WiMax Operator's Manual

46 CHAPTER 3 ■ STRATEGIC PLANNING OF SPECTRUM AND SERVICES
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