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Optimized pilot structure for PS-PDM ultrahigh-order QAM coherent optical transmission
Optics Letters
|March 15, 2024
Summary
A new pilot structure for probabilistic shaped (PS)-polarization division multiplexing (PDM) M-ary quadrature amplitude modulation (MQAM) enhances coherent optical transmission. This method improves nonlinear equalization and spectral efficiency for higher data rates.
Area of Science:
- Optical Communications
- Signal Processing
Background:
- Probabilistic shaping (PS) in M-ary quadrature amplitude modulation (MQAM) is crucial for advanced coherent optical transmission.
- Polarization division multiplexing (PDM) is a standard technique to double spectral efficiency.
Purpose of the Study:
- To propose and demonstrate a novel pilot structure for PS-PDM-MQAM coherent optical systems.
- To enable simultaneous use of pilot symbols across all digital signal processing (DSP) modules.
Main Methods:
- A general pilot structure using a portion of PS-MQAM symbols as pilots with identical information entropy.
- Simultaneous application of pilot symbols in polarization de-multiplexing, frequency offset estimation, carrier phase recovery, and nonlinear/linear equalization.
Main Results:
- The proposed MQAM pilot structure effectively captures signal nonlinearities, enhancing nonlinear equalization performance.
- Remarkable spectral efficiencies of 16.190 bit/s/Hz for 1024QAM and 20.381 bit/s/Hz for 4096QAM were achieved.
- Optimized pilot ratio of 5% was identified for maximizing achievable information rates (AIRs).
Conclusions:
- The novel pilot structure offers significant performance improvements in PS-PDM-MQAM systems.
- This approach enhances nonlinear equalization and boosts spectral efficiency.
- The optimized pilot ratio maximizes data transmission rates in coherent optical systems.
