Performance optimization of spatial diversity antenna using hybrid combination for terrestrial optical wireless communication

The coherent laser signals of optical wireless communication suffer dramatic intensity fluctuations due to the atmospheric turbulence effect. A larger receiver aperture could only increase the average laser intensity without adaptive optics. Adaptive optics and wavefront reconstruction are popular in laser wireless transmission systems. Still, the alternative spatial diversity receivers are more convenient and economical to mitigate the irradiance scintillation, in which the antenna array combines multiple signals in digital signal processing or analog laser beams coherent combination. We provide channels correlated spatial diversity models and compare the performances of digital and optical combinations. In addition, reception experiments with a 19-aperture optical combination for horizontal 2 km transmission showed a ten times increase in average optical intensity and decreased scintillation index to 16 %. The large-scale spatial diversity receivers of 64-aperture that adopt hybrid optical and digital combinations are proposed to reduce the complexity of digital processing or cascaded optical combination structure.