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How Your Cellphone Works…. Matthew C. Valenti Lane Department of CSEE. And Why Sometimes it Doesn’t…. How many cellular subscribers are there worldwide? In the US?. Wireline access lines. 176.4 million Mar. 05. Wireless subscribers (cellular and PCS). 3 rd generation. 2 nd generation.

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how your cellphone works

How Your Cellphone Works…

Matthew C. Valenti

Lane Department of CSEE

the wireless revolution

Wireline access lines

176.4 million

Mar. 05

Wireless subscribers (cellular and PCS)

3rd

generation

2nd

generation

1st generation

1000

The Wireless Revolution

100

Millions of Subscribers

10

1

0.1

2004

1983

1986

1989

1992

1995

1998

2001

wireless growth in US alone

Source: www.ctia.org

largest carriers in us
Largest Carriers in US
  • Cingular, 49.1 million (GSM)
  • Verizon, 43.8 million (CDMA)
  • Sprint, 24.8 million (CDMA)
  • T-mobile, 17.3 million (GSM)
  • Nextel, 16.2 million (iDen)

In the US, the wireless industry brings in $100B/yr.

wireless worldwide
Wireless Worldwide
  • Over 1 billion subscibers.
  • Penetration Rates for Select Countries
    • Taiwan: 101%
    • U.K: 100%
    • Italy: 96%
    • Netherlands: 94%
    • Germany: 84%
    • France: 76%
    • Japan: 65%
    • United States: 59%
    • Russia: 50%
    • India: 9%
    • China: 38%

Growing Fast

slide7

PCS: 1.85-2.0 GHz

Cellular: 824-894 MHz

how crowded is the spectrum
How Crowded is the spectrum
  • 176.4 million subscribers
  • 220 MHz available for Wireless
  • So just give each subscriber 0.8 Hz of dedicated bandwidth (0.4 Hz each direction), right?
  • Problem: cellular signal occupies:
    • 200 kHz (GSM)
      • 550 distinct channel pairs.
      • Time division multiple access divides channels into 8 subchannels.
      • So 4400 “conversations”
    • 1.25 MHz (CDMA)
      • 88 distinct channel pairs.
      • Code division multiple access divides each channel into 64 subchannels
      • So 5632 “conversations”
the cellular concept
The Cellular Concept
  • Transmit power drops off with distance.
  • When you are far-enough away you can re-use the channel.
  • Similar concept to frequency re-use for radio and television stations.

Ch #1

Ch #2

Ch #3

Ch #1

Low power transmitter, Frequency is re-used

the cellular concept11
The Cellular Concept

Set #1

Set #2

Set #3

Set #2

Set #3

Ch #1

Set #4

Set #1

Lower power transmitters provide coverage to a small

portion of the service area. Frequency is reused

cell patterns
Cell Patterns

Idealized Cells

Idealized Coverage

Footprint

Reality!

the cellular concept14
Break the metropolitan area into small areas

Each area is approximated with a hexagonal cell.

A base station is located at the center of each cell.

Each cell is assigned only a fraction of the total number of channels.

Cells that are sufficiently far apart can reuse the same frequency.

The Cellular Concept

Cluster #1

Cluster #2

A

F

B

A

B

G

F

E

C

G

E

D

C

A

D

F

B

G

E

C

D

Cluster #3

frequency reuse
Frequency Reuse

2

1

2

5

1

5

4

4

3

7

3

7

6

6

2

1

5

4

3

7

N = 7

6

cell pattern n 4
Cell Pattern N = 4

2

1

3

2

2

4

1

3

3

1

4

2

4

3

1

4

sectorized antennas
Sectorized Antennas
  • Further interference reduction by using sectorized antennas.
hand off
Hand Off

Ch #2

Ch #1

  • Mobile must be transferred between cells as it moves
  • Hard handoff
  • Soft handoff (CDMA)
  • Softer handoff (sectorized antennas)
wireless propagation
Wireless Propagation
  • Fading
    • Due to relative motion between TX and RX.
  • Multipath
    • Due to signal reflections.
  • Diffraction
    • Signal bending around objects (mountain, buildings)
  • Shadowing
    • Obstructions that attenuate signal (foliage)
  • Interference
    • Other signals
  • Noise
    • Thermal excitement of electrons in receiver.
    • Background noise in space.
but all is not lost
But all is not lost…
  • Source Coding
    • Companding: Reduces BW needed by voice.
  • Channel Coding
    • Forward Error Correction Coding.
    • By adding parity bits to transmitted data, errors can be corrected.
  • Advanced Receiver Processing
    • Equalizer: Undoes multipath
  • This is the type of stuff that EE’s working in the communications industry work on!
to learn more a lot more
To Learn More (A Lot More)…
  • Wireless Networking
    • CPE 493g
    • 9-10 AM, M-W-F
    • ESB 801
    • Valenti
    • EE 327 and STAT 215 prereq’s.
  • Wireless Communication Systems
    • EE 562
    • Reynolds
    • 12 PM – 1 PM M-W-F
    • ESB 201
    • Reynolds
    • EE 461 and/or EE 513 prereq’s.