Receiver Data-Aided Automatic Frequency Control Low SNR
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Solution Overview
Problem
Conventional automatic frequency control (AFC) systems in communication systems face performance degradation at low signal-to-noise ratio (SNR) levels, particularly in the 'coverage enhancement' mode of LTE specifications, where the receiver struggles to accurately track the transmitter's frequency due to low SNR conditions.
Innovation Solution
The method involves using duplicated frames carrying the same data symbols, even when scrambled with different sequences, to estimate the frequency offset between the transmitter and receiver. This includes identifying data symbols in multiple frames, estimating the frequency offset using both pilot and data symbols, and resolving any ambiguity in the estimation to adjust the receiver's frequency effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional AFC techniques are used relying solely on pilot symbols, then the system operates with standard complexity, but the frequency offset estimation accuracy degrades at low SNR levels
Solution Approach 1:
The patent combines pilot symbols and data symbols to estimate frequency offset. Specifically, it uses both known pilot symbols and repeated data symbols from multiple frames to jointly estimate the frequency offset, thereby improving estimation accuracy at low SNR conditions where pilot-only methods fail.
Solution Approach 2:
The patent utilizes repeated copies of data symbols across multiple frames. By transmitting the same data in multiple frames and using these repeated symbols for frequency offset estimation, the system gains additional reliable reference points for accurate frequency tracking in low SNR environments.
2Reliability
If duplicated frames with scrambled data symbols are used for frequency offset estimation, then the estimation reliability improves at low SNR, but the processing complexity increases
Solution Approach 1:
The patent changes the approach by using repeated data symbols from multiple frames with different scrambling sequences. Instead of relying solely on pilot symbols, it exploits the temporal repetition of data across frames and the known scrambling structure to improve estimation reliability without requiring additional hardware complexity.
Solution Approach 2:
The system uses feedback from multiple received frames to improve frequency offset estimation. By accumulating information from repeated transmissions and using the known scrambling sequences, the receiver can iteratively refine its frequency offset estimate, improving reliability through feedback-based processing.
Data Source
AI summary
A method in a receiver includes receiving from a transmitter a signal including at least first and second frames that carry same data. First and second data symbols are identified in the respective first and second frames, wherein the first symbol has a same data value as the second data symbol. A frequency offset between the transmitter and the receiver is estimated based at least on the identified first and second data symbols. A frequency of the receiver is adjusted based on the estimated frequency offset.