CN101112009A - RFID carrier sensing method and RFID system adopting the method - Google Patents

Abstract

The invention discloses an RFID carrier sensing method and an RFID system adopting the method. An RFID system capable of increasing the probability of detecting an empty channel and reducing the influence of interference between readers/writers is provided. This RFID system includes: a reader/writer having a reader/writer main body and a polarization-switchable antenna for transmitting continuous carrier waves; modulation, and return an acknowledgment signal to the reader/writer. The reader/writer main body judges the level of the received interference signal, determines a channel and a polarization direction that make the level of the interference signal lower than a threshold value, and performs The reply signal from the tag is received.

Description

RFID carrier sensing method and RFID system adopting the method

technical field

The present invention relates to a radio frequency ID (RFID: Radio Frequency Identification) carrier sense method, and an RFID reader/writer and RFID system using radio frequency ID.

Background technique

In recent years, in terms of reading ID information recorded on a tag, a system that uses magnetic coupling with a tag to read or an RFID system that uses a radio frequency to read tag information has been developed and used.

As for the latter RFID system for reading using a radio frequency, as an example, ETSI (European Telecommunications Standards Institute) (Draft ETSI EN 302 208-1V1.1.1 (2003-12)) has published a European standard. In Draft ETSI EN 302 208-1 V1.1.1 (2003-12) the use of an RFID system with a maximum power of 2W utilizing the 865MHz to 868MHz frequency band is disclosed.

Here, there are cases where a plurality of readers/writers operate adjacent to each other to become an RFID system. Figure 1 shows an example of this state.

In FIG. 1, the signal transmitted by the corresponding reader/writer #1 (#2) has disturbance 3 to another reader/writer #2 (#1), so that there is a reader/writer A problem that the reception performance of writers #1 and #2 deteriorates. To solve this problem, carrier sense is performed before transmission to reduce the influence of interference 3, and a channel that is not currently used by other reader/writer #2 (#1) is searched. In addition, a method is adopted: if there is a free channel, use the free channel; if there is no free channel, wait until the free channel is found.

In other words, FIG. 2 shows a method of employing such carrier sense. FIG. 2 is a flowchart of the reading operation of the individual reader/writer in FIG. 1 for tag information.

According to FIG. 2, each of the readers/writers #1 and #2 is constituted by a reader/writer main body portion 1a and an antenna 1b.

First, the initial channel (frequency bandwidth) is set by the reader/writer main body 1a (step S1), and then the level of the carrier wave received in the initial channel thus set is measured by the antenna 1b as an interference signal (step S1). S2). If the level of the interference signal is greater than the threshold (step S3, No), the channel cannot be used, so the interference level of other channels is taken as the measurement target. In other words, it is determined whether the measurement of all channels has been performed, and if there is a channel that has not been measured (step S4, No), then the channels are switched sequentially (step S5) to return to the same interference level measurement (step S2) .

In the case that the measurement to all channels has been carried out (step S4, Yes), the waiting time is randomly set (step S6), and the process returns to the initial channel setting again after passing through the set waiting time (step S1) , and repeat the process.

If the interference level is equal to or less than the threshold in the interference level measurement (step S2) (step S3, Yes), then the channel whose interference level is equal to or less than the threshold is determined (step S7), and then the command signal is sent (step S7). S8).

FIG. 3 shows a command signal transmitted by the antenna 1b of the reader/writer #1 (#2) and a response signal from the tag 2a (2b). As shown in FIG. 3A, readers/writers #1 and #2 transmit unmodulated continuous wave CW, and modulate the unmodulated continuous wave CW by means of a command signal, thereby utilizing a fixed right The continuous wave CW is transmitted with circular polarization.

Upon receiving the command signal from the corresponding reader/writer #1 and #2, the tags 2a and 2b pass as tag information the characteristic information including the information (ID) for identifying the item to which the tag belongs to the unmodulated The continuous carrier wave CW is modulated to respond (see step S9: FIG. 3B ). Readers/writers #1 and #2 receive the reply signal and end communication (step S10).

Furthermore, another method used is a method according to which the control device collectively controls a plurality of readers/writers #1 and #2 and controls the transmission timing of each reader/writer.

The former method, following the flow of Figure 2, involves performing carrier sense as described above to search for channels not currently being used by other readers/writers and use the free channel if one exists The method faces the problem that there are a large number of readers/writers and the waiting time is long. Furthermore, in the case of the latter method involving performing centralized control by means of a control device, when there are a large number of readers/writers, there is a problem that the allocated communication time is short.

Contents of the invention

Therefore, the object of the present invention is to eliminate the long waiting time of the transmission timing of each reader/writer or the time allocated to these readers/writers even when there are a plurality of readers/writers in the RFID system. The communication time of the reader is short, and it is to reduce the influence of mutual interference that occurs when a plurality of readers/writers are adjacent to each other.

As a first aspect, there is provided an RFID system for solving the above-mentioned problems, which has: a reader/writer having a reader/writer main body and an antenna capable of polarization switching, and which transmits continuously a carrier wave; and a tag that modulates the continuous carrier wave using tag information and sends a response signal back to the reader/writer, wherein the reader/writer main body judges the received the level of an interference signal, determining a channel and a polarization direction in which the level of the interference signal is equal to or less than a threshold, and receiving the response signal from the tag according to the determined channel and polarization direction.

According to a second aspect, the RFID system for solving the above-mentioned problems according to the first aspect is configured such that: the antenna capable of polarization switching is capable of switching between right-handed circular polarization and left-handed circular polarization; and the reader/ The writer main body section detects a channel whose level of an interference signal to be received in the case of right-handed circular polarization or left-handed circular polarization is equal to or smaller than the threshold value.

According to a third aspect, the RFID system for solving the above-mentioned problems according to the first aspect is configured such that: the polarization-switchable antenna is capable of switching between horizontal polarization and vertical polarization; and the reader/writer The main body section detects a channel whose level of an interference signal to be received is equal to or smaller than the threshold value in the case of horizontal polarization or vertical polarization.

According to a fourth aspect, the RFID system that solves the above-mentioned problems has: a reader/writer having a reader/writer main body and a plurality of antennas each having a characteristic polarization, and which transmits a continuous carrier wave; and a tag that modulates the continuous carrier wave with tag information and sends an acknowledgment signal back to the reader/writer, wherein the reader/writer main body responds to the Each channel judges the level of an interference signal to be received by each of the plurality of antennas, determines an idle channel and antenna whose judged level of the interference signal is equal to or smaller than a threshold value, and transmits the signal via the determined The channel receives the reply signal from the tag by means of the determined antenna.

According to a fifth aspect, the RFID system that solves the above-mentioned problems is the RFID system according to any one of the first to fourth aspects, wherein the channels are individual bands of frequency bands divided into a plurality of bandwidths.

According to a sixth aspect, the RFID system that solves the above problems is the RFID system according to any one of the first to fourth aspects, wherein the tag is composed of a patch antenna and an LSI, and the LSI is connected to the sticker The chip antennas are connected in parallel and have an interface portion having a capacitive component that resonates with the inductive component.

A carrier sense method for an RFID system that solves the above-mentioned problems is a carrier sense method for an RFID system that has, as far as the first aspect is concerned, a reader/writer with a reader/writer an input body and an antenna capable of polarization switching, and which transmits a continuous carrier wave; and a tag, which modulates the continuous carrier wave using tag information, and sends a response signal back to the reader/writer, so The method has the steps of: in the reader/writer, sequentially measuring the interference signal level using a specific channel for all switchable polarizations of the antenna; when the interference signal level to be measured is greater than a threshold , measure the interference signal level by switching the specific channel to other channels; determine the channel and polarization direction for which the interference signal level thus measured does not exceed the threshold; and set to receiving the continuous carrier wave modulated with the tag information sent back from the tag with the determined antenna polarization direction.

The carrier sense method of an RFID system that solves the above-mentioned problems is a carrier sense method of an RFID system that has, as far as the second aspect is concerned, a reader/writer having a reader/writer An input body part and a plurality of antennas respectively provided with different polarization directions, and which transmit a continuous carrier wave; and a tag, which modulates the continuous carrier wave using tag information, and sends a response signal back to the reader/ Writer, the method has the steps of: in the reader/writer, for each polarization of the plurality of antennas, using a specific channel to sequentially measure the interference signal level; when the interference signal to be measured When the level is greater than the threshold value, measure the interference signal level by switching the specific channel to other channels; determine the channel and polarization direction set to the interference signal level measured in this way without exceeding the threshold value an antenna; and configured to receive the response signal from the tag using the determined channel and antenna.

A first aspect of a reader/writer that solves the above-mentioned problems is a reader/writer of an RFID system that has a reader/writer main body and an antenna capable of polarization switching and transmits a continuous carrier wave to a tag. a writer, wherein a level of the received interference signal is judged, and a channel and a polarization direction of the antenna for which the level of the interference signal is equal to or less than a threshold value are determined, and on the determined channel and in The determined polarization direction receives a response signal, which is generated by modulating the continuous carrier wave with tag information, and is sent back by the tag.

A second aspect of the reader/writer that solves the above-mentioned problems is a reader/writer for an RFID system that has a reader/writer main body and a plurality of antennas each having a characteristic polarization and transmits a continuous carrier wave to a tag. a reader/writer, wherein the reader/writer main body section judges, for each of a plurality of channels, the level of an interference signal to be received by each of the plurality of antennas, and determines an idle channel and antenna whose level of the interference signal is judged to be equal to or less than a threshold value, and receiving a response signal modulated with tag information using the continuous carrier wave via the determined channel by means of the determined antenna generated and sent back by the tag.

The features of the present invention will become more apparent through the preferred embodiments which will be described with reference to the following drawings.

The present invention enables a high probability of detecting an idle channel and can reduce interference effects between readers/writers.

Description of drawings

FIG. 1 depicts an example of the state of a case where a plurality of readers/writers operate adjacent to each other to become an RFID system;

Fig. 2 has described the clear channel detection method using carrier sense;

FIG. 3 depicts a command signal transmitted by the antenna 1b of the reader/writer #1 (#2) and a response signal from the tag 2a (2b);

FIG. 4 shows the features of the present invention in the case where a plurality of readers/writers #1 and #2 operate adjacent to each other to become an RFID system;

5 is a conceptual diagram of a configuration example of a reader/writer to which the present invention is applied;

FIG. 6 is a conceptual diagram of another reader/writer embodiment;

Figure 7 is a conceptual block diagram of an embodiment of a tag 2a (2b);

Fig. 8 is the operation flow of the embodiment of the present invention based on the premise of reader/writer and tag construction;

FIG. 9 shows a command signal transmitted by the antenna 1b of the reader/writer #1 (#2) and a response signal from the tag 2a (2b);

FIG. 10 shows the relationship between polarization directions 1 to n and channels Ch1 to Ch4 determined using the implementation process of FIG. 8; and

Figure 11 shows an embodiment using multiple antennas, each of which is assigned a specific polarization direction.

Detailed ways

Embodiments of the present invention will be described below based on the accompanying drawings. The embodiments described below enable the present invention to be understood, and the technical scope of the present invention is not limited thereto.

Fig. 4 shows a situation where a plurality of readers/writers #1 and #2 operate adjacent to each other so as to become an RFID system, and compared with Fig. 1, when carrier sensing is a feature of the present invention, providing Function 4 to control the polarization direction of the antenna 1b of the reader/writer.

FIG. 5 is a conceptual diagram of a configuration example of readers/writers #1 and #2 to which the present invention is applied.

In FIG. 5 , an antenna 1 b includes an antenna element 10 and a polarization direction control unit 20 . The polarization direction control section 20 shown in FIG. 5 has a function of switching the polarization direction of the antenna element 10 to right-handed circular polarization and left-handed circular polarization. The antenna element 10 comprises two orthogonal dipoles, the horizontal dipole connected to the switch 15 and the vertical dipole connected to the switch 16 .

The reader/writer main body 1 a transmits a transmission signal TXSIG to the transmission/reception switch 14 of the polarization direction control unit 20 , and inputs a reception signal TRSIG from the transmission/reception switch 14 . Also, the reader/writer main body section 1 a transmits a polarization switching signal PWSW to the switch control section 11 of the polarization direction control section 20 .

Both hybrid circuits 12 and 13 have input to them a transmission signal TXSIG and output signals phase-shifted by 0° and 90°. The switch control section 11 controls switching of the switches 14 , 15 , and 16 in accordance with a polarization switching signal PWSW from the reader/writer main body section 1 a.

In other words, when the reader/writer main body section 1a transmits the polarization switching signal PWSW specifying the right-handed circular polarization to the switch control section 11, the switch control section 11 supplies the switches 14, 15, and 16 to make the output terminal of the switch 14 o1 and the input terminal I1 of the switches 15 and 16 are valid switch switching signals.

On the contrary, when the reader/writer #1 sends the polarization switching signal PWSW specifying the left-handed circular polarization to the switch control section 11, the switch control section 11 supplies the switches 14, 15, and 16 so that the output terminals o2 of the switch 14 and Input terminals I2 of switches 15 and 16 are active switching signals.

Therefore, when a 0° phase-shifted signal is supplied to the horizontal dipole antenna element of antenna 10 through switch 15 and a 90° phase-shifted signal is supplied to the vertical dipole antenna element of antenna 10 through switch 16, right-handed circular polarization is produced. Conversely, when a 90° phase-shifted signal is supplied to the horizontal dipole antenna element of antenna 10 through switch 15 and a 0° phase-shifted signal is supplied to the vertical dipole antenna element of antenna 10 through switch 16, left-handed circular polarization is generated.

FIG. 6 is a conceptual diagram of a configuration example of another reader/writer including a function for controlling the polarization direction of the antenna 10 to switch between horizontal polarization and vertical polarization.

In FIG. 6 , an antenna 1 b includes an antenna element 10 and a polarization direction control section 20 as in the embodiment in FIG. 5 . The reader/writer main unit 1 a transmits a transmission signal TXSIG to the transceiver switch 14 of the polarization direction control unit 20 , and receives a reception signal TRSIG from the transceiver switch 14 . Further, the reader/writer main body section 1 a sends a horizontal and vertical polarization switching signal PWSW to the switching control section 11 of the polarization direction control section 20 .

When the reader/writer main body 1a sends the polarization switching signal PWSW specifying the horizontal polarization to the switch control section 11, the switch control section 11 enables the output terminal o1 of the switch 14 to provide the horizontal dipole antenna of the antenna 10 The element provides a polarization switching signal PWSW. On the contrary, when the reader/writer main body 1a transmits the polarization switching signal PWSW specifying the vertical polarization to the switch control section 11, the switch control section 11 enables the output terminal o2 of the switch 14 to provide the vertical polarization of the antenna 10. The polar antenna element provides the polarization switching signal PWSW.

Therefore, in the embodiment shown in FIG. 6, it is possible to switch the polarization direction of the antenna 10 to be horizontal or vertical based on the polarization switching signal PWSW from the reader/writer main body 1a, and it is also possible only to The antenna 10 is constituted by the structure shown.

Figure 7 is a conceptual block diagram of an embodiment of a tag 2a (2b). The tag 2 a ( 2 b ) is composed of an antenna unit 30 and an LSI chip 31 . As an example, the antenna section 30 is constituted by a patch antenna, and has an inductance L as an equivalent circuit. The LSI chip 31 has a capacitor element C at the interface.

The LSI chip 31 and the interface portion of the antenna portion 30 are connected in parallel. Therefore, if the inductance L of the antenna part 30 and the capacitive component C of the interface part have a resonance relationship, the continuous wave CW transmitted by the reader/writer can be received, and the continuous wave CW can be supplied to the LSI with the maximum power The control unit CONT of the chip 31 .

The control section CONT of the LSI chip 31 modulates the continuous wave CW according to the supplied power by means of the characteristic information including identification information related to the commodity prepared with the label attachment, thereby making it possible to adjust the polarizing direction along a fixed polarization direction (for example, the horizontal direction) ) transmits the resulting modulated continuous wave CW from the antenna section 30 to the reader/writer.

Now, an operation flow according to an embodiment of the present invention based on the premise of such a reader/writer and tag construction will be described with reference to FIG. 8 .

In FIG. 8, an initial channel (frequency band) is first set in the reader/writer main body 1a (step S1), and then an initial antenna polarization is set (step S11). Now, as described above in the embodiment of FIG. 5, when the initial antenna polarization is right-handed circular polarization, the switch control section 11 enables the output terminal o1 of the switch 14, and makes the 0° phase-shifted output of the hybrid circuit 12 terminal and the input terminal I1 of the switch 15 are valid. Similarly, the switch control unit 11 enables the 90° phase shift output terminal of the hybrid circuit 12 and the input terminal I1 of the switch 16 .

In the case of this setting, the level of the carrier wave received by the antenna 10 is measured as an interference signal (step S2). If the interference signal level is greater than the threshold (step S3, No), the channel cannot be used.

Then, the polarization direction (left-handed circular polarization direction in this case) for which no measurement has been performed is judged without changing the channel (step S12), and the antenna polarization is switched to the left-handed circular polarization direction (step S13). Therefore, the processing after the interference level measurement (step S2 ) is continued again in the switched polarization direction.

Therefore, the same is true for the measurement of all polarizations, and if the level of the interference signal is greater than the threshold value (step S3, No), the interference level of other channels is made the measurement target. In other words, if it is judged that the measurement of all the channels has been performed, and if there is a channel for which the measurement has not been performed (step S4, No), then the channels are switched sequentially (step S5), and the process returns to the same interference level measurement (step S2).

In the case that the measurement to all channels has been performed (step S4, Yes), the waiting time is randomly set (step S6), and after the set waiting time has passed, the process returns to the initial channel setting again (step S1 ), and repeat the above process.

In addition, if the interference level is equal to or less than the threshold in the interference level measurement (step S2) (step S3, YES), the use channel and the antenna polarization direction whose interference level is equal to or less than the threshold are determined (step S7), and A command signal is sent (step S8).

Here, FIG. 9 shows a command signal transmitted by the antenna 1b of the reader/writer #1 (#2) and a response signal from the tag 2a (2b).

As shown in FIG. 9A , readers/writers #1 and #2 modulate the continuous wave CW with a frame signal using the determined use channel and antenna polarization direction (for example, right-handed circular polarization). It has a command signal and a preamble signal Pre and a check signal CRC respectively located before and after the command signal.

As shown in FIG. 9B, when the tags 2a and 2b receive command signals from the corresponding readers/writers #1 and #2, by using the feature information and identification information of the tagged item as tag information, by The frame signal also having the preamble signal Pre and the check signal CRC located before and after it modulates the continuous wave CW, thereby reflecting the continuous wave CW to the corresponding readers/writers #1 and #2.

Readers/writers #1 and #2 receive the reply signal and end communication (step S10).

FIG. 10 shows the relationship between channels Ch1 to Ch4 and polarization directions 1 to n determined using the flow of the embodiment of FIG. 8 . In FIG. 10, hatched areas indicate the case where the interference signal level is equal to or less than the threshold and the corresponding channel (frequency bandwidth) and polarization can be used in the reader/writer.

In addition, although the configuration in which the reader/writer has one antenna 1b and switches the polarization direction of the antenna is exemplified in the above description, the application of the present invention is not limited to or limited by this configuration . In other words, as shown in FIG. 11 , a structure is also possible in which a plurality of antennas 101b to 10nb to which respective specific polarization directions are set are connected to the reader/writer main body portion 1a, and selection control is performed so that A specific antenna corresponding to the polarization set by the reader/writer main body portion 1a is effective.

Furthermore, in FIG. 11, in terms of being able to variably control the polarization direction of each of the plurality of antennas 101b to 10nb as shown in FIG. 5 or FIG. communication channel.

Industrial availability

As described above, while in the conventional method, the configuration searches for available channels only with fixed polarization, according to the present invention, a state in which an interfering signal level is equal to or less than a threshold is searched for using a combination of channels and polarization directions. According to the features of this configuration, it is possible to provide an RFID system that makes the probability of detecting an idle channel higher and reduces the influence of interference between readers/writers. Therefore, the present invention greatly contributes to industry.

This application is a continuation of International Application PCT/JP2005/001319 filed on January 31, 2005.

Claims (16)

1. rfid system, this rfid system comprises:

Reader/writer, it has reader portion and can carry out the antenna that polarization switches, and it sends continuous carrier; With

Label, it uses label information that described continuous carrier is modulated, and answer signal is sent it back described reader/writer,

Wherein, the level of the interference signal that is received is judged by described reader portion, determine that the described level of described interference signal is equal to or less than the channel and the polarization direction of threshold value, and receive described answer signal from described label by determined channel and polarization direction.

2. rfid system according to claim 1, wherein,

The described antenna that can carry out the polarization switching can switch between right-hand circular polarization and Left-hand circular polarization; And

The interference signal that will receive detects in described reader portion under the situation of right-hand circular polarization or Left-hand circular polarization level is equal to or less than the channel of described threshold value.

3. rfid system according to claim 1, wherein,

The described antenna that can carry out the polarization switching can switch between horizontal polarization and vertical polarization; And

The interference signal that will receive detects in described reader portion under the situation of horizontal polarization or vertical polarization level is equal to or less than the channel of described threshold value.

4. rfid system, this rfid system comprises:

Reader/writer, a plurality of antennas that it has reader portion and has the feature polarization separately, and it sends continuous carrier; With

Label, it uses label information that described continuous carrier is modulated, and answer signal is sent it back described reader/writer, wherein,

The level of the interference signal that will be received by each antenna in described a plurality of antennas is judged by described reader portion at each channel in a plurality of channels, determine that the level of the described interference signal judged is equal to or less than the channel and the antenna of threshold value, and receive described answer signal by determined antenna from described label via determined channel.

5. according to claim 1 or 4 described rfid systems, wherein, described channel is each band that is divided into the frequency band of a plurality of bandwidth.

6. according to claim 1 or 4 described rfid systems, wherein, described label is made of paster antenna and LSI, and described LSI and described paster antenna are connected in parallel and have interface portion, and described interface portion has the capacitance component with Inductive component generation resonance.

7. the carrier sensing method of a rfid system, described rfid system has: reader/writer, it has reader portion and can carry out the antenna that polarization switches, and it sends continuous carrier; And label, it uses label information that described continuous carrier is modulated, and answer signal is sent it back described reader/writer,

Said method comprising the steps of: in described reader/writer,

All polarizations that can switch at described antenna utilize particular channel sequentially to measure interference signal level;

When the interference signal level that will measure during,, described particular channel measures described interference signal level by being switched to other channels greater than threshold value;

Determine that the described interference signal level that records does not so surpass the channel and the polarization direction of described threshold value; And

Set on determined channel and receive described answer signal from described label with determined day linear polarization.

8. the carrier sensing method of rfid system according to claim 7, wherein,

The described antenna that can carry out the polarization switching can switch between right-hand circular polarization and Left-hand circular polarization; And

The interference signal that will receive detects in described reader portion under the situation of right-hand circular polarization or Left-hand circular polarization level is equal to or less than the channel of described threshold value.

9. the carrier sensing method of rfid system according to claim 7, wherein,

The described antenna that can carry out the polarization switching can switch between horizontal polarization and vertical polarization; And

The interference signal that will receive detects in described reader portion under the situation of horizontal polarization or vertical polarization level is equal to or less than the channel of described threshold value.

10. the carrier sensing method of a rfid system, described rfid system has: reader/writer, it has reader portion and a plurality of antennas that are respectively arranged with different polarization directions, and it sends continuous carrier; And label, it uses label information that described continuous carrier is modulated, and answer signal is sent it back described reader/writer,

Said method comprising the steps of: in described reader/writer,

At each polarization of described a plurality of antennas, utilize particular channel sequentially to measure interference signal level;

When the interference signal level that will measure during,, described particular channel measures described interference signal level by being switched to other channels greater than threshold value;

Determine to be set to the described interference signal level that records like this and do not surpass the channel of described threshold value and the antenna of polarization direction; And

Set for and utilize determined channel and antenna to receive described answer signal from described label.

11. according to claim 7 or 10 described rfid systems, wherein, described channel is each band that is divided into the frequency band of a plurality of bandwidth.

12. according to claim 7 or 10 described rfid systems, wherein, described label is made of paster antenna and LSI, described LSI and described paster antenna are connected in parallel and have interface portion, and described interface portion has the capacitance component with Inductive component generation resonance.

13. the reader/writer of a rfid system, described reader/writer have reader portion and can carry out the antenna that polarization switches, and send continuous carrier to label, wherein,

Judge the level of the interference signal that is received, and determine that the described level of described interference signal is equal to or less than the channel and the polarization direction of the described antenna of threshold value, and

Receive answer signal on determined channel and with determined polarization direction, this answer signal utilizes label information that described continuous carrier is modulated and produced, and is sent by described label.

14. reader/writer according to claim 13, wherein,

The described antenna that can carry out the polarization switching can switch between right-hand circular polarization and Left-hand circular polarization; And

The interference signal that will receive detects in described reader portion under the situation of right-hand circular polarization or Left-hand circular polarization level is equal to or less than the channel of described threshold value.

15. reader/writer according to claim 13, wherein,

The described antenna that can carry out the polarization switching can switch between horizontal polarization and vertical polarization; And

The interference signal that will receive detects in described reader portion under the situation of horizontal polarization or vertical polarization level is equal to or less than the channel of described threshold value.

16. the reader/writer of a rfid system, described reader/writer have reader portion and have a plurality of antennas of feature polarization separately, and send continuous carrier to label, wherein,

The level of the interference signal that will be received by each antenna in described a plurality of antennas is judged by described reader portion at each channel in a plurality of channels, determine that the level of the described interference signal judged is equal to or less than the channel and the antenna of threshold value, and receive answer signal by determined antenna via determined channel, this answer signal utilizes label information that described continuous carrier is modulated and produced, and is sent by described label.

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