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WLAN Grundlagen
ITG Informationstagung "Wireless LAN"
Prof. Dr. Andreas SteffenZürcher Hochschule WinterthurProf. Dr. Jean-Frédéric Wagen
Ecole d‘ingénieurs et d‘architectes de Fribourg
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Contents
• WLAN IEEE 802.11 Architecture
• WLAN Frequency Bands
• WLAN Data Rates & Throughput
• WLAN Coverage & Range
• WLAN Standards & Compatibility
• References
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IEEE 802.11 WLAN ArchitectureWired LAN
Access Point(AP)
Wireless Station(STA)
• Basic Service Set (BSS) operating in infrastructure mode controlled by access point
Wireless Station(STA)
STA
STA
• Independent Basic Service Set (IBSS) operating in ad hoc modeforms a peer-to-peer network
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IEEE 802.11 Extended Service Set (ESS)
Bridging based on theInter-Access-Point Protocol
(IAPP)"Roaming"
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Synchronisation and Power Management
Wired LANSTA AP
- sends periodic beaconfor synchronization
- AP will cache messagesfor dozing STA
- is either awake or dozing- must inform AP- must wake-up periodically.
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replies with CTScontaining TX duration
IEEE 802.11 CSMA-CA and TX Reservation
Hidden Terminal Problem
sends RTScontaining TX duration
sets NAV via RTS
sets NAV via CTS
CSMACarrier SenseMultiple Access
CACollision Avoidance
TXTransmit
RTSRequest to Send
CTSClear to Send
NAVNetwork Allocation Vector
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ISM Unlicensed Frequency Bands
Audio
AM BroadcastShort-Wave Radio FM Broadcast
Television Infrared Wireless LAN
Cellular (840MHz)NPCS (1.9GHz)
ExtremelyLow
VeryLow
Low Medium High VeryHigh
UltraHigh
SuperHigh
Infrared VisibleLight
Ultra-violet
X-Rays
902–928 MHz26 MHz
Remote Control,etc.
902902––928 MHz928 MHz26 MHz26 MHz
Remote Control,Remote Control,etc.etc.
5.2 GHz100 MHz
(IEEE 802.11a)HIPERLAN 1+2
5.2 GHz5.2 GHz100 MHz100 MHz
(IEEE 802.11a)(IEEE 802.11a)HIPERLAN 1+2HIPERLAN 1+2
2.4–2.4835 GHz83.5 MHz
(IEEE 802.11b)Microwave Ovens
2.42.4––2.4835 GHz2.4835 GHz83.5 MHz83.5 MHz
(IEEE 802.11b)(IEEE 802.11b)Microwave OvensMicrowave Ovens
Industrial, Scientific and Medical Band
© 2001, Cisco Systems, Inc.
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IEEE 802.11 DSSS Frequency Channel Plan
1 2 3 4 5 6 7 8 9 10 11
1
2
3
4
5
6
7
8
9
10
11
Channel
Frequency2400 248324372412 MHz
22 MHz
5 MHz
12 13
2462 2472
12
13
• 13 channels in Europe (ETSI) from 2412 MHz to 2472 MHz, spaced by 5 MHz. Only first 11 channels available in USA.
• 22 MHz carrier bandwidth.• Only 3-4 non-overlapping channels (USA: 1,6,11 / ETSI: 1,5,9,13).
BAKOM recommends channels 1,7,13 for use in Switzerland
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ITG Informationstagung "Wireless LAN"
WLANData Rates & Throughput
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IEEE 802.11 DSSS Radio Interface
• 1 Mbps 1 Msymbol/s BPSK spread by 11 chip Barker code,(-4 dB Bandwidth = 11 MHz, main lobe = 22 MHz), IEEE 802.11
• 2 Mbps 1 Msymbol/s QPSK spread by 11 chip Barker code(-4 dB Bandwidth = 11 MHz, main lobe = 22 MHz), IEEE 802.11
• 5.5 Mbps 2 Msymbol/s QPSK like symbols spread by 8 chip Complementary Code Keying (CCK). IEEE 802.11b
• 11 Mbps 4 Msymbol/s QPSK like symbols spread by 8 chip Complementary Code Keying (CCK). IEEE 802.11b
• 54 Mbps OFDM with max. 52 sub-carriers, IEEE 802.11a / IEEE 802.11g
raw bit rate is not equalto net bit rate or throughput !
raw bit rate is not equalto net bit rate or throughput !
• 50% max. of the raw bit rate (good reception quality, no interference)
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office
2 Mbps
IEEE 802.11b Maximum Distance Range
100 m
semi-open2 Mbps
semi-open11 Mbps
open11 Mbps 2 Mbps
open
office11 Mbps
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ETSI regulations at 2.4 GHz:EIRP = G ⋅ P < 100 mW
Antenna Input Power P = 100 mW / G Reception Gain G
Point-to-point WLAN connectionsusing directional antennas
Effective Isotropic Radiated Power (EIRP)
Typical single antenna gainG = 10 .. 24 dBi
Covered distanced ≈ 1 .. 3 km
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ITG Informationstagung "Wireless LAN"
WLAN
Standards & Compatibility
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Scope of IEEE 802.11 Standard
3
4
5
6
7
OSI layers• Original IEEE 802.11 standard specifies layer 1
and lower part of layer 2 only• For multi-vendor WLAN roaming, bridging and
routing standards are needed
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IEEE 802.11 Task Group Outline
• 802.11 Specification of WLAN MAC and PHY layers(IR, FH and DSSS at 2.4 GHz), ratified in 1997/1999
• 802.11a PHY layer at 5 GHz (54 Mbps DSSS), ratified in 1999
• 802.11b 11 Mbps DSSS at 2.4 GHz, ratified in 1999
• 802.11c Improvements of the MAC layer (Internal Sub-Layer Service)
• 802.11d Update (frequency spectrum regulations)
• 802.11e Improvements of the MAC layer (Quality of Service)
• 802.11f Inter-Access Point Protocol (IAPP)
• 802.11g Higher Data rate (>20 Mbps) at 2.4 GHz
• 802.11h Dynamic Channel Selection and Transmit Power Control mechanisms
• 802.11i Authentication and Security
http://grouper.ieee.org/groups/802/11/QuickGuide_IEEE_802_WG_and_Activities.htm
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References[1] IEEE 802.11 (= ISO/IEC 8802-11: 1999), Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY) Specifications, ANSI/IEEE Std 802.11,1999 Edition, http://ieee802.org/11.
[2] IEEE Std 802.11b-1999 (Supplement to ANSI/IEEE Std 802.11, 1999 Edition),Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Higher-Speed Physical Layer Extension in the 2.4 GHz Band,ISBN 0-7381-1812-5, http://ieee802.org/11.
[3] BAKOM – Bundesamt für Kommunikation,www.bakom.ch/imperia/md/content/deutsch/telecomdienste/factsheets/factsheet_wlan.pdf
[4] Jean-Frédéric Wagen ([email protected]), EIF, and Andreas Steffen, ZHW,Swisscom Seminar – Access Technologies, Fribourg, October 2002.
[5] Vincent Bieri ([email protected]), Wireless LAN (WLAN) – An Introduction,Séminaire Technique, EIA-FR, March 2002