CN104506970A - Polling passive optical network optical layer detection method based on optical pre-coding - Google Patents

Abstract

The invention discloses a polling type passive optical network optical layer detection device and method based on optical precoding. The device includes three modules: a detection pulse precoding module, a link fault identification module and a decoder module. The detection pulse precoding module and the link fault identification module are connected to the optical line terminal (OLT) equipment and the feed-in fiber through the optical circulator and the wavelength division multiplexer, and the feed-in fiber is connected to each Distributed optical fibers are connected at the end of each distributed optical fiber to each user end through different decoders. The present invention utilizes the precoded detection pulse signal and adopts polling mode to monitor the fiber link failure of only one target user at a time. Since the length of the branch link to be monitored is known, the detection time window is reduced to a very small time window, which reduces the coherence distance of codewords and improves the accuracy of the monitoring system.

Description

Optical layer detection method of polling passive optical network based on optical precoding

technical field

The invention belongs to the technical field of optical fiber communication and relates to a polling type passive optical network optical layer detection method based on optical precoding.

Background technique

In recent years, PON (Passive Optical Network) technology in the field of optical access has been widely used. The continuous development of passive optical network PON technology not only improves the data transmission rate, but also increases the number of bearer users. Therefore, any failure (breakage, aging or bending loss) of any optical link (feeder fiber and distribution fiber) in the PON network will lead to the loss of a large amount of data information, reduce user satisfaction, and bring economic losses to network operators. Therefore, PON link fault detection methods have received increasing attention in the past few years. The traditional optical time domain reflectometer OTDR (Optical Time Domain Reflectometer) is widely used in the remote detection of point-to-point links. In the point-to-multipoint PON system, OTDR technology has great limitations: all distributed optical fiber The reverse signals of each path are superimposed on each other at the optical splitter located at the remote node, and it is difficult to distinguish which distribution fiber branch a certain reverse signal comes from.

After searching the existing literature, it was found that in order to make up for the shortcomings of the OTDR-based PON link monitoring system, M.M.Rad et al. proposed a passive optical network link monitoring method based on optical coding OC (Optical Coding). In the literature, three different coding mechanism link monitoring schemes are proposed: 1) PON link monitoring scheme based on multi-wavelength optical orthogonal coding MW-OOC (Multi-Wavelength Optical Orthogonal Code), the monitoring system is used in the optical distribution network No active devices are used, no self-energy modules are newly added at the ONU end, and centralized automatic monitoring of link status is adopted at the local end. However, the system has many limitations in terms of practicability: more encoder/decoder components, higher cost, larger volume, larger insertion loss of the encoder, which reduces the quality of the encoded signal; limited codeword space, and poor network scalability ; 2) The PON link monitoring scheme based on periodic code PC (Optical Code), the decoder of this scheme has simple structure, low implementation cost and small insertion loss, but the system still has some shortcomings: PC code word correlation is relatively low Poor, the reflection signal identification process is more complicated. The corresponding identification algorithm is complex; the reflectivity of the first FBG in the PC encoder is fixed at 38%, and the manufacturing process requires high requirements. Once there is an error in the reflectivity, the amplitude of the optical encoding signal will be greatly changed and the judgment result will be affected. And the 38% partial reflectivity also increases the encoder insertion loss; when the network users are large (more than 64 users), the fiber insertion line between FBGs becomes longer and the code size is larger; 3) based on incremental pulses Position IPPC (Incremental Puse-Positioned Code) link monitoring scheme, which uses two-dimensional wavelength time domain coding to distinguish different fiber branches according to different cavity lengths. The use of pulses of different wavelengths is only to improve the correlation characteristics of the codeword, and has not been used to further increase the encoding capacity; in addition, this scheme also decodes the summarized reflected signal, the reflected signal spectrum is complex and diverse, the decoding coherence distance is large, and the decoding process is relatively complicated .

After searching, it was found that X.Zhou, X.Sun et al. proposed a PON link monitoring scheme based on the two-dimensional frequency hopping periodic code 2-DFHPC (2-D Frequency Hopping/Periodic Code), which has a larger codeword Capacity and small coherence distance, etc., but this scheme decodes the summarized reflection signals, the reflection signal spectrum is complex and diverse, the coherence distance is still on the order of meters, the probability of multi-user interference is high, and the decoding process is relatively complicated. The above four different coding mechanism link monitoring schemes all adopt the method of randomly assigning optical codewords, and assign different optical codewords to different optical fiber branches. The monitoring time window range is large, which increases the codeword coherence distance and reduces The accuracy and efficiency of the judgment of the monitoring system.

Contents of the invention

Technical problem: The purpose of the present invention is to address the deficiencies of the existing technology, and propose a method that greatly reduces the coherence distance of codewords, improves the accuracy of the monitoring system, and can meet the reliability and survivability requirements of the next-generation optical access network. A polling passive optical network optical layer detection method based on optical precoding that reduces fault repair time, reduces network operating costs, and improves service quality.

Technical solution: The polling type passive optical network optical layer detection device based on optical precoding of the present invention includes a detection pulse precoding module, an optical circulator, a wavelength division multiplexer, a link fault identification module, and an optical line terminal device , feeding optical fiber, optical splitter, distributed optical fiber, decoder module and user end, the detection pulse precoding module is connected to the first port of the optical circulator, and the link fault identification module is connected to the optical circulator The third interface is connected, the second port of the optical circulator is connected to the U-band demultiplexing port of the wavelength division multiplexer, the C-band demultiplexing port of the wavelength division multiplexer is connected to the optical line terminal equipment, and the wavelength division multiplexer's The multiplexing port is connected to the input end of the optical splitter at the remote node through the feed-in fiber, and the multi-channel output end of the optical splitter is respectively connected to the network side ports of the decoders in the decoder module through multiple distributed optical fibers , the user-side port of each decoder in the decoder module is correspondingly connected to each user end.

In the device of the present invention, the detection pulse precoding module and the link fault identification module are located at the central office, and the decoder module is located at the end of the distributed optical fiber.

The polling type passive optical network optical layer detection method based on optical precoding of the present invention comprises the following steps:

The detection pulse precoding step: the detection pulse precoding module generates a two-dimensional multi-wavelength optical pulse train signal in the U-band, and the signal passes through the optical circulator and the wavelength division multiplexer in turn, feeds into the optical fiber, and then enters the optical splitter;

Link fault identification step: the two-dimensional multi-wavelength optical pulse train signal enters each distributed optical fiber after being split by the optical splitter, and then decodes and reflects at the decoder connected to the end of the distributed optical fiber, and the reflected The decoded signal passes through the distributed optical fiber, the optical splitter, the feed optical fiber, the wavelength division multiplexer and the optical circulator in sequence, and then enters the link fault identification module for link fault identification.

In the preferred solution of the method of the present invention, the polling link fault detection method is adopted in the link fault identification step, specifically: the decoders at the end of each distributed optical fiber correspond to a two-dimensional multi-wavelength optical pulse signal, and each In the detection time window, only one distributed optical fiber link is detected at a time; in different detection time windows, each distributed optical fiber link is detected one by one.

Beneficial effect: compared with the prior art, the present invention has the following advantages:

The present invention utilizes the precoded detection pulse signal and adopts polling mode to monitor the fiber link failure of only one target user at a time. The polling method has not been adopted in the existing technology. The detection pulse signal is applied to each target user, and the reflected detection signal is superimposed at the optical splitter. becomes larger, the detection accuracy of the system decreases. Since the monitored branch link length is known in the present invention, the monitoring time window can be significantly reduced to a small range, the coherent distance of the code word is greatly reduced, and the accuracy of the monitoring system is improved. The present invention meets the reliability and survivability requirements of the rapidly developing next-generation optical access network, reduces fault repair time, reduces network operating costs, improves service quality, attracts more users, and further promotes the research and development of the next-generation broadband access network technology and apply.

Description of drawings

Fig. 1 is a schematic diagram of the detection device of the present invention;

Fig. 2 is a schematic diagram of a reflected signal spectrum after decoding an optical precoded signal in an embodiment.

Detailed ways

Below in conjunction with embodiment and accompanying drawing, technical solution of the present invention is described in detail:

Figure 1 is a schematic diagram of a polling passive optical network optical layer detection device based on optical precoding, including a detection pulse precoding module, an optical circulator, a wavelength division multiplexer, a link fault identification module, an optical line terminal device, Feed-in optical fiber, optical splitter, distributed optical fiber, decoder module and user end, the detection pulse precoding module is connected to the first port of the optical circulator, and the link fault identification module is connected to the first port of the optical circulator Three interface connections, the second port of the optical circulator is connected to the U-band demultiplexing port b of the wavelength division multiplexer, the C-band demultiplexing port a of the wavelength division multiplexer is connected to the optical line terminal equipment, and the wavelength division multiplexer The multiplexing port c of the optical splitter is connected to the input end of the optical splitter at the remote node through the feed-in fiber, and the multiple output ends of the optical splitter are respectively connected to the network side of each decoder in the decoder module through a plurality of distributed optical fibers Port A is connected, and the user-side port B of each decoder in the decoder module is connected to each user end correspondingly.

The polling type passive optical network optical layer detection method based on optical precoding of the present invention comprises the following steps:

Detection pulse precoding step: the detection pulse signal of the present invention adopts U-band transmission, which is transparent to C-band transmission of uplink and downlink data, and there is no mutual interference. The detection pulse precoding module generates a two-dimensional multi-wavelength optical pulse train signal in the U-band, and the signal passes through the optical circulator and wavelength division multiplexer in turn, feeds into the optical fiber, and then enters the optical splitter;

Link fault identification step: the two-dimensional multi-wavelength optical pulse train signal enters each distributed optical fiber after being split by the optical splitter, and then is connected to the end of the distributed optical fiber and decoded by a decoder located at the front end of the user end And reflection, at the end of the distributed optical fiber link, the C-band is used to transmit the uplink and downlink data transparently, and the optical precoded signal is decoded at the decoder at the end of the distributed optical fiber. After decoding and reflection, the relative positions of the optical precoded signals change, and the matching decoder makes the optical precoded signals completely overlap in the time domain to form a single strong pulse; while in other optical fiber links In the path, the decoded signal is dispersed in the time domain, as shown in Figure 2, the schematic diagram of the reflected signal spectrum after decoding the optical precoded signal. The decoded signal decoded and reflected by the decoder passes through the distributed optical fiber, the optical splitter, the feed optical fiber, the wavelength division multiplexer and the optical circulator in sequence, and then enters the link fault identification module for link fault identification.

The polling link fault detection method is adopted in the link fault identification step, specifically: the link fault identification module located in the central office will automatically start the ranging function when each ONU user goes online and registers, and the optical fiber link The length of the path is known, so the detection period of the returned optical decoding signal is also known, which is the round-trip time of the optical detection signal on the PON optical fiber link, and is equal to the length of each distributed optical fiber link One to one correspondence. Since the length of the detected target optical fiber link is determined, the target detection time window can be narrowed to a small time window, and in each detection time window, only one distributed optical fiber link is detected at a time; in different Within the detection time window, each distributed optical fiber link is detected one by one. In the detection time window, after receiving and signal processing by the link fault identification module, the return detection signal of the target optical fiber link can be judged through the pulse amplitude judgment threshold, and the link status information of the target optical fiber branch can be obtained, as shown in Figure 2 The schematic diagram of the reflected signal spectrum after decoding the optical precoded signal is shown.

An example is listed below: in FIG. 1, n ONU users are assigned n different optical precoding signals C ₁ , C ₂ , . . . , C _n . The detection period of each optical fiber link with different distribution is determined as T ₁ , T ₂ , . . . , T _n . In period T ₁ , detect the target link 1, send the detection optical precoded signal C ₁ , decode it at the end of link 1, and obtain a single pulse signal superimposed by multi-wavelength pulses in the time domain, and return to the central office line terminal equipment, and the decoders on other links cannot obtain the superimposed single pulse signal due to the code word mismatch, as shown in the reflected signal spectrum after decoding the optical precoded signal in Figure 2; similarly, in the period T ₂ , the detection By distributing the optical fiber links 2, sending the detection light precoded detection pulse C ₂ , and so on, the polling link detection can be realized.

The foregoing embodiments are only preferred implementations of the present invention. It should be pointed out that those skilled in the art can make several improvements and equivalent replacements without departing from the principle of the present invention. Technical solutions requiring improvement and equivalent replacement all fall within the protection scope of the present invention.

Claims (4)

1. A polling passive optical network optical layer detection device based on optical precoding, characterized in that the detection device includes a detection pulse precoding module, an optical circulator, a wavelength division multiplexer, and a link fault identification module , optical line terminal equipment, feeding optical fiber, optical splitter, distributed optical fiber, decoder module and user end, the detection pulse precoding module is connected to the first port of the optical circulator, and the link fault identification module It is connected to the third interface of the optical circulator, the second port of the optical circulator is connected to the U-band demultiplexing port (b) of the wavelength division multiplexer, and the C-band demultiplexing port (a) of the wavelength division multiplexer is connected to the optical Line terminal equipment connection, the multiplexer port (c) of the wavelength division multiplexer is connected to the input end of the optical splitter at the remote node through the feed-in fiber, and the multiple output ends of the optical splitter pass through multiple distributed optical fibers They are respectively connected to the network-side ports (A) of the decoders in the decoder module, and the user-side ports (B) of the decoders in the decoder module are connected to the respective user terminals correspondingly. 2. The polling type passive optical network optical layer detection device based on optical precoding according to claim 1, wherein the detection pulse precoding module and the link fault identification module are located at the central office, and the The decoder module is located at the end of the distributed fiber. 3. A polling type passive optical network optical layer detection method based on optical precoding, characterized in that, the detection method is based on the device described in claim 1 or 2, comprising the following steps; The detection pulse precoding step: the detection pulse precoding module generates a two-dimensional multi-wavelength optical pulse train signal in the U-band, and the signal passes through the optical circulator and the wavelength division multiplexer in turn, feeds into the optical fiber, and then enters the optical splitter; Link fault identification step: the two-dimensional multi-wavelength optical pulse train signal enters each distributed optical fiber after being split by the optical splitter, and then decodes and reflects at the decoder connected to the end of the distributed optical fiber, and the reflected The decoded signal passes through the distributed optical fiber, the optical splitter, the feed optical fiber, the wavelength division multiplexer and the optical circulator in sequence, and then enters the link fault identification module for link fault identification. 4. The polling type passive optical network optical layer detection method based on optical precoding according to claim 3, wherein the polling type link fault detection method is adopted in the link fault identification step, specifically : The decoders at the end of each distributed optical fiber correspond to a two-dimensional multi-wavelength optical pulse signal. In each detection time window, only one distributed optical fiber link is detected at a time; Fiber optic links are tested one by one.