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800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
800 mhz analog cdma cellular phones
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800 mhz analog cdma cellular phones

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  • 1. How cell phones work Julia Wang Derek Juang Derrick Chou Andy Ng Jed Kim
  • 2. Cellular Phones: The Facts <ul><li>400 million cell users in the world </li></ul><ul><li>60% of Europeans </li></ul><ul><li>40% of Americans </li></ul><ul><li>20% of US teenagers (more girls than boys) </li></ul>
  • 3. Cell Phone = Radio? <ul><li>Combination of telephone and radio ideas </li></ul><ul><li>First mobile communications: “radio telephone” </li></ul><ul><li>Requires powerful transmitter; minimal channels </li></ul>
  • 4. Millions of Users, Millions of Frequencies? <ul><li>Typical analog carrier has 832 frequencies </li></ul><ul><li>Division of coverage area into “cells” </li></ul><ul><li>Each cell about 10 miles (26 km) </li></ul><ul><li>Frequency reuse in each cell allows millions of simultaneous users </li></ul>
  • 5. Inside the Cell Phone <ul><li>Components: </li></ul><ul><ul><li>Circuit board </li></ul></ul><ul><ul><li>Antenna </li></ul></ul><ul><ul><li>Liquid Crystal Display </li></ul></ul><ul><ul><li>Keyboard </li></ul></ul><ul><ul><li>Microphone </li></ul></ul><ul><ul><li>Speaker </li></ul></ul><ul><ul><li>Battery </li></ul></ul>One of the most intricate devices used daily Copyright © 1998-2002 Howstuffworks, Inc.
  • 6. Circuit Board <ul><li>Analog-to-Digital, Digital-to-Analog converters </li></ul><ul><li>Digital Signal Processor (DSP) </li></ul><ul><li>Radio Frequency (RF) Control </li></ul><ul><li>RF Amplifiers </li></ul><ul><li>Power Control </li></ul><ul><li>ROM and Flash memory </li></ul><ul><li>Microprocessor </li></ul>Front Back
  • 7. Circuit Board: Flash memory, Microprocessor Flash Memory Microprocessor
  • 8. LCD Display Keypad Cell-phone speaker, microphone and battery backup
  • 9. Cellular Access Technologies <ul><li>The 3 most common cell-phone network technologies for transmitting information are: </li></ul><ul><ul><li>Frequency Division Multiple Access (FDMA) </li></ul></ul><ul><ul><li>Time Division Multiple Access (TDMA) </li></ul></ul><ul><ul><li>Code Division Multiple Access (CDMA) </li></ul></ul><ul><li>Allows for multiple access by splitting calls </li></ul>
  • 10. FDMA <ul><li>FDMA puts each call on a separate frequency </li></ul><ul><ul><li>Separates spectrum into distinct channels by splitting it into uniform bands of bandwidth </li></ul></ul><ul><li>Mainly used for analog transmission </li></ul><ul><li>Capable of carrying digital information, but not an efficient method for that type of transmission </li></ul>
  • 11. FDMA Diagram
  • 12. TDMA <ul><li>With TDMA, a narrow band that has a bandwidth of 30 kHz and is 6.7 ms long is split time-wise into three time slots </li></ul><ul><ul><li>Each conversation gets to transmit for 1/3 of the time </li></ul></ul><ul><ul><li>Possible because voice data converted into digital information that is compressed allowing for less transmission time </li></ul></ul><ul><li>Electronics Industry Alliance and Telecommunications Industry Association, IS-54 and IS-136 </li></ul><ul><li>3x capacity of analog system with same no. Channels </li></ul><ul><li>Operates at 800 MHz (IS-54) or 1900 MHz (IS-136) frequency bands </li></ul>
  • 13. TDMA Diagram
  • 14. TDMA/GSM <ul><li>TDMA is used as access technology for GSM </li></ul><ul><ul><li>Implemented in a different and incompatible way from IS-136 </li></ul></ul><ul><ul><li>Uses encryption for more secure calls </li></ul></ul><ul><ul><li>900 MHz and 1800 MHz bands in Europe and Asia </li></ul></ul><ul><ul><li>1900 MHz in United States </li></ul></ul><ul><ul><li>International standard for Europe, Australia, most of Asia and Africa. </li></ul></ul><ul><ul><li>SIM cards used to store connection data and identification no.’s required to access provider </li></ul></ul>
  • 15. CDMA <ul><li>After data is digitized, CDMA spreads it out over bandwidth (spread spectrum) </li></ul><ul><ul><li>Each call assigned unique sequence code, used to spread over bandwidth, and to recover signal at receiver </li></ul></ul><ul><ul><li>Multiple calls are put on top of each other </li></ul></ul><ul><ul><li>CDMA systems require an accurate time-stamp on each piece of signal to recover signal, so it references the GPS for information </li></ul></ul><ul><li>8 to 10 calls can be carried on same channel space as an analog AMPS call </li></ul><ul><li>Basis for IS-95, operates in 800 MHz and 1900 MHz frequency bands </li></ul>
  • 16. CDMA Diagram
  • 17. AMPS (Advanced Mobile Phone System) <ul><li>Analog cell phone standard, established in 1983 </li></ul><ul><li>First used in Chicago </li></ul><ul><li>Uses range of frequencies between 824Mhz and 894 MHz </li></ul><ul><li>Pair of frequencies, one for transmit and one for receive create one channel </li></ul><ul><li>Standard analog voice channel - 30kHz, comparable to a wired telephone </li></ul>
  • 18. AMPS (Advanced Mobile Phone System) <ul><li>Transmit and receive frequencies are separated by 45 MHz </li></ul><ul><li>Only operate in the 800 MHz band; therefore, not many features (like email, web browsing) offered </li></ul>
  • 19. Analog vs. Digital <ul><li>Analog </li></ul><ul><li>Thomas Edison – phonograph </li></ul><ul><li>sound collecting diaphragm-> needle-> rotating aluminum cylinder </li></ul><ul><li>Eventually modified to become the “modern” phonograph, signals are amplified electronically </li></ul><ul><li>Analog wave is vibration created by sound </li></ul><ul><li>Storage and playback of an analog wave – simple but fidelity is not very good </li></ul><ul><li>Fidelity – the similarity between the original signal and the reproduced signal </li></ul>
  • 20. Analog vs. Digital <ul><li>Digital </li></ul><ul><li>Goal was to create a recording with very high fidelity and perfect reproduction </li></ul><ul><li>Converts analog wave into a stream of numbers and records the numbers and not the wave </li></ul><ul><li>Analog to digital converter (ADC) </li></ul><ul><li>Digital to analog converter (DAC) </li></ul><ul><li>Sampling rate, sampling precision </li></ul><ul><li>Amount of digital data goes up significantly </li></ul>
  • 21. Analog vs. Digital LOW sample rate and sampling precision HIGH sample rate and sampling precision
  • 22. Digital technology <ul><li>Same radio technology as analog but different way of compressing the voice </li></ul><ul><li>Easier to compress and manipulate to fit more channels within a given bandwidth, more efficient </li></ul><ul><li>Converts voice signal into binary information(1s and 0s) and then compression of it allows between 3 to 10 digital cell phone calls to occupy the space of a 1 analog call </li></ul>
  • 23. Digital Technology <ul><li>Frequency-shift keying (FSK) </li></ul><ul><li>- uses two frequencies (one for 1s & the other for 0s) </li></ul><ul><li>- alternates between the two frequencies </li></ul><ul><li>modulation and encoding schemes </li></ul><ul><li>- convert the analog ->digital, compress it->analog </li></ul><ul><li>- acceptable level of voice quality maintained </li></ul><ul><li>Cell phones need a lot of processing power </li></ul>
  • 24. Cellular vs. PCS <ul><li>“ digital cellular”, paging, caller ID and email </li></ul><ul><li>PCS has smaller cells and larger number of antennas. </li></ul>8 3 Time slots 200 KHz 30 KHz Channel spacing 1850 MHz- 1990 MHz 824 MHz- 894 MHz Frequency PCS Cellular
  • 25. Dual band, Dual mode Triband, Trimode <ul><li>What is Dual band? </li></ul><ul><ul><li>CDMA digital cellular (800 MHz) or CDMA digital PCS (1900 MHz). </li></ul></ul><ul><li>What is Triband? </li></ul><ul><ul><li>GSM 900, 1800 and 1900 (MHz) </li></ul></ul><ul><li>Dual Mode </li></ul><ul><ul><li>AMPS and TDMA </li></ul></ul><ul><ul><li>Analog and digital </li></ul></ul><ul><li>Trimode </li></ul><ul><ul><li>Two digital (CDMA and TDMA) and analog </li></ul></ul><ul><ul><li>Two bands in digital and analog </li></ul></ul>
  • 26. Cell phone towers
  • 27. Cell phone towers cont. The box houses the radio transmitters and receivers that let the tower communicate with phones. The radios connects with the antennae on the tower through thick cables.
  • 28. Cell phone disposal <ul><li>135 million registered cell phones today. </li></ul><ul><li>By 2005, there will be at least 200 million cell phones in use and another 500 million older phones to be disposed. </li></ul><ul><li>Toxins that accumulate in the environment </li></ul><ul><ul><li>arsenic, antimony, beryllium, cadmium, copper, lead, nickel and zinc  cancer and neurological disorders </li></ul></ul><ul><li>Recycling Program </li></ul>
  • 29. Risks <ul><li>Brain Tumors? </li></ul><ul><li>The brain cancer patients did not report more cellular phone use overall than the controls. </li></ul><ul><li>Side of the head on which the brain cancer occurred and the side on which the cellular phone was used – no link. </li></ul>
  • 30. Future of Cellular Technology <ul><li>GAIT </li></ul><ul><li>General Packet Radio Services </li></ul><ul><ul><li>2.5G </li></ul></ul><ul><ul><li>3G </li></ul></ul><ul><li>Java-Enabled Phones </li></ul><ul><li>Bluetooth </li></ul><ul><li>More than Phones </li></ul>
  • 31. Sources <ul><li>http://www.cancer.org/eprise/main/docroot/PUB/content/PUB_3_8X_Environmental_Carcinogens-Cellular_Phones_and_Risk_of_Brain_Tumors </li></ul><ul><li>http://www.usatoday.com/life/cyber/tech/2002/05/07/cell-phone-pollution.htm </li></ul><ul><li>http://www.howstuffworks.com/ </li></ul>

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