Wireless LANs and PANs
01204325: Data Communication
and Computer Networks
Adapted from lecture slides by Behrouz A. Forouzan
© The McGraw-Hill Companies, Inc. All rights reserved
Materials taken from lecture slides by Karl and Willig
Asst. Prof. Chaiporn Jaikaeo, Ph.D.
[email protected]
http://www.cpe.ku.ac.th/~cpj
Computer Engineering Department
Kasetsart University, Bangkok, Thailand
Outline




Electromagnetic spectrum and ISM bands
IEEE 802.11 (Wi-Fi)
Bluetooth
IEEE 802.15.4
2
Electromagnetic Spectrum
RF range


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
3
ISM Bands



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Industrial, Scientific, and Medical frequency
bands
Can operate without FCC licenses
Tx output power  1 watt
Eliminate cost and time consuming for licenses
915 MHz*
2.45 GHz
26
MHz
902
MHz
928
MHz
5.8 GHz
100 MHz
2.40
GHz
150 MHz
2.50
GHz
5.725
GHz
5.875
GHz
* Region 2 only
4
Wireless LANs:
IEEE 802.11 (Wi-Fi)
IEEE 802.11


IEEE Standard for Wireless LANs
Covers both physical and data link layers
Wi-Fi Access points
Wi-Fi Router
6
WLAN Architectures


Basic Service Set (BSS)
Extended Service Set (ESS)
7
Basic Service Set (BSS)
(Ad hoc mode)
(Infrastructure mode)
8
Extended Service Set (ESS)
9
IEEE 802.11 Physical Layer
IEEE 802.11 MAC
802.11
802.11a
802.11b
802.11g
802.11n
1-2 Mbps
2.4 GHz
FHSS
DSSS
IR
6-54 Mbps
5 GHz
OFDM
1-11 Mbps
2.4 GHz
DSSS
6-54 Mbps
2.4 GHz
OFDM
DSSS
7.2-150 Mbps
2.4, 5 GHz
OFDM
10
IEEE 802.11b/g Channels
See http://en.wikipedia.org/wiki/List_of_WLAN_channels
11
IEEE 802.11 MAC Layer
PCF – Point Coordination Function (controlled access)
DCF – Distributed Coordination Function (random access)
12
CSMA/CA Used by 802.11

Basic CSMA/CA not enough

"Hidden Terminal Problem"
A
B
C
13
CSMA/CA With RTS/CTS
A
B
C
D
RTS
CTS
NAV
Data
NAV
ACK
NAV
 Network Allocation Vector
(Virtual Carrier Sensing)
14
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
15
Wireless PANs: Bluetooth
Bluetooth Standard


Wireless Personal Area Network
technology
Designed for connecting devices with
different functionalities:


Telephone, mouse, keyboard, camera, etc.
Standard  IEEE 802.15.1
17
Bluetooth Piconet
18
Bluetooth Scatternet
19
Bluetooth Layers
20
Bluetooth Communication

Single slave
21
Bluetooth Communication

Multiple slaves
22
Low-Rate Wireless PANs:
IEEE 802.15.4
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
24
IEEE 802.15.4 Physical

Operating frequency bands
Channel 0
Channels 1-10
868.3 MHz
902 MHz
868MHz (20 kbps)
2.4 GHz
PHY
2.4 GHz
2 MHz
928 MHz
915 MHz (40 kbps)
Channels 11-26
2.4 GHz (250 kbps)
5 MHz
2.4835 GHz
25
IEEE 802.15.4 MAC
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Single channel at any one time
Combines contention-based and schedulebased schemes
Asymmetric: nodes can assume different
roles
26
IEEE 802.15.4 Devices
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Full function device (FFD)
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Any topology
Network coordinator capable
Talks to any other device
Reduced function device (RFD)
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Limited to star topology
Cannot become a network coordinator
Talks only to a network coordinator
Very simple implementation
27
IEEE 802.15.4 Topologies
28