Need to restart to detect wireless again, (Xubuntu 11.10 AMD 32 bit)

Question

My wireless connection tends to break from time to time. When that happens, there are no wireless networks displayed in Network Manager. WICD can't detect any either. The only thing I can do is to reboot and after that my wireless works until the next connection drop out.

What I've tried so far:

Using the hardware switch doesn't work. If I try that even with a working connection, I can't unblock it without a restart.

lshw -C network:

  *-network
       description: Wireless interface
       product: AR242x / AR542x Wireless Network Adapter (PCI-Express)
       vendor: Atheros Communications Inc.
       physical id: 0
       bus info: pci@0000:05:00.0
       logical name: wlan0
       version: 01
       serial: 00:1c:26:cb:ed:7b
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress msix bus_master cap_list ethernet physical wireless
       configuration: broadcast=yes driver=ath5k driverversion=3.0.0-28-generic firmware=N/A ip=192.168.198.101 latency=0 link=yes multicast=yes wireless=IEEE 802.11bg
       resources: irq:19 memory:f0400000-f040ffff

lspci:

05:00.0 Ethernet controller: Atheros Communications Inc. AR242x / AR542x Wireless Network Adapter (PCI-Express) (rev 01)

Tried this advice to reload the network driver, but it didn't help:

$ sudo modprobe -r ath5k
$ sudo modprobe ath5k

Also, sudo restart network-manager or sudo /etc/init.d/networking restart didn't help.

dmesg | grep -i firmware lists some error even when my connection works:

[24.771652] [Firmware Bug]: ACPI(Z00P) defines _DOD but not _DOS

Apparently brightness control has some problems too, I googled "Acer Aspire 5520 has backlight broken". (that's my laptop)

Anyway, I'd appreciate if someone could help me to get the wireless to restart without a reboot.