A wireless local area network (WLAN) radio-frequency identification (RFID) tag
system provides location finding in a wireless local area network (WLAN), using
a WLAN channel. Interference with the WLAN is prevented by either using a sniffer
circuit to determine that no network transmission is in progress, using a modified
coding sequence or preamble to cause standard WLAN receivers to ignore the RFID
tag transmissions, or transmitting a message using a standard WLAN signal addressed
to an address not corresponding to a unit within the WLAN. Location units (LUs)
and a master unit (MU) within the WLAN receive the RFID tag transmissions and can
determine the location of a tag by triangulation based on differences between the
signals received at the location units from the tag. The master unit receives the
signal information from the location units and computes the location of the tag.
Time-difference-of-Arrival (TDOA), received signal strength indication (RSSI) or
other triangulation techniques may be used.