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Joint phase noise and frequency offset estimation and mitigation for optically coherent QAM based on adaptive
Igor Tselniker1, Netta Sigron, Moshe Nazarathy
1EE Department, Technion, Israel Institute of Technology, Technion City, Haifa 32000, Israel.
Optics Express
|May 9, 2012
Summary
This study introduces an improved coherent Minimum Shift Keying (MSK) Detector (MSDD) carrier recovery system for Quadrature Amplitude Modulation (QAM) systems. The novel MSDD system effectively mitigates phase noise and Carrier Frequency Offset (CFO) with an infinite capture range.
Area of Science:
- Optical Communications
- Digital Signal Processing
- Advanced Modulation Techniques
Background:
- Carrier recovery is crucial for coherent optical systems, especially with advanced modulation formats like Quadrature Amplitude Modulation (QAM).
- Existing carrier recovery systems often struggle with Carrier Frequency Offset (CFO) and phase noise, requiring complex structures.
- Previous work established a coherent MSDD system for Quadrature Phase Shift Keying (QPSK).
Purpose of the Study:
- To extend the coherent MSDD carrier recovery system to QAM operation.
- To characterize the Carrier Frequency Offset (CFO) mitigation capabilities of the MSDD for QAM systems.
- To introduce an improved MSDD system that automatically adapts to channel statistics for optimal phase-noise mitigation.
Main Methods:
- Numerical investigation of an improved Minimum Shift Keying (MSK) Detector (MSDD) carrier recovery system for QAM.
- Demonstration of the adaptive structure's dual functionality for phase noise and CFO mitigation.
- Performance evaluation using 16-QAM with coherent-grade lasers and comparison with existing carrier recovery techniques.
Main Results:
- The improved MSDD system automatically mitigates both phase noise and CFO without separate structures.
- The system exhibits an in-principle infinite CFO capture range, surpassing prior systems.
- For 16-QAM, the MSDD system offers superior performance-complexity tradeoffs compared to blind-phase-search and maximum likelihood detection methods.
- Variants with reduced complexity and slightly degraded performance are presented.
- The system supports seamless, on-the-fly switching between different m-QAM constellation sizes (e.g., 16-QAM and QPSK).
Conclusions:
- The novel adaptive MSDD carrier recovery system effectively handles phase noise and CFO in QAM systems.
- The system's infinite CFO capture range and adaptive capabilities offer significant advantages for optical networks.
- The ability to dynamically switch modulation formats enhances network flexibility and efficiency.
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