Reception method, transmission method, reception device, transmission device, and communication system

Abstract

The present invention provides a reception method for a communication system (10) comprising a reception device (40), the reception device (40) having a normal reception mode and a power-saving mode, with two or more subcarriers from among subcarriers defined by OFDM being defined as a plurality of first subcarriers. The reception method includes: a step (S42) of acquiring the signal levels of the plurality of first subcarriers in a modulated signal that has been modulated according to OFDM; a step (S44) of assigning a plurality of subcarrier symbols on the basis of the signal levels of the plurality of first subcarriers; a step (S46) of assigning, to the modulated signal, a received symbol determined on the basis of the plurality of subcarrier symbols; and a step (S48) of changing the operating mode of the reception device (40) on the basis of the received symbols, wherein, in step (S48), the operating mode of the reception device (40) is changed from the power-saving mode to the normal reception mode if the received symbol and a mode-changing symbol match.

Description

Receiving method, transmitting method, receiving device, transmitting device, and communication system

[0001] The present disclosure relates to a receiving method, a transmitting method, a receiving device, a transmitting device, and a communication system.

[0002] Conventionally, communication systems using PLC (Power Line Communication) and the like have been known. For example, an electric scooter has multiple control levers and switches arranged on its body. A PLC communication system, which does not require any wiring other than a power line, is a communication system for transmitting control signals from these control levers and switches and is therefore highly convenient because it is easy to install. Specifically, when the motor output is controlled by a control lever arranged on the handle of the electric scooter and information such as speed is displayed on a display placed on the handle, a control signal is transmitted via a transmitter, a PLC line, and a receiver of the communication system. In such a system, the display, communication system, and motor are powered by a battery. In the above communication system, when the scooter is not being driven, the receiver and the like are maintained in a low-power mode (so-called sleep mode) that consumes less power. This reduces the power consumption of the communication system and the like, thereby increasing the battery operating time.

[0003] JP 2009-21678 A

[0004] In the above-described communication system, when a receiving device or the like is switched from a power saving mode to a normal mode, a wake-up signal is transmitted from a transmitting device to a receiving device. For example, a signal with a predetermined time waveform is transmitted as the wake-up signal. However, noise is likely to be generated from a motor or the like in a PLC line of an electric kick scooter. Therefore, if noise is superimposed on the wake-up signal having the predetermined time waveform, the receiving device may be unable to identify the wake-up signal or may erroneously determine the noise as a wake-up signal. The communication system described in Patent Document 1 describes a noise cancellation technique, but the noise cancellation technique described in Patent Document 1 is a technique that can be used only when the receiving device is in normal mode, and therefore cannot be used to cancel noise from the wake-up signal.

[0005] Therefore, an object of the present disclosure is to provide a receiving method and the like that can realize a wake-up signal with high noise resistance.

[0006] In order to achieve the above object, a receiving method according to an embodiment of the present disclosure includes a transmitting device and a receiving device, and transmits a plurality of signals using Orthogonal Frequency Division Multiplexing (OFDM). a receiving method in a communication system that communicates using an OFDM (Orthogonal Frequency Division Multiplexing) system, the receiving device having, as operation modes, a normal reception mode and a power saving mode that consumes less power than the normal reception mode, and two or more subcarriers among a plurality of subcarriers defined by the OFDM system are defined as a plurality of first subcarriers, the receiving method including: a receiving step of receiving a modulated signal modulated using the OFDM system; a signal level acquisition step of acquiring a signal level of each of the plurality of first subcarriers in the modulated signal; a subcarrier code assignment step of assigning a plurality of subcarrier codes corresponding to each of the plurality of first subcarriers based on the signal level of each of the plurality of first subcarriers; a receiving code assignment step of assigning a receiving code determined based on the plurality of subcarrier codes to the modulated signal; and an operating mode change step of changing the operating mode of the receiving device based on the receiving code,

[0007] In order to achieve the above object, a transmission method according to one embodiment of the present disclosure is a transmission method in a communication system that includes a transmitting device and a receiving device and communicates using an OFDM system, wherein the receiving device has, as its operating modes, a normal reception mode and a power saving mode that consumes less power than the normal reception mode, and the transmitting device has, as its operating modes, a normal transmission mode and a wakeup signal transmission mode in which a wakeup signal is transmitted to change the operating mode of the receiving device from the power saving mode to the normal reception mode, and the transmission method includes a mapping step that determines data to be transmitted on each of a plurality of subcarriers defined by the OFDM system, an IFFT step that performs an inverse fast Fourier transform on each of the plurality of subcarriers, and a D / A conversion step that converts digital data output in the IFFT step into analog data, wherein the wakeup signal includes a plurality of codes corresponding to the plurality of subcarriers, and in the wakeup signal transmission mode, the digital data input to the D / A conversion step is the digital data output in the IFFT step when the data determined in the mapping step corresponds to the wakeup signal.

[0008] In order to achieve the above object, a receiving device according to one embodiment of the present disclosure is a receiving device that communicates using an OFDM system, the receiving device having operating modes including a normal receiving mode and a power saving mode that consumes less power than the normal receiving mode, and of a plurality of subcarriers defined by the OFDM system, two or more subcarriers are defined as a plurality of first subcarriers, the receiving device including: a signal level acquisition unit that receives a modulated signal modulated using the OFDM system and acquires a signal level of each of the plurality of first subcarriers in the modulated signal; a subcarrier code allocation unit that allocates a plurality of subcarrier codes corresponding to each of the plurality of first subcarriers based on the signal level of each of the plurality of first subcarriers; a receiving code allocation unit that allocates a receiving code determined based on the plurality of subcarrier codes to the modulated signal; and an operating mode change unit that changes the operating mode of the receiving device based on the receiving code, and when the receiving code matches a predetermined mode change code, the operating mode change unit changes the operating mode of the receiving device from the power saving mode to the normal receiving mode.

[0009] In order to achieve the above object, a transmitting device according to one embodiment of the present disclosure is a transmitting device that communicates with a receiving device using an OFDM system, wherein the receiving device has, as its operating modes, a normal reception mode and a power saving mode that consumes less power than the normal reception mode, and the transmitting device has, as its operating modes, a normal transmission mode and a wakeup signal transmission mode in which a wakeup signal is transmitted to change the operating mode of the receiving device from the power saving mode to the normal reception mode, and the transmitting device includes: a mapping unit that determines data to be transmitted on each of a plurality of subcarriers defined by the OFDM system; an IFFT unit that performs an inverse fast Fourier transform on each of the plurality of subcarriers; and a D / A conversion unit that converts digital data output by the IFFT unit into analog data, wherein the wakeup signal includes a plurality of codes corresponding to the plurality of subcarriers, and in the wakeup signal transmission mode, the digital data input to the D / A conversion unit is the digital data output by the IFFT unit when the data determined by the mapping unit corresponds to the wakeup signal.

[0010] In order to achieve the above object, a communication system according to one embodiment of the present disclosure is a communication system that includes a transmitting device and a receiving device and communicates using an OFDM system, wherein the receiving device has, as operating modes, a normal receiving mode and a power saving mode that consumes less power than the normal receiving mode, and among a plurality of subcarriers defined by the OFDM system, two or more subcarriers are defined as a plurality of first subcarriers, and the receiving device includes: a signal level acquisition unit that receives a modulated signal modulated using the OFDM system and determines a signal level of each of the plurality of first subcarriers in the modulated signal; a subcarrier code allocation unit that allocates a plurality of subcarrier codes corresponding to each of the plurality of first subcarriers based on the signal level of each of the plurality of first subcarriers; a receiving code allocation unit that allocates a receiving code determined based on the plurality of subcarrier codes to the modulated signal; and an operating mode change unit that changes the operating mode of the receiving device from the power saving mode to the normal receiving mode when the receiving code matches a predetermined mode change code.

[0011] The present disclosure can provide a receiving method that can realize a wake-up signal with high noise resistance.

[0012] 1 is a first block diagram showing an overview of the functional configuration of a communication system according to the first embodiment. FIG. 2 is a second block diagram showing an overview of the functional configuration of the communication system according to the first embodiment. FIG. 3 is a block diagram showing the functional configuration of a transmission device according to the first embodiment. FIG. 4 is a diagram showing an example of a wake-up signal according to the first embodiment. FIG. 5 is a block diagram showing the functional configuration of a reception device according to the first embodiment. FIG. 6 is a block diagram showing the functional configuration of a wake-up signal detection unit according to the first embodiment. FIG. 7 is a graph showing the frequency of a signal output by an oscillator according to the first embodiment. FIG. 8 is a schematic graph showing the frequency distribution of a modulated signal corresponding to the wake-up signal shown in FIG. 3. FIG. 9 is a schematic graph showing the frequency distribution of an output signal of a mixer when a modulated signal according to the first embodiment and a signal of frequency f1 are input to the mixer. FIG. 10 is a schematic graph showing the frequency distribution of an output signal of a mixer when a modulated signal according to the first embodiment and a signal of frequency f2 are input to the mixer. FIG. 11 is a schematic graph showing the frequency dependency of the gain of a low-pass filter according to the first embodiment. FIG. 12 is a schematic graph showing an example of the frequency distribution of an output signal of a low-pass filter according to the first embodiment. FIG. 13 is a sequence diagram showing an overview of a method for changing an operation mode in the communication system according to the first embodiment. FIG. 14 is a flowchart showing a transmission method in the communication system according to the first embodiment. It is a flowchart showing a receiving method in the communication system according to the embodiment 1. It is a block diagram showing a functional configuration of a transmitting device according to the embodiment 2. It is a diagram explaining an example of the configuration of a receiving code according to a modified example.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. The numerical values, shapes, materials, specifications, components, component placement and connection configurations, steps, and step order shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not described in the independent claims that represent the highest concept of the present disclosure will be described as optional components. Furthermore, each drawing is not necessarily an exact illustration. In each drawing, substantially identical components are assigned the same reference numerals, and duplicated descriptions may be omitted or simplified.

[0014] (First embodiment) A receiving method, a transmitting method, a receiving device, a transmitting device, and a communication system according to a first embodiment will be described.

[0015] [1-1. Communication System] A communication system according to this embodiment will be described with reference to Figures 1A and 1B. Figures 1A and 1B are first and second block diagrams, respectively, showing an overview of the functional configuration of a communication system 10 according to this embodiment. Figures 1A and 1B also show a power source 90 that supplies power to the communication system 10.

[0016] As shown in FIG. 1A , a communication system 10 according to this embodiment includes a transmitting device 20 and a receiving device 40, and communicates using Orthogonal Frequency Division Multiplexing (OFDM). In this embodiment, the communication system 10 further includes a communication line 80 connecting the transmitting device 20 and the receiving device 40. The communication system 10 is applied to, for example, an electric kick scooter. The communication system 10 can be used for remote speed control of the electric kick scooter. Specifically, when a driver of the electric kick scooter operates a command signal input device such as a speed switch located on the handle of the electric kick scooter, a command signal corresponding to the operation is transmitted to the transmitting device 20 of the communication system 10. A signal corresponding to the command signal is transmitted to the receiving device 40 via the transmitting device 20 and the communication line 80. Then, a control signal corresponding to the command signal is transmitted from the receiving device 40 to a control device such as a motor device of the electric kick scooter. In this embodiment, the communication system 10 uses a PLC. That is, in the communication system 10, communication is performed using a power line for supplying power from a power source 90 to the transmitting device 20 and the receiving device 40.

[0017] 1A shows an example in which the communication system 10 includes one transmitting device 20 and one receiving device 40, but the configuration of the communication system 10 is not limited to this. For example, the communication system 10 may include one or more transmitting devices 20 and one or more receiving devices 40 connected to each other via a communication line 80.

[0018] The power supply 90 supplies power to the communication system 10. As the power supply 90, for example, a battery or the like can be used.

[0019] The communication line 80 is a line for communication between the transmitting device 20 and the receiving device 40. In this embodiment, the communication line 80 is also used as a power line for supplying power from a power source 90.

[0020] Note that the communication line 80 does not necessarily have to be used to supply power from the power source 90 to the transmitting device 20 and the receiving device 40. In other words, the communication system 10 does not necessarily have to use PLC. For example, as shown in FIG. 1B , power may be supplied from the power source 90 to the transmitting device 20 and the receiving device 40 using a power line other than the communication line 80.

[0021] The transmitting device 20 is a device that communicates with the receiving device 40 using the OFDM system. In this embodiment, the transmitting device 20 receives a command signal and transmits a modulated signal to the receiving device 40 based on the command signal. The transmitting device 20 has at least a normal transmission mode and a wake-up signal transmission mode in which a wake-up signal is transmitted to change the operating mode of the receiving device 40 from a power-saving mode to a normal reception mode. In this embodiment, the transmitting device 20 further has a power-saving mode in which power consumption is lower than in the normal transmission mode. In the normal transmission mode, the transmitting device 20 transmits a modulated signal corresponding to the received command signal to the receiving device 40. When the transmitting device 20 receives a command signal in the power-saving mode, the operating mode of the transmitting device 20 switches to the wake-up signal transmission mode and transmits a wake-up signal to the receiving device 40 to switch the operating mode of the receiving device 40 from the power-saving mode to the normal reception mode. The operation mode of the transmitting device 20 switches to the normal transmission mode when a ready signal indicating that the operation mode of the receiving device 40 has been switched to the normal reception mode is received from the receiving device 40 .

[0022] The configuration of the transmitting device 20 according to this embodiment will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the functional configuration of the transmitting device 20 according to this embodiment.

[0023] As shown in FIG. 2 , a transmitting device 20 according to this embodiment includes an input IF unit 21, a sequence control unit 22, a signal storage unit 23, a primary modulation unit 24, a selection unit 25, a mapping unit 26, an IFFT (Inverse Fast Fourier Transform) unit 27, and a D / A conversion unit 28.

[0024] The input IF unit 21 is an interface that receives a command signal transmitted to the transmission device 20. When the input IF unit 21 receives the command signal, the operation mode of the transmission device 20 switches from a power saving mode to a wake-up signal transmission mode. In this embodiment, when the input IF unit 21 receives the command signal, it transmits a trigger signal to the sequence control unit 22. When the input IF unit 21 receives a wake-up completion signal from the sequence control unit 22, the transmission device 20 switches to a normal transmission mode, and the input IF unit 21 transmits command data corresponding to the command signal to the primary modulation unit 24.

[0025] The sequence control unit 22 is a processing unit that controls the selection unit 25. In the wake-up signal transmission mode, the sequence control unit 22 transmits a signal to cause the selection unit 25 to output a wake-up signal. In the normal transmission mode, the sequence control unit 22 transmits a signal to cause the selection unit 25 to output a signal from the primary modulation unit 24. In the wake-up signal transmission mode and the power saving mode, the sequence control unit 22 may transmit a signal to stop the operation of the primary modulation unit 24. When the sequence control unit 22 receives a ready signal from the receiving device 40, it switches the operation mode of the transmitting device 20 to the normal transmission mode. In the normal transmission mode, the sequence control unit 22 may transmit a signal to cause the primary modulation unit 24 to operate.

[0026] The signal storage unit 23 stores a signal corresponding to the wake-up signal. The signal storage unit 23 outputs the wake-up signal to the selection unit 25. In this embodiment, the wake-up signal includes a plurality of codes corresponding to a plurality of subcarriers defined by the OFDM system. That is, there is a one-to-one correspondence between each of the plurality of subcarriers and each of the plurality of codes. For example, the code value of each of the plurality of codes is either 0 or 1. In this embodiment, the code value of at least one code is 0. Of the plurality of subcarriers defined by the OFDM system, two or more subcarriers may be defined as a plurality of first subcarriers, and the wake-up signal may include a plurality of codes corresponding to the plurality of first subcarriers. That is, the wake-up signal may be a code corresponding to a plurality of first subcarriers that are a portion of the plurality of subcarriers. In this embodiment, all of the subcarriers defined by the OFDM system are defined as a plurality of first subcarriers.

[0027] An example of a wake-up signal stored in the signal storage unit 23 will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of a wake-up signal according to this embodiment. Fig. 3 shows an example of a combination of subcarrier numbers indicating each of a plurality of subcarriers and codes corresponding to each of the plurality of subcarriers. Note that Fig. 3 shows an example in which the number of subcarriers is eight, but the number of subcarriers is not limited to this. For example, the number of subcarriers may be around 200.

[0028] In a signal transmitted in normal transmission mode, the multiple data corresponding to the multiple subcarriers are generally not zero. Therefore, the receiving device 40 can reliably identify whether the received modulated signal corresponds to a wake-up signal or a normal signal. Furthermore, the power consumption by the wake-up signal detection unit 50 for this identification can be reduced. Furthermore, the wake-up signal according to this embodiment is not a time waveform, but is composed of multiple codes corresponding to the multiple subcarriers, so it can be easily distinguished from noise applied to all of the multiple subcarriers.

[0029] The primary modulation unit 24 is a processing unit that modulates the command data received from the input IF unit 21. The primary modulation unit 24 outputs the modulated command data to the selection unit 25. The primary modulation unit 24 performs modulation using, for example, binary phase shift keying (BPSK) or quadrature amplitude modulation (QAM). The primary modulation unit 24 may stop operating in the power saving mode based on a signal from the sequence control unit 22.

[0030] The selector 25 selects a signal to be output to the mapping unit 26. In this embodiment, the selector 25 selects one of the wake-up signal, which is an input signal from the signal storage unit 23, and the input signal from the primary modulator 24, based on a signal from the sequence controller 22, and outputs the selected signal to the mapping unit 26.

[0031] The mapping unit 26 is a processing unit that determines data to be transmitted on each of a plurality of subcarriers defined by the OFDM system. The mapping unit 26 determines data to be transmitted on each of a plurality of subcarriers based on the signal input from the selection unit 25, and outputs a signal including the determined data to the IFFT unit 27.

[0032] The IFFT unit 27 performs an inverse fast Fourier transform on each of the subcarriers, and outputs the inverse fast Fourier transformed digital data to the D / A conversion unit 28.

[0033] The D / A conversion unit 28 is a processing unit that converts the digital data output by the IFFT unit 27 into analog data. The analog data is transmitted as a modulated signal to the receiving device 40 via the communication line 80. In the wake-up signal transmission mode, the digital data input to the D / A conversion unit 28 is the digital data output by the IFFT unit 27 when the data determined by the mapping unit 26 corresponds to the wake-up signal. In the normal transmission mode, the digital data input to the D / A conversion unit 28 is the digital data output by the IFFT unit 27 when the data determined by the mapping unit 26 corresponds to the input signal from the primary modulation unit 24.

[0034] The receiving device 40 is a device that communicates using the OFDM system. The receiving device 40 receives a modulated signal from the transmitting device 20 via a communication line 80. The receiving device 40 outputs a control signal based on the received modulated signal. The receiving device 40 has two operating modes: a normal reception mode and a power saving mode that consumes less power than the normal reception mode. The configuration of the receiving device 40 will be described using FIG. 4. FIG. 4 is a block diagram showing the functional configuration of the receiving device 40 according to this embodiment. FIG. 4 also shows the transmitting device 20, a power supply 90, and a communication line 80.

[0035] As shown in FIG. 4, the receiving device 40 includes a signal processing unit 42, a switch 44, and a wake-up signal detection unit 50.

[0036] The signal processing unit 42 demodulates the modulated signal transmitted from the transmitting device 20. In the normal reception mode, the signal processing unit 42 demodulates the modulated signal to output a control signal corresponding to a command signal input to the transmitting device 20. More specifically, the signal processing unit 42 performs processes such as A / D conversion, fast Fourier transform, and demodulation.

[0037] The A / D conversion process converts the modulated signal, which is analog data, into digital data. The fast Fourier transform process performs a fast Fourier transform on the digital data. The demodulation process performs demodulation corresponding to the modulation performed by the primary modulation unit 24 of the transmitting device 20.

[0038] In the power saving mode, the signal processing unit 42 does not perform any processing. In the present embodiment, the power supply from the power supply 90 is stopped in the power saving mode. This makes it possible to reduce power consumption in the power saving mode. Note that the method for reducing power consumption in the signal processing unit 42 is not limited to this. For example, the power consumption in the signal processing unit 42 may be reduced by stopping the supply of a clock signal, which determines the operation timing of the signal processing unit 42, to the signal processing unit 42 without stopping the power supply from the power supply 90.

[0039] The signal processing unit 42 transmits a ready signal to the transmitting device 20 when the operation mode of the receiving device 40 is switched from the power saving mode to the normal receiving mode.

[0040] The switch 44 switches the state of power supply from the power supply 90 to the signal processing unit 42. In the present embodiment, the switch 44 also switches the state of modulated signals supplied from the transmitting device 20 to the signal processing unit 42. The switch 44 is inserted in the middle of the line connecting the power supply 90 and the transmitting device 20 to the signal processing unit 42, and switches the connection state (on state or off state) between the power supply 90 and the transmitting device 20 and the signal processing unit 42 based on a signal from the wake-up signal detection unit 50.

[0041] Note that the configuration of the switch 44 and other components is not limited to this. For example, if the receiving device 40 has a separation circuit that separates the power supplied from the power source 90 via the communication line 80 from the modulated signal supplied from the transmitting device 20 via the communication line 80, the switch 44 may switch only the power supply state out of the supply states of the power and the modulated signal to the signal processing unit 42. In this case, the modulated signal may be constantly supplied to the signal processing unit 42. Even with such a configuration, the power consumption in the signal processing unit 42 can be reduced.

[0042] The wake-up signal detection unit 50 is a processing unit that detects a wake-up signal included in a modulated signal transmitted from the transmitting device 20. When the wake-up signal detection unit 50 detects a wake-up signal in the power-saving mode, it switches the operation mode of the receiving device 40 from the power-saving mode to the normal reception mode. In this embodiment, the operation mode of the receiving device 40 is switched from the power-saving mode to the normal reception mode by switching the switch 44 from the off state to the on state and starting the supply of power from the power supply 90 to the signal processing unit 42. In this embodiment, switching the switch 44 from the off state to the on state also starts the supply of a modulated signal from the transmitting device 20 to the signal processing unit 42.

[0043] The configuration of the wake-up signal detection unit 50 will be described with reference to Fig. 5. Fig. 5 is a block diagram showing the functional configuration of the wake-up signal detection unit 50 according to this embodiment.

[0044] As shown in FIG. 5, the wake-up signal detection unit 50 according to this embodiment includes a signal level acquisition unit 60, a subcarrier code allocation unit 70, a reception code allocation unit 51, and an operation mode change unit 52.

[0045] The signal level acquisition unit 60 receives a modulated signal modulated by the OFDM method by the transmitting device 20, and acquires the signal level of each of a plurality of first subcarriers in the modulated signal. In this embodiment, the signal level acquisition unit 60 has an oscillator 61, a mixer 62, a low-pass filter 63, and a measurement unit 64.

[0046] The oscillator 61 is a device that outputs signals having frequencies equivalent to those of the plurality of subcarriers. The output signal of the oscillator 61 will now be described with reference to FIG. 6. FIG. 6 is a graph showing the frequencies of the signals output by the oscillator 61 according to this embodiment. In this embodiment, as shown in FIG. 6, the oscillator 61 sequentially outputs signals having frequencies (f1 to f8) equivalent to those of the plurality of subcarriers. In the example shown in FIG. 6 , oscillator 61 outputs a signal of frequency f1 from time t0 to time t1, outputs a signal of frequency f2 (>f1) from time t1 to time t2, outputs a signal of frequency f3 (>f2) from time t2 to time t3, outputs a signal of frequency f4 (>f3) from time t3 to time t4, outputs a signal of frequency f5 (>f4) from time t4 to time t5, outputs a signal of frequency f6 (>f5) from time t5 to time t6, outputs a signal of frequency f7 (>f6) from time t6 to time t7, and outputs a signal of frequency f8 (>f7) from time t7 to time t8.

[0047] The mixer 62 is a circuit that multiplies the modulated signal by the output signal of the oscillator 61. Here, the output signal of the mixer 62 will be described.

[0048] The modulated signal input to the mixer 62 is expressed by the following equation (1), where n=1, 2, . . . , 8.

[0049] Σ(An×sin(2n×fn×t))=Σ(An×sin(ωn×t)) (1)

[0050] In equation (1), An is the amplitude of the component of frequency fn of the modulated signal.

[0051] The output signal of the oscillator 61 is expressed by the following equation (2).

[0052] B × sin(2n × fosc × t) = B × sin(ω × t) (2)

[0053] Therefore, the output signal of the mixer 62 is expressed by the following equation (3).

[0054] Σ(An×sin(ωn×t))×B×sin(ω×t) = Σ(An×B×sin(ωn×t)×sin(ω×t)) =(1 / 2) ×Σ(An×B×(cos((ωn−ω)×t)−cos((ωn+ω)×t))) (3)

[0055] Here, the frequency ((ωn+ω)×t) is larger than ((ωn-ω)×t), and assuming that the high frequency components will be filtered later by the low-pass filter 63, ignoring the term cos((ωn+ω)×t)), the above equation (3) can be approximated by the following equation (4).

[0056] (1 / 2)×Σ(An×B×(cos((ωn-ω)×t))) (4)

[0057] Here, when ω1 is substituted for ω and n=2, 3, . . . , equation (4) is expressed as the following equation (5).

[0058] A1×B×(1 / 2)×cos(0) +(1 / 2)Σ(An×B×(cos((ωn-ω)×t))) =A1×B×(1 / 2) +(1 / 2)Σ(An×B×(cos((ωn-ω)×t))) (5)

[0059] Here, the term cos((ωn-ω)×t) is ignored because it is a high-frequency component compared to A1×B×(½). Therefore, when the frequency of the signal from oscillator 61 is f1, the signal level of the term where the frequency of the output signal from mixer 62 is zero can be calculated as A1×B×(½).

[0060] Similarly, when the frequency of the signal from oscillator 61 is one of frequencies f2 to f8, the signal level of the term where the frequency of the output signal from mixer 62 is zero can be calculated as An×B×(1 / 2) (n=2, 3, ..., 8).

[0061] For example, the frequency distribution of the modulated signal corresponding to the wake-up signal shown in Fig. 3 will be described with reference to Fig. 7. Fig. 7 is a schematic graph showing the frequency distribution of the modulated signal corresponding to the wake-up signal shown in Fig. 3.

[0062] The frequency distribution of the output signal of the mixer 62 when such a modulated signal and a signal of frequency f1 or frequency f2 are input to the mixer 62 will be described with reference to Figures 8 and 9. Figure 8 is a schematic graph showing the frequency distribution of the output signal of the mixer 62 when the modulated signal according to this embodiment and a signal of frequency f1 are input to the mixer 62. Figure 9 is a schematic graph showing the frequency distribution of the output signal of the mixer 62 when the modulated signal according to this embodiment and a signal of frequency f2 are input to the mixer 62.

[0063] 8, when a signal of frequency f1 is output from oscillator 61 to mixer 62, a component corresponding to the component of frequency f1 of the modulated signal is output from mixer 62 as a component of frequency 0. Furthermore, components corresponding to the components of frequencies f3, f5, and f8 of the modulated signal are output from mixer 62 as components of frequencies f3-f1, f5-f1, and f8-f1.

[0064] 9, when a signal of frequency f2 is output from oscillator 61 to mixer 62, a component corresponding to the component of frequency f2 of the modulated signal is output from mixer 62 as a component of frequency 0. Furthermore, components corresponding to the components of frequencies f3, f5, and f8 of the modulated signal are output from mixer 62 as components of frequencies f3-f2, f5-f2, and f8-f2.

[0065] The low-pass filter 63 is a filter that reduces high-frequency components and passes low-frequency components in the output signal from the mixer 62. An example of the characteristics of the low-pass filter 63 will be described with reference to Figs. 10 and 11. Fig. 10 is a schematic graph showing the frequency dependence of the gain of the low-pass filter 63 according to this embodiment. Fig. 11 is a schematic graph showing an example of the frequency distribution of the output signal of the low-pass filter 63 according to this embodiment.

[0066] 10, low-pass filter 63 according to this embodiment reduces frequency components equal to or greater than frequency f2-f1, and passes only components near frequency 0. As a result, for example, when a signal such as that shown in FIG. 8 is input to low-pass filter 63, only components near frequency 0 are output from low-pass filter 63, as shown in FIG.

[0067] By using the oscillator 61, mixer 62, and low-pass filter 63 as described above, it is possible to generate a signal in which waveforms corresponding to the intensities of the subcarriers are arranged in the time axis direction.

[0068] The measurement unit 64 measures the signal level of each subcarrier of the modulated signal. In this embodiment, the signal level of each of the multiple first subcarriers is measured by measuring the signal level of the component near frequency 0 of the output signal of the low-pass filter 63. For example, an envelope detection circuit can be used as the measurement unit 64. The measurement unit 64 outputs the measured signal level.

[0069] The subcarrier code allocation unit 70 allocates a plurality of subcarrier codes corresponding to the plurality of first subcarriers, respectively, based on the signal levels of the plurality of first subcarriers. In this embodiment, the subcarrier code allocation unit 70 includes a comparator 71 and a table creation unit 72.

[0070] Comparator 71 compares the signal level of each of the multiple first subcarriers output from measurement unit 64 with a predetermined threshold, and outputs a determination result of whether the signal level is larger or smaller. Furthermore, in comparator 71, the predetermined threshold used to compare the signal level of each of the multiple first subcarriers is the same. In other words, the signal level of each of the multiple first subcarriers is compared with the same threshold.

[0071] The table creation unit 72 creates a table in which each of the multiple subcarrier codes is assigned based on the comparison result by the comparator 71 between a predetermined threshold and each signal level of the multiple first subcarriers. The table creation unit 72 creates a table in which, for example, each of the multiple first subcarriers, the signal level of each of the multiple first subcarriers (or the signal level indicated by the output signal of the comparator 71), and each of the multiple subcarrier codes are associated with each other. For example, the table creation unit 72 assigns 1 to the subcarrier code corresponding to a first subcarrier whose signal level is greater than the predetermined threshold, and assigns 0 to the subcarrier code corresponding to a first subcarrier whose signal level is equal to or less than the predetermined threshold. The table creation unit 72 can identify which first subcarrier each signal level corresponds to based on, for example, a clock signal that defines the signal output timing of the oscillator 61.

[0072] The reception code allocation unit 51 allocates a reception code determined based on a plurality of subcarrier codes to the modulated signal. In this embodiment, the reception code allocation unit 51 outputs the reception code to the operation mode change unit 52. The code length of the reception code is equal to the number of first subcarriers. That is, the reception code allocation unit 51 directly uses the plurality of subcarrier codes as the plurality of codes included in the reception code. Note that the code length of the reception code does not have to be equal to the number of first subcarriers. For example, one code included in the reception code may be generated based on two or more of the plurality of subcarrier codes. Furthermore, the reception code may include information identifying a transmitter that transmitted the modulated signal. For example, if the communication system 10 includes a plurality of transmitting devices 20, the plurality of transmitting devices 20 may each have a wake-up signal corresponding to a different reception code. This allows the receiving device 40 to identify the transmitting device 20 that is the source of the transmission, if the communication system 10 includes a plurality of transmitting devices 20.

[0073] The operation mode change unit 52 changes the operation mode of the receiving device 40 based on the received code. When the received code matches a predetermined mode change code, the operation mode change unit 52 changes the operation mode of the receiving device 40 from the power saving mode to the normal reception mode. When the received code does not match the mode change code, the operation mode change unit 52 maintains the operation mode of the receiving device 40 without changing it. Note that any code can be used as the mode change code. A wake-up signal corresponding to the arbitrarily determined mode change code is used in the transmitting device 20.

[0074] [1-2. Operation Mode Changing Method in Communication System] An overview of the operation mode changing method in the communication system 10 according to this embodiment will be described with reference to Fig. 12. Fig. 12 is a sequence diagram showing an overview of the operation mode changing method in the communication system 10 according to this embodiment. Fig. 12 shows a method for changing the operation modes of the transmitting device 20 and the receiving device 40 of the communication system 10 from a power saving mode to a normal transmission mode and a normal reception mode, respectively.

[0075] As shown in FIG. 12, when the transmitting device 20 in the power saving mode receives a command signal, the operating mode is switched from the power saving mode to the wake-up signal transmission mode (S1).

[0076] Next, the transmitting device 20 transmits a wake-up signal to the receiving device 40 (S2). In this embodiment, the transmitting device 20 transmits to the receiving device 40 a wake-up signal modulated by the OFDM method.

[0077] Next, upon receiving the wake-up signal, the receiving device 40 switches its operation mode from the power saving mode to the normal receiving mode (S3).

[0078] Next, after switching the operation mode to the normal reception mode, the receiving device 40 transmits a ready signal to the transmitting device 20 (S4), thereby notifying the transmitting device 20 that the operation mode of the receiving device 40 has been switched to the normal reception mode.

[0079] Next, when the transmitting device 20 receives a ready signal from the receiving device 40, it switches the operation mode from the wake-up signal transmission mode to the normal transmission mode (S5).

[0080] Next, the transmitting device 20 switches the operation mode to the normal transmission mode, and then transmits command data corresponding to the command signal to the receiving device 40 (S6).

[0081] As described above, in the communication system 10 according to the present embodiment, the transmitting device 20 and the receiving device 40, which are in the power saving mode, are switched to the normal transmission mode and the normal reception mode, respectively.

[0082] [1-3. Transmission Method in Communication System] A transmission method in communication system 10 according to this embodiment will be described with reference to Fig. 13. Fig. 13 is a flowchart showing the transmission method in communication system 10 according to this embodiment.

[0083] The transmitting device 20 of the communication system 10 receives a command signal while in the power saving mode (S10). In this embodiment, the input IF unit 21 of the transmitting device 20 receives the command signal.

[0084] Next, the transmitting device 20 switches the operation mode from the power saving mode to the wake-up signal transmission mode (S12).

[0085] Next, the transmitting device 20 selects data corresponding to the wake-up signal as data to be transmitted (S14). In this embodiment, the selecting unit 25 of the transmitting device 20 selects data corresponding to the wake-up signal as data to be transmitted based on a signal from the sequence control unit 22. The wake-up signal includes a plurality of codes corresponding to a plurality of subcarriers.

[0086] Next, the transmitting device 20 performs mapping by determining data to be transmitted on each of a plurality of subcarriers defined by the OFDM system (S16). In this embodiment, the mapping unit 26 of the transmitting device 20 determines data to be transmitted on each of a plurality of subcarriers.

[0087] Next, the transmitting device 20 performs an inverse fast Fourier transform on each of the plurality of subcarriers (S18). In this embodiment, the IFFT unit 27 of the transmitting device 20 performs an inverse fast Fourier transform on each of the plurality of subcarriers.

[0088] Next, the transmitting device 20 converts the digital data output in step S12 into analog data (S20). In this embodiment, the D / A conversion unit 28 of the transmitting device 20 converts the digital data output from the IFFT unit 27 into analog data.

[0089] Next, the transmitting device 20 receives a ready signal from the receiving device 40 that has received the wake-up signal (S22). In this embodiment, the sequence control unit 22 of the transmitting device 20 receives the ready signal.

[0090] Next, the transmitting device 20 switches the operation mode from the wake-up signal transmission mode to the normal transmission mode (S24). In this embodiment, the sequence control unit 22 transmits a signal to the selection unit 25, causing the selection unit 25 to select the signal from the primary modulation unit 24. The sequence control unit 22 also starts the operation of the primary modulation unit 24.

[0091] Next, the transmitting device 20 transmits command data corresponding to the command signal to the receiving device 40 (S26). In this embodiment, the input IF unit 21 transmits the command data corresponding to the command signal to the primary modulation unit 24. The primary modulation unit 24 modulates the command data and transmits the modulated command data to the selection unit 25. The selection unit 25 selects the modulated command data from the primary modulation unit 24 and outputs it to the mapping unit 26. The mapping unit 26 determines the data to be transmitted on each of the multiple subcarriers based on the modulated command data. The IFFT unit 27 performs an inverse fast Fourier transform on each of the multiple subcarriers. The D / A conversion unit 28 of the transmitting device 20 converts the digital data output from the IFFT unit 27 into analog data and transmits it to the receiving device 40 as a modulated signal.

[0092] As described above, according to the transmission method of the present embodiment, by transmitting a wake-up signal to the receiving device 40 operating in a power saving mode, the operating mode of the receiving device 40 can be switched to a normal reception mode. In this embodiment, the wake-up signal includes multiple codes corresponding to multiple subcarriers defined by the OFDM system, and data corresponding to at least one of the multiple subcarriers can be zero. In a signal transmitted in the normal transmission mode, the multiple data corresponding to the multiple subcarriers are generally not zero. This allows the receiving device 40 to reliably identify whether the received modulated signal corresponds to a wake-up signal or a normal signal. Furthermore, the power consumption of the wake-up signal detection unit 50 for this identification can be reduced. Furthermore, since the wake-up signal according to this embodiment is not a time waveform but is composed of multiple codes corresponding to the multiple subcarriers, it can be easily distinguished from noise applied to the entire multiple subcarriers.

[0093] [1-4. Receiving Method in Communication System] A receiving method in communication system 10 according to this embodiment will be described with reference to Fig. 14. Fig. 14 is a flowchart showing the receiving method in communication system 10 according to this embodiment.

[0094] 14, receiving device 40 in communication system 10 receives a modulated signal modulated by the OFDM method when the operating mode is the power saving mode (S40). In this embodiment, wake-up signal detection unit 50, which operates even in the power saving mode, receives the modulated signal.

[0095] Next, the wake-up signal detector 50 of the receiving device 40 acquires the signal level of each of the plurality of first subcarriers in the modulated signal (S42). In this embodiment, the signal level acquirer 60 of the wake-up signal detector 50 acquires the signal level.

[0096] Next, the wakeup signal detection unit 50 assigns a plurality of subcarrier codes corresponding to the plurality of first subcarriers, respectively, based on the signal levels of the plurality of first subcarriers (S44). In this embodiment, the subcarrier code assignment unit 70 of the wakeup signal detection unit 50 assigns a plurality of subcarrier codes corresponding to the plurality of first subcarriers, respectively.

[0097] Next, the wakeup signal detection unit 50 assigns a reception code determined based on the plurality of subcarrier codes to the modulated signal (S46). In this embodiment, the reception code assignment unit 51 of the wakeup signal detection unit 50 assigns the reception code to the modulated signal.

[0098] Next, the wakeup signal detection unit 50 changes the operation mode of the receiving device 40 based on the received code (S48). In step S48, the operation mode change unit 52 of the wakeup signal detection unit 50 changes the operation mode of the receiving device 40 from the power saving mode to the normal receiving mode if the received code matches a predetermined mode change code.

[0099] Next, the receiving device 40 transmits a ready signal to the transmitting device 20 (S50). In this embodiment, the signal processing unit 42 of the receiving device 40 transmits the ready signal to the transmitting device 20.

[0100] As described above, according to the receiving method of the present embodiment, by transmitting a wake-up signal to the receiving device 40 operating in a power-saving mode, the operating mode of the receiving device 40 can be switched to a normal receiving mode. In this embodiment, the wake-up signal includes multiple codes corresponding to multiple subcarriers defined by the OFDM system, and data corresponding to at least one of the multiple subcarriers can be zero. In a signal modulated using the OFDM system, the multiple data corresponding to the multiple subcarriers are generally not zero. This allows the receiving device 40 to reliably identify whether the received modulated signal corresponds to a wake-up signal or a normal signal. Furthermore, the power consumption of the wake-up signal detector 50 for this identification can be reduced. Furthermore, since the wake-up signal according to this embodiment is not a time waveform but is composed of multiple codes corresponding to the multiple subcarriers, it can be easily distinguished from noise applied to the entire multiple subcarriers.

[0101] [1-5. Effects, etc.] The following describes various aspects and effects of the receiving method, transmitting method, receiving device 40, transmitting device 20, and communication system 10 according to the present embodiment.

[0102] A receiving method of aspect 1 according to this embodiment is a receiving method in a communication system 10 that includes a transmitting device 20 and a receiving device 40 and communicates using the OFDM system, in which the receiving device 40 has, as operation modes, a normal receiving mode and a power saving mode that consumes less power than the normal receiving mode, and of a plurality of subcarriers defined by the OFDM system, two or more subcarriers are defined as a plurality of first subcarriers, and the receiving method includes a receiving step of receiving a modulated signal modulated using the OFDM system, a signal level acquisition step of acquiring a signal level of each of the plurality of first subcarriers in the modulated signal, a subcarrier code assignment step of assigning a plurality of subcarrier codes corresponding to each of the plurality of first subcarriers based on the signal level of each of the plurality of first subcarriers, a receiving code assignment step of assigning a receiving code determined based on the plurality of subcarrier codes to the modulated signal, and an operation mode change step of changing the operation mode of the receiving device 40 based on the received code, and in the operation mode change step, if the received code matches a predetermined mode change code, the operation mode of the receiving device 40 is changed from the power saving mode to the normal receiving mode.

[0103] According to the receiving method of aspect 1, by transmitting a wake-up signal to a receiving device 40 operating in a power-saving mode, the operating mode of the receiving device 40 can be switched to a normal receiving mode. The wake-up signal includes multiple codes corresponding to multiple subcarriers defined by the OFDM system, and data corresponding to at least one of the multiple subcarriers can be zero. In a signal modulated using the OFDM system, the multiple data corresponding to the multiple subcarriers are generally not zero. This allows the receiving device 40 to reliably identify whether the received modulated signal corresponds to a wake-up signal or a normal signal. Furthermore, the power consumption by the wake-up signal detection unit 50 for this identification can be reduced. Furthermore, since the wake-up signal according to this embodiment is not a time waveform but is composed of multiple codes corresponding to the multiple subcarriers, it can be easily distinguished from noise applied to the entire multiple subcarriers.

[0104] In the receiving method of aspect 2 according to this embodiment, in the subcarrier code allocation step of the receiving method according to aspect 1, each of the plurality of subcarrier codes may be allocated based on a result of comparison between a predetermined threshold and the signal level.

[0105] This allows easy assignment of subcarrier codes, for example, by setting the subcarrier code to 1 when the signal level is greater than a predetermined threshold, and setting the subcarrier code to 0 when the signal level is equal to or less than the predetermined threshold.

[0106] In the receiving method of aspect 3 according to this embodiment, in the subcarrier code allocation step of the receiving method described in aspect 2, the predetermined threshold value that is compared with the signal level of each of the multiple first subcarriers may be the same.

[0107] This simplifies the receiving method.

[0108] A receiving method of aspect 4 according to the present embodiment is the receiving method according to any one of aspects 1 to 3, wherein the received code may include information for identifying a source that has transmitted the modulated signal.

[0109] This allows the receiving device 40 to easily identify the transmitting device 20 that is the source of the modulated signal, for example, when the communication system 10 includes a plurality of transmitting devices 20.

[0110] A receiving method of aspect 5 according to the present embodiment is the receiving method according to any one of aspects 1 to 4, wherein the code length of the received code may be equal to the number of the plurality of first subcarriers.

[0111] This simplifies the receive code allocation step.

[0112] The receiving method of aspect 6 according to the present embodiment may be the receiving method according to any one of aspects 1 to 5, in which any code can be used as the mode change code.

[0113] This allows for greater freedom in reception methods.

[0114] A transmission method of aspect 1 according to this embodiment is a transmission method in a communication system 10 that includes a transmitting device 20 and a receiving device 40 and communicates using the OFDM system, wherein the receiving device 40 has, as its operating modes, a normal reception mode and a power saving mode that consumes less power than the normal reception mode, and the transmitting device 20 has, as its operating modes, a normal transmission mode and a wake-up signal transmission mode in which a wake-up signal is transmitted to change the operating mode of the receiving device 40 from the power saving mode to the normal reception mode, and the transmission method includes a mapping step that determines data to be transmitted on each of a plurality of subcarriers defined by the OFDM system, an IFFT step that performs an inverse fast Fourier transform on each of the plurality of subcarriers, and a D / A conversion step that converts digital data output in the IFFT step into analog data, wherein the wake-up signal includes a plurality of codes corresponding to the plurality of subcarriers, and in the wake-up signal transmission mode, the digital data input to the D / A conversion step is digital data that is output in the IFFT step when the data determined in the mapping step corresponds to the wake-up signal.

[0115] According to the transmission method of aspect 1, by transmitting a wake-up signal to a receiving device 40 operating in a power-saving mode, the operating mode of the receiving device 40 can be switched to a normal reception mode. The wake-up signal includes multiple codes corresponding to multiple subcarriers defined by the OFDM system, and data corresponding to at least one of the multiple subcarriers can be zero. In a signal transmitted in normal transmission mode, the multiple data corresponding to the multiple subcarriers are generally not zero. This allows the receiving device 40 to reliably identify whether the received modulated signal corresponds to a wake-up signal or a normal signal. Furthermore, the power consumption of the wake-up signal detection unit 50 for this identification can be reduced. Furthermore, since the wake-up signal according to this embodiment is not a time waveform but is composed of multiple codes corresponding to the multiple subcarriers, it can be easily distinguished from noise applied to the entire multiple subcarriers.

[0116] The receiving device 40 of aspect 1 according to this embodiment is a receiving device 40 that communicates using the OFDM system, and has, as its operating modes, a normal receiving mode and a power saving mode that consumes less power than the normal receiving mode. Of the multiple subcarriers defined by the OFDM system, two or more subcarriers are defined as multiple first subcarriers. The receiving device 40 includes: a signal level acquisition unit 60 that receives a modulated signal modulated using the OFDM system and acquires the signal level of each of the multiple first subcarriers in the modulated signal; a subcarrier code assignment unit 70 that assigns multiple subcarrier codes corresponding to each of the multiple first subcarriers based on the signal level of each of the multiple first subcarriers; a receiving code assignment unit 51 that assigns a receiving code determined based on the multiple subcarrier codes to the modulated signal; and an operating mode change unit 52 that changes the operating mode of the receiving device 40 from the power saving mode to the normal receiving mode when the receiving code matches a predetermined mode change code.

[0117] The receiving device 40 of the first aspect provides the same effects as the receiving method of the first aspect.

[0118] The transmitting device 20 of aspect 1 according to this embodiment is a transmitting device 20 that communicates with a receiving device 40 using the OFDM system, wherein the receiving device 40 has, as its operating modes, a normal reception mode and a power saving mode that consumes less power than the normal reception mode, and the transmitting device 20 has, as its operating modes, a normal transmission mode and a wakeup signal transmission mode in which a wakeup signal is transmitted to change the operating mode of the receiving device from the power saving mode to the normal reception mode, and the transmitting device 20 includes a mapping unit 26 that determines data to be transmitted on each of a plurality of subcarriers defined by the OFDM system, an IFFT unit 27 that performs an inverse fast Fourier transform on each of the plurality of subcarriers, and a D / A conversion unit 28 that converts digital data output by the IFFT unit 27 into analog data, wherein the wakeup signal includes a plurality of codes corresponding to the plurality of subcarriers, and in the wakeup signal transmission mode, the digital data input to the D / A conversion unit 28 is digital data that is output by the IFFT unit 27 when the data determined by the mapping unit 26 corresponds to the wakeup signal.

[0119] The transmitting device 20 of the first aspect provides the same effects as the transmitting method of the first aspect.

[0120] A communication system 10 of aspect 1 according to this embodiment is a communication system 10 that includes a transmitting device 20 and a receiving device 40 and communicates using the OFDM system, wherein the receiving device 40 has, as its operating modes, a normal receiving mode and a power saving mode that consumes less power than the normal receiving mode, and among a plurality of subcarriers defined by the OFDM system, two or more subcarriers are defined as a plurality of first subcarriers, and the receiving device 40 includes a signal level acquiring unit 60 that receives a modulated signal modulated using the OFDM system and determines the signal level of each of the plurality of first subcarriers in the modulated signal, a subcarrier code assigning unit 70 that assigns a plurality of subcarrier codes corresponding to each of the plurality of first subcarriers based on the signal level of each of the plurality of first subcarriers, a receiving code assigning unit 51 that assigns a receiving code determined based on the plurality of subcarrier codes to the modulated signal, and an operating mode changing unit 52 that changes the operating mode of the receiving device 40 from the power saving mode to the normal receiving mode when the receiving code matches a predetermined mode change code.

[0121] The communication system 10 of the first aspect provides the same effects as the receiving method of the first aspect.

[0122] (Embodiment 2) A transmitting device according to embodiment 2 will be described. The transmitting device according to this embodiment differs from the transmitting device 20 according to embodiment 1 mainly in the configuration of a signal storage unit that stores a signal corresponding to a wake-up signal. The transmitting device according to this embodiment will be described below with reference to FIG. 15, focusing on the differences from the transmitting device 20 according to embodiment 1. FIG. 15 is a block diagram showing the functional configuration of the transmitting device 120 according to this embodiment.

[0123] As shown in FIG. 15, the transmitting device 120 according to this embodiment includes an input IF unit 21, a sequence control unit 22, a signal storage unit 123, a primary modulation unit 24, a selection unit 25, a mapping unit 26, an IFFT unit 27, and a D / A conversion unit 28.

[0124] In this embodiment, the selector 25 receives the output signal of the IFFT unit 27 and the signal corresponding to the wake-up signal from the signal storage unit 123 .

[0125] The signal storage unit 123 stores a signal corresponding to the wake-up signal. In this embodiment, when a wake-up signal similar to that in the first embodiment is input to the mapping unit 26, the signal storage unit 123 stores a signal equivalent to the signal output from the IFFT unit 27. That is, the signal storage unit 123 maps the wake-up signal to a plurality of subcarriers and stores a signal equivalent to the signal obtained by performing an inverse fast Fourier transform. Specifically, the signal storage unit 123 stores, for example, data obtained by discretizing the time waveform of the signal. As a result, the storage capacity required for the signal storage unit 123 is significantly larger than the storage capacity required for the signal storage unit 23 in the first embodiment. However, because the mapping unit 26 and the IFFT unit 27 do not need to process the wake-up signal, power consumption in the wake-up signal transmission mode can be reduced compared to the first embodiment.

[0126] (Modifications, etc.) While the receiving method and the like according to the present disclosure have been described above based on the embodiments, the present disclosure is not limited to these embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications that a person skilled in the art could conceive of to the embodiments and other forms constructed by combining some of the components of the embodiments are also included within the scope of the present disclosure.

[0127] For example, in each of the above embodiments, the code length of the received code is equal to the number of the plurality of first subcarriers, but the configuration of the received code is not limited to this. Hereinafter, other configuration examples of the received code will be described with reference to Fig. 16. Fig. 16 is a diagram illustrating an example of the configuration of the received code according to a modified example.

[0128] In step S46 (received code allocation step) shown in Fig. 14, the multiple subcarrier codes are allocated to multiple groups, and a group code is assigned to each of the multiple groups based on the subcarrier codes included in each of the multiple groups among the multiple subcarrier codes, and a received code may be assigned based on the group code assigned to each of the multiple groups. In the example shown in Fig. 16, nine subcarriers of frequencies f1 to f9 are defined. When the intensity of each subcarrier is greater than a threshold, a subcarrier code of 1 is assigned, and when the intensity of each subcarrier is equal to or less than the threshold, a subcarrier code of 0 is assigned. In the example shown in Fig. 16, the nine subcarrier codes are allocated to three groups of frequencies f1 to f3, f4 to f6, and f7 to f9 according to the frequency of the subcarrier (first subcarrier), and a group code is assigned based on three subcarrier codes included in each group among the nine subcarrier codes.

[0129] In the example shown in Figure 16, the group code is determined based on the most common code value among the multiple subcarrier codes in each of the multiple groups. That is, in the group corresponding to the subcarriers of frequencies f1 to f3, the most common code value of the subcarrier codes, 1, is assigned as the group code. Similarly, in the group corresponding to the subcarriers of frequencies f4 to f6, the most common code value, 1, is assigned as the group code. In the group corresponding to the subcarriers of frequencies f7 to f9, the most common code value, 0, is assigned as the group code. In this modification, the receiving code may be assigned based on the group code assigned to each of the multiple groups. For example, in the example shown in Figure 16, the receiving code may be assigned based on three group codes, 1, 1, and 0.

[0130] 16 , the multiple groups may be determined based on the range of frequencies of the subcarriers (first subcarriers). That is, the frequency of the first subcarriers included in each of the multiple groups may be adjacent to the frequency of other first subcarriers included in the same group. In other words, the frequency of one of the multiple first subcarriers corresponding to any one subcarrier code included in each of the multiple groups among the multiple subcarrier codes may be adjacent to the frequency of one of the multiple first subcarriers corresponding to another subcarrier code included in the group other than the one subcarrier code included in the group.

[0131] As described above, by using the group code, the receiver 40 can reliably detect the wake-up signal even when noise is superimposed on a specific subcarrier. In other words, the noise resistance of the wake-up signal can be further improved.

[0132] Furthermore, the frequencies of the subcarriers corresponding to the subcarrier codes included in each group do not have to be adjacent. For example, in the nine subcarriers shown in FIG. 16 , the frequencies of the subcarriers corresponding to the subcarrier codes included in the first group may be f1, f4, and f7, the frequencies of the subcarriers corresponding to the subcarrier codes included in the second group may be f2, f5, and f8, and the frequencies of the subcarriers corresponding to the subcarrier codes included in the third group may be f3, f6, and f9. By dispersing the frequencies of the subcarriers corresponding to the subcarrier codes included in each group in this way, the receiving device 40 can reliably detect the wake-up signal, for example, even if noise is superimposed on the frequency band from frequency f1 to frequency f3. In other words, the noise resistance of the wake-up signal can be further improved.

[0133] In addition, in each of the above embodiments, the wakeup signal detector 50 detects the wakeup signal from the modulated signal, which is analog data, but the configuration of the wakeup signal detector is not limited to this. For example, the wakeup signal detector may detect the wakeup signal from digital data obtained by A / D conversion of the modulated signal.

[0134] The following embodiments may also be included within the scope of one or more aspects of the present disclosure.

[0135] (1) Some of the components constituting each of the above-mentioned transmitting device 20 and receiving device 40 may be a computer system comprising a microprocessor, ROM, RAM, hard disk unit, display unit, keyboard, mouse, etc. A computer program is stored in the RAM or hard disk unit. The microprocessor achieves its function by operating in accordance with the computer program. Here, the computer program is composed of a combination of multiple instruction codes that indicate commands to a computer to achieve a predetermined function.

[0136] (2) Some of the components constituting each of the above-described transmitting device 20 and receiving device 40 may be configured as a single system LSI (Large Scale Integration). A system LSI is an ultra-multifunctional LSI manufactured by integrating multiple components on a single chip, and specifically, is a computer system configured including a microprocessor, ROM, RAM, etc. A computer program is stored in the RAM. The system LSI achieves its functions by the microprocessor operating in accordance with the computer program.

[0137] (3) Some of the components constituting each of the above-mentioned transmitting device 20 and receiving device 40 may be composed of an IC card or a standalone module that can be attached to or detached from each device. The IC card or the module is a computer system composed of a microprocessor, ROM, RAM, etc. The IC card or the module may include the above-mentioned ultra-multifunctional LSI. The IC card or the module achieves its functions when the microprocessor operates according to a computer program. The IC card or the module may be tamper-resistant.

[0138] (4) Furthermore, some of the components constituting each of the above-described transmitting device 20 and receiving device 40 may be the computer program or the digital signal recorded on a computer-readable recording medium, such as a flexible disk, hard disk, CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray (registered trademark) Disc), semiconductor memory, etc. Alternatively, they may be the digital signal recorded on such a recording medium.

[0139] In addition, some of the components constituting each of the above-mentioned transmitting device 20 and receiving device 40 may be configured to transmit the computer program or the digital signal via a telecommunications line, a wireless or wired communication line, a network such as the Internet, data broadcasting, etc.

[0140] (5) The present disclosure may be realized as the above-described methods. It may also be realized as a computer program for implementing these methods by a computer, or as a digital signal comprising the computer program. Furthermore, the present disclosure may be realized as a non-transitory computer-readable recording medium, such as a CD-ROM, on which the computer program is recorded.

[0141] (6) The present disclosure may also be a computer system having a microprocessor and a memory, the memory storing the computer program, and the microprocessor operating in accordance with the computer program.

[0142] (7) The program or the digital signal may also be implemented by another independent computer system by recording it on the recording medium and transferring it, or by transferring the program or the digital signal via the network, etc.

[0143] (8) The above-described embodiments and modifications may be combined with each other.

[0144] The present disclosure can be used as a communication system capable of realizing a wake-up signal with high noise resistance, for example, in a remote speed control system for an electric kick scooter.

[0145] 10 Communication system 20, 120 Transmitter 21 Input IF section 22 Sequence control section 23, 123 Signal storage section 24 Primary modulation section 25 Selection section 26 Mapping section 27 IFFT section 28 D / A conversion section 40 Receiving device 42 Signal processing section 44 Switch 50 Wake-up signal detection section 51 Reception code allocation section 52 Operation mode change section 60 Signal level acquisition section 61 Oscillator 62 Mixer 63 Low-pass filter 64 Measurement section 70 Subcarrier code allocation section 71 Comparator 72 Table creation section 80 Communication line 90 Power supply

Claims

1. A receiving method in a communication system that has a transmitting device and a receiving device and communicates using an OFDM (Orthogonal Frequency Division Multiplexing) system, wherein the receiving device has, as operation modes, a normal receiving mode and a power saving mode that consumes less power than the normal receiving mode, and among a plurality of subcarriers defined by the OFDM system, two or more subcarriers are defined as a plurality of first subcarriers, and the receiving method includes a receiving step of receiving a modulated signal modulated by the OFDM system, a signal level acquisition step of acquiring a signal level of each of the plurality of first subcarriers in the modulated signal, a subcarrier code allocation step of assigning a plurality of subcarrier codes corresponding to each of the plurality of first subcarriers based on the signal level of each of the plurality of first subcarriers, a receiving code allocation step of assigning a receiving code determined based on the plurality of subcarrier codes to the modulated signal, and an operation mode change step of changing the operation mode of the receiving device based on the receiving code, the operation mode changing step changes the operation mode of the receiving device from the power saving mode to the normal receiving mode when the received code matches a predetermined mode change code.

2. The receiving method according to claim 1, wherein in said subcarrier code allocation step, each of said plurality of subcarrier codes is allocated based on a result of comparison between a predetermined threshold value and said signal level.

3. The receiving method according to claim 2, wherein the predetermined threshold value with which the signal level of each of the plurality of first subcarriers is compared in the subcarrier code allocation step is the same.

4. The receiving method according to claim 1, wherein the receiving code includes information for identifying a source that transmitted the modulated signal.

5. The receiving method according to claim 1, wherein the code length of the received code is equal to the number of the first subcarriers.

6. The receiving method according to claim 1, wherein any code can be used as the mode change code.

7. The receiving method according to claim 1, wherein in said receiving code allocation step, said plurality of subcarrier codes are allocated to a plurality of groups, a group code is assigned to each of said plurality of groups based on a subcarrier code included in each of said plurality of groups among said plurality of subcarrier codes, and said receiving codes are assigned based on the group code assigned to each of said plurality of groups.

8. The receiving method according to claim 7, wherein the frequency of one of the plurality of first subcarriers corresponding to any one of the plurality of subcarrier codes included in each of the plurality of groups is adjacent to the frequency of one of the plurality of first subcarriers corresponding to another subcarrier code included in the group other than the one subcarrier code included in the group.

9. The receiving method according to claim 7 or 8, wherein the group code is determined based on the most common code value in each of the plurality of groups among the plurality of subcarrier codes.

10. A transmission method in a communication system which has a transmitting device and a receiving device and communicates using an OFDM system, wherein the receiving device has as its operating modes a normal reception mode and a power saving mode which consumes less power than the normal reception mode, and the transmitting device has as its operating modes a normal transmission mode and a wakeup signal transmission mode which transmits a wakeup signal for changing the operating mode of the receiving device from the power saving mode to the normal reception mode, the transmission method comprising: a mapping step which determines data to be transmitted on each of a plurality of subcarriers defined by the OFDM system; an IFFT step which performs an inverse fast Fourier transform on each of the plurality of subcarriers; and a D / A conversion step which converts digital data output in the IFFT step into analog data, the wakeup signal including a plurality of codes corresponding to the plurality of subcarriers, and in the wakeup signal transmission mode, the digital data input to the D / A conversion step is the digital data output in the IFFT step when the data determined in the mapping step corresponds to the wakeup signal.

11. A receiving device for communicating using an OFDM system, the receiving device having as its operating modes a normal receiving mode and a power saving mode consuming less power than the normal receiving mode, and of a plurality of subcarriers defined by the OFDM system, two or more subcarriers are defined as a plurality of first subcarriers, the receiving device comprising: a signal level acquisition unit that receives a modulated signal modulated using the OFDM system and acquires a signal level of each of the plurality of first subcarriers in the modulated signal; a subcarrier code allocation unit that assigns a plurality of subcarrier codes corresponding to each of the plurality of first subcarriers based on the signal level of each of the plurality of first subcarriers; a receiving code allocation unit that assigns a receiving code determined based on the plurality of subcarrier codes to the modulated signal; and an operating mode change unit that changes the operating mode of the receiving device based on the receiving code, and when the receiving code matches a predetermined mode change code, the operating mode change unit changes the operating mode of the receiving device from the power saving mode to the normal receiving mode.

12. A transmitting device that communicates with a receiving device using an OFDM system, wherein the receiving device has, as its operating modes, a normal receiving mode and a power saving mode that consumes less power than the normal receiving mode, and the transmitting device has, as its operating modes, a normal transmission mode and a wakeup signal transmission mode in which a wakeup signal is transmitted to change the operating mode of the receiving device from the power saving mode to the normal receiving mode, and the transmitting device comprises: a mapping unit that determines data to be transmitted on each of a plurality of subcarriers defined in the OFDM system; an IFFT unit that performs an inverse fast Fourier transform on each of the plurality of subcarriers; and a D / A conversion unit that converts digital data output by the IFFT unit into analog data, wherein the wakeup signal includes a plurality of codes corresponding to the plurality of subcarriers, and in the wakeup signal transmission mode, the digital data input to the D / A conversion unit is the digital data output by the IFFT unit when the data determined by the mapping unit corresponds to the wakeup signal.

13. A communications system comprising a transmitting device and a receiving device, and communicating using an OFDM method, wherein the receiving device has as its operating modes a normal reception mode and a power saving mode consuming less power than the normal reception mode, and among a plurality of subcarriers defined by the OFDM method, two or more subcarriers are defined as a plurality of first subcarriers, and the receiving device comprises: a signal level acquisition unit that receives a modulated signal modulated using the OFDM method and determines a signal level of each of the plurality of first subcarriers in the modulated signal; a subcarrier code allocation unit that allocates a plurality of subcarrier codes corresponding to each of the plurality of first subcarriers based on the signal level of each of the plurality of first subcarriers; a receiving code allocation unit that allocates a receiving code determined based on the plurality of subcarrier codes to the modulated signal; and an operating mode change unit that changes the operating mode of the receiving device based on the receiving code, and when the receiving code matches a predetermined mode change code, changes the operating mode of the receiving device from the power saving mode to the normal reception mode.

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