fallsem2014 15 cp4404 10 jul 2014 rm01 introduction to wc

8/11/2019 FALLSEM2014 15 CP4404 10 Jul 2014 RM01 Introduction to WC

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Wireless, Mobile Networks 6-2

Elements of a wireless network

networkinfrastructure


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wireless hosts laptop, smartphone

run applications

may be stationary (non-mobile) or mobile

wireless does notalways mean mobility




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base station typically connected to

wired network

relay - responsible forsending packets

between wired networkand wireless host(s) inits area

e.g., cell towers,802.11 accesspoints




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wireless link typically used to

connect mobile(s) tobase station

also used as backbone

link multiple access

protocol coordinateslink access

various data rates,transmission distance




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infrastructure mode base station connects

mobiles into wirednetwork

handoff: mobile

changes base stationproviding connectioninto wired network




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ad hoc mode no base stations

nodes can onlytransmit to othernodes within linkcoverage

nodes organizethemselves into anetwork: route

among themselves



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Wireless network taxonomy

single hop multiple hops

infrastructure

(e.g., APs)

no

infrastructure

host connects to

base station (WiFi,

WiMAX, cellular)

which connects tolarger Internet

no base station, no

connection to larger

Internet (Bluetooth,ad hoc nets)

host may have to

relay through several

wireless nodes to

connect to largerInternet: mesh net

no base station, no


Internet. May have to

relay to reach othera given wireless node

MANET, VANET


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Wireless Link Characteristics (1)

important differences from wired link .

decreased signal strength: radio signal attenuatesas it propagates through matter (path loss)

interference from other sources: standardized

wireless network frequencies (e.g., 2.4 GHz)shared by other devices (e.g., phone); devices(motors) interfere as well

multipath propagation: radio signal reflects offobjects ground, arriving ad destination at slightlydifferent times

. make communication across (even a point to point)wireless link much more difficult


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SNR: signal-to-noise ratio larger SNReasier to

extract signal from noise (a

good thing)

SNR versus BER tradeoffs

given physical layer:increase

power -> increase SNR-

>decrease BER

given SNR:choose physical

layer that meets BERrequirement, giving highest

thruput

SNR may change with mobility:

dynamically adapt physical layer

(modulation technique, rate)

10 20 30 40

QAM256 (8 Mbps)

QAM16 (4 Mbps)

BPSK (1 Mbps)

SNR(dB)

BER

10-1

10-2

10-3

10-5

10-6

10-7

10-4


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Wireless network characteristics

Multiple wireless senders and receivers create

additional problems (beyond multiple access):

AB

C

Hidden terminal problem

B, A hear each other B, C hear each other

A, C can not hear each othermeans A, C unaware of theirinterference at B

A B C

As signalstrength

space

Cs signal

strength

Signal attenuation:

B, A hear each other

B, C hear each other

A, C can not hear each otherinterfering at B


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IEEE 802.11 Wireless LAN

802.11b 2.4-5 GHz unlicensed spectrum

up to 11 Mbps

direct sequence spread

spectrum (DSSS) in physicallayer

all hosts use same chippingcode

802.11a 5-6 GHz range up to 54 Mbps

802.11g

2.4-5 GHz range up to 54 Mbps

802.11n: multiple antennae 2.4-5 GHz range up to 200 Mbps

all use CSMA/CA for multiple access

all have base-station and ad-hoc network versions


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Chapter 6 outline

6.1 Introduction

Wireless

6.2Wireless links,

characteristics CDMA

6.3 IEEE 802.11 wireless

LANs (Wi-Fi)

6.4Cellular InternetAccess

architecture

standards (e.g., GSM)

Mobility

6.5Principles: addressing

and routing to mobile users

6.6Mobile IP

6.7Handling mobility in

cellular networks

6.8Mobility and higher-layer

protocols

6.9Summary


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Wi l M bil N k 6 18


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wireless hosts laptop, smartphone

run applications

may be stationary (non-mobile) or mobile

wireless does notalways mean mobility



Wi l M bil N t k 6 19


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base station typically connected to

wired network

relay - responsible forsending packetsbetween wired networkand wireless host(s) inits area

e.g., cell towers,802.11 accesspoints





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wireless link typically used to

connect mobile(s) tobase station

also used as backbonelink

multiple accessprotocol coordinateslink access

various data rates,transmission distance





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Characteristics of selected wireless

links

Indoor10-30m

Outdoor50-200m

Mid-range

outdoor200m4 Km

Long-range

outdoor5Km20 Km

.056

.384

1

4

5-11

54

2G: IS-95, CDMA, GSM

2.5G: UMTS/WCDMA, CDMA2000

802.15

802.11b

802.11a,g

3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO

4G: LTWE WIMAX

802.11a,g point-to-point

200 802.11n

Datarate(M

bps)

Wireless Mobile Networks 6 22


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infrastructure mode base station connects

mobiles into wirednetwork

handoff: mobilechanges base stationproviding connectioninto wired network





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ad hoc mode no base stations

nodes can onlytransmit to othernodes within linkcoverage

nodes organizethemselves into anetwork: route

among themselves




24/27


Wireless network taxonomy

single hop multiple hops

infrastructure

(e.g., APs)

no

infrastructure

host connects to

base station (WiFi,

WiMAX, cellular)

which connects tolarger Internet

no base station, no


Internet (Bluetooth,ad hoc nets)

host may have to

relay through several

wireless nodes to

connect to largerInternet: mesh net

no base station, no


Internet. May have to

relay to reach other

a given wireless node

MANET, VANET

Wireless Mobile Networks 6-25


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important differences from wired link .

decreased signal strength: radio signal attenuatesas it propagates through matter (path loss)

interference from other sources: standardized

wireless network frequencies (e.g., 2.4 GHz)shared by other devices (e.g., phone); devices(motors) interfere as well

multipath propagation: radio signal reflects offobjects ground, arriving ad destination at slightlydifferent times

. make communication across (even a point to point)wireless link much more difficult

Wireless Mobile Networks 6-26


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SNR: signal-to-noise ratio larger SNReasier to

extract signal from noise (a

good thing)

SNR versus BER tradeoffs

given physical layer:increase

power -> increase SNR-

>decrease BER

given SNR:choose physical

layer that meets BER

requirement, giving highest

thruput

SNR may change with mobility:

dynamically adapt physical layer

(modulation technique, rate)

10 20 30 40

QAM256 (8 Mbps)

QAM16 (4 Mbps)

BPSK (1 Mbps)

SNR(dB)

BER

10-1

10-2

10-3

10-5

10-6

10-7

10-4


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fallsem2014 15 cp4404 10 jul 2014 rm01 introduction to wc

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