mkirk
Posts: 47
Joined: Tue Mar 06, 2018 4:21 pm

Sustained WiFi speed on Pi 3B?

Wed May 08, 2019 6:29 pm

We are trying to benchmark Pi 3B WiFi speeds with iperf, iperf3 and nuttcp. Transferring TCP mode with unlimited rate.
Running Raspbian Stretch release. 2.4 GHz, channel 6 on-board WiFi in ad-hoc mode (no Access point or router) - on-board chip antenna
One Pi 3B is server the other is a client. Test is in a RF screen room (Faraday cage) to block external interference. Units are < 2 meters apart.

At startup of test, we achieve around 40 Mbps which matches a benchmark I found on this site (38.8 Mbps)

This data rate can be maintained for 30 minutes to 8 hours, but then the data rate abruptly drops to 6 Mbps and stays there.
If the iperf test on client side is stopped and restarted (server side stays running) -- sometimes speed returns to 40 Mbps but in some cases is stuck at 6 Mbps rate.

We also notice that the client side WiFi module (CYW43438) is hot to touch. Could it be overheating and reducing data rate?
I would think once cooled down, the fallback algorthim would attempt higher data speeds.

Any ideas would be helpful. Perhaps there is a configuration parameter in WiFi driver that we can modify?

Regards,
Mike K.

mkirk
Posts: 47
Joined: Tue Mar 06, 2018 4:21 pm

Re: Sustained WiFi speed on Pi 3B?

Wed May 08, 2019 6:39 pm

Also should note that WiFi CYW43438 chip is only capable of +19 dBm (80 mW ) of Tx power, but iwconfig shows it is +31dBm (> 1 watt).

So iwconfig not an accurate indication of Tx power.

wlan0 IEEE 802.11 ESSID:"pi45ap"
Mode:AdHoc Frequency:2.437 GHz Access Point: B8:27:EB:0C:56:F6
Tx-Power=31 dBm
Retry short limit:7 RTS thr:off Fragment thr:off
Power Management:off

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