Changes between Version 23 and Version 24 of 802.11/wlan_exp/app_notes/dcf_with_multiple_flows

Timestamp:

Apr 17, 2014, 9:58:20 AM (10 years ago)

Author:

chunter

Comment:

--

802.11/wlan_exp/app_notes/dcf_with_multiple_flows

@@ -120 +120 @@
 == Experiment 2: Symmetric with Hidden Stations ==
 
-In this second experiment, we modify the attenuation values in the experimental setup such that each flow sees the same path loss as the first experiment, but the path loss between the two STA nodes is dramatically larger. Topologically speaking, this is an extreme hidden node problem: STA 1 and STA 2 can each "see" the AP, but they cannot see one another.
+In this second experiment, we modify the attenuation values in the experimental setup such that each flow sees the same path loss as the first experiment, but the path loss between the two STA nodes is dramatically larger. Topologically speaking, this is an extreme hidden node problem: STA 1 and STA 2 can each "see" the AP, but they cannot see one another. Note: this experiment resets the CW changes we made to the AP at the end of the prior experiment. Each node is running a completely standard 802.11 Reference Design.
 
 ==== Experiment Details ====
@@ -160 +160 @@
 }}}
 
+The hidden node problem has massively reduced the achievable throughput of Flows 3 and 4 since they cannot carrier-sense one another to avoid collisions. Using the event log, we can look deeper into the design to see some very interesting behaviors.
+
+||  [[Image(wiki:802.11/wlan_exp/app_notes/dcf_with_multiple_flows/figs:hidden.png, width=600)]]  ||
+||  ''Throughput Timeline'''  ||
+
+Notice that Flows 3 and 4 are very unstable. They do not simply oscillate around some nominal throughput like they did in the first experiment.