Device RF Fingerprints

With wireless systems it is very difficult to predict the propagation of radio waves and detect the presence of interfering signals without the use of test equipment. Radio waves don’t travel the same distance in all directions — instead walls, doors, elevator shafts, people, and other obstacles offer varying degrees of attenuation, which cause the Radio Frequency (RF) radiation pattern to be irregular and unpredictable. In order to achieve optimal reliability and throughput for your WiFi( 802.11) wireless network it is necessary to detect and identify sources of interference that impact negatively on its performance.

There are a multitude of electronic devices that transmit RF energy into the airspace.  WiFi(802.11 b/g) operates in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band.  This particular range of frequencies (2.401 GHz through 2.473 GHz) is public and its use does not require licensing by the FCC. As a result, this band tends to get rather crowded – not only with 802.11 devices but also microwaves, bluetooth devices, cordless phones, baby monitors, audio/video senders, wireless cameras, etc

Below are four Examples  of  RF  Fingerprints:

1.Example:#No wifi traffic on 2.4Ghz

The air space is relatively quiet and there are no wireless devices transmitting in the 2.4 GHz band. Notice the maximum value on the Y-axis has a signal strength of -90 dBm, which is very weak. The reason you see peaks (and the output isn’t totally flat) is this display has enabled automatic scaling, such that the largest peak (regardless of how small it really is) will fill-up the screen. We know this is what background noise looks like because the maximum value on the Y-axis is -90 dBm.

noise_only

2.Example:#Microwave on action

A microwave oven is running. Here you can see that it emits RF energy across the entire 2.4 GHz band.

microwave_on_action

3. Example:#Cordless Phone

A 2.4 GHz cordless phone has been powered on.  Notice the height of the peak in the vicinity of channel 1 is around -60 dBm. This is strong enough to knock-out wireless networks configured to use WiFi channel 1. In addition, because of the way that channels overlap the first peak would probably also interfere with a wireless network using channel 2.

cordless_phone

4.Example :#Wifi Activity on spectrum

Shows the pattern of activity from a wireless network (configured to use WiFi channel 6) as it is actively transmitting a large stream of data.

channel_6_wifi_activity

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WiFi Chipsets @ their action:

Today  I was sitting at my home and working on personal PC was able to sense Low WiFi speed. So i took another laptop of mine able to work with decent speed. Note: 1st laptop  is around 2 + years old .

Tried to run my  favorite windows command on both the Machine:

wifitest3

your seeing the performance of 5 Ghz VS 2.4Ghz and its Wifi chipset in  action.

The first laptop with Intel 7260 AC adapter and my 2+ year old laptop is running Atheros  AR9485WB-EG.

#Intel 7260 AC adapter is a 2*2 spacial stream and works with both 2.4 and 5ghz frequency and its an 802.11 AC adapter that can operate at 867mbps

#Whereas, Qualcom Atheros AR9485WB-EG is an 1*1 spacial Stream adapter and can operate only on 2.4 ghz and its an 802.11 N standard adapter that can operate at a speed of 150 Mbps.

This proves 2 things,

#Why 5Ghz.

#Why to refresh new hardware (WiFi chipset in my case). Just couple of old clients reporting slowness doesn’t mean WiFi network is slow.

And finally why both of them didn’t run at top of their MCS rate supported?? Yes, your right  its because of SNR.

Example I have got a capture of 2.4 ghz around.

wifitest4

Yes, its running on channel 2, co-channel and adjust channel interference will get us a low SNR , apart from the RSSI.