A shared local oscillator spatial diversity PM-CO-OFDM systems based on group timing synchronization and diversity branch phase correction in satellite-to-ground optical communications

Due to the complexity and strong fluctuations of atmosphere turbulence, it is always a challenging task to mitigate atmospheric turbulence effects in space optical communications. In this paper, we demonstrate a shared local oscillator (LO) spatial diversity polarization multiplexing coherent optical orthogonal frequency division multiplexing (PM-CO-OFDM) system based on group timing synchronization and diversity branch phase correction in downstream low earth orbit satellite-to-ground (LEO-StG) optical communications. For the shared LO coherent receiver system, the maximal ratio combining (MRC) technique is used at the receiver to improve the system performance, and the diversity gain is found to depend on the relative phase offset (RPO) among the different branches. Simulation results under different turbulence channels not only demonstrate that the RPO can be effectively compensated by group timing synchronization and diversity branch phase correction, but also show the improvement in receiver sensitivity. Furthermore, the number of optimal branches is also investigated. The superiorities of such spatial diversity scheme make it highly desirable for potential application in LEO-StG optical communications. •A shared LO spatial diversity systems is proposed for downstream LEO-StG communications.•The relative phase offset among the branches can be effectively compensated.•The receiver sensitivity is obviously improved under different turbulence regimes.•The optimal branch number is 4 when both system complexity and diversity gain are considered.