Tag estimation method and tag identification method for RFID system

• US 8,115,602 B2
• Filed: 02/07/2008
• Issued: 02/14/2012
• Est. Priority Date: 11/23/2007
• Status: Active Grant

• Current Assignee: Intellectual Discovery Co., Ltd.
• Original Assignee: Sungkyunkwan University Foundation For Corporate Collaboration (SungKyunKwan University)
• Inventors: Lee, Taejin, Eom, Junbong
• Primary Examiner(s): Zimmerman, Brian
• Assistant Examiner(s): YANG, JAMES J
• Application Number:
  US12/027,756
• Publication Number:
  US 20090134975A1
• Time in Patent Office: 1,468 Days
• Field of Search: 340/825, 340 101- 106, 3405721-5729, 340/1.1, 235375-385, 370/448
• US Class Current: 340/10.2
• 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 7/10049 binary tree
• CPC Class Codes: H04W 8/005 Discovery of network devices, e.g. terminals

Abstract

Provided are a tag estimation method and a tag identification method using the same in a RFID system. In the tag estimating method, a reader divides tags in an identifiable area into a predetermined number of groups. Tags are identified by applying a pilot frame L_p to a first group among the divided groups. The reader calculates a collision probability P_coll of tags after the pilot frame ends. Then, unidentified tags of the first group, which are not identified for the pilot frame, are identified by allocating an additional pilot slot L_add at an end of the pilot frame or generating a new frame L₁ according to the collision probability Pcoll.

Claims

1. A method for estimating the number of tags in a RFID system, comprising the steps of:

a) at a reader, dividing tags in an identifiable area into a predetermined number of groups;

b) identifying tags of a first group among the divided groups determined in step a), by applying a pilot frame L_p to the first group;

c) at the reader, calculating a collision probability P_coll of tags of the first group after the pilot frame L_p ends; and

d) identifying unidentified tags of the first group, which are not identified for the pilot frame L_p, by allocating an additional pilot slot L_add at an end of the pilot frame L_p or generating a new frame L₁ according to the collision probability P_coll by comparing the collision probability P_coll with a predetermined threshold P_th,

wherein if the collision probability P_coll is smaller than the predetermined threshold P_th, the additional pilot slot L_add is allocated at the end of the pilot frame L_p, to identify unidentified tags in the first group, and

wherein if the collision probability P_coll is larger than the predetermined threshold P_th, unidentified tags in the first group are identified by generating the new frame L₁ after the pilot frame L_p.

2. The method of claim 1, wherein in step a), the reader uses a bit mask to divide tags into a predetermined number of groups.

3. The method of claim 1, wherein in the additional pilot slot L_add, tags transmit identification numbers thereof to the reader when respective random counters of the tags, which continuously decrease from the pilot frame L_p, become 0, and

collided tags in the additional pilot slot L_add each select 0 or 1 as the respective random counter and each remaining unidentified tag increases the respective random counter by 1, after the collided tags in the additional pilot slot L_add select 0 or 1 as the respective random counter each of the collided and remaining unidentified tags decreases the respective random counter sequentially and transmits an identification number at a time slot where the respective random counter becomes 0.

4. The method of claim 3, wherein in the new frame L₁, each unidentified tag, which is not identified in the pilot frame L_p, begins counting a new respective random counter and transmits an identification number to the reader when the new respective random counter become 0, and

collided tags in the new frame L₁ each select 0 or 1 as the new respective random counter and each remaining unidentified tag increases the new respective random counter by 1, after collided tags in the new frame L₁ select 0 or 1 as the new respective random counter each of the collided and remaining unidentified tags sequentially decreases the new respective random counter and transmits an identification number at a time slot where the new respective random counter becomes 0.

5. The method of claim 4, wherein a size of the new frame L₁ is decided with a minimum value of n that satisfy an equation:

6. The method of claim 1, wherein the tags are uniformly divided among the predetermined number of groups.

7. The method of claim 1, wherein the collision probability P_coll is calculated by dividing a number of time slots where a collision occurs in a pilot frame L_p by a number of total time slots of the pilot frame.

8. A method for identifying tags in a RFID system, comprising the steps of:

a) at a reader, dividing tags in an identifiable area into a predetermined number of groups;

b) identifying tags of a first group among the divided groups determined in step a), by applying a pilot frame L_p to the first group;

c) at the reader, calculating a collision probability P_coll of tags after the pilot frame ends;

d) identifying unidentified tags of the first group, which are not identified for the pilot frame, by allocating an additional pilot slot L_add at an end of the pilot frame or generating a new frame L₁ according to the collision probability P_coll by comparing the collision probability P_coll with a predetermined threshold P_th,

wherein if the collision probability P_coll is smaller than the predetermined threshold P_th, the additional pilot slot L_add is allocated at the end of the pilot frame L_p, to identify unidentified tags in the first group, and

wherein if the collision probability P_coll is larger than the predetermined threshold P_th, unidentified tags in the first group are identified by generating the new frame L₁ after the pilot frame L_p;

e) deciding an optimal frame size L_opt based on the number of tags of the first group, which are estimated through steps a) to d);

f) identifying tags in a second group among the divided groups determined in step a), by applying the decided optimal frame size L_opt; and

g) identifying tags of a current group among the divided groups determined in step a), by applying an optimal frame size L_opt decided based on a number of identified tags in a previous group among the divided groups determined in step a) and repeating step g) for identifying tags in remaining groups among the divided groups determined in step a) after the second group.

9. The method of claim 8, wherein the optimal frame size L_opt is decided by differentiating an equation for the number n of tags identified in the previous group, where the equation is:

10. The method of claim 9, wherein the optimal frame size L_opt is 0.88n where n is the number of identified tags in the previous group.

11. The method of claim 10, wherein in steps f) and g), each of the tags transmits an identification number to the reader when a respective random counter becomes 0, tags collided in a corresponding frame select 0 or 1 as the respective random counter and each remaining unidentified tag increases a respective random counter by 1, and after tags collided in the corresponding frame select 0 or 1 as the respective random counter each of the collided and remaining unidentified tags sequentially decreases the respective random counter and transmits an identification number at a time slot where the respective random counter becomes 0.

12. The method of claim 8, wherein the tags are uniformly divided among the predetermined number of groups.

13. The method of claim 8, wherein the collision probability P_coll is calculated by dividing a number of time slots where a collision occurs in a pilot frame L_p by a number of total time slots of the pilot frame.