JP2010035038A - Communication device, communicating system and communication method - Google Patents

Communication device, communicating system and communication method Download PDF

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JP2010035038A
JP2010035038A JP2008196918A JP2008196918A JP2010035038A JP 2010035038 A JP2010035038 A JP 2010035038A JP 2008196918 A JP2008196918 A JP 2008196918A JP 2008196918 A JP2008196918 A JP 2008196918A JP 2010035038 A JP2010035038 A JP 2010035038A
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channel
communication
channels
carrier sense
empty
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JP5099445B2 (en
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Koji Ando
Jun Katsura
Takehiro Kawai
浩次 安藤
潤 桂
武宏 河合
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Omron Corp
オムロン株式会社
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Abstract

<P>PROBLEM TO BE SOLVED: To achieve a high speed communication while preventing radio interference. <P>SOLUTION: A communication method is carried out by using a mirror subcarrier system where a channel different from a channel for use in a transmission wave is used for a reception wave, and a reception system for receiving the reception wave by using either of a lower-side band and an upper-side band. Prior to carrying out communication, carrier sensing is conducted to check whether or not there is an empty channel, and then communication is started by selecting a communication mode according to the channel empty state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a communication device, a communication system, and a communication method for performing wireless data communication with a data carrier.

  In Japan and Europe, when building an RFID system using radio waves in the UHF band, the usable frequency band is narrow. FIG. 11 is a diagram illustrating a channel arrangement example of the UHF band. As shown in the figure, in Japan, nine channels are divided by dividing the 2MHz band from 952.0 to 954.0MHz by the 200kHz width. In Europe, the 2MHz band from 865.6 to 867.6MHz is arranged. Ten channels divided by a width of 200 kHz are arranged.

  In addition, when transmitting a reflected wave from an RFID tag to a reader / writer, in Japan, only a modulation method that emits a reflected wave with a radio wave having the same frequency as the center frequency of the reader / writer, called the FM0 method, has been used so far. (See FIG. 12 (a)). RFID tags, particularly passive RFID tags, are not equipped with a channel filter so that they can respond to any type of radio wave, so it is not possible to distinguish between a desired wave and an interference wave. In addition, high-power radio waves are transmitted because of the need to supply power to the RFID tag. For this reason, when a plurality of communication devices such as reader / writers are installed close to each other, radio wave interference occurs between the reader / writers, and the reading performance of the RFID tag deteriorates. In order to avoid this radio wave interference, in Japan, a carrier sense called LBT is obligated by the Radio Law.

  LBT (Listen Before Talk) measures (senses) the received power intensity of a carrier wave (carrier) before communicating between a reader / writer and an RFID tag, and determines whether or not a communicable frequency band is available. It is to confirm. That is, for radio waves transmitted from the reader / writer to the RFID tag, the received power intensity of a channel in the frequency band is measured, and if the measured received power intensity is equal to or higher than a predetermined level, the channel is in use. Judgment is made to wait for transmission, and if it is less than a predetermined level, it is judged that the channel is unused, and transmission is performed to prevent interference with adjacent reader / writers.

  In this way, it is stipulated that by performing carrier sense, the available state of a usable channel is checked before the reader / writer starts communication, and if there is an available channel, radio waves of that frequency are transmitted. There is no particular rule as to which channel to select and use when there are one free channel. Therefore, conventionally, as one of the available channel selection methods, for example, there is a method used in the wireless communication apparatus described in Patent Document 1.

  In this method, when a used channel is selected from the free channels searched at the time of carrier sense, the used channel is selected according to the free status of the adjacent channel, and the communication speed of the selected used channel is adjacent. A configuration is adopted in which communication is started at a maximum speed at which communication is possible according to the channel usage status. With this configuration, high-speed communication is possible according to the channel availability.

The method adopted in Patent Document 1 is suitable for the FM0 method because it enables high-speed communication while preventing radio wave interference. However, in the FM0 system, for example, the maximum number of reader / writers that can simultaneously emit radio waves in an area of 500 m 2 is nine (Note: The size of the area varies depending on the environmental conditions). A channel idle waiting transmission time (hereinafter referred to as “transmission waiting time”) occurs.

  Specifically, referring to FIG. 13A, for example, when the continuous transmission time is 100 msec and 30 reader / writers are installed, the transmission waiting time may be about 220 msec. When the continuous transmission time is 500 msec and 50 reader / writers are installed, there is a possibility that the transmission waiting time is about 10 times 2150 msec. As the number of reader / writers increases, this transmission waiting time becomes longer as shown in the graph of FIG.

  In order to solve such a problem of transmission waiting time, a mirror subcarrier method (hereinafter referred to as “MS method”) is adopted in Japan due to a recent revision of the Radio Law. The MS method is a modulation method that makes it easy to avoid interference between reader / writers by shifting the reflected wave of the RFID tag to a frequency different from the transmission wave of the reader / writer. By shifting the frequency of the reflected wave of the RFID tag, it is possible to prevent the weak reflected wave of the RFID tag from being drowned out by strong radio waves generated by other reader / writers (see FIG. 12B). By adopting this MS method, the transmission waiting time becomes unnecessary, and further, the restriction prescribed in the conventional LBT, that is, the restriction that transmission cannot be performed within 50 msec once transmission is completed becomes unnecessary. Thus, the number of reader / writers installed can be increased.

  Even after the adoption of this MS method, there is a demand in the industry that high-speed communication is possible while preventing radio wave interference, and the present inventors also apply the method described in Patent Document 1 above. Thought to do. However, in this method, if the MS method is simply applied to the method described in Patent Document 1 including the restriction that high-speed communication cannot be performed unless both channels adjacent to the transmission channel are free, radio interference can be prevented. High-speed communication was not suitably realized, and further improvement was necessary.

JP 2008-148215 A

  The present invention provides a communication device, a communication system, and a communication method capable of increasing a communication speed while preventing radio wave interference by performing data communication by dynamically changing a communication mode under the MS method. For the purpose.

  In order to achieve the above object, the present invention is a communication apparatus for performing wireless data communication with a data carrier using one or a plurality of channels on a frequency band divided into a plurality of sections, A transmission unit that transmits a transmission signal using a first channel from a communication device, a second channel that is a channel different from the first channel, and a single sideband from a data carrier A receiving unit that receives the received signal, a storage unit that stores a communication mode for specifying a use area of the second channel, and a control unit that dynamically changes the communication mode. Data communication with a data carrier is performed by dynamically changing the mode.

  Here, the “data carrier” is, for example, an RFID tag or an IC card, and the “communication device” is a reader or a reader / writer that can wirelessly communicate with the RFID tag. In addition, the RFID tag mentioned here includes a passive type that does not have a power source, an active type that has a power source, a tag that is attached to a package or a product, a tag or a tag, etc. Various forms are included, including various forms, such as those in which an IC chip is mounted and data can be read and written.

  The first channel means one channel among the channels on the frequency band divided into a plurality, and the second channel means a channel different from the first channel. That is, the present invention adopts a so-called MS system in which the transmission channel and the reception channel are different from each other, unlike the conventional FM0 method in which the transmission and reception channels are the same. .

  The single sideband (hereinafter referred to as “SSB”) is amplitude-modulated, thereby lowering the lower sideband (LSB) on the lower frequency side and centering on the carrier wave, and the upper sideband on the high frequency side. (USB) occurs, but this is a modulation scheme that transmits baseband information using one of the sidebands. In the present invention, the SSB is used when the communication device receives and demodulates the received signal from the data carrier. In the wireless communication device described in Patent Document 1, demodulation is performed using a double sideband (hereinafter referred to as “DSB”), and both the LSB side and USB side channels are free. However, it is necessary to use only the channel on either the LSB side or the USB side by using the SSB. Therefore, high-speed communication is possible while preventing radio wave interference.

  Here, the “communication mode” is for specifying the use area of the second channel. For example, the use area is specified by the location of the channel to be used and the number of channels to be used. is there. If the channel to be used is an empty channel, radio interference can be further suppressed, and if the communication speed is increased, the frequency band tends to widen. Therefore, if the number of channels to be used is increased, higher speed communication is possible. It becomes. For this reason, in the present invention, a communication mode is provided, and the communication mode can be changed to prevent radio wave interference and enable high-speed communication.

  In the present invention, the second channel may be composed of one channel or a plurality of continuous channels, and the control unit selects the number of channels of the second channel in descending order. The communication mode may be changed dynamically. The higher the communication speed, the wider the frequency band and the need for multiple channels, so it is possible to select the communication mode in descending order of the number of channels to be used. It becomes possible to make it maximum.

  Further, in the present invention, before performing data communication, it has carrier sense means for performing carrier sense for searching for a vacant state of each channel by measuring the received power intensity of each channel, and the carrier sense means If there is a free channel as a result of the search, the control unit may be configured to set the communication mode so that data communication is performed using this free channel. After checking the empty channel and setting the communication mode so that this empty channel is selected, if data communication is performed, radio wave interference can be prevented and more than one continuous empty channel exists as a result of the search. Can communicate by selecting a plurality of empty channels, and as a result, high-speed communication is also possible.

  On the other hand, before performing data communication, it has carrier sense means for performing carrier sense for searching for the free state of each channel by measuring the received power intensity of each channel. When there is no channel, the control unit may be configured to set the communication mode so that the adverse effect on the data carrier communication due to the received power intensity (interference wave) is minimized. As a result of carrier sense, all channels may be used. However, even if the channel is used, the usage level (degree), that is, the received power intensity measured in each channel is different, so in the present invention, the data carrier by this received power intensity (interference wave) is different. The communication mode is set so that the adverse effect on communication is minimized, and data communication is performed. With this configuration, data communication can be performed in a state where there is a low possibility of radio wave interference even in a situation where there is no empty channel.

  In the present invention, before performing data communication, a carrier sense means for performing carrier sense for searching for an empty state of each channel by measuring the received power intensity of each channel, and for each channel, A free channel information storage unit for storing information on free state, and the control unit is configured to refer to the free state information and set a communication mode so that data communication is performed through a channel having a lot of free state. May be.

  Also, in the present invention, before data communication is performed, information regarding the channel availability obtained by performing carrier sense for searching for the availability of each channel by measuring the received power intensity in units of channels is stored in advance. And a control unit configured to refer to information related to a free state and set a communication mode so that data communication is performed using a channel having a lot of free states. May be.

  Further, according to the present invention, before performing data communication, carrier sense means for performing carrier sense for searching for a free state of each channel by measuring received power intensity in units of channels, and for each carrier sense. An empty channel information accumulating unit for accumulating information on available channels, and the control unit acquires the channel available probability of each channel from the available channel information accumulating unit when a plurality of empty channels are searched by carrier sense. At the same time, the communication mode is set so as to perform data communication by checking the channel vacancy probability with the immediately preceding vacant channel searched by carrier sense and selecting the channel with the highest channel vacancy probability among the immediately preceding vacant channels. You may comprise so that it may set.

That is, in the present invention, carrier sense is performed, and an empty channel state is searched using only the latest information in time, thereby setting not only a pattern for performing data communication by setting a communication mode, but also the following: In this way, a pattern for setting the communication mode is also applicable. In particular,
(1) A pattern in which communication mode is set so as to perform data communication by accumulating information related to channel availability for each carrier sense, and selecting a channel having the largest availability in the past.
(2) Without providing a free channel information storage unit for storing a free channel state for each carrier sense, information on a free channel state is stored in advance in a storage medium (CD-ROM, FD, etc.), and from this storage medium A pattern for setting a communication mode for acquiring data on an empty channel state, selecting the one having the largest empty state in the past, and performing data communication.
(3) When a plurality of vacant channels are searched by carrier sense, the channel vacancy probability of each channel accumulated in the vacant channel information accumulating unit is acquired, and data communication is performed by selecting the channel having the highest vacancy probability. A pattern to set the communication mode to do.
Etc.

  Note that the information regarding the channel availability state is not only information directly indicating the channel availability status, but also, for example, indirectly indicating the channel availability status by indicating the status of each channel used for data communication. In correspondence with this, the vacancy probability also includes direct and indirect notations.

  The communication mode is set in the communication device of the present invention in which the control unit sets the communication mode so that the adverse effect on the communication with the data carrier due to the received power (interference wave) is minimized when there is no empty channel. At the same time, after the communication mode is set, or when data communication is performed. When data communication is performed without selecting an empty channel, radio interference is more likely to occur than when an empty channel is selected. It is going to warn to let you know that you are not doing. This warning may be in any form such as a warning sound, a warning message, or a warning light.

  The communication apparatus of the present invention can be suitably applied to a reader or a reader / writer that is used in an RFID system that requires countermeasures against interference due to carrier sense, such as a reader / writer of a high-power UHF band or a low-power UHF band. .

  A communication system according to the present invention includes any one of the communication apparatuses described above and a data carrier capable of data communication with the communication apparatus.

  In the communication system of the present invention, when there is no empty channel, the control unit sets a communication mode so that the received power intensity is the lowest, an external control device capable of communicating with the communication device, A data carrier capable of data communication with the communication device, and the communication device warns the external control device when the communication mode is set, after the communication mode is set, or when data communication is performed. When the signal is transmitted and the external control device receives the warning signal, the external control device issues a warning to the user.

  The present invention is a communication method for performing wireless data communication with a data carrier using one or a plurality of channels on a frequency band divided into a plurality, and using the first channel A first step of transmitting a transmission signal and a second channel that uses a second channel that is different from the first channel and receives a reception signal from a data carrier using a single sideband. And a third step of dynamically changing a communication mode for specifying a use area of the second channel, and performing data communication with a data carrier by dynamically changing the communication mode. Features.

  The second channel may consist of one channel or a plurality of consecutive channels.

  The communication mode may be dynamically changed so that the number of channels of the second channel is selected in descending order.

  When there is a free channel as a result of the search, having a fourth step of performing carrier sense for searching for the free state of each channel by measuring the received power intensity of each channel before performing data communication Alternatively, the communication mode may be set so that data communication is performed using this empty channel.

  When there is no empty channel as a result of the search, having a fourth step of performing carrier sense for searching for the free state of each channel by measuring the received power intensity of each channel before performing data communication Alternatively, the communication mode may be set so that the received power intensity is the lowest.

  Before performing data communication, the fourth step of performing carrier sense for searching for the free state of each channel by measuring the received power intensity in units of channels, and information on the free state of the channel every time carrier sense is performed And the control unit may set the communication mode so as to perform data communication through a channel having a lot of free states with reference to information on the free state.

  Before performing data communication, measure the received power intensity of each channel to search for the free state of each channel. By performing carrier sense, the channels with many free states are stored in advance. The communication mode may be set so as to perform data communication.

  Before performing data communication, the fourth step of performing carrier sense for searching for the free state of each channel by measuring the received power intensity in units of channels, and storing information on available channels each time carrier sense is performed. And when a plurality of empty channels are searched by carrier sense, the channel empty probability of each channel is obtained from the accumulated information on the empty channels and searched by carrier sense. The communication mode may be set so that data communication is performed by collating the immediately preceding empty channel that is an empty channel with the channel empty probability and selecting the channel having the highest channel empty probability among the immediately preceding empty channels.

  Note that the wording interpretation, operational effects, technical idea, and the like in the communication system and communication method of the present invention are the same as those corresponding to the communication apparatus of the present invention described above.

  According to the present invention, a so-called MS system and single sideband are used, and data communication with a data carrier is performed by dynamically changing a communication mode. Thereby, it is possible to provide an environment in which high-speed communication can be performed while preventing radio wave interference.

  Further, in the present invention, in addition to the above configuration, if the communication mode is set based on the information on the free channel immediately before the data communication by carrier sense or the information on the free channel in the past and the data communication is performed, The occurrence of interference can be further suppressed and high-speed communication is also possible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a reader / writer which is an embodiment of a communication apparatus of the present invention.

  As shown in the figure, the reader / writer 1 of this embodiment is a device that performs wireless data communication with an RFID tag (not shown) that is a data carrier using radio waves. More specifically, the reader / writer 1 selects an optimum communication mode, that is, for example, selects a reception channel to be used from nine channels in the UHF band shown in FIG. The data stored in the memory is read and written, and includes a control unit 2, a transmitter 3, a transmission unit 4, a reception unit 5, a circulator 6, and an antenna 7 described below. ing.

Control unit 2 is for controlling the transmission and reception between the reader writer 1 and the RFID tag mainly generates and outputs a transmission signals S 1 to be transmitted to the RFID tag, the received signal S 2 received from the RFID tag To process. The configuration of the control unit 2 will be described in detail with reference to FIG.

Transmitter 3 is used to set the carrier frequency of the transmission signals S 1 based on the control signal S 3 from the control unit 2, in the present embodiment is constituted by a PLL circuit.

Transmission unit 4, and outputs a read signal or write signal to the RFID tag as a transmission signal S 1, a digital-analog converter 41, modulator 42, and includes a high-frequency amplifier 43. First digital-to-analog converter 41 outputs the transmission data outputted from the control unit 2 as a baseband signal S 4 is converted into an analog signal from a digital signal. Next, the modulator 42 modulates the carrier wave f 0 having a predetermined frequency set by the transmitter 3 with the baseband signal S 4 input from the digital-analog converter 41, and transmits the readout signal when the carrier signal f 0 is transmitted. 0 is unmodulated. Further, the high frequency amplifier 43 performs power amplification of the RF signal input from the modulator 42. The transmission signal S 1 output from the high frequency amplifier 43 is radiated from the antenna 7 via the circulator 6 and the low-pass filter 8.

Receiving unit 5 is for inputting a signal returned from the RFID tag as the received signal S 2, band-limiting filter 51, a low noise amplifier 52, demodulator 53, amplifier 54 and an analog-digital converter 55. Since the received signal S 2 which is input through the band-limiting filter 51 is a weak radio wave by the reflected wave of the RFID tag is outputted to the demodulator 53 is amplified by the low noise amplifier 52. Here demodulator 53, the carrier f 0 of a predetermined frequency of the received signal S 2 which is input from the oscillator 3 to demodulate the baseband signal S 4. The baseband signal S 4 that is demodulated is power-amplified is inputted to the amplifier 54. Further analog-to-digital converter 55 outputs a baseband signal S 4 which is amplified from an analog signal into a digital signal. Then, the received signal S 2 output from the analog-digital converter 55 is processed is input to the control unit 2.

  Here, when receiving the received signal, the SSB is used to receive and demodulate either the LSB signal or the USB signal (hereinafter referred to as “communication using the SSB modulation method”. ("SBS communication", a reception signal when using the low frequency side is called "LSB signal", and a reception signal when using the high frequency side is called "USB signal"). Unlike the DSB used in the wireless communication device described in Patent Document 1, it is sufficient that either the LSB side or the USB side is free. Becomes higher.

In this embodiment, since the RFID tag uses a passive tag that does not incorporate a power source, the communication method between the reader / writer 1 and the RFID tag is a half-duplex method, and the antenna 7 is used for transmission and reception. The transmission signal S 1 and the reception signal S 2 are separated by the circulator 6. That is, the transmission signal S 1 output from the transmission unit 4 at the time of transmission is guided to the antenna 7 via a low-pass filter 8 from the circulator 6, it is radiated from the antenna 7 to the outside of the RFID tag. On the other hand, at the time of reception, the received signal S 2 from the RFID tag received by the antenna 7 is guided from the circulator 6 to the receiving unit 5 through the low-pass filter 8.

  FIG. 2 is a diagram illustrating a configuration of a control unit in the reader / writer.

As shown in the figure, the control unit 2 includes a transmission data generation unit 21 and an encoding unit 22. The transmission data generated by the transmission data generation unit 21 is encoded by the encoding unit 22, and the encoded data is encoded. The transmission data is output to the digital / analog converter 41 as a digital signal. The control unit 2 and the decoding section 23 includes a reception data processing section 24, decoded by the decoding unit 23 a digitized received signal S 2 is inputted from the analog digital converter 55, the decoding The received data is processed by the received data processing unit 24.

  In the present embodiment, the decoding method used in the decoding unit 23 is a modulation method that shifts the reflected wave of the RFID tag to a frequency different from the transmission wave of the reader / writer and makes it easy to avoid interference between the reader / writer, This is a so-called mirror subcarrier system (MS system). By shifting the frequency of the reflected wave of the RFID tag, it is possible to prevent the weak reflected wave of the RFID tag from being extinguished by the strong radio wave generated by another reader / writer.

  Further, the control unit 2 includes an FFT processing unit 25, a channel selection processing unit 27, and a memory 26. First, the FFT processing unit 25 performs a fast Fourier transform process using a digital signal input from the analog-digital converter 55 during carrier sensing. That is, the FFT processing unit 25 extracts each frequency component included in the digital signal by performing fast Fourier transform processing on the digital quantity data input from the analog-digital converter 55, as shown in FIG. The distribution data of received power intensity for each frequency band is acquired and output.

  The memory 26 stores a communication unit for specifying a communication speed, a channel to be used, the number of channels to be used, and the like, and free channel information accumulation for accumulating information on a channel free state every time carrier sense is performed. It is a memory | storage means which functions as a part.

The channel selection processing unit 27 stores distribution power intensity distribution data for each frequency band input from the FFT processing unit 25 at the time of carrier sense in the memory 26, and is free based on the reception power intensity distribution data read from the memory 26. Performs processing to evaluate the channel and select and set the optimum communication mode. Therefore, the control signal S 3 for setting the carrier frequency of the transmission signal S 1 is output to the transmitter 3 . The communication mode selection process will be described in detail with reference to FIG.

  FIG. 3 is a diagram illustrating a passive RFID communication method and a spectrum state in each communication period.

  As described above, the reader / writer 1 according to the present embodiment employs a passive RFID communication method, and radio waves transmitted from the reader / writer 1 to the RFID tag serve to supply electromotive force for operating the RFID tag. Therefore, it is radiated at a high output from the antenna 7. As shown in the figure, a read command is transmitted as a modulated wave from the antenna 7 of the reader / writer 1 during the communication period from the reader / writer 1 to the RFID tag. At this time, the RFID tag demodulates and analyzes the read command. In addition, an option for designating the transmission rate of a signal to the RFID tag can be added at the time of command transmission, and the transmission rate can be changed for each communication. FIG. 2B shows the modulated wave spectrum of the reader / writer 1 whose band is limited in the channel.

  On the other hand, in the communication period from the RFID tag to the reader / writer 1, the reader / writer 1 transmits an unmodulated continuous carrier wave CW from the antenna 7. Then, radio waves are returned from the RFID tag to the reader / writer 1 with a slight delay. The antenna impedance of the RFID tag changes according to the data in the memory inside the tag. As a result, the amount of reflection of the radio wave from the reader / writer 1 changes according to the change in the antenna impedance of the tag, and is returned as a weak signal modulated by the tag data.

  The impedance modulation speed of the RFID tag is determined by the transmission speed specified in the transmission command. FIG. 4C shows a modulated wave spectrum of a weak signal due to a change in impedance between the continuous carrier wave CW of the reader / writer 1 and the RFID tag. In the present invention, since the MS method and the SSB modulation method are used as described above, the channels used for the carrier wave and the received wave are different, and only one side band is used. Here, a case where a USB signal is used is illustrated.

  As the data transmission rate from the RFID tag to the reader / writer 1 increases, there is a characteristic that the frequency band becomes wider. That is, when the communication speed is high, the occupied band of the single sideband is widened and is easily affected by other carrier waves.

  Therefore, the reader / writer 1 of this embodiment searches for an empty channel by carrier sense, changes the communication mode according to the empty state of the channel, and selects the communication speed according to the number of empty channels, thereby enabling the reader / writer. 1 and the RFID tag are improved in communication efficiency.

  FIG. 4 is a diagram showing the relationship between received power intensity distribution data and empty channels.

  As described above, the FFT processing unit 25 of the control unit 2 executes the fast Fourier transform process using the digital signal input from the analog-digital converter 55 at the time of carrier sensing, so that the channel unit as shown in FIG. The measured received power intensity distribution data is acquired. In the figure, the horizontal axis indicates nine channels (Ch) that can be used as transmission frequency bands in the UHF band, and the vertical axis indicates the level of received power intensity (dBm).

  Here, the threshold value Th1 is set to a level that adversely affects data carrier communication, for example, −74 dBm. In the illustrated example, the channels whose measured received power intensity is less than the threshold Th1, that is, four channels Ch2, Ch3, Ch6, and Ch9 are free channels that can be communicated. An optimum communication mode, that is, a communication mode that maximizes the communication speed while preventing radio wave interference is selected and set in accordance with the searched empty channel state.

  Next, the operation will be described with reference to FIGS. In addition, although the pattern which starts data communication after performing carrier sense here is demonstrated, carrier sense is not necessarily required.

  FIG. 5 is a flowchart showing an example of communication mode selection processing in the control unit, FIG. 6 is a schematic diagram when the communication mode is mode 1, FIG. 7 is a schematic diagram when the communication mode is mode 2, and FIG. FIG. 9 is a schematic diagram showing a modification of the communication mode, and FIG. 10 is an explanatory diagram for explaining the channel occupation degree check process.

  In the figure, the reader / writer 1 first stops the transmission of radio waves from the antenna 7 and performs carrier sense prior to data communication with the RFID tag (S601). That is, the received power intensity is measured for all channels (Ch 1 to 9) in the UHF transmission frequency band via the antenna 7 and the receiving unit 5, and the channel selection processing unit 27 receives the received power intensity distribution data from the FFT processing unit 25. Based on, a free channel whose received power intensity is less than the carrier sense level (−74 dBm) of the threshold Th1 is searched. In the example of FIG. 4, four channels Ch2, Ch3, Ch6, and Ch9 correspond to empty channels. Here, the threshold value Th1 is set to −74 dBm, but this is an example, and the threshold value may be changed according to the surrounding environment.

  Next, the channel selection processing unit 27 temporarily stores distribution data of received power intensity for each frequency band input from the FFT processing unit 25 at the time of carrier sensing in the memory 26, and information on an empty channel for each channel. Are stored as a history (S602). As information regarding the free channel, although not shown here, for example, in addition to the information that directly indicates the free state of the channel, the information of the channel is indirectly indicated by notifying the situation in which each channel is used for data communication. Including those that indicate the availability.

As a result of the carrier sense, the control unit 2 checks whether there are continuous free channels for 3 Ch (S603). If there are continuous free channels for 3 Ch (Y in S603), set the communication mode to the mode 1 (S604), and outputs a control signal S 3 with respect to the oscillator 3, the data communication is started (S612).

  In the present embodiment, this mode 1 is the communication mode with the fastest communication speed, and then the communication speed decreases in the order of mode 2 to be described later, and then mode 3.

  FIG. 6 schematically shows this mode 1, and in FIG. 6A, when the transmission channel is Ch: n, other channels Ch: n-3, n-2 other than n are shown. , N−1, n + 1, n + 2, and n + 3, three consecutive channels are selected as reception channels. That is, mode 1 is a communication mode that enables high-speed communication by selecting three consecutive channels as reception channels.

  For example, as a result of carrier sense, if three consecutive channels of Ch: n-1, n-2, and n-3 adjacent to Ch: n are free, SSB communication using the LSB signal is performed. Just do it. On the other hand, when three consecutive channels Ch: n + 1, n + 2, and n + 3 adjacent to Ch: n are free, SSB communication using a USB signal may be performed. FIG. 6A shows a case where three channels Ch: n-1, n-2, and n-3 are used. Note that these three channels do not necessarily have to be adjacent to the transmission channel. For example, as shown in FIG. 6B, Ch: n-1 is used as a transmission channel of another reader / writer, and Ch: n-2, n-3, and n-4 continuous three channels. Is available, SSB communication is possible using these three channels.

In the process of S604, a process of checking which three consecutive channels are selected and selecting which channel is a reception channel, and a predetermined communication speed for the transmitter 3 are selected. it is intended to include a process of outputting a control signal S 3 to give instructions. For example, as a result of carrying out carrier sense, if channels of Ch: n−1, n−2, n−3, n + 1, n + 2, and n + 3 are free, n−1, n−2, and n−3 Three channels, or three channels n + 1, n + 2, and n + 3 can be selected, and in this case, a selection process for selecting which one to receive is included. In this case, for example, the one using the LSB signal is used preferentially, the channel number is selected in order from the smallest (low frequency), the reception channel is selected so as to be far from the transmission channel, etc. A description to be selected may be set in advance.

On the other hand, as a result of the processing in S603, if there are no consecutive free channels for 3Ch, it is next checked whether there are continuous free channels for 2Ch (S605). if the amount of idle channel exists (S605 of Y), the setting the communication mode to the mode 2 (S606), and outputs a control signal S 3 with respect to the oscillator 3, the data communication is started (S612 ).

  In the present embodiment, this mode 2 is a communication mode with the next highest communication speed after the mode 1.

  FIG. 7 schematically shows this mode 2. In FIG. 7A, when the transmission channel is Ch: n, channels other than n are Ch: n-3, n-2. , N−1, n + 1, n + 2, and n + 3, two consecutive channels are selected as reception channels. That is, mode 2 is a communication mode in which two consecutive channels are selected as reception channels and high-speed communication next to mode 3 is possible.

  For example, as a result of carrier sense, when two consecutive channels of Ch: n−1 and n−2 adjacent to Ch: n are free, SSB communication using an LSB signal may be performed. On the other hand, when two consecutive channels of Ch: n + 1 and n + 2 adjacent to Ch: n are free, SSB communication using a USB signal may be performed. FIG. 7A shows the case where two channels of Ch: n−1 and n−2 are used. Note that these two channels do not necessarily have to be adjacent to the transmission channel. For example, as shown in FIG. 7B, Ch: n-1 is used as a transmission channel of another reader / writer, and two consecutive channels of Ch: n-2 and n-3 are free. In some cases, SSB communication is possible using these two channels.

In the process of S606 as well as the process of S604, the process of checking which channel is two consecutive channels and selecting which channel is the reception channel, and predetermined communication with the transmitter 3 it is intended to include a process of outputting a control signal S 3 which gives an instruction to select a speed. Details are the same as the processing in S604 described above, and will be omitted.

On the other hand, as a result of the processing of S605, if there are no consecutive free channels for 2Ch (N in S605), then it is checked whether there are free channels for 1Ch (S607), 1Ch. if the amount of idle channel exists (S607 of Y), the set communication mode to mode 3 (S608), and outputs a control signal S 3 with respect to the oscillator 3, the data communication is started (S612 ).

  In the present embodiment, mode 3 is a communication mode with a low communication speed, but only one empty channel is required.

  FIG. 8 schematically shows this mode 3. In FIG. 8A, when the transmission channel is Ch: n, other channels other than n are Ch: n-3, n-2. , N−1, n + 1, n + 2, and n + 3, a case where one channel is selected as a reception channel is shown. That is, mode 3 is a communication mode in which one channel is selected as a reception channel for communication.

  For example, if a channel of Ch: n−1 adjacent to Ch: n is free as a result of carrier sense, SSB communication using an LSB signal may be performed. On the other hand, when the Ch: n + 1 channel adjacent to Ch: n is free, SSB communication using a USB signal may be performed. FIG. 8A shows a case where a channel of Ch: n−1 is used. Note that this one channel does not necessarily have to be adjacent to the transmission channel. For example, as shown in FIG. 8B, when Ch: n-1 is used as a transmission channel of another reader / writer and Ch: n-2 is free, the channel of n-2 is set. SSB communication is possible using this. When n-1 and n-2 are used, SSB communication is possible using the n-3 channel.

In the process of S608 as well as the process of S604, a process of checking which channel is a channel and selecting which channel is a reception channel, and a predetermined communication speed for the transmitter 3 are set. it is intended to include a process of outputting a control signal S 3 which gives an instruction to select. Details are the same as the processing in S604 described above, and will be omitted.

  Note that the communication modes listed here are merely examples, and various other communication modes can be set. As an example, there is a modification of the communication mode as shown in FIG. This communication mode is a communication mode in which the reception channel is used for 3 Ch, but the reception channel is set to one channel by performing signal processing inside the device. In this communication mode, a communication speed equivalent to that in mode 1 can be set. However, there is a possibility that the communication distance will be lower than that in mode 1. For example, when the center frequency of the received signal is deviated, necessary information is cut, which may reduce the communication distance.

  As a result of performing the process of S607, if there are no empty channels for 1 Ch, that is, if there are no empty channels in all the channels other than the transmission channel n, the channel occupation degree check is performed next. Processing is performed (S607). In short, the channel occupancy level check process is a process for checking the degree of channel use.

  Specifically, even if the received power intensity is not recognized as an empty channel as a result of carrier sense, the measured received power intensity is not uniform as shown in FIG. 4, for example. For example, referring to FIG. 4, the channels having the received power strength Th1 or higher are five channels of Ch1, 4, 5, 7, and 8, which do not correspond to all the empty channels, but the received power strength is compared. Ch7 has the highest received power intensity, and Ch4 and Ch8 are very close to the received power intensity Th1, which is the threshold value of the free channel.

  Therefore, even if there is no vacant channel due to carrier sense, radio wave interference can be prevented and in some cases minimized if the communication mode is selected so that the received power intensity due to the interference wave is reduced. I can do it. In the past, if there were no free channels, communication had to be waited for. By checking the channel occupancy level in this way, without waiting for communication, radio wave interference was prevented, and in some cases it was minimized. In addition, high-speed communication is possible.

  In the present invention, a method as shown in FIG. 10 is adopted as the channel occupancy degree check process.

  An example of the interference wave level that affects tag communication for each channel for each communication mode is described in the table shown in FIG. For example, if the level of the interference wave is ch: n-3: -80 dBm or less, n-2: -80 dBm or less, n-1: -80 dBm or less, even if the high speed mode 1 is selected, tag communication is affected. Because the interference wave is below the level that gives

  An example of the actual interference wave level for each channel is described in the table shown in FIG. In addition, “an interference wave level for each channel for each mode” and “an example of an interference wave level for each channel” are shown. In this case, for example, for mode 3, the ch: n-3 interference wave is at a level at which tag communication can be performed without any problem, but n-2 and n-1 are levels of interference waves that affect tag communication. It is. Similarly, the interference wave levels that affect modes 1 and 2 are also affected. Therefore, in this case, modes 1, 2, and 3 cannot be used.

  However, even when the channel is used, there are a case where the channel is used to such an extent that tag communication cannot be performed at all, and a case where the channel is used to such an extent that the success rate of tag communication is slightly reduced.

  Therefore, by carrying out the following, if the tag communication success rate is slightly lowered, a certain mode can be selected and communication with the tag can be performed. As this method, the difference between the actual interference wave level and the influence interference wave level is calculated, and tag communication may be performed if the total value is a certain value or more. For example, in the case of mode 3, the difference A, difference B, and difference C between the received power intensity of the interference wave shown in FIG. 10C and the interference wave level for each channel n-3, n-2, n-1 to add. Similarly, the difference is calculated for modes 1 and 2, and the total value is calculated. Then, a mode that has the least influence on tag communication may be selected from the total value. The above value may be arbitrarily set by the user based on past experience, and the communication mode having the highest or lowest numerical value may be selected as a result of calculating the total value.

  For example, in this case, when the total value is calculated by taking the difference of the interference wave level for each channel from the interference wave level of each channel for each mode, the total value is -120 dBm for mode 1 and-for mode 2. 60 dBm, mode 3 is −30 dBm, and the total value of mode 3 is the highest. Therefore, in this case, if mode 3 is selected, it is possible to avoid further affecting the tag communication. When the method of taking the difference is reversed, that is, when the total value is calculated by taking the difference of the interference wave level of each channel for each mode from the actual interference wave level of each channel, the total value is low. When the mode is selected, it is possible to avoid affecting the tag communication. Here, for the sake of easy understanding, the difference or the like is calculated from the power value in units of dBm, but the difference may be calculated after converting the power dBm value to the power true value.

  Other examples are described in FIGS. 10D and 10E. That is, the interference wave level for each channel for each mode is shown in FIG. 10 (a), but the actual channel interference level for each channel shows the degree of channel occupancy when shown in FIG. 10 (d). In this case as well, if the total difference is calculated in the same manner as described above, Mode 1 is −60 dBm, Mode 2 is −30 dBm, Mode 3 is +30 dBm, and Mode 3 has the highest total value. Therefore, in this case, if mode 3 is selected, it is possible to avoid further affecting the tag communication. Here, for the sake of easy understanding, the difference or the like is calculated from the power value in units of dBm, but the difference may be calculated after converting the power dBm value to the power true value.

  After the processing of S609 and S610, the corresponding communication mode is selected and communication is started (S612). However, in this case, since communication is performed using a channel that is not an empty channel as a reception channel, strictly speaking, there is a possibility that radio wave interference may occur compared to communication using an empty channel. The communication quality is poor. Therefore, in the present embodiment, an instruction signal for displaying a warning message is transmitted to an external control device (not shown) connected to the reader / writer 1, and the external control device that has received the instruction signal displays the warning message. (S611). Note that this warning may be configured not only to display a message, but also to issue a warning by, for example, a warning light or a warning sound.

  In addition to the above-described embodiment, the following modifications may be applied to the communication mode selection process in the control unit 2.

<Modification 1>
First, it is a process of selecting a communication mode without performing carrier sense by using information relating to an empty channel accumulated in the past. That is, in the above-described embodiment, carrier sense is executed prior to data communication. However, in the first modification, the carrier sense is not used, and information on the channel availability is referred to, and the channel having more idle status is used. Set the communication mode to perform data communication.

  In the first modification, before the data communication, the channel availability obtained by performing carrier sense for searching for the availability of each channel by measuring the received power intensity in units of channels is performed. It has an empty channel information storage unit (not shown) in which information is stored in advance.

  For example, in a reader / writer in which the reader / writer is set at a fixed position and used under the same environment every day, the situation where the channel is free is relatively standardized. In such a case, it is not necessary to perform carrier sense every time, and since the start of data communication can be performed quickly by omitting carrier sense, the convenience for the user is improved.

  In the first modification, instead of performing carrier sense, only the information regarding the channel vacancy state accumulated in advance is used, and the subsequent processing (S603 to S612) in the above embodiment is the same.

<Modification 2>
In the second modification, when a plurality of empty channels are searched by carrier sense, the control unit 2 acquires the channel empty probability of each channel from the memory 26 (empty channel information storage unit) and is searched by carrier sense. The communication mode is set so that data communication is performed by checking the channel vacancy probability with the immediately preceding vacant channel, which is an vacant channel, and selecting the channel with the highest channel vacancy probability among the immediately preceding vacant channels. . With this configuration, the communication mode can be selected more efficiently.

  That is, for example, carrier sense is performed before communication, but it is assumed that the radio wave environment changes during communication. That is, when carrier sense is performed, six channels n-3, n-2, n-1, n + 1, n + 2, and n + 3 are free. However, the time for communicating with the RFID tag is generally several seconds. It is fully assumed that the channel conditions will change during the few seconds. Therefore, it is possible to select an efficient communication mode by determining by combining past history information and latest information. In other words, it is assumed that the n-3, n-2, n-1, n + 1, n + 2, and n + 3 channels are free in the latest information. It is possible to use n-3, n-2, and n-1 in mode 1 and n + 1, n + 2, and n + 3 in mode 1, but in the past history information, there are n + 2 channels available. If it is low, n-3, n-2, and n-1 may be used instead of n + 1, n + 2, and n + 3 in mode 1.

  As another utilization method of past information, in the above embodiment, as the channel occupancy degree check, the difference between the level affected by each mode and the actual interference wave level is calculated. By setting it to 2, it is possible to utilize past information. That is, when all channels are used, it is possible to select the mode with the highest communication probability from the latest information and past information. For example, when the interference wave level is -40 dBm in the latest information and -60 dBm in the previous information, the difference is not calculated from -40 dBm in the latest information, but the average of -40 dBm and -60 dBm. May be used as the interference wave level, and the level affected by each mode and the difference may be calculated from the interference wave level. Note that the processing of S601 to S612 is executed before communication is completed and new communication is performed.

  In the above-described embodiment, an example in which the communication device of the present invention is applied to a high-power UHF band reader / writer has been described. However, the present invention is not limited to this, and it is necessary to take measures to prevent interference by carrier sense. As long as it is used in the system, it can be similarly applied to a low-power UHF band reader / writer and other frequency band communication devices.

1 is a diagram showing a configuration of a reader / writer which is a wireless communication apparatus of the present invention. The figure which shows the structure of the control part in a reader / writer. The figure which shows the communication state of a passive type RFID, and the spectrum state of each communication period. The figure which shows the relationship between received power intensity distribution data and an empty channel. The flowchart figure which shows an example of the channel selection process in a control part. The schematic diagram which shows the case where communication mode is mode 1. FIG. The schematic diagram which shows the case where communication mode is mode 2. FIG. The schematic diagram which shows the case where communication mode is mode 3. FIG. The schematic diagram which shows the modification of communication mode. Explanatory drawing for demonstrating a channel occupation degree check process. The figure which shows the channel arrangement | positioning example of a UHF band. It is a figure for demonstrating a modulation system, (a) is FM0 system, (b) is explanatory drawing for demonstrating each MS system. Explanatory drawing for demonstrating the generation | occurrence | production state of the transmission waiting time in the past.

Explanation of symbols

1 Reader / Writer (communication device)
2 Control Unit 21 Transmission Data Generation Unit 22 Encoding Unit 23 Decoding Unit 24 Received Data Processing Unit 25 FFT Processing Unit 26 Channel Selection Processing Unit 27 Memory 3 Transmitter 4 Transmitting Unit 41 Digital Analog Converter 42 Modulator 43 High Frequency Amplifier 5 Receiving section 51 Band limiting filter 52 Low noise amplifier 53 Demodulator 54 Amplifier 55 Analog to digital converter 6 Circulator 7 Antenna 8 Low pass filter S 1 Transmission signal S 2 Reception signal S 3 Control signal S 4 Baseband signal f 0 Carrier

Claims (19)

  1. A communication device that performs wireless data communication with a data carrier using one or a plurality of channels on a frequency band divided into a plurality of sections,
    A transmission unit that transmits a transmission signal from the communication device using the first channel;
    A receiver that uses a second channel, which is a channel different from the first channel, and that receives a received signal from a data carrier using a single sideband;
    A storage unit storing a communication mode for specifying a use area of the second channel;
    A controller that dynamically changes the communication mode,
    A communication apparatus, wherein a control unit performs data communication with a data carrier by dynamically changing a communication mode.
  2.   The communication apparatus according to claim 1, wherein the second channel includes one channel or a plurality of continuous channels.
  3.   The communication device according to claim 2, wherein the control unit dynamically changes the communication mode so that the number of channels of the second channel is selected in descending order.
  4. Before performing data communication, it has carrier sense means for performing carrier sense to search for the free state of each channel by measuring the received power intensity in units of channels,
    3. The communication according to claim 1, wherein when there is an empty channel as a result of the search by the carrier sense means, the control unit sets a communication mode so as to perform data communication through the empty channel. apparatus.
  5. Before performing data communication, it has carrier sense means for performing carrier sense to search for the free state of each channel by measuring the received power intensity in units of channels,
    5. As a result of the search by the carrier sense means, if there is no free channel, the control unit sets a communication mode suitable for the received power intensity. The communication device according to item.
  6. Before performing data communication, carrier sense means for performing carrier sense for searching for a free state of each channel by measuring the received power intensity of each channel,
    An empty channel information accumulating unit that accumulates information on channel availability every time carrier sense is performed,
    The communication device according to claim 1 or 2, wherein the control unit sets a communication mode so as to perform data communication through a channel having a lot of free states with reference to information on the free state.
  7. Free channel information storage in which information about the free state of the channel obtained by performing carrier sense to search the free state of each channel by measuring the received power intensity in units of channels before data communication is stored in advance Part
    The communication device according to claim 1 or 2, wherein the control unit sets a communication mode so as to perform data communication through a channel having a lot of free states with reference to information on the free state.
  8. Before performing data communication, carrier sense means for performing carrier sense for searching for a free state of each channel by measuring the received power intensity of each channel,
    A free channel information storage unit that stores information about free channels every time carrier sense is performed;
    When a plurality of empty channels are searched for by carrier sense, the control unit obtains the channel empty probability of each channel from the empty channel information storage unit, and immediately before the empty channel searched for by carrier sense and the channel empty 3. The communication apparatus according to claim 1, wherein the communication mode is set so that data communication is performed by comparing the probability and selecting a channel having the highest channel vacancy probability among the immediately preceding vacant channels.
  9.   7. The communication apparatus according to claim 6, wherein a warning is issued at the same time as the communication mode is set, after the communication mode is set, or when data communication is performed.
  10.   A communication system comprising the communication device according to claim 1 and a data carrier capable of data communication with the communication device.
  11. A communication device according to claim 6, an external control device capable of communicating with the communication device, and a data carrier capable of data communication with the communication device,
    The communication device transmits a warning signal to the external control device at the same time when the communication mode is set, after the communication mode is set, or when data communication is performed, and the external control device outputs the warning signal. A communication system characterized by issuing a warning to a user when received.
  12. A communication method for performing wireless data communication with a data carrier using one or a plurality of channels on a frequency band divided into a plurality,
    A first step of transmitting a transmission signal using a first channel;
    A second step of using a second channel, which is a channel different from the first channel, and receiving a received signal from the data carrier using a single sideband;
    A third step of dynamically changing a communication mode for specifying a use area of the second channel,
    A communication method comprising performing data communication with a data carrier by dynamically changing a communication mode.
  13.   The communication method according to claim 12, wherein the second channel includes one channel or a plurality of continuous channels.
  14.   The communication method according to claim 12, wherein the communication mode is dynamically changed so that the number of channels of the second channel is selected in descending order.
  15. Before performing data communication, the method includes a fourth step of performing carrier sense for searching for a free state of each channel by measuring the received power intensity of each channel,
    14. The communication method according to claim 12 or 13, wherein if there is an empty channel as a result of the search, a communication mode is set so that data communication is performed using the empty channel.
  16. Before performing data communication, the method includes a fourth step of performing carrier sense for searching for a free state of each channel by measuring the received power intensity of each channel,
    The communication method according to claim 12 or 13, wherein if there is no free channel as a result of the search, a communication mode suitable for the received power intensity is set.
  17. A fourth step of performing carrier sense for searching for a free state of each channel by measuring received power intensity in units of channels before performing data communication;
    A fifth step of accumulating information about channel availability every time carrier sense is performed,
    The communication method according to claim 12 or 13, wherein the control unit sets a communication mode so as to perform data communication through a channel having a lot of free states with reference to information on the free state.
  18.   Before performing data communication, measure the received power intensity of each channel to search for the free state of each channel. By performing carrier sense, the channels with many free states are stored in advance. 14. The communication method according to claim 12, wherein a communication mode is set so as to perform data communication.
  19. A fourth step of performing carrier sense for searching for a free state of each channel by measuring received power intensity in units of channels before performing data communication;
    A fifth step of accumulating information about available channels every time carrier sense is performed,
    When a plurality of empty channels are searched by carrier sense, the channel empty probability of each channel is obtained from the information on the accumulated empty channels, and the previous empty channel and channel empty probability that are empty channels searched by carrier sense are acquired. 14. The communication method according to claim 12 or 13, wherein the communication mode is set so that data communication is performed by selecting a channel having the highest channel availability probability among the immediately preceding idle channels.
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