A radio signal based object location system is provided wherein location devices
are provided on articles for use in locating the articles, and wherein a database
is maintained relating characteristics of radio signal transmissions between the
location devices and fixed devices to locations within an area. A method is provided
for maintaining the database to reflect propagation conditions. Location devices
are provided at fixed positions within the area. Data representing radio signal
transmission characteristics between the fixed position location devices and fixed
devices is recorded. Transmissions between the fixed position location devices
and the fixed devices is monitored to determine changes in the characteristics
of radio signal transmissions from the recorded data.
