December 2016 13
more limited the range for a given
transmitter power and antenna gains.
A 2. 4 GHz Wi-Fi signal will travel
farther than a 5 GHz Wi-Fi signal with
all conditions being the same. This is
both good news and bad news. The
good news is that at some distance,
the signal is just too weak to interfere
with someone else on the same
frequency. The bad news is that the
communications range is just too
short for reliable service. This feature
or limitation allows frequencies to be
shared or reused, which is one of the
key solutions to utilizing spectrum.
Spectrum Management
Spectrum is sacred ground,
so must be protected and used
as necessary; that is why it is
government regulated. All countries
in the world have spectrum regulatory
services. In the United States, these
are the Federal Communications
Commission (FCC) and National
Telecommunications and Information
Administration (NTIA). The FCC
addresses the consumer and
commercial spectrum, while the NTIA
oversees the military and government
spectrum.
The NTIA offers a master
spectrum chart (small version shown
in Figure 1; full-size version available
at the article link) that you can
download from www.ntia.doc.gov/
page/2011/united-states-frequency-
allocation-chart. This gives you a look
at the massive complexity involved in
allocating and managing spectrum.
These sites are also worth a visit
if you are hungry for more spectrum
related material: www.fcc.gov and
www.ntia.gov.
If you want to know more about
the spectrum, get a copy of the Code
of Federal Regulations (CFR) Title 47
Parts 0 through 100 that contain all of
the FCC’s rules and regulations. Part
2 covers the frequency allocations
for the various services. Parts 15 and
18 cover short-range wireless and
electromagnetic interference (EMI)
regulations. Go to https://www.fcc.
gov/general/rules-regulations-title- 47
for more details.
Keep in mind that there are two
types of spectrum: unlicensed and
licensed. Unlicensed spectrum can
be used without prior FCC approval
if the related rules and regulations are
precisely followed. Licensed spectrum
is strictly awarded and policed by
the FCC for specific services such
as radio and TV broadcasting, land
mobile, cellular, satellite, and radar.
Minimizing the Spectrum
Problem
The spectrum limitations have
been known for years. Fortunately,
the industry has been at work
trying to resolve the problem with
technological and management
solutions. Here are just a few
approaches you may not be aware of.
Take advantage of spatial
diversity. Spatial diversity is essentially
the same as frequency reuse. This is
the idea that different services may
use the same frequency bands if they
purposely avoid others that could
interfere. Keeping a distance from
one another is the main idea. Use
less power to limit range of coverage.
Use highly directive gain antennas
to focus the communications and
reduce interference to others. This
also boosts effective radiated power
extending the range.
The cellular industry uses spatial
diversity to get multiple uses out
of its frequency assignments by
using sectorized antennas and by
controlling handset power. Proper
cell site spacing and antenna focusing
greatly improve spectrum utilization
efficiency.
Move to the higher frequencies.
If you need more bandwidth to
achieve the desirable higher data
rates, go where the bandwidth is:
at the higher frequencies. Move
from UHF to microwave or from
microwave to the millimeter wave
bands. There has been a steady shift
to the higher frequencies over the
years as semiconductor technology
has enabled higher frequency
devices.
Cellular service has moved
from UHF to low microwaves as LTE
service expanded. Now, work on
the 5G cellular system is producing
another move to the millimeter
THE LATEST IN NETWORKING AND WIRELESS TECHNOLOGIES
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Name Frequency Range Applications
Low Frequency (LF) 30 to 300 kHz Navigation, time standards.
Medium Frequency (MF) 300 kHz to 3 MHz Marine/aircraft navigation, AM broadcast.
High Frequency (HF) 3 to 30 MHz AM broadcasting, mobile radio, amateur radio, short-wave
broadcasting.
Very High Frequency (VHF) 30 to 300 MHz Land mobile, FM/TV broadcast, amateur radio.
Ultra High Frequency (UHF) 300 MHz to 3 GHz Cellular phones, mobile radio, wireless LAN, PAN.
Super High Frequency (SHF)
Millimeter wave range
3 to 30 GHz Satellite, radar, backhaul, TV, WLAN, 5G cellular.
Extremely High Frequency (EHF) 30 to 300 GHz Satellite, radar, backhaul, experimental, 5G cellular.
TeraHertz, Tremendously High
Frequency (THF) or Far Infrared (FIR)
300 GHz to IR R & D, Experimental.
