Blind Equalization Based on Modified Third-Order Moment Algorithm for PAM-PPM Optical Signals in FSO Communication

Area of Science:

• Optical Communications
• Signal Processing

Background:

• Free-space optical (FSO) communication systems face challenges from atmospheric turbulence, impacting signal quality.
• Pulse Amplitude Modulation-Pulse Position Modulation (PAM-PPM) is a key technology for high-speed FSO.

Purpose of the Study:

• To propose and evaluate a novel blind equalization scheme to mitigate turbulence effects on PAM-PPM signals in FSO.
• To enhance the robustness and performance of FSO communication systems.

Main Methods:

• Development of a modified third-order moment algorithm (MTOMA) for blind equalization.
• Comparison of MTOMA with fourth-order moment algorithms like Constant Modulus Algorithm (CMA) and Modified Constant Modulus Algorithm (MCMA).
• Simulation analysis under various atmospheric turbulence conditions and pointing errors.

Main Results:

• MTOMA demonstrates greater robustness to noise than CMA and MCMA without increased complexity.
• MTOMA achieves faster convergence rates across weak, moderate, and strong turbulence conditions.
• MTOMA significantly improves bit error rate (BER) performance compared to CMA and MCMA.

Conclusions:

• The proposed MTOMA is an effective solution for mitigating turbulence-induced distortion in PAM-PPM FSO systems.
• MTOMA offers a superior alternative to existing algorithms, enhancing communication reliability and speed.
• Further BER improvement is possible by combining MTOMA with the Decision-Directed Least Mean Square (DDLMS) algorithm post-convergence.