Changes between Version 11 and Version 12 of 802.11/wlan_exp/app_notes/tutorial_hop_mac/fast_hopping

Timestamp:

Aug 3, 2015, 4:06:34 PM (9 years ago)

Author:

chunter

Comment:

--

802.11/wlan_exp/app_notes/tutorial_hop_mac/fast_hopping

@@ -433 +433 @@
 == Characterization ==
 
-
+To first characterize the design, we can use an oscilloscope to explicitly measure the frequency of frequency re-tune events as well as the duration of time it takes to re-tune the radio. In our implementation of {{{poll_hop()}}} above, we wrapped the call to the radio controller that tuned to a new frequency with a set and clear of the [wiki:802.11/Usage/UserIO#DebugHeaderSignals software debug GPIO] signals. The following oscilloscope captures were taken by probing the software debug pins on both the AP and STA WARP v3 hardware.
 
 ||  [[Image(wiki:802.11/wlan_exp/app_notes/tutorial_hop_mac/figs:scope_plots.png, width=800)]]  ||
 ||  '''Oscilloscope Plots'''  ||
+
+In the above captures, the yellow signal corresponds to the debug pin on the AP and the blue signal corresponds to the debug pin on the STA. There are three key observations from the above captures:
+
+1. The period between re-tune events is around 4.096 ms. This is consistent with our code above that set {{{TS_USEC_SHIFT}}}.
+1. The re-tune duration is about 93 µs. This time, plus our guard interval of an additional 96 µs, represents overhead in our implementation since this is time that a node can neither transmit nor receive. 189 µs out of a 4096 µs dwell time gives us an effective duty cycle of 95%.
+1. The rise of the debug signal of the STA occurs within a couple µs of the rise of the debug signal at the AP. The jitter here is an artifact of the over-the-air synchronization occurring with the 802.11's TSF synchronization. The fact this value is so small informs us that our 96 µs of guard interval above is probably over provisioned and can be significantly reduced without incurring additional loss.
 
 ||  [[Image(wiki:802.11/wlan_exp/app_notes/tutorial_hop_mac/figs:xput.png, width=800)]]  ||