RFID Terms ...

From Air Force Materiel Command, Definitions of RFID Terms ...

... "RFID Multiple Tag Read Capability. In some instances it is necessary to identify all tags in a given area. This can always be accomplished if one tag at a time is placed in the RF field of the interrogator. However, if the tags are randomly spread out over an area, it is desirable for the interrogator to transmit a command over the entire area (this is known as an omni-directional signal transmission) requesting the identity of all tags. If all tags were to simultaneously respond to that command then the various RF signals would interfere with each other and the interrogator would receive only RF noise. Many systems have been developed which allow the tags to be individually heard by the interrogator thus avoiding the RF chaos of many interfering signals. This multiple tag reading capability is usually achieved by randomizing the response of each tag into different time slots or having each tag respond at a slightly different non-interfering frequency. " ...