Multi-Interval Frequency Offset Estimation Beyond Nyquist Limits
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Solution Overview
Problem
Existing frequency offset estimation methods in communication systems, such as OFDM, are limited by the Nyquist frequency, which restricts the detection of larger frequency offsets, particularly in scenarios like high-speed trains where rapid frequency changes occur, leading to inaccurate estimates.
Innovation Solution
A method that uses multiple frequency offset estimators with different time distances between symbols to calculate a corrected estimate by determining integer values that align frequency values across estimates, allowing for detection of frequency offsets beyond the Nyquist frequency through combinations and probability maximization, and in noisy environments, using signal-to-noise ratios for optimal estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the distance between two received symbols is increased to improve measurement precision, then the frequency offset estimation precision is improved, but the Nyquist frequency (maximum detectable frequency offset) is reduced
Solution Approach 1:
The patent divides the frequency offset estimation task into multiple segments by using multiple different time distances between symbol pairs. Instead of relying on a single distance, the system uses a first time distance for initial estimation and a second time distance for refinement, allowing the system to overcome the Nyquist limit of any single estimation method.
Solution Approach 2:
The patent introduces a new dimension to the estimation problem by using multiple time distances simultaneously. This transforms the single-dimensional estimation (one time distance) into a multi-dimensional approach where the system can resolve frequency offsets beyond the Nyquist limit by combining information from different time domains.
2Difficulty of detecting and measuring
If the time distance between symbols is reduced to increase Nyquist frequency, then the maximum detectable frequency offset is improved, but the measurement precision deteriorates
Solution Approach 1:
The patent segments the estimation process into two stages: first using a short time distance to capture high-frequency components and establish an initial estimate, then using a longer time distance to refine the measurement and improve precision. This segmentation allows the system to achieve both high Nyquist frequency and high measurement precision.
3Device complexity
If a single frequency offset estimator is used to simplify the system, then the device complexity is reduced, but the ability to handle rapid frequency changes is limited
Solution Approach 1:
The patent merges multiple frequency offset estimators with different time distances into a unified estimation system. The first frequency offset estimator uses a first time distance while the second estimator uses a second time distance, and their results are combined to provide comprehensive frequency offset information that can handle rapid frequency changes.
Solution Approach 2:
The combined estimation system provides universal functionality by being able to handle both small frequency offsets with high precision and large frequency offsets beyond the Nyquist limit. The system can adapt to various frequency change scenarios including high-speed train movements and rapid frequency jumps.
Data Source
AI summary
A frequency offset of a received signal comprising a number of subsequently received data symbols is estimated. A first estimate is determined from a calculated change in phase of the received signal between two received symbols having a first time distance between them. At least one further estimate is determined from a calculated change in phase of the received signal between two received symbols having a different time distance. A frequency periodicity is determined for each estimate from the distance between the two received symbols from which the estimate was determined. A set of integer values is determined for each estimate so that frequency values calculated for each estimate as the frequency periodicity multiplied by the integer value added to the estimate are at least approximately equal to each other, and a corrected estimate of the frequency offset is determined from the integer values.