针对脉冲位置调制(PPM)和差分脉冲位置调制(DPPM)等方法存在的问题，提出了一种新的双宽度多脉冲位置调制(DDMPPM)。给出了相应的编码结构，分析了传输容量、带宽需求和平均功率效率，研究了弱湍流信道模型下的差错性能，并与开关键控(OOK)、脉冲位置调制(PPM)、多脉冲位置调制(MPPM)、脉冲宽度调制(PWM)和差分脉冲位置调制(DPPM)等调制方式进行了比较。理论分析和仿真结果表明，DDMPPM 的误包率与MPPM 相近，劣于PPM 和DPPM，但明显优于OOK 和PWM，而且比PPM 和PWM 具有更高的带宽效率和传输容量；另外DDMPPM 与PPM 和MPPM 一样，符号长度固定，不会引起调制器等待或缓冲器溢出等问题，同时增加了内置符号同步能力，简化了接收机的设计，因而在自由空间光通信网络中将具有一定的应用前景。

A new modulation scheme called Dual-Duration-Multi-Pulse Position Modulation (DDMPPM) is proposed for free-space optical communication systems by resolving the problems which exist in Pulse Position Modulation (PPM) and Differential Pulse Position Modulation (DPPM). After introducing symbol structure, information transmission rate, bandwidth requirement and average transmission power are studied. Meanwhile, the packet error rate is analyzed based on weak turbulence channel mode. After compared with On-off Keying (OOK), PPM, MPPM, PWM and DPPM, the theoretical and simulation results show that the Packet error rate of DDMPPM, which corresponds to MPPM, is higher than that of PPM and DPPM, but obviously less than OOK and PWM. DDMPPM has no problem such as overflow and underflow in the buffer by fixing the symbol length, and has built-in symbol synchronization. Hence, DDMPPM is superior in free space optics communication systems.