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69 lines
1.9 KiB
Markdown
69 lines
1.9 KiB
Markdown
---
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title: "23-wireless-mobile"
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aliases:
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tags:
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- cosc203
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- lecture
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---
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More wireless phones that wired phones.
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More mobile broadband than fixed broadband
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two different challenges
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- communication over wireless link
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- mobility: handling the mobile user to changes point of attachment
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elements
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- wireless hosts
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- does not always mean mobile
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- base station
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- connected to wired network
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- relay: sendig packets between wired network and wireless hosts in its "area"
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- e.g., cell towers
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- wireless link
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- used to connect mobile to base station, also used as backbone link
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- various transmission rates, distances, frequency bands
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architecture
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- infrastructure mode
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- base station connect mobiles to wired network
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- handoff: mobile changes base station
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- ad hoc mode
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- no base stations
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- can only transmit to other nodes within link coverage
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- nodes organize themselves into a network: route among themselves
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wireless link
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- deccreased signal strength: radio signal attentuates as it travels
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- interference from other sources: frequency shared by other technologies
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- multipath propagation: signal reflects of objects arriving at sightly different times
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SNR BER tradeoffs
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- SNR - signal to noise ratio
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- larger SNR is easire to extract signal
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- BER - bit error rate
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- larger SNR => smaller BER
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- many parameters at physical level which alter SNR
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hidden terminal problem
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- multiple wireless sender, recievers create additional problems (beyond multiple access):
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- 
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- 
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# WLAN and wireless link
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Standards created and maintaned by IEEE
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- covers data link layer and physical layer
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- all use CSMA/CA for multiple access, and have base station and ad-hoc versions
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WLAN architecture
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- wireless hosts communicates with base station (A)
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# CSMA/CA
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# Hidden terminal problem
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# Cellular networks
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# 4G LTE
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