Ticket #1972 (closed defect: wontfix)

Opened 8 years ago

Last modified 8 years ago

Wifi interferes with Bluetooth

Reported by: Mercury Owned by: openmoko-devel
Priority: normal Milestone:
Component: unknown Version:
Severity: normal Keywords: bluetooth, wifi, interference, a2dp
Cc: Blocked By:
Blocking: Estimated Completion (week):
HasPatchForReview: no PatchReviewResult:
Reproducible:

Description

Issue

Bluetooth and wifi don't seem to coexist. There are lag issues with bluetooth when using wifi.

Reproducing

1) Listen to something with A2DP headphones (I imagine any other high bandwidth bluetooth activity will experience the same problem, but this is what I was testing with)
2) Start up wifi, and run opkg update (Once again, I'm sure any other high bandwidth wifi activity will experience the same problem)
3) Notice that the sound gets choppy, and stops when you're done downloading.

Software

  • Latest update from unstable feed
  • opkg list_installed attached

Attachments

list_installed (43.1 KB) - added by Mercury 8 years ago.

Change History

Changed 8 years ago by Mercury

comment:1 Changed 8 years ago by zecke

If you look at the schematics you see that wifi and bt are already cooperative (at least there is a wire inbetween the two modules).

What do you expect? You have a finite resource and both bluetooth and wlan try to fully claim it... Unless you drastically limit the network bandwidth (which you can do on linux) but then you have other wlan and bt devices in your reach making further claims...

comment:2 Changed 8 years ago by Mercury

Ah I see. So there's no flaw here? It's just a limitation of the hardware?

comment:3 Changed 8 years ago by werner

If the throughput of WLAN is reduced by the same ratio as the throughput that
BT gets, and vice versa, then things should be okay. E.g., if you measure the
throughput of each alone as WLAN_solo and BT_solo, and again with both active
as WLAN_shared and BT_shared, you should roughly obtain
~100% <= WLAN_shared/WLAN_solo+BT_shared/BT_solo <= ~200%
for any coexistence solution.

What coexistence in its most primitive form (and I think that's what we have)
does is to make sure that they don't send at the same time. So they don't
create situations where both try to occupy the same frequency, resulting in
neither being heard, and not only this transmission being lost, but also more
time lost to recovery.

Here's a good introduction to the issue:
http://focus.ti.com/pdfs/vf/bband/coexistence.pdf

If you do the calculation from above on the data in that paper for a distance
of 50ft, you obtain roughly 25% for WLAN and 10% for BT, resulting in 35%
bandwidth utilization for uncoordinated sharing. (Under, I presume, otherwise
ideal conditions.)

  • Werner

comment:4 Changed 8 years ago by john_lee

  • Status changed from new to closed
  • HasPatchForReview unset
  • Resolution set to wontfix
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