I have 3 raspberry with Wireshark installed, and trying to sniff wifi probe request to get RSSI of a device and calculate device's position using triangulation. But most of the times only one or two Pi are getting probe request. Pi are arrange in a equilateral triangle of 10 mtrs. Is this normal behaviour or some implementation issue ?
Normal or not depends on the real configuration. If you get the device-under-test close to each sniffer device, does it register? If so, the configuration and capability is likely OK. However, you just may not have the receive capability on the wireless adapters to pick up devices that are far away. Far is a relative term - you should be able to experiment and see far you get and still be able to pick up the probes. interference could be an issue as well - depends on how clean your environment is. Different physical wifi adapters will have different capabilities. One of those really small USB ones might look great, but nothing is free: the antenna is terrible. Packet loss is the single biggest issue in the wifi environment, so it has to be managed.
Something like this with an external antenna might do best:
Hi Bob,
The device is well within range of sniffer RPis. For instance if the device is at the center of equilateral triangle, ideally each RPi should sniff the probe request. But this is not happening.
The device is well within range of sniffer RPis
No evidence is provided to suggest this is true, therefore, as of now, I classify this as an assumption. In the middle of the triangle, what is the RSSI/receive for each sniffer device? With sufficient receive signal strength proven, then you can go onto the next possible issue: packet loss. With no other detail, it is tough to determine root cause.
Do some of the sniffers never pick up the probes? Sometimes? Only in certain cases?
Are the three sniffer devices in an open room? Or is one on the other side of a steel wall?
Are one or more the sniffers more susceptible to interference, maybe coexistence/cochannel/adjacent channel, than another?
What is the channel utilization at each location?
Are the configurations set to a static channel for all sniffer adapters, or are you scanning?
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