Wideband Receiver FFT Filtering for Narrow-Band Interference Excision
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Solution Overview
Problem
Conventional adaptive filter designs for interference mitigation in wide-band communication systems are inefficient in terms of hardware resources, particularly in portable wireless communications where memory and processing power are limited, and suffer from spectral leakage and main lobe spreading issues.
Innovation Solution
The proposed solution involves a filter device and method that uses a combination of signal processing techniques, including doubling the input sample size for FFT, applying windowing functions, and processing in the magnitude domain to reduce spectral leakage and hardware requirements, while effectively excising narrow-band interference using a noise floor calculation and adjustment factors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional adaptive filter designs are used for interference mitigation in wide-band communication systems, then interference suppression capability is achieved, but hardware resource utilization (memory and processing power) increases
Solution Approach 1:
The patent extracts only the essential components needed for interference mitigation by implementing a simplified filter structure that uses selective frequency bin processing rather than full adaptive filtering across the entire spectrum. This extraction approach maintains interference suppression while reducing memory and processing requirements.
Solution Approach 2:
The frequency spectrum is segmented into discrete frequency bins, and only those bins containing interference (identified by exceeding the noise floor threshold) are processed. This segmentation allows the system to focus computational resources only on affected portions of the spectrum rather than processing the entire wide-band signal.
2Reliability
If narrow-band excision is performed in the frequency domain, then narrow-band interference removal is improved, but spectral leakage and main lobe spreading occur
Solution Approach 1:
The patent converts the harmful spectral leakage effect into a beneficial detection mechanism by using the leaked energy to identify interference locations through noise floor comparison. The same phenomenon that causes distortion is utilized to detect and target interference bins for excision.
Solution Approach 2:
The system changes the parameter threshold for interference detection by comparing frequency bin magnitudes against a dynamically calculated noise floor rather than using fixed thresholds. This parameter adaptation allows accurate interference identification while minimizing the impact of spectral leakage effects.
Data Source
AI summary
A filter for a radio receiving device doubles a sample size of a digital baseband signal to form an enhanced data set and after widowing performs a Fast Fourier Transform (FFT) to facilitate calculation of instantaneous magnitude values and average magnitude values for each of a plurality of frequency bins. A noise floor is calculated based on the average magnitude values of a plurality of the frequency bins, and the noise floor is then used to identify frequency bins which contain an interfering signal. If it is determined that a frequency bin contains spectral energy associated with an interfering signal, then the instantaneous magnitude value of the frequency bin is selectively reduced, after which an inverse FFT operation and inverse window operation is performed.