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Wireless Technology

Wireless Technology. Radio Transmission. Oscillating electron generates electromagnetic waves with the frequency of the oscillation Many electrons must be excited in an antenna for a strong signal. Cellular Telephones. Original Mobile Telephones One transmitter/receiver

Jeffrey
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Wireless Technology

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  1. Wireless Technology

  2. Radio Transmission • Oscillating electron generates electromagnetic waves with the frequency of the oscillation • Many electrons must be excited in an antenna for a strong signal

  3. Cellular Telephones • Original Mobile Telephones • One transmitter/receiver • Limited number of channels • For good service can support about 20 subscribers per channel Transmitter/ Receiver Mobile Phone

  4. Cellular Telephones • Divide Region into Cells • One cellsite per cell • Channels can be reused in non-adjacent cells Yes No Can Reuse Ch. 232? Uses Channel 232 No No Yes Yes No No Channel 232 Used in 4 cells No

  5. Cellular Telephones • Reuse • Without reuse, only 20 users per channel for good service • If reused 3 times, 60 subscribers per channel • Reuse Rule (Rough) • Reuse factor = Number of cells / 7 • If 20 cells, reuse factor is about 3

  6. Handoffs • When you move to another cell within the same system • You are transferred automatically to that cell’s cellsite

  7. Roaming • Take your cellphone to another city • Use it there to send and receive • Not always possible technically • May be limited procedurally because of high rates of cellular fraud in some areas • Don’t confuse this with handoff, which takes place within a cellular system between cells

  8. Control • Mobile Telephone Switching Office • Controls cellsites, handoffs, etc. • Calls go to/from MTSO • Connects to POP at LEC to link to traditional telephone (wireline) carriers POP at LEC MTSO

  9. Placing a Call • Enter number, hit send • Cellphone broadcasts request • Several cellsites receive, send to MTSO • MTSO assigns cellphone to cellsite with loudest signal • MTSO sends message to cellphone, telling it what incoming, outgoing channels to use

  10. Receiving a Call • MTSO has each cellsite broadcast cellphone’s ID number • Cellphone transmits a response • Responses from cellsites go to MTSO • MTSO selects loudest cellsite • MTSO sends message to cellphone, giving channels and telling the cellphone to ring

  11. First Generation Cellular • Analog or Digital Operation • Initially analog; initially analog in U.S. using the AMPS standard • Europe and the rest of the world started with a large number of incompatible analog systems but settled on the digital GSM standard

  12. First-Generation Cellular • Large Cells • Usually only 20-40 per city • Limits channel reuse • Limited Number of Channels • In U.S., 832 two-way channels • No Compression • Each voice signal required a full two-way channel

  13. First-Generation Cellular • How Many Subscribers Can You Support? • 20 cells • Channel reuse is about 3 (20/7) • 832 channels • With channel reuse, 2,496 effective channels • 20 users per available channel • So only about 50,000 subscribers per city • Engineering tricks can extend, but only somewhat

  14. Second-Generation Cellular • Personal Communication Service (PCS) • Or Personal Communication Network (PCN) • More channels • About 2,500 • Smaller cells permit more channel reuse • Don’t just say “smaller cells;” be explicit about channel reuse

  15. Potential System Capacity (Roughly) • Category 1st Gen 2nd Gen • Cells/City 30 100 • Channel reuse (cells/7) ~4 ~14 • Channels 800 2,500 • Effective channels 3,200 35,000 • With compression *3,200 105,000 • Subscribers (x20/channel) 64,000 2,000,000 • *No compression in 1st generation

  16. Second-Generation Cellular • Smaller cells • PCS Cellphones • Do not have to transmit as far because cells are smaller • Cellphones can be less expensive because use less power

  17. Second-Generation Cellular • Most of World • Standardizing on DCS Technology • Based on GSM and usually called GSM • U.S. • FCC did not specify a standard • Different carriers use different technologies • Some have standardized on GSM • Your cellphone may not work with another carrier • Limits roaming

  18. Generations: Recap 1st 2nd Analog/Digital Both A&D Digital Cells Large Small Channels (Approx.) 800 2500 Compression No Yes U.S. Standardization AMPS Poor International Standards GSM DCS

  19. TDMA • A technology for delivering digital wireless service using time-division multiplexing (TDM). • TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. • In this way, a single frequency can support multiple, simultaneous data channels. • TDMA is used by the GSM digital cellular system.

  20. CDMA • Every channel uses the full available spectrum. • Individual conversations are encoded with a pseudo-random digital sequence. The mobile phone is then instructed to decipher only a particular code to pluck the right conversation off the air. • Increased privacy is inherent in CDMA technology. CDMA phone calls will be secure from the casual eavesdropper. • Excellent voice quality and longer battery life.

  21. Third-Generation (3G) • Smarter Devices • Devices will have the power of a small PC • Greater Number of Uses • Data, including internet access • Graphics and even video

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