On the Performance of Coherent OFDM Systems in Free-Space Optical Communications

This paper presents a new model of a coherent orthogonal frequency division multiplexing free space optical communication (OFDM-FSO) system that can be tuned with the virtual local oscillator, under the Gamma-Gamma atmospheric turbulence channel, not only considering the intensity scintillation but considering the phase noise caused by atmospheric turbulence effect on the performance of the system as well. The mapping mode of the OFDM signal uses 16-quadrature amplitude modulation (QAM) with better performance. On this basis, we derived the closed form of the symbol error rate and interrupt probability, respectively. In this paper, we analyzed under the premise of the different number of subcarriers, the influence of each parameter of atmospheric channel on the bit error, and the communication interrupt performance of the OFDM-FSO system, respectively. The results show that the coherent OFDM-FSO system can obtain higher sensitivity and can overcome the bad atmosphere influence to obtain good performance of the system.