Transmit alternate laser selection with time diversity for FSO communications

Area of Science:

• Optical Communications
• Wireless Communication Systems
• Signal Processing

Background:

• Free-space optical (FSO) communication systems face performance degradation due to atmospheric turbulence and pointing errors.
• Limited time diversity in turbulent channels restricts the effectiveness of conventional diversity techniques.
• Intensity Modulation/Direct Detection (IM/DD) systems are susceptible to channel impairments.

Purpose of the Study:

• To introduce a novel Transmit Alternate Laser Selection (TALS) scheme for FSO systems.
• To enhance system reliability and achieve significant diversity gain under limited time diversity conditions.
• To mitigate the effects of atmospheric turbulence and misalignment fading.

Main Methods:

• Proposed a transmit diversity technique utilizing rotating selection of Time Diversity Order (TDO) from available lasers.
• Implemented repetition coding with TDO information bits, retransmitting each bit TDO times.
• Derived closed-form asymptotic bit error-rate (BER) expressions considering Gamma-Gamma turbulence and misalignment fading models.

Main Results:

• The TALS scheme effectively exploits available time diversity in turbulent channels.
• Achieved significant diversity gain, with a derived diversity order of (2L + 1 - TDO)TDO/2.
• The proposed scheme demonstrates improved performance in moderate-to-strong turbulence and misalignment conditions.

Conclusions:

• The TALS scheme offers a robust solution for improving FSO communication performance.
• The method effectively leverages limited time diversity and channel state information (CSI).
• The derived BER expressions provide valuable analytical tools for system design and performance evaluation.