Licensed Spectrum

Within the lower microwave region, licensed spectrum for broadband public services is
relatively scanty, and only two significant allocations exist. The first, called Wireless Communications
Service (WCS), is located at 2.3GHz and has only 30MHz of bandwidth. The second,
called Multichannel Multipoint Distribution System (MMDS), is located in the 2.5GHz to
2.7GHz region and provides the operator with almost 200MHz of spectrum.
The WCS spectrum was originally allocated to AT&T on an experimental basis, and the
latter set up the Project Angel program to exploit it. Another license was issued to the nowdefunct
Metricom that used these frequencies in conjunction with unlicensed spectrum to
provide Internet access. Originally, Project Angel was intended to support a fixed wireless telephone
system, an arrangement often referred to as wireless local loop, but as the experiment
progressed the network evolved into a high-speed access service. AT&T eventually abandoned
the project, and licenses were made available to other operators.
The MMDS spectrum is generally considered the most desirable licensed spectrum in the
lower microwave region, at least in the United States. Originally intended for one-way “wireless
cable” television programming distribution, the MMDS spectrum was sold to hundreds of
licensees across the United States, some with strong regional presences extending across
scores of metropolitan markets and some confined to a single market. With few exceptions,
MMDS television distribution systems have failed, and most of the local licenses have been
sold to a handful of telecommunications giants, chief among them Sprint and BellSouth.
I will dispense with any detailed history of attempts to utilize this spectrum for data,
attempts that began in the late 1990s on an experimental basis and were seriously under way
by the year 2000. One such deployment, that of Sprint, managed to attract some 90,000
subscribers across a number of metropolitan markets, but that company has not taken on
new subscribers for more than a year and has given little indication of its plans for this spectrum
in the future. Rumor has it that Sprint simply did not understand how to properly market
line-of-sight RF technology, which resulted in huge losses through rolling trucks to dissatisfied
customers and proving to them that they really could not receive a signal because of some
obstruction between their location and the base station. Others have suggested that the
company could not operate the network cost effectively with first-generation equipment and
ceased expansion to await the arrival of better radios. Other progenitors, such as BellSouth and
MCI, proceeded more cautiously, setting up what were in effect merely pilot programs. No one
to date can be said to have achieved a solid success in the MMDS bands within the United
States.
The fairly stringent line-of-sight requirement of first-generation equipment was a major
impediment for the pioneers, one that put them at serious competitive disadvantage with
cable and digital subscriber line (DSL) service providers. But a further serious problem was
presented by the distribution of spectrum within the MMDS bands.
The MMDS spectrum is divided into thirty-three 6MHz channels, 6MHz being the bandwidth
of analog broadcast television channels according to the National Television Standards
Committee (NTSC) standard in force since 1941. Interspersed among the MMDS channels are
Instructional Television Fixed Service (ITFS) television channels allocated to nonprofit institutions
such as churches and schools and used for educational and instructional television. The
presence of these intervening channels severely hampered the MMDS system operator in a
number of ways. It placed significant constraints on the design of the radio by requiring tight
filters to keep out interference from neighboring ITFS channels and to mitigate interference from the MMDS transmissions themselves and severely limited the flexibility of the network
operator in assigning spectrum to users or in the choice of a modulation system.
Some MMDS operators leased channels from ITFS licensees to control a block of
contiguous spectrum, but that option was not always available, and the presence of multiple
operators within the MMDS bands made for a nearly untenable situation.
In 2004 the FCC reallocated the spectrum in 2.5GHz to 2.7GHz range to permit larger
blocks of contiguous spectrum, which has resulted in a vast improvement. Whether it will lead
to the creation of successful services in these bands remains to be seen.
MMDS spectrum is not widely available to independent operators in the United States,
but it can be leased or purchased in certain communities, generally in rural areas where the
licenses are still held by failing MMDS television system operators. I should also point out that
by aggregating spectrum in MMDS and the 2.4GHz ISM band, an operator can command
approximately 260MHz, a very considerable swath of bandwidth. I think that MMDS spectrum,
where obtainable at a reasonable price, is potentially very valuable. Incidentally, MMDS spectrum
is available in many other places in the world, generally at around the same frequencies.
One further note: Several years ago a company calling itself Clearwire leased large
amounts of ITFS spectrum in various markets throughout the United States. In 2004 Clearwire
dissolved and transferred its leases to a new company called Clearwire Ltd., which is owned by
former cellular telephone magnate Craig McCaw, who subsequently leased and purchased
additional spectrum in the United States and Canada. The new Clearwire marks the largest
independent effort to establish broadband wireless services in the United States, and the
industry as a whole is watching it closely.
The next licensed bands of importance reside at 18GHz and 23GHz. Both bands are designated
for point-to-point connections and provide roughly 100MHz of bandwidth. Local
licenses for the band located at 23GHz are readily obtainable and are low cost. To date, 23GHz
has been used primarily for high-capacity wireless bridges for enterprise networks and has
been little used by service providers. Both bands are well suited to providing fairly high
capacity backhaul services, and both operate strictly line of sight. Ranges of up to several miles
are possible with suitable antennas.
A pair of 400MHz wide bands is located just above 24GHz adjacent to an unlicensed band
mentioned in the previous section. The first band extends from 24.25GHz to 24.45GHz, and the
second runs from 25.05 to 25.25GHz. This licensed spectrum, which is designated Digital Electronic
Message Service (DEMS) by the FCC, became the almost exclusive domain of Teligent, a
company that went bankrupt in 2001 and then reorganized. Most of the spectrum was subsequently
acquired by First Avenue Networks, a Virginia-based independent carrier. Spectrum in
this region is also available in a number of Latin American countries.
The 24GHz-licensed band is designated for point-to-multipoint, as well as point-to-point
use, and is strictly line of sight. Transmission distances are somewhat greater than for higher
millimeter microwave frequencies.
Spectrum at 26GHz is widely available for point-to-point transmissions in Europe and
Asia but not in the United States.
Several bands of frequencies between 28GHz and 31GHz have been designated for pointto-
multipoint services known as Local Multipoint Distribution Service (LMDS). Frequency
divisions are as follows: 27.5GHz to 28.35GHz, 29.1GHz to 29.25GHz, 31.0GHz to 31.75GHz,
31.75GHz to 31.225GHz, and 31.225GHz to 31.300GHz. Most of the spectrum in these bands in
the United States was purchased in FCC auctions some years ago by a few large corporate entities,
including XO Communications and Winstar. Spectrum at 28GHz is commonly used in Latin America and Europe, as well as in North America, though exact frequency allocations
differ from country to country.
LMDS spectrum is only spottily available today in the marketplace in the United States.
Some scattered independents in secondary and tertiary markets own such spectrum and may
be induced to sell it in some instances, but the largest players, though all bankrupt now,
disposed of their holdings in blocs, or else were rescued and refinanced. LMDS bands have the
capacity to support a great deal of traffic, but they are strictly line of sight, and the links are
undependable beyond a couple of kilometers. I think LMDS can provide the basis of profitable
services in selected markets, but I am skeptical as to the viability of point-to-multipoint architectures
at these frequencies. Provisioning very fat point-to-point pipes to high-value
customers and using these frequencies for cellular backhaul probably makes more sense.
The next licensed frequency of interest is located in two bands in the 38GHz region and
provides more than 500MHz of bandwidth in the United States and in Canada. The 38GHz
frequency is widely used in Latin America as well as in the United States, but frequency allocations
are quite different there from those in North America. This is a region of deep water vapor
attenuation, and ranges are even shorter than is the case for LMDS. To date this spectrum has
been used for point-to-point and point-to-consecutive point services. ART and Winstar
purchased great numbers of local licenses several years ago, but neither established a nationwide
footprint, and both in fact went bankrupt. Some 38GHz licenses are available today as
distressed assets. Most of the strictures applying to LMDS also apply to 38GHz except that the
useful range is considerably less.
Another licensed band is available at 39GHz, and for all practical purposes it is similar to
the 38GHz band. First Avenue (
    

) has bought a great deal of this
spectrum and leases it, primarily for backhaul, to other carriers. A further band extending from
75GHz to 85GHz has been allocated to a single carrier, Loea, on an experimental basis.
Recently the FCC has allocated additional licensed spectrum in the region extending from
70GHz to 90GHz and has made it available on an expedited basis, as has been the case with
18GHz and 23GHz.