针对现有光空间脉冲位置调制频谱效率低、激光器利用率不高等问题, 将分层技术与空间脉冲位置幅度调制相结合, 提出了一种适合于大气激光通信的多层空间脉冲位置幅度调制方案.通过 额外增加少量几个激光器构成多层结构, 并通过脉冲位置幅度调制中的脉冲位置携带比特信息, 不同层通过脉冲幅度得到区分.介绍了系统中层映射、空间脉冲位置幅度映射及其逆映射的原理, 并 推导出该方案的误码率表达式.利用蒙特卡洛仿真方法进一步验证了该方案的正确性, 并与传统空间调制系统的性能进行了对比.结果表明: 与传统光空间调制系统相比, 所提方案提高了系统的频 谱效率, 且所用激光器数目更少.在传输比特相同的条件下, 相对于(32,4,128)-空间脉冲位置调制系统, (9,4,8,2)-多层空间脉冲位置幅度调制系统的频谱效率提高了16倍, 当误码率为10－3时, 其信噪比改善了约1 dB, 且所用激光器数目不到前者的1/3.其中, 括号中的参数分别表示激光器数目、探测器数目、采用调制方式的阶数及层数, 层数为1时忽略.

In order to solve the problems of low spectral efficiency and low laser utilization of existing optical spatial pulse position modulation, a layered spatial pulse position amplitude modulation method suitable for atmospheric laser communication is proposed by combining layering technology with spatial pulse position amplitude modulation. In this method, a small number of additional lasers are added to form a multilayer structure, and the pulse position in the pulse position amplitude modulation is used to carry bit information, and the pulse amplitude is used to distinguish different layers. The principle of system layer mapping, spatial pulse position amplitude mapping and its inverse mapping is descripted in detail. Moreover, the bit error rate expression of the proposed scheme is derived. The Monte Carlo simulation method is utilized to further verify its reliability and compare it with the traditional spatial modulation methods. Simulation results show that the proposed scheme can greatly improve the spectral efficiency and reduce the used laser number. For example, at the same transmission bits, the spectral efficiency of (9,4,8,2)- spatial pulse position amplitude modulation scheme is 16 times that of (32,4,128)- spatial pulse position modulation scheme. When bit error rate is 10－3, our proposal improves the signal-to- noise ratio by about 1 dB with employ less than 1/3 number of lasers that used in the (32,4,128)- spatial pulse position modulation scheme. Among them, the parameters in parentheses respectively indicate the number of lasers, the number of detectors, the order of the modulation method, and the number of layers, which are ignored when the number of layers is 1.