8.1 Broadband wireless without satellites or fiber

Most of the high-profile advances in broadband and high bit rate communications, increasingly for Internet on-ramps, are the province of new and planned satellite constellations and DWDM fiber systems. The latter are described in Chapter 3 and broadband satellite systems are discussed in Chapter 9.

However, neither satellite nor fiber represents the only possibilities for the delivery of broadband wireless services far from it. It is well known that microwave or millimeter-wave signals will travel through the atmosphere, and in fact this is how it all began.

During the second half of the twentieth century the term microwave generally meant one of two possibilities: either line-of-sight terrestrial communications or else something one cooked with very efficiently. Before fiber optics gained the undisputed lead in terrestrial communications systems, line-of-sight microwave links with their dish-festooned towers were clearly visible across most industrial countries. Prior to the 1980s most links were analog, using FM and FDM, although more recently digital transmission has been implemented.

Many of these types of systems, now almost entirely digital, remain in operation, and in some instances the installation of new links continues. This approach is vital in regions where it would be completely uneconomic to install fiber-optic cables due to either low population density or rigorous terrain, or both these factors. These types of links often involve very broad overall bandwidths, to accommodate large numbers of channels, but the individual services are usually of a relatively narrowband nature.

In this...