WO2021047504A1

WO2021047504A1 - Fiber-optic repeater and passive intermodulation signal detection method and system thereof

Info

Publication number: WO2021047504A1
Application number: PCT/CN2020/113996
Authority: WO
Inventors: 朱哲科; 金淮东; 朱露敏; 王文元
Original assignee: 三维通信股份有限公司
Priority date: 2019-09-10
Filing date: 2020-09-08
Publication date: 2021-03-18
Also published as: CN110611534A; CN110611534B

Abstract

The present application relates to a fiber-optic repeater and a passive intermodulation signal detection method and system thereof. The passive intermodulation signal detection method for a fiber-optic repeater comprises: when a detection starting signal is detected, generating a training sequence and a test signal; inputting the training sequence and the test signal into a peak cancellation factor unit at the same time, stopping inputting a baseband signal, and performing downlink processing until the training sequence and the test signal reach a duplexer; acquiring, at the duplexer, a passive intermodulation signal generated by the test signal, and performing uplink processing until the passive intermodulation signal reaches a digital down-conversion unit; and calculating power of a zero intermediate frequency signal obtained after being processed by the digital down-conversion unit, so as to acquire a detection result. Said method can accurately calculate a non-linear index of an external passive device by means of an algorithm inside an fiber-optic repeater, without the need of changing hardware, thereby improving the installation quality and the efficiency of positioning a faulty passive device in engineering applications.

Description

Optical fiber repeater station and its passive intermodulation signal detection method and system

Related application

This application claims the priority of the Chinese patent application filed on September 10, 2019, the application number is 201910853550.0, and the invention title is "Optical fiber repeater and its passive intermodulation signal detection method and system", the entire content of which is approved The reference is incorporated in this application.

Technical field

This application relates to the field of communication technology, and in particular to an optical fiber repeater station and its passive intermodulation signal detection method and system.

Background technique

Passive intermodulation refers to a phenomenon in which signals with two or more frequency components pass through passive components (such as coaxial cables, connectors, antennas, loads, etc.) to generate new frequency components in addition to harmonics. In high-power systems, due to the high-power characteristics, traditional passive linear devices produce strong nonlinear effects, resulting in a new set of frequencies such as (PIM3, PIM5, etc.). If these spurious PIM signals fall on the receiver In the frequency band, and the power exceeds the minimum amplitude of the useful signal in the system, the sensitivity of the receiver will be reduced, the uplink throughput rate and the cell coverage of the radio frequency module will be affected, and the system capacity of the wireless communication system will be reduced.

The traditional high-power mobile digital optical fiber repeater system does not have the ability to detect the intermodulation value of passive components. After the equipment leaves the factory, due to the non-linearity of external passive components such as connecting lines, antennas, and loads, high intermodulation values will enter the upstream receiving channel, resulting in the deterioration of the upstream receiving capability of the repeater system. However, relying on existing methods, engineers can only blindly replace antenna components, couplers, loads, and even replacement equipment one by one, hoping to locate specific causes, spend a lot of time and energy, and solve problems with low efficiency.

Summary of the invention

According to various embodiments of the present application, a method for detecting passive intermodulation signals of an optical fiber repeater station is provided. The optical fiber repeater station includes a near-end machine and a remote machine, and the method is applied to the remote end. Machines, including:

When the detection switch-on signal is detected, a training sequence and a test signal are generated; the training sequence is extracted from a normal broadband modulation signal and is used to calibrate the digital predistortion processing; the test signal is a sine wave signal;

Processing the training sequence and the test signal by a crest reduction factor at the same time, stopping the input of the baseband signal, and performing downlink processing until reaching the duplexer;

Obtain the passive intermodulation signal generated by the test signal at the duplexer, and perform uplink processing to the digital down-conversion unit;

Perform power statistics on the zero-IF signal obtained after processing by the digital down-conversion unit to obtain the detection result.

In one of the embodiments, the test signal is two sets of constant envelope narrowband single tone signals with the same power.

In one of the embodiments, the power and frequency of the test signal are adjustable.

In one of the embodiments, when the frequency point of the test signal changes after adjustment, the frequency point of the passive intermodulation signal is automatically calculated according to the working center frequency of the optical fiber repeater, and the frequency point of the passive intermodulation signal is calculated for the received signal. The zero-IF baseband signal performs frequency point shifting.

In one of the embodiments, the test signal comes from the outside of the optical fiber repeater or is generated inside the optical fiber repeater.

In one of the embodiments, the step of performing power statistics on the zero-IF signal obtained after processing by the digital down-conversion unit to obtain the detection result includes:

Select frequency to obtain the signal of the target frequency;

Filtering, filtering the frequency-selected signal to obtain the narrowband signal of the target frequency;

Power calculation, calculate the power of the filtered signal as the passive intermodulation value.

In one of the embodiments, a comb filter or a finite-length unit impulse response filter is used for filtering and extraction.

In one of the embodiments, the test signal and the training sequence are selected to be suitable for the 900MHz frequency band, and the passive intermodulation signal is a fifth-order signal; or, the test signal and the training sequence are selected as It is suitable for the 1800MHz frequency band, and the passive intermodulation signal is a 7th order signal.

According to various embodiments of the present application, an optical fiber repeater station is also provided, including:

Near-end machine, coupled with base station;

The remote machine is connected with the near-end machine through an optical fiber,

The remote machine is provided with a test signal generator in the downlink and a power calculator in the uplink;

The test signal generator is used to generate a training sequence and a test signal when the detection-on signal is detected, and input them into the crest reduction factor unit of the downlink; the training sequence is extracted from a normal wideband modulated signal and is used for digital Predistortion processing for calibration; the test signal is a sine wave signal;

The power calculator is used to perform power statistics on the zero-IF signal obtained after processing by the digital down-conversion unit to obtain the detection result.

According to various embodiments of the present application, another optical fiber repeater station is also provided, including:

Near-end machine, coupled with base station;

The remote unit is used to obtain the externally input training sequence and test signal when the detection switch-on signal is detected, and input them into the crest reduction factor unit of the downlink; the training sequence is extracted from the normal wideband modulation signal and used To calibrate the digital predistortion processing; the test signal is a sine wave signal;

The remote machine is provided with a power calculator in the uplink, which is used to perform power statistics on the zero-IF signal obtained after processing by the digital down-conversion unit to obtain the detection result.

According to various embodiments of the present application, there is also provided a passive intermodulation detection system for an optical fiber repeater, including:

Optical fiber repeater station, using the above-mentioned optical fiber repeater station that can generate test signals internally;

The load to be tested is connected to the optical fiber repeater through a coupler;

The first attenuator is connected to the other output end of the coupler;

A duplexer, respectively connected to the optical fiber repeater and the first attenuator;

The spectrum analyzer is connected to the duplexer through the second attenuator.

According to various embodiments of the present application, another passive intermodulation detection system for an optical fiber repeater is also provided, including:

Optical fiber repeater station, using the above-mentioned optical fiber repeater station that can receive external test signals;

The load to be tested is connected to the optical fiber repeater;

A signal device for generating the test signal;

High intermodulation duplexers, respectively connected to the optical fiber repeater and the signal device;

The spectrum analyzer is connected to the high intermodulation duplexer.

The above-mentioned optical fiber repeater and its passive intermodulation signal detection method and system have the following advantages: in the remote machine, CPRI, IR, DUC, CRF, DPD and other processing are all realized in FPGA. When the system provides training sequences and test signals, there is no need to change the hardware, relying on the internal algorithm of the fiber optic repeater, you can accurately calculate the nonlinear index of the external passive components, and improve the installation quality in engineering applications and locate the problem passive components s efficiency.

Description of the drawings

In order to better describe and explain the embodiments and/or examples of those inventions disclosed herein, one or more drawings may be referred to. The additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed inventions, the currently described embodiments and/or examples, and the best mode of these inventions currently understood.

Figure 1 is a structural diagram of a traditional digital optical fiber repeater.

Fig. 2 is a structural diagram of a digital optical fiber repeater according to an embodiment of the present application.

Fig. 3 is a flowchart of a passive intermodulation signal detection method for a digital optical fiber repeater according to an embodiment of the present application.

Fig. 4 is a flowchart of the power calculation steps in Fig. 3.

Fig. 5 is a structural diagram of another digital optical fiber repeater according to an embodiment of the present application.

Fig. 6 is a structural diagram of another digital optical fiber repeater according to an embodiment of the present application.

detailed description

In order to facilitate the understanding of this application, and to make the above objectives, features and advantages of this application more comprehensible, specific implementations of this application will be described in detail below with reference to the accompanying drawings. In the following description, many specific details are set forth in order to fully understand the application, and the preferred embodiments of the application are shown in the accompanying drawings. However, this application can be implemented in many different forms and is not limited to the implementation described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of this application more thorough and comprehensive. This application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of this application. Therefore, this application is not limited by the specific embodiments disclosed below.

In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present application, "a plurality of" means at least two, such as two, three, etc., unless specifically defined otherwise. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise specifically defined.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of this application. The terminology used herein is only for the purpose of describing specific embodiments, and is not intended to limit the application. The term "and/or" as used herein includes any and all combinations of one or more related listed items.

In the description of this application, it should be understood that the terms "upper", "lower", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the drawings. The method or positional relationship is only for the convenience of describing the application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the application .

Figure 1 is a structural diagram of a traditional digital optical fiber repeater. The digital optical fiber repeater 10 includes a near-end machine 110 and a far-end machine 120. The near-end machine 110 is coupled with the base station 91, and obtains downlink data from the base station 91. The remote machine 120 is connected to the near-end machine 110 through an optical fiber 130, obtains downlink data from the near-end machine 110, processes the data in the downlink 122 and transmits it to the outside through the antenna 140. The remote machine 120 also receives the client's signal through the antenna 140, processes it in the uplink 124, and transmits it to the near-end machine 110 through the optical fiber 130. The near-end machine 110 sends the received uplink data to the base station 91.

When data is downlinked, as shown in Figure 1, the near-end machine 110 couples the radio frequency signal of the base station 91, passes through the duplexer 111, the SAW filter 112, the gain device 113, etc., and then passes to the mixer 114 and the intermediate frequency After the filter 115, it enters the analog-to-digital conversion chip 116 for analog-to-digital conversion. The digital signal obtained after the analog-to-digital conversion is processed by the FPGA chip for digital down-conversion 117, converted into a zero-IF baseband signal, and then compressed by the in-phase quadrature data processing unit 118, and the data is re-logically processed in the general public radio interface unit 119 It is packaged into a common public radio interface (CPRI) protocol data format, and then the data is converted in parallel through the SERDES interface, and then the electrical signal is converted into an optical signal through the optical module for optical fiber transmission through the optical fiber 130.

As shown in Figure 1, the FPGA chip in the remote machine 120 recovers the serial signal from the SERDES interface, and then recovers the baseband signal that needs to be processed by parsing the CPRI protocol, logic processing, and decompression; the FPGA chip then recovers the baseband signal Perform digital up-conversion (DUC) processing, then pass crest factor reduction processing (CFR) and digital pre-distortion processing (DPD), and convert digital signals to analog signals through digital-to-analog conversion chips; and after mixing, filtering, and output The radio frequency signal is sent to the power amplifier module for signal amplification and output.

Uplink: The wireless signal is received by the antenna 140 of the remote unit 120. After the remote unit 120 is amplified by low-noise amplification and RF gain devices, it is digitally down-converted through the mixer, and then filtered by the intermediate frequency. Analog-to-digital conversion (ADC); after digital-to-analog conversion, the FPGA chip performs digital down-conversion processing, and its data processing method and design method are consistent with the downlink 122; after the FPGA chip compresses the baseband signal and processes the CPRI framing , Sent to the optical port through the built-in SERDES interface, and then connected to the near-end machine 110 through an optical fiber; the mechanism of the near-end machine 110 for processing the uplink and the mechanism for processing the downlink is the inverse transformation, which will not be repeated here.

As shown in FIG. 2, the near-end machine 210 is coupled with the base station 92, and the remote machine 220 and the near-end machine 210 are connected by an optical fiber. This method is the same as traditional technology. In order to realize the detection of the passive intermodulation signal of the optical fiber repeater, the training sequence and the test signal are input in the downlink 222 of the remote machine 220, and the passive intermodulation signal thus generated is detected in the uplink 224 at the same time. Perform power calculations to obtain test results.

With reference to Figures 2 and 3, a method for detecting passive intermodulation signals of an optical fiber repeater includes the following steps:

S100: When the detection switch-on signal is detected, a training sequence and a test signal are generated. The detection start signal is used to instruct the system to start the detection of the passive intermodulation signal, and may be generated by an interface switch, or may be generated when the system is powered on and self-checked. The training sequence is extracted from a normal wideband modulated signal and used to calibrate the digital predistortion processing (DPD). According to the current DPD calibration technology, directly inputting the test signal without the training sequence will cause the DPD to be abnormal, thereby affecting the detection accuracy and range of the intermodulation value. The test signal is a sine wave signal. In one embodiment, the test signal is two sets of constant envelope narrowband single tone signals with the same power.

S200: Simultaneously input the training sequence and the test signal to the crest factor reduction processing unit 225 (CFR), and stop the input of the baseband signal, and perform downlink processing to the duplexer. Before the test starts, the crest factor reduction processing unit 225 obtains the digital up-conversion processing baseband signal from the digital up-conversion unit 223, and sends the crest factor reduction processing to the digital predistortion processing unit 227. After the start of the test, the baseband signal will no longer be input to the crest factor reduction processing unit 225, instead the test signal and training sequence will be input.

The subsequent downstream processing includes converting the digital signal into an analog signal through a digital-to-analog conversion chip; and after mixing and filtering, the radio frequency signal is output to the power amplifier module for signal amplification and output. Due to the non-linear effect of passive components, a set of passive intermodulation signals will be generated on the transmitting side (TX_DUP) of the duplexer 229. The passive intermodulation signals just fall into the upstream band of the remote unit 220, thereby affecting receive.

S300: Obtain a passive intermodulation signal at the duplexer 229, and perform uplink processing to a digital down-conversion unit (DDC). The passive intermodulation signal is the passive intermodulation signal caused by various reasons of the system to be detected in this application. Since the frequency of the passive intermodulation signal falls within the uplink band, it is received on the receiving side (RX_DUP) of the duplexer 229, and then a series of uplink processing will be performed.

The upstream processing includes low-noise amplification, radio frequency gain devices and other signal amplification, digital down-conversion through the mixer, and then intermediate frequency filtering, enters the analog-to-digital conversion module (ADC), and then performs digital down-conversion processing. The output from the digital down-conversion processing unit is a zero-IF baseband signal.

S400: Perform power statistics on the zero-IF baseband signal processed by the digital down-conversion unit (DDC) to obtain a detection result. When the signal is transmitted in a linear system, it changes proportionally and linearly, and the harmonic components of the signal basically do not affect the fundamental wave. When the system has a nonlinear effect, the signal will become the superposition of the original fundamental wave and the corresponding harmonic, and the harmonic will be intermodulated with other carriers on the transmission line. In turn, some new frequencies were created. When the power of the system is large enough, the signals of these new frequencies cannot be ignored. Through power statistics, the power of each frequency component of the passive intermodulation signal can be obtained, thereby obtaining the characteristics of the passive intermodulation signal, and then determining the nonlinear index of the external passive components such as external antennas and loads.

In the remote machine 220 of the optical fiber repeater 20, CPRI, IR, DUC, CRF, DPD and other processing are all implemented in FPGA. When the system provides training sequences and test signals, there is no need to change the hardware, relying on the internal algorithm of the fiber optic repeater, you can accurately calculate the nonlinear index of the external passive components, and improve the installation quality in engineering applications and locate the problem passive components s efficiency.

In one embodiment, the power and frequency of the test signal are adjustable. The power and frequency of the test signal are adjustable, which can improve the flexibility of the test. The power and frequency of the test signal are adjusted by algorithms in the FPGA. This adjustment can read various preset common power and frequency point configurations, or it can be adjusted according to the debugger's input.

In one embodiment, when the frequency point of the test signal changes, the frequency point of the passive intermodulation signal is automatically calculated according to the working center frequency of the optical fiber repeater, and the frequency point is shifted. When the test signal and the training sequence are applicable to the 900MHz frequency band, the passive intermodulation signal is a fifth-order signal (PIM5); or, when the test signal and the training sequence are applicable to the 1800MHz frequency band, Then the passive intermodulation signal is a 7th order signal (PIM7). For the 900MHz frequency band, the frequency point of the PIM5 passive intermodulation signal is automatically calculated, and then moved to the zero intermediate frequency. Moving to zero IF can facilitate low-pass filtering and subsequent power calculations.

The power and frequency of the test signal are adjustable, plus the automatic calculation and movement of the frequency of the passive intermodulation signal makes the detection of the passive intermodulation signal flexible and controllable, and fully automated, simple and easy.

In an embodiment, as shown in FIG. 4, the steps of processing and power statistics on the zero-IF signal after DDC processing include:

Step S410: frequency selection, and a signal of the target frequency is obtained. Since the frequency of PIM5 or PIM7 can be automatically calculated, the target frequency is the frequency components in the passive intermodulation signal.

Step S420: filtering, filtering the frequency-selected signal to obtain the narrowband signal of the target frequency. In one embodiment, a comb filter or a finite-length unit impulse response (FIR) filter is used for filtering and extraction, and the digital signal of PIM5 or PIM7 that is higher than the noise floor is extracted. Using this filtering method can reduce the use of multipliers and save FPGA hardware resources while ensuring the attenuation of the sidelobes.

Step S430: power calculation. The calculated power value is the intermodulation value generated by the current passive device. The following formula can be used for calculation:

Passive intermodulation value = Pt-Gmax-(Pout_max-3)

Among them, Pt is the measured output power of the uplink intermodulation frequency point, Gmax is the maximum uplink gain, and Pout_max is the nominal maximum output power of the downlink.

In one embodiment, the test signal comes from the outside of the fiber optic repeater or is generated inside the fiber optic repeater.

In the remote machine 320 shown in FIG. 5, a training sequence and a test signal are generated internally. The optical fiber repeater 30 includes:

The near-end machine 310 is coupled with the base station 93;

The remote machine 320 is connected with the near-end machine 310 through an optical fiber,

The remote machine 320 has a test signal generator 323 in the downlink 322, and a power calculator 325 in the uplink 324;

The test signal generator 323 is used to generate a training sequence and a test signal when the detection switch-on signal is detected; the training sequence is extracted from a normal broadband modulation signal and used to calibrate the DPD; the test signal is a sine wave signal;

The power calculator 325 is used to perform power statistics on the zero-IF baseband signal that has undergone DDC processing.

The remote machine 420 shown in FIG. 6 receives training sequences and test signals from the external 50. The optical fiber repeater 40 includes:

The near-end machine 410 is coupled with the base station 94;

The remote machine 420 is connected to the near-end machine 410 through an optical fiber,

The remote machine 420 is used to obtain the externally input training sequence and test signal and input it into the CFR of the downlink 422 when the detection switch-on signal is detected; the training sequence is extracted from the normal broadband modulated signal and used to DPD performs calibration; the test signal is a sine wave signal;

The remote unit 420 is provided with a power calculator 425 in the uplink 424 for processing and power statistics of the zero-IF signal after DDC processing.

Another embodiment of a passive intermodulation detection system for an optical fiber repeater station includes:

Optical fiber repeater station, using the optical fiber repeater station shown in Figure 5;

The first attenuator is connected to the other output end of the coupler;

The above-mentioned detection system realizes the detection of the intermodulation value of the external antenna, load, coupler, etc. through the optical fiber repeater.

The passive intermodulation detection system of an optical fiber repeater station in an embodiment includes:

The tested equipment uses the optical fiber repeater shown in Figure 6;

The load to be tested is connected to the optical fiber repeater;

Signal device, used to generate the test signal; the signal device includes 2 signal sources;

The spectrum analyzer is connected to the high intermodulation duplexer; the spectrum analyzer is used to obtain the above-mentioned measured output power Pt.

The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the various technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, All should be considered as the scope of this specification.

The above-mentioned embodiments only express several embodiments of the present invention, and the descriptions are relatively specific and detailed, but they should not be understood as limiting the scope of the invention patent. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

A method for detecting passive intermodulation signals of an optical fiber repeater station, wherein the optical fiber repeater station includes a near-end machine and a remote machine, and the method is applied to the remote machine and includes:

When the detection switch-on signal is detected, a training sequence and a test signal are generated; the training sequence is extracted from a normal broadband modulation signal and is used to calibrate the digital predistortion processing; the test signal is a sine wave signal;

The training sequence and the test signal are processed by a crest reduction factor at the same time, the input of the baseband signal is stopped, and the downstream processing is performed until it reaches the duplexer;

Obtain the passive intermodulation signal generated by the test signal at the duplexer, and perform uplink processing to the digital down-conversion unit;

Perform power statistics on the zero-IF signal obtained after processing by the digital down-conversion unit to obtain the detection result.
The method according to claim 1, wherein the test signal is two sets of constant envelope narrowband single tone signals with the same power.
The method according to claim 2, wherein the power and frequency of the test signal are adjustable.
The method according to claim 3, wherein when the frequency of the test signal changes after being adjusted, the frequency of the passive intermodulation signal is automatically calculated according to the working center frequency of the optical fiber repeater. Point and move the signal frequency to zero intermediate frequency.
The method according to claim 1, wherein the test signal comes from the outside of the optical fiber repeater station, or is generated inside the optical fiber repeater station.
The method according to claim 1, wherein the step of performing power statistics on the zero-IF signal obtained after processing by the digital down-conversion unit to obtain a detection result comprises:

Select frequency to obtain the signal of the target frequency;

Filtering, filtering the frequency-selected signal to obtain the narrowband signal of the target frequency;

Power calculation, calculate the power of the filtered signal as the passive intermodulation value.
The method according to claim 6, wherein a comb filter or a finite-length unit impulse response filter is used for filtering and extraction.
The method according to claim 1, wherein the test signal and the training sequence are selected to be suitable for the 900MHz frequency band, and the passive intermodulation signal is a 5th order signal; or,

The test signal and the training sequence are selected to be suitable for the 1800MHz frequency band, and the passive intermodulation signal is a 7th order signal.
An optical fiber repeater station, including:

Near-end machine, coupled with base station;

The remote machine is connected with the near-end machine through an optical fiber,

The remote machine is provided with a test signal generator in the downlink and a power calculator in the uplink;

The test signal generator is used to generate a training sequence and a test signal when the detection-on signal is detected, and input them into the crest reduction factor unit of the downlink; the training sequence is extracted from a normal wideband modulated signal and is used for digital Predistortion processing for calibration; the test signal is a sine wave signal;

The power calculator is used to perform power statistics on the zero-IF signal obtained after processing by the digital down-conversion unit to obtain the detection result.
An optical fiber repeater station, including:

Near-end machine, coupled with base station;

The remote machine is connected with the near-end machine through an optical fiber,

The remote unit is used to obtain the externally input training sequence and test signal when the detection switch-on signal is detected, and input them into the crest reduction factor unit of the downlink; the training sequence is extracted from the normal wideband modulation signal and used To calibrate the digital predistortion processing; the test signal is a sine wave signal;

The remote machine is provided with a power calculator in the uplink, which is used to perform power statistics on the zero-IF signal obtained after processing by the digital down-conversion unit to obtain the detection result.
A passive intermodulation detection system for an optical fiber repeater station, including:

The optical fiber repeater station adopts the optical fiber repeater station according to claim 9;

The load to be tested is connected to the optical fiber repeater through a coupler;

The first attenuator is connected to the other output end of the coupler;

A duplexer, respectively connected to the optical fiber repeater and the first attenuator;

The spectrum analyzer is connected to the duplexer through the second attenuator.
A passive intermodulation detection system for an optical fiber repeater station, including:

The optical fiber repeater station adopts the optical fiber repeater station according to claim 10;

The load to be tested is connected to the optical fiber repeater;

A signal device for generating the test signal;

High intermodulation duplexers, respectively connected to the optical fiber repeater and the signal device;

The spectrum analyzer is connected to the high intermodulation duplexer.