A fast evaluation method for the impact of reflection crosstalk in circulator-based fronthaul system

Abstract

The present invention discloses a rapid evaluation method for the reflection crosstalk influence of a circulator fronthaul system, and relates to the field of optical communication technology. The method comprises: taking the DU side of the circulator fronthaul system as the local end and the AAU side as the opposite end, connecting a power test device to any receiving end of a local multiplexer for demodulating optical signals; obtaining a reflection equivalent influence factor of the receiving end based on the power test device, which is defined as the power difference between the power of the optical signal transmitted by the opposite end reaching the receiving end of the local end and the power difference between the reflected optical signal of the corresponding optical signal transmitted by the local end reaching the receiving end of the local end; comparing the reflection equivalent influence factor with a threshold value under predetermined conditions to evaluate the influence weight of the reflected optical signal on the circulator fronthaul system, and then determining whether the transmission line meets the design or construction requirements.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a method for quickly evaluating the influence of reflection crosstalk on a circulator fronthaul system. Background Art

[0002] Limited by optical fiber resources, the 5G fronthaul bearer solution mainly adopts wavelength division multiplexing technology. At present, the wavelength division scheme in the fronthaul system is mainly implemented based on CWDM. In order to expand the capacity of the 5G fronthaul system, the characteristics of the mutually different conduction of the circulator ports are generally used to realize bidirectional transmission of the same wavelength in a single optical fiber. The single-fiber bidirectional system based on the circulator solution is relatively common in the field of optical communications. The corporate standard "Q / CT 2692-2021" of China Telecom Group Co., Ltd. has relevant indicator definitions for the circulator-based fronthaul solution. The current specific implementation method of the 5G fronthaul system based on the circulator solution is generally placed in the multiplexer to meet the corporate standards of China Telecom.

[0003] This solution can achieve double capacity transmission in a single fiber without changing the wavelength of the optical module, and can be used for other wavelengths besides CWDM. However, the characteristics of the circulator ports being mutually different also bring risks, such as Figure 1 As shown in the figure, the three ports of circulator 1 are Port1, Port2, and Port3. When the same wavelength single fiber is bidirectionally transmitted, the local transmission signal is conducted from port1 to port2, and the opposite transmission signal is conducted from port2 to port3. When there is a reflection point in the transmission line, the local transmission signal is reflected by each reflection point and then superimposed together, and then conducted from port2 to port3. That is, the reflected signal of the local transmission signal and the opposite transmission signal are mixed together at port3 to form crosstalk noise, which the local receiver cannot distinguish, causing system failure.

[0004] For line reflection, OTDR (Optical Time-Domain Reflectometer) can be used to scan whether the welding points and joints are normal. However, OTDR equipment is lacking at the fronthaul site, and OTDR can only obtain the reflection situation of each point, but cannot obtain the result of reflection superposition, let alone the impact of reflection and its superposition on the receiving end signal. It is also difficult to ensure the reflection accuracy. Summary of the invention

[0005] In response to the above problems and technical needs, the inventors have proposed a rapid evaluation method for the impact of reflection crosstalk on the circulator fronthaul system. Based on the test results of the power testing equipment, the method can quickly evaluate the impact of the reflected light signals superimposed by the joints and fusion points at different positions in the transmission line on the signal performance of the receiving end.

[0006] The technical solution of the present invention is as follows:

[0007] A fast evaluation method for the influence of reflection crosstalk in a circulator-based fronthaul system includes the following steps:

[0008] Take the DU side of the circulator-based fronthaul system as the local end and the AAU side as the remote end, and connect a power test device to any receiving end of the local multiplexer for demultiplexing optical signals.

[0009] Obtain the reflection equivalent influence factor based on the test results of the power test device, which is defined as the power difference between the power of the optical signal transmitted from the remote end reaching the receiving end of the local end and the power of the reflected optical signal of the corresponding optical signal transmitted from the local end reaching the receiving end of the local end.

[0010] Compare the reflection equivalent influence factor with the threshold under predetermined conditions to evaluate the influence weight of the reflected optical signal on the circulator-based fronthaul system.

[0011] A further technical solution thereof is that obtaining the reflection equivalent influence factor based on the test results of the power test device includes:

[0012] For the local multiplexer for multiplexing optical signals, turn off the transmitting end with the same wavelength as the receiving end; for the remote multiplexer for multiplexing optical signals, turn on the transmitting end with the same wavelength as the receiving end, then the test result of the power test device is the power of the optical signal transmitted from the remote end reaching the receiving end of the local end via the transmission line, denoted as RB1_1;

[0013] For the local multiplexer for multiplexing optical signals, turn on the transmitting end with the same wavelength as the receiving end; for the remote multiplexer for multiplexing optical signals, turn off the transmitting end with the same wavelength as the receiving end, then the test result of the power test device is the power of the reflected optical signal generated by the optical signal transmitted from the local end reaching the receiving end of the local end via the transmission line, denoted as RB1_2;

[0014] The reflection equivalent influence factor is denoted as ΔB1, then ΔB1 = RB1_1 - RB1_2.

[0015] A further technical solution thereof is that comparing the reflection equivalent influence factor with the threshold under predetermined conditions to evaluate the influence weight of the reflected optical signal on the circulator-based fronthaul system includes:

[0016] For the 5G fronthaul system based on a circulator, under the predetermined conditions that the rate of each channel of the system is 25 Gbps, BER <= 5E-5, and the optical signal transmitted from the remote end meets the sensitivity of the local receiver:

[0017] If ΔB1 > 23, the reflected optical signal has no influence on the circulator-based fronthaul system, and the influence of reflection crosstalk in the transmission line is ignored during evaluation;

[0018] If ΔB1 < 20, the influence of the reflected optical signal on the circulator-based fronthaul system is in the high-weight range. The influence of the reflection crosstalk in the transmission line cannot be ignored during evaluation, and the transmission line needs to be detected.

[0019] If 20 <= ΔB1 <= 23, the influence of the reflected optical signal on the circulator-based fronthaul system is in the medium-weight range. Combine the local receiver background noise and the signal quality itself to comprehensively evaluate whether the influence of the reflection crosstalk in the transmission line can be ignored.

[0020] A further technical solution thereof is that the method further includes:

[0021] Take the AAU side of the circulator-based fronthaul system as the local end and the DU side as the remote end, and sequentially execute the step of connecting a power test device to any receiving end of the local multiplexer for demultiplexing the optical signal, so as to quickly evaluate the influence of the reflection crosstalk on the local receiving end.

[0022] A further technical solution thereof is that the wavelengths of the corresponding transmitted optical signals on the AAU side and the DU side are the same, and the wavelength accuracies are both within the requirements of the fronthaul system specification. The channel bandwidths of the multiplexers can all cover the wavelengths of the transmitted optical signals.

[0023] The beneficial technical effects of the present invention are:

[0024] For the circulator-based fronthaul system, by comparing the test results of the power test device with the threshold values under predetermined conditions, it is possible to directly determine the influence of the reflected optical signals superimposed at different positions such as connectors and fusion splices in the transmission line on the system, and further determine whether the transmission line meets the design or construction requirements. This evaluation method is simple to test, can greatly improve the problem analysis efficiency and reduce the construction cost, and has great guiding significance for the 5G fronthaul system based on the circulator. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the port reciprocity of the circulator.

[0026] Figure 2 It is a schematic diagram of the fronthaul system based on the circulator solution.

[0027] Figure 3 It is a flowchart of a fast evaluation method for the influence of reflection crosstalk in a circulator-based fronthaul system. Detailed Embodiments

[0028] The following further describes the specific embodiments of the present invention with reference to the drawings.

[0029] This application discloses a fast evaluation method for the influence of reflection crosstalk in a circulator-based fronthaul system, and this method is applied to Figure 2Schematic typical fronthaul system based on the circulator scheme, where multiplexers MUX1 to MUX4 are used for wavelength multiplexing and demultiplexing and can be considered the same. The wavelengths of the corresponding transmitted optical signals on the active antenna unit (AAU) side and the distributed unit (DU) side are the same, that is, TA1 corresponds to TB1, TA2 corresponds to TB2... TAn corresponds to TBn. The wavelengths between TA1 to TAn and between TB1 to TBn are different, and the wavelength accuracy is within the requirements of the fronthaul system specification. The channel bandwidth of the multiplexer can cover the wavelengths of the transmitted optical signals. Taking the CWDM system as an example, within the full temperature range, its signal wavelength range is ITU wavelength + / - 6.5 nm. At the same temperature, the wavelength deviation of the optical module is small; the wavelength at the transmission end of the MUX is required to satisfy > ITU + / - 6.5 nm.

[0030] As Figure 3 shown, taking the receiving end RB1 on the DU side as an example for illustration, the method includes the following steps:

[0031] Step 1: Take the DU side of the fronthaul system based on the circulator as the local end and the AAU side as the peer end, and connect a power test device to the receiving end RB1 of the local multiplexer MUX2 for demultiplexing the optical signal.

[0032] Optionally, the power test device used in this application is a handheld simple power meter for on-site analysis and testing in the fronthaul system, or other power meters with more functions and higher precision can also be used. This application does not limit this.

[0033] Step 2: Obtain the reflection equivalent influence factor based on the test result of the power test device, denoted as ΔB1.

[0034] Step 21: For the local multiplexer MUX1 for multiplexing the optical signal, turn off the transmitting end TB1 with the same wavelength as the receiving end RB1; for the peer multiplexer MUX3 for multiplexing the optical signal, turn on the transmitting end TA1 with the same wavelength as the receiving end RB1. Then, the power of the peer transmitted optical signal emitted by TA1, after being multiplexed by MUX3, enters the transmission line through the circulator 2, and after passing through the ODF (Optical Distribution Frame), transmission optical fiber, connector loss, and splicing loss, it is conducted from Port2 to Port3 of the circulator 1 and enters the local end, and after being demultiplexed by MUX2, it reaches RB1. At this time, the test result of the power test device is denoted as RB1_1, which belongs to the effective signal power.

[0035] Step 22: For the local multiplexer MUX1 for multiplexing optical signals, turn on the transmitting end TB1 with the same wavelength as the receiving end RB1; for the peer multiplexer MUX3 for multiplexing optical signals, turn off the transmitting end TA1 with the same wavelength as the receiving end RB1. Then, after the power of the local transmitted optical signal emitted by TB1 is multiplexed by MUX1, it enters the transmission line through the circulator 1. During transmission through the line, reflections occur at different-position flange joints, different-position fusion joints, and end-face suspensions (or poor contacts) at different positions. The reflection values may vary greatly, but all are transmitted in the AAU→DU direction, conducted through Port 2 of the circulator 1 to Port 3 and enter the local end, and reach RB1 after being demultiplexed by MUX2. At this time, the test result of the power test equipment is recorded as RB1_2. This signal contains the superposition of reflections at different positions and belongs to the power of invalid signals, which will cause crosstalk interference to the valid signals.

[0036] Step 23: Calculate ΔB1 = RB1_1 - RB1_2, where the units of RB1_1 and RB1_2 are dBm, and the unit of ΔB1 is dB.

[0037] Step 3: Compare the reflection equivalent impact factor with the threshold under the predetermined conditions to evaluate the impact weight of the reflected optical signal on the circulator-based fronthaul system.

[0038] For the 5G fronthaul system based on the circulator, under the predetermined conditions that the rate of each channel of the system is 25 Gbps, the bit error rate BER <= 5E-5, and the peer transmitted optical signal meets the sensitivity of the local receiver:

[0039] If ΔB1 > 23, the reflected optical signals superimposed at different positions in the line have no impact on the circulator-based fronthaul system, and the reflection crosstalk impact in the transmission line is ignored during evaluation.

[0040] If ΔB1 < 20, the impact of the reflected optical signals superimposed at different positions in the line on the circulator-based fronthaul system is in the high-weight range, and the reflection crosstalk impact in the transmission line cannot be ignored during evaluation, and the transmission line needs to be detected.

[0041] If 20 <= ΔB1 <= 23, the impact of the reflected optical signals superimposed at different positions in the line on the circulator-based fronthaul system is in the medium-weight range, and it is comprehensively evaluated whether the reflection crosstalk impact in the transmission line can be ignored in combination with the local receiver background noise and the signal quality itself. Under this condition, it is generally recommended to detect the transmission line.

[0042] Similarly, the calculation method of the reflection equivalent impact factors ΔB2~ΔBn of the receiving ends RB2 - RBn on the DU side is the same as that of ΔB1. Figure 2It can be known that the MUX and the circulator are integrated, and the return loss of the device itself is greater than 45 dB (that is, the reflection impact caused by the return loss of the device itself can be ignored). Assuming that the performance of the receiver is the same and the loss differences of each wavelength channel of MUX1 to MUX4 are not considered, the impacts of ΔB1 to ΔBn on the fronthaul system are the same. That is, the reflected optical signals at different positions in the line and the optical signals transmitted from the opposite end are superimposed within a certain wavelength range, and the impact effects are the same. Any one of the signal wavelengths can be used for testing to determine the impact of reflection crosstalk.

[0043] Similarly, the calculation method of the reflection equivalent impact factors ΔA1 to ΔAn of the receiving ends RA1 to RAn on the AAU side is the same as that of ΔB1. However, it should be noted that for the single-fiber bidirectional fronthaul system, due to the directionality of reflection, there may be certain differences in the crosstalk impacts of ΔA1 to ΔAn and ΔB1 to ΔBn on the receivers on the AAU side and the DU side. Simply put, in the same line (with the same fusion splices and connectors), reflection may cause abnormal reception on the DU side, but it does not necessarily cause abnormal reception on the AAU side. The reason is that the reflection values may vary greatly when tested in different directions. Therefore, the fast evaluation method also includes:

[0044] Step 4: Take the AAU side of the fronthaul system based on the circulator as the local end and the DU side as the opposite end, and sequentially execute the step of connecting a power test device to any receiving end of the local multiplexer MUX4 for demultiplexing optical signals, and repeat Steps 2 and 3 to quickly evaluate the impact of reflection crosstalk on the local receiving end.

[0045] In this embodiment, since the wavelengths of the reflected optical signal crosstalk at any receiving end of the fronthaul system based on the circulator are the same as the wavelengths of the transmitted signals, they cannot be isolated physically and are equivalent to noise. Moreover, it is also impossible to analyze the two types of signals with the same wavelength at the receiving end using an optical spectrum analyzer. By adopting the fast evaluation method provided in this application, by comparing the test results of the power test device with the threshold under predetermined conditions, it is possible to directly determine the impact of the reflected optical signals superimposed at different positions such as connectors and fusion splices in the transmission line on the system, and further determine whether the transmission line meets the design or construction requirements. This evaluation method is simple to test, can greatly improve the problem analysis efficiency and reduce the construction cost, and has great guiding significance for the 5G fronthaul system based on the circulator.

[0046] It should be noted that the order of evaluating the reflection crosstalk impact on the AAU-side receiving end and the DU-side receiving end of the circulator fronthaul system is not in particular order, and steps 21 and 22 are also not in particular order. It should be understood that although the steps in the flowcharts involved in the embodiments described above are displayed in sequence as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise clearly stated in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, at least part of the steps in the flowcharts involved in the embodiments described above may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be executed in turn or alternating with other steps or at least part of the steps or stages in other steps.

[0047] The above is only a preferred embodiment of the present application, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A fast evaluation method for the impact of reflection crosstalk in circulator fronthaul system, It is characterized in that The method comprises: The DU side of the circulator-based fronthaul system is used as the local end and the AAU side is used as the opposite end. A power test device is connected to any receiving end of the local multiplexer used for demodulating optical signals. Obtain the reflection equivalent impact factor based on the test results of the power test equipment, which is defined as the difference between the power of the optical signal transmitted by the other end reaching the receiving end of the local end and the power of the reflected optical signal of the corresponding optical signal transmitted by the local end reaching the receiving end of the local end; Comparing the reflection equivalent impact factor with a threshold value under a predetermined condition to evaluate the impact weight of the reflected optical signal on the circulator-based fronthaul system; The obtaining of the reflection equivalent impact factor based on the test result of the power test equipment includes: For the local multiplexer used for combining optical signals, close its transmitting end with the same wavelength as the receiving end; for the opposite multiplexer used for combining optical signals, open its transmitting end with the same wavelength as the receiving end, then the test result of the power test equipment is the power of the optical signal transmitted from the opposite end to reach the local receiving end through the transmission line, which is recorded as RB1_1; For the local multiplexer used for combining optical signals, turn on its transmitting end with the same wavelength as the receiving end; for the opposite multiplexer used for combining optical signals, turn off its transmitting end with the same wavelength as the receiving end. Then the test result of the power test device is the power of the reflected optical signal generated by the transmission line of the local transmitting optical signal reaching the local receiving end, which is recorded as RB1_2; The reflection equivalent influence factor is recorded as ΔB1, then ΔB1=RB1_1-RB1_2.

2. According to claim 1, the rapid evaluation method for the reflection crosstalk impact based on the circulator fronthaul system, It is characterized in that The comparing the reflection equivalent impact factor with a threshold value under a predetermined condition to evaluate the impact weight of the reflected optical signal on the circulator-based fronthaul system includes: For a 5G fronthaul system based on a circulator, under the conditions that the rate of each channel of the system is 25 Gbps, BER <= 5E-5, and the optical signal transmitted by the opposite end meets the predetermined sensitivity of the local receiver: If ΔB1>23, the reflected optical signal has no effect on the circulator-based fronthaul system, and the reflection crosstalk effect in the transmission line is ignored during the evaluation; If ΔB1<20, the influence of the reflected optical signal on the circulator-based fronthaul system is in a high-weight range, and the reflection crosstalk influence in the transmission line cannot be ignored during the evaluation, and the transmission line needs to be tested; If 20<=ΔB1<=23, the influence of the reflected optical signal on the circulator-based fronthaul system is in the middle weight range, and a comprehensive assessment is made on whether the influence of the reflected crosstalk in the transmission line can be ignored in combination with the background noise of the local receiver and the quality of the signal itself.

3. According to claim 1, the rapid evaluation method for the reflection crosstalk impact based on the circulator fronthaul system, It is characterized in that The method further comprises: Take the AAU side of the circulator fronthaul system as the local end and the DU side as the remote end, and sequentially execute the step of connecting a power test device to any receiving end of the local multiplexer for demultiplexing optical signals, so as to quickly evaluate the impact of reflection crosstalk on the local receiving end.

4. The rapid evaluation method for the impact of reflection crosstalk based on the circulator fronthaul system according to any one of claims 1-3, characterized in that the wavelengths of the corresponding transmitted optical signals on the AAU side and the DU side are the same, and the wavelength accuracies are both within the requirements of the fronthaul system specification, and the channel bandwidths of the multiplexer can all cover the wavelengths of the transmitted optical signals.

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