Turbulence induced fading mitigation in satellite optical communications using a single subcarrier time delay diversity

A single subcarrier intensity modulation (SIM) with time delay diversity (TDD) is proposed to mitigate atmospheric turbulence-induced fading in satellite optical communications. As the scintillation causes signal to fade randomly, time delay longer than the channel correlation time is used on the orthogonal phase of the subcarrier to avoid the signal totally fading. In order not to have the adaptive threshold, the maximum order of phase-shift keying (PSK) in SIM is QPSK. Therefore, it can be applied to TDD by separating QPSK into BPSK. Simulations are conducted under the atmospheric channel, which is modeled based on the Kolmogorov power-law spectrum and Taylor frozen hypotheses. The simulation results demonstrate that the in-phase and quadrature phase of the subcarrier can be adopted as the orthogonal resources in TDD scheme.