05339073 is referenced by 120 patents and cites 4 patents.

Access control equipment includes an interrogation unit which emits an interrogation signal, and a plurality of transponders, each transponder having a stored identity code different from that of the other transponders. This identity code includes a plurality of fields each holding a selected information bit. The interrogation signal is controlled so as simultaneously to interrogate the fields of all transponders within range in a serial manner. A group reply signal is sent back to the interrogation unit from any transponder having, in the field being interrogated, a bit matching that required by the interrogation signal. The interrogation unit is arranged to determine, from the series of received reply signals, the identity of each and every valid transponder within range.

Title
Access control equipment and method for using the same
Application Number
229646
Publication Number
5339073
Application Date
March 25, 1991
Publication Date
August 16, 1994
Inventor
Brian J Stanier
Stockton on Tees
GB
Harold Dodd
Blyth
GB
Agent
David P Gordon
Assignee
Identec
GB
IPC
G06F 7/04
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