Multi-carrier Receiver Carrier Frequency Offset Correction

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Solution Overview

Problem

In multi-carrier communication systems, carrier frequency offset issues lead to inaccurate data recovery, particularly in OFDM and DMT techniques, due to oscillator frequency drift and Doppler effects, causing inter-channel interference.

Innovation Solution

A multi-carrier receiver corrects carrier frequency offset by processing pilot symbols in the time domain and using a phase locked loop (PLL) to track pilot phases, reducing computational complexity and immune to phase noise, while determining and correcting the offset in both time and frequency domains.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If carrier frequency offset correction is performed in frequency domain, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvecarrier frequency offset measurement precisionVSAvoidcomputational complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces the conventional frequency-domain correction mechanism with a time-domain correction mechanism. Instead of using complex frequency-domain processing (FFT-based methods), the invention uses time-domain signal processing with correlation-based offset estimation and time-domain equalization, thereby reducing computational complexity while maintaining correction effectiveness

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the domain parameter from frequency domain to time domain for carrier frequency offset correction. By transforming the correction operation from frequency domain (requiring FFT and complex mathematical operations) to time domain (using correlation and simple multiplication), the invention reduces computational burden while achieving the same correction objective

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If pilot symbols are processed in frequency domain, then measurement precision is improved, but device complexity increases

Engineering Contradiction:

Improvepilot phase tracking precisionVSAvoidcomputational complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent substitutes frequency-domain pilot processing with time-domain pilot processing. Instead of performing FFT on pilot symbols and processing them in frequency domain, the invention processes pilot symbols directly in time domain using correlation methods and phase tracking, eliminating the need for complex frequency-domain transformations while maintaining tracking precision

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent extracts the essential function of pilot symbol processing from the frequency-domain context and implements it independently in the time domain. By separating the pilot processing function from the frequency-domain pipeline and implementing it in time domain, the invention reduces overall system complexity while preserving measurement precision

Inventive Principle:

Principle #2Taking out (Extraction)

3Reliability

If conventional frequency domain correction is used, then data recovery accuracy is maintained, but productivity decreases

Engineering Contradiction:

Improvedata recovery accuracyVSAvoidprocessing speed

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent replaces the computationally intensive frequency-domain correction system with a faster time-domain correction system. By substituting FFT-based methods with time-domain correlation and equalization, the invention achieves the same data recovery accuracy with significantly reduced processing time and higher throughput

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent performs carrier frequency offset estimation and correction in the time domain before frequency-domain processing is required for data extraction. By preliminary correcting the offset in time domain, the invention avoids the need for complex iterative frequency-domain correction, thereby speeding up the overall processing pipeline

Inventive Principle:

Principle #10Preliminary action

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 computational complexity and ensures accurate data recovery by correcting carrier frequency offset variations within a packet duration, improving the reliability of multi-carrier communication systems.

Implementation Method 1

using a phase locked loop (PLL) to track pilot phases

Methodology Applied

Scientific EffectPhase locked loop:

Implementation Method 2

determining and correcting the offset in both time and frequency domains

Methodology Applied

Scientific EffectFrequency offset correction:

Data Source

PatentUS7817736B2Correcting for carrier frequency offset in multi-carrier communication systems

Publication Date: 2010.10.19 TEXAS INSTRUMENTS INC

AI summary

A multi-carrier (MC) receiver receives a multi-carrier signal containing data symbols as well as pilot symbols. The MC receiver estimates a carrier frequency offset in a downconverted base-band multi-carrier signal in the frequency domain based on deviations of one or more characteristics of the pilot signals from predetermined values, and corrects for the offset in the time domain. In an embodiment, a second order phase locked loop (PLL) estimates the phase of the pilot signals to determine the carrier frequency offset. Changes in pilot phases caused due to the time domain correction are cancelled to allow the PLL to minimize deviations from the lock position.