Interrogator used in RFID system

• US 8,164,425 B2
• Filed: 11/01/2006
• Issued: 04/24/2012
• Est. Priority Date: 07/27/2004
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Tanaka, Yoshinori
• Primary Examiner(s): Zimmerman, Brian
• Assistant Examiner(s): Jiang, Yong Hang
• Application Number:
  US11/591,101
• Publication Number:
  US 20070052524A1
• Time in Patent Office: 2,001 Days
• Field of Search: 340/10.2, 340/10.1, 340/10.3, 340/9.11, 340/9.12, 340/9.13, 340/10.4, 340/10.42
• 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: H04B 1/38 Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving

Abstract

In RFID system having a plurality of reader/writers, the interface between the reader/writers can be reduced without any degradation of communication throughput. The plurality of reader/writers transmit/receive radio signals to/from RF tags. The reader/writers inform their operation modes to each other, whereby they can recognize the usage statuses of channels for communication with the RF tags. If a channel selected by a particular reader/writer is occupied by another reader/writer for a long time, the particular reader/writer selects another channel immediately. If a channel selected by a particular reader/writer is temporarily occupied by another reader/writer, the particular reader/writer waits for a release of that channel.

Claims

1. An interrogator used in a system including a plurality of interrogators, the interrogator comprising:

a selection unit configured to select a channel from a plurality of channels in the system;

an interference level detection unit configured to detect an interference level of the channel selected by the selection unit;

a notification unit configured to notify one or more other interrogators in the system of at least one piece of notification information that includes

channel identifying information which identifies one of the plurality of channels,

usage status information to which one of a plurality of values that include a first value and a second value is set, and

interrogator identifying information which identifies the interrogator;

a reception unit configured to receive a piece of the notification information from any other one of the plurality of interrogators;

a determination unit configured to determine whether the selected channel is usable on a basis of

the usage status information included in a notified piece of the notification information that includes the channel identifying information identifying the selected channel and that has been notified from another interrogator and received by the reception unit and

the interference level of the selected channel detected by the interference level detection unit;

a communication unit configured to perform wireless communication with a tag using the selected channel when the selected channel is usable;

a channel change unit configured to cause the selection unit to select another channel when the selected channel is not usable; and

a memory configured to store operation mode information indicating one of a plurality of operation modes that include a first operation mode and a second operation mode, wherein

when the communication unit starts the wireless communication with the tag using the selected channel, the notification unit generates a first or second piece of the notification information and notifies the one or more other interrogators of the generated first or second piece of the notification information,

the first piece of the notification information includes information identifying the selected channel set as the channel identifying information, the first value set as the usage status information, and the interrogator identifying information,

the second piece of the notification information includes the information identifying the selected channel set as the channel identifying information, the second value set as the usage status information, and the interrogator identifying information,

the first value indicates that the interrogator identified by the interrogator identifying information occupies a channel identified by the channel identifying information continuously for a long time,

the second value indicates that the interrogator identified by the interrogator identifying information temporarily uses a channel identified by the channel identifying information,

the notification unit generates the first piece of the notification information if the operation mode information indicates the first operation mode when the communication unit starts the wireless communication with the tag using the selected channel, and

the notification unit generates the second piece of the notification information if the operation mode information indicates the second operation mode when the communication unit starts the wireless communication with the tag using the selected channel.

2. The interrogator according to claim 1, wherein

the plurality of values include a third value, and

when the communication unit ends the wireless communication with the tag using the selected channel, the notification unit generates a piece of the notification information by setting the information identifying the selected channel as the channel identifying information and by setting the third value as the usage status information and notifies the one or more other interrogators in the system of the generated piece of the notification information.

3. The interrogator according to claim 2, wherein

the determination unit determines that the selected channel is not usable when the interference level of the selected channel exceeds a threshold and when the selected channel is identified by the channel identifying information included in a piece of the notification information that is notified of by another interrogator in the system and received by the reception unit and that includes the first value set as the usage status information.

4. The interrogator according to claim 2, wherein

the determination unit determines that the selected channel is not usable when the interference level of the selected channel exceeds a threshold and when the selected channel is identified by the channel identifying information included in a piece of the notification information that is notified of by another interrogator in the system and received by the reception unit and that includes the third value set as the usage status information.

5. The interrogator according to claim 2, further comprising

a monitor unit configured to monitor, when the interference level of the selected channel exceeds a threshold and the selected channel is identified by the channel identifying information included in a piece of the notification information that is notified of by another interrogator in the system and received by the reception unit and that includes the second value set as the usage status information, whether a particular piece of the notification information that includes the information identifying the selected channel as the channel identifying information and the third value set as the usage status information is received by the reception unit from another interrogator in the system within a prescribed time, wherein

the determination unit determines the selected channel is usable if the particular piece of the notification information is received by the reception unit within the prescribed time, and determines the selected channel is not usable if the particular piece of the notification information is not received by the reception unit within the prescribed time.

6. The interrogator according to claim 2, wherein

the determination unit determines, when the interference level of the selected channel is lower than a threshold, that the selected channel is usable regardless of which piece of the notification information is received by the reception unit from another interrogator in the system.

7. The interrogator according to claim 2, wherein

the interference level detection unit monitors whether the interference level of the selected channel becomes lower than a threshold within a prescribed time when the interference level of the selected channel exceeds the threshold and when the selected channel is identified by the channel identifying information included in a piece of the notification information that is notified of by another interrogator in the system and received by the reception unit and that includes the second value set as the usage status information, wherein

the determination unit determines the selected channel is usable if the interference level of the selected channel becomes lower than the threshold within the prescribed time, and determines the selected channel is not usable if the interference level of the selected channel does not become lower than the threshold within the prescribed time.

8. The interrogator according to claim 1, wherein

the plurality of values include a fourth value, and

when the interference level detection unit starts to detect the interference level, the notification unit generates a piece of the notification information by setting the information identifying the selected channel as the channel identifying information and by setting the fourth value as the usage status information and notifies the one or more other interrogators in the system of the generated piece of the notification information.

11. The interrogator according to claim 1, wherein the reception unit receives the piece of notification information via a network to which the plurality of interrogators are connected.

9. An interrogator used in a system including a plurality of interrogators, the interrogator comprising:

a selection unit configured to select a channel from a plurality of channels for communication with a tag in the system;

a notification unit configured to notify one or more other interrogators in the system of at least one piece of notification information that includes

channel identifying information which identifies one of the plurality of channels,

usage status information to which one of a plurality of values that include a first value and a second value is set, and

interrogator identifying information which identifies the interrogator;

a reception unit configured to receive a piece of the notification information from any other one of the plurality of interrogators;

a channel change unit configured to cause the selection unit to select another channel when a first piece of the notification information that includes information identifying the selected channel set as the channel identifying information and the first value set as the usage status information is received by the reception unit from one of the plurality of interrogators;

a communication unit configured to perform wireless communication with a tag while sharing the selected channel with one or more other interrogators in a time-sharing manner when a second piece of the notification information that includes the information identifying the selected channel set as the channel identifying information and the second value set as the usage status information is received by the reception unit from one of the plurality of interrogators; and

a memory configured to store operation mode information indicating one of a plurality of operation modes that include a first operation mode and a second operation mode, wherein

when the communication unit starts the wireless communication with the tag using the selected channel, the notification unit generates a third or fourth piece of the notification information and notifies the one or more other interrogators of the generated third or fourth piece of the notification information,

the third piece of the notification information includes the information identifying the selected channel set as the channel identifying information, the first value set as the usage status information, and the interrogator identifying information,

the fourth piece of the notification information includes the information identifying the selected channel set as the channel identifying information, the second value set as the usage status information, and the interrogator identifying information,

the third value indicates that the interrogator identified by the interrogator identifying information occupies a channel identified by the channel identifying information continuously for a long time,

the fourth value indicates that the interrogator identified by the interrogator identifying information temporarily uses a channel identified by the channel identifying information,

the notification unit generates the third piece of the notification information if the operation mode information indicates the first operation mode when the communication unit starts the wireless communication with the tag using the selected channel, and

the notification unit generates the fourth piece of the notification information if the operation mode information indicates the second operation mode when the communication unit starts the wireless communication with the tag using the selected channel.

12. The interrogator according to claim 9, wherein the reception unit receives the piece of notification information via a network to which the plurality of interrogators are connected.

10. A system comprising:

a plurality of interrogators; and

a network configured to connect the plurality of interrogators, wherein each interrogator includes;

a selection unit configured to select a channel from the plurality of channels;

an interference level detection unit configured to detect an interference level of the channel selected by the selection unit;

a notification unit configured to notify one or more other interrogators in the system of at least one piece of notification information that includes

channel identifying information which identifies one of the plurality of channels,

usage status information to which one of a plurality of values that include a first value and a second value is set, and

interrogator identifying information which identifies an interrogator including the notification unit;

a reception unit configured to receive a piece of the notification information from any other one of the plurality of interrogators;

a determination unit configured to determine whether the selected channel is usable on a basis of

the usage status information included in a notified piece of the notification information that includes the channel identifying information identifying the selected channel and that has been notified from another interrogator and received by the reception unit and

the interference level of the selected channel detected by the interference level detection unit;

a communication unit configured to perform wireless communication with a tag using the selected channel when the selected channel is usable;

a channel change unit configured to cause the selection unit to select another channel when the selected channel is not usable; and

a memory configured to store operation mode information indicating one of a plurality of operation modes that include a first operation mode and a second operation mode, wherein

when the communication unit starts the wireless communication with the tag using the selected channel, the notification unit generates a first or second piece of the notification information and notifies the one or more other interrogators of the generated first or second piece of the notification information,

the first piece of the notification information includes information identifying the selected channel set as the channel identifying information, the first value set as the usage status information, and the interrogator identifying information,

the second piece of the notification information includes the information identifying the selected channel set as the channel identifying information, the second value set as the usage status information, and the interrogator identifying information,

the first value indicates that the interrogator identified by the interrogator identifying information occupies a channel identified by the channel identifying information continuously for a long time,

the second value indicates that the interrogator identified by the interrogator identifying information temporarily uses a channel identified by the channel identifying information,

the notification unit generates the first piece of the notification information if the operation mode information indicates the first operation mode when the communication unit starts the wireless communication with the tag using the selected channel, and

the notification unit generates the second piece of the notification information if the operation mode information indicates the second operation mode when the communication unit starts the wireless communication with the tag using the selected channel.

13. The system according to claim 10, wherein the reception unit receives the piece of notification information via the network.