spectrum expansion while not compromising incumbent spectrum uses. It examines new approaches to spectrum sharing, such as licensed shared access (LSA) and dynamic frequency selection (DFS), which in some ways build upon the more-established success of unlicensed, short-range and low-power devices (i.e., Wi-Fi) and the less-established “white spaces” systems.1 These sharing approaches may be useful complements to existing options, such as spectrum auctions, tender processes and spectrum re-farming, which have been used to award spectrum in cases where there are multiple applicants for the same spectrum. The analysis also considers the use of “small cell” and “local area” network topologies to augment traditional mobile cellular networks. And in the near future, efforts will increasingly focus on using cognitive radio systems to “sense and avoid” other transmitters in a dynamic, real-time way. The various experiments in sharing and spectrum management explored in this chapter prompt several questions. How practical are these sharing innovations in many countries, and how should regulators protect rights of use and access – the traditional rationale for spectrum licensing – for all users who need that access? These questions are just now starting to be explored. But there is a broader question: are such fluid sharing and licensing strategies really needed – and if so, where and in what circumstances? 3.2 The evolution of spectrum licensing It is common to perceive of spectrum as real estate, with spectrum management taking on the role of land management. In this analogy, allocation becomes a form of zoning, and a licence becomes a kind of spectrum deed or lease agreement. The holder has certain rights of usage, which are determined and articulated in regulations, licence terms or concessions. The government retains some of the spectrum for its own uses, and it even may set aside some spectrum “land” for the public good – a sort of spectrum “park” for everyone’s common use. Spectrum with good propagation characteristics is often called “beach-front property” because of its high utility for mobile services, broadcasting and other important uses. The analogy of spectrum to land is so useful that in many ways, it has come to influence the very way most people conceive of spectrum and how it is used.Some spectrum engineers and policy-makers, however, have come to view the land-use analogy as overly limiting. In their view, thinking of spectrum as a static resource or commodity is not helpful in a policy environment that increasingly emphasizes ways to squeeze more usage out of the same laws of physics. After all, radio-frequency spectrum isn’t land. It is a means of transporting radio frequency energy, in the form of signals, from transmitters to receivers. One cannot mine spectrum. It cannot be trapped, saved, contained, transported or stored. Spectrum will never be “used up” or exhausted. It is not even Earth-bound (scientists are now receiving signals from a 36-year-old space probe, Voyager 1, at the very edge of our solar system).2 On the other hand, there is no doubt that spectrum is a natural resource that is limited in terms of the amount of usable frequencies and the number of users that can have access to specific frequencies. Perhaps it is helpful to think of spectrum in terms of resilience and agility. In other words, the best way to approach spectrum is by exploring and pioneering better ways to transmit and receive signals among more users without disrupting one another’s messages. Rather than being about ownership (tacit or otherwise), spectrum licensing and management is properly a task of increasing access while avoiding harmful interference. The hope is, increasingly, that science, regulations and technology will help deliver on that goal.3.2.1 Current Spectrum Assignment Models Before exploring the new experimentation in spectrum licensing, it might be useful to review how spectrum is currently assigned and how those methods have evolved. This is important, because in many ways, new ideas about spectrum licensing represent an evolution from existing frameworks.62 Trends in Telecommunication Reform 2015