Patent ID: 6150934
Filing Date: 2000-11-21
Classification: G01S,G06K

Abstract:
A contactless electronic communication system comprising a base station and a plurality of transponders, the base station comprising transmission means for emitting an electromagnetic field defining a communication volume in which a plurality of transponders are situated, each transponder comprising means for receiving said electromagnetic field and means for generating, in response to said electromagnetic field, an identification message readable by the base station, said base station further comprising means for receiving said identification message emanating from any transponder among said plurality of transponders, and processing means for checking the validity of said identification message, wherein the base station comprises means for generating during or following said identification message, communication initiation signals destined to said plurality of transponders, said base station providing a communication initiation signal to each transponder from which it receives an identification message, each transponder including means for opening a communication window in response to said communication initiation signal only when said communication initiation signal is received during a predetermined period relative to the generation of said identification message.