Preamble Synchronization for Large Frequency Error Reception

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Solution Overview

Problem

Existing communication systems face challenges in achieving high performance time and frequency synchronization, especially when frequency uncertainty is large relative to the symbol rate, leading to limited data rate flexibility and poor accuracy in frequency estimation.

Innovation Solution

A method involving a preamble with two parts: a first portion with a predetermined bit sequence repeated multiple times for initial frequency estimation, followed by a Barker bit sequence for refined time and frequency synchronization, and optionally a third step for further frequency and phase estimation using least squares analysis.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If cross-correlation is used for synchronization, then accuracy is improved when frequency error is small, but it becomes infeasible when frequency error is large

Engineering Contradiction:

Improvesynchronization accuracyVSAvoidfrequency error tolerance

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The synchronization process is divided into two distinct stages: a first stage using auto-correlation to obtain a coarse frequency estimate that can handle large frequency errors, and a second stage using cross-correlation to achieve fine synchronization accuracy. This segmentation allows each method to operate within its optimal range, resolving the contradiction between accuracy and frequency error tolerance.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If signal differentiation is used to handle large frequency errors, then frequency error tolerance is improved, but noise enhancement occurs at low SNR

Engineering Contradiction:

Improvefrequency error toleranceVSAvoidsynchronization accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The auto-correlation operation is performed as a preliminary step before cross-correlation. This preliminary action provides a coarse frequency estimate that enables subsequent cross-correlation to be performed with proper frequency compensation, avoiding the noise enhancement problem of differentiation while still handling large frequency errors.

Inventive Principle:

Principle #10Preliminary action

3Adaptability or versatility

If auto-correlation is used for frequency estimation, then frequency error tolerance is improved, but estimation accuracy decreases with large frequency uncertainty

Engineering Contradiction:

Improvefrequency error toleranceVSAvoidfrequency estimation accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The auto-correlation result serves as an intermediary that provides a coarse frequency estimate. This intermediary estimate is then used to pre-compensate the signal before applying cross-correlation, which provides the final accurate frequency and timing estimation. The intermediary step bridges the gap between handling large frequency errors and achieving high estimation accuracy.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12483455B2Transmitting data or determining a frequency and timing estimate of a received signal

Publication Date: 2025.11.25 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

Methods and apparatus are provided, including in an example a method for transmitting data, wherein the data includes a preamble. The method comprises transmitting the data including the preamble, wherein the preamble includes a first portion comprising a predetermined bit sequence repeated a predetermined number of times, and a second portion comprising a Barker bit sequence.