JP2008060932A - Rf tag reader and rf tag system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an RF tag reader and RF tag system which can surely prevent interference under the listen before talk (LBT) system. <P>SOLUTION: Before transmitting a carrier, reader-writers RW1 and RW2 detect the carrier for a carrier detection time Tc or longer for each channel. Only when a contiguous channel comprising a channel used for supplying power to an RF tag, a channel used for transmitting signals to the RF tag, and a channel used for receiving signals from the RF tag can be secured; the reader-writer RW1 and RW2 start transmission of the carrier. During transmission of the carrier, a band occupation signal covering all the frequency bands of the channels which the reader-writers use for communication with the RF tag is transmitted at time intervals (T0 and T1) shorter than the carrier detection time Tc for a time (T2) which other reader-writers can detect the carrier or longer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an RF tag reader and an RF tag system that supply power to an RF tag by transmitting a carrier and communicate with the RF tag.

  In this type of RF tag system, when a plurality of reader / writers are installed and used within a range where radio waves can reach each other, the radio waves transmitted from the reader / writers interfere with each other and cannot communicate with the RF tag. Therefore, the LBT (Listen Before Talk) system is adopted in Japan as a technique for preventing interference. Each reader / writer detects a carrier for a predetermined carrier detection time for a predetermined frequency channel (hereinafter referred to as a channel) for a predetermined carrier detection time before transmitting the carrier, and performs communication on an empty channel.

Such carrier detection (carrier sense) before communication is also disclosed in Patent Documents 1 and 2. In the empty channel detection method described in Patent Document 1, a transmitting station side modulates and transmits a composite signal of voice information and a channel number signal indicating the number of a channel in use, and a receiving station side When the carrier is detected by sequentially scanning the reception channel, the audio information in the demodulated signal and the channel number signal are separated. In addition, the radio control signal transmission method described in Patent Document 2 monitors the radio frequency for control and the radio wave status of all slots that can be used in advance when transmitting a radio wave for control between a base station and a mobile station. Transmission is started by selecting an unused radio wave from among the monitored radio waves.
JP-A-5-110522 JP-A-8-256373

  After detecting the carrier, the reader / writer transmits an unmodulated carrier for power supply on an empty channel, and after the RF tag that has received power starts operating, modulates the carrier by ASK modulation or the like to perform data communication. Do. When the carrier is modulated, the frequency band is widened. In the RF tag system, the frequency band used for power supply from the reader / writer to the RF tag is different from the frequency band used for communication between the reader / writer and the RF tag. Become.

  FIG. 10 shows carrier transmission timings of two reader / writers RW1 and RW2 arranged close to each other. When the reader / writers RW1 and RW2 communicate with the RF tag, the reader / writers RW1 and RW2 continue to transmit an unmodulated carrier for supplying power, and perform data communication with the RF tag only when necessary during that time. For example, when the reader / writer RW1 is only supplying power to the RF tag and is not communicating with the RF tag, the other reader / writer RW2 disposed in the vicinity of the reader / writer RW1 receives power by carrier detection processing. The supply frequency band (ch3) is detected, but the communication frequency bands (ch1, ch2, ch4, ch5) cannot be detected. As a result, the frequency bands for communication of the reader / writers RW1 and RW2 (ch4 and ch5 in FIG. 10) may overlap even though the carrier detection processing is executed, and the reader / writers RW1 and RW2 communicate with the RF tag. There is a risk of interference.

  To cope with this, a configuration is possible in which each reader / writer transmits a channel in use with each other using the empty channel detection method described in Patent Document 1, but the synthesis of audio information and a channel number signal is possible. A circuit and a separation circuit are required, which causes problems such as circuit complexity and increased processing time. In recent years, a sharing technique for preventing mutual interference between reader / writers has been introduced into the RF tag system, and it is necessary to take measures to prevent interference under the technical requirements (technical specifications).

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an RF tag reader and an RF tag system that can reliably prevent interference under the LBT system.

  According to the means described in claim 1, the RF tag reader has each of a frequency band used for power supply to the RF tag, a frequency band used for signal transmission to the RF tag, and a frequency band used for signal reception from the RF tag. Carrier transmission is started when no carrier is detected for a predetermined carrier detection time or more for all the channels corresponding to. The RF tag reader then transmits a band occupation signal including all frequency bands used for communication with the RF tag at intervals shorter than the carrier detection time for the period until the carrier transmission is stopped after that. Send more than detectable time.

  As a result, other RF tag readers detect carriers in all channels corresponding to the frequency band of the band-occupied signal in the carrier detection process before transmission of their own. Start sending. Therefore, each RF tag reader can keep ensuring that all the channels corresponding to the most widened frequency band that is planned to be used for communication with the RF tag are not used by other RF tag readers, thereby preventing interference. Can do. In addition, the carrier detection of this means detects a relatively large level band-occupying signal transmitted by the RF tag reader, not a minute level response signal transmitted by the RF tag, so that the presence of the carrier can be reliably detected. Can do.

  According to the means described in claim 2, since a dummy signal not involved in communication with the RF tag is transmitted as a band occupied signal at an interval shorter (eg, constant) than the carrier detection time, transmission of the band occupied signal is performed. Control can be simplified.

  According to the third aspect of the present invention, since the carrier is modulated with random data to generate a dummy signal (band-occupied signal), the dummy signal includes the frequency band for power supply and the frequency for signal transmission. Includes all bands and frequency bands for signal reception. Also, no special data pattern preparation is required.

  According to the means described in claim 4, since the communication with the RF tag is performed in the transmission gap of the dummy signal, the dummy signal and the communication signal do not overlap with each other, and the communication with the RF tag is not hindered.

  According to the means described in claim 5, when the frequency band of the transmission signal to the RF tag includes all the frequency bands used in communication with the RF tag, the band occupation including the transmission signal to the RF tag is included. Since the digitized signal is transmitted at an interval shorter than the carrier detection time, the transmission frequency of the dummy signal not involved in communication with the RF tag can be reduced as much as possible. In addition, since communication with the RF tag is preferentially performed, it is possible to prevent the transmission of the communication signal from being delayed due to the transmission of the dummy signal as much as possible.

  According to the means described in claim 6, the RF tag reader performs carrier detection processing for a predetermined channel during carrier transmission, and when communicating with the RF tag, the RF tag reader uses each frequency band used for communication with the RF tag. Based on the detection result of the carrier for the corresponding channel, communication with the RF tag is performed using the maximum continuous channel in the channel where no carrier is detected. That is, if the above-mentioned band occupation signal is transmitted, the maximum frequency band to be used can be secured, but even if another RF tag reader uses a part of it, the remaining empty channel has the maximum frequency band. Thus, communication with the RF tag can be performed without interference at a communication speed as fast as possible.

  According to the means described in claim 7, by configuring an RF tag system from each of the above-described RF tag readers and an RF tag that operates by receiving power supply from the RF tag reader, it is ensured under the LBT system. Interference can be prevented.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 2 is a block diagram showing an electrical configuration of a reader / writer that performs non-contact communication with an RF tag. The reader / writer includes a control unit 1, a transmission circuit 2, a transmission antenna 3, a reception antenna 4, a reception circuit 5, a frequency channel detection unit 6, and the like that are configured by a microcomputer.

  The transmission circuit 2 includes an oscillator 7 that generates a carrier signal (carrier signal) corresponding to a transmission frequency commanded from the control unit 1, a modulation unit 8 that modulates the carrier signal according to transmission data output from the control unit 1, And an amplifier 9 that amplifies the modulated signal and transmits it as a radio wave signal via the transmission antenna 3. The reception circuit 5 includes a demodulation unit 10 that demodulates a signal received via the reception antenna 4 and a decoding unit 11 that decodes reception data from the demodulated reception signal.

  The frequency channel detection unit 6 receives a signal received via the receiving antenna 4, detects the presence / absence of a carrier (carrier wave signal) in each frequency channel (hereinafter referred to as a channel), and outputs it to the control unit 1 Thus, the carrier detection means is configured together with the control unit 1. The control unit 1 (corresponding to a communication control unit) communicates with the RF tag while supplying power to the RF tag, and writes data to and reads data from the RF tag. In addition, the control unit 1 includes a memory 12 as a storage unit, and stores in the memory 12 carrier detection presence / absence information of each channel input from the frequency channel detection unit 6.

Next, the operation of the present embodiment will be described with reference to FIGS. 1 and 3 to 6.
FIG. 3 shows a configuration example of an RF tag system in which the reader / writers RW1, RW2, and RW3 having the above-described configuration are arranged close to each other and communicate with the RF tags TAG1 to TAG4, respectively. A range indicated by a broken line is a range in which the transmission radio wave (carrier) of the reader / writer RW1 can be detected, and indicates a range in which radio wave interference occurs between the reader / writers RW2 and RW3 arranged inside the range. A range indicated by a solid line indicates a range in which communication and power supply can be performed from the reader / writer RW1 to the RF tag. In the arrangement shown in FIG. 3, the reader / writer RW1 can communicate and supply power to the RF tags TAG1 and TAG2.

  FIG. 1 shows carrier transmission timings of RW1 and RW2 among reader / writers RW1 to RW3, and FIG. 4 shows DSB frequency channels used in this RF tag system. The vertical axis in FIG. 4 represents the signal level of the transmission radio wave. Channels that can be used for communication are ch1 to ch11, and the channel width (frequency band) used by the reader / writers RW1 to RW3 to supply power to the RF tag is 1, as shown in FIG.

  Further, the channel width (frequency band) used for signal transmission of commands and data from the reader / writers RW1 to RW3 to the RF tags TAG1 to TAG4 is 3, as shown in FIG. 4B, and the RF tags TAG1 to TAG4. As shown in FIG. 4C, the channel width (frequency band) used for signal reception in response to IDs and data from the reader / writers RW1 to RW3 is 5 as shown in FIG. Therefore, the channel width (frequency band) necessary for communication between the reader / writers RW1 to RW3 and the RF tags TAG1 to TAG4 is 5, as shown in FIG. However, this is an example, and the channel width (frequency band) used for signal transmission / reception may be appropriately set according to the communication speed. In general, a higher channel speed requires a wider channel width.

  The reader / writers RW1 to RW3 detect the presence / absence of carriers for ch1 to ch11 for a predetermined carrier detection time Tc or longer before transmitting the carriers. FIG. 5 is a flowchart showing the contents of the carrier transmission start process executed by the control unit 1 before carrier transmission. When communication with the RF tag is required, the control unit 1 inputs the detection result of the carrier of each channel from the frequency channel detection unit 6 at least during the carrier detection time Tc and stores it in the memory 12 (step S1, S2). In this case, each channel may be detected in order, or a plurality of channels may be detected collectively.

  When the carrier detection time Tc elapses (step S2; YES), the process proceeds to step S3, and the number of channels in which carriers are detected is subtracted from the usable channel width (11 channels in the present embodiment) to continuously exist. Calculate the channel width. Then, the process proceeds to step S4, and it is determined whether or not a channel width necessary for communication can be secured in an empty channel. The channel width necessary for communication refers to the channel width including the channel used for power supply, the channel used for signal transmission, and the channel used for signal reception as described above (in this embodiment, as shown in FIG. 4D). 5 channels).

  If the channel width necessary for communication can be secured, a transmission frequency is set in step S5, and the frequency is instructed to the oscillator 7 in step S6 to start carrier transmission. On the other hand, when the channel width necessary for communication cannot be secured, the carrier transmission start process is terminated without executing steps S5 and S6 (that is, without performing carrier transmission).

  The reader / writer RW1 shown in FIG. 1 can secure a channel width (ch1 to ch5) necessary for communication in the carrier transmission start process, and therefore starts carrier transmission using one of them, ch3. To do. As shown in FIG. 3, the RF tags TAG1 and TAG2 are operable by receiving power supplied from the unmodulated carrier. The reader / writer RW1 transmits a band occupation signal after the start of carrier transmission and before the time T0 (<carrier detection time Tc) elapses. The band occupying signal is a signal that includes all frequency bands (ch1 to ch5 shown in FIG. 4D) necessary for communication with the RF tag, and is a dummy signal that does not participate in communication with the RF tag. is there. The transmission time T2 of the band occupation signal is set to be longer than the time during which the other reader / writers RW2 and RW3 can detect the presence of the carrier.

  FIG. 6 shows a waveform example of this band occupation signal. FIG. 6A is a dummy signal generated by combining waveforms having different frequency components, and FIG. 6B is a dummy signal generated using random data as transmission data by Manchester code. Among these, according to the generation method shown in FIG. 6B, it is only necessary to use the data determined by the random number as the transmission data, and a dedicated band occupation signal generation circuit is not required.

  The reader / writer RW1 continues to transmit the band occupation signal every time T1 shorter than the carrier detection time Tc after the carrier transmission is started and after the band occupation signal is transmitted for the first time until the carrier transmission is stopped. . As described above, the transmission time T2 of the band occupation signal is longer than the time during which the other reader / writers RW2 and RW3 can detect the presence of the carrier. As a result, during the carrier transmission of the reader / writer RW1, if the other reader / writers RW2 and RW3 execute the carrier transmission start process in order to start the carrier transmission, the reader / writer RW1 must always be in the carrier detection time Tc. Band-occupied signals (ch1 to ch5) to be transmitted are detected.

  For example, since the reader / writer RW2 shown in FIG. 1 detects carriers in all of ch1 to ch5 during the carrier detection time Tc, the channel width required for communication except for ch1 to ch5 is set in step S4 shown in FIG. Determine whether it can be secured. In this example, since ch6 to ch11 are empty channels, the reader / writer RW2 sets ch7 to ch11 as a transmission frequency necessary for communication, and instructs the oscillator 7 to set the frequency of ch9 to start carrier transmission. .

  Similarly to the reader / writer RW1, the reader / writer RW2 transmits a band occupation signal before the time T0 (<Tc) elapses after the start of carrier transmission, and thereafter the time T1 (<Tc ) A band occupation signal is transmitted every time. As a result, the reader / writers RW1 and RW2 (and RW3) can detect each other's channels used by each other, and the channel width necessary for communication is ensured for channels other than the channel from which the carrier is detected, causing interference. Nothing will happen.

  As described above, the reader / writer used in the RF tag system of the present embodiment detects the carrier for each channel for the carrier detection time Tc or more before transmitting the carrier, and uses the channel RF for power supply to the RF tag. An LBT (Listen Before Talk) system that starts carrier transmission when a continuous channel composed of a channel used for signal transmission to the tag and a channel used for signal reception from the RF tag can be secured is adopted. During carrier transmission, a band occupation signal including all the frequency bands of the channel used by the reader / writer for communication with the RF tag is detected by the other reader / writer at intervals shorter than the carrier detection time Tc. Send more than possible time.

  As a result, other reader / writers within the radio wave interference range always detect the band occupation signal transmitted by the reader / writer that started transmission of the carrier before detecting the carrier before transmission. Avoid carrier transmission. Accordingly, the reader / writer can keep ensuring that all channels corresponding to the frequency band used for communication with the RF tag are not used by other reader / writers, and reliably prevents interference under the LBT system. Can do.

  The reader / writer detects a relatively large level band-occupying signal transmitted from another reader / writer, not a minute level response signal transmitted from the RF tag, so that the presence of the carrier can be reliably detected. In addition, since the reader / writer communicates with the RF tag in the transmission gap of the band occupation signal, the band occupation signal and the communication signal do not overlap with each other, and communication with the RF tag is not hindered.

(Second Embodiment)
FIG. 7 is a flowchart of the carrier transmission start process showing the second embodiment of the present invention, in which the same processing steps as those in FIG. 5 are given the same step numbers. This embodiment has the same configuration as that of the first embodiment described above except for this carrier transmission start process.

  When the free channel width is calculated in step S3, the control unit 1 of the reader / writer proceeds to step S7, and obtains communication conditions that allow communication with the calculated free channel width. For example, even if the planned communication speed cannot be obtained with the calculated free channel width, if the RF tag system does not cause any problems even if the communication speed is reduced, the communication speed that can be communicated with the free channel width is communicated. The conditions are set (steps S8 and S9), the transmission frequency is set, and carrier transmission is started (steps S5 and S6). However, if there is no communication condition that allows communication with the calculated available channel width, such as an RF tag system that cannot reduce the communication speed, steps S9, S5, and S6 are not executed (that is, carrier transmission is performed). The carrier transmission start process is terminated. According to the present embodiment, it is possible to realize communication that effectively uses an empty channel.

(Third embodiment)
Next, a third embodiment of the present invention will be described with reference to FIG.
FIG. 8 shows carrier transmission timings of the reader / writers RW1 and RW2 in the same RF tag system as in FIG. When the frequency band of the transmission signal to the RF tag includes all the frequency bands of the channels used in communication with the RF tag, the reader / writer of the present embodiment converts the transmission signal to the RF tag to the band occupation signal. Considering it part, the band occupation signal is transmitted at an interval shorter than the carrier detection time Tc.

  In the case shown in FIG. 8, the reader / writer RW1 performs read / write communication with respect to the RF tag using all the secured ch1 to ch5. Therefore, every time T1 (<Tc) including this transmission signal is performed. The band occupation signal is transmitted. Similarly, the reader / writer RW2 also performs read / write communication with respect to the RF tag using all of the reserved ch7 to ch11, so that the band is occupied every time T1 (<Tc) including this transmission signal. A signal is being transmitted.

  According to the present embodiment, since the transmission signal to the RF tag can be effectively used as part of the band occupation signal, the transmission frequency of the dummy band occupation signal not involved in communication can be reduced as much as possible. it can. In addition, since communication with the RF tag can be preferentially performed, it is possible to prevent the transmission of the communication signal from being delayed due to the transmission of the dummy band occupation signal as much as possible. Also according to the present embodiment, it is possible to reliably prevent interference under the LBT method as in the first embodiment.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described with reference to FIG.
FIG. 9 shows carrier transmission timings of the reader / writers RW1 and RW2 in the same RF tag system as in FIG. The reader / writer RW2 has the same configuration as that of the first embodiment. Similarly to the reader / writer RW2, the reader / writer RW1 adopts the LBT method, and during carrier transmission, a band occupation signal including all frequency bands of channels used for communication with the RF tag is transmitted at intervals shorter than the carrier detection time Tc. Send. Further, the reader / writer RW1 inputs the carrier detection result of each channel from the frequency channel detection unit 6 even during carrier transmission, executes carrier detection processing, and writes the result into the memory 12. .

  In the RF tag system, as described above, interference does not occur originally, but the carrier detection at the carrier detection time Tc is insufficient due to, for example, the reception electric field strength of the reader / writer RW2 temporarily decreasing. In some cases, the channels used for communication may rarely overlap. FIG. 9 shows a case where the reader / writer RW2 sets ch5 to ch9 as the channel width necessary for communication and starts communication, so that the reader / writer RW1 and RW2 overlap ch5.

  Since the reader / writer RW1 always performs carrier detection processing, the control unit 1 secures ch1 to ch5 based on the latest carrier detection result stored in the memory 12 when communicating with the RF tag. Whether or not communication is possible is determined. In the case shown in FIG. 9, since the carrier is detected at ch5, the necessary channel width (within the empty channel region at that time and within the maximum continuous channel range in which no carrier is detected) ch2 to ch4) are set to communicate with the RF tag.

  According to this configuration, the communication speed of the reader / writer RW1 is lower than the scheduled communication speed, but communication with the RF tag can be performed at the highest possible communication speed using the largest continuous channel in the empty channel without interference. It can be carried out. In addition, the reader / writer RW1 can suppress the time during which the communication speed is lowered as short as possible by using again a channel in which no carrier is detected for a predetermined determination time T3 as an empty channel.

(Other embodiments)
The present invention is not limited to the embodiments described above and shown in the drawings, and can be modified or expanded as follows, for example.
The band occupation signal may be generated using any method as long as the signal includes all the frequency bands used in communication with the RF tag.
In each embodiment, the reader / writer of the RF tag has been described as an example, but the present invention can be similarly applied to an RF tag reader.
The transmission antenna 3 and the reception antenna 4 may be shared (integrated).

The figure which is the 1st Embodiment of this invention and shows the carrier transmission timing of a reader / writer Block diagram showing electrical configuration of reader / writer The figure which shows the structural example of RF tag system The figure which shows the frequency channel and signal level which are used in the RF tag system Flow chart showing carrier transmission start processing Waveform diagram of band-occupied signal FIG. 5 equivalent view showing the second embodiment of the present invention FIG. 1 equivalent view showing a third embodiment of the present invention FIG. 1 equivalent view showing a fourth embodiment of the present invention 1 equivalent diagram showing the prior art

Explanation of symbols

  In the drawings, 1 is a control unit (communication control unit, carrier detection unit), 6 is a frequency channel detection unit (carrier detection unit), RW1 to RW3 are reader / writers (RF tag readers), and TAG1 to TAG4 are RF tags.

Claims (7)

In an RF tag reader that supplies power to an RF tag by transmitting a carrier and communicates with the RF tag,
Carrier detection means for detecting a carrier for a predetermined channel before transmitting the carrier;
Channels corresponding to frequency bands used for power supply to the RF tag, frequency bands used for signal transmission to the RF tag, and frequency bands used for signal reception from the RF tag in communication with the RF tag The carrier detection means starts the carrier transmission when no carrier is detected for a predetermined carrier detection time or more, and then stops the carrier transmission at an interval shorter than the carrier detection time. An RF tag reader, comprising: a communication control means for transmitting a band occupation signal including all the frequency bands used in communication with an RF tag for a time at which another RF tag reader can detect a carrier.   The RF tag reader according to claim 1, wherein the communication control unit transmits a dummy signal not involved in communication with the RF tag as the band occupation signal.   3. The RF tag reader according to claim 2, wherein the communication control means generates the dummy signal by modulating a carrier with random data.   4. The RF tag reader according to claim 2, wherein the communication control means performs communication with the RF tag in a transmission gap of the dummy signal.   When the frequency band of the transmission signal to the RF tag includes all the frequency bands used in communication with the RF tag, the communication control means includes the transmission signal to the RF tag and occupies the band. The RF tag reader according to claim 1, wherein the signal is transmitted at an interval shorter than the carrier detection time. The carrier detection means is configured to perform carrier detection processing for a predetermined channel even during carrier transmission,
The communication control means, when communicating with the RF tag during carrier transmission, based on the carrier detection result by the carrier detection means for the channel corresponding to each frequency band used in communication with the RF tag, The RF tag reader according to any one of claims 1 to 5, wherein communication with the RF tag is performed using a maximum continuous channel within the channel in which no carrier is detected. 7. An RF tag system comprising: the RF tag reader according to claim 1; and an RF tag that operates by receiving power from the RF tag reader.

Images