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Experimental analysis of singularity-avoidance techniques for CMA equalization in DP-QPSK 112-Gb/s optical systems
Valery N Rozental1, Thiago F Portela, Diego V Souto
1OCNLab, Department of Electrical Engineering, University of Brasilia, Brazil.
Optics Express
|September 22, 2011
Summary
We experimentally compared three algorithms for digital signal processing in 112-Gb/s receivers, finding the Constrained algorithm best for mitigating signal singularities during system startup.
Area of Science:
- Optical communications
- Digital signal processing
- Telecommunications engineering
Background:
- The singularity problem in digital coherent receivers can degrade signal quality.
- Existing algorithms for mitigating singularities, such as Constrained, Two-Stage, and Multi-User CMA, have not been extensively compared experimentally.
- Accurate emulation of real-world transmission impairments is crucial for evaluating receiver performance.
Purpose of the Study:
- To experimentally compare the performance of Constrained, Two-Stage, and Multi-User Constant Modulus Algorithms (CMAs) in mitigating singularities in DP-QPSK 112-Gb/s receivers.
- To evaluate the effectiveness of these algorithms under realistic transmission conditions, including amplifier noise, polarization mode dispersion (PMD), and chromatic dispersion.
- To identify the most suitable algorithm for system startup and overall performance.
Main Methods:
- Experimental investigation of DP-QPSK 112-Gb/s receivers.
- Implementation and comparison of three CMA algorithms: Constrained, Two-Stage, and Multi-User.
- Emulation of transmission impairments: amplifier noise, first-order PMD, and chromatic dispersion.
- Systematic evaluation of singularity mitigation capabilities under varied conditions.
Main Results:
- All tested algorithms (Constrained, Two-Stage, Multi-User CMA) effectively mitigated signal singularities.
- The Constrained and Multi-User algorithms, designed for system startup, outperformed the Two-Stage algorithm in specific scenarios.
- The Two-Stage algorithm showed limitations as it does not differentiate between system startup and steady-state operation.
- The Constrained algorithm demonstrated high effectiveness and low computational complexity.
Conclusions:
- The Constrained CMA algorithm is recommended for mitigating singularities in DP-QPSK 112-Gb/s receivers due to its effectiveness and computational efficiency.
- Algorithm choice is critical, especially during system startup, where specialized algorithms like Constrained and Multi-User show advantages.
- Experimental validation under emulated impairments confirms the practical applicability of these digital signal processing techniques.
