Multiple transmitter performance with appropriate amplitude modulation for free-space optical communication.

Area of Science:

• Optical communications
• Atmospheric physics
• Signal processing

Background:

• Free-space optical communication signals experience intensity fluctuations due to atmospheric turbulence, leading to signal fades.
• The gamma-gamma probability density function models scintillation for single beams.
• Multiple independent beams can mitigate scintillation, but true independence is challenging.

Purpose of the Study:

• To develop a generalized model for irradiance distribution from multiple, partially correlated beams in free-space optical communication.
• To evaluate the effectiveness of this model against wave-optics simulations.
• To assess the performance improvement offered by pulse-position modulation in conjunction with multi-beam transmission.

Main Methods:

• Developed an approximate analytical model for the probability distribution of irradiance from the sum of partially correlated beams.
• Conducted wave-optics simulations to validate the analytical model.
• Implemented and analyzed a pulse-position modulation scheme to combat signal fades.

Main Results:

• The generalized model accurately predicts irradiance distribution for partially correlated beams.
• Increased number of transmitted beams demonstrably reduces scintillation.
• Pulse-position modulation significantly enhances performance compared to traditional on/off keying.

Conclusions:

• The developed model provides a more realistic approach to mitigating scintillation in free-space optical communications.
• Multi-beam transmission is an effective strategy for reducing signal fades caused by atmospheric turbulence.
• Combining multi-beam techniques with advanced modulation schemes like pulse-position modulation offers substantial performance gains.