Cryptography – Particular algorithmic function encoding
Patent
1992-10-30
1995-09-12
Swann, Tod R.
Cryptography
Particular algorithmic function encoding
340572, 34082554, H04K 100
Patent
active
054504929
DESCRIPTION:
BRIEF SUMMARY
The present invention relates in general to communication systems, and more particularly to an electronic identification system comprising one or more portable transponders for transmitting an information signal in response to entering an electromagnetic excitation field.
Electronic identification systems are well known in the art for effecting automatic identification of objects, animals and people, and are used in situations where elementary line of sight systems such as bar codes cannot be used. Such prior art identification systems typically comprise a plurality of electronic transponders (commonly referred to as electronic tags or simply tags) which are attached to the particular objects to be identified, and at least one interrogator (that is a controlled transmitter and receiver, sometimes referred to as a reader) for exciting the transponders into transmitting response signals which are then detected by the interrogator, decoded and converted into information for display to a human operator, or transmitted as data to a computer.
One such identification system is described in United Kingdom patent application GB 2,112,607 (Senelco Limited) which discloses a system comprising a transponder having a receiver for receiving a transmitted signal S1, a generator for generating a further carrier signal S2, logic means for modulating the signal S2 according to a coded mathematical relationship with the received signal S1, and a transmitter for transmitting the signal S2. Specifically, the carrier frequency of the signal S2 is disclosed as being a multiple or a fraction of the frequency S1.
United Kingdom patent application GB 2,157,132 (Senelco Limited) also discloses an identification system of the form discussed above in connection with the '607 specification, but in addition incorporates circuitry for receiving a reply signal (e.g. information signal) from the transponder, checking the reply signal for possible contention between reply signals from different transponders which arrive at the same time, and initiating retransmission of the reply signals in the event such a contention situation is detected. Specifically, the tag receives a signal from the interrogator which it compares with stored information in order to determine whether the message transmitted by the tag has been received by the interrogator for confirming that the tag has been identified by the interrogator and can therefore fall silent. Contention in this system is resolved by sophisticated duplex communications between reader and tag in order to achieve simultaneous identification of numerous tags.
As with the '607 specification, the circuitry in the '132 disclosure incorporates means for deriving a received carrier signal at the transponder, and using the derived carrier signal to provide a transmission signal which is related to and therefore dependent on the sustained presence of the received signal from the interrogator.
Additional prior art systems are well known for teaching transmission of the transponder information signals which are dependent on the received interrogation signal, as follows:
European patent application 0,310,127 (Texas Instruments) teaches a transponder arrangement which transmits an information signal at a predetermined carrier frequency related to the frequency of a received RF interrogation pulse.
United Kingdom patent application GB 2,202,981 (Satellite Video Systems Ltd.) discloses a system incorporating a transponder designed to modify a received interrogation signal in a variable manner and then retransmit the modified signal for reception by the interrogation unit.
United Kingdom patent application GB 2,163,324 (Electromatic) discloses a system in which energy is extracted from a detected interrogation signal, compared to a reference level and then supplied to the remainder of the transponder circuit for enabling generation and transmission of the information signal.
European patent application 0,253,368 (Amtech Corporation) discloses an identification system comprising a reader and a transponder, the
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Hall Christopher S.
Hook Christopher D.
Disys Corporation
Swann Tod R.
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