Coarse Frequency Offset Estimation in OFDM Systems
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing frequency offset estimation methods for OFDM systems, such as ICDC and CIR-based methods, are cumbersome and prone to false results when dealing with large frequency offsets, especially in standards like DAB and T-DMB, requiring more complexity and computation to support extended detection ranges.
Innovation Solution
The method involves selecting a predefined subset of frequency offsets, computing ICDC for each, sorting candidates, and selectively searching outside this range to find additional candidates, combining ICDC and CIR-based methods to estimate coarse frequency offsets without significant complexity increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the ICDC method is used to estimate frequency offset, then the method is simple to implement, but it returns false results due to periodicity in phase reference symbols and becomes cumbersome when there are many possible frequency shifts to search
Solution Approach 1:
The patent segments the frequency offset search space into a predefined subset (e.g., 401 frequency shifts in DAB/T-DMB Mode I) and applies ICDC method only within this subset. This segmentation reduces the computational burden while maintaining reliability by limiting the search to a manageable range where ICDC remains effective.
Solution Approach 2:
The patent merges ICDC method with CIR-based method to overcome their individual limitations. ICDC provides a simple initial estimation within the predefined subset, while CIR-based verification confirms the accuracy and eliminates false results caused by periodicity in phase reference symbols.
2Reliability
If the CIR based method is used to estimate frequency offset, then it has better performance, but it requires even greater complexity since one inverse fast Fourier transform must be performed for each frequency shift
Solution Approach 1:
The patent segments the application of CIR-based method to only those frequency shifts identified as candidates by the ICDC method within the predefined subset. This selective application reduces the number of IFFT operations from potentially hundreds to just a few verification steps, significantly lowering computational complexity while maintaining high performance.
Solution Approach 2:
The patent performs preliminary frequency offset estimation using the simpler ICDC method to identify candidate frequency shifts before applying the more complex CIR-based verification. This preliminary action filters out most frequency shifts, so the computationally intensive CIR-based method is only applied to a small number of candidates.
3Adaptability or versatility
If the search range for frequency offset is extended to support large frequency deviations, then the detection capability is improved, but the complexity of existing methods increases significantly
Solution Approach 1:
The patent defines a predefined subset of frequency shifts (e.g., covering ±200 kHz in DAB/T-DMB Mode I) and applies ICDC method within this subset. This segmentation allows the system to handle large frequency deviations while keeping the per-subset complexity manageable through the simple ICDC approach.
Solution Approach 2:
The patent applies the computationally intensive CIR-based method only partially - specifically, only to verify candidate frequency shifts identified by ICDC within the predefined subset. This partial application provides sufficient verification capability for large frequency offsets without requiring full CIR-based processing for all possible frequency shifts.
Data Source
AI summary
The present invention provides methods for selecting the coarse frequency offset estimation in an orthogonal frequency division multiplexing system that may include: searching within a predefined subset for a set of frequency offset candidates; selectively searching outside the predefined subset for additional frequency offset candidates; and combining one or more ICDC method and CIR based method to select the coarse frequency offset.