Optical Satellite Communications: Design Considerations and Research Outlook

Since the early days of space communications, radio waves have served as the carriers of information. It is only very recently that laser links light up the sky, tapping from the vast amount of bandwidth in the terahertz regime of the electromagnetic (EM) spectrum. In this chapter, we dive into the trade-offs between radio frequency (RF) and free space optics (FSO) connections. Thanks to the much higher carrier frequency, FSO brings clear advantages for high data rate, large distance, and/or ultra-secure communications. However, there are some challenges associated with it challenges including demanding pointing requirements, turbulence- and pointing-induced fading, and the need for line-of-sight operations. We shortly highlight various use cases and discuss the design trade-offs to arrive at high data rate, robust, low-latency, and high-availability connections. The chapter concludes with an outlook to the next generation of FSO terminals and addresses topics including software-defined, adaptive FSO as well as multiuser multi-beam communications and concludes on the convergence of RF and FSO technologies, holding the promise to unlock the best of both worlds.