Post on 12-Jan-2016
Communication Research Labs Sweden AB
Introduction toWireless communication and WLAN
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Background / History
Two competitive standards:• IEEE 802.11• ETSI HiperLan/2
IEEE 802.11• Ethernet based• Standard in 1997 (2 Mbps)
HiperLan/2• ATM based (Asynchronous Transfer Mode)• Excellent support for Quality of Service• Obsolete!
IEEE – Institute for Electric and Electronic Engineers (USA)ETSI – European Telecommunication Standardization Institute (Europe)HIPERLAN - High Performance Radio Local Area Network.
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Background / History
In 1999, early IEEE 802.11 products suffered from interoperability problems.
The Wi-Fi Alliance is a trade group consisting of almost all 802.11 equipment producers. (Over 260 members)
Products with the Wi-Fi logo has been interoperability tested with other Wi-Fi products.
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IEEE 802.11 Chip Vendors
Most common chipset producers:• Atheros• Broadcom• Intel• Intersil (Prism)• Proxim (Orinoco)
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Different Typesof
Networks
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Personal Area Network (PAN)
The interconnection of devices within the range of an individualperson, typically within a range of 10 meters.
Examples• Interconnection of wearable computer components• Connection of headset and head display with mobile phone
Technologies for realization• IrDA (Infrared)• IEEE 802.15
• Bluetooth, ZigBee, UltraWideband(UWB)
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Local Area Network (LAN)
A LAN supplies networking capability to a group of computers in close proximity to each other such as within an office environment.
Examples• Interconnection of printers, stationary and mobile devices within an office• Internet access at university, airports etc. (Hot Spots)• Interconnection of inHome entertainment
Technologies for realization• IEEE 802.11 (WLAN)• Digital Enhanced Cordless Telephony (DECT)
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Wireless Access Technologies Local/ Personal Area Networks
DECT
High Speed
Vehicular
Rural
Vehicular
Urban
Pedestrian
Indoor
Fixed Urban
Personal Area
0.01 0.1 1 10 100 1000 Data rate(Mb/s)
IEEE 802.11b IEEE 802.11g
IEEE 802.11a
IEEE 802.11n
IEEE 802.15.4Zigbee
IEEE 802.15.1Bluetooth
IEEE 802.15.3 IEEE 802.15.3a
Local Area
Personal Area
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Metropolitan Area Network (MAN)
A MAN supplies networking capability to a city or metropolitan area.
Examples• Wireless interconnection of operator networks with WLAN• Wireless DSL solution• Broadband Wireless for last mile to connect homes through wireless to network operators
Technologies for realization• IEEE 802.16
• WiMAX• IEEE 802.11a/b/g (Mesh)
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Wireless Access Technologies Metropolitan Area Network (MAN)
High Speed
Vehicular
Rural
Vehicular
Urban
Pedestrian
Indoor
Fixed Urban
Personal Area
0.01 0.1 1 10 100 1000 Data rate(Mb/s)
IEEE 802.11b IEEE 802.11g
IEEE 802.11a
IEEE 802.11n
Metro Area
WiMAX 801.16
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Characteristicsof
Wireless Networks
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Characteristics of Wireless Networks
Frequency Regulation• Useful spectrum almost occupied
High Bit Error Rate and Packet Loss Rate• Due to interference with engines, lightning etc.
Shared Medium Communication
High Delay and Jitter• Due to high error rate, error control and MAC mechanisms
Low data rate•54 Mbps in WLAN (shared), 53 kbps in GSM/GPRS
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Signal Propagation
Transmission Range• Communication possible• Low error rate
Detection Range• Detection of signal is possible• No communication is possible
Interference Range• Signal may not be detected• Increased background noise
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TheIEEE 802.11 Family
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802.11 LAN architecture
• Wireless host communicates with base station (or AP)
• Basic Service Set (BSS) (aka “cell”) in infrastructure mode use same frequency and contains: • wireless hosts or station (STA)• access point (AP): base station• ad hoc mode: hosts only IBSS (Independent Basic Service Set
sharing same frequency
• Distribution System • Interconnects several BSS to form a logical ESS (Extended
Service Set).
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IEEE 802.11 Overview
Mobile terminal
Access Point Fixed
terminal
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IEEE 802.11b
Facts• 2.4 GHz - 2.485 GHz divided into 11 channels at different frequencies• Has 3 non-overlapping frequencies• Approximately range: 38 meters indoors and 140 meters outdoors
Data Rates• 1 Mbit/s (legacy 802.11)• 2 Mbit/s (legacy 802.11)• 5.5 Mbit/s• 11 Mbit/s
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IEEE 802.11b (cont.)
802.11b and 802.11g equipment could occasionally suffer interference from microwave ovens or cordless telephones.
Bluetooth devices, while operating in the same 2.4 GHz band, do not interfere with 802.11b and 802.11g (in theory!): frequency hopping spread spectrum signaling method for BT (FHSS) VS direct sequence spread spectrum signaling method (DSSS) for 802.11.
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IEEE 802.11g
Facts• 2.4 GHz - 2.485 GHz divided into 11 channels at different frequencies• Has 3 non-overlapping frequencies• Approximately range: 38 meters indoors and 140 meters outdoors
Data Rates• 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s
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IEEE 802.11a
Facts• 5.15 GHz – 5.25 GHz / 5.25 GHz – 5.35 GHz• 5.49 GHz – 5.725 GHz / 5.725 GHz – 5.85 GHz• Has 23 non-overlapping frequencies• Approximately range: 35 meters indoors and 120 meters outdoors• 802.11a devices are never affected by products operating on the 2.4 GHz band• Reasonably free from interference
Data Rates• 6, 9, 12, 18, 24, 36, 48, 54 Mbit/s
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Hidden and exposed terminal problems
BA C
Range of terminal A
Range of terminal C
will collide with transmission from A at B
Hidden Terminal Problem
A CB D
Range of terminal B
Range of terminal C
Exposed Terminal Problem
cannot send to D due to carrier sense
currently transmittingwants to transmit
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IEEE 802.11: Multiple Access
• Avoid collisions: 2+nodes transmitting at same time• 802.11: CSMA - sense before transmitting
• Don’t collide with ongoing transmission by other node
• 802.11: no collision detection!• difficult to receive (sense collisions) when transmitting due to weak
received signals (fading)
• can’t sense all collisions in any case: hidden terminal, fading
• goal: avoid collisions: CSMA/CA (Collision Avoidance)
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802.11 frame: addressing
Framecontrol
duration
2 2Address
1Address
2Address
3seq
controlAddress
4payload
6 6 6 62 0-2312CRC
4
Address 1: MAC address of wireless host or AP to receive this frame. Used by stations to filter packets
Address 2: MAC address of wireless host or AP transmitting this frame. Receiver thus identifies ACK target
Address 3: MAC address of router interface to which AP is attached. Depends on To and From bits in Frame control field
Address 4: used only in ad hoc mode to identify original source of WDS (wireless distribution system) frames
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802.11 MAC Layer Overhead
Data rate (Mbps) Approximate Throuput (Mbps)
802.11b 11 6
802.11g (802.11b in cell) 54 8
802.11g (no 802.11b in cell) 54 22
802.11a 54 25
Source: Cisco Systems, Inc.
Network Capacity Approximations for 802.11b, 802.11g and 802.11a
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Wireless Security
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Wireless Security
• MAC-address filtering• SSID Broadcast• Authentication• Encryption
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Wireless Security - WEP
WEP (Wired Equivalent Privacy)• Part of the 802.11 standard• Encryption standard: RC4
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Wireless Security - WPA
WPA (Wi-Fi Protected Access)• Encryption standard: RC4• Authentication• Encryption• Pre-shared Key (PSK)• IEEE 802.1x (authentication server)
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Wireless Security – WPA2
WPA2 (Wi-Fi Protected Access) – IEEE 802.11i• Encryption standard: AES• Authentication• Encryption• Pre-shared Key (PSK)• IEEE 802.1x (authentication server)
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Wireless Security – Other
Higher layer security measures such as:• IPSec• SSL• ...