Signal processing device and signal processing method

Abstract

To realize a demodulation method of a frequency shift modulation signal in which a high noise resistance and a low-operation cost are achieved.SOLUTION: A signal processing device (1A) comprises: a first determination part (131) that determines whether a frequency of a frequency shift modulation signal is a first frequency or a second frequency by measuring a frequency characteristic amount of the frequency shift modulation signal; and a second determination part (132) that performs a Fourier transformation against a segment of the frequency shift modulation signal corresponded to a first condition expressing that the frequency shift modulation signal receives an influence of a noise on the basis of the determination result, and determines that the frequency of the frequency shift modulation signal of the segment is the first frequency or the second frequency.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a signal processing device and a signal processing method. [Background technology]

[0002] Patent Document 1 discloses a wireless receiving device that converts a multilevel FSK (Frequency Shift Keying) modulated wave received by a receiving antenna into a digital signal, performs a fast Fourier transform on the digital signal, and generates demodulated data. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6229518 Summary of the Invention [Problem to be solved by the invention]

[0004] However, while the demodulation method of demodulating a frequency shift keying signal using a Fourier transform as in Patent Document 1 has high noise resistance compared to other demodulation methods that do not use a Fourier transform, it has a problem of high computational costs.

[0005] An object of one aspect of the present invention is to provide a method for demodulating a frequency shift keying signal that achieves both high noise resistance and low computational cost. [Means for solving the problem]

[0006] In order to solve the above problems, a signal processing device according to one embodiment of the present invention is a signal processing device that demodulates a frequency shift keyed signal in which each bit of digital data corresponds to a first frequency or a second frequency, and includes a first determination unit that determines whether the frequency of the frequency shift keyed signal is the first frequency or the second frequency by measuring a periodic feature of the frequency shift keyed signal, and a second determination unit that performs a Fourier transform on a section of the frequency shift keyed signal that meets a first condition representing that the frequency shift keyed signal is affected by noise, based on a determination result of the first determination unit, and determines whether the frequency of the frequency shift keyed signal in that section is the first frequency or the second frequency.

[0007] According to the above configuration, by performing a Fourier transform only on a section in which it is not possible to accurately determine whether the frequency of a frequency shift keying signal is the first frequency or the second frequency by a method of determining whether the frequency is the first frequency or the second frequency without performing a Fourier transform, it is possible to achieve both high noise resistance and low computational cost.

[0008] In the above signal processing device, a section of the frequency shift keyed signal representing one bit includes a plurality of periods of an analog signal, and the first determination unit determines whether each period included in each section of the frequency shift keyed signal representing one bit is the first frequency or the second frequency by measuring each period of the plurality of periods of the analog signal, and determines whether the frequency of the section is the first frequency or the second frequency based on a frequency determination result for each period of the section of the frequency shift keyed signal.

[0009] The section of the frequency shift keying signal representing one bit includes a plurality of periods of the analog signal. According to the above configuration, the periodic characteristics of each period of the analog signal are measured to determine whether the frequency of each period is the first frequency or the second frequency, and the frequency of the section is determined based on the result of the determination. By making such a determination, demodulation can be performed faster than a demodulation method using a Fourier transform.

[0010] In the above signal processing device, the signal processing device further includes a pulse generating unit that converts each of multiple periods of an analog signal included in a section of the frequency shift keyed signal representing one bit into a pulse signal, and the first determination unit measures a rise or fall period of the pulse signal to determine, for each section of the frequency shift keyed signal representing one bit, whether the frequency of the pulse signal is the first frequency or the second frequency, and determines whether the frequency of the section is the first frequency or the second frequency based on a determination result of the frequency of the pulse signal for multiple periods included in the section of the frequency shift keyed signal representing the one bit.

[0011] According to the above configuration, a plurality of cycles of analog signals included in the section of the frequency shift keying signal representing one bit are converted into pulse signals, and the rising or falling cycles of the pulse signals are measured to determine whether the frequency of each pulse signal is the first frequency or the second frequency. Then, based on the determination result, it is determined whether the frequency of each section is the first frequency or the second frequency. By making such a determination, demodulation can be performed faster than a demodulation method using a Fourier transform. Furthermore, by converting an analog signal into a pulse signal, the rising or falling waveform becomes steep, making it easier to measure the cycle with higher accuracy than with an analog signal. Furthermore, a digital signal can determine the cycle at a lower sampling rate than an analog signal, which is advantageous from the viewpoint of the sampling cycle.

[0012] In the above signal processing device, the first condition is that a proportion of the pulse signal or the analog signal for a plurality of periods included in a section of the frequency shift keying signal representing the 1 bit, the frequency of which is determined to be the first frequency, is within a predetermined range.

[0013] In the above signal processing device, the first condition is that, among multiple periods of the pulse signal or the analog signal included in a section of the frequency shift keying signal representing one bit, the frequency of the signal is not determined to be the first frequency for a first predetermined number of consecutive times or more, and the frequency of the signal is not determined to be the second frequency for a second predetermined number of consecutive times or more.

[0014] In the above signal processing device, the first condition is that, of the pulse signal or the analog signal for a plurality of periods included in a section of the frequency shift keyed signal representing the one bit, the frequency of the signal is determined to be the first frequency for a third predetermined number of consecutive times or more, and the frequency of the signal is determined to be the second frequency for a fourth predetermined number of consecutive times or more.

[0015] In the above signal processing device, the first condition is that the number of times that the first determination unit determines the frequency in a section of the frequency shift keying signal representing the 1 bit is less than the number of periods of the analog signal included in that section.

[0016] In the above signal processing device, the frequency shift keyed signal includes a redundant code used for determining success or failure of demodulation of the frequency shift keyed signal, and the second determination unit performs the success or failure determination based on the redundant code for the frequency shift keyed signal having no section that meets the first condition, and performs the Fourier transform on the frequency shift keyed signal determined to have failed in demodulation in the success or failure determination, and determines whether the frequency of each section of the frequency shift keyed signal is the first frequency or the second frequency.

[0017] According to the above configuration, when demodulation fails for a frequency shift keying signal that does not have a section that satisfies the first condition, demodulation using Fourier transform is performed on the frequency shift keying signal. In this way, even if demodulation using a method that does not use Fourier transform fails, appropriate demodulation can be performed.

[0018] In the above-described signal processing device, the second determination unit performs the Fourier transform on a section that satisfies a second condition among sections of the frequency shift keying signal determined to have failed in the success / failure determination, and determines whether a frequency of the section that satisfies the second condition is the first frequency or the second frequency.

[0019] According to the above configuration, when demodulation fails for a frequency shift keying signal that does not have a section that satisfies the first condition, demodulation using Fourier transform is performed for the section that satisfies the second condition. In this way, when demodulation using a method that does not use Fourier transform fails, the computation cost can be reduced by performing Fourier transform only on the section that satisfies the second condition.

[0020] In the above signal processing device, the second condition is that a section of the frequency shift keying signal representing the 1 bit includes a signal that the first determination unit determines to be the first frequency and a signal that the first determination unit determines to be the second frequency.

[0021] In the above signal processing device, the second condition is that the number of times that the first determination unit determines the frequency in a section of the frequency shift keying signal representing the 1 bit is less than the number of periods of the analog signal included in that section.

[0022] The signal processing device further comprises a notification unit that notifies a degree of noise in the frequency shift keying signal according to the number or length of sections of the frequency shift keying signal that has been subjected to the Fourier transform.

[0023] According to the above configuration, the degree of noise in the frequency shift keying signal is notified according to the number or length of sections of the frequency shift keying signal that has been subjected to Fourier transform. By notifying the degree of noise in the frequency shift keying signal, it is possible to encourage users and managers to improve the communication environment.

[0024] A signal processing method according to one aspect of the present invention is a signal processing method for demodulating a frequency shift keyed signal in which each bit of digital data corresponds to a first frequency or a second frequency, the method including: a first determination process for determining whether the frequency of the frequency shift keyed signal is the first frequency or the second frequency by measuring a periodic feature of the frequency shift keyed signal; and a second determination process for performing a Fourier transform on a section of the frequency shift keyed signal that satisfies a first condition indicating that the frequency shift keyed signal is affected by noise, based on a determination result of the first determination process, to determine whether the frequency of the frequency shift keyed signal in that section is the first frequency or the second frequency.

[0025] According to the above configuration, by performing a Fourier transform only on a section in which it is not possible to accurately determine whether the frequency of a frequency shift keying signal is the first frequency or the second frequency by a method of determining whether the frequency is the first frequency or the second frequency without performing a Fourier transform, it is possible to achieve both high noise resistance and low computational cost. Effect of the Invention

[0026] According to one aspect of the present invention, it is possible to achieve both high noise resistance and low computational cost. [Brief description of the drawings]

[0027] [Figure 1] 1 is a block diagram showing a configuration of a signal processing device according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram used to explain the processing of a first determination unit. [Diagram 3] FIG. 13 is a diagram illustrating an example of a demodulation failure frame. [Figure 4] FIG. 13 is a diagram showing an example of a demodulation unstable frame. [Diagram 5] 5 is a flowchart showing an example of the flow of a signal processing method according to the first embodiment of the present invention. [Figure 6] 6 is a flowchart showing an example of the flow of a demodulation interpolation process shown in FIG. 5. [Figure 7]FIG. 11 is a block diagram showing a configuration of a signal processing device according to a second embodiment of the present invention. [Figure 8] This is a diagram used to explain a method of combining failed communication results to demodulate an FSK signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, an embodiment according to one aspect of the present invention (hereinafter, also referred to as "the present embodiment") will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and the description thereof will not be repeated.

[0029] [Embodiment 1] §1 Examples of application Fig. 1 is a block diagram showing an example of the configuration of a signal processing device according to a first embodiment of the present invention. The signal processing device 1A shown in Fig. 1 is an RFID (Radio Frequency IDentification) reader / writer. The signal processing device 1A communicates with a transponder 2 via an antenna ANT. The transponder 2 is an RFID tag and stores predetermined digital data. The digital data is a binary bit string of 0 or 1. The signal processing device 1A transmits an ASK (Amplitude Shift Keying) signal to the transponder 2. Upon receiving the ASK (Amplitude Shift Keying) signal, the transponder 2 transmits a frequency shift keying signal corresponding to the predetermined digital data.

[0030] Specifically, when the bit of the digital data is 0, the transponder 2 transmits an analog signal modulated to a first frequency for a predetermined period. The analog signal is, for example, a sine wave signal. On the other hand, when the bit of the digital data is 1, the transponder 2 transmits an analog signal modulated to a second frequency for a predetermined period. For example, when the bit of the digital data is 0, the transponder 2 transmits an analog signal modulated to 134.2 kHz for 16 periods. On the other hand, when the bit of the digital data is 1, the transponder 2 transmits an analog signal modulated to 123.2 kHz for 16 periods. Hereinafter, the frequency shift keying signal transmitted by the transponder 2 is referred to as an FSK (Frequency Shift Keying) signal. A section of the FSK signal for a predetermined period corresponding to each bit of the digital data is referred to as a frame. The length of one frame varies depending on the value of the corresponding bit of the digital data.

[0031] The signal processing device 1A has a plurality of methods for demodulating the FSK signal received from the transponder 2. In a first method for the signal processing device 1A to demodulate the FSK signal, frequency analysis is performed by a Fourier transform such as a short-time Fourier transform (STFT) to determine whether the frequency of each frame of the FSK signal is a first frequency or a second frequency. A demodulation method using a Fourier transform can accurately demodulate even when there is noise interference, but it tends to take longer to perform calculations than other methods.

[0032] The second method in which the signal processing device 1A demodulates the FSK signal does not use a Fourier transform. For example, the signal processing device 1A generates a pulse signal based on the received FSK signal, measures the period of the FSK signal (an example of a periodic feature) by measuring the period of the rising or falling edge of the pulse signal, and determines whether the frequency of each frame of the FSK signal is the first frequency or the second frequency. Hereinafter, the second method in which the signal processing device 1A demodulates the FSK signal is referred to as a pulse period measurement demodulation method. Although the pulse period measurement demodulation method has a shorter calculation time than the demodulation method using the Fourier transform, when noise interference is received from the surrounding environment of the signal processing device 1A, it may not be possible to accurately determine whether the frequency of each frame of the FSK signal is the first frequency or the second frequency.

[0033] Therefore, the signal processing device 1A first demodulates the FSK signal using the pulse period measurement demodulation method, and then executes a demodulation method using Fourier transform for frames that cannot be accurately determined using the pulse period measurement demodulation method. In this way, the FSK signal demodulation method can achieve both high noise resistance and low calculation cost.

[0034] §2 Configuration Example A signal processing device 1A shown in FIG. 1 includes a sampling unit 11, a decoding unit 12, a control unit 13, an encoding unit 14, a modulation unit 15, a first amplifier circuit AMP1, an antenna ANT, a resonant circuit C, a filter circuit FLT, and a second amplifier circuit AMP2.

[0035] The control unit 13 executes a program to control each unit of the signal processing device 1A. The control unit 13 controls the encoding unit 14, the modulation unit 15, and the first amplifier circuit AMP1 to transmit an ASK signal to the transponder 2. When the transponder 2 receives the ASK signal, it transmits an FSK signal to the signal processing device 1A. The FSK signal transmitted by the transponder 2 includes a preamble indicating the start of the signal and a redundant code used to determine whether communication between the signal processing device 1A and the transponder 2 has been successful. The signal processing device 1A has a receiving circuit consisting of a resonant circuit C, a filter circuit FLT, and a second amplifier circuit AMP2, and receives the FSK signal transmitted by the transponder 2.

[0036] The sampling unit 11 has a pulse generating unit 111 and an AD converter unit 112. The FSK signal received from the transponder 2 is input to the sampling unit 11. The decoding unit 12 has a pulse counting unit 121, an STFT unit 122, and a data storage unit 123.

[0037] The pulse generating unit 111 of the sampling unit 11 and the pulse counting unit 121 of the decoding unit 12 are used in a method for demodulating an FSK signal without using a Fourier transform. The pulse generating unit 111 further includes a pulse generating circuit using, for example, a comparator. The pulse generating unit 111 generates a pulse signal based on the FSK signal received from the transponder 2. The pulse signal generated by the pulse generating unit 111 becomes high level when the FSK signal is equal to or greater than a predetermined value, and becomes low level when the FSK signal is less than the predetermined value. The pulse counting unit 121 measures the period of the rising edge of the pulse signal generated by the pulse generating unit 111. The pulse counting unit 121 will be described in detail later.

[0038] The AD converter unit 112 of the sampling unit 11 and the STFT unit 122 of the decoding unit 12 are used in a method for demodulating an FSK signal using Fourier transform. The AD converter unit 112 performs AD conversion on the FSK signal received from the transponder 2. The STFT unit 122 receives the FSK signal that has been AD converted by the AD converter unit 112. The STFT unit 122 performs a short-time Fourier transform on the AD-converted FSK signal, thereby performing a spectrum transform.

[0039] The control unit 13 functions as a first determination unit 131, a second determination unit 132, and a notification unit 133 by executing a program.

[0040] (1st judgment part) The first determination unit 131 determines whether the frequency of the FSK signal is the first frequency or the second frequency without performing a Fourier transform. The first determination unit 131 refers to the measurement result of the rising edge period of the pulse signal by the pulse counter 121, and determines whether the frequency of each frame included in the FSK signal is the first frequency or the second frequency.

[0041] FIG. 2 is a diagram used to explain the processing of the first judgment unit 131. In the explanation using FIG. 2, it is assumed that the transponder 2 transmits an FSK signal corresponding to the transmission data "0101" shown in the upper part of FIG. 2 to the signal processing device 1A. An example of the FSK signal corresponding to the transmission data "0101" is shown in the middle part of FIG. 2. Here, for the sake of simplicity of explanation, the FSK signal is drawn as a square wave. The FSK signal does not have to be a square wave, and may be a waveform that changes continuously and smoothly, such as a sine wave signal. In a frame (section) corresponding to the transmission data "0", 16 periods of an analog signal corresponding to the first frequency are included. In a frame (section) corresponding to the transmission data "1", 16 periods of an analog signal corresponding to the second frequency are included. Although not shown in FIG. 2, the pulse signal generated by the pulse generation unit 111 is a square wave including a plurality of pulses that rise or fall in a period corresponding to the first frequency or a period corresponding to the second frequency. In the example shown in FIG. 2, the first frequency is higher than the second frequency. Therefore, the length of the frame corresponding to the transmission data "0" is T L is the length of the frame corresponding to the transmission data "1", T H 2 shows the count value counted by pulse counter 121. Pulse counter 121 increases the count value at a constant rate according to the time elapsed from the timing when the pulse signal rises. This count value indicates the period of the pulse signal generated by pulse generator 111 and the period of the analog signal.

[0042] The first decision unit 131 shown in FIG. 1 decides whether the frequency of the frame of the FSK signal that is the source of the pulse signal is the first frequency or the second frequency based on the count value when the pulse signal rises. When the count value when the pulse signal rises is smaller than threshold 50, the first decision unit 131 decides that the frequency of the pulse is the first frequency. When the count value when the pulse signal rises is equal to or greater than threshold 50, the first decision unit 131 decides that the frequency of the pulse is the second frequency. The pulse count unit 121 resets the count value at the timing when the pulse signal rises. By converting the analog signal to a pulse signal by the pulse generation unit 111, the rising or falling waveform becomes steep, making it easier to measure the period with higher accuracy than with an analog signal. In addition, a digital signal is more advantageous from the viewpoint of the sampling period because the period can be decided at a lower sampling rate than an analog signal.

[0043] When the FSK signal is not interfered with by noise, in a frame corresponding to transmission data "0", the first decision unit 131 decides that the frequencies of all 16 cycles of the pulse signal are the first frequency. Based on the decision result, the control unit 13 decides that the value of the bit corresponding to that frame is 0. In a frame corresponding to transmission data "1", the first decision unit 131 decides that the frequencies of all 16 cycles of the pulse signal are the second frequency. Based on the decision result, the control unit 13 decides that the value of the bit corresponding to that frame is 1.

[0044] When the FSK signal is interfered with by noise, the determination result of the first determination unit 131 may be a mixture of a pulse signal of the first frequency and a pulse signal of the second frequency in the same frame. When the determination result of the first determination unit 131 in each frame satisfies at least one of the first conditions exemplified below, the control unit 13 cannot accurately determine whether the value of the bit corresponding to the frame is a value corresponding to the first frequency or a value corresponding to the second frequency based on the determination result of the first determination unit 131. This first condition can be rephrased as a condition indicating that the FSK signal is affected by noise interference. (1-1) The proportion of pulse signals determined by the first determination unit 131 to have the first frequency is within a predetermined range. (1-2) The pulse signal determined by the first determination unit 131 to have the first frequency does not continue for a first predetermined number of times or more, and the pulse signal determined by the first determination unit 131 to have the second frequency does not continue for a second predetermined number of times or more. (1-3) The pulse signals determined by the first determination unit 131 to have the first frequency continue for a third predetermined number or more, and the pulse signals determined by the first determination unit 131 to have the second frequency continue for a fourth predetermined number or more.

[0045] A frame that satisfies at least one of the above conditions (1-1) to (1-3) is called a demodulation failure frame. In condition (1-1), the predetermined range is, for example, 6 to 9 when one frame contains 16 periods of a pulse signal. In conditions (1-2) and (1-3), the first to fourth predetermined numbers are, for example, 5 times when one frame contains 16 periods of a pulse signal. The first to fourth predetermined numbers may be set individually or to the same value.

[0046] Fig. 3 is a diagram showing an example of a demodulation-failed frame. In frame A1 shown in Fig. 3, the first determination unit 131 determines that the number of pulse signals is the first frequency based on the count value counted by the pulse counting unit 121, and the number of pulse signals is the second frequency, so that the condition (1-1) is met.

[0047] Furthermore, when the FSK signal satisfies the following second condition, the value of the bit corresponding to the frame may not be accurately determined based on the determination result of first determination section 131. (2-1) Both a pulse signal that the first determination unit 131 has determined to be of the first frequency and a pulse signal that the first determination unit 131 has determined to be of the second frequency are included. (2-2) The number of pulse signals determined by the first determination unit 131 is less than a predetermined number.

[0048] A frame that satisfies at least one of the above conditions (2-1) and (2-2) is called a demodulation unstable frame. In condition (2-2), the predetermined number is, for example, the number of pulse signals to be included in one frame. When one frame contains 16 periods of pulse signals, for example, the predetermined number is 16. Even if a frame of an FSK signal does not fall under a demodulation failure frame, it may fall under a demodulation unstable frame.

[0049] Fig. 4 is a diagram showing an example of a demodulation unstable frame. In the frame shown in Fig. 4, the count value is reset at an unintended timing due to noise interference, and the first judgment unit 131 judges the frequency as the first frequency instead of the second frequency. As a result, the frame shown in Fig. 4 does not satisfy any of the above conditions (1-1) to (1-3), but does satisfy the condition (2-1). When a communication success / failure judgment is performed using a redundant code, an FSK signal including a frame such as that shown in Fig. 4 is judged as a communication failure.

[0050] (Second judgment section) The second determination unit 132 in FIG. 1 performs a Fourier transform on a frame in which it is not possible to accurately determine whether the bit value of the FSK signal corresponds to the first frequency or the second frequency based on the determination result in the first determination unit 131, and determines whether the frequency of the FSK signal of the frame is the first frequency or the second frequency. That is, the second determination unit 132 executes a demodulation method using a Fourier transform on a demodulation failure frame that corresponds to the first condition. For example, the second determination unit 132 inputs the FSK signal AD-converted by the AD converter unit 112 for the frame A1 in FIG. 3 to the STFT unit 122. The STFT unit 122 performs a frequency analysis using a short-time Fourier transform on the frame A1 in FIG. 3. The second determination unit 132 determines whether the frequency of the FSK signal of the frame A1 is the first frequency or the second frequency based on the frequency analysis result.

[0051] Furthermore, even if the value of the bit indicated by the FSK signal does not satisfy the first condition based on the result of the determination by the first determination unit 131, if the communication has failed and the second condition is satisfied, the second determination unit 132 executes a demodulation method using Fourier transform. For example, the second determination unit 132 inputs the FSK signal AD-converted by the AD converter unit 112 to the STFT unit 122 for the frame shown in Fig. 4. The STFT unit 122 performs frequency analysis using short-time Fourier transform for the frame shown in Fig. 4. The second determination unit 132 determines whether the frequency of the FSK signal in the frame shown in Fig. 4 is the first frequency or the second frequency based on the result of this frequency analysis.

[0052] The notification unit 133 notifies the degree of noise in the FSK signal according to the number (length) of frames that have been Fourier transformed in the second determination unit among the frames of the FSK signal. For example, the notification unit 133 notifies a PLC (Programmable Logic Controller) 3, which is a higher-level device of the signal processing device 1A, of the number of frames that have been Fourier transformed in the second determination unit. The PLC 3 notifies the information to, for example, a computer (not shown) used by a user and manager of the signal processing device 1A. This makes it possible to urge the user and manager of the signal processing device 1A to improve the communication environment by notifying them of the degree of noise in the FSK signal. The notification unit 133 may notify the information to a computer (not shown) without going through the PLC 3.

[0053] (Data Storage Division) Data storage unit 123 stores the demodulated results of the FSK signal in a predetermined storage unit.

[0054] Fig. 5 is a flowchart showing an example of the flow of a signal processing method according to the first embodiment of the present invention. Fig. 5 is a flowchart showing an example of a signal processing method executed by the control unit 13 when the signal processing device 1A receives an FSK signal from the transponder 2. When the control unit 13 receives an FSK signal, it inputs the FSK signal to the pulse generating unit 111 and the AD converter unit 112 of the sampling unit 11.

[0055] The control unit 13 repeats the following processes from S11 to S14 for each frame of the FSK signal. In S11, the control unit 13 acquires a count value from the pulse counter 121 at the timing when the pulse signal generated by the pulse generator 111 rises. In the following S12, the control unit 13 functions as the first determination unit 131 and determines whether the frequency of each pulse signal included in the frame is the first frequency or the second frequency based on the count value counted by the pulse counter 121. In the following S13, the control unit 13 extracts demodulation-failed frames and demodulation-unstable frames based on the determination result of the first determination unit 131 executed in S12. The control unit 13 determines a frame that satisfies at least one of the first conditions (1-1) to (1-3) as a demodulation-failed frame based on the determination result of the first determination unit 131 executed in S12. The control unit 13 determines that a frame that satisfies at least one of the second conditions (2-1) and (2-2) is a demodulation unstable frame based on the determination result of the first determination unit 131 executed in S12. In S14, the control unit 13 controls the AD converter unit 112 to AD convert the FSK signal input to the AD converter unit 112. The output result of the AD converter unit 112 is stored in a predetermined storage unit.

[0056] After executing the processes from S11 to S14 for all frames included in the FSK signal, the control unit 13 judges whether or not a demodulation-failed frame has been extracted in S13 (S15). If a demodulation-failed frame has been extracted (S15: YES), the control unit 13 executes a demodulation interpolation process, which will be described later with reference to FIG.

[0057] When a demodulation-unstable frame has not been extracted (S15: NO), the control unit 13 performs a judgment of the success or failure of the communication (S16). When the control unit 13 judges that the communication is successful (S16: YES), for example, by error detection using a redundant code (e.g., cyclic redundancy check), the control unit 13 ends the process of FIG. 5. On the other hand, when the control unit 13 judges that the communication is unsuccessful (S16: NO), for example, by error detection using a redundant code, the control unit 13 judges whether or not a demodulation-unstable frame has been extracted in S13 (S18). When a demodulation-unstable frame has been extracted (S18: YES), the control unit 13 executes a demodulation interpolation process shown in FIG. 6. The demodulation interpolation process will be described later with reference to FIG. 6. When a demodulation-unstable frame has not been extracted (S18: NO), the control unit 13 judges that the communication between the signal processing device 1A and the transponder 2 has failed. When the control unit 13 determines that the demodulation unstable frame has not been extracted (S18: NO), for example, the signal processing device 1A retries communication with the transponder 2.

[0058] Fig. 6 is a flowchart showing an example of the flow of the demodulation and interpolation process. The demodulation and interpolation process shown in Fig. 6 is executed, for example, when a positive decision is made in S15 or S18 in Fig. 5.

[0059] The control unit 13 functions as the second determination unit 132. That is, the control unit 13 reads the output result of the AD converter unit 112 from a predetermined storage unit for the demodulation failure frame or demodulation unstable frame extracted in S13 of FIG. 5 (S21 of FIG. 6), outputs the output result of the AD converter unit 112 read from the predetermined storage unit to the STFT unit 122, performs a short-time Fourier transform, and performs frequency analysis (S22). In the following S23, the control unit 13 determines whether the frequency of the frame is the first frequency or the second frequency based on the frequency analysis result in S22. When the result of the frequency analysis is the first frequency, the control unit 13 determines that the bit of the frame is 0, and when the result of the frequency analysis is the second frequency, the control unit 13 determines that the bit of the frame is 1 (S23). The control unit 13 repeats the processes from S21 to S23 for the demodulation failure frame or demodulation unstable frame extracted in S13 of FIG. 5. When the control unit 13 is executing the demodulation interpolation process shown in Fig. 6 as a result of an affirmative decision being made in S15 of Fig. 5, the control unit 13 repeats the processes from S21 to S23 of Fig. 6 for the demodulation-unstable frame when the control unit 13 is executing the demodulation interpolation process shown in Fig. 6 as a result of an affirmative decision being made in S18 of Fig. 5. On the other hand, when the control unit 13 is executing the demodulation interpolation process shown in Fig. 6 as a result of an affirmative decision being made in S18 of Fig. 5, the control unit 13 repeats the processes from S21 to S23 of Fig. 6 for the demodulation-unstable frame.

[0060] In S24, the control unit 13 functions as the notification unit 133 and notifies the PLC 3 or the like of the degree of noise in the FSK signal according to the number (length) of frames demodulated by frequency analysis using Fourier transform. In the following S25, the control unit 13 performs a judgment of the success or failure of communication. For frames that are neither demodulation-failed nor demodulation-unstable frames, the control unit 13 performs a judgment of the success or failure of communication based on the redundant code using the demodulation result of the FSK signal based on the measurement result of the pulse counting unit 121, and for demodulation-failed or demodulation-unstable frames, the control unit 13 performs a judgment of the success or failure of communication based on the redundant code using the judgment result of S23. If the control unit 13 judges that the communication is successful by error detection using the redundant code (e.g., cyclic redundancy check) (S25: YES), the control unit 13 ends the process of FIG. 6. On the other hand, if the control unit 13 judges that the communication is unsuccessful by error detection using the redundant code (S25: NO), for example, the control unit 13 judges that the communication between the signal processing device 1A and the transponder 2 has failed. [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0061] (Configuration of signal processing device 1B) FIG. 7 is a block diagram showing an example of the configuration of a signal processing device according to a second embodiment of the present invention. The signal processing device 1B shown in FIG. 2 includes a sampling unit 21 instead of the sampling unit 11 in the signal processing device 1A. The other configurations in the signal processing device 1B are the same as those in the signal processing device 1A. The sampling unit 21 includes an AD converter unit 211, but does not include a pulse generating unit 111. The AD converter unit 211 in the sampling unit 21 performs AD conversion on the FSK signal received from the transponder 2. The AD converter unit 211 is different from the AD converter unit 112 in the signal processing device 1A in that the output of the AD converter unit 211 is output to the pulse counting unit 121 as a pulse signal. The pulse counting unit 121 measures the period of the rising edge of the pulse signal generated by the AD converter unit 211. The AD converter unit 211 outputs the output to the STFT unit 122, similar to the AD converter unit 112.

[0062] §3 Variations In the above embodiment and modified example, the pulse counter 121 measures the period of the rising edge of the pulse signal generated by the pulse generator 111, but this is not limited to the above. For example, the pulse counter 121 may measure the period of the falling edge of the pulse signal generated by the pulse generator 111.

[0063] In the above embodiment and modified example, in the demodulation method without using the Fourier transform, it is decided to judge whether the frequency of the FSK signal is the first frequency or the second frequency by referring to the measurement result of the rise or fall period of the pulse signal. However, the demodulation method without using the Fourier transform is not limited to this method.

[0064] In the above embodiment and modified example, in the demodulation method using the Fourier transform, the STFT unit 122 performs a short-time Fourier transform and spectrum transform on the FSK signal that has been AD converted by the AD converter unit 112. However, the demodulation method using the Fourier transform is not limited to this method.

[0065] In the above embodiment and modified example, when the judgment result of the first judgment unit 131 for each frame corresponds to at least one of the conditions (1-1) to (1-3), the value of the bit corresponding to the frame cannot be accurately judged based on the judgment result of the first judgment unit 131. However, the first condition under which the value of the bit corresponding to the frame cannot be accurately judged is not limited to the conditions (1-1) to (1-3). For example, some of the conditions (1-1) to (1-3) may not be included in the first condition, or the condition (2-2) may be included in the first condition.

[0066] The flow of the signal processing method according to an embodiment of the present disclosure is not limited to that shown in Fig. 5. For example, the control unit 13 may not perform either of the determinations of S15 and S18 in Fig. 5. When the determination of S15 in Fig. 5 is not performed, the control unit 13 may execute the processes of S11 to S14 for all frames included in the FSK signal, and then proceed to the process of S16 to determine whether the communication has been successful. When the determination of S18 in Fig. 5 is not performed, the control unit 13 may proceed to the demodulation interpolation process shown in Fig. 6 if it is determined that the communication has failed in the determination of the success or failure of the communication in S16 (S16: NO).

[0067] In the above embodiment and modified example, when it is determined in S18 of Fig. 5 that a demodulation unstable frame has not been extracted, the control unit 13 determines that communication between the signal processing device 1A and the transponder 2 has failed, and retries communication with the transponder 2. When communication with the transponder 2 fails again as a result of retrying communication, the control unit 13 may combine the demodulation results of the FSK signal stored in the data storage unit 123 to demodulate the FSK signal.

[0068] FIG. 8 is a diagram used to explain a method for demodulating an FSK signal by combining failed communication results. The upper diagram of FIG. 8 shows an example of an FSK signal in a first communication with the transponder 2 and a count value counted by the pulse counter 121. The lower diagram of FIG. 8 shows an example of an FSK signal in a second communication with the transponder 2 and a count value counted by the pulse counter 121. In the example shown in FIG. 8, in the first communication with the transponder 2, frame A2 is extracted as a demodulation unstable frame, and it is determined that the communication has failed. Then, in the second communication with the transponder 2, frame A4 corresponding to the same bit position as frame A2 is not extracted as a demodulation failed frame or a demodulation unstable frame, but another frame A5 is extracted as a demodulation unstable frame, and it is determined that the communication has failed. In the first communication with the transponder 2, if frame A3 corresponding to the same bit position as frame A5 is not extracted as a demodulation failed frame or a demodulation unstable frame, the FSK signal may be demodulated based on the judgment result of the first judgment unit 131 for frame A3 stored in the data storage unit 123.

[0069] In the above embodiment, the second determination unit 132 performs a Fourier transform on a frame for which it is not possible to accurately determine whether the bit value of the FSK signal corresponds to the first frequency or the second frequency based on the determination result of the first determination unit 131, and determines whether the frequency of the FSK signal of the frame is the first frequency or the second frequency. However, the second determination unit 132 may also perform a separate Fourier transform on a frame for which it is possible to accurately determine whether the bit value of the FSK signal corresponds to the first frequency or the second frequency based on the determination result of the first determination unit 131, and determine whether the frequency of the FSK signal of the frame is the first frequency or the second frequency. The control unit 13 may compare the determination result of the second determination unit 132 with the demodulation result of the FSK signal stored in the data storage unit 123, and adjust the setting of the first determination unit 131. For example, the control unit 13 may adjust the predetermined range in the condition (1-1) and the values ​​of the first to fourth predetermined numbers in the conditions (1-2) and (1-3) based on the comparison result.

[0070] In the above embodiment, the pulse counter 121 measures the period of the rising edge of the pulse signal based on the pulse signal generated by the pulse generator 111 or the AD converter 211. However, the pulse counter 121 may measure the period at which the FSK signal received from the transponder 2 exceeds a predetermined threshold. The first determination unit 131 may determine whether the frequency of each period of the FSK signal is the first frequency or the second frequency based on the measurement result. In the first and second conditions, the pulse signal may be read as the period of the FSK signal.

[0071] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0072] 〔summary〕 A signal processing device according to a first aspect of the present invention is a signal processing device that demodulates a frequency shift keyed signal in which each bit of digital data corresponds to a first frequency or a second frequency, and includes a first determination unit that determines whether the frequency of the frequency shift keyed signal is the first frequency or the second frequency by measuring a periodic feature of the frequency shift keyed signal, and a second determination unit that performs a Fourier transform on a section of the frequency shift keyed signal that meets a first condition indicating that the frequency shift keyed signal is affected by noise based on a determination result of the first determination unit, and determines whether the frequency of the frequency shift keyed signal in that section is the first frequency or the second frequency.

[0073] A signal processing device according to a second aspect of the present invention is the signal processing device according to the first aspect, wherein a section of the frequency shift keyed signal representing one bit includes a plurality of periods of an analog signal, and the first determination unit determines whether each period included in each section of the frequency shift keyed signal representing the one bit is the first frequency or the second frequency by measuring each period of the plurality of periods of the analog signal, and determines whether the frequency of the section is the first frequency or the second frequency based on a frequency determination result for each period of the section of the frequency shift keyed signal.

[0074] A signal processing device according to a third aspect of the present invention is the signal processing device according to the first aspect, further comprising a pulse generating unit that converts each of multiple periods of an analog signal included in a section of the frequency shift keyed signal representing one bit into a pulse signal, and the first determination unit measures a period of a rising or falling edge of the pulse signal to determine whether the frequency of the pulse signal is the first frequency or the second frequency for each section of the frequency shift keyed signal representing the one bit, and determines whether the frequency of the section is the first frequency or the second frequency based on a result of the determination of the frequency of the pulse signal for multiple periods included in the section of the frequency shift keyed signal representing the one bit.

[0075] A signal processing device according to a fourth aspect of the present invention is the signal processing device according to the second or third aspect, wherein the first condition is that the proportion of the pulse signal or analog signal whose frequency is determined to be the first frequency among a plurality of periods of the pulse signal or the analog signal included in a section of the frequency shift keying signal representing the 1 bit is within a predetermined range.

[0076] A signal processing device according to a fifth aspect of the present invention is a signal processing device according to any one of the second to fourth aspects, wherein the first condition is that, among a plurality of periods of the pulse signal or the analog signal included in a section of the frequency shift keying signal representing the one bit, the frequency of the signal is not determined to be the first frequency for a first predetermined number of consecutive times or more, and the frequency of the signal is not determined to be the second frequency for a second predetermined number of consecutive times or more.

[0077] A signal processing device according to a sixth aspect of the present invention is a signal processing device according to any one of the second to fifth aspects, wherein the first condition is that, among a plurality of periods of the pulse signal or the analog signal included in a section of the frequency shift keying signal representing the one bit, the frequency of the signal is determined to be the first frequency for a third predetermined number of consecutive times or more, and the frequency of the signal is determined to be the second frequency for a fourth predetermined number of consecutive times or more.

[0078] A signal processing device according to a seventh aspect of the present invention is a signal processing device according to any one of the second to sixth aspects, wherein the first condition is that the number of times that the first judgment unit judges the frequency in a section of the frequency shift keying signal representing the one bit is less than the number of periods of the analog signal included in the section.

[0079] A signal processing device according to an eighth aspect of the present invention is the signal processing device according to any one of the second to seventh aspects, wherein the frequency shift keyed signal includes a redundant code used to determine whether demodulation of the frequency shift keyed signal is successful, and the second determination unit performs the success / failure determination based on the redundant code for the frequency shift keyed signal having no section that meets the first condition, and performs the Fourier transform on the frequency shift keyed signal determined to have failed in the success / failure determination, to determine whether the frequency of each section of the frequency shift keyed signal is the first frequency or the second frequency.

[0080] A signal processing device according to a ninth aspect of the present invention is the signal processing device described in the eighth aspect, wherein the second judgment unit performs the Fourier transform on a section of the frequency shift keying signal that is judged to have failed in demodulation in the success / failure judgment and that satisfies a second condition, and judges whether the frequency of the section that satisfies the second condition is the first frequency or the second frequency.

[0081] A signal processing device according to aspect 10 of the present invention is the signal processing device described in aspect 9, wherein the second condition may include, in a section of the frequency shift keying signal representing the 1 bit, a signal that the first judgment unit judges to be the first frequency and a signal that the first judgment unit judges to be the second frequency.

[0082] A signal processing device according to an eleventh aspect of the present invention is a signal processing device according to any one of the ninth and tenth aspects, wherein the second condition is that the number of times that the first judgment unit judges the frequency in a section of the frequency shift keying signal representing the one bit is less than the number of periods of the analog signal included in the section.

[0083] A signal processing device according to a twelfth aspect of the present invention may be the signal processing device according to any one of the first to eleventh aspects, further comprising a notification unit that notifies a degree of noise in the frequency shift keying signal depending on the number or length of sections of the frequency shift keying signal on which the Fourier transform has been performed.

[0084] A signal processing method according to a thirteenth aspect of the present invention is a signal processing method for demodulating a frequency shift keyed signal in which each bit of digital data corresponds to a first frequency or a second frequency, and includes a first determination process for determining whether the frequency of the frequency shift keyed signal is the first frequency or the second frequency by measuring a periodic feature of the frequency shift keyed signal, and a second determination process for performing a Fourier transform on a section of the frequency shift keyed signal that satisfies a first condition indicating that the frequency shift keyed signal is affected by noise, based on a determination result of the first determination process, and determining whether the frequency of the frequency shift keyed signal in that section is the first frequency or the second frequency. [Explanation of symbols]

[0085] 1A, 1B Signal Processing Device 2 Transponder 11, 21 Sampling section 12 Decoding section 13 Control section 111 Pulse generation unit 112, 211 AD converter section 121 Pulse counter 122 STFT section 131 1st Judgment Department 132 Second Judgment Section 133 Notification Department

Claims

1. A signal processing device that demodulates a frequency shift keying signal in which each bit of digital data corresponds to a first frequency or a second frequency, a first determination unit that determines whether a frequency of the frequency shift keying signal is the first frequency or the second frequency by measuring a periodic feature of the frequency shift keying signal; a second determination unit that performs a Fourier transform on a section of the frequency shift keying signal that satisfies a first condition representing that the frequency shift keying signal is affected by noise based on a result of the determination by the first determination unit, and determines whether a frequency of the frequency shift keying signal in the section is the first frequency or the second frequency; A signal processing device comprising:

2. a section of the frequency shift keying signal representing one bit includes a plurality of periods of an analog signal; The first determination unit is determining whether each period of the analog signal corresponds to the first frequency or the second frequency by measuring each period of the analog signal for each period included in each section of the frequency shift keying signal representing one bit; 2. The signal processing device according to claim 1, further comprising: determining whether the frequency of a section of the frequency shift keying signal is the first frequency or the second frequency based on a result of determining the frequency for each period of the section of the frequency shift keying signal.

3. the signal processing device further includes a pulse generating unit that converts a plurality of periods of analog signals included in a section of the frequency shift keying signal representing one bit into pulse signals, The first determination unit is determining whether the frequency of the pulse signal is the first frequency or the second frequency for each section of the frequency shift keying signal representing one bit by measuring a period of the rise or fall of the pulse signal; 2. The signal processing device according to claim 1, further comprising: a step of determining whether a frequency of a section of the frequency shift keying signal representing one bit is the first frequency or the second frequency based on a determination result of the frequency of the pulse signal for a plurality of periods included in the section.

4. 4. The signal processing device according to claim 2, wherein the first condition is that a proportion of the pulse signal or the analog signal having a frequency determined to be the first frequency among a plurality of periods of the pulse signal or the analog signal included in a section of the frequency shift keying signal representing the one bit is within a predetermined range.

5. 4. The signal processing device according to claim 2 or 3, wherein the first condition is that, among a plurality of periods of the pulse signal or the analog signal included in a section of the frequency shift keying signal representing one bit, the frequency of the signal is not determined to be the first frequency for a first predetermined number of consecutive times or more, and the frequency of the signal is not determined to be the second frequency for a second predetermined number of consecutive times or more.

6. 4. The signal processing device according to claim 2 or 3, wherein the first condition is that, of a plurality of periods of the pulse signal or the analog signal included in a section of the frequency shift keying signal representing one bit, the frequency of the signal is determined to be the first frequency a third predetermined number of times or more consecutively, and the frequency of the signal is determined to be the second frequency a fourth predetermined number of times or more consecutively.

7. 4. The signal processing device according to claim 2, wherein the first condition is that the number of times that the first determination unit determines the frequency in a section of the frequency shift keying signal representing one bit is less than the number of periods of the analog signal included in the section.

8. the frequency shift keying signal includes a redundant code used to determine whether demodulation of the frequency shift keying signal is successful; The second determination unit is performing the success / failure determination based on the redundant code for the frequency shift keying signal in which no section corresponding to the first condition exists; 4. The signal processing device according to claim 2, further comprising: a step of performing the Fourier transform on the frequency shift keyed signal determined to have failed in the demodulation success / failure determination, and determining whether a frequency of each section of the frequency shift keyed signal is the first frequency or the second frequency.

9. The second determination unit is 9. The signal processing device according to claim 8, further comprising: a section of the frequency shift keying signal determined to have failed in demodulation in the success / failure determination, the Fourier transform is performed on a section that satisfies a second condition, and the signal processing device determines whether a frequency of the section that satisfies the second condition is the first frequency or the second frequency.

10. 10. The signal processing device according to claim 9, wherein the second condition is that a section of the frequency shift keying signal representing the one bit includes a signal determined by the first determination unit to have the first frequency and a signal determined by the first determination unit to have the second frequency.

11. 10. The signal processing device according to claim 9, wherein the second condition is that the number of times that the first determination unit determines the frequency in a section of the frequency shift keying signal representing one bit is less than the number of periods of the analog signal included in the section.

12. 2. The signal processing device according to claim 1, further comprising a notification unit that notifies a degree of noise in the frequency shift keying signal in accordance with a number or length of sections of the frequency shift keying signal on which the Fourier transform has been performed.

13. 1. A signal processing method for demodulating a frequency shift keying signal in which each bit of digital data corresponds to a first frequency or a second frequency, comprising the steps of: a first determination process for determining whether the frequency of the frequency shift keying signal is the first frequency or the second frequency by measuring a periodic feature of the frequency shift keying signal; a second determination process for performing a Fourier transform on a section of the frequency shift keying signal corresponding to a first condition representing that the frequency shift keying signal is affected by noise based on a determination result of the first determination process, and determining whether the frequency of the frequency shift keying signal in the section is the first frequency or the second frequency; A signal processing method comprising:

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