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第 2 讲 无线网络与移动终端

§2.1 无线通信与网络§2.2 移动终端及接入

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Mobile Computing Architecture

Server

MU(mobile unit)

MSS(mobile support

station)

Fixed network

Wireless radio cell (19.2Kbps) WLAN

无线通信技术

调制解调技术DSSSFHSSOFDM

无线接入技术CSMA/CA ALOHATDMACDMAOFDMA…

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无线网络 P31 图 无线个域网 无线局域网络 无线城域网 无线广域网 卫星通信网络

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无线个域网 红外技术 蓝牙技术 UWB ZigBee NFC

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红外通信技术 Low cost and not interfered by radio signal. Can connect up to 2 miles with line-of-sight. There are two standards: IrDA and 802.11 IR. IrDA (Infrared Data Association) compatible:

Use regular Infrared.Data rate from 9.6 kbps to 4 Mbps.Must follow the IrDA specification.

Wireless Ethernet 802.11 IR:Use diffused Infrared, without line-of-sight.Can connect to LAN.Standard not updated for a while.Signal can be swamped by sunlight.Bandwidth is still limited.

Bluetooth

Also defined as 802.15b. Variation 802.15c at higher data rate and 802.15d consuming

little power. Connect devices up to a distance of 10m. Use master/slave design, known as a piconet. Built upon scattered net with many piconets. Support up to 7 active slaves, and 255 in total. Support 13 specific applications, including service discovery,

LAN access and FTP. Bandwidth 1 to 10 Mbps. Low power consumption. Higher cost than infrared, but low cost compared with wireless

LAN.

Bluetooth Network Topology

Radio DesignAll radios are symmetric (can be master or slave)

Pico-net• 1 master:

• 7 active slaves• 200+ parked slaves

• Each network has a unique hopping pattern / ID

M

A

P

P

P

Scatternet• Multiple pico-nets co-located• Device can be on multiple pico-

nets (Performance tradeoff)

M

A

A

A

P

P

ZigBee

IEEE 802.15.4, brother of Bluetooth Low cost, low power consumption High node density, long range Low data rate Mainly used for

Human Input Devices Remote controller

Mouse, keyboard…

Sensors (WSN)

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ZigBee Network Topology

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UWB （超宽带） IEEE 802.15.3 Short distance: 2m-10m, Very low power consumption Impulse based waveforms (simple)

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2.4 GHz

Narr

ow

ban

dN

arr

ow

ban

d

0 1 0 1

3 10 GHzfrequency

Ult

raw

ideb

an

dU

ltra

wid

eb

an

d Time-domain behavior Frequency-domain behavior

time

1 0 1

(FCC Min=500Mhz)

Near Field Communication (NFC)

Very simple wireless communication setup Very small distance (<20cm) Low data rate (~400k) Similar to Infrared (using RF instead)

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比较 NFC: 消费支付；红外：设备控制；蓝牙：设备通

信互联； ZigBee ：大量节点（ WSN ）

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红外 NFC 蓝牙 ZigBee WiFi UWB

传输速率 115kbps 424kbps 1-3Mkbps 20-250kbps

>150Mbps 1Mbps

传输距离 5m 10cm 10-100m 100-300m >100m 100m

频段 / 13.5G 2.45G 2.45G 2.45G 、 5G

2.45G

通信协议 IrDA ISO18092…

IEEE802.15.1

IEEE802.15.4

IEEE802.11

IEEE802.15.3

功耗 低 很低 低 低 低 低安全性 高 高 中 中 中 高成本 低 低 高 中 高 中方便性 高 高 中 中 中 中

无线局域网（ WLAN ） Most common variant is 802.11n, with data rate up to

150Mbps. Alternative version 802.11a/b/g. Compatible with Ethernet using access point. Can also support ad hoc networking. High bandwidth. Initially high cost, but now becomes very affordable.

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网络协议与标准

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protocol

Release Freq.(GHz)

Bandwidth (MHz)

Data rate (Mbps) Modulation

Approx. range (m)indoor outdoor

— Jun 1997

2.4 20 1, 2 DSSS, FHSS

20 100

a Sep 1999

5 20 6, 9, 12, 18, 24, 36, 48, 54 OFDM 35 1203.7 — 5,000

b Sep 1999

2.4 20 5.5, 11 DSSS 38 140

g Jun 2003

2.4 20 6, 9, 12, 18, 24, 36, 48, 54 OFDM, DSSS

38 140

n Oct 2009

2.4/5 20 7.2, 14.4, 21.7, 28.9, 43.3, 57.8, 65, 72.2

OFDM 70 250

40 15, 30, 45, 60, 90, 120, 135, 150[B]

70 250

ac (draft)

Nov. 2011

5 80 433, 867160 867, 1.73 Gbit/s, 3.47 Gbit/s,

6.93 Gbit/s

Infrastructure networksAccess point + mobile station

Medium access: collision: wireless nodes and AP are not coordinated

collision free: AP controls medium access

Ad-hoc (peer-to-peer) networks

medium access: collision

wireless node may transfer data (router)

网络拓扑

BSS (Basic Service Set)

AP

wired network

802.11 - Architecture of an infrastructure

Distribution System

802.x LAN

802.11 LAN

BSS2

802.11 LAN

BSS1 STA1

STA2

STA3

ESSExtended Service Set

AP Portal

AP

Station (STA)terminal with access mechanisms to the wireless medium and radio contact to the access point

Basic Service Set (BSS)group of stations using the same radio frequency

Access Pointstation integrated into the wireless LAN and the distribution system

Portalbridge to other (wired) networks

Distribution Systeminterconnection network to form one logical network (EES: Extended Service Set) based on several BSS

802.11 - Architecture of an infrastructure

802.11 - Architecture of an ad-hoc network

802.11 LAN

IBSS

STA1

STA2

STA3

Direct communication within a limited range

Station (STA):terminal with access mechanisms to the wireless medium

Independent Basic Service Set (IBSS):group of stations using the same radio frequency

IEEE standard 802.11

mobile terminal

access point Fixed terminal

infrastructurenetwork

802.11 PHY 802.3 PHY

802.11 MAC 802.3 MAC

LLC

802.3 PHY

802.3 MAC

LLC

IP

TCP

Application

802.3 PHY

802.3 MAC

LLC

IP

TCP

Application

移动自组网（ MANET ） Mobile Ad hoc NETworks Multi-hop wireless links Peer-to-peer forwarding 802.11based, usually

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无线传感器网络（ WSN ） Wireless Sensor Networks Monitoring Ad hoc configuration ZigBee, 802.11…

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无线 Mesh 网（ WMN ） Wireless Mesh Network Hierarchical, ad hoc backbone Extension of WLAN 802.11, 802.11s

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车载网 VANET

Vehicular Ad-Hoc Network Hybrid networks V2V, V2I 802.11p, 3G, etc.

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无线城域网（ Wireless MAN) WiMAX (Worldwide Interoperability for Microwave

Access)Also called broadband wireless network.Standard 802.16.Assume service delivery to buildings which will not move.Due to signal attenuation, different modulation schemes give different baud rates and hence bandwidths to clients at different distance.All services are connection-oriented.

Constant bit rate service.Real-time variable bit rate service.Non-real-time variable bit rate service.Best-efforts service.

Very high aggregate bandwidth.High bandwidth to each subscriber.

无线广域网 蜂窝通信网络 Base station + mobile terminal 1G: AMPS

analog access

2G: GSM 、 CDMAdigital access

2.5G ： CPCD 、 EDGE 、 GPRS

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3G Technology

WCDMA 、 CDMA2000 、 TD-SCDMA 2 Mbps, stationary;384 kbps, walking;144 kbps

driving. Multimedia (music / game playing), Internet

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Example of UMTS 3G Network

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4G technology

LTE Advanced and/or IEEE 802.16m ? Wireless broadband infrastructure to support multimedia

information society. Entirely packet switched networks. All digital network elements. Expectation include

High bandwidth of 50 - 100 Mbps.Low system cost.Ubiquitous connection.Seamless integration with wired network and the support of IPv6.Adaptive resource and spectrum management with proper QoS.Software radio.High quality multimedia.

Wireless Communications

Technology

1G 2G 2.5G 3G 4G

Name AMPS D-AMPS/ GSM/ CDMA

CDPD/ EDGE/ GPRS

WCDMA/ CDMA-2000

MC-CDMA/ OFDMATBD

Format Analog Digital Digital Digital Digital

Bandwidth 30 kHz (for voice)

8 – 23 kbps

19.2 – 384 kbps

144 kbps – 2 Mbps

50 – 100 Mbps

Feature Large cells, small number of calls per cell

Most commonly used

Based on 2G to deliver also data packets

High quality services, great variety of services

Ubiquitous connection uses IPv6

卫星通信网络 Act as transponder for signal and data transfer. Geostationary Earth Orbit (GEO)

Satellite at stationary position.Long delay.High energy consumption.

Low Earth Orbit (LEO)Satellite at lower orbit.Lower energy consumption, but frequent change of satellite.

移动终端 Mobile terminal/mobile client/mobile station/mobile

node… Laptop, SmartPhone, Tablet, PDA, Netbook, sensor

node, vehicle, ...

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移动终端系统 Mobile phone / tablet

AndroidIOSWinPhoneSymbian BadaOPhone

OthersTinyOS ： sensorLinux ： router 、 notebookWindows ： notebookOS X ： notebook

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移动 Internet 接入 基于 Cellular 网络 vs. 基于 Ethernet 网络协议的改进

网络层、传输层应用层

WAP ： Open Mobile Alliance iMode ：日本 DoCoMo 公司

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Characteristics/Challenges

Resource constraintsBandwidth, power, memory, CPU power, etc…

FailuresLink breakage (interference, mobility)

Node failures Mobility Openess …

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Summary

Various wireless networksFlat vs. hierarchical

Ad hoc vs. infrastructure Various mobile devices

Handheld, laptop, vehicle…

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Review Questions

1. 辨析 WLAN 、 IEEE 802.11 与 WiFi 三个概念的关系

2. 什么是 LTE ？

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