OFDM Pilot Sub-carrier Position Determination via Correlation
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Solution Overview
Problem
Existing methods for determining the positions of pilot sub-carriers in OFDM symbols are either inaccurate in multipath fading and low signal noise ratio conditions or sensitive to clock frequency offsets, which can lead to incorrect frame and frequency synchronization.
Innovation Solution
A method that extracts theoretical and hypothetical pilot sequences from both a theoretical and received OFDM symbol, calculates correlations between adjacent elements, and selects the sequence with the maximum modulus value to determine pilot sub-carrier positions, thereby shortening determination time and increasing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the first method (utilizing periodic distribution and energy characteristics) is used to determine pilot sub-carrier positions, then the determination time is short, but the accuracy deteriorates in seriously multipath fading and low signal noise ratio conditions
Solution Approach 1:
The patent performs preliminary fractional frequency offset estimation and correction before determining pilot sub-carrier positions. This preliminary action prepares the received OFDM symbol by compensating for frequency offsets, creating a better foundation for subsequent pilot position detection and improving accuracy without significantly increasing total determination time
Solution Approach 2:
The patent introduces an intermediary correlation calculation process that compares received pilot sequences with expected pilot sequences. This intermediary step acts as a mediator between the raw received signal and the final position determination, enabling accurate detection even in multipath fading conditions by identifying the correlation peak
2Measurement precision
If the second method (utilizing periodic distribution and correlation characteristics) is used to determine pilot sub-carrier positions, then the resolution performance is higher, but the method becomes sensitive to errors caused by clock frequency offsets and requires at least two OFDM symbol periods
Solution Approach 1:
The patent performs preliminary fractional frequency offset estimation and correction using only one OFDM symbol period before pilot position determination. This preliminary action eliminates the need to wait for multiple symbol periods, achieving high accuracy with single-symbol processing time
Solution Approach 2:
The patent changes the approach from utilizing correlation between strong pilot signals (which is sensitive to clock frequency offsets) to utilizing correlation between expected and received pilot sequences after frequency offset correction. This parameter change in the detection method makes the system immune to clock frequency offset errors while maintaining high resolution performance
3Measurement precision
If the second method is used to determine pilot sub-carrier positions, then the resolution performance is higher, but the reliability deteriorates due to sensitivity to clock frequency offsets that may cause wrong decisions
Solution Approach 1:
The patent applies preliminary anti-action by performing fractional frequency offset estimation and correction before pilot position determination. This preemptive measure counteracts the harmful effect of clock frequency offsets before they can cause wrong decisions, ensuring reliable synchronization
Solution Approach 2:
The patent introduces an intermediary frequency offset correction process that mediates between the received signal and the pilot position detection. This intermediary action eliminates the direct sensitivity to clock frequency offsets, making the determination process reliable and immune to such errors
Data Source
AI summary
Techniques for determining positions of pilot sub-carriers in a received OFDM symbol are described. Components of pilot sub-carriers from a theoretical OFDM symbol are extracted to form M theoretical pilot sequences according to M possible distributions in frequency domain of the pilot sub-carriers in the theoretical OFDM symbol. Components of pilot sub-carriers from the received OFDM symbol are also extracted to form K hypothetical pilot sequences according to K possible distributions in frequency domain of pilot sub-carriers in the received OFDM symbol. The correlations of every two adjacent elements of the theoretical pilot sequences are calculated to get M corresponding theoretical correlation sequences, and the correlations of every two adjacent elements of the hypothetical pilot sequence are also calculated to get K corresponding hypothetical correlation sequences. Sequence correlations between the hypothetical correlation sequences and the theoretical correlation sequences are then calculated. The positions of pilot sub-carriers in the received OFDM symbol can be determined from the one that has the maximum modulus value.