1. ECE, UMD
Introduction to Wireless Network
Peng Li

2. Motivation
Why we use Wireless Network
 Mobility
 Ease of use
 Installation Simplicity and Flexibility
 Cost
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3. Outline
The elements in Wireless Network
1
Spread Spectrum
2
OFDM
3
Wireless Data Services
4
Summary
5
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4. The elements in Wireless Network
Data
Format
Wireless
Network
Network
Structure
Radio
Signals
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5. The elements in Wireless Network
In terms of the OSI reference model
 Data format controls several of high layers.
 Network Structure includes the wireless
network interface adapters and base stations that
send and receive the radio signals.
 Radio signal operates at physical layers.
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6. Spread Spectrum
What’s the modulation method
for Radio signal in Wireless
Network ?
 AM ?
 FM ?
 PCM ?
 Something else ?
Spread Spectrum !
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7. Spread Spectrum
What’s Spread Spectrum ?
 Spread spectrum is a family of
methods for transmitting a
single radio signal using a
relatively wide segment of the
radio spectrum.
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8. Spread Spectrum
Frequency-Hopping
FHSS
Spread Spectrum
Direct-Sequence Spread
DSSS
Spectrum
Orthogonal Frequency
OFDM
Division Multiplexing
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9. OFDM
What’s OFDM ?
 OFDM is a combination of modulation
and multiplexing.
 OFDM is a special case of FDM
(Frequency Division Multiplex).
 The main concept in OFDM is
orthogonality of the sub-carriers.
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10. OFDM
OFDM System Diagram
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11. OFDM
Benefits of OFDM
 Very easy and efficient in dealing with
multi-path
 Robust again narrow-band interference
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12. Wireless Data Services
Wi-Fi
Cellular Mobile Wireless Services
WiMAX
Bluetooth
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13. Wireless Data Services
Wi-Fi
 It covers the various IEEE 802.11
technologies (including
802.11n, 802.11b, 802.11g, and 802.11a).
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14. Wireless Data Services
Wi-Fi Characteristics
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15. Wireless Data Services
Wi-Fi Type Frequency Modulation
802.11a 5 GHz OFDM
802.11b 2.4 GHz DSSS
802.11g 2.4 GHz OFDM
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16. Wireless Data Services
Cellular Mobile Wireless Services
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17. Wireless Data Services
WiMAX
Worldwide Interoperability for Microwave Access, The technology is

based on the IEEE 802.16 standard (also called WirelessMAN).
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18. Wireless Data Services
Bluetooth
 Bluetooth is an FHSS system that splits the radio
signal into tiny pieces. It moves among 79
different frequencies 1,600 times per second in
the same unlicensed 2.4 GHz range as 802.11b
and 802.11g Wi-Fi services.
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19. Summary
 Connecting your computer to the Internet (or a
local network) by radio offers several advantages
over connecting the same computer through a
wired connection.
 First, wireless provides convenient access for
portable computers; it’s not necessary to find a
cable or network data outlet.
 Second, it allows a user to make a connection
from more than one location and to maintain a
connection as the user moves from place to
place.
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20. ECE, UMD
Q&A