Mesh/Spectrum

We use three different methods to map out spectrum usage.

Wifi channel usage scan

Most wifi chipsets are capable of reporting:

• How many access points are on each channel
• With how much power each access point is being received

These measurements don't account for how many clients are using the APs how much of the time and with how much power. There can be several high-powered access points all operating on the same channel in one area, but if they are unused then they will only minimally interfere with other nodes. This type of scan cannot detect if the access points are in use.

See the software tools page for suggestions on using this type of scan.

Atheros spectral scan

The Atheros AR92xx and AR93xx chipsets have a spectral scan mode that outputs FFT data for the entire range of the chip.

Ubiquiti AirOS has a built-in java applet that visualizes the spectral scan output. Unfortunately it does not provide any kind of documented API.

Support for atheros spectral scan has as far as we know not yet been implemented into the open source Linux kernel driver, but there is an effort to support this functionality. Here are some resources:

• A kernel driver patch adding spectral scan support + gui
  • Looks like an updated version of the above
• A GUI for visualizing the spectral scans
• Adrian's information
• Some general info

Frequency analyzer scan

Using a frequency analyzer or software-defined radio with a wide frequency range, it's possible to scan the actual frequency usage across the entire range of interest. Elonics 4000 can scan from 64 mhz to 2.2 ghz and only costs about $25.