Transcript An Examination of Wireless Network Interference

An Examination of Wireless
Network Interference
Troy L. Behmer
COSC 352
Spring 2010
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What is Wireless Interference?
• The most significant problem that wireless
communications face.
– It is due to the large amount of electromagnetic
waves that saturate Earth’s atmosphere.
• Signals from these like Planes, radio stations, and
satellites are constantly flying through the air over our
heads.
• These signals make it difficult because they cloud or
block, that frequencies that are needed to transmit
information.
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Useful Terms
• Access point:
– A device that accepts
wireless signals from
nodes on a network, and
then retransmits the
information to the rest
of the network.
– Placement of these
devices is an important
point to consider when
designing a WLAN.
3
Useful Terms
• Diffraction:
– When a wireless signal
splits into secondary waves
when it encounters an
obstruction.
– As you can see in the
image; when the signal
meets a jagged surface like
the corner of the table, it
breaks into many smaller
‘secondary’ waves.
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Useful Terms
• Scattering:
– The diffusion, or
reflection of a signal in
multiple directions.
– As scattering of a signal
continues to occur, the
signal will lose its
integrity and die off.
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Useful Terms
• Reflection:
– Reflection happens when the signal just completely bounces off
the object.
• Reflection can be good because clients don't have to rely of having the
access point within the line of site. Signals can be transmitted and
bounced off large buildings to a client.
• Reflection can be bad if it causes signals to bleed into an unneeded area.
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Types of Interference
• White noise:
– Is a random signal with a flat power spectral density. The
signal contains equal power within a fixed bandwidth at
any center frequency
• Example: the humming you sometimes hear through a phone line.
• Radio Frequency interference:
– Other devices in the vicinity are operating on the same
radio frequency, causing interference.
• Example: neighbor or nearby business.
• Physical interference:
– Any large physical object that obstructs the path of the
signal.
• Example: tree or building
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Types of Interference
• Electrical interference:
– Interference will be high near places such as power
plants, or any kind of major electrical conduit.
• Environment factors:
– Extreme weather conditions such as lightning or
heavy fog can cause the strength of a wireless signal
to fail.
• As you will see later, water is decent blocker of
electromagnetic waves.
• Explaining why fog would cause interference.
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Sources of Interference
• Internal Sources
– Any device that operates on the 2.1 to 2.4 GHz
bandwidth.
• These include
– Microwaves operating within 10 feet of an access point or
receiving device.
– Cordless/cellular phones/Bluetooth devices
– Walkie-talkies/ baby monitors
– Certain types of LCD monitors, which run between channels
11 and 14.
» These emit harmonic interference
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Sources of Interference
• External Sources
– Other wireless networks operating at the same
frequency.
• Example: Neighboring Businesses
– Power stations, whose many pieces of equipment
radiate ambient radio waves that can cause
interference.
– High voltage power lines, and electrical train stations.
• Living or working near these types of places will effect your
network
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Effects of Building Materials
Type of Barrier
Interference potential
Wood
Low
Plaster
Low
Synthetic material
Low
Glass
Low
Water
Medium
Bricks
Medium
Marble
Medium
Paper rolls
High
Concrete
High
Bulletproof glass
High
metal
Very high
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Solutions to Interference
• Analyze desired area BEFORE installing the
WLAN.
– Once sources of interference are identified,
remove them, or simply turn them off.
• Set up your WLAN so that you are able to take
advantage of reflection, diffraction, and
scattering
– Take into account the Line of sight principle
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Solutions to Interference
• Interference from another network
– Change the frequency accepted by your access
point by changing the channel number
– Replacing your 2.4 GHz access points with 5.0 GHz
models
• Purchase the latest version of WLAN hardware
and software
– These come with more advanced interference
eliminating algorithms.
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References
• Apple. February 4th, 2010. Apple Product
Support. February 20th, 2010.
<http://support.apple.com/kb/HT1365>.
• Jim Geier. “Minimizing 802.11 Interference
Issues”. Wi-Fi Planet. January 11th, 2002. February
20th, 2010. <http://www.wifiplanet.com/tutorials/article.php/953511>.
• Dean, Tamara. Network+ Guide to Networks.
Boston: Course Technology, 2009.
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