Free-space Optical (FSO) Platforms: Unmanned Aerial Vehicle (UAV) and Mobile

Abstract

This chapter discusses the emerging technology of unmanned aerial vehicle (UAV)-based free-space optical (FSO) communication links. UAVs are a possible future application for both civil and military use. The large amount of data generated by the UAVs requires high data rate connectivity, thus making FSO communication very suitable. This chapter discusses some important issues using FSO links such as the FSO unit alignment and the beam attenuation/fluctuation due to the atmosphere. The technical challenges for the alignment in tracking and acquisition are addressed. Detailed descriptions are provided in the following areas: alignment and tracking of a FSO link to a UAV, short-length Raptor codes for mobile UAV, and a modulating retroreflector (MRR) FSO communication terminal on a UAV. A new methodology of using multiple UAVs in a cooperative swarm mode is also described. Specific areas for UAV swarms are discussed, such as large and adaptive beam divergence for inter-UAV FSO communication, networking architectures, reliability, and appropriate modulation scheme (pulse position modulation, PPM/on-off keying, OOK; incoherent detection). Another section of this chapter deals with the problem associated with mobile platforms, i.e., tracking in moving vehicles and gimbals. The challenges addressed are: variation in receiver beam profile of the FSO link and variation in received optical power due to constantly changing transmitter/receiver separation. Some basic building blocks for high-speed mobile ad hoc networks (MANET) using FSO is described with protocols operating under high mobility. An FSO structure is described which can achieve angular diversity, spatial reuse, and are multielement. The link performance of mobile optical links in the presence of atmospheric turbulence is provided for a FSO-based mobile sensor network. Mobile communication challenges and potential solutions are discussed.