Transcript Chapter 10

Wireless# Guide to Wireless
Communications
Chapter 10
Wireless Wide Area Networks
Objectives
• Describe wireless wide area networks (WWANs) and
how they are used
• Describe the applications that can be used on a
digital cellular telephone
• Explain how cellular telephony functions
• List features of the various generations of cellular
telephony
• Discuss how satellite transmissions work
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Cellular Telephone Applications
• Digital cellular telephones can be used to:
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Browse the Internet
Send and receive short messages and e-mails
Participate in videoconferencing
Receive various sorts of information
Run a variety of business applications
Connect to corporate networks
Watch television or on-demand movies
Take and transmit pictures and short movies
Locate family members and employees using GPS
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Cellular Telephone Applications
(continued)
• Short Message Services (SMS)
– One of the most widely used applications
– Allows for the delivery of short, text-based messages
between wireless devices
• Messages are limited to about 160 characters
– Applications
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Person-to-person
Agent-to-person
Information broadcast services
Software configuration
Advertising
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How Cellular Telephony Works
• Keys to cellular telephone networks
– Cells
• City cells measure approximately 10 square miles
• At the center of each cell is a cell transmitter connected
to a base station
• Each base station is connected to a mobile
telecommunications switching office (MTSO)
– Link between the cellular network and the wired
telephone world
– Controls all transmitters and base stations
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How Cellular Telephony Works
(continued)
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How Cellular Telephony Works
(continued)
• Keys to cellular telephone networks (continued)
– Transmitters and cell phones operate at low power
• Enables the signal to stay confined to the cell
• Signal at a specific frequency does not go far beyond
the cell area
– Same frequency can be used in other cells at the
same time
– Except in adjacent cells
• Cell phones have special codes
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How Cellular Telephony Works
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How Cellular Telephony Works
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How Cellular Telephony Works
(continued)
• When user moves within the same cell
– Transmitter and base station for that cell handle all of
the transmissions
• As the user moves toward the next cell
– A handoff process occurs
• Roaming
– User moves from one cellular network to another
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How Cellular Telephony Works
(continued)
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How Cellular Telephony Works
(continued)
• Steps to receive a call
– Cell phone listens for the SID being transmitted by the
base station on the control channel
– Phone compares SID with its programmed SID
• If they match, phone is in a network owned by carrier
– If SIDs do not match, phone is roaming
– When a call comes in, MTSO locates the phone
through the registration request
– User can move to another cell
– Phone and transmitter can change frequencies
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How Cellular Telephony Works
(continued)
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Digital Cellular Telephony
• Cellular telephones have been available since the
early 1980s in the United States
• Most industry experts outline several generations of
cellular telephony
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First Generation Cellular Telephony
• First Generation (1G)
– Uses analog signals modulated using FM
– Based on Advanced Mobile Phone Service (AMPS)
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Operates in the 800-900 MHz frequency spectrum
Each channel is 30 KHz wide with a 45 KHz passband
There are 832 frequencies available
Uses Frequency Division Multiple Access (FDMA)
FDMA allocates a single cellular channel with two
frequencies to one user at a time
• 1G networks use circuit-switching technology
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First Generation Cellular Telephony
(continued)
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First Generation Cellular Telephony
(continued)
• Circuit-switching technology
– Makes a dedicated and direct physical connection
• Between the caller and the recipient
• Analog signals are prone to interference
– Do not have the same quality as digital signals
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Second Generation Cellular Telephony
• Second Generation (2G)
– Transmits data between 9.6 Kbps and 14.4 Kbps
• In the 800 MHz and 1.9 GHz frequencies
– 2G networks are also circuit-switching
– 2G systems use digital transmissions
– Digital transmission benefits
• Uses the frequency spectrum more efficiently
• Over long distances, the quality of the voice
transmission does not degrade
• Difficult to decode and offer better security
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Second Generation Cellular Telephony
(continued)
• Second Generation (2G) (continued)
– Digital transmission benefits (continued)
• Digital transmissions use less transmitter power
• Enables smaller and less expensive individual receivers
and transmitters
• Multiple access technologies
– Time Division Multiple Access (TDMA)
– CDMA
– Global System for Mobile communications (GSM)
• Uses a combination of FDMA and TDMA technologies
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Second Generation Cellular Telephony
(continued)
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Second Generation Cellular Telephony
(continued)
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2.5 Generation Cellular Telephony
• 2.5 Generation (2.5G)
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Interim step between 2G and 3G
Operates at a maximum speed of 384 Kbps
2.5G networks are packet-switched
Advantages of packet switching
• Much more efficient
– Can handle more transmissions over a given
channel
• Permits an always-on connection
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2.5 Generation Cellular Telephony
(continued)
• 2.5G network technologies
– General Packet Radio Service (GPRS)
• For TDMA or GSM 2G networks
• Uses eight time slots in a 200 KHz spectrum and four
different coding techniques
– Enhanced Data rates for GSM Evolution (EDGE)
• Can transmit up to 384 Kbps
• Based on a modulation technique called 8-PSK
– CDMA2000 1xRTT
• Operates on two 1.25 MHz-wide frequency channels
• Supports 144 Kbps packet data transmission
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Third Generation Cellular Telephony
• Third Generation (3G)
– Intended to be a uniform and global standard for
cellular wireless communication
• Standard data rates
– 144 Kbps for a mobile user
– 386 Kbps for a slowly moving user
– 2 Mbps for a stationary user
• 3G network technologies
– CDMA2000 1xEVDO
• For 2.5G CDMA2000 1xRTT networks
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Third Generation Cellular Telephony
(continued)
• 3G network technologies (continued)
– CDMA2000 1xEVDV will be the successor of
CDMA2000 1xEVDO
– Wideband CDMA (W-CDMA)
• For 2.5G EDGE networks
– High-Speed Downlink Packet Access (HSDPA)
• Beyond W-CDMA
• Uses a 5 MHz W-CDMA channel, variety of adaptive
modulation, multiple in multiple out (MIMO) antennas,
and hybrid automatic repeat request (HARQ)
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Third Generation Cellular Telephony
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Third Generation Cellular Telephony
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Third Generation Cellular Telephony
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Third Generation Cellular Telephony
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Client Software
• Internet surfing or videoconferencing require client
software
– To operate on a wireless digital cellular device
• Common types of clients
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WAP
i-mode
Java
BREW
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Wireless Application Protocol (WAP
and WAP Version 2)
• Wireless Application Protocol (WAP) and WAP2
– Provide a standard way to transmit, format, and
display Internet data
• For devices such as cell phones
• WAP was developed in 1997
– Enables devices to send and receive Internet textonly data
• WAP cell phone runs a microbrowser
– Uses Wireless Markup Language (WML) instead of
HTML
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Wireless Application Protocol (WAP
and WAP Version 2) (continued)
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Wireless Application Protocol (WAP
and WAP Version 2) (continued)
• WAP gateway (sometimes called WAP proxy)
– Computer running special conversion software
– Used to translate between WML and HTML
– Many features of HTML are not supported in WML
• Extensible Markup Language (XML)
– Defined by the World Wide Web Consortium (W3C)
– Uses tags to describe how an item should be
displayed on the screen
• WML document is called a deck
– Contains one or more blocks, known as cards
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Wireless Application Protocol (WAP
and WAP Version 2) (continued)
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Wireless Application Protocol (WAP
and WAP Version 2) (continued)
• WAP2 is based on XHTML (an extension of HTML
version 4)
– Displays graphics and multiple font styles on color
screen equipped mobile devices
– Includes a protocol stack that allows it to support
TCP/IP directly
– Defines a new profile, an extension of XML,
specifically to support mobile devices
– WAP2 is backward compatible with WAP version 1
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i-Mode
• i-mode
– Internet access system
– Owned by the Japanese corporation NTT DoCoMo
– Based on compact HTML (cHTML)
• A subset of HTML designed for mobile devices
• cHTML has its own set of tags and attributes
• i-mode users pay for the service
– By the amount of information downloaded plus a
service charge
• WAP services are charged by the connection time
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Java
• Java programming language
– Developed by Sun Microsystems
– Object-oriented language used for general-purpose
business programming
• As well as interactive Web sites
• Java 2 Micro Edition (J2ME)
– Subset of Java specifically developed for
programming wireless devices
– Enables a cellular phone to access remote
applications and e-mail
• As well as run programs on the cellular phone itself
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Binary Runtime Environment for
Wireless (BREW)
• BREW is a thin software environment
– Very small program that resides on a wireless device
• Capable of running applications that can be
downloaded by the device on demand
– BREW is compatible with Java, C, and C++
• BREW efficiently uses small amount of memory
– Occupies only a small amount of flash memory
– Dynamically allocates RAM for applications
• BREW can be used with other applications
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Digital Cellular Challenges and
Outlook
• Users will benefit the most from digital cellular
telephony
– Once the industry settles on a single cellular standard
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Competing Technologies
• There is no single road to 3G digital telephony
– Europe standards
• W-CDMA and HSDPA
– China and South Korea standards
• CDMA2000 1xEVDO
– Japan standard
• W-CDMA
– United States standards
• HSDPA and CDMA2000 1xEVDO
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Limited Spectrum
• Spectrum
– Single largest factor limiting the development of 3G
• Although 3G can operate at almost any spectrum
– Industry tries to use the same part of the spectrum for
3G communications around the world
• 1.710 to 1.855 GHz and 2.520 to 2.670 GHz
• U.S. Department of Defense currently uses the 1.7
GHz band for satellite control and military purposes
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Costs
• High monthly service fees for data transmission
• User cost for 3G pales in comparison to costs for the
carriers to build entire 3G networks
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Other Wireless Options
• Top speed for a 3G user is 10 Mbps downstream
– 802.11g WLANs offer speeds of over 54 Mbps
• Coverage area of a single WLAN is far less than a
digital cellular network
– Deploying multiple access points can create large
areas of coverage
• Higher power consumption and the large number of
electronic components of 802.11g
– Factors that have kept this technology from being
implemented in cellular phone handsets
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Other Wireless Options (continued)
• Impact of WiMAX
– Two distinct kinds of WWAN set-up
• 802.16-2004 and 802.16e
– 802.16e WiMAX network can be overlaid on an
existing cellular tower infrastructure
• Provides mobile users with lower cost access to data at
speeds equivalent to EVDO
– 802.16-2004WiMAX
• Provides Internet and cable TV access to rural areas
and remote cities
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Satellite Broadband Wireless
• Use of satellites for personal wireless
communication is fairly recent
• Satellite use falls into three broad categories
– Satellites are used to acquire scientific data and
perform research in space
– Satellites look at Earth from space
– Satellites include devices that are simply reflectors
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Satellite Broadband Wireless
(continued)
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Satellite Transmissions
• Satellites generally send and receive on one of four
frequency bands
• Frequency band affects the size of the antenna
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Satellite Transmissions (continued)
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Satellite Transmissions (continued)
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Satellite Transmissions (continued)
• Class and Type of Service
– Satellites can provide two classes of service
• Consumer class service
– Shares the available bandwidth between the users
• Business class service
– Offers dedicated channels with dedicated
bandwidth
– Types of connectivity
• Point-to-point, point-to-multipoint, and multipoint-tomultipoint
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Satellite Transmissions (continued)
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Satellite Transmissions (continued)
• Modulation techniques
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Binary phase shift keying (BPSK)
Quadrature phase shift keying (QPSK)
Eight-phase shift keying (8-PSK)
Quadrature amplitude modulation (QAM)
• Multiplexing techniques
– Permanently assigned multiple access (PAMA)
– Multi-channel per carrier (MCPC)
– Demand assigned multiple access (DAMA)
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Low Earth Orbit (LEO)
• Low earth orbit (LEO) satellites
– Circle the Earth at an altitude of 200 to 900 miles
– Must travel at high speeds
• So that the Earth’s gravity will not pull them back into
the atmosphere
– Area of Earth coverage (called the footprint) is small
• LEO systems have a low latency
– Use low-powered terrestrial devices (RF transmitters)
– Round trip time: 20 to 40 milliseconds
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Low Earth Orbit (LEO) (continued)
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Low Earth Orbit (LEO) (continued)
• LEO satellites groups
– Big LEO
• Carries voice and data broadband services, such as
wireless Internet access
– Little LEO
• Provides pager, satellite telephone, and location
services
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Medium Earth Orbit (MEO)
• Medium earth orbit (MEO) satellites
– Orbit the Earth at altitudes between 1,500 and 10,000
miles
– Some MEO satellites orbit in near-perfect circles
• Have a constant altitude and constant speed
– Other MEO satellites revolve in elongated orbits
called highly elliptical orbits (HEOs)
• Advantages
– MEO can circle the Earth in up to 12 hours
– Have a bigger Earth footprint
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Medium Earth Orbit (MEO) (continued)
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Medium Earth Orbit (MEO) (continued)
• Disadvantage
– Higher orbit increases the latency
– Round trip time: 50 to 150 milliseconds
• HEO satellites
– Have a high apogee (maximum altitude) and a low
perigee (minimum altitude)
– Can provide good coverage in extreme latitudes
– Orbits typically have a 24-hour period
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Geosynchronous Earth Orbit (GEO)
• Geosynchronous earth orbit (GEO) satellites
– Stationed at an altitude of 22,282 miles
– Orbit matches the rotation of the Earth
• And moves as the Earth moves
– Can provide continuous service to a very large
footprint
• Three GEO satellites are needed to cover the Earth
– Have high latencies of about 250 milliseconds
– Require high-powered terrestrial sending devices
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Geosynchronous Earth Orbit (GEO)
(continued)
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Geosynchronous Earth Orbit (GEO)
(continued)
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Geosynchronous Earth Orbit (GEO)
(continued)
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Experimental Technologies
• NASA has been experimenting with ultra-lightweight,
solar-powered, high-flying aircraft since the 1990s
– To be used in place of a satellite or ground-based
antenna tower infrastructure
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Satellite Technology Outlook
• Satellites can provide wireless communication
– In areas not covered by cellular or WiMAX
• Satellites today are enabling carriers to offer
– Internet access and voice calls to passengers and
crews across large oceans
• And in high latitudes and remote corners of the Earth
• Can also make these services available in many
other unpopulated areas
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Summary
• In cellular telephone networks, the coverage area is
divided into sections called cells
• Handoff vs. roaming
• Cellular technology generations
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First generation (1G)
Second generation (2G)
2.5 generation (2.5G)
Third generation (3G)
• Short Message Services (SMS)
– Allows for the delivery of short, text-based messages
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Summary (continued)
• 2.5GWAP-enabled cell phones run a tiny browser
program called a microbrowser
• 3G cell phones allow Internet surfing or
videoconferencing using WAP2
• Java 2 Micro Edition (J2ME)
– Subset of Java specifically developed for programming
wireless devices
• BREW is a runtime environment that resides on a
wireless device
• Issues preventing digital cellular acceptance include
– Competing cellular technologies and lack of standards
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Summary (continued)
• Introduction of WiMAX technologies
– May have a significant impact on how 3G
technologies are eventually employed
• Satellites used for wireless data connectivity
– Employ common modulation and multiplexing
techniques
• Satellite orbit types
– LEO satellites
– MEO satellites
– GEO satellites
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