CN110971882A

CN110971882A - CMTS fiber-to-the-home method

Info

Publication number: CN110971882A
Application number: CN201911265529.5A
Authority: CN
Inventors: 周涛
Original assignee: GUANGDONG DONYAN NETWORK TECHNOLOGIES CO LTD
Current assignee: GUANGDONG DONYAN NETWORK TECHNOLOGIES CO LTD
Priority date: 2019-12-11
Filing date: 2019-12-11
Publication date: 2020-04-07

Abstract

The invention discloses a method for a CMTS to home, which comprises the following steps: in the uplink direction, the uplink light of the RFoG ONU is firstly separated into an optical receiving module of the RFoG pon, then an optical signal is converted into an RF electric signal, then a plurality of paths of RF electric signals are sent to a coupler to be mixed, and finally the mixed RF electric signal is sent to a return receiver of a machine room through backward light; in the downlink direction, firstly, the mixed 2-wavelength light 1550/1610nm is separated into 1550nm, then, the light is sent to the optical splitter, the light separated by the optical splitter is sent to the output side combiner of the RFoG pon, and finally, the light is transmitted to the RFoG ONU from the output port of the RFoG pon in the whole downlink direction without photoelectric conversion. The invention is suitable for the transformation of the RFoG network of any traditional scheme, is beneficial to later-stage engineering maintenance, and has the advantages of reducing the convergent noise and the background noise, saving the main line optical fiber resource, having no OBI in the RFoG network no matter what uplink mode the CMTS adopts, and the like.

Description

CMTS fiber-to-the-home method

Technical Field

The invention relates to the technical field of optical fibers, in particular to an improved CMTS fiber-to-the-home method.

Background

The RFoG technology is a CMTS fiber to the home solution based on cable tv fiber network and based on rf transmission, which makes the original CMTS network smoothly scalable to the FTTH network. In a cable television bidirectional transmission network constructed by applying RFoG technology, a forward channel is completely the same as a traditional CMTS network, and a broadcast transmission service is adopted, so that the fundamental difference is on a return channel. The working mode of a laser of a reverse light emission component of an optical node (RFoG ONU) adopting the RFoG technology is a burst mode, and the data sent by a CM is used for controlling the optical node to return the working state of the laser to be turned on or turned off.

After the conventional CMTS network introduces the RFoG technology, it is not only convenient to move the optical node forward to improve the user bandwidth, but also can effectively suppress the aggregate noise of the upstream backhaul channel, and a comparison between the conventional CMTS network and the RFoG network is shown in fig. 2 and fig. 3.

However, the RFoG technology also has a major problem, and most CMTS systems currently employ SCDMA uplink access, and optical signals from different RFoG ONUs usually use the same wavelength. However, in practice, there are still slight differences between these wavelengths due to differences in the generation steps. Generally, these different light waves do not create much problem. When two (or more) return light waves are exactly the same and return signals are sent simultaneously (overlappingly), the rf output of the return system will generate broadband noise. The OBI (Optical band Interference) is a physical phenomenon that two or more RFoG ONUs (Optical Network Units) return transmitters work at close frequency and simultaneously transmit signals to the same return receiver. The CMTS allows for overlapping of upstream bursts on different frequencies, which does not pose a problem on conventional HFCs. However, in the CMTS system using the RFoG technology, the caused noise can greatly affect the operation of the CMTS, which causes the transmission efficiency of the CMTS return signal to be reduced, or even the CMTS return signal cannot operate. As shown in fig. 4.

To overcome the inherent drawbacks of RFoG technology, one of the following two techniques is currently used to resolve uplink conflicts.

1. RFoG technology with CMTS working upstream in TDMA mode:

as shown in fig. 6, after RFoG is used in the CMTS network, only burst transmission can be used on the backhaul channel (upstream), and one of the benefits is that the upstream burst transmission mode can solve the background noise during the off period of the transmission module, that is, the RFoG ONU will not generate any noise when there is no data upstream. Secondly, when the cable modem of the network optical node band is sharply reduced or even only one cable modem is carried, the convergence noise is greatly reduced. However, RFoG requires the original CMTS to operate efficiently when TDMA is accessed, i.e., the CMTS needs to control all CMs to have only one CM uploading data within a certain timestamp.

The advantages and disadvantages of the adopted RFoG + TDMA and the traditional RFOG access are as follows:

(1) the advantages are that: when two (or more) return light waves just send signals at the same time (overlap), the radio frequency output of the return system generates broadband noise, and when the RFoG + TDMA is adopted, the phenomenon can be effectively avoided, namely, the OBI can be eliminated

(2) The method has the following defects: at present, most of CMTS and CM systems adopt SCDMA uplink technology, and when the TDMA uplink technology is adopted, the uplink bandwidth is obviously reduced.

2. The uplink direction of the RFoG ONU adopts transmitting modules with different wavelengths.

When the difference of the transmission wavelength of each RFoG ONU hung under a machine room return optical receiver (burst receiving mode) is more than 0.5nm, the OBI phenomenon is not obvious. If RFoG ONUs with different emission wavelengths are adopted, an operator needs to accurately control the wavelength of each RFoGONU, the RFoG ONUs cannot be replaced mutually, the engineering installation and maintenance must be strictly required, the installation and maintenance cost is high, more spare parts are added, and the engineering is difficult to realize.

There is no better solution to overcome the above two drawbacks of the improved RFoG, and provide a solution to solve the above rf og uplink collision in the SCDMA mode, and to be compatible with the former terminal device in the previous CMTS or the modification of the RFoG network?

The present invention solves the above technical problems.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the CMTS fiber-to-the-home method with simple construction is provided, can be compatible with the scene that the existing network RFoG ONU transmits the same wavelength in the whole network, and realizes that the RFoG network eliminates OBI, so that the RFoG deployment process is not limited by various conditions.

The technical scheme adopted by the invention for solving the technical problems is as follows:

the invention provides a method for a CMTS to home, which comprises the following steps: in the uplink direction, the uplink light of the RFoG ONU is firstly separated into an optical receiving module of the RFoG pon, then an optical signal is converted into an RF electric signal, then a plurality of paths of RF electric signals are sent to a coupler to be mixed, and finally the mixed RF electric signal is sent to a return receiver of a machine room through backward light; in the downlink direction, firstly, the mixed 2-wavelength light 1550/1610nm is separated into 1550nm, then, the light is sent to the optical splitter, the light separated by the optical splitter is sent to the output side combiner of the RFoGpon, and finally, the light is transmitted to the RFoG ONU from the output port of the RFoG pon in the whole downlink direction without photoelectric conversion.

The CMTS fiber-to-the-home method comprises the following steps:

step 1, mixing 2-wavelength light 1550/1610nm at an output end of an RFoG pon, and separating 1610nm uplink light in an uplink direction through a combiner-combiner;

step 2, light of up 1610nm enters a burst light receiving module, and the receiving module converts the optical signal into an RF electrical signal;

step 3, mixing the RF electric signals converted by all the receiving modules of the RFoG pon on a coupler;

step 4, converting the RF electric signal mixed by the coupler into a 1610nm optical signal through reverse light;

step 5, transmitting the optical signal of 1610nm to a return optical receiver of a machine room after the optical signal of the reverse light passes through an input end multiplexer/demultiplexer of the RFoG pon;

step 6, light of 1610nm is adopted in the whole uplink direction, and in order to solve OBI, the light is firstly converted into an electric signal, and the electric signal is mixed and then converted into an optical signal for back transmission;

step 7, designing the adopted uplink to be 1610nm light, or matching RFoG onus of other uplink wavelengths by changing windows of a branching and combining device and a burst receiving module in the RFoG pon;

step 8, mixing 2-wavelength light 1550/1610nm at the input end of the RFoG pon, and separating 1550nm downlink light in a downlink direction through a combiner/divider;

9, enabling the downlink 1550nm light to enter an output side combiner of the RFoG pon after passing through the optical splitter;

step 10, mixing the downlink 1550nm light to an output port of an RFoG pon by an output side combiner;

step 11, downlink whole-course optical transmission without photoelectric conversion; the number of output ports of the optical splitter is the number of output ports of RFoG pon.

The CMTS fiber to the home method may employ the following devices, including: the system comprises a reverse optical transmitter which inputs RF electric signals, a burst optical receiving module, an RF coupler, a combiner-combiner and an optical splitter.

The reverse optical transmitter adopts the transmission process from radio frequency to light wave, and relevant indexes of the reverse optical transmitter comprise: a DFB laser is adopted, the optical wavelength is 1610 +/-10 nm, the output optical power is more than or equal to-3 dBm, the radio frequency is 5-65 MHz, and the radio frequency input impedance is 75 omega.

The port number of the burst light receiving module corresponds to the number of output ports of the RFoG PON, the input port of the RFoG PON is connected to a return light receiver of the CMTS system of the machine room, and the output port of the RFoG PON is connected to the RFoG ONU.

The number of the output ports of the RFoG PON is 4, 8, 16 and 32, which is convenient for planning and reducing the production cost.

The burst light receiving module detects the envelope of a digital RF signal to control the driving of the laser, the laser is modulated and output when a signal exists, the laser is switched off when no signal exists, and no light is output.

The RF coupler employs a 5-200MHz radio frequency mixer for mixing radio frequency signals of different frequency spectra.

The branching and combining device adopts a 1610nm and 1550nm three-port double-window branching and combining device and is used for separating and mixing 1610nm and 1550nm optical signals.

The optical splitter adopts a 1550nm optical splitter, the output index meets the standard of the optical splitter, and the number of the output ports of the optical splitter is the same as that of the output ports of the RFoG PON.

Compared with the prior art, the invention has the following main advantages:

(1) the RFoG ONU reduces the length of a coaxial cable close to a user side, and reduces the convergent noise and the background noise.

(2) The RFoG PON can be cascaded, and when the network adopts small optical nodes, only one trunk optical fiber is needed for a port of one CMTS, so that the trunk optical fiber resource is saved obviously.

(3) No OBI exists in the RFoG network regardless of which upstream mode the CMTS employs.

This is the most important point affecting performance.

(4) The OBI suppression assembly (RFoG PON) and an optical receiver of a machine room can transmit long distance to reach 50 km.

In the traditional RFoG network, after light passes through a 1:32 optical splitter, uplink attenuation is about 18db, and the maximum transmission optical power of RFoG onus is considered to be 3dbm, so that the transmission to a return receiver of a machine room can be guaranteed to be 10 km. After the RFoG PON is adopted, the distance between the rfogpon and the RFoG ONU can be guaranteed to be 10km when the distance is 1: 32. The transmitting power of the returned light of the RFoG PON is-3 dbm, the sensitivity of a returned receiver of the following data machine room is about-19 dbm, the loss between the RFoG PON and a returned receiving module of the machine room can reach 16db, and the distance between the RFoG PON and the machine room can reach more than 50 km.

The following data: the following test items all involved the use of variable optical attenuators +10 km of fiber for the optical link.

And the return optical receiver in the uplink adopts the RFOG technology to connect the related technical parameters of the four-way optical node.

And when the test network works normally, the test network transmits back the lowest receivable optical power of the optical receiver.

And rfog onus is adjusted to be in a non-burst sending mode (debugging mode), the CM works normally under the low receiving optical power of-19 dBm when the reverse optical receiver works in an AGC (automatic gain control) working state, and when the receiving optical power is below-20 dBm, the internal software of the reverse optical receiver turns off an attenuator, the CM is disconnected, and the receivable limit optical power is not detected.

The rfog onus is adjusted to be in a burst sending mode (normal mode), the CM works normally when the attenuation is set to be 0 under the low receiving optical power of-19 dBm in the working state of the MGC, and the CM is disconnected when the attenuation is set to be more than 5 dB.

In the test, it is found that when the reverse optical receiver is in the MGC operating state and the reverse optical receiving power is continuously reduced, the CM output level is correspondingly increased until the maximum CM output level is increased to 55 dBmv; conversely, as the reverse optical receive power is increased, the CM output level gradually decreases, dropping the CM line as low as 80 dBuv.

(5) The method is suitable for the transformation of the RFoG network of any traditional scheme, and is beneficial to later engineering maintenance.

When the customer's RFoG ONU transmission wavelength is not 1610nm, it is only necessary to change the 1610nm wavelength in the splitter window to be uniform with the customer.

Drawings

FIG. 1 is a schematic diagram of the present invention.

Figure 2 is a schematic diagram of a conventional CMTS network architecture.

Fig. 3 is a schematic diagram of a network structure using RFoG technology.

Fig. 4 is an OBI that is one of the legacy RFoG system limitations.

Figure 5 is a simplified block diagram of a typical CMTS networking.

Fig. 6 is a simplified block diagram of a typical RFoG networking.

Fig. 7 is a model of OBI inhibition of constitutive uplinking.

Fig. 8 is an OBI inhibition composition downlink model.

Fig. 9 is a burst receive module principle in an OBI suppression component that converts an optical signal to an RF electrical signal.

Detailed Description

The present invention will be further described with reference to the following examples and drawings, but the present invention is not limited thereto.

The invention overcomes many problems of various current schemes mentioned in the background art, as shown in fig. 1, is suitable for SCDMA mode access, also solves the problems of engineering and convenient installation and maintenance, and is compatible with the same RFoG ONU used in the whole network. The equipment of this scheme is called OBI suppression equipment and is temporarily named as RFoG PON.

1) How to implement OBI suppression in SCDMA mode:

an OBI suppression component body integrating a set of multi-channel wave combiner, multi-channel burst light receiving module, RF circuit coupler, reverse light emitting module and optical splitter, which is called RFoG PON for short.

2) Ascending model:

as shown in fig. 7: the device integrates n wave combiners to receive return optical signals (1610nm) sent by the RFoG-ONU, each wave combiner transmits the return optical signals (1610nm) to one connected burst optical receiving module, the n burst optical receiving modules convert the optical signals into n RF electric signals with different frequencies, then the n RF electric signals are connected to the radio frequency coupler in a centralized mode to synthesize one path of RF signals to the reverse optical transmitter, and finally the reverse optical transmitter inputs the optical signals (1610nm) to the wave combiners to finish uplink output.

3) A downlink model:

as shown in fig. 8: an input side combiner integrated with equipment receives downlink 1550nm optical signals and transmits the signals to a 1: and the output side of the optical splitter sends n paths of signals to the n output side wave combining modules, and the wave combiner finishes the output of the downlink optical signals.

The invention provides a method for a CMTS to home, which comprises the following steps: in the uplink direction, uplink light of the RFoGONU is firstly separated into an optical receiving module of the RFoG pon, then optical signals are converted into RF electric signals, then the multi-channel RF electric signals are sent into a coupler to be mixed, and finally the mixed RF electric signals are sent to a return receiver of a machine room through backward light; in the downlink direction, firstly, the mixed 2-wavelength light 1550/1610nm is separated into 1550nm, then, the light is sent to the optical splitter, the light separated by the optical splitter is sent to the output side combiner of the RFoGpon, and finally, the light is transmitted to the RFoG ONU from the output port of the RFoG pon in the whole downlink direction without photoelectric conversion.

The method comprises the following steps:

The invention solves the problem that OBI is difficult to eliminate in a scdma mode in the RFoG deployment process by a set of OBI (optical beacon interference) inhibition equipment which is temporarily named as RFoGPON, and is compatible with the same RFoG ONU used in the whole network.

The RFoG PON device employed in the present invention is an active device, as shown in fig. 1: the device comprises a reverse optical transmitter, a burst optical receiving module, an RF coupler, a branching and combining device and a 1550nm optical splitter.

The reverse optical transmitter is an existing device, and mainly aims to convert an uplink coupled RF radio frequency signal into a 1610nm optical signal and transmit the optical signal back to a back transmission receiving module of a machine room, and relevant indexes of the reverse optical transmitter are shown in the following table:

the burst receiving module is composed of a burst receiving optical module of 1610nm, as shown in fig. 9. The number of receiving ports of all burst light receiving modules is equal to the number of output ports of the RFoG PON, the input ports of the RFoG PON are connected to a return light receiver of the CMTS system of the computer room, and the output ports of the RFoG PON are connected to the RFoG ONU. The number of outlets of the RFoG PON is 4, 8, 16 and 32, which is convenient for planning and reducing the production cost.

The burst light receiving module detects the envelope of a digital RF signal to control the driving of the laser, the laser is modulated and output when a signal exists, the laser is switched off when no signal exists, and no light is output. One end of the burst receiving module is connected with the RF coupler, and the other end of the burst receiving module is connected with the branching and combining device at the output end.

The RF coupler adopts a radio frequency mixer of 5-200MHz for mixing radio frequency signals of different frequency spectrums, in particular mixing the radio frequency signals of different frequency spectrums in the uplink direction.

The branching and combining device adopts a 1610nm and 1550nm three-port double-window branching and combining device, and the purpose of the branching and combining device is mainly to separate and mix 1610nm and 1550nm optical signals.

Claims

1. A CMTS fiber-to-the-home method is characterized in that upstream light of an RFoG ONU is firstly separated into an optical receiving module of an RFoG pon in an upstream direction, then an optical signal is converted into an RF electric signal, then a plurality of paths of RF electric signals are sent into a coupler to be mixed, and finally the mixed RF electric signal is sent to a return receiver of a machine room through backward light; in the downlink direction, firstly, the mixed 2-wavelength light 1550/1610nm is separated into 1550nm, then, the light is sent to the optical splitter, the light separated by the optical splitter is sent to the output side combiner of the RFoG pon, and finally, the light is transmitted to the RFoG ONU from the output port of the RFoG pon in the whole downlink direction without photoelectric conversion.

2. The CMTS fiber to the home method of claim 1, comprising the steps of:

3. A CMTS fiber to the home method of claim 1 or 2, employing equipment comprising: the system comprises a reverse optical transmitter which inputs RF electric signals, a burst optical receiving module, an RF coupler, a combiner-combiner and an optical splitter.

4. The CMTS fiber to the home method of claim 3, wherein the reverse optical transmitter uses rf to lightwave transmission, and the relevant criteria include: a DFB laser is adopted, the optical wavelength is 1610 +/-10 nm, the output optical power is more than or equal to-3 dBm, the radio frequency is 5-65 MHz, and the radio frequency input impedance is 75 omega.

5. The CMTS fiber to the home method of claim 3, wherein the number of ports of the burst optical receiving module corresponds to the number of outlets of an RFoG PON, wherein the inlets of the RFoG PON are connected to a backhaul optical receiver of the machine room CMTS system, and wherein the outlets of the RFoG PON are connected to RFoG ONUs.

6. The CMTS fiber to the home method of claim 5, wherein: the number of outlets of the RFoG PON is 4, 8, 16 and 32, which is convenient for planning and reducing the production cost.

7. The CMTS fiber to the home method of claim 5, wherein the burst receive module detects an envelope of the digital RF signal to control the laser drive, the laser modulating output when there is a signal, the laser turning off when there is no signal, and no light output.

8. The CMTS fiber to the home method of claim 3, wherein the RF coupler employs a 5-200MHZ RF mixer for mixing RF signals of different frequency spectra.

9. A CMTS fiber to the home method as claimed in claim 3 wherein the combiner employs a 1610nm and 1550nm three port dual window combiner for splitting and mixing 1610nm and 1550nm optical signals.

10. The CMTS fiber to the home method of claim 3, wherein the splitter is a 1550nm splitter, and the output criteria meets the splitter criteria, and the number of splitter outputs is the same as the number of RFoG PON outputs.