Method of preventing collisions between RFID readers in RFID system

• US 8,222,997 B2
• Filed: 01/07/2007
• Issued: 07/17/2012
• Est. Priority Date: 01/12/2006
• Status: Expired due to Fees

• Current Assignee: KT&C Co., Ltd.
• Original Assignee: KT&C Co., Ltd.
• Inventors: Shin, Kwang-Yoon
• Primary Examiner(s): Mehmood, Jennifer
• Assistant Examiner(s): GIRMA, FEKADESELASS
• Application Number:
  US12/160,710
• Publication Number:
  US 20090002129A1
• Time in Patent Office: 2,018 Days
• Field of Search: None
• US Class Current: 340/10.1
• 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 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H04W 74/0816 with collision avoidance
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

Disclosed herein is a method of preventing collisions between readers in an RFID system. The method includes a first step of RFID readers selecting transmitting channels by examining channels, a second step of transmitting signals via the selected transmitting channels, a third step of receiving signals via channels having the same frequencies as the selected transmitting channels; a fourth step of determining whether a collision has occurred by examining the status of the signals that are received via the transmitting channels; a fifth step of, if, as a result of the determination at the fourth step, it is determined that a collision between the readers has occurred, repeating the first to fourth steps after delays of random time periods based on a predetermined equation, and a sixth step of, if, as a result of the fourth step, no collision between readers is detected, communicating with the corresponding RFID tags.

Claims

1. A method of preventing collisions between a plurality of Radio Frequency Identification (RFID) readers in an RFID system, the method comprising:

a first step of selecting, by each of the plurality of RFID readers, transmitting channels by examining predetermined channels;

a second step of transmitting, by the plurality of RFID readers, transmit signals via the selected transmitting channels;

a third step of receiving, by the plurality of RFID readers, receive signals from one or more RFID tars via receiving channels having same frequencies as the selected transmitting channels;

a fourth step of determining whether a collision between the plurality of RFID readers has occurred by examining status of the receive signals that are received via the receiving channels having same frequencies as the selected transmitting channels;

a fifth step of, if, as a result of the determination at the fourth step, it is determined that the collision between the plurality of RFID readers has occurred, generating random time periods based on a predetermined equation for the plurality of RFID readers respectively, and repeating, by the plurality of RFID readers respectively, the first to the fourth steps after delays of the random time periods for each the plurality of RFID reader, in order to prevent the plurality of RFID readers transmitting signals at the same time and

a sixth step of, if, as a result of the fourth step, the collision between the plurality of RFID readers is not determined, communicating with the corresponding one or more RFID tags;

wherein, the first step is performed using a LBT (Listen Before Talk) algorithm to select the transmitting channels;

wherein the random time periods of the fifth step are determined by the following equation;

T=n×

t_response

where n is a random number and t_response is a tag response time.

2. The method as set forth in claim 1, wherein the fourth step is performed by determining that the collision between the plurality of RFID readers has occurred if the status of the receive signals is noise status.

3. The method as set forth in claim 1, wherein the second step is performed by transmitting data, the third step is performed by receiving data, and the fourth step is performed by comparing the transmitted data with the received data, and determining that the collision has occurred if the transmitted data does not coincide with the received data.