ECE 250: Wireless Communications and Networking Lecture 1

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ECE 250 Wireless Communications
andNetworkingLecture 1

• Prof. Volkan Rodoplu
• UCSB
• Spring 2005

• Acknowledgments Prof. Ted Rappaport,
• Prof. Narayan Mandayam, Prof. Andrea Goldsmith

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OSI Model
Computer Science
Electrical Engineering
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Why go wireless ?

• Advantages
• Sometimes it is impractical to lay cables
• User mobility
• Cost

• Limitations
• Bandwidth
• Fidelity
• Power
• (In)security

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Wired Vs. Wireless Communication
Each cable is a different channel
One media (cable) shared by all
High signal attenuation
Signal attenuation is low
High interference noise co-channel interference
adjacent channel interference
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Wireless Systems Range Comparison
1,000 Km
100 Km
10 Km
1 Km
100 m
10 m
1 m
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Cellular Systems
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Growth of Cellular Subscribers
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Cellular System Evolution
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Understanding wireless communication
Tx
Rx

• How does signal propagate ?
• How much attenuation take place ?
• How does signal look like at the receiver ?

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EM Spectrum
X rays
Gamma rays
visible
UV
infrared
?
1 MHz
1 kHz
1 GHz
1 THz
1 PHz
1 EHz
Propagation characteristics are different in each
frequency band
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Radio Propagation
Three basic propagation mechanisms
Scattering ? gtgt D
Diffraction ? ? D
Reflection ? ltlt D

• Propagation effects depend on not only on the
  specific portion of spectrum used for
  transmission, but also on the bandwidth (or
  spectral occupancy) of the signal being
  transmitted
• Spatial separation of Tx-Rx

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Propagation
The higher frequencies will usually encounter
more loss in real world situations
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Path loss in dB
Path loss from source to d2 70dB
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The Cluttered World of Radio Waves
hills
girders
rain
hallways
windows
vehicles
trees
walls
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Wireless Networks
Ubiquitous Communication Among People and Devices
Wireless Internet access Nth generation
Cellular Wireless Ad Hoc Networks Sensor Networks
Wireless Entertainment Smart Homes/Spaces Automat
ed Highways All this and more