Joint timing/frequency offset estimation and correction based on FrFT encoded training symbols for PDM CO-OFDM...

Area of Science:

• Optical Communications
• Signal Processing
• Information Theory

Background:

• Polarization Division Multiplexing (PDM) and Coherent Optical Orthogonal Frequency-Division Multiplexing (CO-OFDM) are advanced techniques for high-capacity optical transmission.
• Accurate estimation of timing offset (TO) and frequency offset (FO) is critical for the performance of PDM-CO-OFDM systems.
• Existing estimation methods can struggle with poor optical signal-to-noise ratio (OSNR) and nonlinear interference.

Purpose of the Study:

• To propose a novel joint timing offset (TO) and frequency offset (FO) estimation algorithm for PDM-CO-OFDM systems.
• To leverage the time-frequency properties of fractional Fourier transform (FrFT) encoded training symbols for improved estimation.
• To evaluate the robustness and accuracy of the proposed algorithm against classical methods.

Main Methods:

• A joint TO and FO estimation algorithm is developed utilizing the time-frequency characteristics of FrFT encoded training symbols.
• The algorithm's performance is compared to the classical Schmidl & Cox method.
• Experimental verification is performed in a 106.8 Gbit/s 16-QAM PDM-CO-OFDM transmission system.

Main Results:

• The proposed algorithm demonstrates robust TO estimation even with low OSNR and nonlinear interference.
• A wide FO estimation range of [-5GHz, +5GHz] is achieved with normalized estimation errors below 0.008.
• Experimental results confirm the algorithm's effectiveness and accuracy without inducing bit error rate (BER) degradation.

Conclusions:

• The proposed joint TO/FO estimation algorithm offers a robust and accurate solution for PDM-CO-OFDM systems.
• The FrFT-based approach enhances performance in challenging OSNR conditions.
• The algorithm is experimentally validated and suitable for high-speed optical transmission systems.