Here is the some steps which will help you to resolve the issue.
Set the data rates to 'Best range'.
Recommended to set the APs to non-overlapping channels.
Suggested to reduce the size of the cell by changing the power settings.
Here is the URL for the troubleshooting and administration for the AP. It may help you
http://www.cisco.com/en/US/docs/wireless/access_point/12.3_4_JA/configuration/guide/s34trb.html