WO2006008797A1 - Wireless communication system, wireless communication method and rf tag reader - Google Patents

Abstract

An RF tag reader capable of reducing mutual interference with another RF tag reader. An RF tag reader comprises transmission means for wireless transmitting a control signal to an RF tag; reception means for wireless receiving a data signal from the RF tag; and status notifying means (330) for wire transmitting, to anther RF tag reader, a reception busy signal (Rx busy) that is in one of a plurality of statuses. The status notifying means (330) wire transmits the reception busy signal of a first status (H level) to the other RF tag reader in response to a commencement of receiving the data signal, and wire transmits the reception busy signal of a second status (L level) to the other RF tag reader in response to a completion of receiving the data signal. The transmission means commences a wireless transmission of a control signal in response to a status change of plural reception busy signals.

Description

 Specification

 Wireless communication system, wireless communication method, and RF tag reader

 Technical field

 The present invention belongs to the technical field of wireless communication between an RF tag and an RF tag reader, and particularly relates to a wireless communication system, a wireless communication method, and an RF tag reader.

 Background art

 In this type of technical field, an RF tag system that uses an RF tag and a reader or writer device (hereinafter referred to as “RF tag reader”) that reads information from or writes information to the RF tag. Is attracting attention. For example, data such as ID is written on the RF tag.

 The RF tag is sometimes referred to as an RFID tag, a wireless tag, an IC tag, or the like. There are various uses for RF tags. As an example, when an article or product with an RF tag attached is successively carried on a belt conveyor, the article can be identified by reading a radio signal from the RF tag with an RF tag reader. .

 [0003] RF tags are generally classified into an active type (active type) and a passive type (passive type). Active RF tags can provide their own power, and the device configuration on the RF tag reader side can be simplified. The latter cannot prepare its own power, and operations such as transmission of HD information are performed by receiving energy from the outside. The passive type is particularly promising from the viewpoint of making RF tags inexpensive. A conventional RF tag system is described in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2003-283367).

 Disclosure of the invention

 Problems to be solved by the invention

[0004] By the way, the RF tag reader power The control signal to the RF tag is transmitted with larger power than the data signal from the RF tag to the RF tag reader. In the passive type in particular, the transmission of the control signal also serves as the power supply, so the control signal is transmitted with a large amount of power. Therefore, when a plurality of RF tag readers are used in close proximity, reception of weak radio signals from the RF tag may be hindered. For example, when a certain RF tag reader receives a radio signal from an RF tag, a control signal from another nearby RF tag reader becomes an interference wave. [0005] One technique for avoiding such interference is to set a large number of hopping patterns and hop various frequencies. This method is mainly used in the United States. However, setting a large number of hopping patterns requires a wide frequency band. Therefore, such a hopping method is not always effective when only a relatively narrow band can be used as in Japan and Europe.

 [0006] Another method for avoiding interference between a plurality of RF tag readers is to perform time-sharing control by determining the time slot for each RF tag reader to operate. In this method, the RF tag reader and RF tag are inactive except for the time slots assigned to them, which is inefficient from the viewpoint of increasing the overall system throughput and the number of RF tags processed.

 [0007] As yet another method, it is conceivable to electromagnetically shield areas close to individual RF tag readers or sharpen the directivity of control signals transmitted by the RF tag readers. However, due to the additional hardware (for example, shield plate) and processing related to directivity control, the hardware and software increase and become complicated, resulting in a problem of increasing costs.

 [0008] The invention described in Patent Document 1 is provided with a control terminal that performs overall control of a plurality of RF tag readers (reader / writers), synchronizes transmission / reception timings of the plurality of RF tag readers, and transmits signals from the RF tags. Trying to receive properly. However, if such a control terminal is provided, the system may be complicated. As the number of RF tag readers increases, the burden on the control terminal increases. Furthermore, this method requires adjustment of the control terminal each time an RF tag reader is added or deleted, and is not necessarily advantageous from the viewpoint of system expandability and flexibility.

 [0009] The present invention has been made in view of at least one of the above problems, and the problem is that a radio communication system, a radio communication method, and an RF that can reduce interference between RF tag readers. It is to provide a tag reader.

 Means for solving the problem

In the present invention, a wireless communication system having a plurality of RF tag readers connected to each other by wire is used. Each RF tag reader includes transmission means for wirelessly transmitting a control signal to the RF tag. Receiving means for wirelessly receiving a data signal from the RF tag; and first status notifying means for wiredly transmitting a reception busy signal in one of a plurality of states to another RF tag reader; Is provided. The first state notifying means wiredly transmits the reception busy signal in the first state to the other RF tag reader in response to the start of reception of the data signal, and in the second state in response to the completion of reception of the data signal. The received busy signal is wired to the other RF tag reader. The transmission means starts wireless transmission of the control signal in response to a plurality of reception busy signals changing state.

 The invention's effect

 [0011] According to the present invention, there is an effect that interference between RF tag readers can be reduced.

 Brief Description of Drawings

FIG. 1 shows an overall view of an RF tag system according to an embodiment of the present invention.

 FIG. 2 is a diagram showing a format of a control signal transmitted from the RF tag reader to the RF tag.

[Fig. 3] A detailed block diagram of the RF tag reader is shown.

 [Figure 4] A detailed block diagram of the RF tag is shown.

 FIG. 5 is a timing chart for explaining an operation according to an embodiment of the present invention.

 FIG. 6 is a partial block diagram of an RF tag reader according to an embodiment of the present invention.

 Explanation of symbols

 [0013] 10 RF tag; 12_1—3 RF tag reader; 14 local area network;

 21 Preamble part; 22 Command part; 23 Parameter part; 24 Data part; 25 CRC;

 302 Noffa; 304 Timing control unit; 306 Monitor unit; 308 Dummy insertion unit; 309 Modulator; 310 Finalore; 312 Mixer; 314 Oscillator; 316 Amplifier; 31 8 Duplexer; 320 Antenna; 322 Amplifier; Finale; 328 Demodulator; 330 Receive busy signal generator;

 41 Antenna; 42 Demodulator; 43 Modulator; 44 Logic part; 45 Memory; 46 Power generation part;

604 Timing control unit; 606 Monitor unit for transmission busy signal; 608 Transmission busy Signal generator

 BEST MODE FOR CARRYING OUT THE INVENTION

 [0014] In the RF tag reader according to one aspect of the present invention, the reception busy signal in the first state of the plurality of states is transmitted from the RF tag reader to another RF tag reader in response to the start of reception of the wireless data signal from the RF tag. Wired to. In response to the completion of reception of the wireless data signal from the RF tag, a reception busy signal in the second state among the plurality of states is wired from the RF tag reader to another RF tag reader. In response to the transition of multiple receive busy signals, wireless transmission of control signals to the RF tag is started.

 [0015] Since each RF tag reader monitors the reception busy signal with each other, when a plurality of RF tag readers have not received all RF tag reader power ¾F tag response signals, the control signals are simultaneously transmitted. Each can be transmitted wirelessly. Thereby, the response signal power of the RF tag can be effectively suppressed from being disturbed by the control signal from another RF tag reader.

 [0016] In one aspect of the present invention, the dummy bit is wirelessly transmitted following the transmission means power control signal of the RF tag reader. As a result, the point in time when the RF tag reader starts a response can be adjusted by the number of dummy bits.

 In one aspect of the present invention, the number of dummy bits to be transmitted is determined according to the difference between the length of the control signal and a predetermined maximum length. Thereby, the period between the start time of the control signal and the transmission completion time of the dummy bit can be set to a fixed period in the system. This aspect is preferable from the viewpoint of easily synchronizing the transmission periods of control signals by a plurality of RF tag readers.

[0018] According to one aspect of the present invention, a transmission unit that wirelessly transmits a control signal to an RF tag, a reception unit that wirelessly receives a data signal from the RF tag, and one of a plurality of states, An RF tag reader comprising state notification means for transmitting a transmission busy signal in the state of (1) to another RF tag reader by wire is used. The state notification means wiredly transmits a transmission busy signal in the first state to the other RF tag reader in response to the start of transmission of the control signal, and transmits a transmission busy signal in the second state in response to the completion of transmission of the control signal. Is wired to the other RF tag reader. The transmission means until a plurality of transmission busy signals transition states The control signal or dummy bit is transmitted wirelessly.

 [0019] Since each RF tag reader monitors the transmission busy signal with each other, the plurality of RF tag readers transmit the control signal to all the RF tag reader powers ¾F, and when the situation is reached, all at once. RF tag force can start to receive response signal. Thereby, it is possible to effectively suppress the response signal of the RF tag from being disturbed by the control signal from another RF tag reader. Furthermore, by monitoring the status of the transmission busy signal, it is possible to determine when all the RF tag readers have finished transmitting the control signal, so that the response of the RF tag can be quickly started. This mode is preferable from the viewpoint of shortening the response command period for transmitting the control signal as much as possible and improving the throughput of the system.

 [0020] The status notification means related to the received busy signal according to one aspect of the present invention and the status notification means related to the transmission busy signal according to one aspect of the present invention may be realized as separate elements or have both functions. It may be realized as one element. In addition, these elements may be realized by software, hardware, or a combination thereof, like other elements related to the present invention.

 Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same elements are denoted by the same reference numerals throughout the drawings.

 Example 1

 [0022] FIG. 1 shows an overall view of an RF tag system according to an embodiment of the present invention. In the figure, elements with reference numbers starting with “1” are the first elements that appear in FIG. 1 in principle. The system includes an RF tag 10, a plurality of RF tag readers 12-1-3, and a local area network (LAN) 14. A plurality of RF tag readers are connected to each other via a wire 16. For simplicity, the power depicted with one RF tag and three RF tag readers is arbitrary.

FIG. 2 is a diagram showing a schematic format of a control signal transmitted from the RF tag reader to the RF tag. As illustrated, the control signal includes a preamplifier unit 21, a command unit 22, a parameter unit 23, a data unit 24, and a CRC unit 25. The preamble part 21 includes a known signal for maintaining synchronization. The command section 22 includes information indicating the content of instructions to the RF tag such as “read” (read) and “write” (write). Top A typical example of a command is a “read” command that wirelessly transmits an ID number in an RF tag. The parameter unit 23 is set with parameters according to the command as required. The data portion 24 includes contents to be given to or written to the RF tag, and in the case of a “read” command, includes a memory address and the like. The CRC unit 25 includes bits for error detection by cyclic redundancy detection.

[0024] FIG. 3 shows a detailed block diagram of the RF tag reader 12-1. In the figure, elements with reference numbers that also begin with a “3” force are in principle the elements that appear first in FIG. The other RF tag readers 12-2 and 3 have the same configuration. The RF tag reader includes a buffer 302, a timing control unit 304, a monitor unit 306, a dummy guard unit 308, a modulator 309, a finalizer 310, a mixer 312 and an oscillator 314 in its wireless transmission path. , 曽 曽 width device 316, duplexer 318, and antenna 320. The RF tag reader has an amplifier 322, a mixer 324, a filter 326, a demodulator 328, and a reception busy signal generation unit 330 (constituting status notification means) in its radio reception path.

 The buffer 302 stores transmission contents (control signal as shown in FIG. 2) input from the LAN 14 side or created by itself. This transmission content is finally transmitted from the antenna 320.

 The timing control unit 304 outputs a control signal stored in the buffer 302 in response to an instruction from the monitor unit 306. If the length (number of bits or time) of the control signal is less than the maximum length of the control signal, the dummy insertion unit 308 is a dummy bit so that the dummy bit is transmitted following the control signal. Is added and output.

 The monitor unit 306 receives a reception busy signal (Rx busy). This reception busy signal is transmitted via wire 16 from another RF tag reader. The monitor unit 306 detects the state change of the received busy signal, and compares the state of the received busy signal generated by another RF tag reader with the time of the state change of the received busy signal generated by itself. Detect the latest point in time. In response to the detection, the timing control means 304 starts transmitting a control signal.

[0028] If the received busy signal is at a high level, for example, it means that the RF tag reader is receiving a radio signal from the RF tag. If the received busy signal is low, the RF tag reader Means that the radio signal from the RF tag is no longer received. The number of received busy signals and the signal level can be set arbitrarily according to the application. For example, the status of the received busy signal may be expressed by 1 bit representing “1” or “0”, or may be expressed using 2 or more bits. No radio signal is transmitted from any RF tag after all the received busy signals from all RF tag readers including itself and others have transitioned from the high level to the low level. Therefore, if the RF tag reader transmits a control signal in response to the state transition of all the received busy signals from the high level to the low level, interference with other RF tag readers can be avoided.

[0029] Modulator 309 modulates a control signal (transmission signal). The modulation method is, for example, amplitude modulation (ASK). Filter 310 band-limits the modulated transmission signal and provides it to mixer 312. The mixer 312 modulates the transmission signal output from the filter 310 using the carrier wave signal from the oscillator 314. The amplifier 316 appropriately amplifies the modulated transmission signal. The amplified transmission signal is wirelessly transmitted from a shared antenna 320 via a duplexer 318.

 In the reception path, the reception signal received via the antenna 320 and the duplexer 318 is input to the amplifier 322. In amplifier 322, the received signal is appropriately amplified and provided to mixer 324. The mixer 324 converts the amplified amplitude modulation signal into a signal demodulated by the carrier signal from the oscillator 314. Filter 326 removes the high frequency component and provides it to demodulator 328. The demodulator 328 demodulates the signal obtained from the filter 326 into data representing a desired ID number or the like. This data is given to the LAN 14 as received data (Rx data).

[0031] While the signal is output from the demodulator 328, the reception busy signal generator 330 outputs a reception busy signal in the first state (for example, high level). To other RF tag readers. The reception busy signal generation unit 330 outputs the reception busy signal in the second state (for example, low level) while the signal is not output from the demodulator 328, and this reception busy signal is also transmitted to other RF tag readers. Wired transmission. Regarding the received busy signal, the received busy signal generated by the received busy signal generator 330 in the RF tag reader 12-1 enters the monitor 306 in the RF tag reader 12-1 via the wire 16. It may be input to the monitor unit 306 via an internal path (not shown) of the RF tag reader 12-1 that is different from the wired 16.

 FIG. 4 shows a detailed block diagram of the RF tag 10. In the figure, elements with reference numbers beginning with “4” are the first elements that appear in FIG. The RF tag includes an antenna 41, a demodulator 42, a modulator 43, a logic unit 44, a memory 45, and a power generation unit 46.

 The antenna 41 receives a control signal from the RF tag reader, which is supplied to the power generation unit 46. The power supply generation unit 46 rectifies the received amplitude modulation signal (control signal after amplitude modulation), converts it into a DC voltage, and supplies power to each element in the RF tag. The demodulator 42 demodulates the received amplitude modulation signal and provides it to the logic unit 44. The logic unit 44 performs an operation according to the contents of the demodulated control signal. When a control signal from the RF tag reader instructs a read operation, data such as an ID number stored in the memory 45 is given to the modulator 43. The modulator 43 modulates the information provided from the logic unit 44 so that it is wirelessly transmitted from the antenna 41. When the control signal force S from the RF tag reader is instructed to write, the information is written in the information force memory 45 indicated by the control signal.

 FIG. 5 is a timing chart for explaining an operation according to an embodiment of the present invention. In the figure, the signals for the three RF tag readers R / W # l-3 and the signals for the three RF tags that communicate with each RF tag reader are shown in three stages. Each of the three stages includes a signal transmitted by the RF tag reader (R / W # ΙΤχ, etc.), a tag response signal, a reception busy signal (R / W # lRx busy, etc.), and a transmission busy signal (R / W # ΙΤχ, etc.). (Busy, etc.) The transmission busy signal will be described in Example 2 described later. For simplicity, it is assumed that each RF tag reader power read command is transmitted wirelessly, and in response, the RF tag wirelessly transmits an ID number. In the figure, the horizontal axis is time, and in general, the response command period to the RF tag reader / RF tag and the response period from the RF tag to the RF tag reader are alternately repeated. Hereinafter, the operation in each period will be described with reference to FIG. 3 and FIG. As mentioned above, the elements with reference numbers starting with “3” are the elements that are listed first in FIG.

 [0035] (First response command period)

RF tag reader 12—1 (R / W # 1) buffers control signals including read commands. 02 and timing control unit 304, and transmit from antenna 320. At time

 11 Control signal transmission is complete. In the illustrated example, the maximum length of the control signal is fixedly set in advance in the system. The control signal that is actually communicated varies in length (number of bits or transmission time) depending on the type of command, the content of the note, etc. The maximum length indicates the maximum length that the control signal can take. In this example, after time t, the next response period starts.

 11

 Dummy bit is added after the control signal at dummy insertion section 308 until time t

A

 Is transmitted from the antenna 320. Therefore, the RF tag does not control signals from time 0 to time t.

 11

 The dummy bit is received from time t to time t.

 11 A

 [0036] The RF tag reader 12_2 (R / W # 2) also wirelessly transmits a control signal including a read command. In the illustrated example, a control signal equal to the maximum length is transmitted.

 [0037] The RF tag reader 12-3 (R / W # 3) also wirelessly transmits a control signal including a read command, and is completed at the time. Thereafter, until the time t when the next response period starts,

 31 A 1 bit is transmitted.

[0038] (First response period)

 At the time of Jt, the RF tag stopped receiving any signal from the RF tag reader.

A

 In response to this, a response to the read command is started. During the period shown as “response” in Fig. 5, information power such as ID number stored in the RF tag is transmitted wirelessly. The RF tag responding to the control signal from the RF tag reader 12-1 completes the response at the time. RF Tagli

 13

 The reader 12-1 creates a high-level reception busy signal (Rx busy) at the start of the RF tag response (reception by the RF tag reader) at the reception busy signal generation unit 330, and wired 1 6 Output to. The reception busy signal before the time is low. RF tag reader 12-

A

 1 makes the reception busy signal low level and outputs it to the cable 16 at the end of the response of the RF tag.

 [0039] Similarly, an RF tag responding to a control signal from the RF tag reader 12-2 responds at time t.

 23 Complete the answer. The RF tag reader 12-2 outputs a high level reception busy signal to the wire 16 at the start of the response of the RF tag. The RF tag reader 12-2 sets the reception busy signal to a low level and outputs it to the cable 16 at the end of the response of the RF tag.

[0040] The RF tag responding to the control signal from the RF tag reader 12-3 completes the response at time t To do. The RF tag reader 12-3 also outputs a high level received busy signal to the wire 16 when the RF tag response starts. The RF tag reader 12-3 sets the reception busy signal to a low level and outputs it to the wire 16 when the response of the RF tag ends.

 [0041] The reception busy signal output from each RF tag reader 12_1-3 is monitored by the monitor unit of the RF tag reader. In particular, the monitor section monitors the time when the state of the received busy signal changes. The monitoring unit detects the timing of the state transition of a plurality of received busy signals including itself and others, and notifies the timing control unit of the latest delay and timing. In other words, all RF tag readers are notified to the power timing control unit that they have received information from their RF tags.

 [0042] For example, the RF tag reader 12-1 monitors its own reception busy signal (RZW #IRX busy) and other RF tag readers 12-2 and 3 reception busy signals with the monitor unit 306. In the example shown, the state transition of the received busy signal is performed at time t, time t, and time t.

 13 23 B This is happening. Of these, the time t is the latest, so at the timing of this time t

 B B

 Notification to the control unit 304 is performed. The timing control unit 304 starts the next response from time t.

 B

 The next control signal is transmitted so as to shift to the answer command period. The same processing is performed for the other RF tag readers 12-2 and 3 as well. RF tag reader 12-3 has its own state transition time t

 B

 Since it is the slowest, it is different from the point RF tag readers 12_1, 2 that shift to the second response command period at their own timing.

[0043] (Second response command period)

 From time ijt, the second response command period begins. RF tag reader 12-1

B

 A control signal including a command is created and transmitted wirelessly. Control signal transmission complete at time t

 16

 To do. The dummy bit is sent after time t until time t when the next response period starts.

 16 C

 Be trusted. The RF tag receives the control signal from time t to time t, and from time t to time t

 Receives dummy bits up to B 16 61.

 C

 [0044] The RF tag reader 12-2 also wirelessly transmits a control signal including a read command. In the example shown, a control signal equal to the maximum length is transmitted.

[0045] The RF tag reader 12-3 also wirelessly transmits a control signal including a read command at time t.

36 to complete. Thereafter, the dummy bit is sent until time t when the next response period starts. Be trusted.

 [0046] (second response period)

 At the time of Jt, the RF tag stopped receiving any signal from the RF tag reader.

C

 In response to this, a response to the read command is started. The RF tag responding to the control signal from the RF tag reader 12-1 completes the response at time t. RF tag reader 12-1

 19

 With the start of the RF tag response, the reception busy signal is set to the high level and output to the wire 16. The RF tag reader 12-1 sets the reception busy signal to a low level and outputs it to the wire 16 when the response of the RF tag is completed.

[0047] Similarly, an RF tag responding to a control signal from the RF tag reader 12-2 responds at time t.

 29 Complete the answer. The RF tag reader 12-2 sets the reception busy signal to a high level and outputs it to the wire 16 at the start of the response of the RF tag. The RF tag reader 12-2 sets the reception busy signal to a low level and outputs it to the wire 16 when the response of the RF tag ends.

[0048] The RF tag responding to the control signal from the RF tag reader 12-3 completes the response at ijt

 D

 To do. The RF tag reader 12-3 also outputs the high reception busy signal to the high level 16 with the start of the RF tag response. The RF tag reader 12-3 sets the reception busy signal to a low level and outputs it to the wire 16 when the response of the RF tag is completed.

The RF tag reader 12-1 monitors the reception busy signal of itself and the reception busy signals from the other RF tag readers 12-2 and 3 by the monitor unit 306. In the example shown, the state transition of the received busy signal occurs at time t, time and time t, respectively. Time t

 19 29 D

 Is the latest, so the timing controller 304 is notified at this time t.

D D

 Is called. The timing control unit 304 sends the next control signal to the next response command.

 D

 Transition to a period. The same processing is performed in the other RF tag readers 12-2 and 3.

[0050] According to the present embodiment, in the response period in which the RF tag responds, the RF tag reader transmits the reception busy signal to the other monitor unit by wire, and all the RF tag responses are completed. After that, all the RF tag readers move to the next response command period all at once. Furthermore, all RF tag readers end the response command period after a certain period of time determined by the maximum length, and shift to the next response period. With that transition, the RF tag begins to respond. In this way, since the operations of multiple RF tag readers are synchronized, weak response from a certain RF tag reader force SRF tag While receiving the signal, it can be effectively avoided that another RF tag reader transmits a strong control signal.

 [0051] When the control signal to be transmitted is less than the maximum length, the RF tag reader transmits a dummy bit after the control signal. As a result, the timing at which the RF tag starts to respond can be made uniform after a period corresponding to the maximum length has elapsed since the start of transmission of the control signal. The response start time of the RF tag is equivalent to the time when the RF tag starts response when it is always transmitted simultaneously from multiple RF tag readers. (If such dummy bits are not transmitted, the RF tag will start to respond individually and receive a large amount of interference as soon as the control signals having different lengths are received. )

 Example 2

 FIG. 6 is a partial block diagram of an RF tag reader according to the second embodiment of the present invention. In the figure, elements having reference numbers starting with “6” are in principle the elements that appear first in FIG. In this embodiment, the RF tag reader includes a no-offer 302, a timing control unit 604, a reception busy signal monitoring unit (Rx busy monitoring unit) 306, and a transmission busy signal monitoring unit (for Tx busy). (Monitor unit) 606, a transmission busy signal generation unit 608 (which constitutes a state notification means), a dummy insertion unit 308, and a reception busy signal generation unit 330. In the figure, the same elements as those described in FIG. 3 have been described and will not be further described.

 The transmission busy signal generation unit 608 outputs a high level transmission busy signal (Τχ busy) to the wire 16 when the timing control unit 604 starts transmission of the control signal. The transmission busy signal generation unit 608 outputs a low level transmission busy signal to the wire 16 when the timing control unit 604 completes transmission of the control signal.

 The transmission busy signal monitor unit 606 monitors its own transmission busy signal through the wire 16. The monitor unit 606 determines the latest state change of all other transmission busy signals, and notifies the timing control unit 604 of the determined timing.

In this embodiment, if the transmission busy signal is at a high level, it means that the control signal is being transmitted, and if it is at a low level, it means that transmission has been completed. All sending business including self and others If one signal is low, it means that all RF tag readers have finished transmitting control signals. Therefore, if all the RF tag readers stop transmitting signals at that time and the RF tag starts to respond, it is possible to avoid interference of the RF tag response signal due to the control signal.

 The timing control unit 604 outputs a control signal stored in the buffer 302 in response to an instruction from the monitor unit 606. The dummy insertion unit 308 adds a dummy bit after the control signal and outputs it so that a dummy bit is transmitted after the control signal until the latest state transition occurs after the control signal is transmitted. . Therefore, the RF tag receives a control signal or a dummy bit following it.

 [0057] In response to the timing notified from the transmission busy monitor unit 606, the timing control unit 604 ends transmission of the control signal or dummy bit and shifts to the next response period.

 [0058] In the example shown in FIG. 5, in the first response command period, a high level is set between time 0 and time t.

 11

 The wireless transmission busy signal is sent from the RF tag reader 12-1 by wire. Time 0 to time t

 A

 In the meantime, a high level transmission busy signal is wired from the RF tag reader 12-2. Time 送信 High level transmission busy signal power from IJ0 to time t From RF tag reader 12-3

 31

 The line is transmitted. Among the timings of state change of these transmission busy signals, the latest timing t is determined by the monitor unit 606, and the transition to the next response period is made at this timing.

 A

 Is done.

 [0059] As in the first embodiment, the transition from the response period to the response command period is performed based on the reception busy signal.

[0060] According to the present embodiment, the timing of the end of the response command period (or the start of the response period) can be made uniform among a plurality of RF tag readers based on the state transition of the transmission busy signal. In this embodiment, the end timing of the response command period can be set earlier (equivalent to that at the latest) than after a preset fixed time has elapsed. For example, the “maximum length” of a control signal is 200 bits, but the maximum length of what is actually transmitted as a control signal is 100 bits. In this case, in the method of the first embodiment, the response command period is a period corresponding to 200 bits, but in the method of the second embodiment, it is equivalent to 100 bits. It only takes a period of time. By using a transmission busy signal, the response command period can be shortened as much as possible.

Claims

The scope of the claims  [1] An RF tag reader that wirelessly communicates with an RF tag,  Transmitting means for wirelessly transmitting a control signal to the RF tag;  Receiving means for wirelessly receiving a data signal from the RF tag;  A first state notification means for wiredly transmitting a received busy signal in one state to another RF tag reader  The first state notification means transmits the reception busy signal in the first state to the other RF tag reader in response to the start of reception of the data signal, and in response to the completion of reception of the data signal. The second state reception busy signal is wired and transmitted to the other RF tag reader, and the transmission means starts wireless transmission of the control signal in response to a plurality of reception busy signals changing state.  An RF tag reader. [2] The transmission means wirelessly transmits a dummy bit following the control signal  The RF tag reader according to claim 1, wherein: [3] The number of dummy bits to be transmitted is determined according to the difference between the length of the control signal and a predetermined maximum length.  The RF tag reader according to claim 2. [4] Second state notification means for transmitting a busy signal in one state to another RF tag reader by wire power from multiple states  The second status notification means wiredly transmits the transmission busy signal of the first status to the other RF tag reader in response to the start of transmission of the control signal, and in response to the completion of transmission of the control signal. Send the second state transmission busy signal to the other RF tag reader by wire.  The RF tag reader according to claim 1, wherein: [5] The transmission means wirelessly transmits the control signal or dummy bits until a plurality of transmission busy signals change state.  The RF tag reader according to claim 4, wherein: [6] An RF tag reader that wirelessly communicates with an RF tag, Transmitting means for wirelessly transmitting a control signal to the RF tag;  Receiving means for wirelessly receiving a data signal from the RF tag;  A status notification means for transmitting a transmission busy signal in one state out of multiple states to another RF tag reader by wire  The state notification means wiredly transmits the transmission busy signal in the first state to the other RF tag reader in response to the start of transmission of the control signal, and in the second state in response to the completion of transmission of the control signal. Send the transmission busy signal to the other RF tag reader by wire,  The transmission means wirelessly transmits the control signal or dummy bit until a plurality of transmission busy signals change state.  An RF tag reader. [7] A wireless communication method between an RF tag and an RF tag reader,  In response to the start of reception of a wireless data signal from the RF tag, a reception busy signal in a first state of a plurality of states is wired from the RF tag reader to another RF tag reader, and the wireless signal from the RF tag is transmitted. In response to the completion of reception of the data signal, the reception busy signal in the second state among the plurality of states is wired from the RF tag reader to the other RF tag reader,  In response to the transition of multiple receive busy signals, wireless transmission of control signals to the RF tag is started.  A wireless communication method. [8] A wireless communication method between an RF tag and an RF tag reader,  In response to the start of transmission of a radio control signal to the RF tag, a transmission busy signal in a first state of a plurality of states is wired from the RF tag reader to another RF tag reader, and the radio control to the RF tag is performed. In response to the completion of signal transmission, the transmission busy signal of the second state among a plurality of states is wired from the RF tag reader to the other RF tag reader,  Radio control signals or dummy bits are transmitted wirelessly from the RF tag reader to the RF tag until multiple transmit busy signals change state A wireless communication method. [9] A wireless communication system having a plurality of RF tag readers wired to each other, and each RF tag reader is  A transmission means for wirelessly transmitting a control signal to the RF tag;  Receiving means for wirelessly receiving a data signal from the RF tag;  A first state notification means for wiredly transmitting a received busy signal in one state to another RF tag reader  The first state notification means transmits the reception busy signal in the first state to the other RF tag reader in response to the start of reception of the data signal, and in response to the completion of reception of the data signal. The second state reception busy signal is wired and transmitted to the other RF tag reader, and the transmission means starts wireless transmission of the control signal in response to a plurality of reception busy signals changing state.  A wireless communication system. [10] A wireless communication system having a plurality of RF tag readers wired to each other, each RF tag reader being  A transmission means for wirelessly transmitting a control signal to the RF tag;  Receiving means for wirelessly receiving a data signal from the RF tag;  A status notification means for transmitting a transmission busy signal in one state out of multiple states to another RF tag reader by wire  The state notification means wiredly transmits the transmission busy signal in the first state to the other RF tag reader in response to the start of transmission of the control signal, and in the second state in response to the completion of transmission of the control signal. Send the transmission busy signal to the other RF tag reader by wire,  The transmission means wirelessly transmits the control signal or dummy bit until a plurality of transmission busy signals change state.  A wireless communication system.