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Possible Duplicate:
How to Install Broadcom / STA Wireless card (BCM43XX)

Upgraded Ubuntu to 11.04, now wireless card does not work when I unplug the laptop

lspci -vvnn | grep 14e4

10:00.0 Ethernet controller [0200]: Broadcom Corporation NetLink BCM5787M Gigabit Ethernet PCI Express [14e4:1693] (rev 02)
30:00.0 Network controller [0280]: Broadcom Corporation BCM4321 802.11a/b/g/n [14e4:4328] (rev 03)
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marked as duplicate by Luis Alvarado, hhlp, gertvdijk, Uri Herrera, Ringtail Jan 6 '13 at 0:58

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

are you connecting to your router using wireless "n" mode? - check the settings in your router. Does it work better when your router is set to either wireless "b" mode or wireless "g" mode? – fossfreedom May 21 '11 at 22:55
Also add to you question the any output from "dmesg" when you disconnect the power. – fossfreedom May 21 '11 at 22:56

You could try finding out what driver your wireless card uses by running

lsmod | egrep "b43|wl|brcm80211"

and then running

sudo rmmod yourdriver
sudo modprobe yourdriver

Since your wireless card is the BCM4321, you're likely running the wl driver (a.k.a. Broadcom STA), so you would run

sudo rmmod wl
sudo modprobe wl
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Thanks, executed the above commands, and now wireless works on battery with my laptop – jhurley May 22 '11 at 12:34
You're welcome :D I'm glad I could help. If you want, you can create a shortcut on the desktop to do that for you: Ubuntu/GNOME/Unity: shortcut to gksudo -- sh -c 'rmmod wl; sleep 2; modprobe wl' OR Kubuntu/KDE: shortcut to kdesudo -- sh -c 'rmmod wl; sleep 2; modprobe wl' – Xiao-Long Chen May 22 '11 at 12:50

pm-powersave turns wireless OFF when switching to battery. See my answer Why is wireless down/strange after switching to battery?

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