Carrier Frequency Offset Compensation in Multicarrier Uplink

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Solution Overview

Problem

In multicarrier communication systems, such as OFDM, carrier frequency offsets between transmitting stations disrupt the orthogonality of subcarriers, leading to increased inter-symbol interference and signal-to-noise ratio degradation, particularly when receiving data from multiple sources.

Innovation Solution

Implementing a method where receiving stations estimate and compensate for carrier frequency offsets using iterative decoding processes and channel estimates, and transmitting stations apply CFO estimates to their signals, maintaining subcarrier orthogonality and reducing intercarrier interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If multiple communication stations transmit simultaneously in a multicarrier system, then system capacity and productivity are improved, but carrier frequency offsets occur that degrade signal quality and orthogonality

Engineering Contradiction:

Improvesystem capacityVSAvoidsignal quality

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies preliminary action by having transmitting stations estimate and compensate for their carrier frequency offsets before simultaneous transmission. Each station performs CFO estimation and compensation in advance, so that when multiple stations transmit simultaneously, their signals arrive at the receiver with corrected frequencies, maintaining subcarrier orthogonality and preventing intercarrier interference.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If carrier frequency offset compensation is performed at the receiving station, then signal quality is improved, but processing complexity and device complexity increase

Engineering Contradiction:

Improvesignal qualityVSAvoidprocessing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies self-service by having each transmitting station independently estimate and compensate for its own carrier frequency offset. Instead of requiring the receiving station to perform complex multi-station CFO compensation, each station autonomously corrects its transmission signal, thereby maintaining signal quality while reducing receiver processing complexity.

Inventive Principle:

Principle #25Self-service

3Measurement precision

If traditional CFO estimation methods are used for multiple transmitting stations, then measurement precision is maintained, but processing time and latency increase

Engineering Contradiction:

ImproveCFO estimation accuracyVSAvoidprocessing latency

Core Design Contradiction:

Measurement precisionVSLoss of time

Solution Approach 1:

The patent applies segmentation by dividing the CFO compensation process into independent per-station operations. Each transmitting station separately estimates and compensates for its own CFO using its assigned training subcarriers, rather than requiring centralized processing of all stations' signals. This segmented approach maintains estimation precision while reducing overall processing latency.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS7426199B2Wireless communication device and method for reducing carrier frequency offsets over a simultaneous multi-user uplink in a multicarrier communication network

Publication Date: 2008.09.16 APPLE INC

AI summary

Each of a plurality of multicarrier wireless communication devices generate a carrier frequency offset (CFO) estimate from a downlink polling frame (302) and apply the CFO estimate to signals prior to transmission to a receiving station over a multi-user uplink.