empirical study of 802.11b wireless networks in the presence of bluetooth interference
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Empirical Study of 802.11b Wireless Networks in the Presence of Bluetooth Interference Cameron McKay and Fukumasa Masuda Institute for Telecommunication Sciences National Telecommunications and Information Administration Boulder, CO [email protected]. Outline. - PowerPoint PPT PresentationTRANSCRIPT
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March 6, 2003 Empirical Study of 802.11b Wireless Networksin the Presence of Bluetooth Interference
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Empirical Study of 802.11bWireless Networks in the Presence
of Bluetooth Interference
Cameron McKay and Fukumasa MasudaInstitute for Telecommunication Sciences
National Telecommunicationsand Information Administration
Boulder, [email protected]
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March 6, 2003 Empirical Study of 802.11b Wireless Networksin the Presence of Bluetooth Interference
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Outline
• Current Wireless Technologies
• The Interference Problem
• Throughput Testing– Setup/Methodology– Results
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Current Wireless Technologies
2.4 GHzBand
5 GHzBand
Two bands commonly usedfor wireless networking
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March 6, 2003 Empirical Study of 802.11b Wireless Networksin the Presence of Bluetooth Interference
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Current Wireless Technologies
5 GHz Band• 5.15 – 5.35 GHz and 5.725 – 5.825 GHz• 300 MHz total• Home to…
– 802.11a (54 Mbps)
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Current Wireless Technologies
2.4 GHz Band• 2.4 – 2.483 GHz
• 83 MHz total
• Home to…
– Bluetooth (1 Mbps)
– 802.11b (11 Mbps)
– 802.11g (54 Mbps)
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Current Wireless Technologies
• Two big players– 802.11b (aka Wi-Fi)
• 11 Mbps• Used for medium-range wireless networks
– 100 m nominally
• 15 – 20 dBm power output
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Current Wireless Technologies
• Two big players– Bluetooth
• 1 Mbps• Frequency-hopping• Included with many cell phones and PDAs• Used for short-range cable replacement
– Syncing PDAs with computers, wireless headsets, connecting cell phones with PDAs/laptops
• Three power classes– 0 dBm: 10 cm range– 4 dBm: 10 m range (most common)– 20 dBm: 100 m range
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The Interference Problem
Bluetooth and 802.11b are complementary (not competing)
technologies that need to coexist…
BUT
Since they use the same 2.4 GHzfrequency band, there will be some
level of interference
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The Interference ProblemF
requ
ency
2.4
GH
z2.
483
GH
z
Time
802.11b Packet 802.11b Packet
802.11b Data Transmission
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The Interference ProblemF
requ
ency
2.4
GH
z2.
483
GH
z
Time
Bluetooth Data Transmission
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802.11b Packet 802.11b Packet
The Interference ProblemF
requ
ency
2.4
GH
z2.
483
GH
z
Time
Combined Data Transmission
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802.11b Packet 802.11b Packet
The Interference ProblemF
requ
ency
2.4
GH
z2.
483
GH
z
Time
Combined Data Transmission
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The Interference Problem
How do Bluetooth devices affect the
speed of nearby 802.11b links?
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Throughput Testing
• Previous work– Simulations– Laboratory Experiments
• idealized conditions
– Few real-world empirical studies
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Throughput Testing
• Our work– Speed measurements under real-world
conditions– Multiple Bluetooth interferers
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Throughput Testing
• Our Testing – Basic Idea– Set up an 802.11b link– Vary its SNR– Measure the link speed without
interference– Activate some Bluetooth devices and
measure the speed again
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Throughput Testing
50 45 40 35 30 25 20 15 10
0
1
2
3
802.11b SNR (dB) measured before interference
Num
ber
of I
nter
fere
rs
In other words, we want to fill in this matrix with speed numbers
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Throughput Testing
• How to measure the SNR?
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Throughput Testing
• How to measure the link speed?– Network testing application (Chariot) would
have been easiest– FTP works just fine (and is free)
• Send a file over the wireless network• Speed = (File Size)/(Time)
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Throughput Testing
Test Setup – Hardware
802.11b Access Point
FTP Server(connected via
100 Mbps Ethernetto the Access Point)
802.11b-equipped Laptop
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Throughput Testing
Test Setup – Hardware
Throughput bottleneck isthe wireless link – speed is
not limited by the FTP serveror the Ethernet segment
100 Mbps11 Mbps
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Throughput Testing
Pair of Bluetooth-equippedcomputers (Interferers)
1 m
Test Setup – Hardware
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Throughput Testing
Test Setup – Hardware
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Results
Data Rate – No Interference
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Results
Data Rate – One Interferer
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Results
Data Rate – One Interferer
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Results
Percentage Network Speed Lost
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Results
Data Rate – Multiple Interferers
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Results
• Single Interferers– 50% network speed lost at SNR of 25 dB
• Multiple Interferers– Effects are highly dependent on SNR
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Questions