中文摘要：

为避免自由空间光通信中的信道衰落，提高抗干扰能力，采用脉冲位置调制（PPM），提出一种基于光子计数的单数据流软入软出迭代解调算法。在受限散粒噪声Poisson信道模型下，推导迭代解调算法，并基于该算法给出4PPM的简化方案。针对重复码和串行级联码分别进行数值仿真并分析其性能，实验结果表明，该简化算法能降低计算复杂度，且易于硬件实现。

英文摘要：

To overcome the channel fading and improve the anti-interference capability in free-space optical communication, a coded Pulse Position Modulation（PPM） photon-counting based iterative demodulation scheme by utilizing Soft-input Soft- output（SISO） for single data stream is proposed, On the assumption of shot noise limited Poisson channels, the iterative demodulation algorithm is derived and on the basis of it, a simplified scheme is proposed for 4-ary PPM. The numerical results under the conditions of Repetition Code（RC） and Serial Concatenated Code（SCC） also with analysis of system performance are illustrated. The simulations show that the scheme can provide a relatively good system Bit Error Rate（BER） performance with low computational complexity and is easy for hardware realization：