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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

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Presentation Transcript

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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


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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


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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


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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


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Handoffs

  • When you move to another cell within the same system

    • You are transferred automatically to that cell’s cellsite


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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


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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


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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


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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


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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


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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


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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


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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


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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


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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


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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


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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


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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.


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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.


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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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