Louthain James A, Schmidt Jason D
Aerospace Components Division, Sensors Directorate, Air Force Research Laboratory, 2241 Avionics Circle, Wright-Patterson AFB, OH 45433-7132, USA.
Opt Express. 2010 Apr 26;18(9):8948-62. doi: 10.1364/OE.18.008948.
Laser propagation through extended turbulence causes severe beam spread and scintillation. Airborne laser communication systems require special considerations in size, complexity, power, and weight. Rather than using bulky, costly, adaptive optics systems, we reduce the variability of the received signal by integrating a two-transmitter system with an adaptive threshold receiver to average out the deleterious effects of turbulence. In contrast to adaptive optics approaches, systems employing multiple transmitters and adaptive thresholds exhibit performance improvements that are unaffected by turbulence strength. Simulations of this system with on-off-keying (OOK) showed that reducing the scintillation variations with multiple transmitters improves the performance of low-frequency adaptive threshold estimators by 1-3 dB. The combination of multiple transmitters and adaptive thresholding provided at least a 10 dB gain over implementing only transmitter pointing and receiver tilt correction for all three high-Rytov number scenarios. The scenario with a spherical-wave Rytov number R=0.20 enjoyed a 13 dB reduction in the required SNR for BER's between 10(-5) to 10(-3), consistent with the code gain metric. All five scenarios between 0.06 and 0.20 Rytov number improved to within 3 dB of the SNR of the lowest Rytov number scenario.
激光在扩展湍流中传播会导致严重的光束扩展和闪烁。机载激光通信系统在尺寸、复杂性、功率和重量方面需要特殊考虑。我们不是使用庞大、昂贵的自适应光学系统，而是通过将双发射机系统与自适应阈值接收机相结合来降低接收信号的可变性，以平均掉湍流的有害影响。与自适应光学方法不同，采用多个发射机和自适应阈值的系统所展现出的性能提升不受湍流强度的影响。对该系统进行开关键控（OOK）模拟表明，通过多个发射机降低闪烁变化可使低频自适应阈值估计器的性能提高1至3分贝。在所有三种高里托夫数场景下，多个发射机与自适应阈值处理相结合相比于仅实施发射机指向和接收机倾斜校正至少提供了10分贝的增益。对于球面波里托夫数R = 0.20的场景，在误码率介于10^(-5)至10^(-3)之间时，所需信噪比降低了13分贝，这与编码增益指标一致。在里托夫数介于0.06至0.20之间的所有五个场景中，性能均提升至最低里托夫数场景信噪比的3分贝范围内。
