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Author Topic: Anyone know anything about Bluetooth ? - coexistence question  (Read 212 times)

Weaver

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I think I have asked about this before, so please forgive me, could do with a recap.

Iíve been reading a little about Bluetooth vs 802.11 WLAN coexistence. I read that there are various technologies that help the two to coexist happily, including firstly Adaptive Frequency Hopping, secondly extra signals from Bluetooth chips, that indicate when a radio in the current system is active transmitting (or receiving ? or active?) 802.11 data so as to allow Bluetooth to wait a mo and hold back avoiding garbling the WLAN signal, and probably other mechanisms too, I forget.

My questions then:

1. Given the availability of AFH, assuming everyone now has this, is it a very good thing to have a free 2.4 GHz 20MHz >:( channel, unused by any SSID? Is it worthwhile, or can things somehow work out well even if all 2.4 GHz channels are in use by WLANs?

2. If you are using channel 11, can Bluetooth use high channels > 13, channels that some WLAN users cannot exploit? If you use channel 11, with that centred on channel 11 (?) so its exploited band goes up to channel, what, 13 ? Is there any space left up there for Bluetooth to hop into, or is it all used ?

3. Same question for channel 13: If you use channel 13, if you can - not sure about the rules for this - is there any space above this band at all?

4. What is the story regarding the possibility of using channel 13 ? Are there some country-specific rules about it ?

5. Anyone have experience from using all of channels 1 + 6 + 11 simultaneously ? (Or even 1+5+9+13 ?)
« Last Edit: May 04, 2021, 01:09:31 AM by Weaver »
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Alex Atkin UK

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Re: Anyone know anything about Bluetooth ? - coexistence question
« Reply #1 on: May 04, 2021, 05:22:15 PM »

All I can say is my performance on 2.4Ghz has dropped over the years as more people got WiFi but I have no problems using Bluetooth, at least over a short range (but its not really designed to go through walls anyway).

Same with my Logitech wireless mouse in dongle mode (it supports Bluetooth as well), works fine even though I think it still uses 2.4Ghz.  I think its most down to proximity of those other networks, they might cause issues when you're trying to hammer WiFi but for low bandwidth things like Bluetooth it doesn't seem to be an issue.
« Last Edit: May 04, 2021, 05:24:57 PM by Alex Atkin UK »
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Weaver

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Re: Anyone know anything about Bluetooth ? - coexistence question
« Reply #2 on: May 05, 2021, 05:33:17 AM »

Alex, do you use all of the 2.4GHz channels?

I havenít yet read anything detailed about Bluetoothís use of RF and the adaptive hopping feature other than that it detects badness (the presence of energy?) on certain channels and marks them as bad, so it stays away in the hopping presumably. But what if all channels have foreign energy present?
« Last Edit: May 05, 2021, 05:38:36 AM by Weaver »
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digbey

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Re: Anyone know anything about Bluetooth ? - coexistence question
« Reply #3 on: May 05, 2021, 11:53:34 AM »

Here's an interesting article on Bluetooth-WLAN Coexistence

https://uk.mathworks.com/help/comm/ug/bluetooth_wlan_coexistence.html

There's also a host of other users of the 2.4 GHz band.

https://en.wikipedia.org/wiki/2.4_GHz_radio_use
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Alex Atkin UK

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Re: Anyone know anything about Bluetooth ? - coexistence question
« Reply #4 on: May 05, 2021, 09:02:55 PM »

Alex, do you use all of the 2.4GHz channels?

Yes and no, there are SSIDs covering all three channels in my area but its unlikely they are all busy at the same time.  Also the weather makes a huge difference to what reaches me from outside but I'd imagine weaker signals just raise the noise floor a little making very little difference in the real world for Bluetooth as its low bandwidth.

Here's an interesting article on Bluetooth-WLAN Coexistence

https://uk.mathworks.com/help/comm/ug/bluetooth_wlan_coexistence.html

From that it looks to me like Bluetooth does indeed use the bits between WiFi networks that were freed from reducing from 22Mhz channel widths to 20Mhz when 802.11g came out.  Of course that doesn't give it complete freedom as I believe part of the reason for doing that is no signal amplifier is perfect so it can spill interference outside its operating channel.
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Weaver

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Re: Anyone know anything about Bluetooth ? - coexistence question
« Reply #5 on: May 07, 2021, 06:26:50 PM »

Sorry Alex, didnít understand your last sentence or two.
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Alex Atkin UK

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Re: Anyone know anything about Bluetooth ? - coexistence question
« Reply #6 on: May 07, 2021, 08:15:51 PM »

WiFi channels were originally 22Mhz wide, this reduced to 20Mhz, leaving a bigger gap between channels.  As Bluetooth uses much smaller channel widths I assume it can benefit from those gaps if only 1, 6, 11 is being used.
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anything