RFID systems with session-dependent replies
RFID systems may be configured to use session-dependent replies. When an RFID tag is involved in a certain inventorying session, the tag may respond to inventorying commands with a reply that is at least partly generated based on the session. For example, the tag may generate a reply with a string that has parity based on the session or includes an identifier for the session. The string may be a random number, a tag identifier or item identifier, or any other suitable data sent from the tag.
1. A method for determining whether a tag reply is intended for a first reader or a second reader, the method comprising:
the first reader transmitting a first inventorying command specifying a first inventorying session associated with a first encoding;
the second reader transmitting a second inventorying command specifying a second inventorying session associated with a second encoding;
receiving a first tag reply;
determining that at least a portion of the first reply is encoded with the first encoding and therefore is responsive to the first reader;
receiving a second tag reply; and
determining that at least a portion of the second reply is encoded with the second encoding and therefore is responsive to the second reader.
2. The method of claim 1 , further comprising:
upon determining that the first tag reply is responsive to the first reader, causing the first reader to acknowledge a first tag that sent the first tag reply; and
upon determining that the second tag reply is responsive to the second reader, causing the second reader to acknowledge a second tag that sent the second tag reply.
3. The method of claim 1 , further comprising:
upon determining that the first tag reply is responsive to the first reader, causing a first tag that sent the first tag reply to invert a flag corresponding to the first inventorying session; and
upon determining that the second tag reply is responsive to the second reader, causing a second tag that sent the second tag reply to invert a flag corresponding to the second inventorying session.
4. The method of claim 1 , wherein the portion of the first tag reply is a random or pseudorandom number.
5. The method of claim 1 , wherein the portion of the first tag reply is one of an algorithmically generated value, a cryptographic value, and a content of a tag memory.
6. The method of claim 1 , further comprising determining a parity of a reply portion based on the value of at least one of a parity bit, a checksum, a cyclic-redundancy-check, an error-detection code, and an error-correction code.
7. The method of claim 1 , further comprising transmitting, from at least one of the first and second readers, an encoding-switch command instructing tags to switch between sending replies with session-dependent encoding and sending replies without session-dependent encoding.
8. The method of claim 7 , further comprising transmitting the encoding-switch command upon determining at least one of:
at least one received signal strength indicator of a received tag reply is below a first threshold; and
a percentage or number of session-dependency-supporting tags in a tag population exceed or fall below a second threshold.
9. A method for determining whether a tag reply is intended for a first reader or a second reader, the method comprising:
the first reader transmitting a first inventorying command specifying a first inventorying session associated with a first encoding;
the second reader transmitting a second inventorying command specifying a second inventorying session associated with a second encoding;
the first reader:
receiving a first tag reply, and
determining that an encoding of at least a portion of the first tag reply corresponds to the first encoding and is therefore responsive to the first inventorying command; and
the second reader:
receiving the first tag reply, and
determining that the encoding of the at least a portion of the first tag reply does not correspond to the second encoding and is therefore not responsive to the second inventorying command.
10. The method of claim 9 , further comprising the first reader acknowledging a tag sending the first tag reply.
11. The method of claim 9 , further comprising, upon determining that the first tag reply is responsive to the first reader, causing a tag sending the first tag reply to invert a flag corresponding to the first inventorying session.
12. The method of claim 9 , wherein the portion of the first tag reply is one of a random or pseudorandom number, an algorithmically generated value, a cryptographic value, and a content of a tag memory.
13. The method of claim 9 , further comprising the first reader transmitting an encoding-switch command instructing tags to switch between sending replies with session-dependent encoding and sending replies without session-dependent encoding.
14. The method of claim 13 , further comprising the first reader transmitting the encoding-switch command upon determining at least one of:
at least one received signal strength indicator of a received tag reply is below a first threshold; and
a percentage or number of session-dependency-supporting tags in a tag population exceed or fall below a second threshold.
15. A Radio Frequency Identification (RFID) reader system comprising:
a first reader transmitting a first inventorying command specifying a first inventorying session associated with a first encoding;
a second reader transmitting a second inventorying command specifying a second inventorying session associated with a second encoding;
the first reader:
receiving a first tag reply, and
determining that at least a portion of the first tag reply is encoded with the first encoding and is therefore responsive to the first inventorying command; and
the second reader:
receiving a second tag reply, and
determining that at least a portion of the second tag reply is encoded with the second encoding and is therefore responsive to the second inventorying command.
16. The reader system of claim 15 , wherein:
the first reader is further configured to acknowledge a tag that sent the first tag reply; and
the second reader is further configured to acknowledge a tag that sent the second tag reply.
17. The reader system of claim 15 , wherein the first reader is further configured to, upon determining that the first tag reply is responsive to the first inventorying command, cause a first tag that sent the first tag reply to invert a flag corresponding to the first inventorying session.
18. The reader system of claim 15 , wherein the portion of the first tag reply is one of a random or pseudorandom number, an algorithmically generated value, a cryptographic value, and a content of a tag memory.
19. The reader system of claim 15 , wherein the first reader is further configured to transmit an encoding-switch command instructing tags to switch between sending session-dependent replies and sending non-session-dependent replies.
20. The reader system of claim 19 , wherein the first reader transmits the encoding-switch command upon determining at least one of:
at least one received signal strength indicator of a received tag reply is below a first threshold; and
a percentage or number of session-dependency-supporting tags in a tag population exceed or fall below a second threshold.