Soft Decision Common Phase Error Estimation in OFDM Systems
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Solution Overview
Problem
In wireless communication systems, especially OFDM systems with high modulation order and carrier frequency, common phase errors (CPE) caused by phase noise and uncompensated frequency offset lead to constellation rotation, degrading performance, and existing pilot signal-based CPE estimation methods are limited by insufficient pilot signals.
Innovation Solution
A soft decision-based decision-directed common phase error (DD-CPE) estimation method that uses the probability of detected data symbols and channel state information to improve CPE estimation, incorporating maximum likelihood (ML) and post minimum mean square error (MMSE) processing for enhanced accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pilot signal based CPE estimation is used, then CPE estimation can be performed, but the estimation quality is limited due to insufficient number of pilot signals
Solution Approach 1:
The system uses the received data symbols themselves (after detection) to perform CPE estimation, rather than relying on external pilot signals. The detected symbols serve dual purposes: as data to be decoded and as references for CPE estimation, eliminating the need for separate pilot signals.
Solution Approach 2:
The patent introduces soft decision information (probabilities) as an intermediary between the detected symbols and the CPE estimation process. This soft information mediates the estimation by providing reliability weights that improve the quality of CPE estimation without requiring additional pilot signals.
2Measurement precision
If hard decision of detected transmit signal is used as known pilot signals, then CPE estimation quality is improved, but accuracy deteriorates in low signal-to-noise ratio environments
Solution Approach 1:
The patent changes the parameter representation from hard decisions (discrete symbol values) to soft decisions (probability distributions). By using probability values that represent the confidence level of each detected symbol, the system maintains better reliability in low SNR conditions while still enabling CPE estimation.
Solution Approach 2:
Instead of making definitive hard decisions on all symbols, the system uses partial information (probabilities) that reflect the uncertainty in detection. This partial action approach allows the CPE estimation to account for detection errors, improving reliability in challenging channel conditions.
Data Source
AI summary
A method and apparatus are provided. The method includes receiving, by at least one antenna of a receiver, at least one signal from a transceiver, detecting at least one data symbol within the at least one signal, determining a probability associated with the at least one detected data symbol, determining channel state information (CSI) of at least one channel between the transceiver and the at least one antenna of the receiver, and estimating a common phase error (CPE) of the at least one signal based on the probabilities associated with the at least one detected data symbol and the CSI of the at least one channel.