Coarse Frequency Synchronization in OFDM Receivers
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Solution Overview
Problem
Conventional coarse frequency synchronization methods in OFDM receivers face challenges in achieving stable frequency synchronization and require significant computational resources, particularly in compensating for sample offsets within a narrow range.
Innovation Solution
A coarse frequency synchronization apparatus and method that includes a buffer for cyclically shifting demodulated signals, a controller for determining summation intervals and symbol time offsets, a weighted phase reference signal generator, and a partial correlation unit to calculate partial correlation values across sub-bands, allowing for accurate estimation of coarse frequency offsets with reduced computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional frequency synchronization method divides the summation interval into sub-bands and compensates for sample offsets within ±15 samples, then coarse frequency synchronization can be achieved, but the device complexity and computational requirements increase significantly
Solution Approach 1:
The patent divides the frequency spectrum into multiple sub-bands and processes correlation calculations separately for each sub-band. This segmentation allows the system to achieve accurate frequency offset estimation across the entire bandwidth while maintaining manageable computational complexity in each individual sub-band processor.
Solution Approach 2:
The patent performs correlation calculations only over a limited summation interval rather than the entire signal duration. By selecting an optimal summation interval length that balances accuracy requirements with computational constraints, the system achieves sufficient frequency synchronization precision without excessive processing requirements.
2Measurement precision
If the summation interval length is increased to improve frequency offset estimation accuracy, then measurement precision improves, but the computational time and complexity increase
Solution Approach 1:
The patent uses a predetermined summation interval that is optimized to provide sufficient frequency offset estimation accuracy without extending over the entire signal duration. This partial action approach achieves the necessary measurement precision while minimizing computational time requirements.
Solution Approach 2:
The patent adjusts the summation interval length as a controllable parameter to optimize the balance between estimation accuracy and computational efficiency. By tuning this parameter according to specific application requirements, the system can adaptively balance precision and processing time.
Data Source
AI summary
An apparatus and method for performing coarse frequency synchronization in an orthogonal frequency division multiplexing (OFDM) receiver includes cyclically shifting a received signal X(k) by a predetermined shift amount d, determining the length of a summation interval according to a phase coherence bandwidth and a number K of sub-bands into which the summation interval is divided, generating and adjusting a symbol time offset according to the number K of sub-bands, generating a weighted phase reference signal Z(k) which is phase-shifted by the symbol time offset and weighted by a weighting vector determined according to a frequency band, partially correlating the shifted signal X(k+d) and the weighted phase reference symbol Z(k) and calculating a partial correlation value for each of the K sub-bands; and determining the shift amount dmax at a maximum sum of the partial correlation values and outputs the shift amount dmax as an estimated coarse frequency offset.