Free-space optical (FSO) communication has shown the capability of providing a way to establish high-bandwidth links for a variety of applications, including intersatellite communication, airborne internet, underwater communication, and interbuilding and indoor communication in urban settings. In addition to the bandwidth advantages, FSO communication also provides advantages in security, license-free connectivity, and compatibility with existing cellular and other radio frequency (RF) networks systems. To design and deploy an FSO system efficiently, it is critical to characterize the link channel and thus to analyze the link transmission capacity for any given scenario. Moreover, the existing modulation methods utilized in RF links cannot be exploited in FSO systems without adaptation to the unique needs and limitations of optical systems. Therefore, the study of optical signal modulation techniques plays a key role in investigating channel efficacy.

This special issue focuses on the current state-of-the-art channel modeling and signal modulation in FSO communication systems. We invite original contributions on a variety of topics for this special issue.

Potential topics include, but are not limited to:

• Line-of-sight (LOS) modeling
• Nonline-of-sight (NLOS) modeling
• Scattering and bouncing models
• Optical sources and detectors modeling
• Weather effects modeling
• Atmospheric turbulence channel modeling
• Underwater modeling
• Analogue intensity modulation
• Digital baseband modulation
• Subcarrier intensity modulation
• Optical polarization shift keying
• OFDM free-space optical communication
• MIMO free-space optical communication