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Digital Cellular Telephony

Digital Cellular Telephony. Chapter 8. Learning Objectives. 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

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Digital Cellular Telephony

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  1. Digital Cellular Telephony Chapter 8

  2. Learning Objectives • 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

  3. Digital Cellular Telephony • 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

  4. Applications • 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, e-mail, video conferencing, and running a variety of programs

  5. Short Message Services (SMS) • 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

  6. How Cellular Telephony Works • 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 8-1 • 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 8-2

  7. Cellular Network

  8. Frequency Reuse

  9. Cellular Telephone Codes • Special codes are associated with cell phones • Codes identify phone, phone’s owner, and carrier or service provider • Table 8-1 summarizes the codes

  10. Cellular Telephone Codes

  11. 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 8-3 • Network in remote area contacts home network to verify that user can make calls and is charged appropriately

  12. Handoff and Roaming

  13. 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

  14. How a Cellular Phone Receives 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 8-4

  15. Receiving a Call

  16. Digital Cellular Telephony • Existing since the early 1980s in the United States, cellular telephony is divided into several generations • First Generation • Second Generation • 2.5 Generation • Third Generation

  17. First Generation • 1G uses analog signals and has 9.6 KHz maximum transmission speed • Based on Advanced Mobile Phone Service (AMPS), 1G uses 800-900 MHz frequency • Each channel is 30 KHz wide with 45 KHz passband • 832 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

  18. First Generation • AMPS uses Frequency Division Multiple Access (FDMA), as illustrated in Figure 8-5 • 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. FDMA

  20. Second Generation • Started in early 1990s, 2G uses digital transmissions to transmits data between 9.5 Kbps and 14.4 Kbps in 800 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

  21. Second Generation • 2G cellular networks use three different multiple access technologies summarized in Table 8-2 • Time Division Multiple Access (TDMA), shown in Figure 8-6, 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 8-7 • Global Systems for Mobile Communications (GSM) divides a 25 MHz channel into 124 frequencies, each 200 KHz, and then uses 8 time slots to transmit up to 9.6 Kbps

  22. TDMA

  23. CDMA

  24. 2G Technologies

  25. 2.5 Generation • 2.5G is regarded as an interim generation • Sparsely deployed 2.5G networks operate at 384 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

  26. 2.5 Generation • 2.5G networks use three technologies • General Packet Radio Service (GPRS) uses 8 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 384 Kbps • CDMA2000 1XRTT supports 144 Kbps packet data transmissions

  27. Third Generation • 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 • 386 Kbps for slowly moving user • 2 Mbps for stationary user

  28. Third Generation • 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 circuit-switched voice channel to transmit at 2 Mbps in fixed position and at 300 Kbps when mobile

  29. Third Generation • Several 3G technologies not yet tested • Actual technologies may be different from those currently proposed • Figure 8-8 shows digital wireless cellular migration paths • Table 8-3 summarizes digital cellular technologies

  30. Digital Wireless Cellular Migration Path

  31. Digital Cellular Technologies

  32. Client Software • 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

  33. Wireless Application Protocol (WAP) • 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 8-9 • Has a microbrowser that uses Wireless Markup Language (WML) instead of HTML, as seen in Figure 8-10 • A WAP Gateway, also called a WAP Proxy, changes HTML into WML before forwarding it to cell phone, as seen in Figure 8-11

  34. WAP Display

  35. HTML Code

  36. WAP

  37. 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 8-12 • 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 8-13

  38. WML Code

  39. WML Deck

  40. i-Mode • 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

  41. Java • 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 email • Can also run programs on cellular phone itself

  42. Binary Runtime Environment for Wireless (BREW) • 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

  43. Limitations and the Future • 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

  44. 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

  45. Digital Cellular Issues and Outlook • 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 802.11a WLANs are less-expensive choices

  46. Chapter Summary • 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

  47. Chapter Summary • 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

  48. Chapter Summary • 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

  49. Chapter Summary • 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 800-900 MHz frequency • Uses Frequency Division Multiple Access (FDMA) • Is circuit-switching technology

  50. Chapter Summary • Second generation, known as 2G, transmits data between 9.6 Kbps and 14.4 Kbps in 800 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

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