OFDM Integer Frequency Offset Estimation via Subcarrier Superposition
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Solution Overview
Problem
Conventional methods for estimating OFDM integer frequency offset are complex and fail to accurately estimate the offset when a time offset is present, requiring high computational load and complexity.
Innovation Solution
A method that generates combined sub-carrier components by superposing received sub-carrier components and performs correlation operations within coherence phase bandwidth intervals to estimate primary and secondary integer frequency offset values, reducing computational complexity by trading off estimation accuracy against complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional frequency offset estimation methods are used, then estimation accuracy is maintained, but computational complexity increases significantly
Solution Approach 1:
The patent segments the frequency offset estimation process into two distinct stages: coarse estimation and fine estimation. The coarse estimation stage uses a reduced search range and simplified correlation operations to quickly eliminate large frequency offsets, while the fine estimation stage focuses on smaller residual offsets with higher precision. This segmentation reduces overall computational complexity by avoiding exhaustive search across the entire possible offset range.
Solution Approach 2:
The patent applies partial action by performing correlation operations only on a subset of subcarriers rather than all subcarriers in the OFDM signal. Specifically, it uses a predetermined number of subcarriers (less than the total available) for the correlation-based frequency offset estimation, thereby reducing the computational load while maintaining sufficient estimation accuracy through the statistical properties of the selected subcarriers.
2Measurement precision
If conventional frequency offset estimation methods are used, then estimation accuracy is maintained, but processing time increases
Solution Approach 1:
By dividing the estimation into coarse and fine stages, the patent reduces total processing time. The coarse stage quickly handles large offsets with computationally simple operations, and the fine stage processes smaller residual offsets with higher precision but lower computational burden. This two-stage approach avoids the time-consuming exhaustive search of conventional single-stage methods.
Solution Approach 2:
The coarse frequency offset estimation is performed as a preliminary step before the fine estimation. This preliminary action removes the bulk of the frequency offset error early in the process, allowing the subsequent fine estimation to operate on a reduced search space and converge faster, thereby reducing overall processing time.
3Measurement precision
If comprehensive correlation operations are performed on all sub-carrier components, then estimation accuracy is improved, but computational load increases
Solution Approach 1:
The patent performs correlation operations on only a predetermined number of subcarriers rather than all subcarriers in the OFDM signal. This partial action reduces computational load by a factor proportional to the ratio of used subcarriers to total subcarriers, while the estimation accuracy is maintained through the use of multiple subcarriers that provide sufficient statistical information for accurate frequency offset determination.
Solution Approach 2:
The patent extracts and uses only the necessary subset of subcarriers for frequency offset estimation, separating this function from the complete set of subcarriers used for data transmission. By taking out only the required number of subcarriers for the correlation operation, the system achieves the desired estimation accuracy with reduced computational energy consumption.
Data Source
AI summary
A method of estimating an orthogonal frequency division multiplexing (OFDM) integer frequency offset is disclosed. The method includes generating N combined sub-carrier components by superposing G received sub-carrier components of N received sub-carrier components constituting received symbol, outputting a primary estimated integer frequency offset value from a candidate value, which makes primary correlated values, obtained with respect to primary integer frequency offset candidate values, to be largest, and outputting a secondary estimated integer frequency offset value from a secondary candidate value, which makes secondary correlated values, obtained with respect to secondary integer frequency offset candidate values based on primary estimated integer frequency offset value, to be largest.