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