Adaptive Filter Structure for Narrowband Interference Reduction
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Solution Overview
Problem
Existing communication systems face challenges in effectively reducing narrowband interference and jamming in HF/VHF/UHF bands, particularly due to the limitations of adaptive filters in handling wideband signals and multiple interferers, which can lead to intersymbol interference and bit errors.
Innovation Solution
The implementation of an adaptive filter system with a variable delay circuit and automatic tap order selection, which adjusts its gain and tap number based on input and output power, demodulator state, and modulation type to selectively apply adaptive filtering and improve multipath performance, thereby reducing narrowband interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If adaptive filters are used to reduce narrowband interference, then interference reduction is improved, but device complexity increases
Solution Approach 1:
The patent implements dynamic adaptation of filter parameters including variable tap order selection and adjustable update gain based on signal conditions. The filter transitions between different operational modes (training mode, tracking mode) with varying complexity levels, allowing the system to optimize between interference reduction performance and computational complexity by adapting the filter's degree of freedom to current channel conditions
Solution Approach 2:
The system dynamically changes key parameters including the number of adaptive taps (tap order), update gain factor, and filter coefficients based on signal power levels, interference characteristics, and channel conditions. This allows the adaptive filter to adjust its complexity and performance characteristics in real-time, resolving the contradiction by using higher complexity only when necessary for effective interference suppression
2Object-affected harmful factors
If the number of adaptive filter taps is increased to handle multiple interferers, then interference reduction is improved, but processing time increases
Solution Approach 1:
The patent implements dynamic tap order selection where the number of adaptive filter taps is adjusted based on the number of detected interferers and signal conditions. The system can increase tap order when multiple interferers are present and reduce tap order when interference is minimal, thereby resolving the contradiction by making processing time variable rather than fixed, adapting computational resources to actual interference levels
Solution Approach 2:
The adaptive filtering process is segmented into distinct operational phases (preamble processing, data processing, training mode, tracking mode) with different tap orders and processing requirements. This segmentation allows the system to use higher computational complexity only during specific phases when needed, rather than maintaining maximum complexity continuously, thus reducing overall processing time while still handling multiple interferers when necessary
3Object-affected harmful factors
If adaptive filtering is applied continuously, then interference reduction is improved, but signal distortion increases
Solution Approach 1:
The patent implements periodic retraining and mode switching where the adaptive filter alternates between training mode (using known preamble sequences) and tracking mode (processing actual data). During training mode, the filter adapts coefficients with higher update gain, while during tracking mode, it maintains coefficients with lower update gain to avoid distorting the actual data signal. This periodic action resolves the contradiction by applying strong adaptive filtering only when training data is available, not continuously on actual communication signals
Solution Approach 2:
The system uses feedback from the demodulator about signal quality, synchronization state, and detected modulation types to control the adaptive filter's operation. The demodulator provides feedback about whether the signal is in preamble or data portion, and the adaptive filter adjusts its update gain and operational mode accordingly. This feedback mechanism ensures the filter reduces interference while maintaining signal quality by reducing filter aggressiveness when processing actual data portions
Data Source
AI summary
A communications system receives a modulated signal that carries encoded communications data. An adaptive filter circuit has a plurality of adaptive filters each having a plurality of non-adaptive and adaptive filter taps with weighted coefficients. At a selected adaptive filter, an interference reduction circuit is responsive to one of at least a received state of a demodulator, the type of modulation used by communication system and the input and output power of adaptive filter for updating the adaptive gain of the adaptive filter, selecting the number and order of adaptive filter taps, separating the spacing of multipath introduced by adaptive filter, controlling input and output normalizing circuits to adaptive filter(s) and selecting if signal passed to demodulator is original received signal or signal output by adaptive filter. A demodulator and decoder receive the filtered output signal and demodulate and decode the signal to obtain the communications data.