flat or curved tops for signal strength plots

[Richard42]

In the signal strength plots in the lower right hand corner of inSSIDer, why do some plots have flat tops and others have rounded tops? In particular, it seems that all 2Wire signals look like bell curves while all other signals look like step functions.

Thanks,
Richard

[MetaGeek]

I would love to answer this question!!!!

The curves actually represent the HR-DSSS BPSK (High-Rate Direct Sequence Spread Spectrum). Basically this is the pattern that a 802.11b signal will make in 2.4GHz spectrum. See attached image (captured by our trusty Wi-Spy) called 802.11b.

The flat tops represent access points that can support ERP-OFDM, which again, is a modulation type in the 2.4GHz band. Basically all 802.11g capable wireless access points are ERP-OFDM but also are backwards compatible with 802.11b/HR-DSSS modulation too.

For our Wi-Spy owners, from my experience, access points broadcast their beacons in HR-DSSS, which may be confusing at first. However simply initiate a download and you will see the traffic change to 802.11g ERP-OFDM.

Summary (TLDR)
inSSIDer now draws the access points just as they would appear in the actual radio frequency space.

[mmiller7]

Summary (TLDR)
inSSIDer now draws the access points just as they would appear in the actual radio frequency space.

THANK YOU! A picture really is worth a thousand words.

I'd read the long explaination you wrote, and I've read dozens of articles trying to visualize this in my head and I hadn't been able to comprehend it with all the differences in frequency algorythms, channel width, etc.

InSSIDer really is much more valuble this way, even if it doesn't "look" as cool.

[Richard42]

Thanks Trent. That makes sense, as all of the curve tops show access speeds of only 18 rather than 36 or 54 for the flat tops.

- Richard42

[MetaGeek]

I'm bumping this thread, simply just to show how great this video is. You can see the difference in the modulation types and the speed decrease as soon as he jumps to a channel used by a lot of APs.

Speed decrease due to co-channel interference

[warquezho]

Based on the reply here, it seems that 802.11g also uses HR-DSSS BPSK (cure line), but when I also read in your reply here http://www.metageek.net/forums/showt...php?4639-graph that when the rate is 12 or greater, it will be drawn in flat line. But in my access point which is 802.11b/g, I can see in inSSIDer that the max rate is 18, but it is drawn in curve line, may I know why?

the yellow line is the one I'm referring to

[MetaGeek]

I'm going to have to submit this as a bug. I don't think that is possible.

[warquezho]

So that yellow line should be a flat line and this is a bug?

[TeeCee]

I'm going to have to submit this as a bug. I don't think that is possible.

I'm sat looking at a display showing one vanilla 11Mb/s printer, umpty-somethinig Cisco access points, all reported as max rate of 18, one iPhone and one access point from A.N.Other manufacturer with a rate of 144.

The Epson's a bell as expected. The iToy and odd Access point are flat. The Ciscos are all bells.

Note that the point I am connected to reports a connection speed of 54 at the client, but the max rate shown for the point is 18. Downloading does not affect the "curviness" of that point. An ftp session gets around 530Kb/s, but the display remains steadfastly bell-shaped and reported as max rate 18.