No term is as misapplied or over generalized as "wireless". Now let's get specific. Wireless is either for personal (lap top, cell phone, PDA) or enterprise use. It can be for indoor or building to building applications. It can transmit point-to-point or omnidirectional (point-to-multipoint).
Our focus is point-to-point wireless for enterprise connections between buildings, whether for WAN (wide area network), last-mile or backup applications. Point-to-multipoint radios are excluded because they deliver dynamic slices of shared traffic that works fine for hot-spots, but falls short of enterprise needs.
Glancing at a color coded chart of the radio spectrum, you can see all the frequencies that are allocated in the U.S. to some particular purpose (e.g., maritime mobile, satellite, broadcasting, etc.). You'll immediately notice that the chart is divided by kilohertz (kHz), megahertz (MHz) and gigahertz (GHz). Point-to-point wireless operates in the gigahertz part of the spectrum which represents "microwave" frequencies. Accordingly, when you see or hear "wireless" in connection with point-to-point corporate or enterprise applications it specifically means "microwave radio".
As you read further you'll understand that one wireless medium can be as different to another as a Focker Triplane to a space shuttle. Also, microwave covers a wide range of frequencies on the radio spectrum. One microwave radio can vary greatly in characteristics from another depending on whether it transmits in the low or high end of the frequency range. So if someone makes a statement like: "You can't get microwave frequencies in Manhattan" or "Microwave is effected by rain" then tune them out because such generalizations are patently false.
Point-to-Point Wireless Solutions
Point-to-point microwave is classified as licensed or unlicensed ("license-free"). This is the main distinction. Unlicensed wireless also includes optical solutions, which use lasers instead of radio signals.
