面向快衰落信道的三维概率整形FSO系统研究OA

To address the challenges of low spectral efficiency and optical power constraints in free space optical(FSO)communication under strong turbulent fast fading channels,this paper proposes a joint transmission scheme combining 3D geometric and probabilistic constellation shaping.This scheme exploits the optimization of the signal space's geometric construction and statistical distribution at the transmitter to directly enhance system robustness against channel fading and nonlinear impairments.First,breaking the dimensional limitations of the traditional 2D complex plane,a 3D signal space based on cubic lattices is constructed.Under the constraint of constant average symbol energy,the spatial degrees of freedom are utilized to significantly increase the minimum Euclidean distance between constellation points.Second,the Maxwell-Boltzmann distribution is introduced to perform probabilistic weighting on the 3D constellation.This concentrates signal energy towards the low-energy geometric center,effectively reducing the average transmit electrical power of DCO-OFDM signals and mitigating clipping distortion caused by the nonlinear region of optoelectronic devices.Simulation results demonstrate that under Gamma-Gamma fast fading channels,the synergistic design of geometric construction and probability distribution yields significant additive gains.At a bit error rate(BER)of 10-3,the proposed scheme achieves a signal-to-noise ratio gain of approximately 3 dB over 3D geometric shaping alone.Furthermore,it outperforms the traditional 2D uniform distribution scheme by more than 10 dB.These results successfully validate the transmission reliability of the system.