Robust multifunctional single-tone training sequence for free-space optical communication in strong turbulence

Area of Science:

• Optical Communications
• Signal Processing
• Turbulence Mitigation

Background:

• Free-space optical (FSO) communication suffers from signal degradation due to atmospheric turbulence.
• Accurate frequency offset estimation (FOE) and phase correction are critical for diversity reception in FSO systems.
• Existing methods face challenges in turbulent environments and with complex diversity combining.

Purpose of the Study:

• To develop a robust FOE method for FSO communication under strong turbulence.
• To propose a low-overhead training sequence for efficient phase correction in diversity branches.
• To demonstrate the effectiveness of the proposed algorithms in a practical FSO system.

Main Methods:

• A novel robust frequency offset estimation (FOE) algorithm is proposed.
• A low-overhead training sequence is designed for inter-branch phase correction.
• A 10-Gbaud dual-polarization quadrature amplitude modulation (QAM) transceiver system was implemented and tested.
• Digital signal processing (DSP) was performed in a simulated turbulent channel environment.

Main Results:

• The proposed FOE method effectively handles frequency offsets in turbulent FSO channels.
• The single training sequence enables efficient phase correction for diversity branches.
• The implemented system demonstrated successful data reception and demodulation.
• The experimental results validate the robustness and effectiveness of the proposed algorithms.

Conclusions:

• The developed FOE technique and phase correction method significantly enhance FSO communication performance in turbulent conditions.
• The proposed low-overhead training sequence simplifies diversity reception implementation.
• This work provides a viable solution for reliable FSO communication systems operating in challenging environments.