Multipath interference detection and localization method and system

Abstract

This invention provides a multipath interference detection and localization method and system, comprising: acquiring an original signal sequence and a decision symbol sequence; calculating the difference between the average occurrence interval of symbols corresponding to the outermost positive level and the average occurrence interval of symbols corresponding to the outermost negative level in the decision symbol sequence, and determining whether the absolute value of the difference is greater than a preset existence judgment threshold; acquiring an error signal between the original signal sequence and the decision symbol sequence, and grouping corresponding decision symbols based on the error signal, quantizing the intensity of the multipath interference based on the difference in the error variance of the grouping of symbols corresponding to the outermost level; performing a time-delay autocorrelation operation on the original signal sequence based on the intensity of the multipath interference, determining the multipath delay caused by the multipath interference, and converting the multipath delay into the physical distance of the reflection point. This invention solves the problem of limited functionality in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of high-speed optical communication signal processing technology, specifically relating to a multipath interference detection and positioning method and system. Background Technology

[0002] With the growth of global data traffic, optical communication systems are evolving towards higher transmission rates and longer transmission distances. Against this backdrop, the impact of signal impairments in fiber optic links on system performance is becoming increasingly prominent. Among these, multipath interference (MPI) is one of the key factors limiting the upper limit of system performance.

[0003] Multipath interference mainly originates from optical signal reflections generated at connectors, joints, or fiber defects in optical fiber links. The reflected signals are superimposed on the main signal at the receiving end, forming intensity-dependent noise, which directly leads to signal eye diagram degradation, increased bit error rate, and in severe cases, even interruption of service transmission.

[0004] Currently, the core requirement for effective monitoring of multipath interference in optical communication systems is to achieve non-intrusive real-time monitoring. That is, without modifying the service signal format, interrupting normal data transmission, or occupying additional transmission bandwidth, it is possible to accurately determine the existence of multipath interference, quantify its intensity, and locate the physical position of the reflection point.

[0005] Patent document CN106033998A discloses a method and apparatus for detecting multipath interference. This scheme determines multipath interference by detecting the bit error rate of NRZ and PAM-n optical signals in optical fiber transmission, and adds an MPI detection code to the optical fiber system, thus solving the problem of multipath interference interfering with PAM-n service optical signals in optical fiber systems. However, the method of inserting specific detection codes or zero-power gaps into the signal and analyzing the changes in these specific signals to detect multipath interference is an intrusive detection method, which will affect normal service transmission and bandwidth utilization.

[0006] In existing technologies, some solutions determine multipath interference by statistically analyzing the error signal characteristics of the received signal. However, these methods are not sensitive enough to weak multipath interference scenarios and their computational logic is relatively complex. Other solutions estimate multipath interference intensity and time delay based on the cross-correlation between the error signal and the target signal. While this can achieve localization, its computational process is complex and depends on the accuracy of the error signal; its performance may degrade in certain noisy environments.

[0007] Overall, existing technologies generally suffer from problems such as limited functionality, intrusion into services, high computational complexity, or inability to accurately locate reflection points, making it difficult to simultaneously meet all the requirements of modern high-speed optical communication systems for low cost, high real-time performance, complete functionality, and precise operation and maintenance.

[0008] This problem urgently needs to be solved. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this invention is to provide a multipath interference detection and positioning method and system.

[0010] A multipath interferometry detection and localization method according to the present invention includes: Step S1: Obtain the original signal sequence and the decision symbol sequence; Step S2: Calculate the difference between the average occurrence interval of the symbols corresponding to the outermost positive level and the average occurrence interval of the symbols corresponding to the outermost negative level in the decision symbol sequence, and determine whether the absolute value of the difference is greater than the preset existence judgment threshold; if the result is yes, it is determined that multipath interference exists, and step S3 is executed; if the result is no, the process ends. Step S3: Obtain the error signal between the original signal sequence and the decision symbol sequence, and group the corresponding decision symbols based on the error signal, and quantify the intensity of the multipath interference according to the difference in error variance of the grouping of symbols corresponding to the outermost level. Step S4: Based on the intensity of multipath interference, perform time-delay autocorrelation calculation on the original signal sequence to determine the multipath delay caused by multipath interference, and convert the multipath delay into the physical distance of the reflection point.

[0011] Preferably, the original signal sequence is a sequence of pulse amplitude modulation (PAM-N) signals, where N is an integer greater than 2, and the decision symbol sequence is obtained by hard decision on the original signal sequence.

[0012] Preferably, the time-delay autocorrelation operation is accelerated by Fast Fourier Transform (FFT).

[0013] Preferably, the expression for the physical distance of the reflection point is:

[0014] Where the symbol · represents multiplication, the symbol · represents multiplication. Indicates the division sign. The physical distance to the reflection point is to be determined. It is a multipath delay. The speed of light in a vacuum This represents the average refractive index of the optical fiber link. It is the unit interval duration of the signal.

[0015] Preferably, in step S3, if the intensity of the multipath interference is greater than a preset intensity alarm threshold, an alarm is triggered.

[0016] A multipath interferometry detection and positioning system according to the present invention includes: Module M1: Acquires the original signal sequence and decision symbol sequence; Module M2: Calculates the difference between the average occurrence interval of symbols corresponding to the outermost positive level and the average occurrence interval of symbols corresponding to the outermost negative level in the decision symbol sequence, and determines whether the absolute value of the difference is greater than a preset existence judgment threshold; if the result is yes, it is determined that multipath interference exists and triggers module M3 to work; if the result is no, it ends. Module M3: Acquires the error signal between the original signal sequence and the decision symbol sequence, and groups the corresponding decision symbols based on the error signal, and quantifies the intensity of the multipath interference according to the difference in error variance of the grouping of symbols corresponding to the outermost level; Module M4: Based on the intensity of multipath interference, performs time-delay autocorrelation calculation on the original signal sequence to determine the multipath delay caused by multipath interference, and converts the multipath delay into the physical distance of the reflection point.

[0017] Preferably, the original signal sequence is a sequence of pulse amplitude modulation (PAM-N) signals, where N is an integer greater than 2; the decision symbol sequence is obtained by hard decision on the original signal sequence.

[0018] Preferably, the time-delay autocorrelation operation is accelerated by Fast Fourier Transform (FFT).

[0019] Preferably, the expression for the physical distance of the reflection point is:

[0020] Where the symbol · represents multiplication, the symbol · represents multiplication. Indicates the division sign. The physical distance to the reflection point is to be determined. It is a multipath delay. The speed of light in a vacuum This represents the average refractive index of the optical fiber link. It is the unit interval duration of the signal.

[0021] Preferably, in module M3, if the intensity of the multipath interference is greater than a preset intensity alarm threshold, an alarm is triggered.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention integrates three major functions: existence detection, intensity quantification, and location tracking. Its technical approach is significantly different from existing technologies, and it solves the problem of limited functionality in existing technologies.

[0023] 2. The entire monitoring process provided by this invention only utilizes normally transmitted service signals, without modifying the signal format or inserting any special symbols, and does not affect service transmission and bandwidth utilization. It is seamlessly compatible with existing pulse amplitude modulation optical communication systems. 3. The existence detection and intensity quantization provided by this invention mainly involve difference and variance operations, which have low computational complexity. The autocorrelation operation of the localization step can also be accelerated by fast Fourier transform, making it suitable for low-cost and low-power integrated implementation on hardware such as digital signal processors or field programmable gate arrays. 4. This invention can directly extract multipath delay by performing autocorrelation processing on the original signal, thereby accurately calculating the physical distance of the reflection point. This provides network operation and maintenance personnel with a powerful tool for quickly locating the source of the fault, greatly improving operation and maintenance efficiency.

[0024] 5. The solution provided by this invention is fully functional, realizing existence detection, intensity quantification and location tracking; it is also a non-intrusive monitoring method with high computational efficiency and can accurately locate reflection points, thereby improving operation and maintenance efficiency. Attached Figure Description

[0025] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the process provided by the present invention. Detailed Implementation

[0026] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0027] To address the problems of existing multipath interferometry monitoring schemes, such as intrusion into services, high computational complexity, and incomplete functionality.

[0028] The method of the present invention includes: acquiring the original signal sequence before decision and the decision symbol sequence obtained by hard decision; calculating the difference in the average occurrence interval of the outermost symmetrical level symbols based on the decision symbol sequence, and determining the existence of multipath interference when the difference exceeds a threshold; calculating the error signal between the original signal and the decision symbols, and grouping them according to the decision symbols, and using the difference in the error variance of the outermost level group to quantify the intensity of multipath interference; performing a time-delay autocorrelation operation on the original signal sequence, determining the multipath delay by finding the correlation peak, and calculating the physical distance of the reflection point based on the multipath delay.

[0029] This invention relates to multipath interference, i.e., MPI real-time monitoring and reflection point localization technology, which is applicable to high-speed optical transmission systems using pulse amplitude modulation, i.e., PAM-N, and is particularly suitable for 800G / 1.6T optical modules, optical transmission modulation and demodulation DSP chips, and long-distance optical fiber communication links. It can realize the parallel execution of service transmission and MPI monitoring, and provide a low-complexity, complete interference detection solution for the operation and maintenance of optical communication systems that can locate reflection positions.

[0030] Example 1: This example provides a method and apparatus for detecting, intensity quantizing, and locating reflection points of multipath interference in an optical communication system employing four-level pulse amplitude modulation signals. In one embodiment of the invention, this technical solution will be described in conjunction with the accompanying drawings.

[0031] According to the present invention, a system includes an optical transmitting device, an optical fiber link, and an optical receiving device.

[0032] Optical transmitting equipment generates and transmits optical signals carrying service data, such as four-level pulse amplitude modulation signals. This optical signal is transmitted over long distances via optical fiber links. In these links, reflection points may form due to factors such as connectors, fusion splices, and microcracks in the fiber. When the optical signal passes through these reflection points, a small portion of the optical power is reflected, forming a reflected signal. This reflected signal either propagates in the reverse direction along the fiber link or, after multiple reflections within the link, arrives at the optical receiving equipment along with the main signal. This superposition of the reflected signal and the main signal is known as multipath interference. The optical receiving equipment is responsible for receiving the optical signal that is a mixture of the main signal and the reflected signal, and processing it to recover the original data. It is understood that the methods and apparatus provided in this invention are primarily implemented within the optical receiving equipment, aiming to comprehensively monitor multipath interference in optical fiber links without interrupting normal services.

[0033] The optical receiving device can be a standalone device or a functional entity integrated into an optical module or other optical network unit. In this embodiment, the optical receiving device includes: a signal acquisition and decision module, a level grouping and indexing module, a multipath interference presence detection module, a multipath interference intensity calculation module, a multipath interference location module, a decision alarm and control module, and a parameter storage module. It should be noted that these modules work together to realize the complete process of the multipath interference detection and location method.

[0034] The multipath interference detection and localization method provided in this embodiment of the invention begins with step S10, namely the signal acquisition and preprocessing step. In the optical receiving device, this step is executed by the signal acquisition and decision module. This module first converts the received optical signal into an electrical signal through a photodetector, and then performs a series of digital signal processing steps, such as dispersion compensation, polarization mode dispersion compensation, clock data recovery, and adaptive equalization, to compensate for various linear impairments introduced by the optical fiber link. After processing, before the final hard decision, a high-quality digital signal sequence can be obtained, which is referred to in this invention as the "original signal sequence before decision," denoted as S. To ensure the reliability of subsequent statistical analysis, the acquired sequence S needs to have sufficient length. For example, in this embodiment, the sequence length n can be set to 2 x 10^6. 6 One sampling point.

[0035] Next, the signal acquisition and decision module performs hard decision on the original signal sequence S, obtaining a decision symbol sequence, denoted as sym. For a four-level pulse amplitude modulation signal, it has four ideal normalized levels, such as {-3, -1, +1, +3}. Hard decision means mapping each sample value in the original signal sequence S to the closest ideal level. For example, if the amplitude of a sample point is 1.8, it will be decided as +1; if the amplitude is 2.5, it will be decided as +3. In this way, a decision symbol sequence sym of the same length as the original signal sequence S is generated.

[0036] Meanwhile, the signal acquisition and decision module also calculates the difference between the original signal sequence S and the decision symbol sequence sym, thereby obtaining the error signal sequence err, i.e., err = S - sym. This error signal sequence reflects the deviation between the actual received signal and the ideal signal, including thermal noise, shot noise, and additional noise and distortion introduced by nonlinear damage such as multipath interference.

[0037] After completing step S10, the signal acquisition and decision module outputs the original signal sequence S, the decision symbol sequence sym, and the error signal sequence err to the subsequent processing modules. Specifically, the decision symbol sequence sym is sent to the level grouping and indexing module, the error signal sequence err is sent to the multipath interference intensity calculation module, and the original signal sequence S is sent to the multipath interference position positioning module.

[0038] Subsequently, the process proceeds to step S20, the existence detection step. This step is mainly completed by the multipath interference existence detection module, whose input comes from the level grouping and indexing module. The level grouping and indexing module first processes the received decision symbol sequence sym, traversing the entire sym sequence and recording the position index of each level symbol (-3, -1, +1, +3) in the sequence. For example, four index lists can be generated: index0, index1, index2, and index3, which store all the positions where the symbols -3, -1, +1, and +3 appear, respectively.

[0039] The multipath interference presence detection module calculates the average interval between symmetrical level symbols in the sequence based on these position index information. In a four-level pulse amplitude modulation signal, there are two pairs of symmetrical levels: (+3, -3) and (+1, -1). Understandably, in the ideal case where multipath interference is absent, since the transmitted data is pseudo-random, the distribution of these symmetrical level symbols in the sequence should also be symmetrical and uniform, meaning their average intervals should be approximately equal. However, the introduction of multipath interference disrupts this symmetry.

[0040] The specific calculation process is as follows: For the outermost level +3 and -3, the multipath interference presence detection module uses index lists index3 and index0 to calculate the interval between adjacent symbols and take the average value to obtain the average occurrence intervals t3 and t0. For example, t3 can be obtained by calculating the difference between adjacent elements in index3 and taking their average value. Similarly, for the inner level +1 and -1, the average occurrence intervals t2 and t1 are calculated.

[0041] Then, the multipath interference presence detection module calculates the difference in the average interval between these two pairs of symmetrical levels, obtaining two differences: δ1 = t3 - t0, and δ2 = t2 - t1. In the ideal case without multipath interference, both differences δ1 and δ2 should approach zero. When multipath interference is present, this symmetry is broken, causing δ1 and δ2 to no longer be zero.

[0042] This embodiment of the invention further utilizes the difference between these two values ​​for judgment, i.e., calculating |δ1 - δ2|. When the absolute value of this difference exceeds a preset existence judgment threshold Threshold_delta, it is determined that multipath interference exists in the optical fiber link. It should be noted that this threshold Threshold_delta can be calibrated offline according to system performance requirements and experimental data, and stored in the parameter storage module. This detection method based on the breaking of symbolic distribution symmetry has the advantages of low computational load and fast response speed, and can be used as an efficient preliminary screening method.

[0043] Following step S20, a judgment step is added to determine whether MPI exists. If the multipath interference detection module determines "no," meaning |δ1 - δ2| has not exceeded the threshold, the current link status is considered good, and there is no need to perform subsequent complex intensity quantization and localization. The process can directly end or return to the starting point for the next monitoring cycle. This effectively avoids unnecessary consumption of computational resources.

[0044] If the judgment result is "yes", it indicates that there may be influential multipath interference in the link, and its severity and source location need to be further assessed.

[0045] At this point, the decision alarm and control module will start the multipath interference intensity calculation module and the multipath interference position positioning module for subsequent processing based on the trigger signal of the multipath interference presence detection module, that is, the process enters steps S30 and S40.

[0046] Step S30 is the intensity quantization step, executed by the multipath interferometry intensity calculation module. This module receives the error signal sequence err and the decision symbol sequence sym from the signal acquisition and decision module. Specifically, the multipath interferometry intensity calculation module divides the error signal sequence err into four groups based on the value of the decision symbol sequence sym: err0, err1, err2, and err3. Here, err0 is the set of all error signal samples with a corresponding decision symbol of -3, err1 is the set of all error signal samples with a corresponding decision symbol of -1, and so on.

[0047] The effect of multipath interference on different levels is asymmetric, typically having the most significant impact on the outermost levels with the largest amplitudes, namely +3 and -3. Specifically, in the presence of multipath interference, the dispersion of the error signal corresponding to the outermost level increases significantly. Therefore, this embodiment utilizes this characteristic to quantify the intensity of multipath interference. The multipath interference intensity calculation module calculates the variances of these four sets of error signals: σ0², σ1², σ2², and σ3². Then, the absolute value of the difference between the error variances corresponding to the outermost level is calculated as the quantification index MPI of the multipath interference intensity. strength The expression is: MPI strength = |σ3² - σ0²| The larger the difference, the stronger the multipath interference.

[0048] To obtain an intensity value that conforms to industry practices and has a clear physical meaning, this quantization value MPI can be used. strengthThe multipath interference (MPI) value is converted to a standard multipath interference value in decibels (dB) through a pre-defined mapping relationship. This mapping relationship can be a lookup table or a fitting function f(·), stored in a parameter storage module. For example, through offline experiments, the correspondence between different MPI intensities, i.e., the |σ3² - σ0²| values ​​measured in decibels, is established. In this embodiment, the calculated MPI intensity value is assumed to be -35 dB.

[0049] Simultaneously or subsequently, step S40, the positioning and tracking step, is executed by the multipath interferometry position localization module. This module receives the original signal sequence S before decision from the signal acquisition and decision module. The core idea of ​​localization is that the reflected signal can be considered as a copy of the main signal after a certain time delay and attenuation.

[0050] Therefore, the original signal sequence S should have a temporal correlation with itself corresponding to the multipath delay.

[0051] The multipath interferometry positioning module performs a time-delay autocorrelation operation on the original signal sequence S. The autocorrelation function R(k) is calculated as: R(k) = Σ[S(i) * S(i+k)], where S(i) represents the i-th original received signal sequence, * denotes the product, and k is the number of delayed sampling points. This operation is performed on a series of delay k values ​​to search for a non-zero k value that results in a significant peak in the autocorrelation function. The position of this peak is k. peak This corresponds to the multipath delay caused by multipath interference. The interval is defined as a unit. To avoid misclassifying random fluctuations caused by noise as relevant peaks, a peak threshold, Threshold_peak, needs to be set. Only peaks exceeding this threshold are considered valid. In this embodiment, it is assumed that in k... peak A significant correlation peak was found at =50000, therefore, multipath delay = 50000 UI.

[0052] Obtain multipath delay Then, the physical distance to the reflection point can be calculated.

[0053] The multipath interference positioning module calculates the location based on this formula:

[0054] Mode In Chinese, the symbol · represents multiplication. Indicates the division sign. It is the physical distance to the reflection point to be determined; The multipath delay is obtained through autocorrelation calculation, and here it is 50000 UI; It is the unit interval duration of the signal. For a system with a baud rate of 107 GBd, ≈ 9.3 picoseconds; It is the speed of light in a vacuum, approximately 3 x 10⁻⁶. 8 meters per second; This is the average refractive index of the optical fiber link, a constant related to the optical fiber material, with a typical value of 1.468. The "2" in the denominator is because the signal travels a round trip from the receiver to the reflection point and back to the receiver; therefore, the one-way distance needs to be divided by 2.

[0055] Substitute the above values ​​into the formula: = (50000 * 9.3x10 - ¹² s * 3x10 8 m / s) / (2 * 1.468) ≈ 47547.7 m ≈ 47.5 km.

[0056] Therefore, the multipath interference positioning module concluded that there is a significant reflection point at a distance of approximately 47.5 kilometers from the optical receiving device.

[0057] Finally, the process proceeds to step S50, the evaluation and alarm step. This step is executed by the decision alarm and control module. This module summarizes all information from the multipath interference presence detection module (multipath interference exists), the multipath interference intensity calculation module (intensity is -35dB), and the multipath interference location module (location is 47.5km).

[0058] The decision alarm and control module compares the quantified multipath interference intensity with the intensity alarm threshold MPI_Th stored in the parameter storage module. Assuming the preset alarm threshold is -30dB, since the currently calculated intensity of -35dB is lower than, and thus better than, -30dB, the decision alarm and control module determines that although multipath interference exists, it has not reached a severity level requiring urgent handling, and therefore does not trigger an alarm. However, it will still report the complete monitoring result—multipath interference present, intensity -35dB, location 47.5km—to the network management system via the communication interface for long-term link quality monitoring and trend analysis.

[0059] The entire process from S10 to S50 constitutes a monitoring cycle. The decision alarm and control module can be configured to execute this method periodically, for example, once every 20 milliseconds, thereby achieving real-time and continuous monitoring of multipath interference.

[0060] Example 2: This example aims to illustrate that the method proposed in this invention has good scalability and can be applied to systems that use higher-order modulation formats, such as eight-level pulse amplitude modulation systems.

[0061] In an eight-level pulse amplitude modulation system, the signal has eight normalized ideal levels, such as {-7, -5, -3, -1, +1, +3, +5, +7}. The optical receiving device used in this embodiment can be completely identical in hardware structure to the optical receiving device in Embodiment 1, but the algorithm parameters and some logic of its internal modules need to be adapted for the eight-level pulse amplitude modulation signal.

[0062] Specifically, when making a hard decision, the signal acquisition and decision module maps the original signal sampling points to one of eight ideal levels.

[0063] In the presence detection step, i.e., step S20, the processing logic of the multipath interference presence detection module is also extended accordingly. The eight-level pulse amplitude modulation signal has four pairs of symmetrical levels: (+7, -7), (+5, -5), (+3, -3), and (+1, -1). The multipath interference presence detection module can calculate the average occurrence interval difference between the outermost symmetrical levels, i.e., +7 and -7. Alternatively, as an optional implementation, to improve the robustness of detection, the average interval difference between all four pairs of symmetrical levels can be calculated, and a more complex decision criterion can be designed accordingly. For example, multipath interference can be determined to exist only when the absolute values ​​of multiple differences simultaneously exceed their respective thresholds, or when a weighted combination of these differences exceeds a total threshold. This approach makes the detection more reliable in more complex noise and signal distortion environments.

[0064] In the intensity quantization step, i.e., step S30, the multipath interference intensity calculation module divides the error signal sequence err into eight groups according to eight decision symbols and calculates the eight corresponding error variances, i.e., from σ0² to σ7². Since the impact of multipath interference on signal level is still more significant with larger amplitudes, the optimal index for quantizing multipath interference intensity remains the difference in error variances of the outermost level. That is, the quantized value of multipath interference intensity can be calculated as: MPI strength = |σ7² -σ0²|. The subsequent process of converting to decibel values ​​through the mapping relationship is the same as in Example 1.

[0065] In the positioning and tracking step, i.e., step S40, the workflow of the multipath interferometric positioning module is exactly the same as in Example 1. This is because it directly processes the original signal sequence S before the decision, and its autocorrelation characteristics do not depend on the modulation order of the signal. Therefore, without any modification to the positioning algorithm itself, it can be directly applied to the eight-level pulse amplitude modulation signal to determine the multipath delay and calculate the distance to the reflection point.

[0066] Therefore, the method framework proposed in this invention has inherent flexibility and scalability. Its core principles, namely symmetry breaking, variance difference of outer layer level error, and autocorrelation of the original signal, are not limited to a specific pulse amplitude modulation order. It can be seamlessly applied to eight-level or even higher-order pulse amplitude modulation optical communication systems by simply adjusting the number of decision levels and the grouping logic, thereby supporting the continuous evolution of future optical communication technologies.

[0067] Example 3: This example proposes a computational optimization scheme for the positioning and tracking step, i.e. step S40, in Examples 1 and 2, aiming to reduce the computational complexity of the delay autocorrelation operation and make it more suitable for efficient real-time implementation on hardware with limited computing resources.

[0068] In Example 1, the multipath interferometric location module finds the multipath delay by directly calculating the delay autocorrelation function R(k) = Σ[S(i) * S(i+k)]. When the delay range to be searched is large, i.e., the maximum value of k Kmax is large, corresponding to long-distance fiber optic links, the complexity of this direct calculation method is approximately O(n * Kmax), where n is the length of the signal sequence. For real-time monitoring systems requiring fast response, this may constitute a computational bottleneck.

[0069] This embodiment utilizes the Wiener-Khinchin theorem in signal processing. This theorem states that the power spectral density of a generalized stationary random process is the Fourier transform of its autocorrelation function, and conversely, its autocorrelation function is the inverse Fourier transform of its power spectral density. Based on this, the internal implementation of the multipath interferometry positioning module in this embodiment is modified to employ an accelerated algorithm based on the Fast Fourier Transform.

[0070] The specific working process is as follows: 1. The multipath interference position localization module acquires the original signal sequence S of length n. To use the Fast Fourier Transform (FFT), the sequence is usually padded with zeros to make its length N', where N' is a power of 2 greater than (n+Kmax) to improve computational efficiency. 2. This module calculates the FFT of S to obtain its spectrum F(S). 3. Then, this module calculates the power spectral density P(S) of the signal. For a real signal S, its power spectral density can be obtained by multiplying its spectrum F(S) by its own complex conjugate. Here, the multiplication is done point by point. 4. This module calculates the inverse FFT of the power spectral density P(S), and the result R is the autocorrelation function sequence of the original signal sequence S. 5. After obtaining the autocorrelation function sequence R, the subsequent steps are exactly the same as in Example 1: that is, finding the peak position k in the sequence R that exceeds the preset peak threshold. peak And using this k peak The physical distance is calculated using the multipath delay τ. .

[0071] By employing this method based on Fast Fourier Transform, the overall computational complexity of autocorrelation operations is significantly reduced from O(n * Kmax) to O(N' * log(N')). Considering that N' and n are on the same order of magnitude, this almost always translates to a substantial improvement in computational efficiency, especially in scenarios requiring the search of large time-delay ranges. This optimization makes it possible to implement real-time multipath interferometry localization over long distances and with large time-delay ranges on cost- and power-sensitive digital signal processors or field-programmable gate arrays, greatly enhancing the engineering practicality of the proposed solution.

[0072] Example 4: This example describes how the method and apparatus provided by the present invention can be integrated into a complete optical communication monitoring system and realize automated alarm and data reporting functions, thereby providing a closed-loop solution for network operation and maintenance.

[0073] In this embodiment, the decision alarm and control module in the optical receiving device plays a core system interface and decision-making central role. This module maintains a connection with the upper-layer network management system through a communication interface, such as an Ethernet interface. In addition to storing the various thresholds mentioned in Embodiment 1, the parameter storage module also pre-configures the address of the network management system and the alarm reporting strategy.

[0074] Assume an optical receiving device is periodically monitoring an optical fiber link. During a certain monitoring cycle, the following events occur: 1. The device executes the multipath interference monitoring process described in Example 1 normally, and the multipath interference detection module determines that multipath interference exists. 2. The multipath interference intensity calculation module calculates the current multipath interference intensity to be -28dB. 3. The multipath interference location module calculates the distance to the reflection point to be 2.1 kilometers. 4. All results are sent to the decision alarm and control module. This module reads the intensity alarm threshold MPI_Th from the parameter storage module as -30dB. 5. The decision alarm and control module compares the results and finds that -28dB > -30dB, meaning the current multipath interference intensity has exceeded the alarm threshold. At this point, the module immediately triggers the alarm logic. 6. The alarm logic first generates a detailed alarm message with a standard data structure, which includes at least: device identifier, alarm event type (e.g., "MPI Exceeded"), alarm level (e.g., "Critical" or "Major"), alarm parameters (e.g., multipath interference intensity: -28dB), and critical location information (e.g., reflection point distance: 2.1km). 7. Subsequently, the alarm and control module encapsulates this alarm message into a message conforming to a network management protocol, such as a Simple Network Management Protocol (SMMP) Trap message or a notification message based on a high-performance Remote Procedure Call (RPC) framework. 8. This message is sent to the preset network management system server via the communication interface. 9. Upon receiving the alarm message, the network management system immediately parses it. The system can highlight the fiber optic link connected to the device reporting the alarm in red on its network topology map and pop up an alarm window, clearly presenting to network maintenance personnel: "[Device Identifier] reports: Severe multipath interference has occurred in the fiber optic link, with an intensity of -28dB. The suspected fault point is located 2.1 kilometers away from this end." Based on this accurate and timely information, maintenance personnel no longer need to perform tedious segment-by-segment troubleshooting. They can directly dispatch maintenance personnel to the vicinity of 2.1 kilometers to use tools such as an optical time domain reflectometer to accurately locate and repair the faulty connector or fiber, thereby greatly shortening the fault diagnosis and service restoration time.

[0075] This embodiment demonstrates how the technical solution of the present invention can be transformed from a simple monitoring tool into an integral part of an automated operation and maintenance system that can proactively discover problems, intelligently analyze them, and provide precise guidance for solving them, thereby significantly improving the reliability and maintainability of optical communication networks.

[0076] The core of this invention is based on the joint detection of level interval difference, group variance difference and original signal autocorrelation, which has no technical overlap with existing "error signal statistics", "power difference calculation" and "error-sign cross-correlation" schemes; This invention requires no modification to the service signal format, no insertion of zero-power gaps, and no occupation of additional transmission bandwidth. It is fully compatible with existing PAM-N modulated optical communication systems and does not affect service throughput. This invention simultaneously possesses three major functions: MPI presence detection, intensity quantization, and reflection point localization, meeting the complete operation and maintenance requirements of "detectable, quantifiable, and localizable". Existing technologies typically only achieve a single function. The existence detection and intensity calculation of this invention only involve interval difference and variance operations, which have low complexity; the positioning module uses autocorrelation operation, which can be accelerated by FFT, and the whole is suitable for DSP chip integration; The original signal autocorrelation scheme provided by this invention supports time delay search, is not limited by the error signal processing window, and is suitable for long-distance optical transmission systems; This invention employs a dual-feature joint decision, namely, interval difference + variance difference, which has strong anti-noise capability; This invention is compatible with all PAM-N systems, with a base greater than 2 and a modulation format. It can be directly applied to scenarios such as 800G / 1.6T optical modules and long-distance optical transmission systems without reconstructing the core logic. The positioning function can be enabled or disabled according to system requirements, flexibly adapting to application scenarios with different cost requirements.

[0077] The present invention also provides a multipath interference detection and positioning system, which can be implemented by executing the process steps of the multipath interference detection and positioning method. That is, those skilled in the art can understand the multipath interference detection and positioning method as a preferred embodiment of the multipath interference detection and positioning system.

[0078] A multipath interferometry detection and positioning system according to the present invention includes: Module M1: Acquires the original signal sequence and decision symbol sequence; Module M2: Calculates the difference between the average occurrence interval of symbols corresponding to the outermost positive level and the average occurrence interval of symbols corresponding to the outermost negative level in the decision symbol sequence, and determines whether the absolute value of the difference is greater than a preset existence judgment threshold; if the result is yes, it is determined that multipath interference exists and triggers module M3 to work; if the result is no, it ends. Module M3: Acquires the error signal between the original signal sequence and the decision symbol sequence, and groups the corresponding decision symbols based on the error signal, and quantifies the intensity of the multipath interference according to the difference in error variance of the grouping of symbols corresponding to the outermost level; Module M4: Based on the intensity of multipath interference, performs time-delay autocorrelation calculation on the original signal sequence to determine the multipath delay caused by multipath interference, and converts the multipath delay into the physical distance of the reflection point.

[0079] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, enabling the system and its various devices, modules, and units to function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered both software modules implementing the method and structures within the hardware component.

[0080] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features of the present invention can be arbitrarily combined with each other.

Claims

1. A multipath interferometry detection and localization method, characterized in that, include: Step S1: Obtain the original signal sequence and the decision symbol sequence; Step S2: Calculate the difference between the average occurrence interval of symbols corresponding to the outermost positive level and the average occurrence interval of symbols corresponding to the outermost negative level in the decision symbol sequence, and determine whether the absolute value of the difference is greater than a preset existence judgment threshold. If the result is yes, then it is determined that multipath interference exists, and step S3 is executed; If the result is negative, the process ends. Step S3: Obtain the error signal between the original signal sequence and the decision symbol sequence, and group the corresponding decision symbols based on the error signal, and quantify the intensity of the multipath interference according to the difference in error variance of the grouping of symbols corresponding to the outermost level. Step S4: Based on the intensity of multipath interference, perform time-delay autocorrelation calculation on the original signal sequence to determine the multipath delay caused by multipath interference, and convert the multipath delay into the physical distance of the reflection point.

2. The multipath interferometry detection and positioning method according to claim 1, characterized in that, The original signal sequence is a sequence of pulse amplitude modulation (PAM-N) signals, where N is an integer greater than 2, and the decision symbol sequence is obtained by hard decision on the original signal sequence.

3. The multipath interferometry detection and positioning method according to claim 1, characterized in that, The time-delay autocorrelation operation is accelerated by Fast Fourier Transform (FFT).

4. The multipath interferometry detection and positioning method according to claim 1, characterized in that, The expression for the physical distance of the reflection point is: Where the symbol · represents multiplication, the symbol · represents multiplication. Indicates the division sign. The physical distance to the reflection point is to be determined. It is a multipath delay. The speed of light in a vacuum This represents the average refractive index of the optical fiber link. It is the unit interval duration of the signal.

5. The multipath interferometry detection and positioning method according to claim 1, characterized in that, In step S3, if the intensity of the multipath interference is greater than a preset intensity alarm threshold, an alarm is triggered.

6. A multipath interferometry detection and positioning system, characterized in that, include: Module M1: Acquires the original signal sequence and decision symbol sequence; Module M2: Calculates the difference between the average occurrence interval of symbols corresponding to the outermost positive level and the average occurrence interval of symbols corresponding to the outermost negative level in the decision symbol sequence, and determines whether the absolute value of the difference is greater than a preset existence judgment threshold; if the result is yes, it is determined that multipath interference exists, and module M3 is triggered to work. If the result is negative, the process ends. Module M3: Acquires the error signal between the original signal sequence and the decision symbol sequence, and groups the corresponding decision symbols based on the error signal, and quantifies the intensity of the multipath interference according to the difference in error variance of the grouping of symbols corresponding to the outermost level; Module M4: Based on the intensity of multipath interference, performs time-delay autocorrelation calculation on the original signal sequence to determine the multipath delay caused by multipath interference, and converts the multipath delay into the physical distance of the reflection point.

7. The multipath interferometry detection and positioning system according to claim 6, characterized in that, The original signal sequence is a sequence of pulse amplitude modulation (PAM-N) signals, where N is an integer greater than 2; the decision symbol sequence is obtained by hard decision on the original signal sequence.

8. The multipath interferometry detection and positioning system according to claim 6, characterized in that, The time-delay autocorrelation operation is accelerated by Fast Fourier Transform (FFT).

9. The multipath interferometry detection and positioning system according to claim 6, characterized in that, The expression for the physical distance of the reflection point is: Where the symbol · represents multiplication, the symbol · represents multiplication. Indicates the division sign. The physical distance to the reflection point is to be determined. It is a multipath delay. The speed of light in a vacuum This represents the average refractive index of the optical fiber link. It is the unit interval duration of the signal.

10. The multipath interferometry detection and positioning system according to claim 6, characterized in that, In module M3, if the intensity of the multipath interference is greater than a preset intensity alarm threshold, an alarm is triggered.

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