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My WiFi is sometimes fine and sometimes very bad. Holding the laptop right next to the access point makes no difference. I'm in a building where I have to share the AP with multiple people (we don't get a wired connection to our apartment...). It seems that either the uplink is saturated, or someone else is using all the available spectrum.

Can I use my laptop to check whether the spectrum is saturated? In the past I've loaned a HackRF from someone, which made it easy to see using tools like sdrangelove. Is there any tool that can use my WiFi card to do the same kind of analysis?

One option is to put the card in monitor mode using airmon-ng, but as far as I know, that would only show me packets from people authenticated with the same AP. I'd also like to see interference from people not on the same AP.

Another tool I know of is wavemon, but it does not seem to be able to show what I am looking for.

Is there any software for Linux that can do this? Anything packaged for Debian Stretch would be ideal.

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Your Wifi card can scan for all access points (AP) and their signal strength and frequency. This information (and much more) is available with iw <wlan-if> scan, so executing a command like

iw wlan0 scan | egrep '^BSS|SSID|signal|freq:'

in regular intervals will give you some idea about other APs, and whether they are interfering.

Your Wifi card also maintains statistics about the connection to the AP you are associate with, so doing

iw wlan0 station dump

will give you some idea about the quality of your connection (signal and bitrate). You may have to stay in one place for some time to have this information become current.

There are applications e.g. for Android phones that display this information graphically, but I don't know any application for Linux, though it wouldn't be particular hard to write one.

  • I don't think this tells me what I'm looking for though. The signal strength only indicates how much power the antenna detected/received; this could be 100% (or whatever dBm corresponds to that) even if the spectrum is 99.9% occupied. The bitrate, as far as I know, remains high even if the medium is occupied when the laptop wants to transmit (in fact, high bitrates are important to have on busy networks: one might even want to kick low bitrate devices off of busy networks because they'll occupy the air for a longer period of time). – Luc Oct 30 '17 at 8:16
  • But that's the information you get easily, so first look at it. If you see APs on the same channel, then likely the interference comes from the outside. If you see lots of retries, that's because of interference. If your bitrate goes down even though you are transmitting/receiving and standing close to the AP, that's because of interference. All good indicators. – dirkt Oct 30 '17 at 8:26
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The sdrangelove package is available on debian stretch , you can install it through:

apt install sdrangelove

sdrangelove:

Osmocom Software Defined Radio

A Qt5 software-defined radio receiver application.

Update

The linssid is a debian packaged tool , to see the APs , interference and signal on the 2.4 and 5 Ghz band .

LinSSID can be used to measure the local performance or to search for an interference free channel to be set in a wireless router (access point or AP). The wireless established link won't be affected by these operations because LinSSID needn't set the monitor mode in network interface.

Some features:

  • Table of locally receivable attach points with many columns of different information and sortable and movable columns.
  • Adjustable speed, real-time update.
  • Graphs of signal strength by channel and over time.
  • AP bandwidth displayed.
  • Works on both 2.4 GHz and 5 GHz channels.

A screenshot from debian

  • I only borrowed a HackRF, I don't have it anymore. Is there software that can do something similar, only for the 2.4GHz band that I'm currently connected to, using standard WiFi hardware? – Luc Oct 29 '17 at 16:33

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