JP4334530B2 - Wireless communication method and wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication method and a wireless communication system that perform wireless communication while changing the communication frequency and causing hopping.

  This type of wireless communication method performs wireless communication while changing the communication frequency and performing hopping, thereby reducing the influence of noise on the communication and improving the use efficiency of the communication frequency.

  On the other hand, in the communication frequency band used for wireless communication, if the communication frequency being used is used redundantly, the communication quality is deteriorated. Also, if the communication power is not biased to a specific frequency, the communication frequency utilization efficiency is reduced.

  For this reason, for example, in Patent Document 1, after measuring interference waves (noise) in the entire communication frequency band used for wireless communication, a frequency with low interference waves is selected and used, thereby reducing communication quality. Preventing the use efficiency of communication frequency.

In Patent Document 2, referring to the communication history of the frequency usage history table, if it is determined that the usage frequency is biased, the frequency corresponding to the shortest time among the past usage times is selected, and the frequency If there is no communication history in the usage history table or there is no bias in the usage frequency, the usage frequency is selected based on random numbers, thereby preventing the communication power from being biased to a specific frequency.
JP-A-6-334630 JP-A-8-32488

  By the way, in the wireless communication method for hopping the communication frequency described in Patent Documents 1 and 2 and the like, it is assumed that communication is possible in the entire band of the communication frequency used for wireless communication. However, depending on the type of wireless communication system that hops the communication frequency, communication is not always possible in the entire band of the communication frequency.

  For example, in the RFID (Radio Frequency Identification) system, the communication frequency band of the wireless tag may be narrower than the communication frequency band of the reader / writer in order to reduce the size of the wireless tag. The wireless tag is not always communicable with the entire band.

  In such a system, when the communication frequency is hopped out of the frequency band in which the wireless tag can communicate, the wireless tag becomes incapable of communication, communication is interrupted, and a communication error occurs. In particular, in the case of a battery-less passive wireless tag, the radio wave received from the reader / writer is converted into electric power and used, so if communication becomes impossible due to hopping, the power supply will be cut off. It was reset, and it was necessary to start communication again. When there was a lot of communication, it became a fatal problem.

  Further, even a wireless tag equipped with a battery and capable of maintaining a communication state has a communication error and a congestion overhead when communication becomes impossible due to hopping.

  Such a problem occurs not only in the RFID system but also in a cellular phone to which a wireless communication method for hopping a communication frequency is applied. In this type of mobile phone, even if the communication frequency band of the mobile phone is essentially the same as the communication frequency band of the radio base station, if the mobile phone itself moves, the propagation state of radio waves changes, and communication that can be transmitted and received Since the frequency changes from moment to moment, communication is not always possible in the entire communication frequency band used for wireless communication. For this reason, the same problem as the above-described wireless tag has occurred.

  Therefore, in the system having such a problem, it is difficult to apply the techniques disclosed in Patent Documents 1 and 2 and it is difficult to reduce the influence of noise and improve the use efficiency of the communication frequency.

  Therefore, the present invention has been made in view of the above-described conventional problems, and stable wireless communication is possible while hopping the communication frequency even if communication is not possible in the entire communication frequency band used for wireless communication. It is an object of the present invention to provide a wireless communication method and a wireless communication system that can be continued to the above, and can reduce the influence of noise and improve the use efficiency of communication frequencies.

  In order to solve the above problems, a wireless communication method of the present invention is a search mode for searching for a communication frequency by hopping a communication frequency in the wireless communication method for performing wireless communication while changing the communication frequency and performing hopping. And an optimization mode for finding a frequency with higher communication strength by performing hopping from the communication frequency with a width smaller than the hopping when a communication frequency capable of communication is found in the search mode.

  Further, following the hopping control in the optimization mode, a stable communication mode is provided in which a communication frequency band in which communication is stable is determined and the communication frequency is hopped in the communication frequency band in which this communication is stable.

  On the other hand, another wireless communication method of the present invention is a wireless communication method for performing wireless communication while changing the communication frequency and performing hopping, and includes a search mode and an optimization mode, and the search mode hops the communication frequency. A first frequency setting step for setting communication quality, and a first quality measurement step for measuring communication quality based on a received signal at the communication frequency during communication at the communication frequency set in the one frequency setting step, The first frequency setting step and the first quality measurement step are repeated until the communication frequency at which the communication quality measured in the first quality measurement step is equal to or higher than a certain communication quality is found, and the optimization mode depends on the search mode. A second frequency setting step of performing hopping from the found communication frequency and setting the communication frequency; During communication at the communication frequency set in the setting step, a second quality measurement step for measuring communication quality based on a received signal at this communication frequency, the current communication quality measured in the two quality measurement step, and the previous communication quality A comparison step for comparing the communication quality, and the communication frequency set in the second frequency setting step is controlled according to the comparison result in the comparison step.

  In the present invention, if the comparison result in the comparison step indicates that the current communication quality is higher than the previous communication quality, the next communication frequency set in the second frequency setting step is set to the previous communication frequency. If the result of comparison in the comparison step is that the current communication quality is lower than the previous communication quality, the second frequency setting step is performed. The next communication frequency set in is shifted in the direction opposite to the frequency shift direction from the previous communication frequency to the current communication frequency.

  Furthermore, in the present invention, in the first and second frequency setting steps, the communication frequency is set using a random number, a specified numerical value table, or a specified code sequence.

  In the present invention, the second frequency setting step, the second quality measurement step, and the comparison step in the optimization mode are repeated a plurality of times.

  Further, in the present invention, following the control of the communication frequency in the second frequency setting step according to the comparison result in the comparison step, the communication quality measured in the two quality measurement step becomes a certain value or more. A stable communication mode for obtaining a frequency band and hopping the communication frequency in this communication frequency band is provided.

  In the present invention, if the comparison result in the comparison step indicates that the current communication quality is not a certain value or more, the next communication frequency set in the second frequency setting step is changed from the previous communication frequency. It is set by shifting in the direction opposite to the frequency shift direction to the current communication frequency.

  Furthermore, the present invention is provided with a bias correction mode for correcting a communication power bias in a communication frequency band in which the communication frequency can be changed by hopping.

  In another wireless communication system of the present invention, the wireless communication method of the present invention is applied.

  According to the wireless communication method of the present invention, in the search mode, the communication frequency is hopped to search for a communicable communication frequency, and in the optimization mode, hopping with a smaller width is subsequently performed from the communication frequency found in the search mode. To find a frequency with higher communication strength. For this reason, even if communication is not possible in the entire communication frequency band used for wireless communication, a communication frequency that can be communicated can be found and the communication frequency can be within the communicable frequency band, and communication cannot be performed midway. There is nothing.

  Furthermore, in the stable communication mode, the communication frequency band in which the communication is stable is determined, and the communication frequency is hopped in the communication frequency band in which the communication is stable, so that the communication can be continued stably and the communication amount is large. Also, communication can be performed normally.

  On the other hand, according to another wireless communication method of the present invention, in the search mode, the communication frequency is set by hopping, and communication is performed based on the received signal of the communication frequency when communication is performed at the set communication frequency. Measurement is performed, and hopping is repeated until a communication frequency at which the measured communication quality is equal to or higher than a certain communication quality is found. Therefore, even if communication is not possible in the entire communication frequency band used for wireless communication, a communication frequency that can be communicated can be found. In the optimization mode, hopping is performed from the communication frequency found in the search mode, the communication frequency is set, and communication is performed based on the received signal at the communication frequency when communication is performed at the set communication frequency. The measured current communication quality is compared with the previous communication quality, and the communication frequency set by hopping is controlled according to the comparison result. For example, if the comparison result shows that the current communication quality is higher than the previous communication quality, the next communication frequency set by hopping is shifted in the frequency shift direction from the previous communication frequency to the current communication frequency. If the comparison result shows that the current communication quality is lower than the previous communication quality, the next communication frequency set by hopping is changed from the previous communication frequency to the current communication frequency. It is set by shifting in the direction opposite to the frequency shift direction. As a result, the communication quality at the communication frequency set by hopping is improved, and communication is not disabled midway.

  The communication frequency is set by hopping using, for example, a random number, a specified numerical table, or a specified code sequence.

  In the optimization mode, communication frequency setting by hopping, communication quality measurement, and communication quality comparison are repeated a plurality of times. As a result, the communication quality at the communication frequency set by hopping gradually increases and communication is not interrupted.

  Further, in the stable communication mode, following the control of the communication frequency according to the comparison result of the communication quality, a communication frequency band in which the measured communication quality becomes a certain value or more is obtained, and the communication frequency is hopped in this communication frequency band. ing. For this reason, communication can be continued stably, and communication can be normally performed even if the amount of communication is large.

  If the communication quality comparison result indicates that the current communication quality is not above a certain value, the next communication frequency set by hopping is opposite to the frequency shift direction from the previous communication frequency to the current communication frequency. It is set by shifting in the direction. Also in this case, the communication quality at the communication frequency set by hopping is high, and communication is not disabled midway.

  Furthermore, a bias correction mode for correcting a communication power bias in a communication frequency band in which the communication frequency can be changed by hopping is provided. For this reason, even if the frequency band that can be communicated in the optimization mode is used unevenly or the communication frequency band that stabilizes the wireless communication in the stable communication mode is used unevenly, the communication power in the communication frequency band becomes uniform. Thus, the communication frequency utilization efficiency does not decrease.

  Further, another wireless communication system of the present invention is the one to which the wireless communication method of the present invention is applied, and therefore has the same operations and effects as this wireless communication method.

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

  FIG. 1 is a block diagram showing an RFID system to which an embodiment of the wireless communication method of the present invention is applied. This RFID system includes a reader / writer 1 and a wireless tag 2, and performs bidirectional wireless communication while changing the communication frequency and causing hopping.

  The reader / writer 1 changes the communication frequency to cause hopping, and at each hopping, transmits a radio wave having the same communication frequency and receives and demodulates the radio wave having the same communication frequency. The wireless tag 2 is a general battery-less passive type. When receiving a radio wave from the reader / writer 1, the radio tag 2 converts the received radio wave into electric power and operates with this electric power. In addition, when the radio tag 2 receives a radio wave from the reader / writer 1, the antenna impedance is controlled to change the reflectance of the radio wave received by the antenna, thereby generating a transmission radio wave.

  Accordingly, the communication frequency is set on the reader / writer 1 side, and the communication frequency on the wireless tag 2 side follows this.

  The reader / writer 1 includes a control unit 11, an oscillator 12, a modulator 13, a power amplifier 14, a circulator 15, an antenna 16, a demodulator 17, an analog-digital converter 18, a data decoder 19, a received power measuring device 20, and a received noise. A power meter 21 is provided.

  The control unit 11 includes a CPU, a memory, an interface, and the like, and controls the entire reader / writer 1.

  Specifically, the control unit 11 hops and sets the communication frequency using a random number or the like, drives and controls the oscillator 12, and outputs the carrier signal of the set communication frequency from the oscillator 12. The carrier signal having the communication frequency of the oscillator 12 is applied to the modulator 13 and the demodulator 17. Further, the control unit 11 outputs transmission data conforming to a communication protocol performed with the wireless tag 2 to the modulator 13.

  When receiving the transmission data from the control unit 11 and the carrier signal of the communication frequency from the oscillator 12, the modulator 13 modulates the carrier signal according to the transmission data, and forms and outputs a transmission signal indicating the transmission data. This transmission signal is amplified by the power amplifier 14, then added to the antenna 16 through the circulator 15, and transmitted as a radio wave from the antenna 16.

  When the radio tag 2 receives the radio wave from the reader / writer 1 as described above, the antenna impedance is controlled to change the reflectance of the radio wave received by the antenna, thereby receiving the data in accordance with the communication protocol. A transmission radio wave indicating is generated.

  The radio wave from the wireless tag 2 is received by the antenna 16 of the reader / writer 1 and becomes a received signal. This received signal is applied to the demodulator 17 through the circulator 15. When the demodulator 17 receives the reception signal from the antenna 16 and the carrier signal of the communication frequency from the oscillator 12, the demodulator 17 demodulates the reception signal using the carrier signal of the communication frequency and indicates the reception data from the wireless tag 2. The signal is formed as a demodulated output, and this analog signal is output to the analog-to-digital converter 18. When the analog signal is input, the analog-to-digital converter 18 performs A / D conversion on the analog signal, and forms and outputs a digital signal G1 indicating data received from the wireless tag 2.

  When the data decoder 19 receives the digital signal G 1 from the analog-digital converter 18, the data decoder 19 decodes the digital signal G 1, reproduces the received data G 2 from the wireless tag 2, and outputs it to the control unit 11. Further, when receiving the digital signal G <b> 1 from the analog-digital converter 18, the reception power measuring unit 20 obtains reception power from the digital signal G <b> 1 and notifies the control unit 11 of the reception power. Further, when receiving the digital signal G1 from the analog-to-digital converter 18, the reception noise power measuring device 21 obtains reception noise power from the digital signal G1 and notifies the control unit 11 of the reception noise power.

  When receiving the received data G2 from the data decoder 19, the control unit 11 processes the received data G2 and obtains an error rate of the received data G2. Further, the control unit 11 uses at least one of the error rate of the received data G2, the received power notified from the received power measuring device 20, and the received noise power notified from the received noise power measuring device 21, to determine the communication quality. And the next communication frequency set by hopping is set based on the determination result.

  Here, for example, bi-directional wireless communication is performed while changing the communication frequency in units of 1 MHz and performing hopping in a frequency band of 2402 to 2425 MHz (bandwidth is 23 MHz). Therefore, the communication frequency is one of 24 communication frequencies 2402 MHz, 2403 MHz,..., 2425 MHz, or 2425 MHz.

  The reader / writer 1 is a stationary type, has sufficient communication capability, and can communicate in the entire band of 2402 to 2425 MHz (bandwidth is 23 MHz). On the other hand, since the wireless tag 2 is prioritized for miniaturization, there is a trade-off relationship between the gain of the antenna and the like and the frequency band in which communication is possible, and communication is possible to maintain the gain of the antenna and the like The width of the frequency band is narrower than the bandwidth 23 MHz at which the reader / writer 1 can communicate.

  For this reason, when the communication frequency is hopped outside the communicable frequency band of the wireless tag 2 on the reader / writer 1 side, the wireless tag 2 becomes unable to communicate, communication is interrupted, and a communication error occurs. . Further, since the wireless tag 2 uses the received radio wave from the reader / writer 1 after converting it into electric power, if communication becomes impossible due to hopping, the power supply is interrupted, and for this reason, the wireless tag 2 is reset. You have to start communication again.

  Therefore, in this embodiment, when the communication frequency is hopped on the reader / writer 1 side, hopping is controlled so that the communication frequency falls within the frequency band in which the wireless tag 2 can communicate. For this reason, even if the wireless tag 2 is not communicable in the entire band of 2402 to 2425 MHz with which the reader / writer 1 can communicate, the wireless tag 2 does not become incapable of communication.

  However, the frequency bands of the plurality of wireless tags 2 are set to be appropriately distributed over the entire band of 2402 to 2425 MHz. Accordingly, the reader / writer 1 needs to control the hopping of the communication frequency so that the communication power is not biased in the entire band of 2402 to 2425 MHz while performing communication with the plurality of wireless tags 2.

  Next, an outline of communication frequency hopping control by the reader / writer 1 will be described with reference to the flowchart of FIG. 2 and the transition diagram of the communication frequency of FIG.

  The reader / writer 1 transmits transmission data while waiting for reception data from the wireless tag 2 while setting the communication frequency to be randomly hopped in units of 1 MHz within 2402 to 2425 MHz in which communication is possible (step S101). Search mode).

  For example, as shown in FIG. 3, the communication frequency f (n) randomly changes as f (1), f (2),... Note that n in f (n) is an integer and corresponds to time.

  At this time, even if the communication frequencies f (1), f (2), f (3), and f (4) are sequentially set, these communication frequencies f (1) to f (4) are communicated with the wireless tag 2. Since it is out of the possible frequency band m, transmission data from the reader / writer 1 is not received by the wireless tag 2, and reception data is not transmitted from the wireless tag 2. Therefore, the reader / writer 1 cannot receive the data received from the wireless tag 2 and, for this reason, determines that there is no wireless tag 2 (“No” in step S102), and repeats the search mode in step S101. .

  Subsequently, when the communication frequency f (5) is set, since the communication frequency f (5) is in the frequency band m in which the wireless tag 2 can communicate, the transmission data from the reader / writer 1 is transmitted to the wireless tag 2. And the received data is transmitted from the wireless tag 2. When the reader / writer 1 receives the reception data from the wireless tag 2, the reader / writer 1 determines that the wireless tag 2 is present ("Yes" in step S102).

  When the reader / writer 1 determines that the wireless tag 2 is present, the reader / writer 1 performs hopping from the communication frequency f (5) searched in the search mode in step S101, and the communication frequency f (n) is the communication of the wireless tag 2. For example, the communication frequencies f (6), f (7), and f (8) are sequentially set so as to fall within the possible frequency band m (the optimization mode in step S103). For this reason, communication does not become impossible on the way.

  The reader / writer 1 determines whether or not the data communication with the wireless tag 2 has ended in the optimization mode of step S103 (step S104). As long as data communication with the wireless tag 2 continues ("continuation" in step S104), it is determined whether the communication power is biased in all bands of 2402 to 2425 MHz (step S105), It is determined whether or not the communication is stable (step S106). At this time, if the communication power is not biased in all bands of the communication frequency (“bias index <first threshold” in step S105) and communication with the wireless tag 2 is not stable (“unstable” in step S106). “), The optimization mode of step S103 is repeated, and the communication frequency f (n) falling within the frequency band m is set each time.

  In the reader / writer 1, when communication power is not biased in all bands of the communication frequency (“bias index <first threshold” in step S <b> 105), communication with the wireless tag 2 becomes stable (step S <b> 106). And “stable”), a frequency band m0 in which the communication of the wireless tag 2 is stable is obtained while continuing hopping from the communication frequency f (8) set in the optimization mode in step S101. For example, the communication frequencies f (9), f (10), f (11), and f (12) are sequentially set by limiting the hopping of the communication frequency (stable communication mode in step S107). Thereby, communication can be continued stably and communication can be normally performed even if the amount of communication is large.

  Even in the stable communication mode of step S107, as long as data communication with the wireless tag 2 continues ("continuation" in step S107), it is determined whether communication power is biased in all bands of the communication frequency (step S105) and It is determined whether or not communication with the wireless tag 2 is stable (step S106).

  When the reader / writer 1 completes data communication with the wireless tag 2 during the optimization mode in step S103 or the stable communication mode in step S107 ("complete" in step S107), or even if communication is not completed. If the communication power is biased in all bands of the communication frequency (“bias index ≧ first threshold” in step S105), the communication frequency is shifted outside the frequency band m0 in order to correct the bias of the communication power. By hopping, for example, communication frequencies f (13), f (14), f (15),... Are sequentially set (bias correction mode in step S108). Thereby, the bias of the communication power in the entire band of the communication frequency is corrected.

  The reader / writer 1 determines whether or not the communication power bias in all bands of the communication frequency has been sufficiently corrected in the bias correction mode in step S108 (step S109). If the communication power bias in the entire communication frequency band is not sufficiently corrected (“bias index ≧ second threshold” in step S109), the bias correction mode in step S108 is continued. If the communication power bias in the entire communication frequency band is sufficiently corrected (“bias index <second threshold” in step S109), the process returns to step S102.

  Next, the search mode (subroutine) in step S101 of FIG. 2 will be described in detail with reference to the flowchart of FIG.

  In the reader / writer 1, the control unit 11 obtains a random number J by a known method, substitutes the random number J into the following equation (1), and obtains and sets the communication frequency f (n) (step S201). More specifically, the communication frequency f (n) that is closest to the value obtained from the following equation (1) is selected from 24 communication frequencies 2402 MHz, 2403 MHz,..., 2425 MHz, and 2425 MHz used as communication frequencies. Set. Thereby, one of 24 communication frequencies 2402 MHz to 2425 MHz is randomly selected, and the communication frequency f (n) is set. Instead of the random number J, a value obtained from a prescribed numerical table or a value obtained from a prescribed code sequence may be used.

f (n) = F + dF × J (1)
However, F is the lowest frequency 2402 MHz of the frequency band 2402 to 2425 MHz in which the reader / writer 1 can communicate. DF has a bandwidth of 23 MHz in the frequency band 2402 to 2425 MHz. Further, the random number J is a value between 0 and 1.

  When the control unit 11 obtains and sets the communication frequency f (n), the control unit 11 outputs a carrier wave signal of the communication frequency f (n) from the oscillator 12 to the modulator 13 and outputs transmission data to the modulator 13. The modulator 13 modulates the carrier wave signal according to the transmission data, forms a transmission signal indicating the transmission data, and outputs it. This transmission signal is transmitted as a radio wave from the antenna 16 (step S202). Thereby, a radio wave having a communication frequency f (n) indicating transmission data is transmitted from the antenna 16.

  At this time, the demodulator 17 receives the carrier signal having the communication frequency f (n) from the oscillator 12, demodulates the received signal from the antenna 16 using the carrier signal, and outputs an analog signal. The analog signal is converted into a digital signal G1 by the analog-digital converter 18, and the digital signal G1 is decoded by the data decoder 19 to obtain received data G2 (step S203). The reception power measuring device 20 obtains reception power from the digital signal G1. Further, the reception noise power measuring device 21 obtains reception noise power from the digital signal G1.

  The control unit 11 then uses at least one of the error rate of the received data G2, the received power obtained by the received power measuring device 20, and the received noise power obtained by the received power measuring device 21 to use the communication quality Q. (n) is determined (step S204).

  For example, the bit error rate BRR and the frame error rate FER are obtained based on the received data G2 (decoded output) of the data decoder 19, and the reciprocal of this error rate is defined as the communication quality Q (n). Such an error rate can be obtained by adding a cyclic code such as CRC (Cyclic Redundancy Checking) to the received data G2.

  Further, the received power obtained by the received power measuring device 20 may be used as the communication quality Q (n). For example, as shown in FIG. 5, the average value of the amplitude of the digital signal G1 from the analog-digital converter 18 can be measured as the received power. When the range of the received power is −80 (dBm) to 0 (dBm), the communication quality is the lowest when the communication quality Q (n) = − 80 (dBm), and the communication quality Q (n) = 0 (dBm ) Is the highest communication quality.

  Alternatively, CNR (Carrier to Noise Ratio) can be obtained as reception noise power by the reception noise power measuring device 21, and the reciprocal of this CNR can be used as the communication quality Q (n). For example, as shown in FIG. 6, the CNR can be obtained by a calculation of subtracting the reception data (decoded output) G2 of the data decoder 19 from the digital signal G1 from the analog-digital converter 18.

  FIG. 7 is a graph showing the relationship between the communication quality Q (n) and the frequency band m with which the wireless tag 2 can communicate. As shown in this graph, the communication quality Q (n) is highest at the center frequency m1 of the frequency band m in which the wireless tag 2 can communicate, and gradually decreases as the distance from the center frequency m1 increases.

  Thus, when the control unit 11 performs transmission / reception at the communication frequency f (n) and obtains the communication quality Q (n), the control unit 11 stores and stores the communication quality Q (n). Then, after the transmission / reception is stopped (step S205), n of the communication frequency f (n) is incremented by one and updated, and n is set next time (step S206), and the process returns to step S102 of FIG.

  In such a search mode, for example, as shown in FIG. 3, communication frequencies f (1), f (2), f (3), and f (4) are sequentially set at random by hopping. A communication protocol between the writer 1 and the wireless tag 2 is attempted, the communication quality Q (n) is measured, and this communication quality Q (n) is stored.

  If the communication protocol is normally performed between the reader / writer 1 and the wireless communication tag 2 from the start of transmission in step S202 to the stop of transmission / reception in step S206, data is transmitted / received between the two, and step S102 in FIG. 2 is performed. It is determined that the wireless tag 2 is present. If the communication protocol is not established between the reader / writer 1 and the wireless communication tag 2, data is not transmitted / received between them, and it is determined that there is no wireless tag 2 in step S102 of FIG.

  Next, the optimization mode (subroutine) in step S103 of FIG. 2 will be described in detail with reference to the flowchart of FIG.

  In the optimization mode, the shift direction and shift width of the communication frequency by hopping are set, the current communication frequency f (n-1) is hopped with the set shift direction and shift width, and the next communication frequency f ( n) is determined and set. By repeating this, hopping of the communication frequency in the optimization mode is performed.

  In the reader / writer 1, the control unit 11 has already stored the measured communication quality Q (n-1) and the previous communication quality Q (n-2), and these communication qualities Q (n-1). And Q (n-2) are compared (step S301). If the current communication quality Q (n-1) is lower than the previous communication quality Q (n-2) ("Q decrease" in step S301), the control unit 11 determines the communication frequency by hopping. -D indicating inversion of the shift direction is set (step S302). This is because the communication quality Q (n) at the next communication frequency f (n) is further deteriorated if the shift direction of the communication frequency by hopping is maintained as it is, so that the shift direction is reversed. is there.

  Subsequently, the control unit 11 changes the maximum shift width A by multiplying the maximum shift width A of the communication frequency by hopping in the optimization mode by the convergence constant dA (step S303). The convergence constant dA is set, for example, in the range of 1 <dA <2, and is used to converge the maximum shift width A by dividing the maximum shift width A by the convergence constant dA in step S312 described later. Accordingly, in step S303, the convergence of the maximum shift width A in the previous step S312 is invalidated. This is because the current communication quality Q (n-1) is lower than the previous communication quality Q (n-2), so that not only the shift direction of the communication frequency by hopping is reversed, but also the maximum shift width The convergence of A is invalidated, and the shift width of the communication frequency by hopping in the inverted shift direction is maintained or increased, and the next communication frequency f (n) is set to the previous communication frequency f (n-2) side. This is because the communication quality Q (n) at the next communication frequency f (n) is restored to the original value.

  Thereafter, the control unit 11 obtains the random number J by a known method, and obtains the current communication frequency f (n−1), the random number J, −D set in step S302, and the maximum shift width A obtained in step S303. Substituting into the following equation (2), the next communication frequency f (n) is obtained and set (step S304). Here, as in the above equation (1), the communication frequency closest to the value obtained by the following equation (2) from 24 communication frequencies 2402 MHz, 2403 MHz,..., 2425 MHz, 2425 MHz used as the communication frequency. Is set as the communication frequency f (n).

f (n) ← f (n−1) + D (A × J + 1) (2)
However, the random number J is a value between 0 and 1. The maximum shift width A is set with 15 MHz as an initial value, for example. Further, in the above formula (2), by adding 1 to the value of A × J, the value of D (A × J + 1) does not become 0, so that the next communication frequency f (n) is the current communication. It is avoided that the frequency f (n-1) is the same.

  If the current communication quality Q (n-1) is improved from the previous communication quality Q (n-2) ("Q improvement" in step S301), the control unit 11 determines the communication frequency by hopping. Since there is no need to change the shift direction and it is not necessary to invalidate the convergence of the maximum shift width A, the process proceeds to step S304 without going through steps S302 and S303. Then, the control unit 11 substitutes the current communication frequency f (n−1), the random number J, D indicating non-inversion of the shift direction of the communication frequency by hopping, and the maximum shift width A into the above equation (2). Next, the next communication frequency f (n) is obtained and set.

  For example, as shown in FIGS. 3 and 7, when hopping from the communication frequency f (5) to the communication frequency f (6), the communication frequency approaches the center frequency m1 of the frequency band m in which the wireless tag 2 can communicate. Therefore, the current communication quality Q (5) is improved over the previous communication quality Q (6). In this case, the communication frequency shift direction by hopping is not changed, the convergence of the maximum shift width A is not invalidated, the communication frequency is shifted smaller in the same direction as the previous time, and the next communication frequency f (7) is set. Will do.

  Further, when hopping from the communication frequency f (6) to the communication frequency f (7), the communication frequency is away from the center frequency m1 of the frequency band m in which the wireless tag 2 can communicate, so the current communication quality Q (6) Is lower than the previous communication quality Q (7). In this case, the communication frequency shift direction by hopping is changed, the convergence of the maximum shift width A is disabled, the communication frequency is greatly shifted in the opposite direction to the previous time, and the next communication frequency f (8) is set. Will do.

  As a result, the communication frequency f (n) is sequentially set as the communication frequencies f (5), f (6), f (7), f (8) by hopping, and the communication frequency f (n) is wireless. It gradually converges to the center of the frequency band m where tag 2 can communicate.

  In this way, when the control unit 11 obtains and sets the next communication frequency f (n), it confirms whether or not the next communication frequency f (n) is in a frequency band of 2402 to 2425 MHz that the reader / writer 1 can communicate with. After that ("YES" in step S305), the process proceeds to the next step S307.

  If the next communication frequency f (n) obtained by the above equation (2) is out of the frequency band in which the reader / writer 1 can communicate (“NO” in step S305), the control unit 11 The next communication frequency f (n) is corrected by substituting the communication frequency f (n-1), -D indicating reversal of the shift direction of the communication frequency due to hopping, and the maximum shift width A into the following equation (3). To reset (step S306). In this case as well, the communication frequency closest to the value obtained by the following equation (3) from the 24 communication frequencies 2402 MHz, 2403 MHz,..., 2425 MHz, 2425 MHz used as the communication frequency, as in the above equation (1). Is set as the communication frequency f (n). The following equation (3) corresponds to a value obtained by deleting the random number J (0 to 1) of the above equation (2). Therefore, the communication frequency f (n) obtained by the following equation (3) is out of the frequency band in which the reader / writer 1 can communicate with the next communication frequency f (n) obtained by the above equation (2). It is shifted to the frequency band side beyond the frequency band that has been lost and returned to this frequency band.

f (n) ← f (n−1) −D (A + 1) (3)
Thereafter, the control unit 11 outputs the carrier signal of the next communication frequency f (n) from the oscillator 12 to the modulator 13, outputs the transmission data to the modulator 13, and the communication frequency f (n) indicating the transmission data. ) Is transmitted from the antenna 16 (step S307).

  At this time, the demodulator 17 receives the carrier signal of the next communication frequency f (n) from the oscillator 12, demodulates the received signal from the antenna 16, and outputs an analog signal. The analog signal is converted into a digital signal G1 by the analog-digital converter 18, and the digital signal G1 is decoded by the data decoder 19 to obtain received data G2 (step S308). Also, the received power is obtained by the received power measuring device 20, and the received noise power is obtained by the received noise power measuring device 21.

  Then, similarly to step S204 in FIG. 2, the control unit 11 includes at least the error rate of the received data G2, the received power obtained by the received power measuring device 20, and the received noise power obtained by the received power measuring device 21. One is used to determine the communication quality Q (n) (step S309).

  Thus, when the control unit 11 performs transmission / reception at the communication frequency f (n) and obtains the communication quality Q (n), the control unit 11 stores and stores the communication quality Q (n). Then, after the transmission / reception is stopped (step S310), n of the communication frequency f (n) is incremented by one and updated, and the next n is set (step S311).

  In addition, the control unit 11 updates the maximum shift width A by dividing the maximum shift width A of the communication frequency by hopping in the optimization mode by the convergence constant dA (step S312). Since 1 <dA <2 as described above, the maximum shift width A is reduced by this update. Further, the maximum shift width A converges by repeating the optimization mode.

  However, as described above, if the current communication quality Q (n-1) is lower than the previous communication quality Q (n-2) ("Q decrease" in step S301), the shift direction is reversed. −D is set (step S302), and the maximum shift width A is changed by multiplying the maximum shift width A by the convergence constant dA (step S303). Therefore, in this case, the previous maximum shift width A before being updated in step S308 of the present optimization mode is used, and thereby the convergence of the maximum shift width A is suppressed.

  Thereafter, the process returns to step S104 in FIG.

  Thus, in the optimization mode, the communication frequency f (n) gradually converges to the center of the frequency band m in which the wireless tag 2 can communicate by hopping.

  Here, based on the comparison between the current communication quality Q (n-1) and the previous communication quality Q (n-2), the communication frequency shift direction by hopping is set. It may be determined whether or not the quality Q (n-1) is a certain value or more, and based on this determination, the shift direction of the communication frequency by hopping may be set. That is, when the current communication quality Q (n-1) is a certain value or more, the next communication frequency f (n) is changed from the previous communication frequency f (n-2) to the current communication frequency f (n). -1) is shifted in the frequency shift direction, and the convergence of the maximum shift width A is not suppressed. If the current communication quality Q (n-1) is not greater than a certain value, the next communication frequency f (n) is changed from the previous communication frequency f (n-2) to the current communication frequency f (n-). Shifting in the direction opposite to the frequency shift direction to 1) suppresses the convergence of the maximum shift width A.

  Next, the stable communication mode (subroutine) in step S107 of FIG. 2 will be described in detail with reference to the flowchart of FIG.

  In order to enter the stable communication mode, it must be determined that communication with the wireless tag 2 has been stabilized in step S106 of FIG. For example, when the maximum shift width A updated in step S312 of FIG. 8 becomes a certain value (for example, 3) or less, it can be determined that communication with the wireless tag 2 has become stable. Further, based on whether or not the communication quality Q (n) is stable, it may be determined whether or not the communication with the wireless tag 2 has been stabilized.

  When the stable communication mode is entered, a frequency band m0 in which the communication of the wireless tag 2 is stable is obtained, and the communication frequency is hopped within this frequency band m0.

  In the reader / writer 1, the control unit 11 stores at least the communication quality Q (n−10) from the previous 10 times to the communication quality Q (n−1) of this time. A communication quality of (for example, −20 (dBm)) or higher is selected, and a communication frequency when the selected communication quality product is obtained is obtained. Then, the maximum value of the obtained communication frequency is set to Fmax, the minimum value is set to Fmin, and the frequency band m0 where the communication of the wireless tag 2 is stabilized is set to Fmin to Fmax (step S401). Therefore, Fmin ≦ m0 ≦ Fmax.

  When the control unit 11 sets the frequency band m0 in which the communication of the wireless tag 2 is stable, the control unit 11 substitutes the random number J into the following equation (4) to obtain and set the next communication frequency f (n) (step S402). . Here, as in the above equation (1), the communication frequency closest to the value obtained by the following equation (4) from 24 communication frequencies 2402 MHz, 2403 MHz,..., 2425 MHz, 2425 MHz used as the communication frequency. Is set as the communication frequency f (n).

f (n) = J (Fmax−Fmin) + Fmin (4)
According to the following equation (4), the next communication frequency f (n) is obtained by adding the minimum value Fmin of the communication frequency to the product of the bandwidth of the frequency band m0 and the random number J (0 to 1). The communication frequency f (n) is set within the frequency band m0 where the communication of the wireless tag 2 is stable. For example, as shown in FIG. 3, the communication frequency f (n) is f (9), f (10), f (11), f (12) in the frequency band m0 where the communication of the wireless tag 2 is stable. Are set sequentially.

  Thus, when the control unit 11 obtains the next communication frequency f (n), the control unit 11 outputs the carrier signal of the next communication frequency f (n) from the oscillator 12 to the modulator 13 and outputs the transmission data to the modulator 13. Then, a radio wave having a communication frequency f (n) indicating transmission data is transmitted from the antenna 16 (step S403).

  At this time, the demodulator 17 receives the carrier signal of the next communication frequency f (n) from the oscillator 12, demodulates the received signal from the antenna 16, and outputs an analog signal. The analog signal is converted into a digital signal G1 by the analog-digital converter 18, and the digital signal G1 is decoded by the data decoder 19 to obtain received data G2 (step S404).

  Then, similarly to step S204 in FIG. 4, the control unit 11 includes at least the error rate of the received data G2, the received power obtained by the received power measuring device 20, and the received noise power obtained by the received power measuring device 21. One is used to determine the communication quality Q (n), and the communication quality Q (n) is stored and stored (step S405).

  Further, after stopping transmission / reception (step S406), the control unit 11 increments and updates n of the communication frequency f (n) by one and sets the next n (step S407). The process returns to step S104.

  As described above, in the stable communication mode, the communication frequency is hopped within the frequency band m0 in which the communication of the wireless tag 2 is stable. Therefore, the communication can be continued stably, and the communication is normally performed even if the communication amount is large. It can be carried out.

  Next, another example of the stable communication mode (subroutine) in step S107 of FIG. 2 will be described in detail with reference to the flowchart of FIG.

  In the reader / writer 1, the control unit 11 compares the measured current communication quality Q (n-1) with the previous communication quality Q (n-2) (step S501). If the current communication quality Q (n-1) is lower than the previous communication quality Q (n-2) ("Q decrease" in step S501), the control unit 11 determines the communication frequency by hopping. -D indicating the inversion of the shift direction is set (step S502). This is because the communication quality Q (n) at the next communication frequency f (n) is further lowered if the shift direction of the communication frequency by hopping is maintained as it is.

  If the current communication quality Q (n-1) is improved from the previous communication quality Q (n-2) ("Q improvement" in step S503), the control unit 11 determines the communication frequency by hopping. Since there is no need to change the shift direction, the process does not go through step S502.

  Thereafter, the control unit 11 obtains the random number J by a well-known method, the current communication frequency f (n−1), the random number J, D or −D, and the maximum shift width A of the communication frequency by hopping in stable communication. Is substituted into the above equation (2) to determine and set the next communication frequency f (n) (step S503). However, the maximum shift width A is smaller than the value of the maximum shift width A in the optimization mode, and is set to 3 MHz, for example.

  The control unit 11 confirms that the next communication frequency f (n) is in the frequency band m0 (Fmin ≦ m0 ≦ Fmax) in which the communication of the wireless tag 2 is stable (“YES” in step S504). ), And proceeds to the next Step S506.

  If the next communication frequency f (n) is out of the frequency band m0 (Fmin ≦ m0 ≦ Fmax) where the communication of the wireless tag 2 is stable (“NO” in step S504), the control unit 11 The next communication frequency f (n) is corrected by substituting the communication frequency f (n-1), -D indicating reversal of the shift direction of the communication frequency due to hopping, and the maximum shift width A into the above equation (3). To reset (step S505). As a result, the next communication frequency f (n) is shifted to the frequency band m0 more than the frequency band that has deviated from the frequency band m0 where the communication of the wireless tag 2 is stable, and returned to this frequency band m0. It will be a thing.

  Thereafter, the control unit 11 tries to transmit and receive data using the next communication frequency f (n) (steps 506 and S507). Then, similarly to step S204 in FIG. 2, the control unit 11 includes at least the error rate of the received data G2, the received power obtained by the received power measuring device 20, and the received noise power obtained by the received power measuring device 21. One is used to determine the communication quality Q (n) (step S508).

  Thus, when the control unit 11 performs transmission / reception at the communication frequency f (n) and obtains the communication quality Q (n), the control unit 11 stores and stores the communication quality Q (n). Further, after the transmission / reception is stopped (step S509), n of the communication frequency f (n) is incremented by one, updated, n is set next time (step S510), and the process returns to step S104 of FIG.

  The process of the flowchart of FIG. 10 is equivalent to a process in which the maximum shift width A in the optimization mode of the flowchart of FIG. 8 is fixed without being converged.

  Next, the bias correction mode (subroutine) in step S108 of FIG. 2 will be described in detail with reference to the flowchart of FIG.

  In order to enter the bias correction mode, it is determined in step S104 in FIG. 2 that communication has been completed, or in step S105, it has been determined that communication power has become biased over the entire communication frequency band in which the reader / writer 1 can communicate. Don't be. In order to determine that the communication power is biased, for example, based on the communication frequency f (n-240) from 240 times before to the current communication frequency f (n-1), 24 communication frequencies 2402 MHz, 2403 MHz,. ..., the usage frequency used as the communication frequency is obtained separately for 2425 MHz and 2425 MHz, the difference between the minimum usage frequency and the maximum usage frequency is set as a bias index, and when this bias index is equal to or greater than the first bias threshold, communication power Is determined to be biased. Here, since the past number of uses is 240 and 24 communication frequencies are used, the bias index is 0 if the use frequency is 10 for any of the 24 communication frequencies. Further, if the minimum usage frequency is 0 and the maximum usage frequency is 30, the bias index is 30. If the first bias threshold is 6, when the bias index is 30, the bias index 30 is equal to or greater than the first bias threshold 6, so it is determined that the communication power is biased.

  Then, when the bias correction mode is entered, it is preferentially selected and used from the lowest communication frequency of the 24 communication frequencies.

  In the reader / writer 1, the control unit 11 selects the one with the lowest usage frequency among the 24 communication frequencies, and obtains and sets the selected communication frequency as the next communication frequency f (n) (step S601).

  The control unit 11 confirms that the next communication frequency f (n) does not match the current communication frequency f (n-1) (“f (n) ≠ f (n−1 in step S602). ) "), The process proceeds to the next step S604.

  When the next communication frequency f (n) matches the current communication frequency f (n-1) ("f (n) = f (n-1)" in step S602), the control unit 11 The communication frequency with the second lowest usage frequency is selected, and the selected communication frequency is reset as the next communication frequency f (n) (step S603). As a result, the next communication frequency f (n) and the current communication frequency f (n-1) are prevented from matching.

  Thereafter, the control unit 11 attempts to transmit / receive data using the next communication frequency f (n) (steps 604 and S605). Then, similarly to step S204 in FIG. 2, the control unit 11 includes at least the error rate of the received data G2, the received power obtained by the received power measuring device 20, and the received noise power obtained by the received power measuring device 21. One is used to determine the communication quality Q (n) (step S606).

  Thus, when the control unit 11 performs transmission / reception at the communication frequency f (n) and obtains the communication quality Q (n), the control unit 11 stores and stores the communication quality Q (n). Further, after the transmission / reception is stopped (step S607), n of the communication frequency f (n) is incremented by one, updated, n is set next time (step S608), and the process returns to step S109 of FIG.

  In step S109 of FIG. 2, it is determined whether or not the communication power bias has been sufficiently corrected. If it is determined that the communication power bias is not sufficiently corrected, the process returns to step S108 and the bias correction mode of the flowchart of FIG. Accordingly, the bias correction mode is repeated until it is determined in step S109 that the communication power bias has been sufficiently corrected.

  For example, if the second bias threshold is 4, as long as the bias index is 4 or more (“bias index ≧ second threshold” in step S109), it is determined that the communication power bias is not sufficiently corrected, When the bias correction mode in step S108 and the flowchart of FIG. 11 is repeated and the bias index becomes less than 4 (“bias index <second threshold” in step S109), it is determined that the communication power bias has been sufficiently corrected. Returning to step S102 of FIG.

  The reason why the second bias threshold (= 4) is made smaller than the first bias threshold (= 6) is that if the second bias threshold matches the first bias threshold, even if the communication power bias is corrected, This is because there is a possibility that the bias index immediately exceeds the first bias threshold in the later optimization mode, and the mode immediately returns to the bias correction mode.

  As described above, in this embodiment, the communication frequency f (n) is hopped in the search mode to search for the communicable communication frequency f (n), and the communication frequency f (n) is subsequently set to the wireless tag in the optimization mode. Since the hopping is controlled so as to be within the communicable frequency band m of 2, the communication of the wireless tag 2 is possible even if the wireless tag 2 is not communicable in the entire communication frequency band of the reader / writer 1. A possible communication frequency can be found and the communication frequency can be within the communicable frequency band m of the wireless tag 2, and communication is not disabled midway. In the stable communication mode, the communication frequency band m0 in which the communication of the wireless tag 2 is stable is obtained, and the communication frequency f (n) is hopped in the communication frequency band m0 in which the communication is stable. Even if there is a large amount of communication, communication can be performed normally. Furthermore, in the bias correction mode, the communication power bias in the communication frequency band in which the reader / writer 1 can communicate is corrected. Therefore, even if the communication power bias occurs in the optimization mode and the stable communication mode, this is eliminated. be able to.

  In addition, this invention is not limited to the said embodiment, It can deform | transform variously. For example, the above equations (1) to (4) for obtaining the communication frequency f (n) may be changed as appropriate.

  In addition, the passive type of the batteryless is exemplified as the wireless tag, but the communication frequency band in which the reader / writer can communicate even if the passive type having the battery or the active type is used. If the communication frequency band in which the wireless tag can communicate is narrower than that, the present invention can be applied.

  Furthermore, the present invention can be applied not only to the RFID system but also to other wireless communication systems such as a mobile phone that hops the communication frequency. Even if the communication frequency band of the mobile phone is essentially the same as the communication frequency band of the wireless base station, if the mobile phone itself moves, the propagation state of radio waves changes, and the communication frequency that can be transmitted and received changes every moment. Therefore, communication is not always possible in the entire communication frequency band used for wireless communication, and the present invention can be applied.

It is a block diagram which shows the RFID system to which one Embodiment of the wireless communication method of this invention is applied. 2 is a flowchart showing an outline of communication frequency hopping control by a reader / writer in the RFID system of FIG. 1. FIG. 2 is a communication frequency transition diagram used to explain an outline of communication frequency hopping control by a reader / writer in the RFID system of FIG. 1. It is a flowchart which shows the search mode of step S101 of FIG. 2 in detail. It is a figure which illustrates the output waveform of the analog digital converter of the reader / writer in the RFID system of FIG. FIG. 2 is a block diagram illustrating a configuration of a reception noise power measuring device of a reader / writer in the RFID system of FIG. 1. 2 is a graph showing a relationship between communication quality Q (n) and a frequency band m in which a wireless tag can communicate in the RFID system of FIG. 1. It is a flowchart which shows the optimization mode of step S103 of FIG. 2 in detail. It is a flowchart which shows in detail the stable communication mode of step S107 of FIG. It is a flowchart which shows in detail the other example of the stable communication mode of step S107 of FIG. It is a flowchart which shows in detail the bias correction mode of step S108 of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reader writer 2 Wireless tag 11 Control part 12 Oscillator 13 Modulator 14 Power amplifier 15 Circulator 16 Antenna 17 Demodulator 18 Analog-digital converter 19 Data decoder 20 Received power measuring device 21 Received noise power measuring device

Claims (10)

In a wireless communication method for performing wireless communication while changing the communication frequency and hopping,
Search mode for hopping communication frequency and searching for communication frequency that can be communicated,
A radio communication method comprising: an optimization mode for finding a frequency with higher communication strength by performing hopping from the communication frequency with a width smaller than the hopping when a communication frequency capable of communication is found in the search mode. .   2. A stable communication mode in which a communication frequency band in which communication is stable is determined following hopping control in the optimization mode, and a communication frequency is hopped in a communication frequency band in which the communication is stable. The wireless communication method described in 1. In a wireless communication method for performing wireless communication while changing the communication frequency and hopping,
It has a search mode and an optimization mode,
The search mode is
A first frequency setting step for setting the communication frequency by hopping;
A first quality measuring step of measuring communication quality based on a received signal of the communication frequency during communication at the communication frequency set in the one frequency setting step,
The first frequency setting step and the first quality measurement step are repeated until a communication frequency at which the communication quality measured in the first quality measurement step is equal to or higher than a certain communication quality is found,
The optimization mode is
Hopping from the communication frequency found in the search mode to set the communication frequency, a second frequency setting step;
A second quality measuring step of measuring communication quality based on a received signal of the communication frequency during communication at the communication frequency set in the two frequency setting step;
A comparison step of comparing the current communication quality measured in the two quality measurement steps with the previous communication quality,
A wireless communication method, comprising: controlling a communication frequency set in a second frequency setting step according to a comparison result in the comparison step. If the comparison result in the comparison step indicates that the current communication quality is higher than the previous communication quality, the next communication frequency set in the second frequency setting step is changed from the previous communication frequency to the current communication frequency. Set by shifting in the frequency shift direction to
If the comparison result in the comparison step indicates that the current communication quality is lower than the previous communication quality, the next communication frequency set in the second frequency setting step is changed from the previous communication frequency to the current communication frequency. 4. The wireless communication method according to claim 3, wherein the wireless communication method is set by shifting in a direction opposite to the frequency shift direction to.   The wireless communication method according to claim 3, wherein in the first and second frequency setting steps, a communication frequency is set using a random number, a specified numerical table, or a specified code sequence.   The wireless communication method according to claim 3, wherein the second frequency setting step, the second quality measurement step, and the comparison step in the optimization mode are repeated a plurality of times.   Following the control of the communication frequency in the second frequency setting step according to the comparison result in the comparison step, a communication frequency band in which the communication quality measured in the two quality measurement step is equal to or greater than a certain value is obtained, and this communication The wireless communication method according to claim 3, further comprising a stable communication mode in which a communication frequency is hopped in a frequency band.   If the comparison result in the comparison step indicates that the current communication quality is not a certain value or more, the next communication frequency set in the second frequency setting step is a frequency from the previous communication frequency to the current communication frequency. The wireless communication method according to claim 3, wherein the wireless communication method is set by shifting in a direction opposite to the shift direction.   The wireless communication method according to claim 1, further comprising a bias correction mode for correcting a bias of communication power in a communication frequency band in which a communication frequency can be changed by hopping.   A wireless communication system to which the wireless communication method according to claim 1 is applied.

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