Issue
Bluetooth interferes with wifi connection when a SIM card is connected.
Measurements
Wired into router ~90 Mbit/s up | ~90 Mbit/s down | ping <1 ms
speed over wifi ~60 Mbit/s up | ~50 Mbit/s down | ping ~15 ms
speed over wifi with bluetooth running ~3 Mbit/s up | ~7 Mbit/s down | ping ~50 ms
This slowdown does not occur unless a SIM-card is connected.
What to do?
In these quarantine times I have spent more time at home making me realize how awfully slow my internet speed was over wifi. Has anyone else experienced something similar? I assume it’s hardware related, but lacking tools I haven’t disassembled and cleaned the module. What do?
Hi Hannes,
You may have a read here.
or
here.
This was a known issue with the FP2 model and some routers. As Wifi 2,4GHz and Bluetooth are using the same frequency band you can try and switch your wifi band to 5GHz.
Furthermore you could change your routers 2,4GHz protocoll.
There are different IEEE 802.11 wifi protocolls.
Try out a different, more recent protocol without xxxb or xxxg.
Hi Patrick,
Thank you for your answer. Seems I would need to buy a new router working on the 5GHz band and/or use more modern wifi protocols.
Is my understanding correct in that this is an effect of bad antennae design in the FP? I say this as I haven’t seen the same issue in any of my previous phones.
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Hi Hannes,
I’m experiencing same at home. I think the router isn’t faulty but the limitation comes according me from the SOC modem.
Maybe I’m wrong, but I’m convinced your router isn’t fully responsible of this inconvenience (Personally, I’m fully working on 5Ghz)…
Switching to the less crowded 5GHz band was my solution as my router was outdated anyway.
Yes, a router with more recent protocols on the 2,4GHz band should do.
Type b & g are quite old already (>10 years).
Switching the WiFi channel may or may not help here.
I don’t think it is a problem of a bad antenna design. Usually manufacturers select specifically matched components to design their SoC. It’s not like having to design everything from scratch.
@Leo_TheCrafter is quite skilled in doing so and also managed to design a complete SoC as an option to upgrade the FP2 if the manufacturer was interested in collaborating. He could explain more in-depth how such an antenna design is made.
After reading through this it is a drawback of the protocol being used causing collisions/overlap due to interference.
More specific can be read here.
Maybe they did not support 802.11b anymore due to it’s age.
Hi Patrick, thanks for your input, your explanations are highly valuable but the device concerned is a FP3, so yes this interferes came according me from the modem design instead of the router.
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The base problem between BT and WiFi remains.
Here is a bit more to read about other users with the FP3 having related issues.
But there are other handsets of different brands with the same behavior on the equal setup. So it does not look like a specific FP3 design problem.
Assumption of @JeroenH to follow may help. 
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Thanks Patrick to have precised a bit more your thoughts
Looking forward to verify my router then.
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I want to chip in here as well. I did some troubleshooting over the last few days and it seems that Bluetooth interferes significantly with 2GHz packet loss on my phone. Have a look here at problem with connectivity.
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