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机载光通信,又称为自由空间光通信(Free Space Optical, FSO),是利用光束作为信号载体,在长视距无遮挡的自由空间信道中实现信号传输的无线通信技术[3-4]。机载光通信系统融合了传统射频数据链通信与光纤通信的优势,如高速率、大带宽、高保密、建网快、无需授权等,可用于航空通信、卫星通信和海上通信等。机载光通信作为激光通信应用的一个主要方向,从20世纪80年代开始,美国、德国、法国等西方国家就已相继开展了大量基于各类航空飞行平台的机载光通信载荷和链路试验研究工作,并已获得了实质性突破。目前,国内也有许多单位先后进行了机载光通信关键技术研究和试验,主要有武汉大学、西安理工大学、长春理工大学、中国科学院上海光学精密机械研究所、桂林激光通信研究所、哈尔滨工业大学、海军航空大学等。
(1)国外研究现状
1980年,美国空军实验室(AFRL)在白沙基地开展了空-地之间KC-135机载飞机激光通信测试项目(AFTS),第一次证明了机载通信终端在空间通信系统中的可行性。1984年,美国空军HAVE LACE项目中进行了两架飞机之间的激光通信试验[5]。1995年,美国Thermo Trex公司开展了机载激光通信装备RILC的研发;1996年,飞机搭载了RILC终端,并完成了空-地之间的激光通信试验;1998年,在两架T-39型飞机上搭载RILC激光通信载荷,进行了空-空激光通信试验;2004~2005年,又先后开展了一系列的试验,完成了两架飞机在高空40000 ft、目标距离100 km、数据速率2.5 Gbps、误码率≤10−6的演示试验[6]。2005年,美国国家喷气动力实验室(JPL)进行了第二代激光通信终端(Optical Communications Demonstrator, OCD)系统的演示试验,并进行了空-地之间激光通信链路试验。2006年,欧洲空间局(European Space Agency, ESA)的LOLA项目在静止轨道卫星Artemis和法国飞机“神秘20”(搭载ELAS通信终端)之间建立了空-星双向激光通信链路。2008年,德国宇航中心ARGOS项目完成了飞行高度3 km、通信距离10~85 km、传输速率155 Mbps的空-地激光通信试验;2010年完成了通信距离10~100 km、传输速率1.25 Gbps的空-地通信链路试验[6]。2009年,在麻省理工学院林肯实验室的FOCAL试验中完成了双獭机与地面端机之间的激光通信链路试验[7]。2010年,美国空军实验室与ITT企业联合进行了FALCON项目,共同研究了空基高速激光通信链路技术,并顺利实现了DC-3飞机之间的双向激光通信试验。2013年,在德国的DODfast项目中完成了战斗机“狂风”和地面移动节点间的空-地激光通信链路试验[7]。2014年,美国通用原子公司进行了空基激光通信系统演示项目(ALCOS),提出了在MQ-9无人机平台上搭载激光通信载荷;2016年,进行了地面试验;2017年完成了飞机搭载测试的验证;并于2020年完成了通信部分试验,在1.064 µm和1.550 µm两个光波波长下实现了无人机低截获率和低检测率的通信链路[8]。2017年,日本Facebook公司尝试以飞行高度为18 km的Aquila高空太阳能无人机为空中激光节点,建设了空中无线网络基站,并试飞成功[9]。近十年以来,美国、法国等先进国家还进行了Gbps量级的高速率无人机-卫星、无人机-地之间的激光通信试验,以及基于高空大型无人机的民用激光通信组网试验研究。
(2)国内研究现状
2006年,武汉大学成功进行了传输速率为42 Mbps的多业务机载激光通信试验;2007年,完成了全空域的机载激光通信自动跟踪伺服系统测试并获得成功。2009年,西安理工大学成功研发了大气激光视频传输系统,并完成了通信距离为3~5 km的全天候无间断实时视频网络数据通信。2011年,长春理工大学在新疆开展了飞艇和水面船舶的双向动态高速率激光通信试验;在黑龙江省某机场进行了低空双直升机之间激光通信试验;2013年,在黑龙江省某机场开展了双固定翼飞机平台间激光通信试验。2016年,中国科学院上海光学精密机械研究所成功进行了3.11 km高空对水下目标的机载激光通信试验。2016年,桂林激光通信研究所的安建欣教授等利用小型旋翼无人机平台研制出了一套空-地激光通信系统,实现了在三种天气情况下的稳定通信;2017年,研制了小型无人机在1.7 km的距离上实现空-地2.5 Gbps的通信试验。海军航空大学进行了机载蓝绿激光通信信道特性以及调制方式的相关研究,并进行了海上机载激光通信试验。2018年至今,赵尚弘等对高空大气信道下航空平台端到端激光通信链路性能、FSO/RF混合传输技术和航空组网进行了一系列理论研究和演示系统样式研制。此外,国内另有其他多家单位针对航空无人机激光通信的大气信道特性、机载光通信理论以及关键技术等进行了系统深入的研究[10-11]。
表 1 国内外机载光通信试验
Table 1. Domestic and foreign aviation wireless laser communication test
Country name Project/
UnitTest time Link type Transmission rate Transmission distance America AFTS 1980 Air–Ground 20 kb/s 20-30 km HAVE LACE 1984 Air–Air 19.2 kb/s 160 km 1996 Air–Ground 1 Gb/s 20-30 km 1998 Air–Air 1 Gb/s 50-100 km OCD 2005 Air–Ground 2.5 Gb/s 20-30 km FOCAL 2009 Air–Ground 2.5 Gb/s 25 km FALCON 2010 Air–Air 2.5 Gb/s 94-132 km ALCOS 2017 GEO–Air 1.8 Gb/s 36000 km France LOLA 2006 GEO–Air 50 Mb/s 38000 km Germany ARGOS 2008 Air–Ground 155 Mb/s 10-85 km 2010 Air–Ground 1.25 Gb/s 10-100 km DOD fast 2013 Air–Ground 1.25 Gb/s >50 km China Shanghai Institute of Optics and Fine Mechanics,
Chinese Academy of Sciences2001 Air–Air 1 Gb/s 50-100 km 2016 Air–Sea - 3.1 km Changchun University of Science and Technology 2011 Air–Sea 1.5 Gb/s 20.8 km 2011 Air–Air 1.5 Gb/s 5-20 km 2013 Air–Air 2.5 Gb/s 136-144 km Research Institute of Laser Communication in Guilin 2016 Air–Ground 1.25 Gb/s 6.7 km 2017 Air–Ground 2.5 Gb/s 1.7 km 国内外机载光通信试验开展情况如表1所示。由国内外研究现状可知:
1) 机载光通信的国内外研究重点大多集中在增加通信距离、提高传输速率、可靠性和安全性、工程实现等几个方面,尤其是针对大型有人机的点对点激光通信试验研究。
2) 国内外大部分研究机构主要面向5~15 km高度的有人机/无人机进行机载光通信试验,近几年才逐渐开始朝着17~25 km的高空无人机平台发展,尝试大型无人机的光通信理论研究和演示试验。
3) 国外对机载光通信的研究和试验开始相对较早,在基础理论、试验和工程化技术方面比较完善。与国外相比较,国内在机载光通信系统的研制与演示试验方面尚有一些差距,目前正处于从理论研究逐步向工程实现转化、从航空平台点-点激光通信向航空组网验证转化的阶段。
因此,国内对机载光通信技术的研究和应用仍存在很大的发展空间,特别是加快推进大型无人机的光通信技术研究与实际应用具有重要意义。
Application of optical communication technology of large-scale UAV based on aviation backbone network
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摘要: 目前,航空骨干网络各平台间采用射频技术,存在传输速率较低、频带资源受限、易受电磁干扰等不足,难以满足航空安全、作战指挥等军事和民用领域对航空数据安全高速传输的要求。而光通信在航空信息高速可靠传输方面具有显著优势,具有超高速率、超大带宽、抗干扰能力强、保密性好等优点。为进一步提高航空骨干网络机间无线通信能力,立足于大型无人机在航空领域的具体应用和机载光通信技术的发展,首先在分析总结国内外机载光通信关键技术的研究现状、已进行试验情况的基础上,针对大型无人机作为骨干网移动中继在当前航空领域的应用场景做出了设想与描述;然后对航空大型无人机机载光通信的需求进行了深入分析;最后系统总结了航空大型无人机激光通信的关键技术、未来发展趋势等。这为机载光通信技术在当前航空领域大型无人机上的应用与发展提供了一定的理论借鉴与依据。Abstract: At present, radio frequency technology is used between platforms in the aviation backbone network, which has shortcomings such as low transmission rate, limited frequency band resources, and susceptibility to electromagnetic interference. It is difficult to meet the requirements for safe and high-speed transmission of aviation data in military and civil fields such as aviation safety and combat command. While optical communication has significant advantages in high-speed and reliable transmission of aviation information, with the advantages of ultra-high speed, ultra-large bandwidth, strong anti-interference ability, and good confidentiality. In order to improve the capability of wireless communication between flight platforms of aviation backbone network, on the basis of analyzing and summarizing of the research status and experiments of key technologies of airborne optical communication at home and abroad, at first this thesis makes an assumption and description for the application scenario of domestic large UAV as backbone network mobile relay in the current aviation field, then analyzes deeply the airborne optical communication requirements of large UAV. At last systematically summarizes the key technologies and future development trend of laser communication of large aviation UAV, which provides a certain theoretical reference and basis for the application and development of airborne optical communication technology in large aviation UAV.
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表 1 国内外机载光通信试验
Table 1. Domestic and foreign aviation wireless laser communication test
Country name Project/
UnitTest time Link type Transmission rate Transmission distance America AFTS 1980 Air–Ground 20 kb/s 20-30 km HAVE LACE 1984 Air–Air 19.2 kb/s 160 km 1996 Air–Ground 1 Gb/s 20-30 km 1998 Air–Air 1 Gb/s 50-100 km OCD 2005 Air–Ground 2.5 Gb/s 20-30 km FOCAL 2009 Air–Ground 2.5 Gb/s 25 km FALCON 2010 Air–Air 2.5 Gb/s 94-132 km ALCOS 2017 GEO–Air 1.8 Gb/s 36000 km France LOLA 2006 GEO–Air 50 Mb/s 38000 km Germany ARGOS 2008 Air–Ground 155 Mb/s 10-85 km 2010 Air–Ground 1.25 Gb/s 10-100 km DOD fast 2013 Air–Ground 1.25 Gb/s >50 km China Shanghai Institute of Optics and Fine Mechanics,
Chinese Academy of Sciences2001 Air–Air 1 Gb/s 50-100 km 2016 Air–Sea - 3.1 km Changchun University of Science and Technology 2011 Air–Sea 1.5 Gb/s 20.8 km 2011 Air–Air 1.5 Gb/s 5-20 km 2013 Air–Air 2.5 Gb/s 136-144 km Research Institute of Laser Communication in Guilin 2016 Air–Ground 1.25 Gb/s 6.7 km 2017 Air–Ground 2.5 Gb/s 1.7 km -
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