Per-tone Equalization for OFDMA Sub-carrier Orthogonality

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Solution Overview

Problem

In OFDMA systems, the cyclic prefix is often insufficient to manage channel impulse responses longer than the prefix length, leading to loss of orthogonality among sub-carriers and performance degradation, especially in rural or suburban environments, while increasing the cyclic prefix reduces data rate and increases transmission overhead.

Innovation Solution

Implementing per-tone equalization, which applies a separate equalization filter to each sub-carrier in the frequency domain based on the severity of inter-symbol interference, allowing for independent optimization of each sub-carrier and reducing computational and memory requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the cyclic prefix length is increased to manage channel impulse responses longer than the prefix length, then orthogonality among sub-carriers is maintained, but data rate decreases and transmission overhead increases

Engineering Contradiction:

Improveorthogonality among sub-carriersVSAvoiddata rate

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent divides the equalization process into per-subcarrier operations in the frequency domain, allowing independent optimization for each subcarrier based on its specific channel conditions and ISI severity, rather than applying a uniform extended cyclic prefix to all subcarriers

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different equalization strategies to different subcarriers based on local channel conditions. Subcarriers experiencing severe ISI receive per-tone equalization while those with mild ISI use simpler equalization, optimizing performance locally for each frequency component

Inventive Principle:

Principle #3Local quality

2Reliability

If per-tone equalization is applied to all sub-carriers, then inter-symbol interference is reduced, but computational and memory requirements increase

Engineering Contradiction:

Improveinter-symbol interference reductionVSAvoidcomputational and memory requirements

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies per-tone equalization selectively only to subcarriers experiencing severe inter-symbol interference, rather than uniformly to all subcarriers. This partial application reduces computational and memory requirements while still addressing the critical ISI problems where they occur

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent changes the equalization parameter (filter application) based on the severity of ISI detected on each subcarrier. By dynamically adjusting which subcarriers receive complex per-tone equalization versus simpler equalization, the system adapts computational resources to actual channel conditions

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8077646B1Equalization in a wireless multiple access communication system

Publication Date: 2011.12.13 MARVELL ASIA PTE LTD

AI summary

An equalization method and apparatus for a communication system having a first transceiver device that communicates with each of a plurality of second transceiver devices receives a data transmission over a subset of frequency sub-carriers allotted to each second transceiver device. The communication channel between first transceiver device and the plurality of second transceiver devices is partitioned in a plurality of frequency sub-carriers of which the frequency sub-carriers allotted to a second transceiver device is a subset. The data transmission is transformed from a time-domain transmission to a frequency domain transmission. An equalization filter is applied separately to each of the frequency sub-carriers within the subset of frequency sub-carriers.