近空间平台位置不稳定条件下的激光链路性能分析

Performance of optical links in near space under instability of platform position

在建立近空间(near space)高空平台(HAP)位置不稳定性模型的基础上,修正了平台位置不稳定引起的光束指向误差因子,并结合gamma-gamma分布大气模型,推导出基于APD探测器的脉冲位置调制(PPM)光链路误符号率。根据误符号率公式,在极限传输距离的条件下,对比分析高空平台不稳定性、大气湍流和APD增益等因素对近空间HAP间光链路性能的影响。仿真结果表明,在相同的系统带宽条件下,误符号率的变化随着跟踪误差的均方差数值增大而增大;最优APD增益值只与信号光功率以及噪声功率的大小有关,而与系统带宽和跟踪误差无关;改变系统带宽能够有效缓解平台不稳定性对平台间光链路性能的影响,并且跟踪误差均方差值越大,链路改善的效果越明显。

Based on the characteristic of high altitude platform （HAP） position instability in near space, the optical pointing error factor due to HAP position instability is modified. Combining the Gamma- Gamma model, the symbol error probability of pulse position modulation （PPM） on inter-platform opti- cal links is derived. Based on the maximum distance of inter-HAP optical links,the effect of the factors, including high altitude platform position instability,atmosphere turbulence and avalanche photo detector （APD） gain,on the performance of inter-platforms is analyzed. The simulation results show that with the same bandwidth, symbol error probability increases with the increase of root mean square （RIMS） tracking error. The optimal APD gain is related with the power of signal and noise,and is independent of bandwidth or tracking error. The influence of platform jitter on inter-HAp optical link could be weak ened by changing the bandwidth. And the bigger RMS tracking error means more obvious improvement of inter-HAp optical links.