Atmospheric optical subcarrier modulation systems using space-time block code

Optical communications through clear atmospheric links can provide high-speed communications where cables cannot be installed easily. However, on atmospheric optical links, the turbulence-induced intensity fluctuations deteriorate the quality of received optical signals. In this paper, we propose two atmospheric optical subcarrier modulation systems using space-time block codes (STBC) with coherent and differential detection to realize high-speed communications on atmospheric optical links. In the proposed systems STBC is used to overcome the influence of the turbulence-induced fading and to get the space diversity gain. We show that the proposed systems can achieve the better bit error rate (BER) than the atmospheric optical subcarrier modulation systems with the single transmit aperture (antenna) in the presence of the scintillation. Moreover, we prove that the differential STBC scheme is 3 dB worse than coherent STBC scheme.