Median Filtering for Pulse Detection and Width Discrimination
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Solution Overview
Problem
Modern radar receivers face challenges in managing noise due to the combination of linear amplifiers and wide bandwidths, which affect pulse detection and pulse width discrimination, especially at low signal levels.
Innovation Solution
A non-linear processor utilizing median filtering to reduce noise in linearly amplified signals while maintaining sharp edge transitions, comprising a first and second linear filter, a magnitude calculation circuit, and a median filter processor to generate a filtered signal for improved pulse detection and characterization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If linear amplifiers with wide bandwidth are used, then receiver sensitivity and bandwidth are improved, but noise management becomes difficult and pulse detection accuracy deteriorates
Solution Approach 1:
A non-linear processing stage is introduced as an intermediary between the linear amplifier and pulse detection. This stage includes a non-linear filter (such as a median filter) that selectively removes noise while preserving pulse signals, thereby managing the noise generated by the linear amplifier without compromising sensitivity
Solution Approach 2:
The patent changes the processing parameter from linear filtering to non-linear filtering. By using non-linear operations (such as median filtering, thresholding, or other non-linear transformations), the system can distinguish between noise and pulse signals based on their different statistical properties, improving noise rejection while maintaining pulse detection capability
2Object-affected harmful factors
If linear filters are used for noise reduction, then noise is reduced, but pulse width discrimination accuracy deteriorates due to attenuation of narrow pulses
Solution Approach 1:
The non-linear filter acts as an intermediary that provides noise reduction without the pulse-width distorting effects of linear filters. Unlike linear filters that attenuate high-frequency components (affecting narrow pulses), non-linear filters preserve edge transitions and pulse widths while still reducing noise through statistical operations
Solution Approach 2:
The patent replaces the mechanical linear filtering approach with a non-linear processing approach. Instead of using frequency-based linear filtering that inherently distorts pulse widths, the system uses non-linear operations that can adaptively preserve pulse characteristics while removing noise based on statistical criteria
3Reliability
If matched filtering is used, then signal detection is improved, but narrow high bandwidth pulses are attenuated
Solution Approach 1:
The patent changes from matched filtering (which assumes known pulse shapes and frequencies) to non-linear filtering that operates on the statistical properties of the signal. This parameter change allows the system to detect and accurately measure narrow pulses without the attenuation problems inherent in matched filtering approaches
Data Source
AI summary
Techniques are provided for non-linear filtering of a signal for improved pulse detection and pulse width discrimination. A system implementing the techniques according to an embodiment includes a first linear filter configured to filter an in-phase component of a received signal to a downsample bandwidth and a second linear filter configured to filter a quadrature phase component of the received signal to the downsample bandwidth. The system also includes a magnitude calculation circuit coupled to outputs of the first linear filter and the second linear filter and configured to generate a magnitude signal based on the filtered in-phase component and the filtered quadrature phase component of the received signal. The system further includes a median filter processor coupled to an output of the magnitude calculation circuit and configured to apply a median filter to the magnitude signal to generate a filtered signal having reduced noise while maintaining sharp edge transitions.