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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
radio transmission
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
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

cellular telephones4
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

cellular telephones5
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
handoffs
Handoffs
  • When you move to another cell within the same system
    • You are transferred automatically to that cell’s cellsite
roaming
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
control
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

placing a call
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
receiving a call
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
first generation cellular
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
first generation cellular12
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
first generation cellular13
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
second generation cellular
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
potential system capacity roughly
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
second generation cellular16
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
second generation cellular17
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
generations recap
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

slide19

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.
slide20

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.
third generation 3g
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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