1 / 56

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

cisco
Télécharger la présentation

Digital Cellular Telephony

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related