1. How Your Cellphone Works…
Matthew C. Valenti
Lane Department of CSEE

2. And Why Sometimes it Doesn’t…
9/17/2018

3. How many cellular subscribers are there worldwide? In the US?

4. The Wireless Revolution
1000
Wireless subscribers (cellular and PCS)
176.4 million
Mar. 05
Wireline access lines
2nd
generation
100
Millions of Subscribers
1st generation 10
3rd
generation 1
0.1
1983
1986
1989
1992
1995
1998
2001
2004
wireless growth in US alone
Source:

5. 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.
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6. 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
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7. Cellular: MHz
PCS: GHz
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8. 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”
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9. Something’s Got to Give…
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10. 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

11. 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

12. 175,368 cell towers in the US
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13. Cell Patterns
Idealized Cells
Idealized Coverage
Footprint
Reality!

14. The Cellular Concept A F B A G F B E C G D E C A D F B G E C D
Cluster #1
Cluster #2
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. A F B A G F B E C G D E C A D F B G E C D
Cluster #3

15. Frequency Reuse 2 2 1 5 1 5 4 4 3 7 3 7 6 6 2 1 5 4 3 7
N = 7 6

16. Cell Pattern N = 4 2 1 3 2 4 2 3 1 3 1 4 2 4 1 3 4

17. Sectorized Antennas
Further interference reduction by using sectorized antennas.
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18. Hand Off Mobile must be transferred between cells as it moves
Ch #2
Ch #1
Mobile must be transferred between cells as it moves
Hard handoff
Soft handoff (CDMA)
Softer handoff (sectorized antennas)

19. Wireless Propagation Fading Multipath Diffraction Shadowing
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.
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20. But all is not lost… Source Coding Channel 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!
9/17/2018

21. 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
EE 461 and/or EE 513 prereq’s.
9/17/2018