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authored by Chuck Bolvin, VP of Technology This
paper will briefly discuss some questions that come up concerning the
use of licensed frequency bands for broadband wireless access (BWA).
The intent is to provide simple answers to these questions without too
much technical detail. By far the most prevalent form of wireless broadband is unlicensed. The FCC has set aside several frequency bands for use with products that don’t require a license to operate from the FCC. These bands are known as the Industrial, Scientific and Medical (ISM) bands. In addition, the 5 GHz bands overlap with another unlicensed service known as the Unlicensed National Information Infrastructure (UNII) bands. UNII bands were intended to foster the growth of information networks on a national level.
These are the most common bands in use. There are several other unlicensed bands that are seeing product offerings as well. Some of these bands are much higher in frequency and have a much higher data carrying capacity but are shorter in range.
The
higher frequency bands are used almost exclusively for point to point
(PTP) and point to multipoint (PTMP) bridging of high speed backbone
links, usually 155Mbps and higher. There
are a few drawbacks to unlicensed operation however. All of the below
items can be countered or thwarted with a professional site survey
from a certified WAV technician. No
coordination of frequencies means the potential for interference from
another system can be considerable. The FCC will not help resolve
conflicts with other users. This is particularly evident in highly
populated metropolitan areas. Other
products such as cordless phones, medical equipment, security systems,
RFID systems, telemetry systems and microwave ovens use the very same
frequency bands. So operation of these devices in close proximity of a
broadband system can cause degradation of the system or cause it to
shut down completely. Output
power is more restricted with unlicensed products meaning the
potential for shorter distances and less coverage. Many
municipalities have avoided using unlicensed bands for public safety
based systems. These systems many times are used for health, welfare
and safety traffic and the potential for an outage due to interference
from another system is unacceptable. For these reasons the move to licensed frequencies has become more evident. The FCC has made the licensing process easier and less costly. In the past licensing could take many weeks and cost several thousand dollars. The licenses also needed to be renewed more frequently, sometimes every year. Now,
the licenses are more in the range of a few thousand dollars and run
for as long as 5 to 10 years depending on the band.
There
are other bands but these are the ones where BWA has been discussed.
The benefits of licensed operation include:
There
are a few drawbacks though. Not all bands have frequencies available.
For example, Sprint and Clearwire “own” approximately 85% of the
2.5GHz MMDS band. The remaining 15% is owned by several educational
and religious groups. In order to obtain a frequency in this band one
must attempt to lease a frequency from one of these organizations.
All
licensed bands usually require the services of a Frequency
Coordinator. An FC is a person or organization that has agreed to take
on the task of assigning frequencies in a geographic area. They look
up the existing assignments and will find a clear frequency for you.
Frequency Coordinators are not a part of the FCC and their services
are fee based. Most
manufactures of licensed products can put a customer in touch with a
Frequency Coordinator for their particular area. Most
Licensed BWA products now seem to be appearing in the 11 GHz,18 GHz,
3.6 GHz, 23GHz, 24GHz and 39GHz bands. With some in the lower 2.3GHz
as well. The time period to obtain a license can vary from a week or so to several weeks. So this isn’t a product that can be installed quickly.
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