Wireless# Guide to Wireless Communications. Objectives

Transcription

1 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 Wireless# Guide to Wireless Communications 2 1

2 Cellular Telephone Applications Digital cellular telephones can be used to: Browse the Internet Send and receive short messages and s 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 Wireless# Guide to Wireless Communications 3 Cellular Telephone Applications 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 Person-to-person Agent-to-person Information broadcast services Software configuration Advertising Wireless# Guide to Wireless Communications 4 2

3 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 Wireless# Guide to Wireless Communications 5 How Cellular Telephony Works Wireless# Guide to Wireless Communications 6 3

4 How Cellular Telephony Works Keys to cellular telephone networks 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 Wireless# Guide to Wireless Communications 7 How Cellular Telephony Works Wireless# Guide to Wireless Communications 8 4

5 How Cellular Telephony Works Wireless# Guide to Wireless Communications 9 How Cellular Telephony Works 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 Wireless# Guide to Wireless Communications 10 5

6 How Cellular Telephony Works Wireless# Guide to Wireless Communications 11 How Cellular Telephony Works 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 Wireless# Guide to Wireless Communications 12 6

7 How Cellular Telephony Works Wireless# Guide to Wireless Communications 13 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 Wireless# Guide to Wireless Communications 14 7

8 First Generation Cellular Telephony First Generation (1G) Uses analog signals modulated using FM Based on Advanced Mobile Phone Service (AMPS) Operates in the 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 Wireless# Guide to Wireless Communications 15 First Generation Cellular Telephony Wireless# Guide to Wireless Communications 16 8

9 First Generation Cellular Telephony 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 Wireless# Guide to Wireless Communications 17 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 Wireless# Guide to Wireless Communications 18 9

10 Second Generation Cellular Telephony Second Generation (2G) Digital transmission benefits 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 Wireless# Guide to Wireless Communications 19 Second Generation Cellular Telephony Wireless# Guide to Wireless Communications 20 10

11 Second Generation Cellular Telephony Wireless# Guide to Wireless Communications Generation Cellular Telephony 2.5 Generation (2.5G) 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 Wireless# Guide to Wireless Communications 22 11

12 2.5 Generation Cellular Telephony 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 Wireless# Guide to Wireless Communications 23 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 Wireless# Guide to Wireless Communications 24 12

13 Third Generation Cellular Telephony 3G network technologies 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) Wireless# Guide to Wireless Communications 25 Third Generation Cellular Telephony Wireless# Guide to Wireless Communications 26 13

14 Third Generation Cellular Telephony Wireless# Guide to Wireless Communications 27 Third Generation Cellular Telephony Wireless# Guide to Wireless Communications 28 14

15 Third Generation Cellular Telephony Wireless# Guide to Wireless Communications 29 Client Software Internet surfing or videoconferencing require client software To operate on a wireless digital cellular device Common types of clients WAP i-mode Java BREW Wireless# Guide to Wireless Communications 30 15

16 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 Wireless# Guide to Wireless Communications 31 Wireless Application Protocol (WAP and WAP Version 2) Wireless# Guide to Wireless Communications 32 16

17 Wireless Application Protocol (WAP and WAP Version 2) 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 Wireless# Guide to Wireless Communications 33 Wireless Application Protocol (WAP and WAP Version 2) Wireless# Guide to Wireless Communications 34 17

18 Wireless Application Protocol (WAP and WAP Version 2) 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 Wireless# Guide to Wireless Communications 35 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 Wireless# Guide to Wireless Communications 36 18

19 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 As well as run programs on the cellular phone itself Wireless# Guide to Wireless Communications 37 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 Wireless# Guide to Wireless Communications 38 19

20 Digital Cellular Challenges and Outlook Users will benefit the most from digital cellular telephony Once the industry settles on a single cellular standard Wireless# Guide to Wireless Communications 39 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 Wireless# Guide to Wireless Communications 40 20

21 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 to GHz and to GHz U.S. Department of Defense currently uses the 1.7 GHz band for satellite control and military purposes Wireless# Guide to Wireless Communications 41 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 Wireless# Guide to Wireless Communications 42 21

22 Other Wireless Options Top speed for a 3G user is 10 Mbps downstream g 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 g Factors that have kept this technology from being implemented in cellular phone handsets Wireless# Guide to Wireless Communications 43 Other Wireless Options Impact of WiMAX Two distinct kinds of WWAN set-up and e e 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 WiMAX Provides Internet and cable TV access to rural areas and remote cities Wireless# Guide to Wireless Communications 44 22

23 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 Wireless# Guide to Wireless Communications 45 Satellite Broadband Wireless Wireless# Guide to Wireless Communications 46 23

24 Satellite Transmissions Satellites generally send and receive on one of four frequency bands Frequency band affects the size of the antenna Wireless# Guide to Wireless Communications 47 Satellite Transmissions Wireless# Guide to Wireless Communications 48 24

25 Satellite Transmissions Wireless# Guide to Wireless Communications 49 Satellite Transmissions 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 Wireless# Guide to Wireless Communications 50 25

26 Satellite Transmissions Wireless# Guide to Wireless Communications 51 Satellite Transmissions Modulation techniques 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) Wireless# Guide to Wireless Communications 52 26

27 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 Wireless# Guide to Wireless Communications 53 Low Earth Orbit (LEO) Wireless# Guide to Wireless Communications 54 27

28 Low Earth Orbit (LEO) 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 Wireless# Guide to Wireless Communications 55 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 Wireless# Guide to Wireless Communications 56 28

29 Medium Earth Orbit (MEO) Wireless# Guide to Wireless Communications 57 Medium Earth Orbit (MEO) 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 Wireless# Guide to Wireless Communications 58 29

30 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 Wireless# Guide to Wireless Communications 59 Geosynchronous Earth Orbit (GEO) Wireless# Guide to Wireless Communications 60 30

31 Geosynchronous Earth Orbit (GEO) Wireless# Guide to Wireless Communications 61 Geosynchronous Earth Orbit (GEO) Wireless# Guide to Wireless Communications 62 31

32 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 Wireless# Guide to Wireless Communications 63 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 Wireless# Guide to Wireless Communications 64 32

33 Summary In cellular telephone networks, the coverage area is divided into sections called cells Handoff vs. roaming Cellular technology generations 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 Wireless# Guide to Wireless Communications 65 Summary 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 Wireless# Guide to Wireless Communications 66 33

34 Summary 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 Wireless# Guide to Wireless Communications 67 34