TRANSMISSION DEVICE, RECEIVING DEVICE, COMMUNICATION SYSTEM, CONTROL CIRCUIT, STORAGE MEDIUM, TRANSMISSION PROCEDURES AND RECEIVING PROCEDURES

Abstract

A transmission device (10) for wirelessly communicating with a receiving device (20), the transmission device comprising: a modulation unit (12) for performing frequency-shift keying modulation on an input information bit sequence to generate a frequency-shift keying symbol; a direct-sequence spreading unit (13) for spreading the frequency-shift keying symbol by direct-sequence spreading using a chirp sequence; and a control unit (11) for controlling a signal to be transmitted to the receiving device in such a way as to prevent a delay wave component in multipath propagation in a frequency-shift keying candidate carrier from occurring in a symbol of two consecutive symbols in a frequency spectrum of a signal obtained by unspreading in the receiving device.

Description

Field of InterestThe present disclosure relates to a transmission device, a reception device, a communication system, a control circuit, a storage medium, a transmission method, and a reception method each for performing wireless communication.BackgroundFrequency shift keying (FSK) is a modulation method in which the frequency of a carrier wave is changed according to information to be transmitted. FSK technology is known to provide much higher power efficiency than phase shift keying (hereinafter referred to as PSK), quadrature amplitude modulation (hereinafter referred to as QAM), etc., because FSK uses a modulation signal with constant envelope amplitude and sets a low input backoff value in a power amplifier. On the other hand, the FSK technology offers lower frequency use efficiency than PSK, QAM, etc.A receiver of a wireless communication system generally employs either coherent detection or non-coherent detection. A coherent detection method in which the phase of a reception signal before demodulation is synchronized with the phase of a transmission signal enables high-accuracy demodulation. In the coherent detection technique, a pilot signal must be transmitted simultaneously to estimate the phase shift generated in the propagation channel. This pilot signal is associated with an overhead that reduces the transmission efficiency. In contrast, a non-coherent detection method that demodulates signals without synchronization between the phases of transmission and reception signals has lower demodulation performance than the coherent detection method, but offers higher transmission efficiency because the overhead of the pilot signal is reduced. With such a non-coherent detection method, the receiving circuit is simplified. In FSK technology, signal power concentrates on different frequencies corresponding to the different transmitted information contents, thereby achieving non-coherent detection very easily through filtering and power detection. For example, in Non-Patent Literature 1, a non-coherent detection technology is described in which the power of each candidate FSK channel is calculated and the channel having the highest power is demodulated as an estimated transmission signal.DE ALMEIDA, I.B.F. [et al.]: IN-phase and quadrature chirp spread spectrum for loT communications, In: IEEE Global Communications Conference, 07-11 December 2020, DOI: 10.1109 / GLOBECOM42002.2020.9348094 describes a method for coherently receiving chirp sequence spread FSK symbols.Reference listNon-patent documentsNon Patent Literature 1: G. M. Vietta, U. Mengali, and D. P. Taylor, "Optimal Non-coherent Detection of FSK Signals Transmitted over Linear Time-Selective Rayleigh Fading Channels", IEEE Transactions on Communications, Vol. 45, No. 11, pp. 1417-1425; Nov. 1997Summary of the InventionTechnical TaskRecently, attention has been directed to a wireless communication system called a low-power wide area (LPWA) that aims at highly reliable information transmission over long distances. Many of the standards for LPWA technology provide that a narrowband primary modulated signal is spread into a broadband secondary modulated signal by spectrum spreading and the secondary modulated signal is transmitted. This enables highly reliable information transmission even in long-distance communication with high transmission losses. For example, in a long range wide area network (LoRaWA), an FSK signal is spread by spectrum spreading based on a direct sequence technique with a propagation sequence that is a chirp signal whose frequency changes linearly with time, and the resultant signal is then transmitted.When an FSK signal is transmitted as a narrow band primary modulated signal as in conventional methods, the FSK signal is hardly affected by frequency selectivity due to multipath propagation in the communication channel. However, when an FSK signal is spread by spectrum spreading and the resulting wide band signal is then transmitted, the frequency selectivity of the communication channel has a great influence on the demodulation performance. In coherent detection, the receiver compensates for the effects of multipath propagation by estimating the transmission channel using a pilot signal, and thus can achieve diversity gain. In contrast, in non-coherent detection as described in Non-Patent Literature 1, the receiver cannot estimate the transmission channel, so that diversity gain is not obtained. In addition, when despreading is performed on a wide band signal having non-removed frequency selectivity distortion due to multipath, the autocorrelation characteristic of the chirp sequence may result in the delayed wave power of multipath propagating entering a candidate FSK carrier during FSK demodulation. As a result, a demodulation error occurs. If the number of delayed wave delay samples corresponding to the previous wave in multipath propagation is an integer multiple of the FSK carrier spacing, the power of the delayed wave will appear in a candidate FSK carrier.The present disclosure has been made in view of the above, and it is an object of the present disclosure to provide a transmission device that transmits a signal to a reception device of a wireless communication system that uses non-coherent detection for chirp spread spectrum frequency shift keying modulation, wherein the signal allows the reception device to avoid a demodulation error due to multipath propagation and benefit from a diversity effect of multipath propagation without using a pilot signal.Solution of the ProblemThis object is achieved by means of articles having the features according to the independent claims. Advantageous embodiments of the invention are the subject matter of the figures, the description and the dependent claims.In order to achieve the above object and achieve the object, the present disclosure provides a transmission device for wirelessly communicating with a reception device. The transmission device includes: a modulation unit to perform frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol; a direct sequence spreading unit to spread the frequency shift keying symbol by direct sequence spreading using a chirp sequence; and a control unit to control a signal to be transmitted to the reception device so as to prevent a delay wave component in multipath propagation from appearing in a frequency shift keying candidate carrier in a symbol of two consecutive symbols in a frequency spectrum of a signal obtained by despreading in the reception device.Advantageous Effects of the InventionA transmission device according to the present disclosure is advantageous in transmitting the signal to the reception device of the wireless communication system using non-coherent detection for chirp spread spectrum frequency shift keying modulation, the signal enabling the reception device to avoid causing the demodulation error due to multipath propagation and benefit from the diversity effect of multipath propagation without using a pilot signal.Brief Description of the DrawingsFIG. 1 is a diagram showing an example configuration of a communication system according to a first embodiment. FIG. 2 is a block diagram showing an example configuration of a transmission device according to the first embodiment. FIG. 3 is a flowchart showing the operation of the transmission device according to the first embodiment. FIG. 4 is a block diagram showing an example configuration of a receiving device according to the first embodiment. FIG. 5 is a flowchart illustrating the operation of the receiving device according to the first embodiment. FIG. 6 is a diagram showing an example configuration of a processing circuit in the transmission device according to the first embodiment when the processing circuit is implemented by a processor and a memory. FIG. 7 is a diagram showing an example of a processing circuit in the transmission device according to the first embodiment when the processing circuit is implemented by a dedicated hardware element. FIG. 8 is a block diagram showing an example configuration of a transmission device according to a second embodiment. FIG. 9 is a flowchart showing the operation of the transmission device according to the second embodiment.DESCRIPTION OF EMBODIMENTSA transmission device, a reception device, a communication system, a control circuit, a storage medium, a transmission method, and a reception method according to the embodiments of the present disclosure will be described in detail below with reference to the drawings.First Embodiment.FIG. 1 is a diagram showing an example configuration of a communication system 1 according to a first embodiment. The communication system 1 has a transmission device 10 and a receiving device 20. The communication system 1 is a wireless communication system that performs wireless communication such that the transmission device 10 transmits a wireless signal and the reception device 20 receives the wireless signal.First, the structure and operation of the transmission device 10 will be described. FIG. 2 is a block diagram showing an example configuration of the transmission device 10 according to the first embodiment. The transmission device 10 includes an FSK carrier distance control unit 11, an FSK modulation unit 12, a direct sequence spreading unit 13, and a transmission antenna 14. FIG. 3 is a flowchart illustrating the operation of the transmission device 10 according to the first embodiment.In the transmission device 10, the FSK carrier distance control unit 11 determines the carrier distance of an FSK symbol generated by the FSK modulation unit 12 (step S 11). The FSK carrier distance control unit 11 outputs the value of the detected carrier distance of the FSK symbol to the FSK modulation unit 12.Based on the carrier distance of the FSK symbol determined by the FSK carrier distance control unit 11, the FSK modulation unit 12 performs FSK modulation on an input information bit sequence (step S 12). Specifically, the FSK modulation unit 12 performs FSK modulation based on a carrier distance K i of an i-th FSK symbol determined by the FSK carrier distance control unit 11, and generates an M-ary FSK signal, i.e., an FSK symbol, as expressed by Equation (1). Formula 1:In Equation (1), m i is a symbol number generated from an i-th information bit sequence input to the FSK modulation unit 12 and is in a range of 0≤m i≤M-1; and N is a direct sequence spread length based on a chirp sequence. That is, M FSK symbols are allocated along the frequency axis to all K i subcarriers starting with the zeroth subcarrier of N subcarriers in total. In the present embodiment, the FSK carrier distance control unit 11 enables control that allows the carrier distance K i to be varied from symbol to symbol so that, in particular, the carrier distance K i and the carrier distance K selected for two consecutive symbols are prime i+1 to each other.In the case of communication channels coherent for two consecutive symbols, delayed wave power in a frequency spectrum obtained by despreading in the receiver 20 can be prevented from appearing in a candidate FSK carrier in the (i-1)th symbol even if delayed wave power appears in a candidate FSK carrier in the i-th symbol. Note that, as described later, the receiver 20 uses this characteristic to detect the position of the delayed wave in the i-th symbol and perform demodulation in consideration of the position of this delayed wave in the demodulation of the (i+1)-th symbol, so that the receiver 20 can achieve diversity gain and it is avoided to cause a demodulation error. The FSK modulation unit 12 can also be referred to simply as a modulation unit below.The direct sequence spreading unit 13 spreads the FSK symbol generated by the FSK modulation unit 12 by direct sequence spreading using a chirp sequence (step S 13). The chirp sequence used in the direct sequence spreading unit 13 is expressed by equation (2). Formula 2:In equation (2), q represents a chirp sequence number. In the present embodiment, chirp sequences whose q values are equal are used for all FSK symbols. The signal generated by the direct sequence spreading unit 13 by direct sequence spreading is expressed by equation (3). Formula 3: Formula 3:The transmitting antenna 14 transmits the signal x n generated by the direct sequence spreading unit 13 to the receiving device 20 by direct sequence spreading (step S 14).In the first embodiment, the FSK carrier distance control unit 11 is a control unit that controls the signal to be transmitted to the receiver 20 so as to prevent the delay wave component in multipath propagation in a candidate FSK carrier from appearing in a symbol of two consecutive symbols in a frequency spectrum of a signal obtained by despreading in the receiver 20. Specifically, the FSK carrier distance control unit 11 changes the carrier distance K i of an FSK symbol per symbol so that the carrier distances K i of FSK symbols selected for two consecutive symbols are prime to each other.The configuration and operation of the receiving device 20 will be described below. FIG. 4 is a block diagram showing an example configuration of the receiving device 20 according to the first embodiment. The receiving device 20 includes a receiving antenna 21, a despreading unit 22, a Fourier transform unit 23, a power calculation unit 24, a metric combining unit 25, an FSK demodulation unit 26, and a delayed wave detection unit 27. FIG. 5 is a flowchart showing the operation of the receiving device 20 according to the first embodiment. Note that the receiving device 20 performs the processing described below for each reception symbol.In the receiving device 20, the receiving antenna 21 receives a signal r transmitted from the transmitting device 10 n( step S 21). The despreading unit 22 despreads the signal r n received by the receiving antenna 21 according to Equation (4) (step S 22). Formula 4: Formula 4: Formula 4:Since the description cannot identify a character with a circumflex or hat character (^) over s n a character with ^ over s n will be referred to as "s n( has)" hereinafter. The Fourier transform unit 23 performs Fourier transform of the length N on the signal s n( obtained by despreading in the despreading unit 22 (step S23). That is, the Fourier transform unit 23 converts the post-despreading signal s having n( ) into a signal along the frequency axis, thereby generating a frequency signal.The power calculation unit 24 calculates the power of each subcarrier of the frequency signal obtained by the conversion performed by the Fourier transform unit 23 (step S 24). From the calculated power values of the individual subcarriers, the power of the subcarrier, which is a candidate point for a candidate FSK carrier, is determined by the power calculation unit 24 as the metric of the corresponding candidate FSK symbol. It is assumed that the carrier distance K i of each transmission symbol determined by the FSK carrier distance control unit 11 of the transmission device 10 is known to the reception device 20.The metric combining unit 25 adds the power of the subcarrier at a position cyclically shifted in the forward direction by the delay sample amount from the candidate point of each candidate FSK carrier to the metric of the corresponding candidate FSK symbol based on the delay sample amount of the delayed wave estimated for symbols up to the symbol immediately before this reception symbol. That is, the metric combining unit 25 calculates a combined metric (step S 25). The metric of the FSK symbol corresponding to the m i- th subcarrier is expressed by equation (5). Formula 5: Formula 5:In Equation (5), L is the total number of the estimated delayed waves; τ l is the delay sampling amount of an Ithdelayed wave; k(P) is the power of a kthsub-carrier calculated by the power calculation unit 24. Note that I=0represents the previous wave and thus τ 0=0. Although Equation (5) expresses combining metrics based on a maximum ratio combining rule, the method of combining metrics used in the metric combining unit 25 is not limited thereto. The metric combining unit 25 may perform the metric combining on the basis of a selection combination rule as expressed in Equation (6). Formula 6:The FSK demodulation unit 26 makes a hard decision on the combined metric of each candidate FSK symbol calculated as described above, and estimates an FSK signal transmitted from the transmitter 10. That is, the FSK demodulation unit 26 performs the FSK demodulation based on a hard decision (step S 26). Note that the hard decision result of the FSK demodulation unit 26 is determined for use in the delayed wave detection unit 27 subsequent to the FSK demodulation unit 26, and does not necessarily need to be used as the final demodulation result. For example, when channel coding is to be performed, the receiver 20 outputs the metric output of the metric combining unit 25 to a channel decoder (not shown) following the receiver 20, and the output to the channel decoder is used as a demodulation result. The FSK demodulation unit 26 may be referred to simply as a demodulation unit hereinafter.The delayed wave detection unit 27 acquires, from the frequency signal, the subcarrier in which the delayed wave power is located, and estimates the delayed wave delay sampling amount τ l from a difference between the position of the estimated subcarrier that carries the delayed wave power and the subcarrier position corresponding to the estimated FSK signal that the delayed wave detection unit 27 has obtained from the FSK demodulation unit 26 preceding the delayed wave detection unit 27 (step S 27). The delayed wave detection unit 27 waves outputs the estimated delay sample amount τ l to the metric combining unit 25. The metric combining unit 25 receives the delay sample amount τ l from the delayed wave detecting unit 27, and uses this delay sample amount τ l to calculate the metric of the next symbol. Note that the delayed wave detection unit 27 can detect the subcarrier having the delayed wave therein by various methods. One of these methods is, for example, estimation based on threshold-based determination using statistical characteristics of noise: a technique for detecting the delayed wave by distinguishing a delay wave component from noise based on the average power, etc. However, the technique for detecting the delayed wave in the present embodiment is not limited thereto. Moreover, the value of the delayed wave delay sample amount τ l output from the delay wave detection unit 27 to the metric combining unit 25 may be based only on a value estimated from the current symbol or may be a higher-accuracy value obtained by averaging the estimated values for the last multiple consecutive symbols, for example. That is, the delay wave detection unit 27 may output, to the metric combining unit 25, the delay sampling amount τ l of the delayed wave estimated based on the last symbol or an average value of the delay sampling amounts τ l of a plurality of delayed waves estimated based on a plurality of last symbols.Next, the hardware configuration of the transmission device 10 will be described. In the transmission device 10, the transmission antenna 14 is an antenna element. The FSK carrier distance control unit 11, the FSK modulation unit 12 and the direct sequence spreading unit 13 are realized in a processing circuit. The processing circuit may be a combination of a processor executing a program stored in a memory and the memory, or a dedicated hardware element. The processing circuit is also referred to as a control circuit.FIG. 6 is a diagram showing an example configuration of a processing circuit 90 in the transmission device 10 according to the first embodiment when the processing circuit is implemented by a processor 91 and a memory 92. The processing circuit 90 illustrated in FIG. 6 is a control circuit and includes the processor 91 and the memory 92. when the processing circuit 90 includes the processor 91 and the memory 92, each function of the processing circuit 90 is implemented in software, firmware, or a combination of software and firmware. The software or firmware is referred to as a program and is stored in the memory 92. In the processing circuit 90, each function is realized by the processor 91 by reading and executing a program stored in the memory 92. That is, the processing circuit 90 includes the memory 92 for storing a program that causes the processing of the transmission device 10. It can also be said that this program is a program that causes the transmission device 10 to execute each functionality implemented in the processing circuit 90. This program may be provided via a storage medium storing the program or via another means such as a communication medium.It can also be said that the above program is a program that causes the transmission device 10 to perform a first step in which the FSK modulation unit 12 performs frequency shift keying modulation on an information bit sequence input to generate a frequency shift keying symbol, a second step in which the direct sequence spreading unit 13 spreads the frequency shift keying symbol by direct sequence spreading using a chirp sequence, and a third step in which the FSK carrier distance control unit 11 controls a signal to be transmitted to the reception device 20 to prevent, the delay wave component upon multipath propagation in a frequency shift keying candidate carrier appears in a symbol of two successive symbols in a frequency spectrum of a signal obtained by despreading in the receiver 20.Here, the processor 91 is, for example, a central processing unit (CPU), a processing unit, a computing unit, a microprocessor, a microcomputer, a digital signal processor (DSP), or the like. Moreover, the memory 92 is, for example, a nonvolatile or volatile semiconductor memory such as a random access memory (RAM), a read only memory (ROM), a flash memory, an erasable programmable ROM (EPROM), or an electrically EPROM (EEPROM) (registered trademark), a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a digital versatile disk (DVD), or the like.FIG. 7 is a diagram showing an example of a processing circuit 93 in the transmission device 10 according to the first embodiment when the processing circuit is implemented by a dedicated hardware element. The processing circuit 93 shown in FIG. 7 is, for example, a single circuit, a group of multiple circuits, a programmed processor, a parallel programmed processor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or a combination thereof. The processing circuitry may be partially implemented by a dedicated hardware element and partially implemented by software or firmware. Thus, the processing circuitry may provide each of the functions described above in a particular hardware element, software, firmware, or a combination thereof.A hardware configuration of the transmission device 10 has been described. The receiving device 20 also has a similar hardware configuration. In the receiving device 20, the receiving antenna 21 is an antenna element. The despreading unit 22, the Fourier transform unit 23, the power calculation unit 24, the metric combining unit 25, the FSK demodulation unit 26, and the delayed wave detection unit 27 are implemented in processing circuits. Similarly to the transmission device 10, the processing circuit may be a combination of a processor executing a program stored in a memory and the memory, or may be a dedicated hardware element.As described above, in spreading an FSK modulated narrow band signal into a wide band signal by spectrum spreading based on a direct sequence technique, the transmission apparatus 10 according to the present embodiment changes the distance of the carrier corresponding to an FSK symbol in FSK modulation based on each transmission symbol. In this way, the transmitting means 10 can prevent a delay wave component from occurring in a candidate FSK carrier in successive symbols, while the conventional non-coherent detection method causes the receiving means 20 to fail in demodulation on this delay wave component. That is, as long as the communication channel is coherent, the transmission device 10 can always avoid the occurrence of a delay wave component in a candidate FSK carrier in one symbol of two consecutive symbols.Moreover, the receiver 20 estimates the delayed wave delay sample amount τ l based on an FSK symbol once demodulated by hard decision, and generates a metric calculated by combining an precursor wave component and a delay wave component using an estimation value obtained for the last or last symbols. This allows the receiver 20 to obtain path diversity gain from the previous and delayed waves. Moreover, the transmitter 10 changes the FSK carrier distance to ensure that the receiver 20 avoids the situation that a delay wave component appears in a candidate FSK carrier in one symbol of two consecutive symbols. Thus, the receiver 20 can accurately estimate the delayed-wave delay sample amount τ l for the symbol in which such a situation does not occur. For the symbol at which this situation occurs, the receiver 20 may separate the delayed wave, resulting in correct demodulation.As described above, the transmitting device 10 is capable of transmitting a signal using non-coherent detection for chirp spread spectrum frequency shift keying to the receiving device 20, the signal enabling the receiving device 20 of the communication system 1 to avoid demodulation error due to multipath propagation and benefit from diversity effect of multipath propagation without using a pilot signal.Second Embodiment.As described in the first embodiment, the transmission means 10 transmits a signal such that the delay wave component does not appear in a candidate FSK carrier in a symbol of two consecutive symbols in the frequency spectrum of a signal obtained by despreading in the reception means 20. In a second embodiment, another method for achieving the same result as that of the first embodiment will be described.FIG. 8 is a block diagram showing an example configuration of a transmission device 10 aaccording to a second embodiment. The transmission device 10 aincludes an FSK modulation unit 12 a, a direct sequence spreading unit 13 a, the transmission antenna 14, and a chirp sequence number control unit 15. FIG. 9 is a flowchart showing the operation of the transmission device 10 aaccording to the second embodiment. Note that the communication system in the second embodiment includes the transmission device 10 ain place of the transmission device 10 of the communication system 1 illustrated in FIG. 1.The FSK modulation unit 12 aperforms FSK modulation (step S 31). The second embodiment is based on the assumption that all symbols in the FSK modulation of the FSK modulation unit 12 ahave the same FSK carrier distance.The chirp sequence number control unit 15 controls the sequence number of the chirp sequence to be used per symbol (step S 32). Specifically, the chirp sequence number control unit 15 changes the value of q in Equation (2) above on a symbolic basis. In particular, the control unit 15 ensures that the chirp sequence numbers selected for two consecutive symbols are prime to each other. As a result, the transmitter 10a changes the subcarrier position at which the delay wave component appears, with the position of the candidate FSK carrier unchanged on a per symbol basis.Based on the sequence number of the chirp sequence determined by the chirp sequence number control unit 15, the direct sequence spreading unit 13 aexpands the FSK symbol generated by the FSK modulation unit 12 aby direct sequence spreading using a chirp sequence (step S 33).The transmitting antenna 14 transmits the signal x n generated by direct sequence spreading by the direct sequence spreading unit 13 ato the receiving device 20 (step S 34).In the second embodiment, the chirp sequence number control unit 15 is a control unit that controls the signal to be transmitted to the receiver 20 so as to prevent the delay wave component in multipath propagation in a candidate FSK carrier from occurring in a symbol of two consecutive symbols in a frequency spectrum of a signal obtained by despreading in the receiver 20. Specifically, the control unit 15 changes the chirp sequence number per symbol such that the chirp sequence numbers for two consecutive symbols are prime to each other.Note that the configuration and operation of the receiving device 20 in the second embodiment are similar to those of the first embodiment, and the description of the configuration and operation of the receiving device 20 in the second embodiment will therefore be omitted.Next, a hardware configuration of the transmission device 10 awill be described. In the transmission device 10 a, the transmission antenna 14 is an antenna element. The FSK modulation unit 12 a, the direct sequence spreading unit 13 a, and the chirp sequence number control unit 15 are implemented in a processing circuit. The processing circuit may be a combination of a processor executing a program stored in a memory and the memory, or a dedicated hardware element.As described above, according to the present embodiment, the transmitter 10 achanges the chirp sequence number from symbol to symbol. Also in this case, the transmission device 10a and the reception device 20 can provide a similar advantage to the first embodiment.The configurations described in the aforementioned embodiments are only examples. These configurations may be combined with another known technology, and configurations of various embodiments may be combined with each other. In addition, a part of these configurations may be omitted and / or changed without departing from the spirit of the present invention.List of reference characters1 Communication system; 10, 10a Transmitter; 11 FSK carrier distance control unit; 12, 12a FSK modulation unit; 13, 13a Direct sequence spreading unit; 14 Transmit antenna; 15 Chirp sequence number control unit; 20 Receiver; 21 Receive antenna; 22 Despreader; 23 Fourier transform unit; 24 Power calculation unit; 25 Metric combining unit; 26 FSK demodulation unit; 27 Delayed wave detection unit.

Claims

A transmission device (10) for wirelessly communicating with a reception device (20), the transmission device comprising: a modulation unit (12) for performing frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol; a direct sequence spreading unit (13) for spreading the frequency shift keying symbol by direct sequence spreading using a chirp sequence; and a control unit (11) for controlling a signal to be transmitted to the reception device so as to prevent a delay wave component in multipath propagation in a frequency shift keying candidate carrier from occurring in a symbol of two consecutive symbols in a frequency spectrum of a signal obtained by despreading in the reception device.The transmission device according to claim 1, wherein the control unit (11) changes the carrier pitch of the frequency shift keying symbol per symbol such that the carrier pitches of the frequency shift keying symbols selected for the two respective consecutive symbols are prime to each other, and the modulation unit (12) performs the frequency shift keying modulation based on the carrier pitch of the frequency shift keying symbol determined by the control unit.The transmission device (10a) according to claim 1, wherein the control unit (15) changes the chirp sequence number per symbol such that the chirp sequence numbers selected for the two successive symbols are prime with each other, and the direct sequence spreading unit (13a) spreads the frequency shift keying symbol by direct sequence spreading based on the chirp sequence number determined by the control unit.A receiving device (20) for wirelessly communicating with a transmitting device, the receiving device comprising: a despreading unit (22) for despreading a signal transmitted from the transmitting device and received by the receiving device; a Fourier transform unit (23) for performing Fourier transform on a signal obtained by despreading to generate a frequency signal; a power calculation unit (24) for calculating a power of each subcarrier in the frequency signal; a metric combining unit (25) for, based on a number of delay samples of a delayed wave, adding the power of a subcarrier at a position cyclically shifted in a forward direction by the number of delay samples from a candidate point of each frequency shift keying candidate carrier to a metric of a corresponding frequency shift keying candidate symbol to calculate a combined metric; a demodulating unit (26) for making a hard decision on the combined metric of each frequency shift keying candidate symbol and estimating a transmitted frequency shift keying signal from the transmitting means; and a delayed wave detection unit (27) for detecting from the frequency signal a subcarrier containing delayed wave power and estimating the number of delayed samples of the delayed wave from a difference between a position of the subcarrier carrying the delayed wave power and a subcarrier position corresponding to the estimated transmitted frequency shift keying signal.The receiving apparatus according to claim 4, wherein the delayed wave detection unit (27) estimates the number of delayed samples of the delayed wave by threshold-based determination using a statistical property of the noise.The receiving device according to claim 4 or 5, wherein the metric combining unit (25) calculates the combined metric by a maximum ratio combining rule or a selection combining rule.The receiving apparatus according to any one of claims 4 to 6, wherein the delayed wave detection unit (27) outputs the number of delayed samples of the delayed wave estimated from a last symbol or an average value of the number of delayed samples of a plurality of delayed waves estimated from a plurality of last symbols.A communication system (1) comprising: the transmitting device according to any one of claims 1 to 3; and the receiving device according to any one of claims 4 to 7.A control circuit for controlling a transmission device (10) to wirelessly communicate with the reception device (20), the control circuit causing the transmission device to: perform frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol; spread the frequency shift keying symbol by direct sequence spreading using a chirp sequence; and control a signal to be transmitted to the reception device such that a delay wave component in multipath propagation in a frequency shift keying candidate carrier is prevented from occurring in a symbol of two consecutive symbols in a frequency spectrum of a signal obtained by despreading in the reception device.A control circuit for controlling a receiving device (20) to wirelessly communicate with a transmitting device (10), the control circuit causing the receiving device to: despread a signal transmitted from the transmitting device and received by the receiving device; perform a Fourier transform on a signal obtained by despreading to generate a frequency signal; calculate the power of each subcarrier in the frequency signal; add, based on a number of delay samples of a delayed wave, the power of a subcarrier at a position cyclically shifted in the forward direction by the number of delay samples from a candidate point of each frequency shift keying candidate carrier to a metric of a corresponding frequency shift keying candidate symbol to calculate a combined metric; performing a hard decision on the combined metric of each frequency shift keying candidate symbol and estimating a transmitted frequency shift keying signal from the transmitting means; and detecting a subcarrier having delayed wave power therein from the frequency signal, and estimating the number of delay samples of the delayed wave from a difference between a position of the subcarrier carrying the delayed wave power and a subcarrier position corresponding to the estimated transmitted frequency shift keying signal.A storage medium storing a program for controlling a transmission device (10) for wireless communication with a receiving device (20), the program causing the transmission device to: perform frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol, spread the frequency shift keying symbol by direct sequence spreading using a chirp sequence, and control a signal to be transmitted to the receiving device such that a delay wave component upon multipath propagation in a frequency shift keying candidate carrier is prevented from occurring in a symbol of two consecutive symbols in a frequency spectrum of a signal obtained by despreading in the receiving device.A storage medium storing a program for controlling a receiving device (20) for wireless communication with a transmitting device (10), the program causing the receiving device to: despread a signal transmitted from the transmitting device and received by the receiving device, perform a Fourier transform on a signal obtained by despreading to generate a frequency signal, calculate the power of each subcarrier in the frequency signal, add, based on a number of delay samples of a delayed wave, the power of a subcarrier at a position cyclically shifted in the forward direction by the number of delay samples from a candidate point of each frequency shift keying candidate carrier to a metric of a corresponding frequency shift keying candidate symbol to calculate a combined metric, performing a hard decision on the combined metric of each frequency shift keying candidate symbol and estimating a transmitted frequency shift keying signal from the transmitting means, and detecting a subcarrier having delayed wave power therein from the frequency signal, and estimating the number of delay samples of the delayed wave from a difference between a position of the subcarrier carrying the delayed wave power and a subcarrier position corresponding to the estimated transmitted frequency shift keying signal.A transmission method for use in a transmission apparatus (10) for wireless communication with a receiving apparatus (20), the transmission method comprising: a first step in which a modulation unit (12) performs frequency shift keying modulation on an input information bit sequence to generate a frequency shift keying symbol; a second step in which a direct sequence spreading unit (13) spreads the frequency shift keying symbol by direct sequence spreading using a chirp sequence; and a third step in which a control unit (11) controls a signal to be transmitted to the receiving apparatus so as to prevent a delay wave component in multipath propagation in a frequency shift keying candidate carrier from occurring in a symbol of two consecutive symbols in a frequency spectrum of a signal obtained by despreading in the receiving apparatus.A receiving method for use in a receiving apparatus (20) for wireless communication with a transmitting apparatus (10), the receiving method comprising: a first step in which a despreading unit (22) despreads a signal transmitted from the transmitting apparatus and received by the receiving apparatus; a second step in which a Fourier transform unit (23) performs Fourier transform on a signal obtained by despreading to generate a frequency signal; a third step in which a power calculation unit (24) calculates the power of each subcarrier in the frequency signal; a fourth step in which a metric combining unit (25), based on a number of delayed wave delay samples, adds the power of a subcarrier at a position cyclically shifted in the forward direction by the number of delay samples from a candidate point of each frequency shift keying candidate carrier to a metric of a corresponding frequency shift keying candidate symbol to calculate a combined metric; a fifth step in which a demodulating unit (26) makes a hard decision on the combined metric of each frequency shift keying candidate symbol and estimates a transmitted frequency shift keying signal from the transmitting means; and a sixth step in which a delayed wave detection unit (27) detects a delayed wave power subcarrier therein from the frequency signal and estimates the number of delayed wave delay samples from a difference between a subcarrier position carrying the delayed wave power and a subcarrier position corresponding to the estimated transmitted frequency shift keying signal.

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