WiMax Operator's Manual

40 CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES
recently this spectrum was only utilized on an experimental basis by Loea, a Hawaiian equipment
manufacturer with deep expertise in radio photography. Loea owned a nationwide
license and had plans to establish networks on a wide scale, though how quickly these can
actually be developed remains uncertain. Recently the E band has become subject to expedited
licensing by the FCC, which means that applicants can obtain licenses on a link-by-link basis,
and can be fairly certain of obtaining licensing if no prior license has been established in the
restricted geographical area irradiated by the narrow-beam point-to-point link.
All of these bands above 40GHz share one thing in common: allocations of bandwidth that
enable them to achieve truly fiberlike throughput speeds. And yet, rather curiously, actual
deployments remain quite uncommon. The largest I am aware of took place in Florida under
the auspices of CAVU-eXpedient, a now defunct high-speed access provider that operated
radio links at 38GHz and 60GHz and backed up the 60GHz links with free-air optical transceivers.
Basing its business plan on a rapid rollout over several southern states, CAVUeXpedient
was unable to obtain third-round funding to continue its expansion and declared
bankruptcy in 2002.
Nevertheless, I see considerable potential in EHF bands because of the relatively enormous
throughputs they support. Services operating in the SHF spectrum may claim to offer
fiberlike speeds, but only EHF services are truly capable of provisioning multigigabit pipes.
Free-Space Optics: Wireless Without the Radio
I mentioned earlier that EHF airlinks can rather easily be paralleled with free-space optical
(FSO) transmission systems. Both FSO and EHF are vulnerable to adverse weather conditions—FSO
to heavy fog and EHF to rain and snow—but, on the other hand, EHF is not much
troubled by fog, and FSO is not obstructed by raindrops. Thus, used together, the two systems
can achieve an availability figure that is at least an order of magnitude better than either alone
over a given distance. And because the normal operating distances of the two technologies are
similar and because both transmit tightly focused line-of-sight beams, the two work well in
tandem.
At the same time, FSO may be considered to be a competitive technology with respect to
802.16 millimeter microwave. It addresses essentially the same market segments and shares a
similar freedom from wireline infrastructure. It is also akin to millimeter microwave in that it is
a young technology, appearing in commercial form in the 1990s and failing to establish a large
market presence thus far.
In at least two other respects, however, the two access technologies are quite divergent.
FSO has the potential to offer significantly higher throughputs than EHF will ever achieve.
Many of the same techniques used in fiber-optic networks, such as dense wave division multiplexing
(DWDM), subcarrier multiplexing, 40GHz modulators, superfine optical filters, and
optical Code-Division Multiple Access (CDMA), can also be used in FSO systems, and terabit
speeds are theoretically possible over short distances. Indeed, some years ago, Lucent
announced it had achieved 80 gigabits per second (Gbps) transmissions in the laboratory using
DWDM alone. Surely that figure can be bettered in time. However, microwave throughputs are
likely to achieve only incremental gains, and even these will require fundamental advances in
high-speed devices and modulator circuits rather than building on technology that already
exists, which is the case with FSO.
We must keep in mind, however, that terabit speeds or even large fractions thereof have
not been demanded of any metro backbone except a lateral access connection extending from