无人机被广泛应用于各种商用/民用领域,并有望在未来十年带来巨大的价值和广阔的商机.在无线网络如4G/5G乃至6G及其新技术的支持下,无人机能够高效地完成空中监测、空中摄像、搜索和救援等任务.特别地,无人机作为空中通信平台/用户的相关应用是近几年的研究热点,而现有的大多数研究集中在陆地环境.本文针对临海通信系统,系统阐述无人机在涉海应用中的前景与挑战.首先介绍无人机类型及应用场景、通信链路和信道特性,然后讨论临海空间中无人机在方位部署、路径规划、能量效率、通信覆盖、干扰控制、远距离数据回传等方面的问题与机遇.最后考虑风对临海无人机通信的影响,以海上浮标数据收集为例,设计了一种无人机循环飞行轨迹,其能够主动适应/利用海风实现高效节能通信.通过系统介绍、问题凝练与案例分析,指引无人机赋能临海通信系统设计.
Background: Unmanned aerial vehicles (UAVs) are widely employed in various commercial or civilian domains with ever-increasing values and business opportunities in current and coming decades. With the support of wireless technologies in 4G/5G and beyond, UAV can efficiently complete various tasks such as aerial surveillance, photography, search and rescue among others. In particular, althoughthe application of UAV for aerial communication platforms or aerial communication users has attracted considerable research interests in recent years, most existing studies focus on terrestrial settings. Note that, for terrestrial scenarios, UAV can be widely applied in wireless communication systems as a mobile base station, relay or data collector. Moreover, favorably due to its high mobility, UAV also qualifies as a flexible and cost-effective tool that can be applied in abroad spectra of marine activities including wireless coverage, surveillance, rescue and data collection. However, limitations of the marine environment and UAV’s size, weight and power (SWAP) constraint have brought great challenges to UAVs to perform maritime communication tasks. On the one hand, it is difficult to accurately model the maritime communication channels. On the other hand, network performance is affected due to the difficulty of deploying communication infrastructures. Additionally, UAVs must be able to withstand strong wind conditions above sea surfaces.
Progress: Amid the rapid increase in applications of UAVs in communications, the continuous improvement of UAV performance and the strategic deployment of realizing land, sea, air and space 3-D communication proposed in the 6G outlook, UAV-enabled offshore communication systems have ushered in great opportunities, but also have faced a series of new challenges. In this study, we systematically present the application of UAVs for marine exploration and exploitation. The types of offshore UAVs and their application scenarios are first introduced, along with the involved communication links and channel characteristics. The role of UAV in the offshore communication system is then discussed, followed by research opportunities and challenges including UAV deployment, path planning, energy efficiency, communication coverage, interference control, and long-range backhaul among others. Finally, as a concrete example, a maritime data collection system with a fixed-wing UAV under windy conditions is investigated, and a novel cyclical trajectory design framework is proposed to proactively adapt to, or utilize, the wind to complete the communication task with significant power savings and reduced computational or trajectory complexity. Through the comprehensive overview, highlighted problems and potential solution techniques as well as the illustrative case study, the practical guidance is provided for designing UAV-enabled offshore communication systems. In addition, issues and challenges outlined in this paper can inspire researchers to develop broader application prospects on this basis.
Perspective: Although scholars have conducted considerable in-depth research in UAV deployment, path planning, energy efficiency, communication coverage, interference control, long-range backhaul and other aspects, a series of urgent problems that need to be solved remain, such as three-dimensional deployment and path planning to realize energy-saving communication, low-cost and wide-covered antenna design, large-scale and continuous marine communication coverage, offshore long-distance and data transmission among others. With the gradual discovery of the importance and necessity of UAV-enabled maritime communication systems, increasing technologies and inventions will help the development of maritime communication systems improve communication efficiency and quality. This improvement enables UAVs to fly freely in marine areas and complete key tasks energy-efficiently such as wide-scale marine communication coverage, high rate marine data collection, rapid response maritime search and rescue among others. Moreover, UAVs can adapt to more prominent or random wind conditions and realize long-distance real-time transmission of big data. Scholars can start with several key technologies and challenges mentioned herein, solve some defects and problems existing in the existing research, as well as gradually accomplish UAV-enabled efficient offshore communication, so that the land, sea, air and space integrated information network can be built.
