Band-Pass Filter Null Alignment for In-Band Interference Rejection
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Solution Overview
Problem
Communications system receivers experience performance degradation due to interference from nearby transceivers operating on overlapping frequency bands, leading to incorrect signal detection and demodulation of signals from alternate or adjacent channels.
Innovation Solution
A band-pass filter is used to generate a filtered signal with a pass-band centered at the null frequency of an alternate or adjacent channel's power spectrum, allowing the system to distinguish between signals received over the target channel and those from other channels by comparing the energy levels of the original and filtered signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the receiver processes signals across the entire frequency band, then it can detect signals from multiple channels, but interference from alternate and adjacent channels degrades receiver performance
Solution Approach 1:
The frequency band is segmented into multiple channels with distinct spectral characteristics. The receiver processes each channel separately by identifying signals whose power spectra exhibit nulls at specific frequencies corresponding to alternate and adjacent channel centers, thereby isolating target channel signals from interfering channels.
Solution Approach 2:
The receiver applies local quality filtering by detecting the presence of nulls at specific frequency locations within the power spectrum. Signals are accepted only if they exhibit the expected null characteristics at alternate and adjacent channel frequencies, applying a local spectral quality criterion to reject out-of-channel interference.
2Measurement precision
If the receiver accepts signals with energy across overlapping frequency bands, then it maintains sensitivity to weak signals, but it incorrectly demodulates signals from alternate and adjacent channels
Solution Approach 1:
Before demodulation, the receiver performs preliminary spectral analysis to detect nulls in the power spectrum at frequencies corresponding to alternate and adjacent channels. This preliminary action identifies and rejects signals that do not match the expected target channel spectral signature, preventing incorrect demodulation while maintaining sensitivity to valid weak signals.
Solution Approach 2:
The receiver uses feedback from spectral null detection to control signal acceptance. The detected power spectrum is analyzed for nulls at specific frequencies, and this feedback determines whether the signal proceeds to demodulation or is rejected, ensuring that only signals with the correct spectral characteristics are processed further.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces interference by accurately determining whether a signal is received over the target channel or an alternate/adjacent channel, preventing incorrect demodulation and improving signal-to-noise ratio selectivity.
Implementation Method 1
filtering a received signal to generate a band-pass filtered signal using a band-pass filter having a pass-band including frequencies located within a central lobe of a power spectrum associated with a target channel
Data Source
AI summary
A method includes filtering a received signal to generate a band-pass filtered signal using a band-pass filter having a pass-band including frequencies located within a central lobe of a power spectrum associated with a target channel of a plurality of channels supported by a communications system. The pass-band is approximately centered at a frequency of a null of a power spectrum associated with at least one other channel of the plurality of channels supported by the communications system. The method includes processing the received signal based on the band-pass filtered signal. The at least one other channel may include at least one of an alternate channel and an adjacent channel of the plurality of channels.