Systems and methods for optimizing communications between an RFID reader and a tag population using non-sequential masking

• US 20070024424A1
• Filed: 07/29/2005
• Published: 02/01/2007
• Est. Priority Date: 07/29/2005
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Symbol Technologies, Inc. (Zebra Technologies Corporation)
• Inventors: Powell, Kevin
• Granted Patent: US 7,425,888 B2
• Time in Patent Office: Days
• US Class Current: 340/10.100
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
• CPC Class Codes: G06K 7/10019 resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08

Abstract

System and methods for optimizing communications between an RFID reader and a population of tags are described. To minimize the amount of data exchanges, the reader and tags use non-sequential bit string or byte masking. In non-sequential bit string masking, the reader transmits an interrogation mask having a plurality of non-sequential sub-masks to the tags. During subsequent collection of the identification sequence, the reader and tags only exchange the non-masked bit positions. The interrogation mask can be determined using superposition processing, historical tendencies, or known identification and/or subset of identification ranges. During superposition processing, the reader determines whether a bit position contains a single value or multiple values for tags in the tag population. If the bit position contains a single value, the bit position is designated as masked. If the bit position contains multiple values, the bit position is designated as non-masked.

Claims

1. A method in a radio frequency identification (RFID) reader for interrogating an RFID tag population having a plurality of tags, comprising the steps of:

(a) transmitting an interrogation mask corresponding to a tag identification sequence to the RFID tag population, wherein the interrogation mask has a plurality of sub-masks that are non-sequentially positioned in the mask and wherein each sub-mask covers at least one bit position; and

(b) performing an abbreviated collection of unmasked bits of the identification sequence from one or more tags in the tag population.

2. The method of claim 1, further comprising:

determining the interrogation mask using superposition processing.

3. The method of claim 2, further comprising:

determining a value for a bit in each masked bit position.

4. The method of claim 1, wherein step (b) includes performing a binary tree traversal to collect the unmasked bits in the identification sequence.

5. The method of claim 3, wherein step (b) further comprises:

(i) transmitting one or more symbols that cause one or more tags in the tag population to engage in binary tree traversal and to transmit a first unmasked bit;

(ii) receiving one or more symbols from the one or more tags;

(iii) determining whether a current bit position in a tag identification sequence being negotiated is a masked bit position;

(iv) if the current bit position is a masked bit position, saving the value for the bit determined during superposition processing;

(v) if the current bit position is not a masked bit position, determining a value for the bit using binary tree traversal processing, saving the value of the bit, and transmitting the value to the tag population; and

(vi) repeating steps (i) through (iv) for each bit position in the identification sequence.

6. The method of claim 3, wherein step (b) further comprises:

(i) transmitting one or more symbols that cause one or more tags in the tag population to engage in binary tree traversal and to transmit its first unmasked bit;

(ii) receiving one or more symbols from the one or more tags;

(iii) determining whether a current bit position in a tag identification sequence being negotiated is a masked bit position;

(iv) if the current bit position is a masked bit position, designating the next bit position as the current bit position;

(v) if the current bit position is not a masked bit position, determining a value for the bit using binary tree traversal processing, saving the value of the bit, transmitting the value to the tag population, and designating the next bit position as the current bit position;

(vi) repeating steps (i) through (iv) for each bit position in the identification sequence; and

(vii) generating a complete identification sequence based on the determined bit values, the interrogation mask, and the values of the bit positions determined during superposition processing.

7. The method of claim 2, wherein step (a)(i) comprises:

(A) transmitting symbols that direct one or more tags in the tag population to engage in superposition processing and to send the value of a bit in a first position of the identification sequence;

(B) receiving one or more symbols from tags associated with a current bit position in the identification sequence;

(C) if a plurality of symbols is received in step (B), designating the current bit position as unmasked;

(D) if a single symbol is received in step (B), designating the current bit position as masked;

(E) transmitting one or more symbols that direct each tag in the tag population to send the value of the bit in a next position of the identification sequence; and

(F) repeating steps (B)-(E) for each bit position in the identification sequence.

8. The method of claim 1, wherein step (a) includes:

(i) transmitting symbols that direct one or more tags in the tag population to engage in superposition processing and to send the value of a bit in a first position of the identification sequence;

(ii) receiving one or more symbols associated with a current bit position in the identification sequence;

(iii) if a plurality of symbols is received in step (ii), designating the current bit position as unmasked and transmitting a value to cause the one or more tags in the tag population to not mask the current bit position;

(iv) if a single symbol is received in step (ii), designating the current bit position as masked and transmitting a value to cause the one or more tags in the tag population to mask the current bit position; and

(v) repeating steps (ii)-(iv) for each bit position in the identification sequence.

9. The method of claim 1, wherein step (a) further includes:

(i) transmitting symbols that direct one or more tags to transition to a state for receiving reader commands; and

(ii) transmitting a non-sequential mask command including an interrogation mask.

10. The method of claim 9, wherein the non-sequential mask command further includes memory bank identifier.

11. The method of claim 1, wherein step (b) includes using a slot based protocol to collect the unmasked bits in the identification sequence for one or more tags in the tag population.

12. The method of claim 11, wherein step (b) includes:

(i) transmitting one or more messages to cause one or more tags in the tag population to transition to a reply state; and

(ii) transmitting one or more messages to cause each of the one or more tags to transmit the unmasked bits of its identification sequence in a message during a reply slot.

13. A method in a radio frequency identification (RFID) tag for communicating with a reader, comprising the steps of:

(a) receiving an interrogation mask corresponding to a tag identification sequence to the RFID tag population, wherein the interrogation mask has a plurality of non-sequential sub-masks that are non-sequentially positioned in the mask and wherein each sub-mask covers at least one bit position; and

(b) performing an abbreviated collection of unmasked bits of the identification sequence.

14. The method of claim 13, wherein step (b) includes performing a binary tree traversal to transmit each unmasked bit of the identification sequence.

15. The method of claim 13, wherein step (b) includes:

(i) transitioning to a reply state upon receipt of one or more messages; and

(ii) transmitting the unmasked bits of the identification sequence in a message during a reply slot.

16. The method of claim 14, wherein step (b) further comprises:

(i) designating a first non-masked bit position as a current bit position;

(ii) transmitting a bit stored in the current bit position;

(iii) receiving a symbol;

(iv) determining whether the received symbol has the same value as the transmitted bit;

(v) if the received symbol has the same value as the transmitted bit, designating a next non-masked bit position as the current bit position and repeating steps (ii) through (iv) for each remaining non-masked bit position; and

(vi) if the received symbol does not have the same value as the transmitted bit, transitioning to a traversal mute state.

17. The method of claim 13, wherein step (a) includes:

(i) receiving one or more symbols causing tag to perform superposition processing;

(ii) designating first bit position of identification sequence as current bit position;

(iii) transmitting bit in current bit position;

(iv) receiving reader bit;

(v) if reader bit has a first value, designating current bit position as masked;

(vi) if reader bit has a second value, designating current bit position as unmasked; and

(vii) repeating steps (iii)-(vi) for each bit position in the identification sequence.

18. The method of claim 13, wherein step (a) includes:

(i) receiving one or more symbols causing tag to transition to a state for receiving commands; and

(ii) receiving a non-sequential mask command including the interrogation mask.

19. The method of claim 18, wherein the non-sequential mask command further includes memory bank identifier.

20. A method in a radio frequency identification (RFID) reader for interrogating an RFID tag population, comprising the steps of:

(a) determining an interrogation mask, wherein the interrogation mask has a plurality of non-sequential sub-masks that are non-sequentially positioned in the mask and wherein each sub-mask covers at least one bit position;

(b) transmitting symbols that direct the tag population to transition to a state for receiving reader commands;

(c) transmitting a non-sequential mask command followed by the interrogation mask;

(d) transmitting symbols that direct the tag population to a state for engaging in a binary tree traversal interrogation; and

(e) performing binary tree traversal to read the non-masked bit positions, wherein the non-masked bit positions are not covered by the sub-masks of the mask.

21. The method of claim 20, wherein step (a) comprises:

(i) transmitting symbols that direct the tag population to engage in superposition processing;

(ii) determining one or more bit positions in the tag identification sequence having a single value for each tag in the tag population; and

(iii) masking each bit position having the single value.