determining an expected response signal, and, for each transmitted signal of the plurality of signals, determining that a response signal type matches an expected response signal type, cross-correlating a set of samples of the response signal, searching for a predetermined characteristic of the expected response signal, and correlating at least a subset of bits of the set of bits of the received response signal with the set of expected bits of the expected response signal. Further, a peak rolling sum correlation and the RTTs are determined.