Magnitude-Squared Coherence Filtering for TDOA Geolocation
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Solution Overview
Problem
Time difference of arrival (TDOA) geolocation systems face challenges in accurately determining the location of a target emitter due to noise and interference, which reduce the signal-to-noise ratio (SNR) and accuracy, especially when signals have deep nulls and propagate through frequency-selective channels.
Innovation Solution
The method involves calculating the magnitude-squared coherence (MSC) of target signals to identify frequencies with low coherence, setting the energy of these frequencies to zero, thereby increasing the signal-to-noise ratio by filtering out noise and reducing signal energy at null frequencies, using a pattern matching algorithm across frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signals are processed through frequency-selective channels to determine TDOA, then geolocation capability is achieved, but noise and interference reduce signal-to-noise ratio and geolocation accuracy
Solution Approach 1:
The patent extracts and removes harmful frequency components from the signal by calculating magnitude-squared coherence between signal pairs and identifying frequencies with low coherence values. These low-coherence frequencies, which represent noise and interference, are selectively eliminated while preserving the useful signal components, thereby improving signal-to-noise ratio and geolocation accuracy
Solution Approach 2:
The patent applies local quality by treating different frequency components differently based on their coherence characteristics. Instead of uniform signal processing across all frequencies, the system identifies specific frequency regions with low coherence (indicating noise dominance) and applies selective filtering only to those regions, while maintaining full signal integrity in high-coherence regions
2Reliability
If all frequency components are processed to maintain signal integrity, then complete signal information is preserved, but noise at certain frequencies reduces overall signal-to-noise ratio
Solution Approach 1:
The patent changes the parameter of signal energy distribution across frequencies by dynamically adjusting which frequency components are retained or eliminated based on magnitude-squared coherence calculations. This selective parameter modification removes noise-dominated frequency components while preserving signal-dominated components, thereby improving overall signal-to-noise ratio without compromising essential signal integrity
Data Source
AI summary
In a geolocation system for determining a geolocation of a target emitter, a method for determining the geolocation. The method comprising: (a) receiving a signal transmitted from the target emitter at each one of a plurality of sensors, a frequency spectrum associated with each signal; (b) determining a pairwise correlation between a first signal and a second signal from among the plurality of signals, the pairwise correlation determined at frequencies or within frequency bands within the frequency spectrum of at least one of the first and second signals; (c) identifying pairwise correlations below a predetermined threshold; (d) filtering the first and second signals by reducing a magnitude of energy at one or more frequencies or within one or more frequency bands to produce first and second filtered signals, the one or more frequencies or the one or more frequency bands selected responsive to pairwise correlations below the threshold; (e) determining a time difference estimate responsive to the first and second filtered signals; (f) repeating steps (b) through (e) for signals received at other of the plurality of sensors to determine additional pairwise time difference estimates; and (g) determining the geolocation of the target emitter from the piecewise time difference estimates.