[论文解读] Interstellar Mission Communications Low Background Regime

Philip Lubin, David G. Messerschmitt+1 more|arXiv (Cornell University)|Jan 23, 2018

Optical Wireless Communication Technologies参考文献 7被引用 4

一句话总结

本文提出了一种针对比邻星的相对论性星际探测器的光学下行链路通信系统，在背景辐射较低的环境下运行，采用直接检测方式并具有高峰均功率比。研究识别出，使用光学波束成形的孔径综合技术以及较短的可见光波长，对于抑制恒星辐射并实现长时间、低数据率任务至关重要。

ABSTRACT

Current attention on interstellar probes for near-term exploration of nearby star systems is focused on low-mass probes that can be accelerated to relativistic speed using propulsion from a ground-based DE beam. We consider the design of an optical communication downlink for the return of scientific data from such a probe at the distance of Proxima Centauri. The conditions under which background radiation can be neglected are quantified, and the design operates within that regime. Direct-detection is preferable to heterodyne, and in that context the transmitter should attain high peak-to-average transmitted power ratios. Based on available electric power sources, the downlink is expected to operate for years or even decades following target encounter, combined with low data rates. There are several areas in which technology innovations are needed, most of them related to Earth-based large-area aperture receiver design with direct detection. A major issue is the choice of multiplexing approach to support multiple probe downlinks and related challenges. Due to the interaction of trajectory parallax effects with field-of-view, we conclude that aperture synthesis with controlled optical beam forming may be required to reject radiation from the target star. Short visible wavelengths for laser communications are also highly advantageous in reducing that radiation. Highly selective optical bandpass filtering is needed to reject unnecessary background radiation, and a short-term data uplink is required to configure the transmit wavelength for variations in probe speed. Fundamental limits on the photon efficiency are compared to a concrete modulation/coding design in the presence of weather-based outages.

研究动机与目标

• 解决相对论性星际探测器飞往比邻星时可靠数据返回的挑战。
• 设计一种在低背景辐射环境中运行的长时长效用光学下行链路系统，以最小化干扰。
• 通过采用高倍峰均功率比的直接检测技术，优化通信性能。
• 克服因轨迹视差导致的地球站接收孔径尺寸和视场限制。
• 通过先进的复用与波束成形技术，实现多探测器下行链路支持。

提出的方法

• 在背景辐射可忽略的条件下建模光学下行链路，重点聚焦于低背景辐射环境。
• 采用直接检测而非外差检测，以降低系统复杂度和功耗需求。
• 利用高倍峰均发射功率比以提升链路预算和光子效率。
• 采用短波长可见光以最小化目标恒星带来的背景辐射。
• 应用高度选择性的光学带通滤波器以抑制非信号背景辐射。
• 引入短期数据上行链路，以根据探测器速度变化动态配置发射波长。

实验结果

研究问题

• RQ1 在何种条件下可忽略光学星际下行链路中的背景辐射？
• RQ2 如何优化直接检测技术以实现长时间、低数据率的星际通信？
• RQ3 具有可控光学波束成形的孔径综合技术在抑制恒星辐射方面发挥何种作用？
• RQ4 轨迹视差效应和视场限制如何影响多探测器下行链路的接收机设计？
• RQ5 光子效率的根本极限是什么？与在气象中断条件下实际调制和编码方案的性能相比如何？

主要发现

• 在恒星和黄道背景辐射可忽略的低背景辐射环境中，下行链路可有效运行。
• 由于系统复杂度和功耗更低，直接检测优于外差检测。
• 发射端采用高倍峰均功率比对于最大化链路性能至关重要。
• 由于轨迹视差效应，必须采用具有可控光学波束成形的孔径综合技术，以有效抑制目标恒星的辐射。
• 短波长可见光显著降低了背景辐射，提升了系统灵敏度。
• 高度选择性的光学带通滤波是抑制非信号辐射的关键，且需要动态上行链路以适应探测器速度变化。