IMPROVED REAL TIME LOCATION SYSTEM

摘要

Portable devices are provided with location data determined at a server computer by comparing radio signal characteristics to a database of characteristics. In one arrangement the server additionally downloads a portion of the database of radio signal characteristics to the portable device and the portable device uses the downloaded portion of the data base to determine if its location has changed. The portable device may either update the location data that it has previously downloaded from the server or alternately may signal the server to provide either updated location data or an increased rate of location data update.