If you had the same issue in Ubuntu8.10, you could found the solution included in the “8.10 Release Notes“.
Atheros ath5k wireless driver not enabled by default
The version of the ath5k driver for Atheros wireless devices included in Linux 2.6.27 interferes with the use of the madwifi driver for some wireless devices and as a result has been disabled by default. Many Atheros chipsets will work correctly with the madwifi driver, but some newer chipsets may not, and the madwifi driver may not work with WPA authentication. If you have an Atheros device that does not work with madwifi, you will want to install the linux-backports-modules-intrepid-generic package, which includes an updated version of the ath5k driver. While not installed by default, this linux-backports-modules-intrepid-generic package is included on the Ubuntu 8.10 CD and DVD images for ease of installation.
Wireless doesn’t work after suspend with ath_pci driver
Wireless devices that use the ath_pci kernel driver, such as the Atheros AR5212 wireless card, will be unable to connect to the network after using suspend and resume. To work around this issue, users can create a file /etc/pm/config.d/madwifi containing the single line:
This will cause the module to be unloaded before suspend and reloaded on resume.