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Wireless LANs and PANs
01204325: Data Communication and Computer Networks
Asst. Prof. Chaiporn Jaikaeo, [email protected]
http://www.cpe.ku.ac.th/~cpjComputer Engineering Department
Kasetsart University, Bangkok, ThailandAdapted from lecture slides by Behrouz A. Forouzan© The McGraw-Hill Companies, Inc. All rights reservedMaterials taken from lecture slides by Karl and Willig
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Outline Electromagnetic spectrum and ISM
bands IEEE 802.11 (Wi-Fi) Bluetooth IEEE 802.15.4
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Electromagnetic Spectrum
Government regulations make specific ranges of the electromagnetic spectrum available for communication
A license is required to operate transmission equipment in some parts of the spectrum Some parts are unlicensed
RF range
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ISM Bands Industrial, Scientific, and Medical
frequency bands Can operate without FCC licenses Tx output power 1 watt Eliminate cost and time consuming for
licenses
26MHz
902MHz
928MHz
915 MHz*
100 MHz
2.40GHz
2.50GHz
2.45 GHz
150 MHz
5.725GHz
5.875GHz
5.8 GHz
* Region 2 only
Wireless LANs:IEEE 802.11 (Wi-Fi)
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IEEE 802.11 IEEE Standard for Wireless LANs Covers both physical and data link
layers
Wi-Fi Access points Wi-Fi Router
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WLAN Architectures Basic Service Set (BSS) Extended Service Set (ESS)
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Basic Service Set (BSS)
(Ad hoc mode) (Infrastructure mode)
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Extended Service Set (ESS)
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IEEE 802.11 Physical Layer
IEEE 802.11 MAC
802.11a 802.11b 802.11g 802.11n
6-54 Mbps5 GHzOFDM
1-11 Mbps2.4 GHz
DSSS
6-54 Mbps2.4 GHzOFDMDSSS
7.2-150 Mbps
2.4, 5 GHzOFDM
802.11
1-2 Mbps2.4 GHz
FHSSDSSS
IR
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IEEE 802.11b/g Channels
See http://en.wikipedia.org/wiki/List_of_WLAN_channels
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IEEE 802.11 MAC Layer
PCF – Point Coordination Function (controlled access)DCF – Distributed Coordination Function (random access)
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CSMA/CA Used by 802.11 Basic CSMA/CA not enough
"Hidden Terminal Problem"
A B C
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CSMA/CA With RTS/CTS
RTS
CTS
Data
ACK
A B C D
NAVNAV
NAV Network Allocation Vector
(Virtual Carrier Sensing)
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IEEE 802.11 and Wi-Fi IEEE 802.11 provides most of the
standards A group of vendors who build
wireless equipment formed the Wi-Fi Alliance A non-profit organization that tests
and certifies wireless equipment using the 802.11 standards
Wireless PANs: Bluetooth
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Bluetooth Standard Wireless Personal Area Network
technology Designed for connecting devices with
different functionalities: Telephone, mouse, keyboard, camera,
etc. Standard IEEE 802.15.1
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Bluetooth Piconet
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Bluetooth Scatternet
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Bluetooth Layers
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Bluetooth Communication Single slave
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Bluetooth Communication Multiple slaves
Low-Rate Wireless PANs:
IEEE 802.15.4
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IEEE 802.15.4 IEEE standard for Low-Rate
WPAN (LR-WPAN) applications Low-to-medium bit rates Moderate delays without too
strict requirements Low cost, low energy
consumption Applications
Home automation and security systems
Smart metering Wireless data collection
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868MHz (20 kbps)
2.4 GHz
868.3 MHz
Channel 0 Channels 1-10
Channels 11-26
2.4835 GHz
928 MHz902 MHz
5 MHz
2 MHz
2.4 GHz PHY
IEEE 802.15.4 Physical Operating frequency bands
915 MHz (40 kbps)
2.4 GHz (250 kbps)
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IEEE 802.15.4 MAC Single channel at any one time Combines contention-based and
schedule-based schemes Asymmetric: nodes can assume
different roles
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IEEE 802.15.4 Devices Full function device (FFD)
Any topology Network coordinator capable Talks to any other device
Reduced function device (RFD) Limited to star topology Cannot become a network coordinator Talks only to a network coordinator Very simple implementation
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IEEE 802.15.4 Topologies
