Carrier Phase Estimation Using Pilot and Data Symbols

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Solution Overview

Problem

Existing carrier phase estimation methods in QAM modulation receivers face instability and accuracy issues due to decision errors, particularly when using decision-directed PLL methods, and linear interpolation between pilot symbols is not robust enough to handle errors effectively.

Innovation Solution

A method that combines decision-directed estimation with pilot-symbol-based estimation, using a phase trajectory function to interpolate carrier phase between pilot symbols based on estimated phases of demodulated data symbols, which includes computing a linear or nonlinear phase trajectory function that fits the phase trajectory at pilot symbols and approximately fits the estimated phases at data symbols, and selecting coefficients based on optimization criteria and spectral density of phase noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If decision-directed PLL method is used for carrier phase estimation, then excellent performance is achieved when no decision errors are made, but decision errors drive the PLL from its stable operating point causing cycle-slip

Engineering Contradiction:

Improvephase estimation accuracyVSAvoidstability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

Pilot symbols are introduced as intermediary reference signals between transmitter and receiver. These known pilot symbols serve as a stable reference that does not suffer from decision errors, allowing the receiver to correct phase drift and pull the PLL back from cycle-slip conditions while maintaining accurate phase estimation between pilot symbols

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

Pilot symbols are transmitted preliminarily at known positions in the signal stream before data symbols. The receiver uses these pre-transmitted pilot symbols to establish phase reference and perform preliminary phase correction, enabling subsequent data symbols to be decoded with accurate phase information

Inventive Principle:

Principle #10Preliminary action

2Ease of operation

If linear interpolation is used between pilot symbols, then phase estimation is provided, but the interpolation is not robust enough to handle errors effectively

Engineering Contradiction:

Improveinterpolation simplicityVSAvoiderror robustness

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The receiver performs decision-directed phase estimation using decoded data symbols and feeds this information back to refine the phase trajectory between pilot symbols. This feedback mechanism allows the system to adapt to actual channel conditions and correct interpolation errors, making the process robust while maintaining simplicity

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS8971424B2Combining pilot-symbol-based phase estimation with data-symbol-based phase estimation

Publication Date: 2015.03.03 CERAGON NETWORKS

AI summary

A method for a receiver to estimate phase of a carrier wave, including receiving a carrier wave carrying pilot symbols and data symbols extending between the pilot symbols, determining phase of the carrier wave at received pilot symbols, and interpolating the phase of the carrier wave at points between pilot symbols based, at least in part, on an estimated phase of demodulated data symbols. Apparatus for estimate phase of a carrier wave, including a unit for determining phase of the carrier wave at received pilot symbols, and a unit for interpolating the phase of the carrier wave at points between pilot symbols based, at least in part, on an estimated phase of demodulated data symbols. Related apparatus and methods are also described.