Raspberry Pi 4 + USB Tethering slow speeds

Hello everyone,

I'm having an issue with my internet speeds and I don't know who is the culprit.

I have 5g in my area, so I have enabled usb tethering from my moto g62 5g phone to raspberry pi 4.
And I am using ethernet cable to get internet on my pc.
I have installed OpenWrt on my raspberry pi 4 few days ago.

The issue(s) I'm having is -

I am having variable speeds -

With this setup I usually get 240-270 Mbps, but sometimes randomly speed drops to around ~100 Mbps.
And miraculously after rebooting the raspberry pi the speed is back to around 240-270 Mbps.

I have thought If temperature of the pi could be a factor and here are the results -

232.40 Mbps @ 53.0'C
203.54 Mbps @ 58.4'C
101.63 Mbps @ 52.5'C
98.98 Mbps @ 52.5'C
(These speedtest and temperatures were taken at different times)

and, After restart -> 239.53 Mbps
so, Temperature doesn't seem to be a factor.

So my suspects are -

  1. Something wrong with raspberry pi 4?
  2. Something wrong with my android phone?
  3. Something wrong with OpenWrt?

On my part I can assure you It's not the 5g network, as I have a rooted phone and I have locked n78 band. And I have never got anywhere near 100 Mbps with n78.

btw, The max speed I have got with this setup is ~270 Mbps only, despite I get ~330 Mbps when I do usb tethering directly to my pc.

Also, I am using Advanced Charging Controller module, to limit the power my phone draws from raspberry pi 4. Currently the phone draws only 1 watt of power from the pi.

In the above references, all speeds I mention is download speed, upload speed is bad and isn't a factor for me here.

So, my question is -

How do I find out what is causing this error and how to fix it (then)?