Robust multifunctional single-tone training sequence for free-space optical communication in strong turbulence

In free-space optical (FSO) communication, the received optical power will be significantly diminished in environments characterized by strong turbulence, making effective frequency offset (FO) estimation challenging and severely degrading signal quality. Additionally, to enhance receiver sensitivity, diversity reception is frequently employed at the receiving end. However, prior to combining the diversity branches, it is essential to perform phase correction between these branches. To address these two challenges, this paper proposes a robust frequency offset estimation (FOE) method and a low-overhead training sequence for phase correction with only one training sequence. Finally, a 10-Gbaud dual-polarization quadrature amplitude modulation (QAM) transceiver system is implemented, where data reception, demodulation, and digital signal processing (DSP) are performed in a simulated turbulent channel, demonstrating the effectiveness of the proposed algorithm.