OFDM Reception Device Frequency Error Correction
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Solution Overview
Problem
Conventional multicarrier transmission systems, such as OFDM, face challenges in quickly correcting carrier frequency errors and clock frequency errors, especially when errors are large, leading to interference among subbands and inaccurate pilot signal extraction, and require additional synchronization symbols for precise frequency estimation.
Innovation Solution
A reception device that utilizes a synchronization symbol string with repeated synchronization patterns to rapidly detect and correct carrier frequency and clock frequency errors by correlating the synchronization pattern with the received signal, allowing for high-precision frequency correction and timing determination using inter-synchronization pattern and inter-symbol phase differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional OFDM reception devices use fast Fourier transform calculation to estimate clock frequency error, then frequency error correction can be performed, but a certain amount of time is necessary until the clock frequency control loop is converged
Solution Approach 1:
The patent performs rough frequency error estimation using guard interval correlation before fast Fourier transform processing. By pre-correcting the frequency error based on the correlation peak phase difference, the system reduces the initial frequency offset, allowing the subsequent FFT-based clock frequency estimation to converge faster with higher precision.
Solution Approach 2:
The frequency error correction process is divided into two stages: rough correction using guard interval correlation and precise correction using FFT-based pilot signal analysis. This segmentation allows the system to first address large frequency offsets quickly, then refine the correction with more accurate but computationally intensive methods.
2Measurement precision
If carrier frequency error is large in conventional OFDM systems, then frequency error correction is needed, but sub bands are not orthogonal to each other causing interference
Solution Approach 1:
The system applies preliminary frequency correction using guard interval correlation to counteract large carrier frequency errors before the FFT processing stage. By pre-adjusting the frequency offset, the system prevents the loss of orthogonality among sub bands that would otherwise occur with large frequency errors, thereby avoiding inter-sub band interference.
3Measurement precision
If phase difference at effective symbol time interval is used for frequency error estimation, then frequency error can be obtained, but only frequency error of sub band interval or smaller can be estimated
Solution Approach 1:
The patent utilizes the guard interval dimension (time domain correlation) to estimate frequency error, which provides information about the overall frequency offset including components larger than the sub band interval. This complements the frequency domain analysis and extends the estimatable frequency error range beyond what single-sub band analysis can provide.
Data Source
AI summary
A reception device according to the present invention receives a transmission frame including a synchronization symbol string, having a synchronization symbol repeated multiple times, inserted before a data symbol string. The synchronization symbol is obtained by synthesizing a plurality of sub band symbols which are mutually orthogonal and having different carrier frequencies. The carrier frequencies of the sub band symbols are located at an equal predetermined frequency interval. The synchronization symbol includes a repeated synchronization pattern. The reception device detects a rough carrier frequency error from a phase difference of a synchronization pattern correlation value to correct the frequency, and then detects a residual frequency error from an inter-symbol phase difference of each sub band to correct the frequency. The reception device detects a sampling clock frequency error from an inter-sub band phase difference to correct the frequency. Thus, the demodulation error of the data symbol is reduced.