Guide to Wireless Communications. Digital Cellular Telephony. Learning Objectives. Digital Cellular Telephony. Chapter 8

Transcription

1 Guide to Wireless Communications Digital Cellular Telephony Chapter 2 Learning Objectives Digital Cellular Telephony 3 Describe the applications that can be used on a digital cellular telephone Explain how cellular telephony functions List and describe the features of the generations of cellular telephony List and describe the four types of client software used on a digital cellular telephone Discuss the issues surrounding 3G implementation 4 Although commonplace, digital cellular telephony is most competitive and complex of all wireless telephony Variety of competing technologies such as GSM and CDMA2000 1XEVDO rather than single standard Competing carriers each push a specific technology Governments have even auctioned off part of wireless spectrum to highest bidder

2 Applications Short Message Services (SMS) New and expanded features and applications are pushing wireless digital cellular networks beyond just voice communications Digital cellular telephony can be used for Internet access, , video conferencing, and running a variety of programs Short Message Services (SMS) delivers text-based messages up to 160 characters directly between wireless devices without using the Internet SMS is popular in Europe and Japan with over 200 billion messages sent annually SMS is slow in reaching the US because of profusion of other wireless digital alternatives 5 6 How Cellular Telephony Works Cellular Network Two keys to cellular telephone networks Coverage area is divided into cells, each with a cell transmitter connected to base station that, in turn, is connected to mobile telecommunications switching office (MTSO) See Figure -1 All the transmitters and cell phones operate at low power level to prevent signals from interfering with other cells that may use same frequencies See Figure -2 7

3 Frequency Reuse Cellular Telephone Codes Special codes are associated with cell phones Codes identify phone, phone s owner, and carrier or service provider Table -1 summarizes the codes 9 10 Cellular Telephone Codes Cellular Telephone Handoffs and Roaming When telephone user moves within same cell, base station handles transmissions Handoff is when user moves to another cell and is automatically associated with base station of that cell Roaming is when user moves beyond coverage area of entire cellular network into remote area, as seen in Figure -3 Network in remote area contacts home network to verify that user can make calls and is charged appropriately 11 12

4 13 Handoff and Roaming 14 How a Cellular Phone Receives a Call Cell phone listens for SID transmitted by base station on control channel If SID matches that programmed into phone, cell phone transmits registration request to base station that MTSO uses If SID does not match, cell phone is roaming and MTSO of remote network contacts MTSO of home network to confirm SID is valid How a Cellular Phone Receives a Call Receiving a Call MTSO locates phone and selects frequency which is sent to phone over control channel As user moves to edge of cell, base stations coordinate through MTSO and instruct phone to change frequencies as it is handed off to another cell See Figure

5 Digital Cellular Telephony First Generation Existing since the early 190s in the United States, cellular telephony is divided into several generations First Generation Second Generation 2.5 Generation Third Generation 1G uses analog signals and has 9.6 KHz maximum transmission speed Based on Advanced Mobile Phone Service (AMPS), 1G uses MHz frequency Each channel is 30 KHz wide with 45 KHz passband 32 frequencies are available, with 790 used for voice traffic and 42 for control channel Two frequencies are required for conversation, so there are actually only 395 voice channels and 21 control channels 17 1 First Generation FDMA AMPS uses Frequency Division Multiple Access (FDMA), as illustrated in Figure -5 User is allocated single channel at a time and is switched to another channel if original one deteriorates or has interference 1G networks use circuit-switching technology Because analog signals are prone to interference, 1G is used basically for voice It has been replaced with improved digital technology 19 20

6 Second Generation Second Generation 21 Started in early 1990s, 2G uses digital transmissions to transmits data between 9.5 Kbps and 14.4 Kbps in 00 MHz and 1.9 GHz frequencies Offers several advantages over analog, including More efficient uses of frequency spectrum Quality of voice transmission does not degrade over distance Better security; more difficult to decode Requires less transmitter power Uses smaller and less expensive individual receivers and transmitters 22 2G cellular networks use three different multiple access technologies summarized in Table -2 Time Division Multiple Access (TDMA), shown in Figure -6, allows 3 times as many calls over a single channel as FDMA Code Division Multiple Access (CDMA) allocates entire spectrum all the time, as seen in Figure -7 Global Systems for Mobile Communications (GSM) divides a 25 MHz channel into 124 frequencies, each 200 KHz, and then uses time slots to transmit up to 9.6 Kbps TDMA CDMA 23 24

7 25 2G Technologies Generation 2.5G is regarded as an interim generation Sparsely deployed 2.5G networks operate at 34 Kbps Packet-switched 2.5G networks have two advantages over circuit switched networks More efficient, increasing traffic from 3 to 5 times over that of circuit-switching Always on with connection kept open all the time 2.5 Generation Third Generation 2.5G networks use three technologies General Packet Radio Service (GPRS) uses time slots in a 200 KHz spectrum to transmit at speeds up to 114 Kbps Enhanced Data Rates for Global Evolution (EDGE) uses new modulation technique to transmit up to 34 Kbps CDMA2000 1XRTT supports 144 Kbps packet data transmissions 3G is intended to be a uniform global worldwide standard for cellular wireless communication International Telecommunications Union (ITN) has outlined standard data rates for wireless digital networks 144 Kbps for a mobile user 36 Kbps for slowly moving user 2 Mbps for stationary user 27 2

8 Third Generation Third Generation 29 Transition from CDMA2000 1XRTT is to CDMA200 1XEVDO with data transmission rates of 2.4 Mbps Must be coupled with CDMA2000 1XRTT for both voice and data transmissions CDMA2000 1XEVDV will send both voice and data Transition from EDGE is Wideband CDMA (WCDMA) Adds packet-switching data channel to circuitswitched voice channel to transmit at 2 Mbps in fixed position and at 300 Kbps when mobile 30 Several 3G technologies not yet tested Actual technologies may be different from those currently proposed Figure - shows digital wireless cellular migration paths Table -3 summarizes digital cellular technologies Digital Wireless Cellular Migration Path Digital Cellular Technologies 31 32

9 Client Software Wireless Application Protocol (WAP) 33 Client software that functions on wireless digital cellular devices provide function and user interface to display or manipulate data Some client software is unique to cellular telephones Other software may be used in a variety of different applications 34 WAP provides standard way to transmit, format, and display Internet data on cellular phones Display only textual data because of slow transmission speed and smaller viewing area, as seen in Figure -9 Has a microbrowser that uses Wireless Markup Language (WML) instead of HTML, as seen in Figure -10 A WAP Gateway, also called a WAP Proxy, changes HTML into WML before forwarding it to cell phone, as seen in Figure -11 WAP Display HTML Code 35 36

10 37 WAP 3 HTML and WML Differences HTML controls layout, color, font, and styling, while WML controls only font size and basic font attributes, as seen in Figure -12 WML uses Extensible Markup Language (XML) and tags that specify how content should be formatted WML document, called a deck, contains one or more blocks called cards that contain small parts of a text document and navigation controls One card is displayed on the cell phone at a time as seen in Figure -13 WML Code WML Deck 39 40

11 i-mode Java i-mode, a Japanese-owned Internet access system, is based on compact HTML (chtml) Has its own set of tags and attributes Users are charged for the service by amount of information downloaded plus a service charge Expect i-mode and WAP to merge into one technology in the future Developed by Sun Microsystems, Java is an object-oriented language that runs on almost any hardware platform Java 2 Micro Edition (J2ME) was specifically developed for programming wireless devices Allows cellular phone to access remote applications and Can also run programs on cellular phone itself Binary Runtime Environment for Wireless (BREW) Limitations and the Future BREW, a runtime environment, is a thin software interface, that resides on wireless device Users can download programs and run them on BREW-enabled devices BREW uses memory efficiently, occupying only a small amount of flash memory and dynamically allocating RAM Can be used in combination with other operating systems and any kind of browser WAP and i-mode allow remote access to the Internet They do not support a rich set of graphics J2ME and BREW are expected to become major platforms for variety of wireless devices 43 44

12 Digital Cellular Issues and Outlook Digital Cellular Issues and Outlook Several issues face digital cellular telephony that prevent its rapid acceptance Competing technologies no single road to 3G digital telephony; competing technologies are incompatible Limited spectrum availability No part of spectrum is designated exclusively for 3G; is enough spectrum available to meet needs Several issues face digital cellular telephony that prevent its rapid acceptance High infrastructure costs 3G telephones may cost as much as $300 with $90 monthly charge; carriers will spend billions for infrastructure necessary for 3G Competition from other wireless options Bluetooth, IrDA, and 02.11a WLANs are lessexpensive choices Two keys to cellular telephone networks are dividing coverage area into cells and using low power levels for transmission At the center of each cell is a cell transmitter that sends and receives radio frequency (RF) signals Low-power levels enable signals to stay confined to the cell and not interfere with other cells that use the same frequencies All cell phones have special codes that identify the owner and carrier or service providers Handoff is when user moves to another cell and is automatically associated with base station of new cell 47 4

13 Roaming occurs when a user moves beyond coverage area of entire cellular network and connects to network in remote area Remote area network communicates with home area to verify that user can make calls and is charged appropriately First generation of wireless cellular technology, known as 1G, uses analog signals and transmits at a maximum speed of 9.6 Kbps 1G uses Advanced Mobile Phone Service (AMPS) standard Operates in MHz frequency Uses Frequency Division Multiple Access (FDMA) Is circuit-switching technology Second generation, known as 2G, transmits data between 9.6 Kbps and 14.4 Kbps in 00 MHz and 1.9 GHz frequencies Circuit-switched digital technology Use three different multiple access technologies: Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA) Global Systems for Mobile (GSM) communications 52 Currently, three variations in 2.5G interim generation of packet-switching network technologies: General Packet Radio Service (GPRS) is for TDMA or GSM 2G networks Enhanced Data Rates for Global Evolution (EDGE) is considered a booster for GPRS systems and can transmit up to 34 Kbps using a new modulation technique CDMA2000 1XRTT supports 144 Kbps packet data transmission and doubles voice capability of current CDMA networks

14 3G digital networks transmit at higher speeds and provide new or expanded applications and features Will require major changes to network infrastructures and a new generation of mobile cellular devices Widely used in Europe and Japan, Short Message Services (SMS) allows delivery of text-based messages directly between wireless devices Client software on cell phone is necessary for Internet surfing or videoconferencing Wireless Application Protocol (WAP) provides a standard way to transmit, format, and display Internet data without requiring rich user interface WAP cell phone runs microbrowser that uses Wireless Markup Language (WML) to display textbased Web content A WAP Gateway must translate between WML and HTML I-mode, another client technology, is based on compact HTML (chtml) It has its own set of tags and attributes Expected I-mode and WAP to merge into one technology in the future Java 2 Micro Edition (J2ME) is a Java subset for programming wireless devices Allows cellular phones to access remote applications and programs as well as run programs Binary Runtime Environment for Wireless (BREW), a thin software interface layer, resides on a wireless device Allows users to download programs and run them on BREW-enabled devices Competing cellular technologies, lack of standards, spectrum limitations, and high costs of implementing 3G technology have prevented rapid acceptance of advanced generations of digital cellular telephony 55 56

15 3G networks have competition from other wireless technologies Top speed for 3G is 2 Mbps standing still, but 02.11a WLANs offer speeds over 100 Mbps while mobile Some carriers install less-expensive stable WLANs in high-traffic hot spots in selected cities as alternative to 3G 57