Communication Research Labs Sweden AB Introduction to Wireless communication and WLAN.

Communication Research Labs Sweden AB

Introduction toWireless communication and WLAN


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.


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.


IEEE 802.11 Chip Vendors

Most common chipset producers:• Atheros• Broadcom• Intel• Intersil (Prism)• Proxim (Orinoco)


Different Typesof

Networks


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)


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)


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


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)


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


Characteristicsof

Wireless Networks


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


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


TheIEEE 802.11 Family


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).


IEEE 802.11 Overview

Mobile terminal

Access Point Fixed

terminal


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


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.


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


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


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


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)


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


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


Wireless Security


Wireless Security

• MAC-address filtering• SSID Broadcast• Authentication• Encryption


Wireless Security - WEP

WEP (Wired Equivalent Privacy)• Part of the 802.11 standard• Encryption standard: RC4


Wireless Security - WPA

WPA (Wi-Fi Protected Access)• Encryption standard: RC4• Authentication• Encryption• Pre-shared Key (PSK)• IEEE 802.1x (authentication server)


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)


Wireless Security – Other

Higher layer security measures such as:• IPSec• SSL• ...

Communication Research Labs Sweden AB Introduction to Wireless communication and WLAN.

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