Performing Spectrum Analysis for troubleshooting
We always need to deal with RF interference when it comes to WLANs troubleshooting. Wi-Fi Access Points are generally operating either on 2.4GHz and 5GHz frequency range, however it is not just Wi-Fi who are using these channels. There are some other common electronic devices such as Bluetooth, Microwave Ovens, Cordless Phone and Wireless Camera, etc.… also operates in the same radio range that creates interference and noise to WLANs.
Spectrum analyzer is the layer 1 diagnostic tool that we often used to perform analysis to identify the RF interference that has caused negative impact on wireless performance. In today’s blog, we will walked through two primary types of spectrum analysis hardware and explore the features that we can leverage to detect non-Wi-Fi interference.
Integrated Spectrum Analyzers
Integrated spectrum analysis use AP chipsets and radios to perform the scanning of the spectrum. It can be used for effective remote troubleshooting. And there will be graphical analysis feedback that can be viewed in the web-based management interface of the AP infrastructure.
Below is an example for spectrum intelligence from Aerohive HiveManager:
There are four different types of graph presented for the captured spectrum.
Real-time FFT
Fast Fourier Transform (FFT) is a mathematic algorithm for computing the frequency spectrum of a received input signal. This line chart indicates the power level of a signal on a channel or frequency monitored.
FFT Duty Cycle
This line chart indicates the amount of time as a percentage of total time a signal is broadcast on a channel or frequency monitored. The FFT Duty Cycle is often referred to as channel utilization.
Swept Spectrogram
This plot displays FFT power levels for monitored channel or frequency over time. It produces a color-coded sweep of spectral information to show the real time FFT.
Swept Spectrogram-FFT Duty Cycle
This plot displays FFT duty cycle for monitored channel or frequency over time. It also produces a color-coded sweep to represent duty cycle information.
Mobile Spectrum Analyzer
Mobile spectrum analyzers use adapters in laptops together with software application for mobile RF analysis. For example, AIrMagnet Spectrum XT and Metageek Wi-Spy DBx are two of the popular mobile spectrum analyzers. These adapters also support external antenna so we can use them with directional antenna for locating interference source.
To test the features of mobile spectrum analyzer, I have got the setup of Metageek WiSpy DBx with Chanalyzer in my testing lab.
Below is what the Chanalyzer Software looks like, it presents a series of interactive graphs and charts with detailed data to tell us more about the spectrum.
We can select different radio bands to start capturing the spectrum data.
For the overview plane which is located at the top right area, we can enable display options to present different set of data that we are currently collecting.
Below the overview plane also contains a lot of additional useful information such as channel table, network table, network graph and utilization graph for the figures.
If we have trouble to identify the pattern of the interference source, Metageek has provided rich sample examples of WiFi and non-WiFi spectrum patterns that we can refer to. See below link:
https://support.metageek.com/hc/en-us/articles/200628894-WiFi-and-non-WiFi-Interference-Examples
Other Reference:
http://docs.aerohive.com/330000/docs/help/english/ng/Content/gui/devices/viewing-spectrum-intelligence-details.htm