Active rfid tag and product surveillance method

An active radio-frequency identification, RFID, tag, comprising:

• a power source;
• a radio transceiver;
• and
• a processing unit, coupled with the power source and the radio transceiver, and configured to cause the following:
• transmitting continuously a signal comprising an own identifier according to a predetermined schedule;
• receiving continuously a plurality of signals comprising a plurality of foreign identifiers transmitted by a plurality of other active RFID tags according to the predetermined schedule;
• measuring a received signal strength indication, RSSI, of each received signal;
• storing each foreign identifier of a signal whose RSSI exceeds a predetermined strength threshold;
• detecting that a signal with a stored foreign identifier is no more received according to the predetermined schedule and marking said stored foreign identifier.

A product surveillance method using active radio-frequency identification, RFID, tags, comprising:

• transmitting, by an active RFID tag, continuously a signal comprising an own identifier according to a predetermined schedule;
• receiving, by the active RFID tag, continuously a plurality of signals comprising a plurality of foreign identifiers transmitted by a plurality of other active RFID tags according to the predetermined schedule;
• measuring, by the active RFID tag, a received signal strength indication, RSSI, of each received signal;
• storing, by the active RFID tag, each foreign identifier of a signal whose RSSI exceeds a predetermined strength threshold;
• detecting, by the active RFID tag, that a signal with a stored foreign identifier is no more received according to the predetermined schedule and marking, by the active RFID tag, said stored foreign identifier.