Communication system, communication method, and communication program

Abstract

To prevent a self-interference signal from being generated while using a fractional spreading factor for an LoRa modulation scheme.SOLUTION: A communication system (1) includes a transmission terminal (2) that performs FSF-LoRa modulation using a spreading factor (s) and a fractional coefficient (ρ) on transmission data to generate a transmission signal, and a gateway (3) that demodulates a reception signal obtained by receiving the transmission signal using the spreading factor and the fractional coefficient and outputs an estimated demodulation signal obtained by estimating the transmission data. The transmission terminal converts transmission data into a combination of symbols, and spreads each of the symbols included in the combination with a first reference chirp signal generated based on a spreading factor and the fractional coefficient. The gateway performs a sampling process on the received signal at a sampling frequency that satisfies a Nyquist criterion to generate an equivalent low-pass signal, and despreads the equivalent low-pass signal with a second reference chirp signal generated based on a spreading factor and the fractional coefficient.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a communication system, a communication method, and a communication program, and can be suitably used for a communication system, a communication method, and a communication program that use, for example, the LoRa modulation method. [Background technology]

[0002] With the development of IoT (Internet of Things), LPWAN (Low Power Wide Area Network), typified by LoRaWAN (Long Range Wide Area Network), is attracting attention. As a communication method for such networks, a modulation and demodulation method using chirp spread spectrum in the physical layer is known.

[0003] In a modulation scheme using chirp spread spectrum, arbitrary data can be expressed by combining multiple types of chirp symbols. Each chirp symbol changes frequency over time. The timing at which the frequency instantaneously switches from maximum to minimum (or from minimum to maximum) varies depending on the type of chirp symbol. Chirp spread spectrum enables communication over relatively long distances with relatively low power consumption. Note that chirp spread spectrum has a trade-off: the higher the spreading factor, the better the noise resistance, but the lower the transmission rate.

[0004] In standardized LoRaWAN, only integer values ​​within a specified range (for example, from 7 to 12) can be selected as the spreading factor. Under these conditions, when two transmission signals sent by two transmitters are simultaneously received by one receiver as a single received signal, it is known that the receiver can receive only one transmission signal if the spreading factors of each transmission signal are the same and the SIR (Signal-to-Interference Ratio) is a specified value (for example, 6 dB) or higher. In this case, if interference cancellation technology is used in the receiver, it will be possible to detect multiple transmission signals, but this will result in the receiver becoming significantly more complex.

[0005] Furthermore, under the above conditions, when two transmission signals transmitted by two transmitters are simultaneously received by one receiver as a single received signal, if the spreading factors of the transmission signals are different and the SIR exceeds a predetermined threshold, the receiver can receive both transmission signals. In this case, the transmission rate will be lower than when the minimum spreading factor is selected for both transmission signals.

[0006] In relation to the above, Non-Patent Document 1 (LoRa Alliance, Inc., "LoRaWAN™ 1.0.3 Specification", 2018, Internet<URL:https: / / lora-alliance.org / sites / default / files / 2018-07 / lorawan1.0.3.pdf> ) discloses the LoRaWAN specification version 1.0.3.

[0007] Furthermore, Non-Patent Document 2 (Saito Ryoya, Adachi Koichi, Fujii Takeo, Kumada Ryota, "Study on Fractional Spreading Factors in LoRa Signals and Proposal of a Demodulation Method," IEICE Technical Report, Kagawa, October 2023) discloses a demodulation method using chirp spread spectrum, which achieves an equivalent non-integer spreading factor. This demodulation method can improve the transmission rate by correcting the previously estimated frequency index, taking into account the inclusion of a self-interference signal in the despread DFT signal. However, this demodulation method imposes a significant processing load on the desired signal, taking into account the influence of the possible presence of a self-interference signal. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] LoRa Alliance, Inc., "LoRaWAN(TM) 1.0.3 Specification," 2018, Internet<URL:https: / / lora-alliance.org / sites / default / files / 2018-07 / lorawan1.0.3.pdf> [Non-patent document 2] Ryoya Saito, Koichi Adachi, Takeo Fujii, Ryota Kumada, "Study on fractional spreading factor in LoRa signals and proposal of demodulation method," IEICE Technical Report, Kagawa, October 2023 Summary of the Invention [Problem to be solved by the invention]

[0009] In view of the above circumstances, an object of the present disclosure is to provide an efficient communication system, communication method, and communication program that utilizes a fractional spreading factor in the LoRa modulation scheme while not generating interference signals that degrade symbol error rate performance during the demodulation process. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0010] The following describes the means for solving the problems using the numbers and symbols used in the description of the invention. These numbers and symbols are added in parentheses for reference purposes to show an example of the correspondence between the claims and the description of the invention. Therefore, the claims should not be interpreted as being limited by the parenthetical descriptions.

[0011] According to one embodiment, a communication system (1) includes a transmitting terminal (2) and a gateway (3). The transmitting terminal (2) generates a transmission signal by applying FSF-LoRa modulation to transmission data using a spreading factor (s) that is an integer equal to or greater than 1 and a fractional coefficient (ρ) that is a positive real number less than 1. The gateway (3) demodulates a received signal that receives the transmission signal using the spreading factor (s) and the fractional coefficient (ρ) and outputs an estimated demodulated signal that estimates the transmission data. The transmitting terminal (2) includes a bit symbol mapping unit (202) and a spreading unit (205). The bit symbol mapping unit (202) converts the transmission data into a combination of symbols of a first integer type. The spreading unit (205) spreads each of the symbols included in the combination with a first reference chirp signal generated based on the spreading factor (s) and the fractional coefficient (ρ). The gateway (3) includes a sampling unit (302) and a despreading unit (304). The sampling unit (302) performs sampling processing on the received signal at a sampling frequency that satisfies the Nyquist criterion to generate an equivalent low-pass signal. The despreading unit (304) despreads the equivalent low-pass signal with a second reference chirp signal that is generated based on the spreading factor (s) and the fractional coefficient (ρ).

[0012] According to one embodiment, a communication method includes generating a transmission signal by applying FSF-LoRa modulation to transmission data using a spreading factor (s) equal to or greater than 1 and a fractional coefficient (ρ) equal to or less than 1 (S12), and demodulating a received signal that receives the transmission signal using the spreading factor (s) and the fractional coefficient (ρ) to output an estimated demodulated signal that estimates the transmission data (S23). Generating the transmission signal (S12) includes converting the transmission data into a combination of symbols of a first integer type and spreading each symbol included in the combination with a first reference chirp signal generated based on the spreading factor (s) and the fractional coefficient (ρ). Outputting the estimated demodulated signal (S23) includes sampling the received signal at a sampling frequency that satisfies the Nyquist criterion to generate an equivalent low-pass signal and despreading the equivalent low-pass signal with a second reference chirp signal generated based on the spreading factor (s) and the fractional coefficient (ρ).

[0013] According to one embodiment, the communication program is a communication program for causing a computing device (22, 32) to execute a predetermined process, the process including: generating a transmission signal by applying FSF-LoRa modulation to transmission data using a spreading factor (s) that is an integer greater than or equal to 1 and a fractional coefficient (ρ) that is a positive real number less than 1 (S12); and demodulating a received signal that receives the transmission signal using the spreading factor (s) and the fractional coefficient (ρ) to output an estimated demodulated signal that estimates the transmission data (S23). Generating the transmission signal (S12) includes converting the transmission data into a combination of symbols of a first integer type, and spreading each of the symbols included in the combination with a first reference chirp signal that is generated based on the spreading factor (s) and the fractional coefficient (ρ). Outputting an estimated demodulated signal (S23) includes performing a sampling process on the received signal at a sampling frequency that satisfies the Nyquist criterion to generate an equivalent low-pass signal, and despreading the equivalent low-pass signal with a second reference chirp signal that is generated based on a spreading factor (s) and a fractional coefficient (ρ). [Effects of the Invention]

[0014] According to one embodiment, efficient LoRa modulation communication can be realized by utilizing a fractional spreading factor in the LoRa modulation method while not generating interference signals that degrade symbol error rate performance during the demodulation process. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment. [Figure 2] FIG. 2 is a block circuit diagram showing an example of the configuration of a transmitting terminal according to an embodiment. [Figure 3] FIG. 3 is a block circuit diagram illustrating an example of a configuration of a gateway according to an embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of processing executed by the transmitting terminal in the communication method according to an embodiment. [Figure 5] FIG. 5 is a flowchart illustrating an example of a process executed by a gateway in a communication method according to an embodiment. [Figure 6] FIG. 6 is a block circuit diagram showing an example of the configuration of a modulator according to an embodiment. [Figure 7] FIG. 7 is a diagram for explaining the LoRa modulation method and the FSF-LoRa modulation method according to the related art. [Figure 8] FIG. 8 is a diagram illustrating the Nyquist rate FSF-LoRa modulation method according to one embodiment. [Figure 9] FIG. 9 is a diagram for explaining the difference between the LoRa modulation method and FSF-LoRa modulation method according to the related art, and the Nyquist rate FSF-LoRa modulation method according to one embodiment. [Figure 10] FIG. 10 is a diagram illustrating a method for generating symbols according to an embodiment. [Figure 11] FIG. 11 is a block circuit diagram showing an example of the configuration of a demodulator according to an embodiment. [Figure 12] FIG. 12 is a graph for explaining the results of the computer simulation. [Figure 13] FIG. 13 is a graph for explaining the results of the computer simulation. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A communication system, a communication method, and a communication program according to the present disclosure will be described below with reference to the accompanying drawings.

[0017] (Embodiment) As shown in Fig. 1, a communication system 1 according to one embodiment includes transmitting terminals 2A and 2B that transmit transmission signals, and a gateway 3 that receives the transmission signals as reception signals. Hereinafter, when there is no need to distinguish between the transmitting terminals 2A and 2B, they may be collectively referred to as transmitting terminals 2. The transmitting terminals 2A and 2B each include a modulator 20A or 20B that modulates transmission data into a transmission signal. When there is no need to distinguish between the modulators 20A and 20B, they may be collectively referred to as modulators 20. In the example of Fig. 1, the total number of transmitting terminals 2 is two, but this is merely an example, and in reality, the communication system 1 may include more transmitting terminals 2.

[0018] As shown in Fig. 2, the transmitting terminal 2 according to one embodiment may be configured like a so-called computer. In the example of Fig. 2, the transmitting terminal 2 includes a bus 21, a computing device 22, a storage device 23, a communication device 24, and an input / output device 25. As an example, the bus 21 is configured to connect the computing device 22, the storage device 23, the communication device 24, and the input / output device 25 so that they can communicate with each other.

[0019] The arithmetic device 22 includes a data generation unit 221, a modulation unit 222, and a transmission unit 223. The storage device 23 includes a program storage unit 231 and a data storage unit 232. The arithmetic device 22 executes a transmission terminal program stored in the program storage unit 231, among the communication programs according to this embodiment, thereby realizing the processing of the data generation unit 221, the modulation unit 222, and the transmission unit 223. The data generation unit 221, the modulation unit 222, and the transmission unit 223 are virtual functional blocks that realize processing through cooperation between the arithmetic device 22 and the storage device 23. The data generation unit 221 generates transmission data represented by a transmission signal transmitted from the transmitting terminal 2 to the gateway 3. The modulation unit 222 operates as the modulator 20 in FIG. 1 and modulates the transmission data onto the transmission signal using a LoRa (Long Range) modulation method. In this embodiment, a Nyquist Rate FSF-LoRa modulation method, which is a type of LoRa modulation method, is used. Details of this modulation method will be described later. The transmitting unit 223 in FIG. 2 controls the communication device 24 to transmit a transmission signal to the gateway 3.

[0020] The transmitting terminal program may be read from the recording medium 230 and stored in the program storage unit 231. The recording medium 230 may be a non-transitory and tangible medium.

[0021] The communication device 24 is controlled by the transmitting unit 223 and transmits a transmission signal to the gateway 3 by wireless communication using an antenna (not shown). The communication device 24 may further be configured to be connectable to a network (not shown). The transmission terminal program may be acquired from the outside via the communication device 24 and stored in the program storage unit 231.

[0022] The input / output device 25 outputs information to the user and accepts operations input by the user. As an example, the input / output device 25 includes a lamp that lights up, a switch that accepts a press operation, and the like.

[0023] As shown in Fig. 3, the gateway 3 according to one embodiment may be configured like a so-called computer. In the example of Fig. 3, the gateway 3 includes a bus 31, a computing device 32, a storage device 33, a communication device 34, and an input / output device 35. As an example, the bus 31 is configured to connect the computing device 32, the storage device 33, the communication device 34, and the input / output device 35 so that they can communicate with each other.

[0024] The arithmetic device 32 includes a receiving unit 321, a demodulating unit 322, and an output unit 323. The storage device 33 includes a program storage unit 331 and a data storage unit 332. The arithmetic device 32 executes a gateway program stored in the program storage unit 331 to realize the processing of the receiving unit 321, the demodulating unit 322, and the output unit 323. The receiving unit 321, the demodulating unit 322, and the output unit 323 are virtual functional blocks that realize processing through cooperation between the arithmetic device 32 and the storage device 33. The receiving unit 321 receives, as a received signal, each of the transmission signals transmitted from the transmitting terminal 2 via the communication device 34. The demodulating unit 322 operates as a demodulator 30 that demodulates the received signal to generate a demodulated signal. The output unit 323 outputs the demodulated signal to the outside.

[0025] The gateway program may be read from the recording medium 330 and stored in the program storage unit 331. The recording medium 330 may be a non-transitory and tangible medium.

[0026] The communication device 34 is controlled by the receiving unit 321 and receives a transmission signal transmitted from the transmitting terminal 2 as a reception signal via wireless communication using an antenna (not shown). The communication device 34 may further be connected to a network (not shown). The gateway program may be obtained from outside via the communication device 34 and stored in the program storage unit 331.

[0027] The input / output device 35 outputs information to the user and accepts operations input by the user. As an example, the input / output device 35 includes a display device that outputs images, a keyboard that accepts key input operations, and the like.

[0028] The processing of a communication method according to one embodiment will be described with reference to the flowcharts of Figures 4 and 5. The processing of the flowchart of Figure 4 is executed by the transmitting terminal 2 and may start when the transmitting terminal 2 is started. The processing of the flowchart of Figure 5 is executed by the gateway 3 and may start when the gateway 3 is started.

[0029] When the processing of the flowchart in Fig. 4 starts, step S11 is executed. In step S11, the data generation unit 221 of the calculation device 22 of the transmitting terminal 2 shown in Fig. 2 generates transmission data. As an example, the transmission data may include digital data representing data acquired by a sensor (not shown) provided in the transmitting terminal 2. The generated transmission data may be stored in the data storage unit 232 in Fig. 2.

[0030] After step S11 in Fig. 4, step S12 is executed. In step S12, the modulation unit 222 of the calculation device 22 in the transmitting terminal 2 shown in Fig. 2 modulates the transmission data to generate a transmission signal. At this time, the modulation unit 222 may read the transmission data from the data storage unit 232 and store the generated transmission signal in the data storage unit 232. When modulating the transmission data, the modulation unit 222 uses the Nyquist rate FSF-LoRa modulation method. Specific processing content of this modulation method will be described later.

[0031] Step S13 is executed after step S12 in Fig. 4. In step S13, the transmitting unit 223 of the arithmetic device 22 of the transmitting terminal 2 shown in Fig. 2 transmits transmission data to the gateway 3. At this time, the transmitting unit 223 may perform a process of reading and transmitting a transmission signal from the data storage unit 232 at a preset timing by, for example, referring to a clock circuit (not shown).

[0032] After step S13 in FIG. 4, the processing of the sending terminal 2 may return to step S11.

[0033] When the processing of the flowchart in Fig. 5 starts, step S21 is executed. In step S21, the receiver 321 of the arithmetic device 32 of the gateway 3 shown in Fig. 3 receives as a received signal the transmission signal transmitted by the transmitting terminal 2 in step S13 in Fig. 4. The received received signal may be stored in the data storage unit 332 in Fig. 3.

[0034] After step S21 in Fig. 5, step S22 is executed. In step S22, the demodulator 322 of the arithmetic device 32 in the gateway 3 shown in Fig. 3 estimates an index of the transmitted data from the received signal to estimate a demodulated signal. At this time, the demodulator 322 may read the received data from the data storage unit 332 and store the estimated index and the estimated demodulated signal in the data storage unit 332. When demodulating the received data, the demodulator 322 uses the Nyquist rate FSF-LoRa modulation method. Specific processing details of this modulation method will be described later.

[0035] Step S23 is executed after step S22 in Fig. 5. In step S23, the output unit 323 of the arithmetic device 32 in the gateway 3 shown in Fig. 3 outputs the estimated demodulated signal to the outside.

[0036] After step S23 in FIG. 5, the processing of the gateway 3 may return to step S21.

[0037] With reference to Figures 6, 7, 8 and 9, the following describes the modulator 20 as the modulation unit 222 in the communication system 1 according to one embodiment, a LoRa modulation method according to a related technology, an FSF-LoRa modulation method according to a related technology, and a Nyquist rate FSF-LoRa modulation method in the communication method according to one embodiment.

[0038] As shown in FIG. 6, the modulator 20 as a modulation unit 222 according to one embodiment includes an input unit 201, a bit symbol mapping unit 202, a cyclic shift amount determination unit 203, a reference chirp signal generation unit 204, a spreading unit 205, and an output unit 206.

[0039] The input unit 201 supplies binary transmission data to the bit symbol mapping unit 202. The bit symbol mapping unit 202 converts the transmission data into information {0, 1} with a number of bits equal to the spreading factor s. s into an index m representing a symbol of the transmission signal based on a predetermined mapping table. The cyclic shift amount determination unit 203 determines the amount of cyclic shift in the time domain for the reference chirp signal based on the index m. The amount of cyclic shift is calculated as shown in the following "Equation 1". The reference chirp signal generation unit 204 converts a reference chirp signal having a chip length T c , a spreading factor s, and a fractional coefficient ρ, where the chip length T c is the reciprocal of the bandwidth W, which represents the range in which the frequency of the chirp signal changes. The first reference chirp signal is expressed as in the following "Equation 2". Spreading section 205 performs spectrum spreading processing using the reference chirp signal from reference chirp signal generation section 204 on the cyclic shift amount from cyclic shift amount determination section 203, to generate a discrete-time signal {x m The output unit 206 generates a discrete-time signal {x m} is output as a transmission signal.

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[0040] As shown in Figure 7, the LoRa signal used in the LoRa modulation method of the related art is a combination of chirp signals whose frequency changes linearly over time. In the example of Figure 7, the chirp signal is an up-chirp signal whose frequency increases over time, but a down-chirp signal whose frequency decreases over time may also be used. The LoRa signal is generated by combining a number of symbols whose total number is equal to the spreading factor s raised to the power of 2, which is obtained by modifying a reference chirp signal using cyclic shift. The length of each symbol on the time axis is the same symbol length T s The symbol length T s The length obtained by dividing by the power of the integer 2 raised to the same number of times as the spreading factor s is the chip length T c The length on the frequency axis of the range in which the frequency changes in each symbol is the same bandwidth W, and the chip length T c is equal to the reciprocal of . Each symbol of the type of power obtained by raising the integer 2 the same number of times as the spreading factor s is distinguished by the different timing at which the frequency switches from the maximum value of the bandwidth W to the minimum value. Therefore, one symbol included in a LoRa signal can represent any of the data of the type of power obtained by raising the integer 2 the same number of times as the spreading factor s.

[0041] The LoRa modulation method allows multiple LoRa signals with different spreading factors to coexist. That is, when a first transmitting terminal 2 transmits a first LoRa signal modulated using a first spreading factor and a second transmitting terminal 2 simultaneously transmits a second LoRa signal modulated using a second spreading factor different from the first spreading factor, the same gateway 3 can simultaneously receive the first LoRa signal and the second LoRa signal and demodulate each signal.

[0042] In the standardized LoRaWAN (Long Range Wide Area Network), an integer between 7 and 12 is used as the spreading factor s. However, in the example of FIG. 7, for easier understanding, the case where the spreading factor s is equal to 2 will be described.

[0043] As shown in Figure 7, the FSF-LoRa signal used in the FSF-LoRa modulation method according to the related art is generated based on a fractional spreading factor, which is obtained by extending the spreading factor s in the LoRa signal to a fraction other than an integer. s The chip length T for each of the symbols c and symbol length T s are multiplied by a factor 1+ρ, where the value ρ is called the fractional coefficient. The fractional coefficient ρ is a real number greater than or equal to 0 and less than 1. Here, the coefficient 1+ρ may be a rational number expressed as a ratio of two integers. That is, the chip length T c and symbol length T s In the FSF-LoRa signal, which is a LoRa signal using the c (s,ρ) is (1+ρ)T c and the symbol length T s (s,ρ) is (1+ρ)T s In the example of Fig. 7, the fractional coefficient ρ is 1 / 4, but this example does not limit the present embodiment.

[0044] The FSF-LoRa modulation method can coexist with the LoRa modulation method. That is, when a first transmitting terminal 2 transmits a first LoRa signal modulated using a first spreading factor and a second transmitting terminal 2 simultaneously transmits a first FSF-LoRa signal modulated using the same first spreading factor and first fractional coefficient, the same gateway 3 can simultaneously receive the first LoRa signal and the first FSF-LoRa signal and demodulate each signal. Similarly, the FSF-LoRa modulation method allows multiple FSF-LoRa signals with different combinations of spreading factors and fractional coefficients to coexist. As a result, the number of selectable purely orthogonal channels in the same communication system 1 increases compared to when only the LoRa modulation method is used.

[0045] On the other hand, in the FSF-LoRa modulation method shown in FIG. 7, demodulation of the received signal requires oversampling using a frequency higher than the sampling frequency. As a result, the Nyquist criterion is not satisfied in the DFT processing included in the demodulation processing, and a self-interference signal may be generated when demodulating the received signal. Non-Patent Document 2 (Saito Ryoya, Adachi Koichi, Fujii Takeo, Kumada Ryota, "Study on Fractional Spreading Factor for LoRa Signals and Proposal of Demodulation Method," IEICE Technical Report, Kagawa, October 2023) is known as a technique for correcting the received signal so that the self-interference signal is not mistaken for the desired signal. However, the processing load required for such correction is significant.

[0046] Therefore, in this embodiment, we propose an FSF-LoRa modulation method that does not require oversampling processing in the demodulation process and satisfies the Nyquist criterion, so that correction processing that takes into account the possibility of the presence of a self-interference signal is not required.To distinguish it from the above-mentioned related technologies, the FSF-LoRa modulation method according to this embodiment will hereinafter be referred to as the Nyquist rate FSF-LoRa modulation method.

[0047] As shown in FIG. 8, in the Nyquist rate FSF-LoRa modulation method according to one embodiment, the Nyquist rate FSF-LoRa signal modulated using the spreading factor s and the fractional coefficient ρ has a symbol length T that is (1+ρ) times longer than the LoRa modulation signal modulated using the same spreading factor s, as in the case of the FSF-LoRa modulation method according to the related art shown in FIG. s (s,ρ) On the other hand, the Nyquist rate FSF-LoRa signal according to the present embodiment of FIG. 8 has a chip length T c The chip length T is equal to c (s,ρ)In this case, the total number of chips included in each symbol in the Nyquist rate FSF-LoRa signal is (1 + ρ) times the total number of chips included in each symbol in the LoRa signal with the same spreading factor s. In addition, in the LoRa modulation method and FSF-LoRa modulation method with the same spreading factor s, the total number of types of symbols obtained by performing cyclic shift processing on the reference chirp signal is 2 s However, the total number of symbols that can be obtained in the Nyquist rate FSF-LoRa modulation method is (1 + ρ)2 s 8, the fractional coefficient ρ is 1 / 4, and in the LoRa modulation method, the total number of chips included in each symbol and the total number of symbol types are both 4, and in the Nyquist rate FSF-LoRa modulation method, the total number of chips included in each symbol and the total number of symbol types are both 5, but this embodiment is not limited to this example.

[0048] The differences between the LoRa modulation method, the FSF-LoRa modulation method, and the Nyquist rate FSF-LoRa modulation method will be explained with reference to the graph in Figure 9. Figure 9 includes three graphs G01, G02, and G03. In all graphs G01, G02, and G03, the horizontal axis represents time and the vertical axis represents frequency. Graph G01 shows an example of a waveform of a reference chirp signal using the LoRa modulation method, indicated by a thick solid line. Graph G02 shows an example of a waveform of a reference chirp signal using the FSF-LoRa modulation method, indicated by a thin solid line. Graph G03 shows an example of a waveform of a reference chirp signal using the Nyquist rate FSF-LoRa modulation method, indicated by a thick dotted line. Note that in the example in Figure 9, the spreading factor s is equal to 2, the fractional coefficient ρ is equal to 1 / 4, and graphs G02 and G03 completely overlap.

[0049] Here, the chip length (1+ρ)·T in the FSF-LoRa signal shown in graph G02 c is the chip length T in the LoRa signal shown in graph G01. cis equal to the product of multiplying the integer 1 by the sum of the fractional coefficient ρ. In the FSF-LoRa modulation method, the total number of chips included in one symbol is the power of the integer 2 multiplied the same number of times as the spreading factor s, just like in the case of the LoRa modulation method. Therefore, in the FSF-LoRa signal shown in graph G02, the symbol length T s (s,ρ) is the chip length (1+ρ) T c is equal to the product of 2 raised to the power of the integer 2 raised to the same number of times as the spreading factor s.

[0050] On the other hand, graph G03 shows the chip length T c is the chip length T in the LoRa signal shown in graph G01. c In the LoRa modulation method, when the total number of chips included in one symbol is a power of the integer 2 raised the same number of times as the spreading factor s, in the Nyquist rate FSF-LoRa modulation method, the total number of chips included in one symbol is (1 + ρ) times that, that is, (1 + ρ) 2 s Therefore, in the Nyquist rate FSF-LoRa signal shown in graph G03, the symbol length T s (s,ρ) is the tip length T c is equal to the product of multiplying the integer 1 times the sum of the fractional coefficient ρ and then multiplying it by the power of the integer 2 raised to the same number of times as the spreading factor s.

[0051] In this way, the symbol length T s (s,ρ) and the symbol length T in the Nyquist rate FSF-LoRa signal shown in graph G03. s (s,ρ)Although the results are consistent, the reasons for this difference are different. Explaining this difference from another perspective, graphs G01, G02, and G03 all have in common the fact that when the frequency of the reference chirp signal increases linearly over time from the upper limit to the lower limit within the bandwidth W, the amount by which the frequency of the reference chirp signal increases with the passage of one chip length is W / 2 for the LoRa modulation method and the Nyquist rate FSF-LoRa modulation method. s and the FSF-LoRa modulation method is W / ((1+ρ) 2 s )

[0052] Here, in the Nyquist rate FSF-LoRa modulation method according to this embodiment, the symbol length T s (s,ρ) The chip length T c The ratio divided by (1+ρ)·2 s is an integer. Therefore, the fractional coefficient ρ is subject to the constraints expressed in the following "Equation 3".

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[0053] A method for generating multiple symbols by cyclically shifting a reference chirp signal will be described with reference to Figure 10. Figure 10 includes two graphs, G21 and G22. Graph G22 is divided into subgraphs, G22A and G22B. In both graphs G21 and G22, the horizontal axis represents time and the vertical axis represents frequency.

[0054] Graph G21 shown in Fig. 10 represents a symbol where index m is equal to 0. The symbol represented by graph G21 is equivalent to the leftmost symbol on the time axis of the Nyquist rate FSF-LoRa signal shown in Fig. 8, and has the same waveform as the reference chirp signal of the Nyquist rate FSF-LoRa modulation method shown as graph G03 in Fig. 9.

[0055] In the graph G22 shown in FIG. 10, the portion consisting of the subgraphs G22A and G22B represents symbols whose index m satisfies the following "Equation 4".

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[0056] The right side of the above equation (4) represents the maximum value of the symbol index usable for each combination of spreading factor s and fractional coefficient ρ in the Nyquist rate FSF-LoRa modulation scheme according to this embodiment. Here, the symbol index value is an integer value ranging from 0 to the difference obtained by subtracting the integer 1 from the maximum number of usable symbol types. In the above example, the spreading factor s is equal to 2, and the fractional coefficient ρ is equal to 1 / 4, so the maximum number of usable symbol types is 5, and the maximum index value is 4. The symbols represented by subgraphs G22A and G22B are equivalent to the rightmost symbols on the time axis in the Nyquist rate FSF-LoRa signal shown in FIG. 8. They have a waveform obtained by increasing the frequency of the reference chirp signal of the Nyquist rate FSF-LoRa modulation scheme shown as graph G03 in FIG. 9 by m times the index of the unit frequency width along the frequency axis, and then shifting the portion above the upper frequency limit f1 of the frequency range so that it continues from the lower frequency limit f0 of the frequency range. This method of calculating a waveform is called a cyclic shift. When the reference chirp signal of the Nyquist rate FSF-LoRa modulation method is expressed as in the following "Equation 5," the symbol obtained by performing cyclic shift processing based on index m is calculated as in the following "Equation 6."

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[0057] When the above various conditions are met, the Nyquist rate FSF-LoRa modulation method according to this embodiment does not require oversampling of the received signal during demodulation, satisfies the Nyquist criterion, does not generate a self-interference signal, and therefore does not require correction processing to take into account the possibility of the presence of a self-interference signal.Furthermore, the Nyquist rate FSF-LoRa modulation method according to this embodiment achieves performance equivalent to full search demodulation by performing the same demodulation processing as the LoRa modulation method.

[0058] With reference to FIG. 11, the demodulator 30 serving as the demodulation unit 322 in the communication system 1 according to the embodiment and the Nyquist rate FSF-LoRa demodulation process in the communication method according to the embodiment will be described.

[0059] As shown in FIG. 11 , the demodulator 30 as a demodulation unit 322 according to one embodiment includes an input unit 301, a sampling unit 302, a reference chirp signal generation unit 303, a despreading unit 304, a DFT (Discrete Fourier Transform) unit 305, an estimation unit 306, a symbol bit mapping unit 307, and an output unit 308.

[0060] The input unit 301 supplies the received signal received by the receiving unit 321 in Fig. 2 to the sampling unit 302 in Fig. 7. The sampling unit 302 performs sampling processing on the received signal to generate an equivalent low-pass signal {r m The reference chirp signal generator 303 generates a reference chirp signal having a chip length T c , a spreading factor s, and a fractional coefficient ρ, where the chip length T cis the reciprocal of the bandwidth W, which represents the range over which the frequency of the chirp signal varies, and the direction in which the frequency increases or decreases over time is opposite between the second reference chirp signal generated by the reference chirp signal generation unit 303 and the first reference chirp signal generated by the reference chirp signal generation unit 204 in FIG. 6. The second reference chirp signal is expressed by the following equation (10). In this embodiment, a case will be described in which the first reference chirp signal is a reference up-chirp signal and the second reference chirp signal is a reference down-chirp signal, but this example does not limit this embodiment. The despreading unit 304 generates an equivalent low-pass signal {r m} is subjected to despreading processing using the reference chirp signal from the reference chirp signal generation section 303 to generate a despread signal. The DFT section 305 performs DFT processing on the despread signal to generate a despread DFT signal {d m The estimation unit 306 generates the despread DFT signal {d m}, an index m of the transmission data is estimated to calculate an estimated index ^m (to be precise, the hat symbol "^" is written above "m"). Based on a predetermined mapping table, the symbol bit mapping unit 307 converts the symbol included in the received signal and represented by the estimated index ^m (to be precise, the hat symbol "^" is written above "m") into an estimated demodulated signal ^{0,1}s (to be precise, the hat symbol "^" is written above "{0,1}s"), which is binary information with the number of bits equal to the spreading factor s. The output unit 308 outputs the estimated demodulated signal ^{0,1}s (to be precise, the hat symbol "^" is written above "{0,1}s") to the outside.

number

[0061] The despread DFT signal {d m} is the despread DFT signal "d m It is a set of "[n]" and can be calculated as in the following "Equation 11", and its absolute value can be calculated as in the following "Equation 12".

number

number

[0062] The estimated index ^m in FIG. 11 (to be precise, the hat symbol "^" is written above "m") is calculated as shown in the following formula (13).

number

[0063] As described above, the communication system 1, communication method, and communication program according to one embodiment enable efficient communication by utilizing a fractional spreading factor in the LoRa modulation scheme while preventing the generation of self-interference signals.

[0064] (Simulation results, part 1) Referring to Fig. 12, the results of a computer simulation of the communication system 1, communication method, and communication program according to one embodiment will be described. Fig. 12 includes five graphs G31, G32, G33, G34, and G35. In all graphs G31, G32, G33, G34, and G35, the horizontal axis represents the average signal-to-noise ratio, and the vertical axis represents the symbol error rate. Graph G31 represents the characteristics of the Nyquist rate FSF-LoRa modulation scheme when the fractional spreading factor is equal to 7, i.e., when the spreading factor s is equal to 7. Graph G32 represents the characteristics of the Nyquist rate FSF-LoRa modulation scheme when the fractional spreading factor is equal to 7.25, i.e., when the spreading factor s is equal to 7 and the fractional coefficient ρ is equal to 0.25. Graph G33 represents the characteristics of the Nyquist rate FSF-LoRa modulation scheme when the fractional spreading factor is equal to 7.5, i.e., when the spreading factor s is equal to 7 and the fractional coefficient ρ is equal to 0.5. Graph G34 represents the characteristics of the Nyquist rate FSF-LoRa modulation scheme when the fractional spreading factor is equal to 7.75, i.e., when the spreading factor s is equal to 7 and the fractional coefficient ρ is equal to 0.75. Graph G35 represents the characteristics of the Nyquist rate FSF-LoRa modulation scheme when the fractional spreading factor is equal to 8, i.e., when the spreading factor s is equal to 8.

[0065] As can be seen from the graph in Figure 12, the larger the fractional spreading factor, the lower the symbol error rate corresponding to the same signal-to-noise ratio. This indicates that in the Nyquist rate FSF-LoRa modulation method according to this embodiment, desirable characteristics of the FSF-LoRa modulation method can be obtained by the same demodulation process as the LoRa modulation method. However, it should be noted that the trade-off is that the data rate decreases as the fractional spreading factor increases.

[0066] (Simulation results, part 2) Referring to Fig. 13, the results of a computer simulation of the communication system 1, communication method, and communication program according to one embodiment will be described. Fig. 13 includes four graphs G41, G42, G43, and G44. In all of the graphs G41, G42, G43, and G44, the horizontal axis represents the average signal-to-noise ratio, and the vertical axis represents the symbol error rate. Graph G41 represents the characteristics of the Nyquist rate FSF-LoRa modulation scheme when the fractional spreading factor is equal to 7, i.e., when the spreading factor s is equal to 7.0. Graph G42 represents the characteristics of the Nyquist rate FSF-LoRa modulation scheme when the fractional spreading factor is equal to 7.5, i.e., when the spreading factor s is equal to 7 and the fractional coefficient ρ is equal to 0.5. Graph G43 represents the characteristics of the Nyquist rate FSF-LoRa modulation scheme when the spreading factor s is equal to 7 and the fractional coefficient ρ is equal to 0.5 when a LoRa signal when the spreading factor s is equal to 7 is simultaneously transmitted as an interfering signal. Graph G44 represents the characteristics of the LoRa modulation scheme when the spreading factor s is equal to 7 and the fractional coefficient ρ is equal to 0.5 when a Nyquist rate FSF-LoRa signal when the spreading factor s is equal to 7 and the fractional coefficient ρ is equal to 0.5 is simultaneously transmitted as an interfering signal.

[0067] 13, the symbol error rate corresponding to the same signal-to-noise ratio is higher when an interfering signal is present than when no interfering signal is present. However, the characteristics when the fractional spreading factor is 7.5 and the interfering signal is present are more advantageous than the characteristics when the fractional spreading factor is 7 and the interfering signal is not present, and therefore the effectiveness of the Nyquist rate FSF-LoRa modulation method according to this embodiment is expected.

[0068] The invention made by the inventor has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited to the embodiments and can be modified in various ways without departing from the spirit of the invention. Furthermore, the features described in the embodiments can be freely combined within the scope of technical compatibility. [Explanation of symbols]

[0069] 1. Communication Systems 2, 2A, 2B transmitting terminal 20, 20A, 20B Modulator 201 Input section 202 Bit Symbol Mapping Unit 203 Cyclic shift amount determination unit 204 Reference chirp signal generator 205 Diffusion section 206 Output section 21 Bus 22 Arithmetic unit 221 Data Generation Unit 222 Modulation section 223 Transmitter 23 Storage device 230 Recording Media 231 Program Memory Unit 232 Data storage unit 24 Communication equipment 25 Input / Output Devices 3 Gateway 30 Demodulator 301 Input section 302 Sampling section 303 Reference chirp signal generator 304 Despreading Unit 305 DFT section 306 Estimation Department 307 Symbol Bit Mapping Unit 308 Output section 31 Bus 32 Arithmetic unit 321 Receiving Unit 322 Demodulation Unit 323 Output Section 33 Storage device 330 Recording Media 331 Program Memory Unit 332 Data storage unit 34 Communication equipment 35 Input / Output Devices f0 lower limit frequency f1 upper limit frequency G01, G02, G03 graphs G21, G22 graphs G22A, G22B, G22C subgraphs G31, G32, G33, G34, G35 graphs G41, G42, G43, G44 graphs s Diffusion rate T c , T c (s,ρ) Tip Length T s , T s (s,ρ) Symbol Length W Bandwidth ρ fractional coefficient

Claims

1. a transmitting terminal that generates a transmission signal by performing FSF (Fractional Spreading Factor)-LoRa (Long Range) modulation on transmission data using a spreading factor that is an integer equal to or greater than 1 and a fractional coefficient that is a positive real number less than 1; a gateway that demodulates a received signal that has received the transmission signal using the spreading factor and the fractional coefficient, and outputs an estimated demodulated signal that estimates the transmission data; Equipped with The transmitting terminal a bit symbol mapping unit that converts the transmission data into a combination of symbols of a first integer number of kinds; a spreading unit that spreads each of the symbols included in the combination with a first reference chirp signal that is generated based on the spreading factor and the fractional coefficient; Equipped with The gateway a sampling unit that performs sampling processing on the received signal at a sampling frequency that satisfies the Nyquist criterion to generate an equivalent low-pass signal; a despreading unit that despreads the equivalent low-pass signal with a second reference chirp signal that is generated based on the spreading factor and the fractional coefficient; Equipped with Communication system.

2. 2. The communication system according to claim 1, the product of the sum of the integer 1 and the fractional coefficient and the power of the integer 2 raised the same number of times as the spreading factor is an integer; Communication system.

3. 3. The communication system according to claim 2, The transmitting terminal a cyclic shift amount determination unit that performs cyclic shift processing on the first reference chirp signal using an index of the symbol corresponding to the transmission data and a predetermined chip length to generate the symbol; Furthermore, the chip length is equal to the chip length of a LoRa modulation scheme using the spreading factor, The symbol length is equal to the chip length multiplied by the integer 1 plus the fractional coefficient. Communication system.

4. 4. The communication system according to claim 3, a frequency width of a range in which the frequency of the first reference chirp signal changes linearly with time is the reciprocal of the chip length; the frequency of the second reference chirp signal varies linearly with time within the range in a direction opposite to the direction in which the frequency of the first reference chirp signal varies linearly with time; Communication system.

5. generating a transmission signal by performing FSF-LoRa modulation on transmission data using a spreading factor that is an integer equal to or greater than 1 and a fractional coefficient that is a positive real number less than 1; demodulating a received signal that has received the transmission signal using the spreading factor and the fractional coefficient, and outputting an estimated demodulated signal that estimates the transmission data; Including, generating the transmit signal converting the transmission data into a combination of symbols of a first integer kind; Spreading each of the symbols included in the combination with a first reference chirp signal generated based on the spreading factor and the fractional coefficient; Including, outputting the estimated demodulated signal performing a sampling process on the received signal at a sampling frequency that satisfies the Nyquist criterion to generate an equivalent low-pass signal; despreading the equivalent low-pass signal with a second reference chirp signal generated based on the spreading factor and the fractional coefficient; Including, Communication method.

6. A communication program for causing a computing device to execute a predetermined process, The process comprises: generating a transmission signal by performing FSF-LoRa modulation on transmission data using a spreading factor that is an integer equal to or greater than 1 and a fractional coefficient that is a positive real number less than 1; demodulating a received signal that has received the transmission signal using the spreading factor and the fractional coefficient, and outputting an estimated demodulated signal that estimates the transmission data; Including, generating the transmit signal converting the transmission data into a combination of symbols of a first integer kind; Spreading each of the symbols included in the combination with a first reference chirp signal generated based on the spreading factor and the fractional coefficient; Including, outputting the estimated demodulated signal performing a sampling process on the received signal at a sampling frequency that satisfies the Nyquist criterion to generate an equivalent low-pass signal; despreading the equivalent low-pass signal with a second reference chirp signal generated based on the spreading factor and the fractional coefficient; Including, Communications program.

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