Interrogator used in RFID system

• US 20070052524A1
• Filed: 11/01/2006
• Published: 03/08/2007
• Est. Priority Date: 07/27/2004
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Tanaka, Yoshinori
• Granted Patent: US 8,164,425 B2
• Time in Patent Office: Days
• US Class Current: 340/10.200
• 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 an RFID system in which usage status information indicating the usage status of a channel for wireless communication with an RF tag are transferred between a plurality of interrogators, comprising:

a selection unit for selecting a channel from a plurality of channels in the RFID system;

an interference level detection unit for detecting the interference level of the channel selected by said selection unit;

a determination unit for determining whether the selected channel is usable or not on the basis of the usage status information of the selected channel notified from other interrogator and the interference level of the selected channel detected by said interference level detection unit;

a communication unit for performing wireless communication with an RF tag using the selected channel when the selected channel is usable; and

a channel change unit for causing said selection unit to select another channel when the selected channel is not usable.

2. The interrogator according to claim 1, wherein

the usage status information identifies a first communication state, a second communication state with priority being lower than the first communication state, and a non-communication state.

3. The interrogator according to claim 1, wherein

the usage status information identifies a first communication state indicating a channel is occupied continuously for long time, a second communication state indicating a channel is used temporarily, and a non-communication state.

4. The interrogator according to claim 2, wherein

said determination unit determines that the selected channel is not usable when the interference level of the selected channel exceeds a threshold and the selected channel is under the first communication state.

5. The interrogator according to claim 2, wherein

said determination unit determines that the selected channel is not usable when the interference level of the selected channel exceeds a threshold and the selected channel is under the non-communication state.

6. The interrogator according to claim 2, further comprising

a monitor unit for monitoring, when the interference level of the selected channel exceeds a threshold and the selected channel is under the second communication state, whether or not a status of the selected channel is changed to the non-communication state within a prescribed time, wherein

said determination unit determines the selected channel is usable if the status of the selected channel is changed to the non-communication state within the prescribed time, and determine the selected channel is not usable if the status of the selected channel is not changed to the non-communication state within the prescribed time.

7. The interrogator according to claim 2, wherein

said determination unit determines, when the interference level of the selected channel is lower than a threshold, that the selected channel is usable regardless of the usage status of the channel.

8. The interrogator according to claim 2, wherein

said interference level detection unit monitors whether or not 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 the selected channel is under the second communication state, wherein

said 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 determine 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.

9. The interrogator according to claim 1, wherein

the usage status information identifies a measurement state, being accessed by the interrogator for channel search, or a non-communication state.

10. An interrogator used in an RFID system comprising a plurality of interrogators, comprising:

a selection unit for selecting a channel from a plurality of channels for communication with an RF tag in the RFID system;

a channel change unit for causing said selection unit to select another channel when the selected channel is estimated to be occupied by other interrogator continuously for long time; and

a communication unit for performing wireless communication with an RF tag while sharing the selected channel with other interrogator by means of time-sharing when the selected channel is estimated to be used temporarily by said other interrogator.

11. An RFID system with a plurality of interrogators for performing wireless communication with an RF tag using a plurality of channels, comprising

a network for connecting the plurality of interrogators;

and

a notification unit for notifying operation mode information indicating an operation mode of each interrogator among the plurality of interrogators via the network, wherein

each interrogator comprises;

a selection unit for selecting a channel from the plurality of channels;

an interference level detection unit for detecting the interference level of the channel selected by said selection unit;

a determination unit for determining whether the selected channel is usable or not on the basis of the operation mode of other interrogator and the interference level of the selected channel detected by said interference level detection unit;

a communication unit for performing wireless communication with an RF tag using the selected channel when the selected channel is usable; and

a channel change unit for causing said selection unit to select another channel when the selected channel is not usable.