Block Linear Equalizer for Multicarrier Systems
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Solution Overview
Problem
Multi-carrier communication systems, such as DMT systems, face channel distortion leading to inter-symbol interference (ISI) and inter-channel interference (ICI), which reduce the signal-to-noise ratio (SNR), particularly in ADSL systems where the channel impulse response is longer than the cyclic prefix length, making it difficult to achieve perfect equalization.
Innovation Solution
A block linear equalizer (BLE) is employed to reduce errors in sub-carriers by adding weighted multiples of neighboring and other symbols, implemented with a TEQ, CP removal, DFT, and noise detection modules, allowing for efficient channel equalization with reduced complexity by using sparse BLE matrices and adaptive algorithms like least-mean squares (LMS) for updating taps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a time-domain equalizer (TEQ) is used to perform channel shortening, then channel equalization is improved, but inter-symbol interference (ISI) cannot be completely eliminated and the lower band-edge remains difficult to equalize
Solution Approach 1:
The patent divides the equalization process into two distinct stages: frequency-domain equalization (FEQ) that handles the majority of channel distortion, and block linear equalization (BLE) that specifically targets residual ISI and ICI. This segmentation allows each equalizer to specialize in different aspects of channel compensation, with FEQ handling the bulk of equalization and BLE providing targeted correction for remaining interference, particularly at the lower band-edge where TEQ alone fails.
Solution Approach 2:
The patent combines frequency-domain equalization and block linear equalization into a hybrid equalization system. The FEQ component processes symbols in the frequency domain to provide initial equalization, while the BLE component operates in the time domain to eliminate residual ISI and ICI. This merging of two different equalization approaches creates a more comprehensive solution that overcomes the limitations of using either method alone.
2Reliability
If a generalized decision-feedback equalizer (GDFE) is used for channel equalization, then equalization performance is improved, but system complexity becomes very large
Solution Approach 1:
The patent segments the complex equalization function into two simpler, more manageable components: FEQ and BLE. Each component has a specific, well-defined role with manageable complexity. The FEQ uses simple frequency-domain filtering, while BLE uses block-based processing with constrained filter lengths. This segmentation avoids the need for a single complex GDFE structure, distributing the equalization burden across two simpler modules.
Solution Approach 2:
The patent applies different equalization strategies to different parts of the signal spectrum and time domain. FEQ handles the frequency-domain characteristics of the channel, while BLE specifically addresses time-domain ISI and ICI. This local specialization allows each equalizer to be optimized for its specific function rather than requiring a universally complex solution that handles all equalization aspects simultaneously.
3Reliability
If the length of the channel impulse response is longer than the cyclic prefix length, then inter-symbol interference (ISI) and inter-channel interference (ICI) increase, but using traditional equalization methods cannot achieve perfect equalization
Solution Approach 1:
The patent merges frequency-domain and time-domain equalization techniques to comprehensively address ISI and ICI caused by long channel impulse responses. The FEQ component compensates for frequency-selective fading, while the BLE component specifically targets residual time-domain interference. This combined approach provides more complete cancellation of interference effects than either method could achieve alone.
Solution Approach 2:
The patent employs adaptive algorithms that use feedback from detected errors to continuously refine equalizer coefficients. The system monitors the residual ISI and ICI after initial equalization and adjusts the BLE filter coefficients accordingly to minimize remaining interference. This feedback mechanism allows the equalizer to adapt to changing channel conditions and optimize performance over time.
Data Source
AI summary
A method and apparatus for channel equalization in a multi-carrier communication system. The method may include receiving a symbol having multiple sub-carriers and reducing an error on at least one of the sub-carriers of the symbol by adding to it, one or more weighted multiples of other sub-carriers. The added weighted multiples may be from neighboring sub-carriers in the same symbol and/or from other symbols in a tone, for example, a previous or next symbol. The apparatus may include a reduced-complexity block linear equalizer.