vault backup: 2022-10-20 10:02:03

content/notes/23-wireless-mobile.md

@@ -15,12 +15,49 @@ two different challenges
 
 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):
+- ![](https://i.imgur.com/SK9pcMz.png)
+- ![](https://i.imgur.com/12vOuH1.png)
 
 # WLAN and wireless link
+Standards created and maintaned by IEEE
+- covers data link layer and physical layer
+![standards table](https://i.imgur.com/werOMuI.png)
+- all use CSMA/CA for multiple access, and have base station and ad-hoc versions
 
-
+WLAN architecture
+- wireless hosts communicates with base station (A)
 
 # CSMA/CA