PASSIVE RFID READER AND OPERATION CONTROL METHOD THEREFOR

• US 20080122581A1
• Filed: 05/09/2007
• Published: 05/29/2008
• Est. Priority Date: 05/10/2006
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: BAE, Ji-Hoon, PARK, Chan-Won, QUAN, Cheng-Hao, CHOI, Gil-Young, LEE, Dong-Han, MO, Hee-Sook, CHAE, Jong-Suk, PYO, Cheol-Sig
• Granted Patent: US 8,653,946 B2
• Time in Patent Office: Days
• 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 7/10356 using a plurality of antennas, e.g. configurations including means to resolve interference between the plurality of antennas
• CPC Class Codes: H04W 74/08 Non-scheduled access, e.g. ALOHA hybrid access H04W74/02

Abstract

Provided is a Radio Frequency Identification (RFID) reader that can minimize collision among RFID readers in an environment where there are a plurality of RFID readers within a limited operating environment by making each RFID reader select a channel at different delay time based on a random value, and a method for controlling operation of the RFID reader. The RFID reader includes a random value generating unit; a reader control unit for adaptively deciding a counter value for generating the random value; an anti-collision unit for preventing collision among a plurality of tags; a reader transmitting unit for generating a reader command message determined by the anti-collision unit, encoding the reader command message, and modulating the reader command message; a reader receiving unit for demodulating and decoding a tag signal; and a channel operation control unit for selecting a channel to be used for the communication with the tag.

Claims

1. A Radio Frequency Identification (RFID) reader, comprising:

a random value generating means for generating a random value for each RFID reader to select a channel at different delay time;

a reader control means for adaptively deciding a counter value for generating the random value, and when the listen time as long as the random value generated in the random value generating means is ended, making a command to select a channel for communication with a tag, and controlling entire operation for acquiring information from the tag;

an anti-collision means for performing control to prevent collision among a plurality of tags and transmitting a communication result between the RFID reader and the tag to the reader control means;

a reader transmitting means for generating a reader command message determined by the anti-collision means, encoding the reader command message, and modulating the reader command message;

a reader receiving means for demodulating and decoding a tag signal received through an antenna and reporting a tag response status to the anti-collision means; and

a channel operation control means for selecting a channel to be used for the communication with the tag upon receipt of a command of the reader control means.

2. The RFID reader of claim 1, wherein the reader control means adaptively decides the counter value based on an environment of an operating environment of the RFID reader.

3. The RFID reader of claim 2, wherein the reader control means makes the listening time for selecting a channel long by increasing the counter value, when there are a large number of RFID readers in the operating environment;

and makes the listening time for selecting a channel short by decreasing the counter value, when there are a small number of RFID readers in the operating environment.

4. The RFID reader of claim 1, wherein the random value generating means generates a random value sequence within a range of 0 to 2^R−

1 based on the arbitrary counter value R set by the reader control means.

5. The RFID reader of claim 4, wherein the random value generating means generates a random value sequence by changing a random seed value for each execution of an algorithm to irregularly generate the random value sequence.

6. The RFID reader of claim 4, wherein the reader control means selects any one value from the generated random value sequence according to the environment within the operating environment of the RFID reader.

7. The RFID reader of claim 1, wherein the channel operation control means includes:

a Listen Before Talk (LBT) mode control means for executing LBT control; and

a random access mode control means for controlling a random access method.

8. The RFID reader of claim 7, wherein the reader control means selects any one between the LBT mode and the random access mode as a channel occupying method to be used for communication with a tag.

9. The RFID reader of claim 8, wherein the LBT mode control means and the random access mode control means share a Phase Locked Loop (PLL) control means.

10. The RFID reader of claim 8, wherein the LBT mode control means performs control to turn on a transmission power source of an RF unit upon receipt of a channel selection command from the reader control means and occupies a channel based on the LBT method.

11. The RFID reader of claim 8, wherein the random access mode control means performs control to turn on a transmission power source of an RF unit upon receipt of a channel selection command from the reader control means and decides a PLL for setting up a channel.

12. The RFID reader of claim 11, wherein the random access mode control means decides the PLL to occupy a pre-defined frequency channel.

13. The RFID reader of claim 11, wherein the random access mode control means selects any one from a channel frequency sequence pre-defined by an operator, and decides the PLL to occupy the selected frequency channel.

14. The RFID reader of claim 8, wherein the reader control means increases the counter value by a predetermined increase value, when the reader control means fails in acquiring tag information from the tag in any one method between the LBT mode and the random access mode.

15. The RFID reader of claim 1, wherein the anti-collision means determines a reader command message and a communication result to be transmitted to the reader control means based on a response status of the tag that is reported from the reader receiving means.

16. A method for controlling operation of an RFID reader in an RFID system having a plurality of RFID readers within an operating environment, comprising the steps of:

a) selecting a random value to select a channel at different delay time for each RFID reader;

b) listening as long as the selected random value and occupying a channel for communication with a tag based on a predetermined channel occupying method;

c) communicating with the tag through the occupied channel; and

d) processing tag information based on a communication result between the RFID reader and the tag.

17. The method of claim 16, further comprising the steps of:

e) setting up an initial parameter;

f) setting up the channel occupying mode for the communication between the RFID reader and the tag; and

g) performing control to turn off a transmission power source of an RF unit.

18. The method of claim 16, wherein the channel occupying mode includes a channel occupying mode based on an LBT method and a channel occupying mode based on a random access method.

19. The method of claim 17, wherein the step a) includes the steps of:

a1) deciding a counter value for generating a random value;

a2) generating a random value sequence based on the counter value and a random seed; and

a3) selecting any one random value from the generated random value sequence.

20. The method of claim 19, wherein the counter value is adaptively decided based on an environment within an operating environment of the RFID reader.

21. The method of claim 20, wherein the counter value deciding step a1) includes the steps of:

a1-1) when there are a large number of RFID readers within the operating environment, deciding a large counter value; and

a1-2) when there are a small number of RFID readers within the operating environment, deciding a small counter value.

22. The method of claim 19, wherein a random value sequence is generated within a range of 0 to 2^R−

1 based on the counter value R in the step a2).

23. The method of claim 22, wherein a random seed value is changed for each execution of an algorithm to irregularly generate the random value sequence in the step a2).

24. The method of claim 18, wherein when the random access method is established as the channel occupying mode, the step b) includes the steps of:

b1) performing control to turn on a transmission power source of an RF unit after listening as long as the selected random value; and

b2) setting up a PLL to occupy one frequency channel.

25. The method of claim 24, wherein the step b) further includes the step of:

b3) listening for a predetermined time for stable operation after the PLL deciding step b2).

26. The method of claim 25, wherein a PLL value corresponding to a pre-defined frequency channel is decided in the PLL deciding step b2).

27. The method of claim 25, wherein any one frequency is selected from a channel frequency sequence pre-defined by an operator and a PLL value corresponding to the selected frequency channel is decided in the PLL deciding step b2).

28. The method of claim 18, wherein when the LBT method is established as the channel occupying mode, the step b) includes the steps of:

b3) generating a frequency channel sequence after listening as long as the selected random value;

b4) selecting any one channel from the generated frequency channel sequence;

b5) measuring a Received Signal Strength Indication (RSSI) of the selected channel, and checking whether the selected channel is available;

b6) when the selected channel is not available, selecting another channel in the frequency channel sequence, and measuring an RSSI of the channel to see if the channel is available; and

b7) performing control to turn on the transmission power source of the RF unit, when the selected channel is available.

29. The method of claim 19, wherein the step c) includes the steps of:

c1) performing control to prevent collision among a plurality of tags and acquiring tag information from each tag through the occupied channel; and

c2) acquiring user data from each tag based on an anti-collision result obtained in the anti-collision step.

30. The method of claim 29, wherein the anti-collision step c1) includes the steps of:

c1-1) generating a selection command to acquire tag information;

c1-2) arbitrarily deciding an Q value which indicates the number of slots, checking the presence of a tag response from each slot, and decreasing the number of the slots by the Q value;

c1-3) initializing the status parameter which indicates the response status of the tag and generating a query command;

c1-4) when not all the slots are listened to, decreasing the number of slots by the Q value, initializing the status parameter, and generating a query repeat command;

c1-5) generating an acknowledgement (Ack) when a normal response is received from the tag according to the query command or the query repeat command; and

c1-6) performing cyclic redundancy check (CRC) onto the data transmitted from the tag and determining the status parameter according to the response status of the tag.

31. The method of claim 30, wherein the status parameter establishment step c1-6) includes the steps of:

c1-6-1) when the CRC test result shows that the tag data are normal and the tag makes a normal response to the ack command, deciding the status parameter as ‘

OK,’

which indicates that the tag data transmitted form the tag are normally processed;

c1-6-2) when no response is transmitted from the tag to the ack command, deciding the status parameter as ‘

No_TAG,’

which indicates that the tag does not make a response; and

c1-6-3) when an error is detected in the CRC test, deciding the status parameter as ‘

CRC_ERR,’

which indicates that there is an error in the CRC.

32. The method of claim 31, wherein when there is no response from the tag to the ack command, the ack command is generated repeatedly by predetermined times, and when the tag does not make a response to the repeated ack commands, the status parameter is decided as ‘

NO_TAG.’

33. The method of claim 31, wherein when there is an error in the CRC test, the ack command is generated repeatedly by predetermined times, and when there is a CRC error in the tag data even after the repeated ack commands, the status parameter is decided as ‘

CRC_ERR.’

34. The method of claim 31, wherein when the communication result between the RFID reader and the tag says that the status parameter is not ‘

OK,’

the counter value is increased by a predetermined increase value in the step a).

35. A method for controlling operation of an RFID reader in an RFID system having a plurality of RFID readers within an operating environment, comprising the steps of:

a) selecting a random value to select a channel at different delay time for each RFID reader;

b) listening as long as the selected random value and establishing a channel for communication with a tag;

c) communicating with the tag through the established channel; and

d) processing tag information based on a communication result between the RFID reader and the tag.

36. The method of claim 35, wherein the step a) includes the steps of:

a1) setting up a counter value for generating a random value;

a2) generating a random value sequence based on the counter value and a random seed; and

a3) selecting any one random value from the generated random value sequence.

37. The method of claim 36, wherein the counter value is adaptively decided based on an environment within an operating environment of the RFID reader.

38. The method of claim 37, wherein the counter value deciding step a1) includes the steps of:

a1-1) when there are a large number of RFID readers within the operating environment, deciding a large counter value; and

a1-2) when there are a small number of RFID readers within the operating environment, deciding a small counter value.

39. The method of claim 37, wherein a random value sequence is generated within a range of 0 to 2^R−

1 based on the counter value R in the step a2).

40. The method of claim 37, wherein a random seed value is changed for each execution of an algorithm to irregularly generate the random value sequence in the step a2).