提出了一种结合副载波强度调制直接探测技术和全光放大转发中继的自由空间光通信（FSO）系统的基本结构，考虑背景噪声和放大自发辐射噪声对系统性能的影响，建立了Gamma-Gamma湍流模型下的全光通信系统模型。提出了两种中继协作方案，即全活跃中继方案与选择中继方案，基于相应的方案给出功率分配方式，仿真对比了中继辅助传输链路与直传链路的中断概率，以及在不同信道参数及中继数下采用这两种方案的系统中断概率。结果表明，中继传输能够明显改善链路的性能，选择中继方案优于全活跃中继方案。

A fundamental structure of all-optical free-space optical communication (FSO) system is presented. The system adopts subcarrier intensity modulation and all-optical amplify-and-forward relaying, and furthermore, it considers the effect of background noise and amplified spontaneous emission noise. A system model of the all-optical relaying FSO system under Gamma-Gamma turbulence condition is established. Two novel cooperative schemes, all-active relaying scheme and selective relaying scheme, are presented, and their corresponding power allocation modes are provided. The outage probability of the relay-assisted transmission is compared with that of the direct link, and the outage probability of the two schemes for different channel parameters and number of relays is analyzed by simulation. The simulation results show that the performance of the link can be improved obviously by the relayed transmission, and the performance of the selective relaying scheme is superior to that of the all-active relaying scheme.