Bài giảng Mạng máy tính - Chapter 7: Wireless and Mobile Networks

Chapter 7

Wireless and

Mobile Networks

Computer

Networking: A Top

Down Approach

7^thEdition, Global Edition

Jim Kurose, Keith Ross

Pearson

April 2016

Wireless and Mobile Networks

7-1

Ch. 7: Wireless and Mobile Networks

Background:

§ # wireless (mobile) phone subscribers now exceeds #

wired phone subscribers (5-to-1)!

§ # wireless Internet-connected devices equals #

wireline Internet-connected devices

• laptops, Internet-enabled phones promise anytime untethered

Internet access

§ two important (but different) challenges

• wireless: communication over wireless link

• mobility: handling the mobile user who changes point of

attachment to network

Wireless and Mobile Networks

7-2

Chapter 7 outline

7.1 Introduction

Mobility

7.5 Principles: addressing and

Wireless

7.2 Wireless links,

characteristics

• CDMA

routing to mobile users

7.6 Mobile IP

7.7 Handling mobility in

cellular networks

7.8 Mobility and higher-layer

protocols

7.3 IEEE 802.11 wireless

LANs (“Wi-Fi”)

7.4 Cellular Internet Access

• architecture

• standards (e.g., 3G, LTE)

Wireless and Mobile Networks

7-3

Elements of a wireless network

network

infrastructure

Wireless and Mobile Networks

7-4

Elements of a wireless network

wireless hosts

§ laptop, smartphone

§ run applications

§ may be stationary (non-

mobile) or mobile

network

infrastructure

• wireless does not always

mean mobility

Wireless and Mobile Networks

7-5

Elements of a wireless network

base station

§ typically connected to

wired network

§ relay - responsible for

sending packets between

wired network and

wireless host(s) in its

infrastructure

“area”

network

• e.g., cell towers,

802.11 access points

Wireless and Mobile Networks

7-6

Elements of a wireless network

wireless link

§ typically used to connect

mobile(s) to base station

§ also used as backbone link

§ multiple access protocol

coordinates link access

network

§ various data rates,

infrastructure

transmission distance

Wireless and Mobile Networks

7-7

Characteristics of selected wireless links

802.11ac

802.11n

1300

450

54

802.11a,g

802.11b

802.11a,g point-to-point

4G: LTWE, WIMAX

5-11

4

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

802.15

1

2.5G: UMTS/WCDMA, CDMA2000

2G: IS-95, CDMA, GSM

.384

.056

Indoor

10-30m

Outdoor

50-200m

Mid-range

outdoor

200m – 4 Km

Long-range

outdoor

5Km – 20 Km

Wireless and Mobile Networks

7-8

Elements of a wireless network

infrastructure mode

§ base station connects

mobiles into wired

network

§ handoff: mobile changes

base station providing

connection into wired

infrastructure

network

Wireless and Mobile Networks

7-9

Elements of a wireless network

ad hoc mode

§ no base stations

§ nodes can only

transmit to other

nodes within link

coverage

§ nodes organize

themselves into a

network: route

among themselves

Wireless and Mobile Networks

7-10

Wireless network taxonomy

multiple hops

single hop

host may have to

relay through several

wireless nodes to

connect to larger

Internet: mesh net

host connects to

base station (WiFi,

WiMAX, cellular)

which connects to

larger Internet

infrastructure

(e.g.,APs)

no base station, no

connection to larger

Internet. May have to

relay to reach other

a given wireless node

MANET, VANET

no base station, no

connection to larger

Internet (Bluetooth,

ad hoc nets)

no

infrastructure

Wireless and Mobile Networks

7-11

Chapter 7 outline

7.1 Introduction

Mobility

7.5 Principles: addressing and

Wireless

7.2 Wireless links,

characteristics

• CDMA

routing to mobile users

7.6 Mobile IP

7.7 Handling mobility in

cellular networks

7.8 Mobility and higher-layer

protocols

7.3 IEEE 802.11 wireless

LANs (“Wi-Fi”)

7.4 Cellular Internet Access

• architecture

• standards (e.g., 3G, LTE)

Wireless and Mobile Networks

7-12

Wireless Link Characteristics (1)

important differences from wired link ….

§ decreased signal strength: radio signal attenuates as 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 off objects

ground, arriving ad destination at slightly different

times

…. make communication across (even a point to point)

wireless link much more “difficult”

Wireless and Mobile Networks

7-13

Wireless Link Characteristics (2)

10^-1

§ SNR: signal-to-noise ratio

• larger SNR – easier to

10^-2

extract signal from noise (a

10^-3

“good thing”)

§ BER: bit error rate

10^-4

§ SNR versus BER tradeoffs

10^-5

• given physical layer: increase

10^-6

power -> increase SNR ->

decrease BER

10^-7

• given SNR: choose physical layer

10

20

30

40

that meets BER requirement,

SNR(dB)

giving highest thruput

QAM256 (8 Mbps)

QAM16 (4 Mbps)

BPSK (1 Mbps)

§ SNR may change with

mobility: dynamically adapt

physical layer (modulation

technique, rate)

Wireless and Mobile Networks

7-14

Wireless network characteristics

Multiple wireless senders and receivers create additional

problems (beyond multiple access):

B

A

C

C’s signal

strength

A’s signal

strength

B

A

space

Hidden terminal problem

§ B,A hear each other

§ B, C hear each other

§ A, C can not hear each other

means A, C unaware of their

interference at B

Signal attenuation:

§ B,A hear each other

§ B, C hear each other

§ A, C can not hear each other

interfering at B

Wireless and Mobile Networks

7-15

Code Division Multiple Access (CDMA)

§ unique “code” assigned to each user; i.e., code set

partitioning

• all users share same frequency, but each user has own

“chipping” sequence (i.e., code) to encode data

• allows multiple users to “coexist” and transmit

simultaneously with minimal interference (if codes are

“orthogonal”)

§ encoded signal = (original data) X (chipping

sequence)

§ decoding: inner-product of encoded signal and

chipping sequence

Wireless and Mobile Networks

7-16

CDMA encode/decode

channel output Z_i,m

.

Z_i,m= d_ic_m

d₀= 1

data

bits

1 1 1 1 1 1

1

d₁= -1

-

- - 1

1 1

-

1

-

1

- - 1

1 1

sender

slot 0

channel

output

slot 1

channel

output

1 1 1

1

1 1 1

1

code

-

1

- - 1

1 1

-

1

- - 1

1 1

slot 1

slot 0

M

.

D_i= SZ_i,mc_m

m=1

M

1 1 1 1 1 1

1

received

input

d₀= 1

-

- - 1

-

- - 1

1 1

1

1 1

d₁= -1

slot 0

channel

output

slot 1

channel

output

1 1 1

1

1 1 1

code

-

1

- - 1

1 1

-

1

- - 1

1 1

receiver

slot 1

slot 0

Wireless and Mobile Networks

7-17

CDMA: two-sender interference

channel sums together

transmissions by sender 1

and 2

Sender 1

Sender 2

using same code as

sender 1, receiver recovers

sender 1’s original data

from summed channel

data!

Wireless and Mobile Networks

7-18

Chapter 7 outline

7.1 Introduction

Mobility

7.5 Principles: addressing and

Wireless

7.2 Wireless links,

characteristics

• CDMA

routing to mobile users

7.6 Mobile IP

7.7 Handling mobility in

cellular networks

7.8 Mobility and higher-layer

protocols

7.3 IEEE 802.11 wireless

LANs (“Wi-Fi”)

7.4 Cellular Internet Access

• architecture

• standards (e.g., 3G, LTE)

Wireless and Mobile Networks

7-19

IEEE 802.11 Wireless LAN

802.11a

802.11b

§ 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

§ 2.4-5 GHz unlicensed spectrum

§ up to 11 Mbps

§ direct sequence spread spectrum

(DSSS) in physical layer

• all hosts use same chipping code

802.11ac

• 5GHz spectrum

• Beamforming

§ all use CSMA/CA for multiple access

§ all have base-station and ad-hoc network versions

Wireless and Mobile Networks

7-20

Bài giảng Mạng máy tính - Chapter 7: Wireless and Mobile Networks - Nguyễn Lê Duy Lai