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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