2. Wireless Application Protocol
Today Lecture
Introduction to wireless communication
Why Wireless communication?
Challenges in wireless communication.
Human Requirements
Wireless vs Mobile
Types of Wireless Communication
Limitations and Difficulties of Wireless Technologies
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3. What is wireless com m unication?
A wireless network enables people to communicate and access
applications and information without wires. This provides freedom of
movement and the ability to extend applications to different parts of a
building, city, or nearly anywhere in the world.
Transfer of voice or data without wires.
Transmitting and receiving voice or data using electromagnetic waves
in open space
The information from sender to receiver is carrier over a well-
defined frequency band (channel)
Each channel has a fixed frequency bandwidth and Capacity (bit-
rate)
Different channels can be used to transmit information in parallel
and independently.
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4. Why Wireless com m unication?
Freedom from wires
– No cost of installing wires or rewiring
– No bunches of wires running here and there
– communications without physical connection
setup, e.g., Bluetooth,WiFi
Global Coverage
– Communications can reach where wiring is
infeasible or costly, e.g., rural areas, old buildings,
battlefield, vehicles, outer space (through
Communication Satellites)
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5. Challenges in wireless com m unication
Stay Connected
– Roaming allows flexibility to stay connected
anywhere and any time
– Rapidly growing market attests to public need for
mobility and uninterrupted access
Flexibility
– Services reach you wherever you go (Mobility).
E.g, you don’t have to go to your lab to check your
mail
– Connect to multiple devices simultaneously (no
physical connection required) 5
6. Techanical Challenges in wireless
com m unication
Efficient Hardware
– Low power Transmitters, Receivers
– Low Power Signal Processing Tools
Efficient use of finite radio spectrum
– Cellular frequency reuse, medium access control
protocols,...
Integrated services
– voice, data, multimedia over a single network
– service differentiation, priorities, resource
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sharing,...
7. Challenges (2)
Network support for user mobility (mobile
scenarios)
– location identification, handover,...
Maintaining quality of service over unreliable
links
Connectivity and coverage
(internetworking)
Cost efficiency
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8. Challenges (3)
Fading
Multipath
Higher probability of data corruption
– Hence, need for stronger channel codes
Need for stronger Security mechanisms
– privacy, authentication,…
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9. H um an Requirem ents
D elay
Packet Loss
BER
D ata Rate
Traffic
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10. Wireless vs Mobile
NOTE : Wireless does not necessarily mean mobile
Wireless Systems may be
– Fixed (e.g., Metropolitan Area Network)
– Portable (e.g., wireless interaction between TV and
VCR)
– Mobile (e.g., mobile phone)
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11. Wired Vs. Wireless Com m unication
Wired Wireless
Each cable is a different channel One media (cable) shared by all
Signal attenuation is low High signal attenuation
No interference High interference
noise; co-channel interference; adjacent
channel interference
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12. Why Wireless Networks
Cabling is som etim es im possible
– Even if possible, cabling is quite expensive
• Mod ern work cond itions require the
flexibility of installation
No cost for re-installation or rewiring
Wireless is convenient and not too expensive
Roaming allows flexibility
– S tay connected anywhere and any tim e
Rapid market growth and application demands
– uninterrupted, fast access regardless of the application
• Consumers and businesses are willing to pay for it
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13. Why go wireless ?
Ad vantages
► S om etim es it is im practical to lay cables
► User m obility
► Cost
Lim itations
► Band wid th
► Fid elity
► Power
► (In) security
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14. Types of Wireless Communication (1)
Radio Transmission
– Easily generated, omni-directionally travel long
distances, easily penetrate buildings
– Problems:
• frequency-dependent
• relative low bandwidth for data communication
• tightly licensed by the governments
Microwave Transmission
– Widely used for long distance communication
– Gives a high S/N ratio, relatively inexpensive
– Problems:
• don’t pass through buildings well
• weather and frequency-dependent 14
15. Types of Wireless Communication (2)
Infrared and Millimeter Waves
– Widely used for short-range communication
– Unable to pass through solid objects
– Used for indoor wireless LANs, not for outdoors
Lightwave Transmission
– Unguided optical signal, such as laser
– Connect two LANs in two buildings via laser
mounted on their roof
– Unidirectional, easy to install, don’t require license
– Problems:
• unable to penetrate rain or thick fog
• laser beam can be easily diverted by turbulent air
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16. Limitations and Difficulties of Wireless
Technologies
Wireless is convenient and less expensive
Limitations and political and technical difficulties
inhibit wireless technologies
Lack of an industry-wide standard
Device limitations
►E.g., small LCD on a mobile telephone can only displaying
a few lines of text
►E.g., browsers of most mobile wireless devices use
wireless markup language (WML) instead of HTML
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17. Limitations and Difficulties of Wireless
Technologies
Technology is still expensive
– Newer technologies are much expensive
• Range is reduced as much as the speed is increased
• Problems of security and confidentiality
Errors occur much more than in wired networks
Interference with other systems
• Detection of collision is impossible
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18. Wireless S ystem s: Range Com parison
1m 10 m 100 m 1 Km 10 Km 100 Km 1,000 Km
Mobile FM MW SW Satellite
WLANs Telephony, Radio Radio Radio Links
IR Blueooth
WLL
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22. Mobile Wireless Networks
What must a mobile network provide ?
– Connectivity with mobility
– Cost-effective sharing of bandwidth
– Performance
• How are mobile networks designed ?
– Layering
– Protocols
– Standards
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23. Role of S tand ard s
Provide (the hope of) interoperability
– Equipment from different vendors
– Existing protocols and software
• Volume in the marketplace
– Broader support by equipment/software vendors Reduced
prices
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24. Classification of Wireless
Networks
Mobility: fixed wireless or mobile
• Communication: Analog or digital
• Topology/Infrastructure: Ad hoc
(decentralized) or centralized (base stations)
• Services: voice or data
• Ownership: public or private
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25. Classification of Wireless
Networks
Area: wid e (WAN), m etropolitan (MAN),
local (LAN), or personal (PAN) area networks
• Medium: S witched (circuit- or
Packet switched )
or broad cast
• Data Rate: Low bit-rate (voice grad e) or high
bit-rate (vid eo, m ultim ed ia)
• Placement: satellite
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26. Current Wireless Systems
Cellular Systems
Wireless LANs
Satellite Systems
Wireless PANs (bluetooth)
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Editor's Notes
CS 698T P. Bhagwat Q1. Can you think of a system whose range of communication is more than satellite links? Q2. Give an example of a system whose range of communication is shorter than IR links. Point to ponder: Why does range of communication increase on logarithm scale?
