This test includes two sets of data. The first set is the test performed with the antenna pointing down in the customary fashion. The second test is performed with the antenna pointing upwards. This second test was performed because, as you can most likely see from the plots, during the first test the top mote closest to the broadcaster had abnormally low RSSI. This is most likely because the mote is above the ground plane and little to no signal can reach it. The offsets for these tests were with the low motes at 0.045m below the broadcaster and the high motes at 0.240m above the broadcaster. Because some ended up below and some ended up above the broadcaster we face an issue because the 7MM antenna has a ground plane that, at closer distances, will have very little broadcasting strength above.
This plot is a boxplot of the data with the mote pointing down in the normal way:
CDF of the data with the mote pointing down in the normal way:
CDF by height of the data with the mote pointing down in the normal way:
From this last plot it appears that the 0.25 and 0.5 distances are swapped for the low and high motes. This is what makes the CDF plot of all the data so inconclusive and causes the closest high mote to appear far away. This is the main reason why we ran the second test. And the data
Boxplot of the data with the mote pointing up:
CDF of the data with the mote pointing up:
If we can somehow clean up the closest mote values the 0.5m CDF is almost a completely vertical line. This is awesome because it provides a clean cut RSSI value that says ‘this mote is x meters away’ and can help discern between far and close motes. This test again had a tanking of the closest high motes RSSI values. We are going to look into this because the ground plane should not be causing this issue. The expected results of the top row would be when like the bottom row of the tests conducted using heights for badge motes because the distances are similar.
Though the comments indicate a good separation (by the CDF), when I look at the boxplots and try to imagine inverting them ( f(RSSI)=distance ), I still see significant areas of overlap between different distances. Or maybe because of the scale of the plot on the webpage, I can’t see so clearly the dividing line. It does appear that some high values for the 0.5m and 0.75m range overlap low values for the 0.25m range. I can’t tell exactly where 0.25m starts and ends looking at these.
Comment by tedherman — October 29, 2009 @ 4:36 pm
You are right, Ted. Actually I think the general concensus in the lab is that the pucks with the 7MM antenna will not work with the badges, which is what this test was checking. We’ll need to come up with a different solution for the badges, but we thought we’d make the pucks and the pagers for a solid version two for now, then move onto the chest-level badges. The vertical lines are nice, but they are sometimes in the wrong order, which is disconcerting
Comment by gthomas — October 29, 2009 @ 7:09 pm