Direct current power line carrier communication method and system

Abstract

The present disclosure relates to a direct current power line carrier communication method and system. The method comprises: obtaining a plurality of channel quality evaluation parameters of a direct current power line channel; performing fusion processing on the plurality of channel quality evaluation parameters to obtain a comprehensive channel quality score; obtaining a preset first threshold and a second threshold; when the comprehensive channel quality score is higher than the first threshold and the current modulation mode is FSK mode, switching to OFDM mode; when the comprehensive channel quality score is lower than the second threshold and the current modulation mode is OFDM mode, switching to FSK mode; when the comprehensive channel quality score is between the first threshold and the second threshold, maintaining the current working mode; and modulating and transmitting coal mine underground communication data under the selected modulation mode. The present disclosure can improve the rate when the channel is good, guarantee the connectivity when the channel deteriorates, and avoid frequent mode oscillation.

Description

Technical Field

[0001] This disclosure relates to the field of wired data communication technology in underground coal mines, and in particular to a DC power line carrier communication method and system. Background Technology

[0002] In the field of DC power line carrier communication (DC-PLC), the channel environment of long-distance power lines exhibits significant characteristics such as strong attenuation, high noise, and time-varying load. Typical transmission media, such as drill pipes, suffer from severe selective frequency attenuation of high-frequency signals during long-distance transmission due to distributed parameter effects. Existing single-carrier modulation schemes, such as frequency shift keying (FSK), while possessing strong anti-attenuation capabilities, suffer from low spectral efficiency, making it difficult to support high-speed data transmission requirements. While multi-carrier schemes, such as orthogonal frequency division multiplexing (OFDM), can improve data rates, they are susceptible to inter-carrier interference in complex time-varying channels, making reliability difficult to guarantee. Furthermore, existing technologies lack systematic optimization solutions for long-distance DC lines, resulting in an inherent contradiction between communication rate and transmission distance, which restricts the application and development of intelligent monitoring services in complex scenarios such as underground drilling. Summary of the Invention

[0003] To overcome the problems existing in related technologies, this disclosure provides a DC power line carrier communication method and system.

[0004] According to a first aspect of the present disclosure, a DC power line carrier communication method is provided, comprising: Multiple channel quality evaluation parameters of a DC power line channel are obtained; the DC power line channel is used for underground communication in coal mines. Multiple channel quality evaluation parameters are fused together to obtain a comprehensive channel quality score. Obtain a preset first threshold and a second threshold; the first threshold is higher than the second threshold. When the overall channel quality score is higher than the first threshold and the current modulation mode is FSK mode, switch to OFDM mode; when the overall channel quality score is lower than the second threshold and the current modulation mode is OFDM mode, switch to FSK mode; when the overall channel quality score is between the first threshold and the second threshold, maintain the current working mode. The underground communication data in the coal mine is modulated and transmitted in the selected modulation mode.

[0005] According to a second aspect of the present disclosure, a DC power line carrier communication system is provided, comprising: The in-hole communication terminal includes a sensor measurement unit, a signal conditioning circuit, a dual-mode PLC modulation unit, a coupling circuit, and a data acquisition controller. The sensor measurement unit is connected to the signal conditioning circuit, the signal conditioning circuit is connected to the data acquisition controller, the data acquisition controller is connected to the dual-mode PLC modulation unit, the dual-mode PLC modulation unit is connected to the coupling circuit, and the coupling circuit is connected to the through-drill pipe. The in-hole communication terminal is used to collect downhole engineering parameters and communicate via a DC power line. The external communication terminal includes an intrinsically safe DC power supply module, a coupling circuit, a dual-mode PLC modulation unit, a protocol management controller, and an RS485 communication unit. The intrinsically safe DC power supply module is connected to the dual-mode PLC modulation unit and the protocol management controller. The coupling circuit is connected to the dual-mode PLC modulation unit and the cable-carrying drill rod. The dual-mode PLC modulation unit is connected to the protocol management controller. The protocol management controller is connected to the RS485 communication unit. The RS485 communication unit is used to connect to a host computer. The external communication terminal is used to communicate with the internal communication terminal and interact with the host computer. The cable-driven drill rod serves as a transmission channel shared by DC power supply and high-frequency communication, connecting the coupling circuit of the in-hole communication terminal and the coupling circuit of the out-of-hole communication terminal. Both the coupling circuit of the in-hole communication terminal and the coupling circuit of the out-of-hole communication terminal include a carrier coupling unit and a carrier processing unit. The carrier coupling unit is used to couple high-frequency carrier signals on the power supply line, and the carrier processing unit is connected to the carrier coupling unit for carrier signal modulation and demodulation. The in-hole communication terminal and the out-of-hole communication terminal execute the method of any one of claims 1 to 7 through the dual-mode PLC modulation unit.

[0006] The technical solutions provided by the embodiments of this disclosure can include the following beneficial effects: by acquiring multiple channel quality evaluation parameters of the DC power line channel in real time and integrating them into a comprehensive score, a comprehensive perception of the time-varying channel state is achieved; by forming a hysteresis interval through a preset first threshold and a second threshold, the system switches from FSK to OFDM to ensure high-speed data transmission when the channel quality is good, and falls back from OFDM to FSK to ensure link connectivity when the channel quality deteriorates, and maintains the current mode unchanged when the channel quality is between the two thresholds, effectively avoiding frequent mode oscillations caused by small fluctuations in channel quality at the threshold boundaries; the data to be transmitted is modulated in the selected modulation mode and transmitted through the DC power line, enabling the communication system to adaptively meet the dual requirements of high-bandwidth data transmission and long-distance reliable connectivity on long-distance DC power lines according to real-time channel conditions.

[0007] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0008] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0009] Figure 1 This is a flowchart illustrating a DC power line carrier communication method according to an exemplary embodiment.

[0010] Figure 2 This is a schematic diagram illustrating a channel quality assessment and adaptive handover process according to an exemplary embodiment.

[0011] Figure 3 This is a schematic diagram illustrating a DC power line carrier communication system according to an exemplary embodiment.

[0012] Figure 4 This is a schematic diagram of an in-hole communication terminal according to an exemplary embodiment.

[0013] Figure 5 This is a schematic diagram of an external communication terminal according to an exemplary embodiment.

[0014] Figure 6 This is a schematic diagram of a PLC power line carrier transmission channel according to an exemplary embodiment.

[0015] Figure 7 This is a schematic diagram of a carrier coupling unit according to an exemplary embodiment.

[0016] Figure 8 This is a schematic diagram of a carrier processing unit according to an exemplary embodiment. Detailed Implementation

[0017] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure.

[0018] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of this disclosure. The singular forms "a" and "the" as used in this disclosure are also intended to include the plural forms unless the context clearly indicates otherwise.

[0019] It should be understood that although the terms first, second, third, etc., may be used to describe various information in embodiments of this disclosure, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of embodiments of this disclosure, and similarly, second information may also be referred to as first information. Depending on the context, the words “if” and “suppose” as used herein may be interpreted as “when”, “when”, or “in response to a determination”.

[0020] Furthermore, various forms of processes shown in the embodiments of this disclosure can be used to reorder, add, or delete steps. For example, the steps described in this disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this disclosure can be achieved, and no limitation is imposed herein.

[0021] It should be noted that the collection, storage, use, processing, transmission, provision, and disclosure of user personal information involved in the technical solution disclosed herein all comply with the provisions of relevant laws and regulations and do not violate public order and good morals.

[0022] Figure 1 This is a flowchart illustrating a DC power line carrier communication method according to an exemplary embodiment, such as... Figure 1 As shown, it should be noted that the DC power line carrier communication method of this disclosure embodiment is applied in a DC power line carrier communication device. For example... Figure 1 As shown, the method may include the following steps: Step 101: Obtain multiple channel quality evaluation parameters for the DC power line channel.

[0023] Among them, the DC power line channel is used for underground communication in coal mines.

[0024] In some embodiments of this disclosure, step 101 may specifically include the following sub-steps: Step a1 involves real-time detection and analysis of the received signal to obtain multiple channel quality evaluation parameters for the DC power line channel.

[0025] Specifically, channel quality evaluation parameters are the core basis for measuring the current transmission quality of DC power line channels. In the scenario of underground cable-driven drill pipes in coal mines, DC power line channels have significant characteristics such as strong attenuation, high noise, and time-varying load. To comprehensively perceive the channel status, embodiments of this disclosure acquire channel quality evaluation parameters from multiple dimensions.

[0026] As an example, a dual-mode power line carrier chip on the receiving side can simultaneously extract various physical layer parameters of the channel when demodulating the received signal.

[0027] It should be noted that the "receiving side" here refers to the party currently receiving data. When the communication terminal inside the hole uploads data to the communication terminal outside the hole, the communication terminal outside the hole is the receiving side; when the communication terminal outside the hole sends instructions to the communication terminal inside the hole, the communication terminal inside the hole is the receiving side.

[0028] These parameters may include, but are not limited to, bit error rate, signal-to-noise ratio, received signal strength, carrier frequency offset, and channel impulse response length.

[0029] By comprehensively acquiring multiple parameters, the risk of a single parameter failing or being misjudged under specific operating conditions can be avoided, providing sufficient data support for subsequent mode switching decisions. It should be noted that all of the above parameters can be extracted in real time at the receiving end using existing digital signal processing technology, without requiring additional hardware overhead.

[0030] In some embodiments of this disclosure, the channel quality evaluation parameters in step 101 include at least bit error rate, signal-to-noise ratio, and received signal strength.

[0031] Specifically, the Bit Error Rate (BER) is the ratio of the number of erroneous bits after statistical demodulation at the receiver to the total number of received bits, and it is the most direct indicator of the transmission reliability of a digital communication system. The Signal-to-Noise Ratio (SNR) is the ratio of the signal power to the noise power estimated by the receiver using pilot signals or training sequences, reflecting the relative strength of the effective signal and background noise in the channel. The Received Signal Strength Indication (RSSI) is a measure of signal strength obtained by measuring the amplitude or energy of the received signal. These three parameters characterize channel quality from three different dimensions: transmission correctness, signal purity, and signal energy, and they complement each other.

[0032] In some embodiments of this disclosure, the channel quality evaluation parameters in step 101 further include carrier frequency offset and channel impulse response length.

[0033] Specifically, Carrier Frequency Offset (CFO) is a parameter extracted and tracked by the OFDM demodulation module at the receiver, reflecting the deviation between the receiver's local oscillator frequency and the transmitter's carrier frequency. In OFDM systems, the orthogonality between subcarriers requires precise alignment of their frequencies. Excessive carrier frequency offset can disrupt this orthogonality, leading to severe inter-carrier interference (ICI). Channel Impulse Response Length (CFO) is a parameter estimated based on multipath delay spread, reflecting the degree of time dispersion of the signal reaching the receiver via multiple paths. In long-distance cable-driven drilling, signal reflection and multipath effects are significant; a longer CFO indicates more severe inter-symbol interference (ISI).

[0034] Step 102: The multiple channel quality evaluation parameters are fused to obtain the comprehensive channel quality score.

[0035] In some embodiments of this disclosure, step 102 may specifically include the following sub-steps: Step b1: Multiple channel quality evaluation parameters are fused using a weighted fusion method to generate a comprehensive channel quality score.

[0036] As an example, the overall channel quality score can be calculated using the following formula: Q = w1·SNR + w2·(1 - BER) + w3·RSSI norm Where Q is the overall channel quality score; SNR is the signal-to-noise ratio, measured in decibels, representing the ratio of received signal power to noise power; a higher SNR indicates a cleaner channel; BER is the bit error rate, the ratio of the number of erroneous bits after statistical demodulation at the receiver to the total number of received bits; a lower BER indicates more reliable transmission; RSSI norm The normalized received signal strength indicator is obtained by measuring the amplitude or energy of the received signal and normalizing it to the [0,1] interval; w1, w2, and w3 are preset weight coefficients, and satisfy w1+w2+w3=1. The magnitude of each weight coefficient reflects the importance of the corresponding parameter in the channel quality evaluation, and can be flexibly adjusted according to the specific application scenario.

[0037] It should be noted that the weighted fusion method described above integrates channel quality parameters from multiple dimensions into a single scalar score Q. This avoids the one-sidedness of evaluating a single parameter and provides a unified quantitative basis for subsequent threshold comparison decisions. The adjustability of the weight coefficients allows the method disclosed in this publication to adapt to different preferences between communication rate and reliability in different scenarios. For example, in scenarios where reliability needs to be prioritized, the weight w2 related to the bit error rate can be appropriately increased. The formula above uses (1 - BER) instead of BER itself as the weighting term because a lower BER indicates better channel quality, which is consistent with the physical meaning that higher SNR and RSSI indicate better channel quality. Therefore, a larger Q value represents better channel quality.

[0038] Step 103: Obtain the preset first threshold and second threshold; the first threshold is higher than the second threshold.

[0039] In some embodiments of this disclosure, step 103 specifically includes: reading a preset first threshold Th from a system register or non-volatile memory. H Second threshold Th L .

[0040] Specifically, the first threshold Th H The first threshold is the high threshold, used to determine whether the conditions for switching from low-rate mode to high-rate mode are met; the second threshold is Th. L The lower threshold is used to determine whether the conditions for switching from high-rate mode to low-rate mode are met. Both thresholds satisfy Th L <Th H The relationship between the two thresholds is such that the difference between them constitutes the hysteresis interval. This dual-threshold design ensures that the system will not trigger mode switching when the channel quality fluctuates slightly around the threshold, thus effectively avoiding the problem of frequent mode oscillations.

[0041] As an example, the first and second thresholds can be preset and stored during system initialization based on the target communication rate requirements and channel characteristics, or they can be dynamically adjusted based on historical statistical data during system operation.

[0042] In some embodiments of this disclosure, before performing step 104 to select the modulation mode based on the comparison results of the comprehensive channel quality score and the first threshold and the second threshold, the following pre-judgment step is also performed: Step e1: Determine whether the absolute value of the carrier frequency offset is greater than the first frequency offset threshold Th. CFO .

[0043] Step e2, if the absolute value of the carrier frequency offset is greater than the first frequency offset threshold Th CFO If the OFDM mode is unavailable, the system will force a switch to FSK mode.

[0044] Step e3: Determine whether the channel impulse response length is greater than the length threshold Th. ISI .

[0045] Step e4, if the channel impulse response length is greater than the length threshold Th ISI If the OFDM mode is unavailable, the system will force a switch to FSK mode.

[0046] Step e5, only when the absolute value of the carrier frequency offset is less than or equal to the first frequency offset threshold Th CFO And the channel impulse response length is less than or equal to the length threshold Th ISI Only when the time is right will the handover decision process based on the comprehensive channel quality score in step 104 be allowed.

[0047] Specifically, carrier frequency offset and channel impulse response length are the "hard prerequisites" for OFDM mode to function properly, and their mechanisms of action differ from those of signal-to-noise ratio (SNR), bit error rate (BER), and received signal strength. SNR, BER, and received signal strength reflect the quality of the channel, can tolerate a certain degree of variation, and provide a quantitative score; while carrier frequency offset and channel impulse response length reflect the feasibility of OFDM demodulation. Once a certain threshold is exceeded, the orthogonality between OFDM subcarriers will collapse instantly, and no matter how high the SNR or how strong the received signal, the demodulated data will be garbled.

[0048] Therefore, these two types of parameters serve as prerequisites for handover decisions or for determining the availability of OFDM mode. When both carrier frequency offset and channel impulse response length meet the basic operating requirements of OFDM mode, subsequent handover decisions based on comprehensive scoring are allowed; otherwise, the system directly forces a handover to FSK mode, and the scoring comparison process in step 104 is no longer executed. This prerequisite judgment mechanism effectively avoids communication interruptions caused by attempting to use OFDM mode when the OFDM demodulation conditions are not met, further improving system reliability.

[0049] In some embodiments of this disclosure, before selecting the modulation mode in step 104 based on the comparison result of the comprehensive channel quality score with the first threshold and the second threshold, the method further includes: determining the multipath delay spread based on the channel impulse response length; when the multipath delay spread exceeds a preset level, increasing the first threshold by a first preset step size and increasing the second threshold by a second preset step size.

[0050] Specifically, the multipath delay spread is positively correlated with the channel impulse response length; the longer the channel impulse response length, the higher the multipath delay spread. When the multipath delay spread exceeds a preset level, it means that the channel frequency-selective fading intensifies, and the orthogonality between OFDM subcarriers is more easily disrupted. At this point, the system increases the first threshold Th by a first preset step size. HAnd increase the second threshold Th by the second preset step size. L Raising the first threshold makes the conditions for the system to switch from FSK to OFDM more stringent, requiring a higher overall channel quality score to switch to OFDM mode. Raising the second threshold makes the conditions for switching from OFDM to FSK more lenient; even a slight decrease in channel quality may trigger a switch to FSK. The overall effect of simultaneously raising the two thresholds is to shift the system's mode selection strategy towards FSK mode, meaning that under conditions of severe multipath propagation, it is more inclined to use the FSK mode, which has stronger multipath resistance. It should be noted that the first and second preset step sizes can be the same value or different values, and can be set according to the system's preference for OFDM and FSK modes in the actual application scenario.

[0051] Step 104: When the overall channel quality score is higher than the first threshold and the current modulation mode is FSK mode, switch to OFDM mode; when the overall channel quality score is lower than the second threshold and the current modulation mode is OFDM mode, switch to FSK mode; when the overall channel quality score is between the first threshold and the second threshold, maintain the current working mode.

[0052] In some embodiments of this disclosure, step 104 may specifically include the following sub-steps: Step c1: Compare the overall channel quality score Q with the first threshold Th. H and the second threshold Th L Compare them.

[0053] Step c2, based on the comparison result, perform the following mode switching decision: when Q>Th H And when the current modulation mode is FSK mode, switch to OFDM mode; when Q <Th L And when the current modulation mode is OFDM, switch to FSK mode; when Th L ≤ Q≤ Th H Regardless of the current mode, the current working mode will remain unchanged and will not be switched.

[0054] Specifically, in the above decision logic, the hysteresis interval formed by the first threshold being higher than the second threshold is a key mechanism to avoid frequent mode oscillations. As channel quality gradually improves from a poor state, the system needs a Q value that exceeds a higher Th value. H Only then will the system switch from FSK to OFDM; conversely, when the channel quality gradually deteriorates from a good state, the system needs a Q value lower than a lower Th value. LOnly then will it switch from OFDM to FSK. This asymmetric switching boundary gives the system "inertia" when the channel quality fluctuates around a threshold. Once switched to a certain mode, the system tends to maintain that mode until the channel quality changes significantly enough before switching again.

[0055] It should be noted that FSK mode is a single-carrier frequency shift keying modulation method, which represents binary data by changing the carrier frequency. It has the advantages of being insensitive to amplitude attenuation and having strong resistance to impulse noise. OFDM mode is an orthogonal frequency division multiplexing multi-carrier modulation method, which distributes high-speed data streams to multiple mutually orthogonal subcarriers for parallel transmission. It has the advantages of high spectrum utilization and high data transmission rate. This disclosure, through the above-mentioned dual-threshold hysteresis switching mechanism, adopts OFDM mode to pursue high speed when the channel quality is good, switches to FSK mode to ensure connectivity when the channel quality deteriorates, and maintains the status quo to avoid oscillation when the channel quality is critical, thus achieving an adaptive balance between speed and reliability.

[0056] Step 105: Modulate and transmit underground communication data in the selected modulation mode.

[0057] In some embodiments of this disclosure, step 105 may specifically include the following sub-steps: Step d1: Pack the underground communication data to be transmitted in the coal mine into a pre-set frame structure format.

[0058] Step d2 involves modulating the packaged data using a dual-mode power line carrier chip in the selected modulation mode.

[0059] Step d3 involves injecting the modulated high-frequency signal into the DC power line via a coupling circuit for transmission.

[0060] Specifically, underground communication data in coal mines can include underground engineering parameters such as drilling pressure, torque, triaxial vibration, rotational speed, annular pressure, and temperature, collected by in-hole communication terminals.

[0061] As an example, a frame structure may include a frame header, a payload, and a check field. The frame header carries the current modulation mode identifier and a timestamp, the payload carries compressed or encoded engineering parameter data, and the check field is used by the receiver for bit error detection.

[0062] The dual-mode power line carrier chip modulates the packaged baseband data into a corresponding high-frequency carrier signal according to the modulation mode (OFDM or FSK) selected in step 104. The modulated high-frequency signal is injected into the DC power line channel formed by the cable drill rod through the DC blocking capacitor and coupling transformer in the coupling circuit, realizing data transmission from the communication terminal inside the borehole to the communication terminal outside the borehole.

[0063] It should be noted that by modulating the data to be transmitted in the selected modulation mode and transmitting it through the DC power line, this disclosure realizes adaptive data communication on a long-distance DC power line according to real-time channel conditions. It can ensure high-speed data transmission when the channel conditions are good, and maintain basic communication without interruption when the channel conditions are poor.

[0064] In some embodiments, such as Figure 2 As shown, after power-on, the system first initializes and establishes an initial communication link using FSK mode to ensure the reliability of the basic connection under unknown channel conditions. After the link is established, multi-dimensional channel quality parameters are continuously collected during communication, including bit error rate, signal-to-noise ratio, received signal strength indication, carrier frequency offset, and channel impulse response length. The collected parameters are weighted and fused to generate a comprehensive channel quality score Q. Subsequently, the system executes multi-level decisions in parallel: when the Q value is higher than a high threshold Th... H If the current mode is FSK, switch to OFDM mode to pursue high-speed transmission; if the Q value is lower than the low threshold Th... L If the current mode is OFDM, it switches to FSK mode to ensure connectivity. When the communication distance exceeds a preset length or the received signal strength is below a preset lower limit, FSK mode is forcibly used or the OFDM subcarrier modulation order is reduced to cope with long-distance attenuation. When a remote switching command is received or manual intervention is required, it forcibly switches to the specified working mode according to the command. If none of the above conditions are met, the current mode remains unchanged. After completing the mode selection and switching, the data to be transmitted is packaged and transmitted through the selected modulation mode, and then the next round of quality acquisition and decision loop begins, thereby realizing adaptive mode scheduling and reliable transmission throughout the communication process.

[0065] In some embodiments of this disclosure, the method further includes: Obtain the communication distance of the DC power line channel; When the communication distance exceeds the preset length, long-distance speed reduction processing is performed; Long-distance speed reduction processing includes: if the current mode is OFDM, switch to FSK mode first; if the communication rate is lower than the preset lower limit after switching to FSK mode, maintain OFDM mode and reduce the subcarrier modulation order of OFDM mode from the current order to the next order.

[0066] Specifically, communication distance refers to the physical length of the transmission link formed between the external communication terminal and the internal communication terminal via the drill pipe cable. As an example, the communication distance can be calculated based on the difference between the received signal strength and a preset reference value for the transmitted signal strength, combined with the attenuation coefficient per unit length of the DC power line. Alternatively, the communication distance can be estimated using the signal-to-noise ratio and bit error rate (BER) parameters from the channel quality evaluation parameters, combined with a preset channel attenuation model. Obtaining the communication distance provides a basis for special handling in long-distance operating conditions.

[0067] Specifically, the preset length can be pre-set based on the electrical characteristics of the cable drill rod and actual test data, for example, it can be set to 1.5 kilometers. When the communication distance exceeds this preset length, signal attenuation intensifies, frequency-selective attenuation in the high-frequency band becomes severe, and the orthogonality between OFDM mode subcarriers is at risk of being compromised. At this point, long-distance speed reduction processing is required to ensure communication reliability.

[0068] Specifically, the communication distance refers to the physical length of the transmission link formed by the external and internal communication terminals via the drill rod. It can be calculated based on the difference between the received signal strength and a preset reference value for the transmitted signal strength, combined with the attenuation coefficient per unit length of the DC power line. Alternatively, it can be estimated using the signal-to-noise ratio and bit error rate combined with a preset channel attenuation model. When the communication distance exceeds the preset length (e.g., 1.5 km), signal attenuation intensifies, frequency-selective attenuation in the high-frequency band becomes severe, and the orthogonality between OFDM subcarriers risks being compromised. In this case, long-distance speed reduction processing is required. The long-distance speed reduction process employs a progressive speed reduction strategy: First, it attempts to switch to FSK mode because FSK uses a single carrier frequency and is significantly less sensitive to frequency-selective fading than OFDM, ensuring reliable connectivity at a lower data rate over long distances. If the communication rate cannot meet data transmission requirements after switching to FSK, OFDM mode is maintained, but the subcarrier modulation order is reduced (e.g., from Quadrature Phase Shift Keying (QPSK) to Binary Phase Shift Keying (BPSK)) to weaken OFDM's sensitivity to channel orthogonality disruption, achieving a trade-off between rate and reliability. It should be noted that this long-distance speed reduction process effectively supplements the automatic handover decision in step 104. Under long-distance conditions, even if the overall channel quality score has not yet triggered the handover conditions in step 104, the system will proactively perform speed reduction to proactively mitigate the risk of communication interruption due to excessive distance.

[0069] It should be noted that the aforementioned long-distance speed reduction process effectively supplements the automatic handover decision in step 104. Under long-distance operating conditions, even if the overall channel quality score has not yet triggered the handover condition in step 104, the system will proactively perform speed reduction processing to proactively avoid the risk of communication interruption due to excessive distance.

[0070] In some embodiments of this disclosure, the method further includes the following steps: receiving a remotely issued forced switching command; and switching to a specified modulation mode according to the forced switching command.

[0071] Specifically, in addition to automatic switching based on comprehensive channel quality scoring and long-distance speed reduction processing based on communication distance, this disclosure also provides an interface for manual intervention. The external communication terminal can send a forced switching command to the internal communication terminal via downlink commands, carrying a target modulation mode identifier (OFDM or FSK). Upon receiving the command, the internal communication terminal immediately switches its current modulation mode to the mode specified in the command and can carry a confirmation message of successful switching in the reply frame. This remote forced switching mechanism meets the need for manual intervention in special operating conditions, such as in downhole equipment debugging, fault diagnosis, or specific testing scenarios. Operators can manually specify the communication mode according to the actual situation, enhancing the system's flexibility and maintainability.

[0072] In some embodiments of this disclosure, the link connection is established using FSK mode during the initial stage of communication.

[0073] Specifically, after the system is powered on, the external communication terminal and the internal communication terminal first establish an initial communication link using FSK mode. The reason for choosing FSK mode instead of OFDM mode in the initial stage is that FSK mode has advantages such as simple circuit structure, insensitivity to amplitude attenuation, and strong resistance to impulse noise. When the system is first powered on, the channel state has not yet been fully assessed; using FSK mode can ensure the establishment of the basic connection with a lower bit error rate, laying the foundation for subsequent channel quality assessment and mode switching. After the link is established and channel quality evaluation parameters begin to be collected and reported normally, the system then decides whether to switch to OFDM mode based on the real-time channel quality. It should be noted that using FSK mode in the initial stage also facilitates interconnection with existing FSK-based power line carrier communication equipment.

[0074] According to the DC power line carrier communication method proposed in this disclosure, multiple channel quality evaluation parameters of the DC power line channel are acquired in real time and fused into a comprehensive score, thereby achieving comprehensive perception of the time-varying channel state. A hysteresis interval is formed by a preset first threshold and a second threshold. When the channel quality is good, the system switches from FSK to OFDM to ensure high-speed data transmission. When the channel quality deteriorates, the system switches back from OFDM to FSK to ensure link connectivity. When the channel quality is between the two thresholds, the current mode remains unchanged, effectively avoiding frequent mode oscillations caused by small fluctuations in channel quality at the threshold boundaries. The data to be transmitted is modulated in the selected modulation mode and transmitted through the DC power line, enabling the communication system to adaptively meet the dual requirements of high-bandwidth data transmission and long-distance reliable connectivity on long-distance DC power lines according to real-time channel conditions.

[0075] Figure 3 This is a block diagram illustrating a DC power line carrier communication system according to an exemplary embodiment. (Refer to...) Figure 3 The system includes an in-hole communication terminal 301, an out-of-hole communication terminal 302, and a cable-connecting drill rod 303.

[0076] The in-hole communication terminal 301 (STA, Station) includes a sensor measurement unit, a signal conditioning circuit, a dual-mode PLC modulation unit, a coupling circuit, and a data acquisition controller. The sensor measurement unit is connected to the signal conditioning circuit, which in turn is connected to the data acquisition controller. The data acquisition controller is connected to the dual-mode PLC modulation unit, which is connected to the coupling circuit. The coupling circuit is connected to the through-drill pipe. The in-hole communication terminal is used to acquire downhole engineering parameters and communicate via a DC power line.

[0077] Specifically, the sensor measurement unit may include a drill pressure sensor (strain gauge force sensor), a torque sensor (torque strain sensor), a triaxial vibration sensor, a speed sensor, annular pressure sensor, and a temperature sensor, used to acquire downhole engineering parameters. The signal conditioning circuit may include an instrumentation amplifier, a low-pass filter, a multiplexer, and an analog-to-digital converter, used to amplify, filter, and digitize the weak signals output by the sensors. The dual-mode PLC modulation unit consists of a dual-mode power line carrier chip and its peripheral circuitry, supporting software configuration for both OFDM and FSK modulation modes. The coupling circuit includes a DC blocking capacitor, a coupling transformer, and a bandpass filter, used to inject the modulated high-frequency signal into the drill pipe and separate the received signal from the DC bus. The data acquisition controller (MCU, Microcontroller Unit) is responsible for multi-channel synchronous data acquisition, parameter calibration and compensation, data packet encoding, modulation mode switching decision, and communication protocol processing.

[0078] In one embodiment, such as Figure 4 As shown, the input signal of the in-hole communication terminal module is a composite signal from the cable-driven drill rod. This signal simultaneously carries DC power supply and high-frequency carrier communication data on the same pair of conductors. The composite signal first enters the coupling circuit, where the high-frequency carrier signal is separated and extracted from the DC bus. The extracted high-frequency signal is then sent to the signal conditioning circuit for filtering and amplitude shaping. The processed signal is then sent to the dual-mode PLC modulation unit for demodulation. After demodulation, the baseband data is obtained and transmitted to the data acquisition controller.

[0079] Meanwhile, the DC power separated by the coupling circuit is sent to the power management unit, which converts the input 18V DC voltage into 5V and 3.3V to provide operating power for the sensor measurement unit, data acquisition controller and dual-mode PLC modulation unit, respectively.

[0080] The sensor measurement unit is used to collect downhole engineering parameters. Its weak output signal is amplified, filtered and converted from analog to digital by the signal conditioning circuit before being sent to the data acquisition controller.

[0081] The data acquisition controller performs synchronous sampling, calibration compensation, and data packet encoding on the one hand, and receives downlink commands demodulated from the PLC modulation unit on the other hand. Based on the channel quality evaluation results, it executes modulation mode switching decisions and sends the packetized uplink data to the dual-mode PLC modulation unit for modulation. The modulated high-frequency signal is then fed back to the cable drill rod through the coupling circuit to realize bidirectional communication with the external communication terminal.

[0082] Through the above methods, the embodiments of this disclosure achieve integrated power supply reception, signal separation and extraction, sensor data acquisition, dual-mode modulation and demodulation, and mode switching decision within the in-hole communication terminal.

[0083] The external communication terminal 302 (CCO, Central Coordinator) includes an intrinsically safe DC power supply module, a coupling circuit, a dual-mode PLC modulation unit, a protocol management controller, and an RS485 communication unit. The intrinsically safe DC power supply module connects to the dual-mode PLC modulation unit and the protocol management controller. The coupling circuit connects the dual-mode PLC modulation unit to the cable-carrying drill rod. The dual-mode PLC modulation unit connects to the protocol management controller, and the protocol management controller connects to the RS485 communication unit, which is used to connect to a host computer. The external communication terminal 302 communicates with the internal communication terminal and interacts with the host computer.

[0084] Specifically, the intrinsically safe DC power supply module converts AC power (e.g., 127VAC) to DC power (e.g., 18VDC), connecting to the drill rod outside the borehole via wires to power the equipment inside the borehole. The coupling circuit has the same structure as the coupling circuit in the borehole communication terminal, used to achieve co-line transmission of DC power supply and high-frequency signals. The dual-mode PLC modulation unit is paired with the dual-mode PLC modulation unit in the borehole communication terminal, using the same model of dual-mode carrier chip to complete signal demodulation and modulation. The protocol management controller is responsible for communication protocol management, data verification and storage, switching command issuance, and interaction with the host computer. The RS485 communication unit is used to transmit the parsed engineering parameters to the host computer via the RS485 bus.

[0085] In one embodiment, such as Figure 5As shown, the input sources of the borehole communication terminal module include two paths: one is an externally supplied 127V AC power supply. This AC power is first fed into an intrinsically safe DC power supply module, which converts the 127V AC power into intrinsically safe 18V DC power. This DC power is then fed into the power management unit for voltage conversion, providing an appropriate operating voltage for the dual-mode PLC modulation unit and protocol management controller within the module. On the other hand, it is injected into the cable-connected drill rod through the DC blocking inductor in the coupling circuit, providing remote DC power supply to the equipment inside the borehole. The other path is a power line carrier signal from the cable-connected drill rod. This signal simultaneously carries DC power supply and high-frequency communication data on the cable-connected drill rod. After the composite signal enters the coupling circuit, the coupling circuit separates and extracts the high-frequency carrier signal from the DC bus. The extracted high-frequency signal is then sent to the dual-mode PLC modulation unit for demodulation. After demodulation, the baseband data is obtained and transmitted to the protocol management controller. The protocol management controller (MCU) is responsible for two aspects: firstly, managing the communication protocol, verifying and storing data, and facilitating bidirectional data exchange with the dual-mode PLC modulation unit; secondly, it transmits the parsed downhole engineering parameters to the RS485 communication unit, which converts the data into RS485 signals and uploads them to the host computer via twisted-pair cable. For the downlink direction, the protocol management controller receives instructions from the host computer via the RS485 communication unit, processes them according to the protocol, and then sends them to the dual-mode PLC modulation unit for modulation. The modulated high-frequency signal is injected into the drill pipe via a coupling circuit, enabling bidirectional communication with the in-hole communication terminal.

[0086] Through the above methods, this embodiment of the present disclosure realizes the integrated integration of AC power input and intrinsically safe DC-DC conversion, collinear coupling of DC power and high-frequency signals, dual-mode modulation and demodulation, protocol management and RS485 bus communication in the external communication terminal, and completes the full-link functions of ground power supply, underground power transmission and bidirectional data communication.

[0087] The cable-connecting drill rod 303 serves as a transmission channel shared by DC power supply and high-frequency communication, connecting the coupling circuit of the communication terminal inside the borehole and the coupling circuit of the communication terminal outside the borehole.

[0088] Specifically, the cable-connected drill pipe is a mining-grade center-connected drill pipe with an integrated independent signal cable (coaxial cable). The drill pipe sections are cascaded in multiple stages via electromagnetic couplers within the joints or through physical connections, thus supporting long-distance transmission with a total length exceeding 2 kilometers. The equivalent circuit of each drill pipe consists of a series resistor R, a series inductance L, a parallel capacitor C, and a parallel conductance G, exhibiting a typical distributed parameter transmission line model.

[0089] The in-hole communication terminal and the out-of-hole communication terminal execute any of the aforementioned methods through a dual-mode PLC modulation unit.

[0090] In some embodiments, such as Figure 6 As shown, the external communication terminal module and the internal communication terminal module are connected by a cable drill rod to form a complete DC power line carrier communication link.

[0091] Specifically, the external communication terminal module is placed outside the borehole and is connected to the external section of the cable-driven drill rod extending into the borehole via a wire. The cable-driven drill rod is a mining center-type cable-driven drill rod with an integrated independent signal cable. Each section of the drill rod is cascaded in multiple stages through an electromagnetic coupler or physical connection in the joint, extending from the external section to the internal section at the bottom of the borehole, forming a long-distance transmission channel with a total length of more than 2 kilometers. The internal communication terminal module is placed inside the measuring probe at the bottom of the borehole and is also connected to the end of the internal section of the cable-driven drill rod.

[0092] During communication, the external communication terminal module injects DC power and a high-frequency carrier signal into the through-hole drill pipe via a coupling circuit. This composite signal is transmitted along the external section of the drill pipe to the internal section, reaching the internal communication terminal module. The internal communication terminal module extracts DC power from the received composite signal to power itself, and simultaneously extracts the high-frequency carrier signal for demodulation to receive downlink commands. For the uplink direction, the internal communication terminal module modulates the collected downhole engineering parameters into a high-frequency carrier signal, injects it into the internal section of the through-hole drill pipe via a coupling circuit, and transmits this signal in the reverse direction along the drill pipe to the external section, where it is received and demodulated by the external communication terminal module to upload data.

[0093] In some embodiments of this disclosure, a carrier coupling unit is used to couple a high-frequency carrier signal onto a power supply line, and a carrier processing unit is connected to the carrier coupling unit for carrier signal modulation and demodulation.

[0094] In some embodiments, such as Figure 7 As shown, the carrier coupling unit includes fuse F1, diode D3, diode D4, inductor U4, inductor U5, capacitor C18, and capacitor C6, wherein: The DC input positive terminal IN_VCC is connected in series with fuse F1, diode D3 anode, diode D4 anode, and inductor U4, and then the PLC+ carrier signal terminal is output. The DC input negative terminal IN_GND is split into two paths: one path leads out to the PLC-carrier signal terminal, and the other path is connected in series with inductor U5 and then grounded to GND. The end of inductor U4 furthest from diode D4 is connected in parallel with capacitors C18 and C6, and the other ends of capacitors C18 and C6 are grounded to GND. Diodes D3 and D4 are connected in series in the same direction to form a bidirectional reverse connection clamping branch. Inductor U4 is connected in series to the positive terminal of the carrier circuit, and inductor U5 is connected in series to the negative terminal grounding branch. Capacitors C18 and C6 are connected in parallel between PLC+ and ground.

[0095] In this embodiment, the carrier coupling unit is integrated into the front end of the coupling circuit of the in-hole communication terminal or the out-of-hole communication terminal. Relying on the long-distance DC power transmission channel formed by the drill rod, it connects to the back-end carrier processing unit via PLC+ and PLC- ports, and works with the dual-mode PLC modulation unit to achieve OFDM / FSK adaptive carrier communication. The 18V intrinsically safe DC power supply in the coal mine is connected to the unit via IN_VCC and IN_GND. In the power transmission path, IN_VCC is connected in series with an overcurrent protection patch fuse F1, diodes D3 and D4 connected in series in the same direction, and a DC blocking choke inductor U4, before leading out to the PLC+ carrier signal terminal. IN_GND is divided into two paths: one directly leads out to the PLC- carrier signal terminal to transmit high-frequency communication signals to the subsequent carrier processing unit; the other is connected in series with a choke inductor U5 and then connected to the system ground GND. A capacitor C18 is connected in parallel at the end of inductor U4 furthest from diode D4. C6 and both have the other end grounded. Fuse F1 uses an organosilicon potting structure to meet the intrinsic safety and explosion-proof requirements of the well. It can quickly melt and cut off the high-voltage DC circuit when the line is short-circuited or overloaded. D3 and D4 are connected in series in the same direction to form a reverse connection clamping branch, which can block the reverse connection of the positive and negative poles of the power supply and instantaneous surge high voltage, and avoid damage to the downstream dual-mode PLC modulation unit and carrier chip. Choke inductors U4 and U5 have the electrical characteristics of passing DC and blocking high frequency. 18V DC power can be fed to the terminal in the well hole without obstruction along the power supply path. At the same time, it constrains the OFDM / FSK high frequency carrier signal of the PLC+ and PLC- ports, preventing the carrier from leaking to the external DC power input terminal and ground GND, which greatly reduces the signal attenuation and noise interference caused by long-distance cable drill pipe. C18 and C6 connected in parallel form a DC power filter network to filter out the power ripple and broadband noise generated by the start and stop of the line load, and stabilize the power supply level of the coupling unit.

[0096] It should be noted that the carrier coupling unit physically isolates the DC power supply path from the high-frequency carrier communication path, retaining the modulated carrier signal completely only at the PLC+ and PLC- ports and transmitting it to the back-end carrier processing unit. After the isolation transformer completes the electrical isolation, the signal is sent to the dual-mode carrier chip. With the system's multi-parameter channel quality assessment and dual-threshold hysteresis adaptive switching mechanism, it ensures the complete transmission of OFDM high-speed signals when the communication distance is short, the channel SNR is high, and the bit error rate is low. In long-distance downhole conditions with depths exceeding 1.5km, severe signal attenuation, and intense pulse noise, it can still stably retain the FSK low-frequency carrier signal, providing a clean and low-loss carrier signal interface for the system to automatically switch to the more reliable FSK mode. It simultaneously realizes the intrinsically safe DC long-distance power supply and dual-mode carrier co-line coupling transmission, solving multiple technical problems such as carrier signal leakage, power supply noise interference, and damage to the communication chip due to reverse connection overcurrent in long-distance DC lines.

[0097] In some embodiments, such as Figure 8As shown, the carrier processing unit includes an isolation transformer T1, a transient suppression diode D9, a transient suppression diode D10, a capacitor C14, a resistor R16, a resistor R17, a resistor R20, a resistor R21, a capacitor C16, a capacitor C17, and a carrier chip U12. A transient suppression diode D9 and a capacitor C14 are connected in parallel between the external bus terminals PLC+ and PLC-. PLC+ and PLC- are respectively connected to the first primary pin (pin 8) and the second primary pin (pin 5) of the isolation transformer T1. A transient suppression diode D10 is connected in parallel between the first secondary pin (pin 3) and the second secondary pin (pin 4) of the isolation transformer T1; The first pin of the secondary winding of T1 is connected to the PLC- of the carrier chip U12 via resistor R16, and the second pin of the secondary winding of T1 is connected to the PLC+ pin of the carrier chip U12 via resistor R17. Capacitors C16 and C17 are connected in parallel between the 3.3V pin and the GND pin of the carrier chip U12. The PLC RX signal is connected to the RX0 pin of U12 via resistor R20, and the PLC TX signal is connected to the TX0 pin of U12 via resistor R21.

[0098] In this embodiment, the carrier processing unit is connected to the front-end carrier coupling unit via PLC+ and PLC- terminals. The OFDM / FSK high-frequency carrier signal from the cable drill pipe first passes through the transient suppression diode D9 connected in parallel between PLC+ and PLC- to absorb line-induced surges and electrostatic high voltage. Capacitor C14 isolates the 18V DC voltage transmitted by the line, allowing only the AC carrier signal to pass through and be sent to the primary winding of the isolation transformer T1. T1 achieves electrical isolation between the underground DC side and the back-end carrier chip, eliminating ground loop interference and meeting the intrinsically safe explosion-proof requirements of coal mines. The secondary winding of the isolation transformer... A transient voltage suppressor diode D10 is connected in parallel to clamp the voltage spikes generated by the transformer coupling to protect the downstream chips. The carrier signal output from the secondary side is fed into the PLC- and PLC+ signal pins of the carrier chip U12 via current-limiting matching resistors R16 and R17 to achieve impedance matching and suppress signal reflection distortion. Capacitors C16 and C17 are connected in parallel between the 3.3V power supply terminal and GND to filter out high-frequency power supply ripple and stabilize the chip's operating voltage. During uplink demodulation, U12 completes carrier signal demodulation to obtain the raw downhole sensing data, which is buffered by current-limiting resistor R20 and output to the PLC chip via the RX0 pin. When transmitting RX data downlink, the control commands issued by the host computer are current-limited by R21 and sent to the TX0 pin. The corresponding OFDM or FSK high-frequency carrier is generated by U12 modulation and then transmitted back to the carrier coupling unit via R16, R17, isolation transformer T1, C14, and PLC+ / PLC- to the drill pipe. The entire unit, together with the channel quality assessment and adaptive mode switching logic of the dual-mode PLC modulation unit, can transmit broadband OFDM signals completely under the high-quality channel in shallow holes, and can also stably demodulate narrowband FSK signals under long-distance, strong attenuation, and high impulse noise conditions. It provides signal isolation, surge protection, impedance matching and integrated modulation and demodulation processing capabilities for downhole bidirectional dual-mode power line carrier communication.

[0099] According to the DC power line carrier communication system proposed in this embodiment, by multiplexing DC power supply and high-frequency carrier transmission channel through cable-connected drill pipe, the in-hole communication terminal can completely collect downhole engineering parameters such as drilling pressure, torque, and vibration. After signal conditioning and data acquisition controller processing, the data is uploaded through dual-mode PLC modulation unit and coupling circuit. The out-of-hole communication terminal relies on intrinsically safe DC power supply to complete the remote power supply in the well. After receiving downhole data, it is synchronously uploaded to the host computer through protocol management controller and RS485 unit, and can also send control commands to the in-hole terminal. The coupling circuit splits the carrier coupling unit and carrier processing unit to complete power supply isolation, carrier signal coupling and modulation and demodulation in stages. At the hardware level, DC power and OFDM / FSK dual-mode carrier signal are made co-linear. With interference-free transmission and a dual-mode PLC modulation unit, it can perform complete communication control logic such as adaptive channel evaluation, dual-threshold hysteresis mode switching, long-distance speed reduction, and remote forced switching. It can achieve high-speed engineering waveform data transmission by relying on OFDM when the shallow hole channel is excellent, and can switch to FSK in the 2km long distance, high noise, and time-varying load of the underground DC line to ensure that the critical control commands are not interrupted. It can balance communication speed and long-distance transmission reliability without the need for additional relay equipment. The entire terminal is modularly integrated and relies on the existing drill pipe cable network, resulting in low deployment cost. At the same time, the circuit layer isolation protection structure meets the intrinsic safety and explosion-proof requirements of underground coal mines, and can be stably adapted to the real-time monitoring and bidirectional control scenarios of underground directional drilling measurement while drilling.

[0100] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein.

[0101] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A DC power line carrier communication method, characterized in that, include: Obtain multiple channel quality evaluation parameters for the DC power line channel; The DC power line channel is used for underground communication in coal mines; Multiple channel quality evaluation parameters are fused together to obtain a comprehensive channel quality score. Obtain a preset first threshold and a second threshold; the first threshold is higher than the second threshold. When the overall channel quality score is higher than the first threshold and the current modulation mode is FSK mode, switch to OFDM mode; when the overall channel quality score is lower than the second threshold and the current modulation mode is OFDM mode, switch to FSK mode; when the overall channel quality score is between the first threshold and the second threshold, maintain the current working mode. The underground communication data in the coal mine is modulated and transmitted in the selected modulation mode.

2. The method according to claim 1, characterized in that, The channel quality evaluation parameters include at least the bit error rate, signal-to-noise ratio, and received signal strength; The process of fusing the channel quality evaluation parameters to generate a comprehensive channel quality score includes: The overall channel quality score is calculated using the following formula: Q = w1·SNR + w2·(1-BER) + w3·RSSI norm Where Q is the overall channel quality score, SNR is the signal-to-noise ratio, BER is the bit error rate, and RSSI is... norm The normalized received signal strength is defined by w1, w2, and w3, which are preset weighting coefficients that satisfy w1 + w2 + w3 = 1.

3. The method according to claim 1, characterized in that, The channel quality evaluation parameters also include carrier frequency offset and channel impulse response length; Before selecting the modulation mode based on the comparison result of the comprehensive channel quality score with the first threshold and the second threshold, the method further includes: If the absolute value of the carrier frequency offset is greater than the first frequency offset threshold, the OFDM mode is determined to be unavailable and the system is forced to switch to FSK mode. If the channel impulse response length is greater than the length threshold, the OFDM mode is determined to be unavailable, and a forced switch to FSK mode is initiated. When the absolute value of the carrier frequency offset is less than or equal to the first frequency offset threshold and the channel impulse response length is less than or equal to the length threshold, the step of selecting the modulation mode based on the comparison result of the channel quality comprehensive score with the first threshold and the second threshold is executed.

4. The method according to claim 1, characterized in that, Also includes: Obtain the communication distance of the DC power line channel; When the communication distance exceeds a preset length, long-distance speed reduction processing is performed; The long-distance deceleration process includes: If the current mode is OFDM, switch to FSK mode first; If the communication rate is lower than the preset lower limit after switching to FSK mode, the OFDM mode will be maintained, and the subcarrier modulation order of OFDM mode will be reduced from the current order to the next level.

5. The method according to claim 1, characterized in that, It also includes the following steps: Receive a forced switch command issued remotely; Switch to the specified modulation mode according to the forced switching command.

6. The method according to claim 1, characterized in that, In the initial stage of communication, the link connection is established using the FSK mode.

7. The method according to claim 1, characterized in that, The channel quality evaluation parameters also include the channel impulse response length; Before selecting the modulation mode based on the comparison result of the comprehensive channel quality score with the first threshold and the second threshold, the method further includes: The degree of multipath delay spread is determined based on the channel impulse response length. When the multipath delay spread exceeds a preset level, the first threshold is increased by a first preset step size and the second threshold is increased by a second preset step size.

8. A DC power line carrier communication system, characterized in that, include: The in-hole communication terminal includes a sensor measurement unit, a signal conditioning circuit, a dual-mode PLC modulation unit, a coupling circuit, and a data acquisition controller. The sensor measurement unit is connected to the signal conditioning circuit, the signal conditioning circuit is connected to the data acquisition controller, the data acquisition controller is connected to the dual-mode PLC modulation unit, the dual-mode PLC modulation unit is connected to the coupling circuit, and the coupling circuit is connected to the through-drill pipe. The in-hole communication terminal is used to collect downhole engineering parameters and communicate via a DC power line. The external communication terminal includes an intrinsically safe DC power supply module, a coupling circuit, a dual-mode PLC modulation unit, a protocol management controller, and an RS485 communication unit. The intrinsically safe DC power supply module is connected to the dual-mode PLC modulation unit and the protocol management controller. The coupling circuit is connected to the dual-mode PLC modulation unit and the cable-carrying drill rod. The dual-mode PLC modulation unit is connected to the protocol management controller. The protocol management controller is connected to the RS485 communication unit. The RS485 communication unit is used to connect to a host computer. The external communication terminal is used to communicate with the internal communication terminal and interact with the host computer. The cable-driven drill rod serves as a transmission channel shared by DC power supply and high-frequency communication, connecting the coupling circuit of the in-hole communication terminal and the coupling circuit of the out-of-hole communication terminal. Both the coupling circuit of the in-hole communication terminal and the coupling circuit of the out-of-hole communication terminal include a carrier coupling unit and a carrier processing unit. The carrier coupling unit is used to couple high-frequency carrier signals on the power supply line, and the carrier processing unit is connected to the carrier coupling unit for carrier signal modulation and demodulation. The in-hole communication terminal and the out-of-hole communication terminal execute the method of any one of claims 1 to 7 through the dual-mode PLC modulation unit.

9. The system according to claim 8, characterized in that, The carrier coupling unit includes a fuse F1, a diode D3, a diode D4, an inductor U4, an inductor U5, a capacitor C18, and a capacitor C6, wherein: The DC input positive terminal IN_VCC is connected in series with fuse F1, diode D3 anode, diode D4 anode, and inductor U4, and then the PLC+ carrier signal terminal is output. The DC input negative terminal IN_GND is split into two paths: one path leads out to the PLC-carrier signal terminal, and the other path is connected in series with inductor U5 and then grounded to GND. The end of inductor U4 furthest from diode D4 is connected in parallel with capacitors C18 and C6, and the other ends of capacitors C18 and C6 are grounded to GND. Diodes D3 and D4 are connected in series in the same direction to form a bidirectional reverse connection clamping branch. Inductor U4 is connected in series to the positive terminal of the carrier circuit, and inductor U5 is connected in series to the negative terminal grounding branch. Capacitors C18 and C6 are connected in parallel between PLC+ and ground.

10. The system according to claim 8, characterized in that, The carrier processing unit includes an isolation transformer T1, a transient suppression diode D9, a transient suppression diode D10, a capacitor C14, a resistor R16, a resistor R17, a resistor R20, a resistor R21, a capacitor C16, a capacitor C17, and a carrier chip U12. A transient suppression diode D9 and a capacitor C14 are connected in parallel between the external bus terminals PLC+ and PLC-. PLC+ and PLC- are respectively connected to the first primary pin and the second primary pin of the isolation transformer T1. A transient suppression diode D10 is connected in parallel between the first and second secondary pins of the isolation transformer T1. The first pin of the secondary winding of T1 is connected to the PLC- of the carrier chip U12 via resistor R16, and the second pin of the secondary winding of T1 is connected to the PLC+ pin of the carrier chip U12 via resistor R17. Capacitors C16 and C17 are connected in parallel between the 3.3V pin and the GND pin of the carrier chip U12. The PLC RX signal is connected to the RX0 pin of U12 via resistor R20, and the PLC TX signal is connected to the TX0 pin of U12 via resistor R21.

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