A method and system for detecting received signals of an industrial frequency communication system

Abstract

The present invention provides a method and system for detecting a received signal of an industrial frequency communication system, comprising: obtaining a modulation mode of an industrial frequency signal to be detected at a receiving end and a modulation signal at a transmitting end; intercepting the industrial frequency signal by using a window function, and performing amplitude subtraction on the intercepted signal; adding a cyclic prefix to the industrial frequency signal after the amplitude subtraction to obtain an industrial frequency signal with a cyclic prefix; and identifying the modulation signal in the industrial frequency signal to be detected based on the modulation mode of the industrial frequency signal with the cyclic prefix and the modulation signal at the transmitting end. The industrial frequency signal detection method adopted by the present invention does not require synchronization of the industrial frequency signal to be detected by a zero-crossing signal, thereby achieving accurate detection of the industrial frequency signal, eliminating the need for configuring a zero-crossing signal generating device, reducing hardware overhead, lowering the requirements for the on-site environment for equipment installation and deployment, avoiding errors caused by transformer phase rotation, and improving the accuracy of industrial frequency signal detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of power frequency communication, and in particular relates to a method and system for detecting a received signal of a power frequency communication system. Background Art

[0002] Power frequency communication technology uses power lines as a channel, exploiting subtle distortions in the power grid's power frequency voltage and current waveforms to carry information. This technology employs a unique signal modulation mechanism, maintaining the frequency of the voltage or current pulse signals between 200 and 600 Hz. This prevents signal attenuation due to line impedance during transmission. The greatest advantage of power frequency communication technology is that the signal can directly penetrate distribution transformers, enabling communication across transformer substations without the need for relays. This technology offers long communication distances and strong anti-interference capabilities.

[0003] Currently, extensive research has been conducted both domestically and internationally on detection algorithms for power frequency received signals. The papers "Application of Differential Technique for Characterization of Waveform Distoration" and "Bidirectional Power Frequency Communication Signal Extraction Based on Differential Techniques" propose using the zero-crossing region of the grid fundamental waveform as the modulation region for power frequency communication system signals. This significantly reduces modulation power and facilitates signal location. The paper "Power Frequency Communication Downlink Demodulation Based on Time-Frequency Analysis and Cross-Correlation Techniques" uses the time-domain amplitude difference between preceding and following power frequency cycles to detect received signals, effectively eliminating the impact of harmonics on power frequency signals and increasing signal strength. The paper "A Practical Power Frequency Communication Uplink Signal Detection Method" proposes a method based on wavelet transforms and the Fast ICA algorithm, effectively suppressing harmonic interference and extracting power frequency communication signals. The paper "A Practical Power Frequency Communication System Signal Detection Method" utilizes correlation detection technology based on time-domain difference technology to detect power frequency signals. The paper "Combined Power Frequency Communication Signal Detection Method" employs an adaptive notch filter combined with a combined algorithm to improve the output signal ratio of power frequency signals. The document "Anti-interference Technology for Power Line Industrial Frequency Communication" proposes complex-valued wavelet analysis anti-interference technology based on an analysis of the characteristics of power line industrial frequency communication signals, background noise and interference factors, which can effectively improve the quality of industrial frequency communication.

[0004] The power frequency signal detection methods described in the aforementioned literature all require a zero-crossing signal as a synchronization signal between the transmitter and receiver. The accuracy of power frequency signal detection depends on the precision of zero-crossing synchronization. Furthermore, in some power distribution network applications, the supply voltage is direct current (DC), making it impossible to obtain a zero-crossing synchronization signal using AC. Therefore, how to detect power frequency carrier signals without relying on a zero-crossing signal is a pressing technical challenge for those skilled in the art. Summary of the Invention

[0005] To overcome the above-mentioned deficiencies of the prior art, the present invention provides a method for detecting a received signal in a power frequency communication system, comprising:

[0006] Obtaining the modulation mode of the power frequency signal to be detected at the receiving end and the modulation signal at the sending end;

[0007] Using a preset window function to intercept the power frequency signal, and performing amplitude subtraction on the intercepted power frequency signal;

[0008] Adding a signal of a preset length at the end of the power frequency signal after the amplitude difference as a cyclic prefix to the front end of the power frequency signal after the amplitude difference, to obtain a power frequency signal with a cyclic prefix;

[0009] Based on the power frequency signal with a cyclic prefix and the modulation mode of the modulation signal at the transmitting end, the modulation signal in the power frequency signal to be detected is identified.

[0010] Preferably, the sliding step of the window function is two power frequency cycles.

[0011] Preferably, the amplitude difference calculation formula is as follows:

[0012] s(i)=r(i+N)-r(i) i=0,...N-1

[0013] Where S(i) is the signal value of the power frequency signal at the i-th sampling point after amplitude difference, r(i) is the signal value corresponding to the i-th sampling point in the first power frequency cycle of the intercepted power frequency signal, r(i+N) is the signal value corresponding to the i-th sampling point in the second power frequency cycle of the intercepted power frequency signal, and N is the number of sampling points of the power frequency signal in one power frequency cycle.

[0014] Preferably, the length of the cyclic prefix is ​​greater than the length of the modulation signal in the power frequency signal.

[0015] Preferably, the calculation formula of the power frequency signal with a cyclic prefix is ​​as follows:

[0016]

[0017] Where S CP (i) is the signal value of the power frequency signal with a cyclic prefix at the i-th sampling point, S(N-l+i) is the signal value of the power frequency signal at the (N-l+i)-th sampling point after amplitude difference, S(il) is the signal value of the power frequency signal at the (il)-th sampling point after amplitude difference, l is the number of sampling points within the cyclic prefix length, and N is the number of sampling points within one power frequency period.

[0018] Preferably, identifying the modulation signal in the power frequency signal to be detected based on the power frequency signal with a cyclic prefix and the modulation mode of the modulation signal at the transmitting end includes:

[0019] Performing template matching on the power frequency signal with the cyclic prefix and the modulated signal stored locally to obtain a template matching output signal;

[0020] Based on the template matching output signal and the modulation mode of the modulation signal at the transmitting end, the modulation signal in the power frequency signal to be detected is identified.

[0021] Preferably, the calculation formula of the template matching output signal is as follows:

[0022]

[0023] Where M(k) is the signal value corresponding to the kth sampling point of the template matching output signal, S CP (k+i) is the signal value corresponding to the (k+i)th sampling point of the power frequency signal with a cyclic prefix, p(i) is the signal value corresponding to the i-th sampling point of the locally stored modulated signal, L is the number of sampling points within the locally stored modulated signal length, and l is the number of sampling points within the cyclic prefix length.

[0024] Preferably, the recognition result calculation formula of the modulation signal is as follows:

[0025] Transmitter modulation mode C1:

[0026] Transmitter modulation mode C2:

[0027] Where R is the recognition result of the modulation signal in the power frequency signal to be detected, M(k) is the signal value corresponding to the kth sampling point of the template matching output signal, λ is the signal detection threshold, and noise is the line noise; C1 and C2 are both the modulation modes of the transmitter.

[0028] Preferably, after the steps of intercepting the power frequency signal using a preset window function and performing amplitude subtraction on the intercepted power frequency signal, and before the step of adding a signal of a preset length at the end of the power frequency signal after the amplitude subtraction as a cyclic prefix to the front end of the power frequency signal after the amplitude subtraction to obtain the power frequency signal with a cyclic prefix, the method further includes performing noise preprocessing on the power frequency signal after the amplitude subtraction, including:

[0029] Perform noise statistics on the power frequency signal after all amplitudes are subtracted within the set noise statistics time to obtain a noise statistical signal;

[0030] Based on the noise statistical signal, the amplitude-differencing power frequency signal is normalized to obtain a normalized amplitude-differencing power frequency signal.

[0031] Preferably, the calculation formula of the noise statistical signal is as follows:

[0032]

[0033] Where n(i) is the signal value of the noise statistical signal at the i-th sampling point, S j (i) is the signal value of the power frequency signal after the jth amplitude difference is made at the i-th sampling point, P is the number of power frequency signals after the amplitude difference is made within the noise statistical period, and N is the number of sampling points of the power frequency signal in one power frequency period.

[0034] Preferably, the calculation formula for normalization is as follows:

[0035]

[0036] Where S norm (i) is the signal value of the power frequency signal at the i-th sampling point after the normalized amplitude difference, n(i) is the signal value of the noise statistical signal at the i-th sampling point, S(i) is the signal value of the power frequency signal at the i-th sampling point after the amplitude difference, and N is the number of sampling points of the power frequency signal in one power frequency cycle.

[0037] Based on the same concept, the present invention also provides a detection system for receiving signals of an industrial frequency communication system, comprising:

[0038] The signal acquisition module is used to obtain the power frequency signal to be detected at the receiving end and the modulation mode of the modulation signal at the sending end;

[0039] an amplitude difference module, configured to intercept the power frequency signal using a preset window function and perform amplitude difference on the intercepted power frequency signal;

[0040] a cyclic prefix adding module, configured to add a signal of a preset length at the end of the power frequency signal after amplitude difference as a cyclic prefix to the front end of the power frequency signal after amplitude difference, thereby obtaining a power frequency signal with a cyclic prefix;

[0041] The signal identification module is used to identify the modulation signal in the power frequency signal to be detected based on the power frequency signal with a cyclic prefix and the modulation mode of the modulation signal at the transmitting end.

[0042] Preferably, the signal recognition module includes:

[0043] A template matching module, configured to perform template matching on the power frequency signal with a cyclic prefix and a locally stored modulated signal to obtain a template matching output signal;

[0044] The end output module is used to identify the modulation signal in the power frequency signal to be detected based on the template matching output signal and the modulation mode of the sending end modulation signal.

[0045] Preferably, the system further includes a noise preprocessing module, the noise preprocessing module including:

[0046] The noise signal generation module is used to perform noise statistics on the power frequency signal after all amplitudes are subtracted within a set noise statistical time period to obtain a noise statistical signal;

[0047] The normalization module is used to perform normalization processing on the power frequency signal after amplitude difference based on the noise statistical signal to obtain a normalized power frequency signal after amplitude difference.

[0048] Compared with the closest prior art, the present invention has the following beneficial effects:

[0049] The present invention provides a method and system for detecting a received signal of an industrial frequency communication system, comprising: obtaining a modulation mode of an industrial frequency signal to be detected at a receiving end and a modulation signal at a transmitting end; intercepting the industrial frequency signal using a preset window function, and performing amplitude subtraction on the intercepted industrial frequency signal; adding a signal of a preset length at the end of the industrial frequency signal after amplitude subtraction as a cyclic prefix to the front end of the industrial frequency signal after amplitude subtraction, to obtain an industrial frequency signal with a cyclic prefix; based on the industrial frequency signal with a cyclic prefix and the modulation mode of the modulation signal at the transmitting end, identifying the modulation signal in the industrial frequency signal to be detected. The industrial frequency signal detection method adopted by the present invention does not require synchronization of the industrial frequency signal to be detected by a zero-crossing signal, thereby achieving accurate detection of the industrial frequency signal, eliminating the need for configuring a zero-crossing signal generating device, reducing hardware overhead, lowering the requirements for the on-site environment for equipment installation and deployment, avoiding errors caused by transformer phase rotation, and improving the accuracy of industrial frequency signal detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic diagram of a method for detecting a received signal in an industrial frequency communication system provided by the present invention;

[0051] Figure 2 A schematic diagram of a detection system for receiving signals of an industrial frequency communication system provided by the present invention;

[0052] Figure 3 This is a structure diagram of an industrial frequency signal modulated in a C1 manner provided in an embodiment of the present invention;

[0053] Figure 4 This is a structure diagram of an industrial frequency signal modulated in a C2 manner provided in an embodiment of the present invention;

[0054] Figure 5A schematic diagram of the structure of power frequency signal detection at a receiving end provided in an embodiment of the present invention;

[0055] Figure 6 A schematic diagram of data interception through a sliding window provided in an embodiment of the present invention;

[0056] Figure 7 A schematic diagram of adding a cyclic prefix provided in an embodiment of the present invention;

[0057] Figure 8 Schematic diagram of template matching output of noise and signal provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0058] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0059] Example 1:

[0060] The embodiment of the present invention provides a method for detecting a received signal of an industrial frequency communication system. Figure 1 As shown, including:

[0061] S1 obtains the power frequency signal to be detected at the receiving end and the modulation mode of the modulation signal at the sending end;

[0062] S2 intercepts the power frequency signal using a preset window function and performs amplitude subtraction on the intercepted power frequency signal; S3 adds a signal of a preset length at the end of the power frequency signal after the amplitude subtraction as a cyclic prefix to the front end of the power frequency signal after the amplitude subtraction, thereby obtaining a power frequency signal with a cyclic prefix;

[0063] S4 identifies the modulation signal in the power frequency signal to be detected based on the power frequency signal with the cyclic prefix and the modulation mode of the modulation signal at the transmitting end.

[0064] Before transmitting information through power frequency signals, signal modulation is required, that is, artificially generating power frequency waveform distortion near the zero crossing point of the power frequency carrier signal to generate a modulated signal to represent the information to be transmitted. During signal modulation, two adjacent power frequency cycle waveforms are used to represent one bit of information, so that one of the power frequency cycle waveforms contains the modulated signal and the other power frequency cycle waveform remains unchanged. There are two ways to generate the modulated signal: Generate the modulated signal in C1 mode. Its structure is shown in the figure below. Figure 3 As shown, the first power frequency cycle contains the modulation signal, indicating "1", and the second power frequency cycle contains the modulation signal, indicating "0". The modulation signal is generated in the C2 mode, and its structure is shown in FIG. Figure 4As shown, the first power frequency cycle contains the modulated signal, representing a "0," while the second power frequency cycle contains the modulated signal, representing a "1." The power frequency signal period, T, is 20 ms. Transmitting one bit of information takes 40 ms, so the power frequency signal transmission rate is 1 / 40 ms = 25 bits / s. The modulation method of the power frequency signal is determined by the signal transmitter and receiver.

[0065] The structural diagram of the power frequency signal detection at the receiving end is as follows Figure 5 As shown, it mainly includes: sliding window, amplitude difference, noise statistics, normalization, adding cyclic prefix, template matching, determining the maximum value, and modulated signal recognition. Specifically:

[0066] 1. Subtraction of sliding window and amplitude

[0067] A window function is pre-set, and a data segment is intercepted from the received signal by sliding the window function. The length is two power frequency cycles, that is, 2T = 40ms, and the sliding step is 2T. The amplitude difference module subtracts the second half of the data intercepted by the sliding window from the first half, that is:

[0068] s(i)=r(i+N)-r(i) i=0,...N-1 (1)

[0069] Where r is the output signal of the sliding window, S(i) is the signal value of the power frequency signal at the i-th sampling point after amplitude difference, r(i) is the signal value corresponding to the i-th sampling point in the first power frequency cycle of the intercepted power frequency signal, r(i+N) is the signal value corresponding to the i-th sampling point in the second power frequency cycle of the intercepted power frequency signal, and N is the number of sampling points of the power frequency signal in one power frequency cycle.

[0070] The noise at the receiving end of power-frequency communication is primarily composed of whole harmonics, with the 50Hz component being the largest, followed by the various harmonics. The higher the harmonic order, the smaller the amplitude. Using amplitude difference can filter out most interference from the fundamental and harmonics, effectively acting as digital filtering and improving anti-interference capabilities.

[0071] 2. Noise preprocessing

[0072] To reduce the impact of input signal amplitude fluctuations on detection accuracy at the receiving end and improve the ability to resist line noise, line noise statistics and normalization processing are required before signal template matching. Noise statistics are performed during channel idle periods (i.e., when power frequency modulated signals are transmitted):

[0073]

[0074] Among them, the noise statistical duration is 2P power frequency cycles, n(i) is the signal value of the noise statistical signal at the i-th sampling point, S j(i) is the signal value of the power frequency signal at the i-th sampling point after the j-th 40ms amplitude difference, P is the number of power frequency signals after the amplitude difference in the noise statistical period, and N is the number of sampling points of the power frequency signal in one power frequency period. The normalized signal is:

[0075]

[0076] Where S norm (i) is the signal value of the power frequency signal at the i-th sampling point after the normalized amplitude difference, n(i) is the signal value of the noise statistical signal at the i-th sampling point, S(i) is the signal value of the power frequency signal at the i-th sampling point after the amplitude difference, and N is the number of sampling points of the power frequency signal in one power frequency cycle.

[0077] 3. Add a cyclic prefix

[0078] Since the zero-crossing signal is not used, the relative position of the power frequency modulation signal in the data intercepted by the sliding window is not fixed. Figure 6 As shown in the figure, the black part is the power frequency modulation signal. The data intercepted by sliding window 1 contains the complete power frequency modulation signal within a power frequency cycle, while the data intercepted by sliding window 2 contains the second half of the modulation signal of the first power frequency cycle and the first half of the modulation signal of the third power frequency cycle. The peak energy will be dispersed during template matching, thereby reducing the accuracy of power frequency signal detection. Therefore, a cyclic prefix is ​​added to the normalized data segment (such as Figure 7 As shown), the data with the last length of the data segment of l is placed at the front of the data segment, that is:

[0079]

[0080] Where S CP (i) is the signal value of the power frequency signal with a cyclic prefix at the i-th sampling point, S(N-l+i) is the signal value of the power frequency signal at the (N-l+i)-th sampling point after amplitude difference, S(il) is the signal value of the power frequency signal at the (il)-th sampling point after amplitude difference, l is the number of sampling points within the cyclic prefix length, and N is the number of sampling points within one power frequency period.

[0081] from Figure 7 As can be seen from the figure, adding a cyclic prefix allows for the assembly of a complete power frequency modulated signal, ensuring peak energy concentration during template matching. The data length after adding the cyclic prefix is ​​N+l. To ensure that a complete power frequency modulated signal can still be assembled in certain extreme scenarios, the cyclic prefix length l must be greater than the length of the power frequency modulated signal.

[0082] 4. Signal detection

[0083] Finally, the data after adding the cyclic prefix is ​​template matched with the locally stored modulated signal:

[0084]

[0085] Where p is the modulated signal template stored locally, M(k) is the signal value corresponding to the kth sampling point of the template matching output signal, and S CP (k+i) is the signal value corresponding to the (k+i)th sampling point of the power frequency signal with a cyclic prefix, p(i) is the signal value corresponding to the i-th sampling point of the locally stored modulated signal, L is the number of sampling points within the locally stored modulated signal length, and l is the number of sampling points within the cyclic prefix length.

[0086] Figure 8 is the template matching output. The line-dot curve is the template matching result for the power frequency modulated signal. It can be seen that there is one negative peak and two positive peaks, while the template matching output for noise has no obvious peaks. By finding the maximum value of |M(k)| and the positive and negative polarity of M(k), it is sent to the modulation signal detection module and compared with the threshold value to identify the received signal:

[0087] Transmitter modulation mode C1:

[0088] Transmitter modulation mode C2:

[0089] Wherein, k=0,…,N+lL, R represents the recognition result of the received signal, λ is the preset threshold value, and if the maximum value of |M(k)| is less than the threshold value, it means that the received signal is line noise and there is no modulation signal from the transmitter.

[0090] Example 2:

[0091] The embodiment of the present invention discloses a detection system for receiving signals of an industrial frequency communication system, such as Figure 2 As shown, including:

[0092] The signal acquisition module is used to obtain the power frequency signal to be detected at the receiving end and the modulation mode of the modulation signal at the sending end;

[0093] an amplitude difference module, configured to intercept the power frequency signal using a preset window function and perform amplitude difference on the intercepted power frequency signal;

[0094] a cyclic prefix adding module, configured to add a signal of a preset length at the end of the power frequency signal after amplitude difference as a cyclic prefix to the front end of the power frequency signal after amplitude difference, thereby obtaining a power frequency signal with a cyclic prefix;

[0095] The signal identification module is used to identify the modulation signal in the power frequency signal to be detected based on the power frequency signal with a cyclic prefix and the modulation mode of the modulation signal at the transmitting end.

[0096] Preferably, the signal recognition module includes:

[0097] A template matching module, configured to perform template matching on the power frequency signal with a cyclic prefix and a locally stored modulated signal to obtain a template matching output signal;

[0098] The end output module is used to identify the modulation signal in the power frequency signal to be detected based on the template matching output signal and the modulation mode of the sending end modulation signal.

[0099] Preferably, the system further includes a noise preprocessing module, the noise preprocessing module including:

[0100] The noise signal generation module is used to perform noise statistics on the power frequency signal after all amplitudes are subtracted within a set noise statistical time period to obtain a noise statistical signal;

[0101] The normalization module is used to perform normalization processing on the power frequency signal after amplitude difference based on the noise statistical signal to obtain a normalized power frequency signal after amplitude difference.

[0102] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0103] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0104] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0105] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit its scope of protection. Although the present application has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that after reading this application, those skilled in the art may still make various changes, modifications or equivalent substitutions to the specific implementation methods of the application, but these changes, modifications or equivalent substitutions are all within the scope of protection of the pending claims of the application.

Claims

1. A method for detecting a received signal in an industrial frequency communication system, characterized in that: include: Obtaining the modulation mode of the power frequency signal to be detected at the receiving end and the modulation signal at the sending end; Using a preset window function to intercept the power frequency signal, and performing amplitude subtraction on the intercepted power frequency signal; Adding a signal of a preset length at the end of the power frequency signal after the amplitude difference as a cyclic prefix to the front end of the power frequency signal after the amplitude difference, to obtain a power frequency signal with a cyclic prefix; Identifying the modulation signal in the power frequency signal to be detected based on the power frequency signal with a cyclic prefix and the modulation mode of the modulation signal at the transmitting end; A window function is pre-set, and a data segment is intercepted from the received signal by sliding the window function. The length is two power frequency cycles, that is, 2T = 40ms, and the sliding step is 2T. The amplitude difference module subtracts the second half of the data intercepted by the sliding window from the first half. The amplitude difference calculation formula is as follows: s(i)=r(i+N)-r(i)i=0,...N-1 Where S(i) is the signal value of the power frequency signal at the i-th sampling point after the amplitude difference is made, r(i) is the signal value corresponding to the i-th sampling point in the first power frequency cycle of the intercepted power frequency signal, r(i+N) is the signal value corresponding to the i-th sampling point in the second power frequency cycle of the intercepted power frequency signal, and N is the number of sampling points of the power frequency signal in one power frequency cycle; The noise at the receiving end of power frequency communication is mainly composed of whole harmonics, among which the 50Hz component is the largest, followed by each harmonic. The higher the harmonic order, the smaller the amplitude. Because the zero-crossing signal is not used, the relative position of the power frequency modulation signal in the data intercepted by the sliding window is not fixed; the data intercepted by sliding window 1 contains the complete power frequency modulation signal within one power frequency cycle, while the data intercepted by sliding window 2 contains the second half of the modulation signal of the first power frequency cycle and the first half of the modulation signal of the third power frequency cycle; Therefore, a cyclic prefix is ​​added to the normalized data segment, and the data with a length of 1 at the end of the data segment is placed at the front of the data segment. That is, the calculation formula of the power frequency signal with a cyclic prefix is ​​as follows: Where S CP (i) is the signal value of the power frequency signal with a cyclic prefix at the i-th sampling point, S(N-l+i) is the signal value of the power frequency signal at the (N-l+i)-th sampling point after amplitude difference, S(il) is the signal value of the power frequency signal at the (il)-th sampling point after amplitude difference, l is the number of sampling points within the cyclic prefix length, and N is the number of sampling points within one power frequency period.

2. The method according to claim 1, wherein The length of the cyclic prefix is ​​greater than the length of the modulation signal in the power frequency signal.

3. The method according to claim 1, wherein The identifying of the modulation signal in the power frequency signal to be detected based on the modulation mode of the power frequency signal with the cyclic prefix and the modulation signal of the transmitting end includes: Performing template matching on the power frequency signal with the cyclic prefix and the modulated signal stored locally to obtain a template matching output signal; Based on the template matching output signal and the modulation mode of the modulation signal at the transmitting end, the modulation signal in the power frequency signal to be detected is identified.

4. The method according to claim 3, wherein The calculation formula of the template matching output signal is as follows: Where M(k) is the signal value corresponding to the kth sampling point of the template matching output signal, S CP (k+i) is the signal value corresponding to the (k+i)th sampling point of the power frequency signal with a cyclic prefix, p(i) is the signal value corresponding to the i-th sampling point of the locally stored modulated signal, L is the number of sampling points within the locally stored modulated signal length, and l is the number of sampling points within the cyclic prefix length.

5. The method according to claim 3, wherein The recognition result calculation formula of the modulation signal is as follows: Transmitter modulation mode C1: k=0,…,N+1L Transmitter modulation mode C2: Where R is the recognition result of the modulation signal in the power frequency signal to be detected, M(k) is the signal value corresponding to the kth sampling point of the template matching output signal, λ is the signal detection threshold, and noise is the line noise; C1 and C2 are both the modulation modes of the transmitter.

6. The method according to claim 1, wherein After the steps of intercepting the power frequency signal using a preset window function and performing amplitude subtraction on the intercepted power frequency signal, and before the step of adding a signal of a preset length at the end of the power frequency signal after the amplitude subtraction as a cyclic prefix to the front end of the power frequency signal after the amplitude subtraction to obtain the power frequency signal with a cyclic prefix, the method further includes performing noise preprocessing on the power frequency signal after the amplitude subtraction, including: Perform noise statistics on the power frequency signal after all amplitudes are subtracted within the set noise statistics time to obtain a noise statistical signal; Based on the noise statistical signal, the amplitude-differencing power frequency signal is normalized to obtain a normalized amplitude-differencing power frequency signal.

7. The method according to claim 6, wherein The calculation formula of the noise statistical signal is as follows: Where n(i) is the signal value of the noise statistical signal at the i-th sampling point, S j (i) is the signal value of the power frequency signal after the jth amplitude difference is made at the i-th sampling point, P is the number of power frequency signals after the amplitude difference is made within the noise statistical period, and N is the number of sampling points of the power frequency signal in one power frequency period.

8. The method according to claim 6, wherein The calculation formula for the normalization process is as follows: Where S norm (i) is the signal value of the power frequency signal at the i-th sampling point after the normalized amplitude difference, n(i) is the signal value of the noise statistical signal at the i-th sampling point, S(i) is the signal value of the power frequency signal at the i-th sampling point after the amplitude difference, and N is the number of sampling points of the power frequency signal in one power frequency cycle.

9. A detection system for receiving signals of an industrial frequency communication system, characterized in that: include: The signal acquisition module is used to obtain the power frequency signal to be detected at the receiving end and the modulation mode of the modulation signal at the sending end; an amplitude difference module, configured to intercept the power frequency signal using a preset window function and perform amplitude difference on the intercepted power frequency signal; a cyclic prefix adding module, configured to add a signal of a preset length at the end of the power frequency signal after amplitude difference as a cyclic prefix to the front end of the power frequency signal after amplitude difference, thereby obtaining a power frequency signal with a cyclic prefix; A signal identification module, configured to identify a modulation signal in the power frequency signal to be detected based on the power frequency signal with a cyclic prefix and a modulation mode of the modulation signal at the transmitting end; The amplitude difference module is specifically used to: pre-set a window function, intercept a piece of data from the received signal by sliding the window function, the length of which is two power frequency cycles, that is, 2T=40ms, and the sliding step is 2T; the amplitude difference module subtracts the second half of the data intercepted by the sliding window from the first half, that is, the amplitude difference calculation formula is as follows: s(i)=r(i+N)-r(i)i=0,...N-1 Where S(i) is the signal value of the power frequency signal at the i-th sampling point after the amplitude difference is made, r(i) is the signal value corresponding to the i-th sampling point in the first power frequency cycle of the intercepted power frequency signal, r(i+N) is the signal value corresponding to the i-th sampling point in the second power frequency cycle of the intercepted power frequency signal, and N is the number of sampling points of the power frequency signal in one power frequency cycle; The cyclic prefix adding module is specifically used for: the noise at the power frequency communication receiving end is mainly composed of whole harmonics, among which the 50Hz component is the largest, followed by each harmonic, and the higher the harmonic order, the smaller the amplitude; Because the zero-crossing signal is not used, the relative position of the power frequency modulation signal in the data intercepted by the sliding window is not fixed; the data intercepted by sliding window 1 contains the complete power frequency modulation signal within one power frequency cycle, while the data intercepted by sliding window 2 contains the second half of the modulation signal of the first power frequency cycle and the first half of the modulation signal of the third power frequency cycle; Therefore, a cyclic prefix is ​​added to the normalized data segment, and the data with a length of 1 at the end of the data segment is placed at the front of the data segment. That is, the calculation formula of the power frequency signal with a cyclic prefix is ​​as follows: Where S cP (i) is the signal value of the power frequency signal with a cyclic prefix at the i-th sampling point, S(N-l+i) is the signal value of the power frequency signal at the (N-l+i)-th sampling point after amplitude difference, S(il) is the signal value of the power frequency signal at the (il)-th sampling point after amplitude difference, l is the number of sampling points within the cyclic prefix length, and N is the number of sampling points within one power frequency period.

10. The system according to claim 9, wherein: The signal recognition module includes: A template matching module, configured to perform template matching on the power frequency signal with a cyclic prefix and a locally stored modulated signal to obtain a template matching output signal; The end output module is used to identify the modulation signal in the power frequency signal to be detected based on the template matching output signal and the modulation mode of the sending end modulation signal.

11. The system according to claim 9, wherein The system further includes a noise preprocessing module, the noise preprocessing module including: The noise signal generation module is used to perform noise statistics on the power frequency signal after all amplitudes are subtracted within a set noise statistical time period to obtain a noise statistical signal; The normalization module is used to perform normalization processing on the power frequency signal after amplitude difference based on the noise statistical signal to obtain a normalized power frequency signal after amplitude difference.

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