OFDM Receiver Phase Tracking Using Squared Data Subcarriers

Solution Overview

Problem

In OFDM systems, especially those following the IEEE 802.11 standard, accurate phase and timing information recovery is challenging, particularly in adverse environments with high noise or low signal levels, where the number of pilot carriers may be insufficient to track phase changes effectively.

Innovation Solution

The method involves using the amplitude of data-bearing subcarriers to determine phase and timing information, specifically by removing the data modulation from PSK-modulated subcarriers through squaring or multiplying operations, allowing for phase offset estimation independent of the data modulation, and averaging phase values for enhanced accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If pilot carriers are used to track phase changes, then phase tracking accuracy is improved, but the number of available carriers for data transmission is reduced and the system becomes more complex

Engineering Contradiction:

Improvephase tracking accuracyVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The invention makes data-bearing subcarriers serve dual purposes: transmitting data and providing phase tracking information. By removing PSK modulation from data subcarriers and using their amplitudes for phase tracking, the system eliminates the need for separate pilot carriers, thereby reducing system complexity while maintaining phase tracking accuracy.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The invention recovers phase information from data subcarriers by removing the data modulation component. Through squaring or multiplying operations, the data modulation is eliminated while preserving the phase offset information, which is then extracted for channel tracking purposes.

Inventive Principle:

Principle #34Discarding and recovering

2Measurement precision

If more pilot carriers are used to track phase changes in adverse environments, then phase tracking accuracy is improved, but signal-to-noise ratio deteriorates due to fewer carriers available for data transmission

Engineering Contradiction:

Improvephase tracking accuracyVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The invention makes data-bearing subcarriers serve dual purposes: transmitting data and providing phase tracking information. By removing PSK modulation from data subcarriers and using their amplitudes for phase tracking, the system eliminates the need for separate pilot carriers, thereby reducing system complexity while maintaining phase tracking accuracy.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The invention changes the parameter used for phase tracking from pilot carrier phases to data subcarrier amplitudes. By squaring or multiplying the modulated subcarrier signals, the data modulation is removed and the amplitude becomes proportional to the phase offset, enabling phase tracking through a different physical parameter.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If data modulation is removed from subcarriers for phase tracking, then phase offset estimation accuracy is improved, but data transmission efficiency is reduced

Engineering Contradiction:

Improvephase offset estimation accuracyVSAvoiddata transmission efficiency

Core Design Contradiction:

Measurement precisionVSProductivity

Solution Approach 1:

The invention makes data-bearing subcarriers serve dual purposes: transmitting data and providing phase tracking information. By removing PSK modulation from data subcarriers and using their amplitudes for phase tracking, the system eliminates the need for separate pilot carriers, thereby reducing system complexity while maintaining phase tracking accuracy.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The invention performs preliminary removal of data modulation from subcarriers before phase tracking, allowing the phase information to be extracted cleanly without data interference. This preliminary processing step enables accurate phase offset estimation while the original data can still be recovered through appropriate demodulation processes.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9160587B2Channel tracking in an orthogonal frequency-division multiplexing system

Publication Date: 2015.10.13 ATMEL CORP

AI summary

A receiver determines phase and frequency information from data signals that carry information from a transmitter to a receiver, instead of or in addition to, information from control signals. In a specific embodiment, the information is obtained from data signals modulated as a binary phase-shift keying (“BPSK”) waveform by demodulation. Other phase-shift keyings might be used instead. Encoded information might be recovered in received OFDM packets by receiving OFDM subcarriers modulated with the two low data rates supported by IEEE 802.11 standard(s) wherein the subcarriers encoding the packet are modulated using binary phase shift keying and the encoding information is at a zero phase or a π (pi) phase offset on each of the subcarriers. Determining the carrier frequency might be done by calculating the square of each of subcarrier signal and/or determining the phase offset of the subcarriers even with information modulated onto the subcarriers.