OFDM DC Offset Removal via Noise Whitening
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Solution Overview
Problem
OFDM systems face performance degradation due to the injection of DC components and uncertainty in carrier frequency offset, leading to inter-carrier interference and noise shaping effects that complicate signal demodulation.
Innovation Solution
A system comprising a high pass DC component filter and a noise whitener is used to remove DC offsets from OFDM signals, with the noise whitener normalizing the power spectral density of noise across subcarrier frequencies to compensate for noise shaping, and the system includes subfilters with coefficients summing to zero and a bypass mechanism for adaptive operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a high pass DC component filter is used to remove DC offset, then DC offset removal is achieved, but noise shaping occurs resulting in non-uniform power spectral density
Solution Approach 1:
The patent converts the harmful noise shaping effect into a beneficial correction opportunity by measuring the non-uniform power spectral density and applying compensating weights. The noise whitener uses the measured noise characteristics to adjust equalization weights, transforming the previously harmful non-uniform noise into a corrected signal with improved detection accuracy.
Solution Approach 2:
The patent implements feedback by measuring the actual noise power spectral density after filtering and using this measurement to adjust the equalization weights. The system continuously monitors the noise characteristics and adapts the whitening weights to compensate for the filtering effects, creating a closed-loop system that optimizes performance.
2Measurement precision
If noise whitening is applied to compensate for noise shaping, then demodulation accuracy is improved, but system complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the noise power spectral density measurements and corresponding whitening weights before actual data demodulation. The system performs the complex noise characterization and weight calculation in advance, so that during operation only simple weight application is needed, reducing real-time computational complexity.
3Manufacturing precision
If subcarrier specific whitening factors are applied, then noise normalization is achieved, but computational load increases
Solution Approach 1:
The patent applies asymmetry by recognizing that not all subcarriers require equal treatment. The system identifies and processes only those subcarriers that are affected by DC offset and noise shaping, applying whitening factors selectively rather than uniformly across all subcarriers. This asymmetric approach reduces computational load while maintaining normalization accuracy where needed.
Data Source
AI summary
Systems and methods for removing a DC offset from an orthogonal frequency division multiplexed (OFDM) signal transmitted over a plurality of subcarrier frequencies. The system includes a receiver. The system further includes a high pass DC component filter configured to reduce a DC component of the orthogonal frequency division multiplexed signal, the high pass DC component filter shaping noise in the orthogonal frequency division multiplexed signal which results in a non-uniform power spectral density of the noise across the plurality of subcarrier frequencies. The system further includes a noise whitener configured to compensate for the noise shaping by the high pass DC component filter by normalizing the non-uniform power spectral density of the noise across the plurality of subcarrier frequencies.