152
Networking Fundamentals
radio interference
interference that
matches the
frequency of a carrier
wave.
technology. First, the two devices that are communicating must be in direct line of
sight of each other. This means that the infrared receiver/transmitter of each device
must be aimed, or at least positioned, in the general direction of the other.
The infrared beam is weak and must be transmitted through an optical
lens to prevent dispersion. The other disadvantage is an infrared beam can
travel a relatively limited distance when compared with wireless radio wave
technologies. Some infrared communication links for networks use a laser to
achieve greater distances.
Even with its disadvantages, infrared can be found in many of the same
applications as Bluetooth. It is commonly used in some models of personal digital
assistants, palm tops, and laptops. Typical data rates for infrared devices are 1 Mbps
and 2 Mbps. Data rates can be much higher when lasers are used for the direct
connection of two LANs.
Radio Interference
Radio interference is interference that matches the frequency of the carrier
wave. The Federal Communications Commission (FCC) is responsible for
dividing the entire electromagnetic spectrum to prevent electronic equipment
from interfering with one another. However, this is not always possible. Think
for a minute how many different devices use and produce electromagnetic
waves—remote controls for remote control cars, remote control airplanes, garage
door openers, television, AM radio, FM radio, satellites, pagers, cellular phones,
Figure 4-4.
The carrier wave
and the data wave
are electronically
combined or
modulated. The
modulated signal
must remain inside
the radio frequency
range or channel
assigned by the FCC.
Wave patterns
represent binary
data patterns
Assigned carrier
wave bandwidth
200 kHz
Carrier wave
Carrier wave
designated as
145 MHz
145 MHz
Data wave
Zoomed close-up of the modulated radio
signal, which is a combination of carrier
wave and data wave patterns
Entire
electromagnetic
spectrum
0 MHz