OFDM Geo-Location Using Time Domain Cross-Correlation
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Solution Overview
Problem
Current geo-location methods for wireless devices using IEEE 802.11 technology face limitations in range and accuracy due to restricted receive sensitivity of airborne measuring stations, particularly in environments with obstructions, which restricts the effective detection and location of target stations.
Innovation Solution
A method and system that enhance the geo-location of wireless devices by determining round-trip times (RTTs) of signals transmitted to and received from target stations, utilizing orthogonal frequency diversity modulation (OFDM) signals, and employing cross-correlation techniques with frequency shifting and rolling sums to improve receive sensitivity and accuracy, even in obstructed environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional 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 of airborne measuring stations
Solution Approach 1:
The patent applies preliminary action by pre-processing the received signal through correlation with expected time-domain symbols before final measurement. The measuring station correlates the received response signal with expected symbols of the acknowledgment packet, which enhances the detectability of weak signals and improves receive sensitivity, thereby resolving the contradiction between measurement precision and reliability
Solution Approach 2:
The patent replaces conventional signal detection methods with correlation-based detection in the time domain. Instead of relying on traditional threshold-based detection that is limited by receiver sensitivity, the system uses correlation with expected time-domain symbols to detect and measure the time of arrival, significantly improving both accuracy and effective detection range
2Measurement precision
If multiple measuring devices are used to determine location through simultaneous measurements, then location accuracy improves, but system complexity increases
Solution Approach 1:
The patent uses copying by creating expected time-domain symbol sequences that represent the anticipated acknowledgment packet structure. These expected symbols serve as reference copies that are correlated with the received signal, enabling accurate time-of-arrival measurement without requiring multiple complex measuring devices, thus improving location accuracy while maintaining system simplicity
Data Source
AI summary
A method in a wireless device (WD) is described. The method is performed for determining a geo-location of a target station using round-trip times (RTTs) of a plurality of signals transmitted by the WD to the target station and a plurality of response signals received from the target station. The method includes determining expected time domain symbols of an expected response signal, and, for each transmitted signal of the plurality of signals, determining a first time, opening a reception window for receiving a response signal, receiving the response signal within the reception window, frequency shifting the expected time domain symbols, and cross-correlating the time domain symbols with the frequency shifted expected time domain symbols. In addition, the method includes determining a peak correlation value, a second time, and the RTT for each one of the transmitted plurality of signals based at least on the first time and the second time.