Association request messages received by one or more access points of a wireless local area network are used to infer the location of a mobile unit requesting association. Association may be refused for security purposed if it is determined that the mobile unit is not within an area services by the wireless...http://www.google.com.tw/patents/US7542770?utm_source=gb-gplus-share專利 US7542770 - Method for mobile unit location estimate in a wireless LAN
