Lower Microwave: Primarily a Residential and Small Business Play

The lower microwave frequencies, are, as you have seen, governed by the 802.16a standard that
actually extends to 11Ghz. Still, in my estimation, typical lower microwave deployments are
best not attempted at frequencies much above 6GHz, and in the United States no commercial
spectrum is available between 6GHz and 18GHz that is authorized for broadband access applications.
Spectral allocations of course vary from one nation to another, but generally the
region between 6GHz and 10GHz has been little used for providing broadband access
anywhere in the world. Although spectral allocations in the lower microwave region vary from one nation to
another, most bands are under 200MHz in width and often under 100MHz. Moreover, most
antenna systems designed for use in these regions simply will not allow the entire bandwidth
to be reused within a few degrees of arc, so network operators must allocate their assigned
spectrum—be it 30MHz, 50MHz, 100MHz, or 200MHz—to a number of contiguous users who
will all be encompassed within the same transmission beam and thus will all be presented with
the full allocated spectrum. Coincidentally, those same users will also be exposed to every
transmission occurring over that spectrum within the sector defined by the antenna beam.
The practical implications are numerous.
First, users are going to get a fairly small allocation of spectrum for their own use, perhaps
no more than a few hundred kilohertz in a fully subscribed network. Second, for reasons of
security, the network operator cannot depend entirely on channelization or modulation
coding to segregate transmissions from one another and to ensure privacy. Instead, further
privacy measures are advisable, preferably ones that entail the encryption of each transmission
and the installation of an encryption key management system to make the encryption
process both transparent to the user and extremely difficult to penetrate on the part of interlopers.
Chapters 6, 8, and 9 discuss such security and encryption methods at length.
The relatively small amounts of bandwidth that can be accorded individual users in the
lower microwave bands restrict the network operator’s ability to court large enterprise
customers, and the basic service offerings end up competing with DSL and cable services for
the small business customer and the small office home office (SOHO) customer. Residential
customers for high-speed access may also be served, but there the wireless operator is apt to
enjoy no particular advantage in markets where DSL and cable are already well entrenched.