METHOD FOR DETERMINING OPTIMAL FRAME SIZE FOR TAG COLLISION PREVENTION IN RFID SYSTEM

• US 20110063085A1
• Filed: 11/23/2009
• Published: 03/17/2011
• Est. Priority Date: 05/23/2007
• Status: Active Grant

• Current Assignee: SK Telecom Co., Ltd.
• Original Assignee: SK Telecom Co., Ltd.
• Inventors: Lee, Donghwan, Kang, Sukil, JANG, HYUNMIN, Lee, Joosik, Yoon, Youngshin, Han, Junghee, Lee, Wonjun
• Granted Patent: US 8,610,544 B2
• Time in Patent Office: Days
• US Class Current: 340/10.2
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365
• CPC Class Codes: H04W 74/08 Non-scheduled access, e.g. ALOHA hybrid access H04W74/02

Abstract

The present invention relates to a method for determining an optimal frame size for tag collision prevention in an Aloha-based RFID system in which frame sizes limited to a certain unit are used to identify tags, the method including the steps of using an RFID for: (a) calculating an estimated optimal frame value for the RFID reader identifying the tags; (b) calculating expected time delays per tag of a left-hand frame size and a right-hand frame size, which show the smallest differences with respect to the estimated optimal frame value, among the frame sizes; (c) comparing, the expected time delay per tag of the left-hand frame size with that of the right-hand frame size; and (d) determining a frame size which has a smaller expected time delay per tag, between the left-hand frame size and the right-hand frame size, to be an optimal frame size.

Claims

1. A method for determining an optimal frame size for tag collision prevention in a radio frequency identification (RFID) system in which frame sizes limited to a certain unit are used to identify tags, the method comprising the steps of:

(a) calculating, by an RFID reader, an estimated optimal frame value, the RFID reader identifying the tags;

(b) calculating, by the RFID reader, expected time delays per tag of a left-hand frame size and a right-hand frame size, which show the smallest differences with respect to the estimated optimal frame value, among the frame sizes;

(c) comparing, by the RFID reader, the expected time delay per tag of the left-hand frame size with that of the right-hand frame size; and

(d) determining, by the RFID reader, a frame size which has a smaller expected time delay per tag, between the left-hand frame size and the right-hand frame size, to be an optimal frame size.

2. The method as claimed in claim 1, wherein, in step (a), the RFID reader calculates the estimated optimal frame value by means of an equation,

3. The method as claimed in claim 1, wherein, in step (b), the RFID reader calculates the expected time delay per tag of the left-hand frame size, and the expected time delay per tag of the right-hand frame size by means of an equation,

4. The method as claimed in claim 1, further comprising a step of (e) transmitting, by the RFID reader, the optimal frame size to the tags.

5. The method as claimed in claim 1, wherein, in step (b), the left-hand frame size is smaller than the estimated optimal frame value, and the right-hand frame size is greater than the estimated optimal frame value.

6. A method for determining an optimal frame size for tag collision prevention in a radio frequency identification (RFID) system in which a plurality of frame sizes are used to identify a plurality of tags, the method comprising the steps of:

(a) calculating, by an RFID reader, a first middle point which is a middle point of the plurality of frame sizes;

(b) calculating, by the RFID reader, an expected time delay per tag with respect to each of the first middle point and first both-sided frame sizes, including a minimum frame size and a maximum frame size among the plurality of frame sizes;

(c) comparing, by the RFID reader, the expected time delay per tag of the first middle with the expected time delays per tag of the first both-sided frame sizes;

(d) determining, by the RFID reader, the first middle point to be an optimal frame size when the expected time delay per tag of the first middle point is smaller than the expected time delays per tag of the first both-sided frame sizes in step (c);

(e) calculating, by the RFID reader, a second middle point, which is a middle point between the first middle point and a first frame size causing a smaller expected time delay per tag between the first both-sided frame sizes when the expected time delay per tag of the first middle point is greater than the expected time delays per tag of the first both-sided frame sizes in step (c), and then calculating an expected time delay per tag with respect to each of the second middle point and second both-sided frame sizes which include the first frame size and the first middle point;

(f) comparing, by the RFID reader, the expected time delay per tag of the second middle point with the expected time delays per tag of the second both-sided frame sizes;

(g) determining, by the RFID reader, the second middle point to be the optimal frame size when the expected time delay per tag of the second middle point is smaller than the expected time delays per tag of the second both-sided frame sizes in step (f); and

(h) repeatedly performing, by the RFID reader, a bisection search process which includes steps (a) to (g) until the optimal frame size is determined from among the plurality of frame sizes, when the expected time delay per tag of the second middle point is greater than the expected time delays per tag of the second both-sided frame sizes in step (f).

7. The method as claimed in claim 6, wherein the RFID reader calculates the expected time delays per tag by means of an equation,

8. The method as claimed in claim 6, further comprising, after step (d), a step of (d1) stopping, by the RFID reader, the bisection search process, and transmitting a frame size of the first middle point to the plurality of tags.

9. The method as claimed in claim 6, further comprising, after step (g), a step of (g1) stopping, by the RFID reader, the bisection search process, and transmitting a frame size of the second middle point to the plurality of tags.

10. The method as claimed in claim 6, further comprising a step of (i) stopping, by the RFID reader, the bisection search process when the optimal frame size is determined in step (h), and transmitting the optimal frame to the plurality of tags.