OVERVIEW

One of the key features of our time is the dramatic increase in the flow of information with respect to the previous centuries. The availability of technologies enabling the exchange of huge amounts of information has induced new needs and opened perspectives unforeseeable until not too long ago. Telesurgery, where the patient is in a small hospital whereas the surgeon is, possibly, on another continent is not a futuristic scenario anymore. A student living in a small village can have access, in principle, to the same information as a colleague living in a big city, provided that he or she is properly connected to the right network and has sufficiently fast access. These examples suggest that connectivity through the proper telecommunications infrastructure is the first basic concept enabling the share of information.

Adopting a very basic classification procedure, connectivity can be insured using wired or wireless technologies. From a historical point of view, even though most of us have experienced the first connection through the wired telephone system, the most primitive forms of telecommunications were wireless and used a very high frequency band, namely the electromagnetic spectrum between, approximately, 4 10 ¹⁴ and 8 10 ¹⁴ Hz. As weird as it might appear, this was the first band allocated for telecommunications at a very low (indeed null) cost. This is, in fact, the region of the electromagnetic spectrum where one of our receivers (our eyes) is tuned. And the reason our eyes...