Patent ID: 6469618
Filing Date: 2002-10-22
Classification: G06K,G07C

Abstract:
A method for identifying a plurality of electronic cards, with each electronic card assigned an identification number encoded on M bits distributed into P blocks of Q bits, the method comprising:reconstructing block-by-block the identification number of each electronic card present in an investigation zone in proximity to an interrogation unit, the block-by-block reconstruction being performed according to an iterative algorithm, and at each iteration the method further comprises transmitting from the interrogation unit an interrogation signal intended for certain electronic cards authorized to respond, all the electronic cards being authorized to respond at a first iteration, and only electronic cards authorized to respond at each subsequent iteration are as yet unidentified electronic cards having an identification number, at least one block of bits is identified during a prior iteration, transmitting a response message for the interrogation unit from each electronic card present in the investigation zone and authorized to respond, the response message comprising at least one service bit transmitted in a time window positioned in a sequence of 2Q successive identical windows for indicating a value of an as yet unidentified block of bits of a corresponding identification number, after all the blocks of bits of an identification number have been identified, transmitting from the interrogation unit a signal for placing the corresponding electronic card on standby so that it is no longer authorized to respond to the interrogation messages transmitted by the interrogation unit; and after identifying and placing on standby the last of the electronic cards that were in the investigation zone during the first iteration, transmitting from the interrogation unit an interrogation signal addressed to all the electronic cards except those already identified and placed on standby.