Communications: electrical – Selective – Interrogation response
Reexamination Certificate
2000-08-03
2004-01-06
Zimmerman, Brian (Department: 2635)
Communications: electrical
Selective
Interrogation response
C342S051000, C375S213000, C340S870030, C380S034000
Reexamination Certificate
active
06674359
ABSTRACT:
The invention relates to a method of identifying several transponders located in the interrogation zone of a reader.
More and more applications materialize in which transponders are used for identifying persons, animals or objects. Stored in these transponders is an identification code in the form of an address containing for example 32 or 64 bits which is the ID of the transponder carrier. In addition, data may be stored in the transponder containing specific information as to the carrier of the transponder. A transponder suitable for such purposes is described for example in EP-B-0 301 127, the specific feature of which is that it has no supply voltage source of its own, it instead generating its energy needed for sending the information and data contained therein from an RF interrogation pulse which it receives from an interrogator. The interrogator sends the RF interrogation pulse every time it wishes to retrieve information and data stored in a transponder existing in the interrogation zone. On receiving the RF interrogation pulse the transponder responds by sending the information and data stored therein.
In more sophisticated transponder systems the interrogator sends an RF interrogation pulse not only so that a transponder in the interrogation zone responds but it is desired to address the transponders present in the interrogation zone individually, i.e. to also send their address from the interrogator so that only the transponder responds whose address agrees with the address sent by the interrogator. This makes it necessary for the interrogator to know, however, which transponders exist in the interrogation zone. Since the range of possible addresses and thus the number of transponders belonging in all to the transponder system is very high, it possibly amounting to several millions, for example, it is of course totally out of the question that the interrogator sends all the addresses one after the other and then waits to see whether a transponder responds. The time needed for this would be prohibitively long, so that such a system would be totally useless for many applications. When it is assumed, for example, that the transponders are located on objects moving past a reader on a flow line conveyor, then the reader needs to “see” relatively quickly which transponder is in its interrogation zone at the time so that it can address these transponders explicitly and retrieve the information and data stored therein. It is thus very important to identify all transponders existing in the interrogation zone of the reader as quickly as possible.
One known method with the aid of which this identifying can be implemented quickly and reliably is described in EP-A2-0 831 618. Referring now to
FIG. 1
the following is a brief discussion of how this known identification method works.
In every interrogation step the interrogator sends an RF interrogation signal which is made use of by the transponders existing in the interrogation zone—among other things—to generate the supply voltage needed for their operation. The first RF interrogation signal sent also includes a, partial address containing 4 bits in the example described, this partial address having the value zero. These 4 bits may be, for example,,the four least significant bits of the full transponder address totalling 32 or also 64 bits. The transponders are configured so that they send their response signal when the partial address received by them corresponds to the partial address in the full address stored therein. Thus, when, as in the assumed case, the partial address sent by the interrogator has the value zero, then all transponders in the interrogation zone whose least-significant 4 bits likewise have the value zero would respond. In the example as shown in
FIG. 1
no such transponder exists in the interrogation zone, this resulting in the interrogator incrementing the partial address by one step and sending an RF interrogation signal accompanied by the partial address having the value 1. For this case too, it is assumed in the example that no transponder exists in the interrogation zone in which the last 4 bits of its address have the value 1.
In the next step in interrogation the partial address sent by the interrogator is incremented to the value 2. In the interrogation zone as shown in
FIG. 1
as the example two transponders exist whose 4 least-significant bit have the value 2. This results in these two transponders sending back at the end of the interrogation signal their response signal to the interrogator, this response signal containing the full address of the two transponders involved. However, the interrogator is unable to distinguish these two addresses, it instead merely being able to “see” that more than one transponder was present with the corresponding address since it received an unreadable response signal hash. The interrogator memorizes the fact that the partial address 2 produced a hit, it then continuing to increment and send the partial address in its value consecutively. After sending the partial address with the value 7 a transponder responds, the reader in this case being able to read the complete transponder address so that in this sequence cycle of the first partial address the address of a transponder has been identified. This is evident from
FIG. 1
, whereby the value 1837 is cited, for example, as the full address, i.e. the last number 7 agreeing with that of the partial address sent by the interrogator, it being this partial address that prompted the return of the full transponder address.
As mentioned, the reader has memorized that several transponders responded to sending the partial address with the value 2. To identify the full address of these two transponders the value of the partial address having resulted in the hit is used as a mask to which a partial address of 4 further bits is added. The mask has the effect that the 4 bits of the transponder address previously compared to the partial address are “masked”, i.e. concealed so that it is not these but the next 4 bits of the transponder address that are compared to the new partial address. The identification procedure is then continued, the mask having the value 2 in each case, whilst the added partial address runs through the sequence of values 0 to 15. In the example as shown in
FIG. 1
a new hit occurs with the partial address having the value 3, whereas at value 4 only one transponder responds so that its address can be identified by the reader. Since the mask has the value 2 and the partial address at which the transponder responded had the value 4 the last two values of the full transponder addresses are the values 2 and 4 as evident from
FIG. 1. A
hit likewise occurs at the partial address value 7, as evident from
FIG. 1
, so that the interrogator memorizes that hits having occurred at partial address value 3 and partial address value 7. These hits need to form the basis of the further interrogation procedures in identifying the transponders involved.
The interrogator now knows that at least two transponders exist in which the mask value 2 and the partial address value 3 are involved. At least two further transponders exist in the interrogation zone which have the mask value 2 and the partial address value 7. This means, in one case, that the transponders have the value 32 at the end of their full addresses and, in the other case, the value 72. The combination of the mask used before and the partial address causing the hit forms for the new interrogation cycle a new mask totalling eight bits, whereby the mask value, in one case, amounts to 32 and, in the other case, to 72. In the subsequent consecutive interrogation procedures the new partial address is incremented in its value from 0 to 15. After sending an RF interrogation signal having the corresponding partial address it is again detected whether one or more transponders respond in the interrogation zone. As evident from
FIG. 1
a transponder responds at the partial address value 8 so that this transponder can be identified from the address it sends back. Part
Aslanidis Konstantin
Atherton Simon
Baumann Adolf
Flaxl Thomas
Hagl Andreas
Brady III Wade James
Shimizu M
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Zimmerman Brian
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