CN113411137A - Uplink optical signal modulation method, optical communication node and system - Google Patents
Uplink optical signal modulation method, optical communication node and system Download PDFInfo
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- CN113411137A CN113411137A CN202110528226.9A CN202110528226A CN113411137A CN 113411137 A CN113411137 A CN 113411137A CN 202110528226 A CN202110528226 A CN 202110528226A CN 113411137 A CN113411137 A CN 113411137A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/548—Phase or frequency modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/40—Transceivers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/06—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
Abstract
The application discloses an uplink optical signal modulation method, an optical communication node and a system, which belong to the technical field of optical communication, wherein the method comprises the following steps: the method comprises the steps that a downlink optical signal sent by a central node is received in a coherent mode according to a local carrier signal generated by a laser; calculating a frequency offset estimation value of the local carrier signal and the downlink optical signal, wherein the frequency offset estimation value is a difference value of central frequencies of the local carrier signal and the downlink optical signal; performing frequency shift and digital-to-analog conversion processing on the uplink baseband signal according to the frequency offset estimation value, wherein the uplink baseband signal is generated according to uplink data, and the digital-to-analog conversion is used for converting the digital signal into an analog signal; and modulating according to the local carrier signal and the uplink baseband signal after the digital-to-analog conversion processing to obtain an uplink optical signal. In the embodiment of the application, the user node can adjust in time according to the frequency hopping condition; and the frequency of the laser is not required to be adjusted, and the uplink optical signal modulation can be realized even if the laser of the user node is not provided with a frequency adjustment interface, so that the manufacturing cost of the user node is reduced.
Description
Technical Field
The present application relates to the field of optical communication technologies, and in particular, to an uplink optical signal modulation method, an optical communication node, and an optical communication system.
Background
With the continuous development of high definition video and Virtual Reality (VR) technologies, the demands of users on the communication capacity and the delay of an optical communication system are higher and higher. In order to increase the communication capacity of the optical communication system and reduce the delay, Frequency Division Multiple Access (FDMA) technology and Code Division Multiple Access (CDMA) technology are applied to the optical communication system.
Taking FDMA as an example, after FDMA is applied to an optical communication system, a single wavelength in the system is divided into a plurality of subcarriers, and each user node in the system flexibly allocates wavelengths and channel resources in the wavelengths. Each user node is connected with a central node in the system through an optical coupler on a link, so that uplink and downlink optical signal transmission is carried out between the user nodes and the central node.
In order to avoid mutual crosstalk between subcarriers used by each user node, a frequency guard interval needs to be reserved between each subcarrier. However, in the uplink optical signal transmission process, since the uplink optical signals are modulated by each user node using its own laser, when the laser of a certain user node generates frequency offset and the frequency offset exceeds the frequency guard interval, crosstalk occurs between the subcarriers used by the user node and adjacent subcarriers.
In order to avoid subcarrier crosstalk caused by frequency offset of the laser, in the related art, after a user node receives a downlink optical signal transmitted by a central node, a frequency offset estimation value of the laser is calculated according to the downlink optical signal and a local carrier signal generated by the laser, so that the laser is subjected to feedback adjustment by using the frequency offset estimation value. Even if the laser generates frequency deviation, the local carrier signal generated by the laser can still keep synchronization with the downlink optical signal through the adjusting mechanism, so that the modulated uplink optical signals are prevented from mutual crosstalk.
However, since the feedback adjustment speed of the laser is slow, when a downlink optical signal or a frequency jump occurs in the laser, the laser cannot be adjusted in time; and when the laser of the user node is not configured with a corresponding frequency adjustment interface, the feedback adjustment cannot be performed.
Disclosure of Invention
In order to solve the problem that in the related technology, because the speed of feedback adjustment of the laser is slow, when a downlink optical signal or the laser generates frequency hopping, the laser cannot be adjusted in time; and when the laser of the user node is not configured with a corresponding frequency adjustment interface, feedback adjustment cannot be performed.
In a first aspect, the present application provides a method for modulating an uplink optical signal, including:
the method comprises the steps that a downlink optical signal sent by a central node is received in a coherent mode according to a local carrier signal generated by a laser;
calculating a frequency offset estimation value of the local carrier signal and the downlink optical signal, wherein the frequency offset estimation value is a difference value of central frequencies of the local carrier signal and the downlink optical signal;
performing frequency shift and digital-to-analog conversion processing on the uplink baseband signal according to the frequency offset estimation value, wherein the uplink baseband signal is generated according to uplink data, and the digital-to-analog conversion is used for converting the digital signal into an analog signal;
and modulating according to the local carrier signal and the uplink baseband signal after the digital-to-analog conversion processing to obtain an uplink optical signal.
In this embodiment, after receiving a downlink optical signal sent by a central node, a user node calculates a frequency offset estimation value of a local carrier signal and the downlink optical signal generated by a laser, and performs frequency shift processing and digital-to-analog conversion processing on a generated uplink baseband signal according to the frequency offset estimation value, so as to modulate an uplink optical signal according to the local carrier signal and the uplink baseband signal after the digital-to-analog conversion processing; because the frequency shift of the laser is already taken into account when the uplink baseband signal is subjected to frequency shift processing, the central frequency of the modulated uplink optical signal is not influenced by the frequency shift of the laser, and the mutual crosstalk of the uplink optical signals caused by the frequency shift of the laser is avoided; meanwhile, compared with the frequency adjustment of the laser, the speed of frequency shift processing of the uplink baseband signal is high, so that the user node can be adjusted in time according to the frequency hopping condition when the frequency hopping of the downlink optical signal or the laser occurs; in addition, in the whole modulation process, the frequency of the laser is not required to be adjusted, and even if the laser of the user node is not provided with a frequency adjustment interface, the user node can also realize uplink optical signal modulation, so that the manufacturing cost of the user node is reduced.
In one possible design, the downstream optical signal has a center frequency f0The frequency offset estimation value is delta f, the uplink baseband signal is an uplink baseband FDMA signal, and the central frequency of the uplink baseband FDMA signal is fsub；
According to the frequency deviation estimation value, the frequency shift and digital-to-analog conversion processing is carried out on the uplink baseband signal, and the processing comprises the following steps:
frequency shifting center frequency of uplink baseband FDMA signal to fsub-Δf；
Converting the uplink baseband FDMA signal subjected to frequency shift processing into an analog signal;
obtaining an uplink optical signal according to the modulation of the local carrier signal and the uplink baseband signal after the digital-to-analog conversion, including:
carrying out Quadrature (IQ) modulation on the local carrier signal and the processed uplink baseband FDMA signal to obtain an uplink optical signal, wherein the center frequency of the uplink optical signal is f0+fsub。
In this embodiment, when the uplink optical signal is obtained based on the modulation of the uplink baseband FDMA signal, the frequency shift is performed based on the original center frequency of the uplink baseband FDMA signal according to the frequency offset estimation value, so that the finally modulated uplink optical signal is only related to the center frequencies of the downlink optical signal and the original uplink baseband FDMA signal, thereby avoiding the uplink optical signal from being affected by the frequency offset of the laser.
In one possible design, the downstream optical signal has a center frequency f0The frequency offset estimation value is delta f, and the uplink baseband signal is an uplink baseband CDMA signal;
and performing frequency shift and digital-to-analog conversion processing on the uplink baseband signal according to the frequency offset estimation value, wherein the processing comprises the following steps:
shifting the center frequency of the uplink baseband CDMA signal to-delta f;
converting the uplink baseband CDMA signal after frequency shift processing into an analog signal;
modulating according to the local carrier signal and the uplink baseband signal after the digital-to-analog conversion processing to obtain an uplink optical signal, including:
IQ modulation is carried out on the local carrier signal and the processed uplink baseband CDMA signal to obtain an uplink optical signal, wherein the central frequency of the uplink optical signal is f0。
In this embodiment, when the uplink optical signal is obtained based on the modulation of the uplink baseband CDMA signal, the center frequency of the uplink baseband FDMA signal is shifted to- Δ f according to the frequency offset estimation value Δ f, so that the center frequency of the uplink optical signal that is finally modulated and the center frequency of the downlink optical signal are kept synchronous, thereby preventing the uplink optical signal from being affected by the frequency offset of the laser.
In one possible design, after coherently receiving a downlink optical signal sent by a central node according to a local carrier signal generated by a laser, the method further includes:
estimating channel parameters according to the downlink optical signals;
and performing channel parameter pre-compensation on the uplink baseband signal according to a channel parameter estimation result, wherein the channel parameter estimation result comprises at least one of dispersion estimation or optical fiber dynamic delay estimation.
In this embodiment, after receiving the downlink optical signal, the user node estimates a channel parameter according to the downlink optical signal, thereby determining the channel quality of the channel with the central node, and performs channel parameter pre-compensation on the uplink baseband signal according to a channel parameter estimation result, thereby reducing the influence of the channel on the transmission of the uplink optical signal, and further improving the transmission quality of the uplink optical signal.
In one possible design, after coherently receiving a downlink optical signal sent by a central node according to a local carrier signal generated by a laser, the method further includes:
and performing analog-to-digital conversion and data signal processing on the received downlink optical signal to recover downlink data, wherein the analog-to-digital conversion is used for converting the analog signal into a digital signal.
In a second aspect, the present application provides an optical communication node comprising: a coherent receiver, an analog-to-Digital converter, a laser, a power divider, a Digital-to-analog converter, a modulator and a Digital Signal Processing (DSP) chip;
the power divider is connected with the laser and used for dividing the local carrier signal generated by the laser into two paths to be output;
the coherent receiver is connected with the power divider and used for carrying out coherent reception on the downlink optical signal according to the local carrier signal output by the power divider to obtain a downlink analog signal;
the analog-to-digital converter is connected with the coherent receiver and used for converting a downlink analog signal output by the coherent receiver into a downlink digital signal;
the DSP chip is connected with the analog-to-digital converter and used for recovering downlink data according to the downlink digital signal and calculating a frequency deviation estimation value of the laser, wherein the frequency deviation estimation value is used for indicating a difference value of the central frequencies of the local carrier signal and the downlink optical signal;
the DSP chip is also connected with the digital-to-analog converter and used for carrying out frequency shift processing on the uplink baseband signal according to the frequency offset estimation value and sending the uplink baseband signal after the frequency shift processing to the digital-to-analog converter, and the digital-to-analog converter is used for converting the uplink baseband signal after the frequency shift processing into an uplink analog signal;
the modulator is respectively connected with the power divider and the digital-to-analog converter and used for modulating according to the local carrier signal and the uplink analog signal output by the power divider to obtain an uplink optical signal.
In this embodiment, after receiving a downlink optical signal sent by a central node in a coherent manner, an optical communication node calculates a frequency offset estimation value of a local carrier signal and the downlink optical signal generated by a laser through a DSP chip, performs frequency shift processing on a generated uplink baseband signal according to the frequency offset estimation value, and modulates the local carrier signal and an uplink analog signal (generated after digital-to-analog conversion of the frequency-shifted uplink baseband signal) generated by the laser through a modulator to obtain an uplink optical signal; because the frequency shift of the laser is already taken into account when the uplink baseband signal is subjected to frequency shift processing, the central frequency of the modulated uplink optical signal is not influenced by the frequency shift of the laser, and the mutual crosstalk of the uplink optical signals caused by the frequency shift of the laser is avoided; meanwhile, compared with the frequency adjustment of the laser, the speed of performing digital frequency shift processing on the uplink baseband signal through the DSP chip is higher, so that when the frequency hopping of the downlink optical signal or the laser occurs, the optical communication node can be adjusted in time according to the frequency hopping condition; in addition, in the whole modulation process, the frequency of the laser is not required to be adjusted, and even if the laser of the optical communication node is not provided with a frequency adjustment interface, uplink optical signal modulation can be realized, so that the manufacturing cost of the optical communication node is reduced.
In one possible design, the DSP chip includes a frequency offset estimation unit, a frequency shift unit, and a baseband signal generation unit;
the frequency offset estimation unit is connected with the analog-to-digital converter and used for calculating a frequency offset estimation value;
the frequency shift unit is respectively connected with the frequency offset estimation unit and the baseband signal generation unit and is used for performing frequency shift processing on the uplink baseband signal output by the baseband signal generation unit according to the frequency offset estimation value.
In one possible design, the downstream optical signal has a center frequency f0The frequency offset estimation value is delta f, the baseband signal generation unit is an FDMA signal generation unit, and the center frequency of the output uplink baseband FDMA signal is fsub；
A frequency shift unit for shifting the center frequency of the uplink baseband FDMA signal to fsub-Δf；
The digital-to-analog converter is used for converting the uplink baseband FDMA signal subjected to frequency shift processing into an uplink analog signal;
modulator of pairIQ modulation is carried out on the local carrier signal and the uplink analog signal to obtain an uplink optical signal, wherein the center frequency of the uplink optical signal is f0+fsub。
In this embodiment, when the uplink optical signal is obtained based on the modulation of the uplink baseband FDMA signal, the frequency shift unit shifts the frequency based on the original center frequency of the uplink baseband FDMA signal according to the frequency offset estimation value, so that the finally modulated uplink optical signal is only related to the center frequencies of the downlink optical signal and the original uplink baseband FDMA signal, thereby avoiding the uplink optical signal from being affected by the frequency offset of the laser.
In one possible design, the downstream optical signal has a center frequency f0The frequency offset estimation value is delta f, and the baseband signal generation unit is a CDMA signal generation unit;
the frequency shift unit is used for shifting the central frequency of the uplink baseband CDMA signal to-delta f;
the digital-to-analog converter is used for converting the uplink baseband CDMA signal after the frequency shift processing into an uplink analog signal;
a modulator for IQ modulating the local carrier signal and the uplink analog signal to obtain an uplink optical signal with a center frequency f0。
In this embodiment, in the embodiment, when the uplink optical signal is obtained based on the modulation of the uplink baseband CDMA signal, the frequency shift unit shifts the center frequency of the uplink baseband FDMA signal to- Δ f according to the frequency offset estimation value Δ f, so that the center frequency of the uplink optical signal that is finally modulated and the center frequency of the downlink optical signal are kept synchronous, thereby avoiding the uplink optical signal from being affected by the frequency offset of the laser.
In one possible design, the DSP chip further includes a channel parameter estimation unit and a channel parameter pre-compensation unit;
the channel parameter estimation unit is connected with the analog-to-digital converter and used for performing channel parameter estimation according to the downlink optical signal and outputting a channel parameter estimation result, wherein the channel parameter estimation result comprises at least one of dispersion estimation or optical fiber dynamic delay estimation;
the channel parameter pre-compensation unit is respectively connected with the channel parameter estimation unit and the baseband signal generation unit and is used for performing channel parameter pre-compensation on the uplink baseband signal according to the channel parameter estimation result.
In this embodiment, after the DSP chip receives the downlink optical signal in a correlated manner, the channel parameter estimation unit estimates the channel parameter, so as to determine the channel quality of the channel between the DSP chip and the central node, and according to the channel parameter estimation result, the channel parameter pre-compensation unit performs channel parameter pre-compensation on the uplink baseband signal, so as to reduce the influence of the channel on the transmission of the uplink optical signal, and further improve the transmission quality of the uplink optical signal.
In a third aspect, the present application provides a chip system, configured to implement the DSP chip in the optical communication node in any one of the possible designs of the second aspect or the second aspect. The chip system may be formed by a chip, and may also include a chip and other discrete devices. The chip may be an Application-Specific Integrated Circuit (ASIC), or may be other types of chips. Optionally, the chip system may further include a processor, configured to support the DSP chip to implement the functions related to the foregoing aspects, for example, to obtain/calculate the signal and/or the frequency offset estimation value related to the foregoing aspects, perform the frequency shift processing in the foregoing aspects, and/or perform the channel parameter pre-compensation processing. In one possible design, the system-on-chip further includes a memory for storing necessary program instructions and data for the DSP chip.
In a fourth aspect, the present application provides an optical communication system comprising: the system comprises a central node and n user nodes, wherein the n user nodes are connected with the central node through an optical coupler, n is not less than 2 and is an integer;
the central node is used for sending downlink optical signals to the n user nodes, and the n user nodes are used for sending uplink optical signals to the central node;
each user node comprises an optical communications node as described in the second aspect above or in any one of the possible designs of the second aspect.
Drawings
Fig. 1 illustrates a system architecture diagram of an optical communication system provided by an embodiment of the present application;
fig. 2 is a schematic diagram of an implementation in which a user node performs optical signal transmission with a central node by using different subcarriers;
fig. 3 is a schematic structural diagram of an optical communication node according to an embodiment of the present application;
fig. 4 is a schematic structural diagram of an optical communication node according to another embodiment of the present application;
fig. 5 is a schematic structural diagram of an optical communication node according to another embodiment of the present application;
fig. 6 is a schematic structural diagram of an optical communication node according to another embodiment of the present application;
fig. 7 is a flowchart illustrating an uplink optical signal modulation method according to an embodiment of the present application.
Detailed Description
Embodiments of the present application will be described in further detail below with reference to the accompanying drawings.
Referring to fig. 1, a system architecture diagram of an optical communication system provided in an embodiment of the present application is shown, where the optical communication system includes a central node 110 and n user nodes 120, where the n user nodes 120 are connected to the central node 110 through an optical coupler 130 (or called optical fiber coupler, english: coupler).
The central node 110 is an optical communication node located on a core network (english: core netwok) side, and is configured to modulate downlink data from the core network into a downlink optical signal (modulated by a local carrier signal generated by an internal laser), and send the downlink optical signal to the user node 120 through a physical channel with the user node 120, where the physical channel between the central node 110 and the user node 120 is an optical fiber.
The user node 120 is an optical communication node located at a user side, and is configured to connect to a user equipment, modulate uplink data from the user equipment into an uplink optical signal (modulated by a local carrier signal generated by a built-in laser), and transmit the uplink optical signal to the central node 110 through a physical channel with the central node 110. In one possible design, the user node 110 is an Optical modem (or Optical modem) connected to the user equipment.
In order to increase the capacity of the optical communication system and reduce the transmission delay, the optical communication system shown in fig. 1 employs FDMA technology or CDMA technology.
After the FDMA technology is applied, a single wavelength in an optical communication system is divided into a plurality of subcarriers (different subcarriers correspond to different frequencies), each user node performs optical signal transmission by using the subcarrier allocated to each user node, correspondingly, a central node transmits downlink optical signals to different user nodes through different subcarriers, and distinguishes uplink optical signals sent by different user nodes according to the subcarriers.
Illustratively, as shown in fig. 2, the user node 1 performs optical signal transmission with the central node by using a subcarrier with a center frequency f1, the user node 2 performs optical signal transmission with the central node by using a subcarrier with a center frequency f2, the user node N performs optical signal transmission with the central node by using a subcarrier with a center frequency fN, and since the subcarriers are different from each other, uplink optical signals received by the central node do not interfere with each other.
After the CDMA technology is applied, a single wavelength in the optical communication system is divided into a plurality of spreading code channels (different spreading code channels correspond to different spreading codes), each user node performs optical signal transmission by using the spreading code channel allocated to each user node, and the central node distinguishes uplink optical signals sent by different user nodes according to different spreading codes. Because the spread spectrum code channels used by each user node are mutually orthogonal, uplink optical signals received by the central node do not interfere with each other.
After applying FDMA or CDMA techniques to an optical communication system, the frequency accuracy and stability of a laser in an optical communication node will directly affect the transmission quality of an optical signal.
Taking FDMA as an example, in the process of transmitting downlink optical signals, all the downlink optical signals are modulated and transmitted by a single laser of a central node, so that when the frequency of the laser deviates, the frequency of each subcarrier deviates to the same direction, and crosstalk cannot occur between the subcarriers; in the process of transmitting the uplink optical signal, each user node performs uplink optical signal modulation through its own laser, and when a laser of a certain user node is subjected to frequency offset, the uplink optical signal sent by the user node will generate crosstalk with uplink optical signals sent by other user nodes. Illustratively, as shown in fig. 2, when the laser in the user node 2 is frequency-shifted, the uplink optical signal transmitted by the user node 2 through the subcarrier 2 will be frequency-shifted, thereby generating crosstalk with the uplink optical signal transmitted by the user node 1.
Although the effect caused by the frequency offset of the laser can be reduced by arranging the frequency guard interval between the subcarriers, the current commercial laser has a higher frequency offset (up to ± 2.5GHz), so that a single wavelength can be separated into a small number of subcarriers (a sufficiently large frequency guard interval needs to be arranged), that is, a single wavelength can be used by a small number of user nodes, and the utilization rate of the wavelength is low. Taking the single wavelength as 50GHz, the frequency range of each subcarrier as 2.5GHz, and the frequency offset of the laser as ± 2.5GHz as an example, the wavelength can be divided into 7 subcarriers of 2.5GHz, and the frequency guard interval between each subcarrier is 5 GHz.
In CDMA, when a laser in a user node undergoes frequency offset, spreading code channels used by the user node are not orthogonal, which causes mutual interference between the spreading code channels and affects normal reception of an uplink optical signal by a central node.
In order to solve the above problem, in the related art, after each user node receives a downlink optical signal transmitted by a central node, a frequency offset estimation value of a local carrier signal generated by a laser and the downlink optical signal is calculated, so that the frequency of the laser is fed back and adjusted according to the frequency offset estimation value, and the central frequencies of the local carrier signal generated by each laser and the downlink optical signal are kept synchronous. When the laser after frequency adjustment is subsequently used for modulating the uplink optical signal, the problem of uplink optical signal crosstalk can not occur.
However, when the laser is feedback-regulated, the laser cannot track frequency hopping in real time when a downlink optical signal or the laser generates frequency hopping (i.e., the frequency changes many times in a short time) because the light source of the laser needs to be modulated and the speed of modulating the light source is slow; in addition, the laser device must be provided with a corresponding frequency adjustment interface to complete the frequency adjustment, which results in a small application range of the above adjustment method.
In the embodiment of the application, the DSP chip of each user node in the optical communication system has a frequency shift function, and through the frequency shift function, the DSP chip performs digital frequency shift processing on the generated uplink baseband signal according to the calculated frequency offset estimation value, and delivers to the debugger to modulate the local carrier signal generated by the laser and the uplink baseband signal after the digital frequency shift processing, thereby eliminating the influence caused by the frequency offset of the laser. Meanwhile, the rate of the digital frequency shift processing is superior to the rate of modulating the laser light source, so that the user node can timely shift the frequency of the uplink baseband signal when the downlink optical signal or the laser generates frequency hopping, the light source of the laser does not need to be adjusted, and the method is suitable for the laser without a frequency adjustment interface. The following description will be made by using exemplary embodiments.
Referring to fig. 3, a schematic structural diagram of an optical communication node according to an embodiment of the present application is shown. The optical communication node may be implemented as a subscriber node 120 in the optical communication system shown in fig. 1, and includes: coherent receiver 310, analog-to-digital converter 320, laser 330, power divider 340, digital-to-analog converter 350, modulator 360, and DSP chip 370.
The optical communication node shown in fig. 3 uses a single light source to realize uplink and downlink optical signal transmission, i.e. the optical communication node only includes one laser 330. In order to implement downlink optical signal reception and uplink optical signal modulation transmission by using a local carrier signal generated by a single laser, the laser 330 is connected to the power divider 340, where the power divider 340 is a two-way power divider for dividing the local carrier signal generated by the laser 330 into two paths to be output, and the power of the two paths of local carrier signals output by the power divider 340 are the same.
During operation, the laser 330 generates a local carrier signal by a local oscillator and inputs the local carrier signal to the power divider 340. Since the laser 330 has a certain frequency offset, the frequency of the output local carrier signal is floated within the frequency offset range. For example, when the predetermined frequency of the laser 330 is 20GHz and the frequency offset range is ± 2.5GHz, the frequency of the local carrier signal output by the laser 330 is within a range of 17.5GHz to 22.5 GHz.
A first power output of the power divider 340 is connected to the coherent receiver 310 for inputting the local carrier signal generated by the laser 330 to the coherent receiver 310.
Accordingly, after the downlink optical signal transmitted through the physical channel reaches the coherent receiver 310, the coherent receiver 31 performs coherent reception on the downlink optical signal by using the local carrier signal, thereby obtaining a downlink analog signal. The coherent receiver 310 may perform coherent reception by using a coherent reception technology mature in the field of optical communication, which is not limited in this embodiment.
After the downlink optical signal is received in a correlated manner to obtain a downlink Analog signal, the coherent receiver 310 inputs the downlink Analog signal into an Analog-to-Digital Converter 320 (ADC), and the Analog-to-Digital Converter 320 converts the downlink Analog signal into a downlink Digital signal.
As a core component of the optical communication node, the DSP chip 370 is connected to the analog-to-digital converter 320, and is configured to receive the downlink digital signal output by the analog-to-digital converter 320 and perform digital signal processing on the downlink digital signal, so as to recover the downlink data modulated in the downlink optical signal.
While recovering the downlink data, the DSP chip 370 calculates a frequency offset estimation value in real time according to the downlink optical signal and the local carrier signal generated by the laser 330, where the frequency offset estimation value is a difference between the central frequencies of the local carrier signal and the downlink optical signal.
In one possible design, as shown in fig. 3, the DSP chip 370 includes a frequency offset estimation unit 371, and the frequency offset estimation unit 371 is connected to the analog-to-digital converter 320 for calculating the frequency offset estimation value.
Illustratively, when the center frequency of the downstream optical signal is f0And when the estimated frequency offset value is Δ f, the frequency of the local carrier signal generated by the laser 330 is f0+Δf。
In contrast to the related art, in which the frequency of the laser 330 is adjusted according to the calculated frequency offset estimation value, in this embodiment, after the DSP chip 370 calculates the frequency offset estimation value, the digital frequency shift processing is performed on the uplink baseband signal according to the frequency offset estimation value.
In one possible design, as shown in fig. 3, the DSP chip 370 further includes a frequency shift unit 372 and a baseband signal generation unit 373. The frequency shift unit 372 is connected to the frequency offset estimation unit 371 and the baseband signal generation unit 373, respectively.
The baseband signal generating unit 373 is connected to the user equipment, and is configured to generate an uplink baseband signal according to uplink data input by the user equipment, where the uplink baseband signal is a digital signal. Optionally, when the optical communication node applies the FDMA technique, the baseband signal generation unit 373 is an uplink baseband FDMA signal generation unit, and is configured to generate an uplink baseband FDMA signal; when the optical communication node applies the CDMA technology, the baseband signal generating unit 373 is an uplink baseband CDMA signal generating unit, and is configured to generate an uplink baseband CDMA signal.
After receiving the frequency offset estimation value and the uplink baseband signal, the frequency shift unit 372 performs digital frequency shift processing on the uplink baseband signal, where the uplink baseband signal after digital frequency shift processing accounts for a center frequency difference between the local carrier signal and the downlink signal. Since the laser 330 does not need to be frequency-adjusted, a frequency adjustment interface is not required to be arranged on the laser 330, and the manufacturing cost of the laser 330 is further reduced.
After the Digital frequency shift processing is performed on the uplink baseband signal by the DSP chip 370, the uplink baseband signal after the frequency shift processing is input into the connected Digital-to-analog converter 350 (DAC for short), and the Digital-to-analog converter 350 converts the uplink baseband signal after the frequency shift processing into an uplink analog signal.
The optical communication node is further provided with a modulator 360, and the modulator 360 is connected to the power divider 340 and the digital-to-analog converter 350 respectively. After receiving the uplink analog signal output by the dac 350, the modulator 360 modulates the uplink analog signal by using the local carrier signal output by the power divider 340 to obtain an uplink optical signal, and finally sends the uplink optical signal to the central node through a physical channel. The modulator 360 is an IQ modulator, and is configured to perform IQ modulation on the local carrier signal and the uplink analog signal.
Because the frequency offset estimation value is included in the uplink baseband signal after the digital frequency shift processing, when the uplink baseband signal is modulated by using the local carrier signal generated by the laser 330, the frequency offset of the laser 330 is eliminated, so that the influence of the frequency offset of the laser on the subcarrier frequency is eliminated, and the mutual crosstalk between adjacent subcarriers is avoided.
To sum up, in this embodiment, after receiving a downlink optical signal sent by a central node in a coherent manner, an optical communication node calculates a frequency offset estimation value of a local carrier signal and the downlink optical signal generated by a laser through a DSP chip, performs frequency shift processing on a generated uplink baseband signal according to the frequency offset estimation value, and modulates the local carrier signal and an uplink analog signal (generated after performing digital-to-analog conversion on the uplink baseband signal after the frequency shift processing) generated by the laser through a modulator to obtain an uplink optical signal; because the frequency shift of the laser is already taken into account when the uplink baseband signal is subjected to frequency shift processing, the central frequency of the modulated uplink optical signal is not influenced by the frequency shift of the laser, and the mutual crosstalk of the uplink optical signals caused by the frequency shift of the laser is avoided; meanwhile, compared with the frequency adjustment of the laser, the speed of performing digital frequency shift processing on the uplink baseband signal through the DSP chip is higher, so that when the frequency hopping of the downlink optical signal or the laser occurs, the optical communication node can be adjusted in time according to the frequency hopping condition; in addition, in the whole modulation process, the frequency of the laser is not required to be adjusted, and even if the laser of the optical communication node is not provided with a frequency adjustment interface, uplink optical signal modulation can be realized, so that the manufacturing cost of the optical communication node is reduced.
In one possible design, when applying FDMA technology to optical communication nodes, in fig. 3, as shown in fig. 4, the baseband signal generation unit 373 in the DSP chip 370 is an FDMA signal generation unit 373a, and the FDMA signal generation unit 373a is used to generate an uplink baseband FDMA signal based on input uplink data, wherein the uplink baseband FDMA signal has a center frequency of fsub。
As shown in fig. 4, the optical communication node receives the downlink optical signal with a center frequency f0And when the frequency offset estimation value calculated by the frequency offset estimation unit 371 is Δ f, the center frequency of the local carrier signal generated by the laser 330 is f0+Δf。
Correspondingly, the frequency shift unit 372 performs digital frequency shift processing on the uplink baseband FDMA signal according to the received frequency offset estimation value Δ f, and outputs the output center frequency fsubAnd an uplink baseband FDMA signal of Δ f (i.e., an uplink baseband FDMA signal after digital frequency shift processing) is converted into an uplink analog signal by the digital-to-analog converter 350 (the center frequency remains unchanged).
Obviously, after the digital frequency shift processing, the center frequency of the uplink optical signal finally output by the optical communication node is only related to the center frequencies of the downlink optical signal and the uplink baseband FDMA signal, and is not related to whether the laser generates frequency offset or not. Because the center frequencies of the downlink optical signals received by different user nodes in the same optical communication system are the same (because both the downlink optical signals are sent by the same center node), and the uplink baseband FDMA signals generated by different user nodes correspond to different subcarriers (namely, the frequencies are different), even if a laser in a user node generates frequency offset, the uplink optical signals output by different user nodes cannot generate crosstalk, and the transmission quality of the uplink optical signals is ensured.
In another possible design, when applying the CDMA technology to the optical communication node, in fig. 3, as shown in fig. 5, the baseband signal generating unit 373 in the DSP chip 370 is a CDMA signal generating unit 373b, and the CDMA signal generating unit 373b is configured to generate an uplink baseband CDMA signal according to input uplink data, where the center frequency of the uplink baseband CDMA signal is (approximately) 0.
As shown in fig. 5, the optical communication node receives the downlink optical signal with a center frequency f0And when the frequency offset estimation value calculated by the frequency offset estimation unit 371 is Δ f, the center frequency of the local carrier signal generated by the laser 330 is f0+Δf。
Correspondingly, the frequency shift unit 372 performs digital frequency shift processing on the uplink baseband CDMA signal according to the received frequency offset estimation value Δ f, and outputs the uplink baseband CDMA signal with the center frequency of- Δ f (i.e., the uplink baseband CDMA signal after digital frequency shift processing), and delivers the uplink baseband CDMA signal to the digital-to-analog converter 350 to be converted into an uplink analog signal (the center frequency remains unchanged). It should be noted that the above digital frequency shift processing is a mathematical frequency shift operation, and accordingly, a negative value of the center frequency after the frequency shift processing does not represent that the center frequency is negative, but indicates that the adjustment is performed in the reverse direction of the positive frequency direction.
Obviously, after the digital frequency shift processing, the center frequency of the uplink optical signal finally output by the optical communication node is kept synchronous with the center frequency of the downlink optical signal, and is independent of whether the laser generates frequency shift (the frequency shift generated by the laser does not affect the spreading code channel). In the same optical communication system, the spread spectrum code channels corresponding to different user nodes are orthogonal to each other, so that the uplink optical signals output by different user nodes can not generate crosstalk, and the transmission quality of the uplink optical signals is ensured.
Since the transmission quality of the optical signal is related to the channel quality, and the uplink optical signal and the downlink optical signal are transmitted through the same channel, in order to improve the transmission quality of the uplink optical signal, in a possible design, on the basis of fig. 3, as shown in fig. 6, the DSP chip 370 further includes a channel parameter estimation unit 374 and a channel parameter pre-compensation unit 375.
The channel parameter estimation unit 374 is connected to the analog-to-digital converter 320, and configured to perform channel parameter estimation according to the downlink optical signal, and output a channel parameter estimation result, where the channel parameter estimation result includes at least one of dispersion estimation or optical fiber dynamic delay estimation. In other possible embodiments, the channel parameter estimation unit 374 may further output other channel parameters for indicating the channel quality, which is not limited in this embodiment.
In a possible design, the channel parameter pre-compensation unit 375 is connected to the channel parameter estimation unit 374 and the baseband signal generation unit 373, respectively, and is configured to perform channel parameter pre-compensation on the uplink baseband signal according to a channel parameter estimation result. Optionally, the channel parameter pre-compensation unit 375 reversely adjusts the dispersion of the uplink baseband signal according to the dispersion estimation, so as to avoid the influence of the optical fiber dispersion on the transmission of the uplink optical signal; the channel parameter pre-compensation unit 375 adjusts the transmission delay of the uplink baseband signal according to the optical fiber dynamic delay estimation, so as to avoid the influence of the optical fiber transmission delay transformation (for example, the optical fiber is deformed due to temperature, and thus the optical fiber transmission delay is influenced) on the uplink optical signal transmission.
In other possible designs, the channel parameter pre-compensation unit 375 is disposed after the frequency shift unit 372 and configured to perform channel parameter pre-compensation on the digitally shifted uplink baseband signal according to a channel parameter estimation result, and the specific setting position of the channel parameter pre-compensation unit 375 is not limited in this embodiment of the application.
The DSP chip or its components included in the embodiments of the present application may be a circuit. The circuit may be implemented by a system-on-chip. The chip system may include: a Central Processing unit (unit cpu), a general-purpose processor, a digital signal processor, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), other Programmable logic devices, transistor logic devices, discrete devices, hardware components, or any combination thereof. Which may implement or perform the various illustrative logical blocks, modules, and circuits described in connection with the disclosure. The DSP chip may also be a combination of chips that performs a computing function, e.g., including one or more microprocessors, DSPs and microprocessors, and the like.
Referring to fig. 7, a flowchart of an uplink optical signal modulation method according to an embodiment of the present application is shown, where the uplink optical signal modulation method is described as being applied to each user node 120 in fig. 1, and the method includes the following steps.
In the embodiment of the application, the user node adopts a single light source to realize uplink and downlink optical signal transmission, so that a local carrier signal generated by a laser is input into two power dividers, and one local carrier signal is output to a coherent receiver by the power dividers, so that the coherent receiver coherently receives a downlink optical signal sent by the central node according to the local carrier signal.
Illustratively, when the user node adopts the optical communication node structure shown in fig. 3, when the frequency offset estimation unit in the DSP chip receives the downlink digital signal input by the analog-to-digital converter, that is, according to the central frequencies of the downlink optical signal and the local carrier signal, the frequency offset estimation value is calculated.
Optionally, after the user node coherently receives the downlink optical signal, the user node performs analog-to-digital conversion on the received downlink optical signal by using an internal analog-to-digital converter to obtain a downlink digital signal, and performs data signal processing on the downlink digital signal, thereby recovering the downlink data modulated in the downlink optical signal.
And 703, performing frequency shift and digital-to-analog conversion processing on the uplink baseband signal according to the frequency offset estimation value, wherein the uplink baseband signal is generated according to uplink data, and the digital-to-analog conversion is used for converting the digital signal into an analog signal.
In one possible design, when the user node applies the FDMA technique, the uplink baseband signal generated by the user node according to the uplink data is an uplink baseband FDMA signal. Illustratively, when the center frequency of the downstream optical signal is f0The frequency offset estimation value is delta f, and the center frequency of the generated uplink baseband FDMA signal is fsubWhen the user node shifts the center frequency of the uplink baseband FDMA signal to fsubΔ f and converts the frequency-shifted uplink baseband FDMA signal into an analog signal (the center frequency remains unchanged).
In another possible design, when the user node applies the CDMA technology, the uplink baseband signal generated by the user node according to the uplink data is an uplink baseband CDMA signal. Illustratively, when the center frequency of the downstream optical signal is f0When the estimated frequency offset value is Δ f, the user node shifts the center frequency of the uplink baseband CDMA signal to- Δ f (the center frequency of the original uplink baseband CDMA signal is 0), and converts the uplink baseband CDMA signal after frequency shift processing into an analog signal (the center frequency remains unchanged).
Because the transmission quality of the optical signal is also related to the channel quality, and the uplink and downlink optical signals are transmitted through the same channel, in order to improve the transmission quality of the uplink optical signal, after the user node receives the downlink optical signal in a related manner, channel parameter estimation is performed according to the downlink optical signal, and channel parameter pre-compensation is performed on the uplink baseband signal according to a channel parameter estimation result, wherein the channel parameter estimation result comprises at least one of dispersion estimation or optical fiber dynamic delay estimation.
Combining with the first design in step 703, the user node performs IQ modulation on the local carrier signal and the processed uplink baseband FDMA signal to obtain an uplink optical signal, where the center frequency of the uplink optical signal is f0+fsub。
Combining with the second design in step 703, the user node performs IQ modulation on the local carrier signal and the processed uplink baseband CDMA signal to obtain an uplink optical signal, where the center frequency of the uplink optical signal is f0。
In this embodiment, after receiving a downlink optical signal sent by a central node, a user node calculates a frequency offset estimation value of a local carrier signal and the downlink optical signal generated by a laser, and performs frequency shift processing and digital-to-analog conversion processing on a generated uplink baseband signal according to the frequency offset estimation value, so as to modulate an uplink optical signal according to the local carrier signal and the uplink baseband signal after the digital-to-analog conversion processing; because the frequency shift of the laser is already taken into account when the uplink baseband signal is subjected to frequency shift processing, the central frequency of the modulated uplink optical signal is not influenced by the frequency shift of the laser, and the mutual crosstalk of the uplink optical signals caused by the frequency shift of the laser is avoided; meanwhile, compared with the frequency adjustment of the laser, the speed of frequency shift processing of the uplink baseband signal is high, so that the user node can be adjusted in time according to the frequency hopping condition when the frequency hopping of the downlink optical signal or the laser occurs; in addition, in the whole modulation process, the frequency of the laser is not required to be adjusted, and even if the laser of the user node is not provided with a frequency adjustment interface, the user node can also realize uplink optical signal modulation, so that the manufacturing cost of the user node is reduced.
Claims (11)
1. A method for modulating an upstream optical signal, the method comprising:
the method comprises the steps that a downlink optical signal sent by a central node is received in a coherent mode according to a local carrier signal generated by a laser;
calculating a frequency offset estimation value of the local carrier signal and the downlink optical signal, wherein the frequency offset estimation value is a difference value of center frequencies of the local carrier signal and the downlink optical signal;
performing frequency shift and digital-to-analog conversion processing on an uplink baseband signal according to the frequency offset estimation value, wherein the uplink baseband signal is generated according to uplink data, and the digital-to-analog conversion processing is used for converting a digital signal into an analog signal, and the uplink baseband signal is an uplink baseband Frequency Division Multiple Access (FDMA) signal or an uplink baseband Code Division Multiple Access (CDMA) signal;
and modulating according to the local carrier signal and the uplink baseband signal after the digital-to-analog conversion processing to obtain an uplink optical signal.
2. The method of claim 1, wherein the downstream optical signal has a center frequency f0The frequency offset estimation value is delta f, the uplink baseband signal is an uplink baseband FDMA signal, and the center frequency of the uplink baseband FDMA signal is fsub；
The frequency shift and digital-to-analog conversion processing of the uplink baseband signal according to the frequency offset estimation value comprises:
frequency-shifting the center frequency of the uplink baseband FDMA signal to fsub-Δf；
Converting the uplink baseband FDMA signal subjected to frequency shift processing into an analog signal;
the modulating according to the local carrier signal and the uplink baseband signal after the digital-to-analog conversion processing to obtain the uplink optical signal includes:
performing quadrature IQ modulation on the local carrier signal and the uplink baseband FDMA signal subjected to digital-to-analog conversion to obtain the uplink optical signal, wherein the center frequency of the uplink optical signal is f0+fsub。
3. The method of claim 1, wherein the downstream optical signal has a center frequency f0The estimated frequency offset value is delta f, and the uplink baseband signal is an uplink baseband CDMA signal;
the frequency shift and digital-to-analog conversion processing of the uplink baseband signal according to the frequency offset estimation value comprises:
shifting the center frequency of the uplink baseband CDMA signal to- Δ f;
converting the uplink baseband CDMA signal after frequency shift processing into an analog signal;
the modulating according to the local carrier signal and the uplink baseband signal after the digital-to-analog conversion processing to obtain the uplink optical signal includes:
performing IQ modulation on the local carrier signal and the uplink baseband CDMA signal after digital-to-analog conversion to obtain the uplink optical signal, wherein the center frequency of the uplink optical signal is f0。
4. The method according to any one of claims 1 to 3, wherein after coherently receiving the downlink optical signal sent by the central node according to the local carrier signal generated by the laser, the method further comprises:
estimating channel parameters according to the downlink optical signals;
and performing channel parameter pre-compensation on the uplink baseband signal according to a channel parameter estimation result, wherein the channel parameter estimation result comprises at least one of dispersion estimation or optical fiber dynamic delay estimation.
5. The method according to any one of claims 1 to 3, wherein after coherently receiving the downlink optical signal sent by the central node according to the local carrier signal generated by the laser, the method further comprises:
and performing analog-to-digital conversion and data signal processing on the received downlink optical signal to recover downlink data, wherein the analog-to-digital conversion is used for converting an analog signal into a digital signal.
6. An optical communication node, characterized in that the optical communication node comprises: the system comprises a coherent receiver, an analog-to-digital converter, a laser, a power divider, a digital-to-analog converter, a modulator and a digital signal processing DSP chip;
the power divider is connected with the laser and used for dividing the local carrier signal generated by the laser into two paths to be output;
the coherent receiver is connected with the power divider and used for performing coherent reception on a downlink optical signal according to the local carrier signal output by the power divider to obtain a downlink analog signal;
the analog-to-digital converter is connected with the coherent receiver and is used for converting a downlink analog signal output by the coherent receiver into a downlink digital signal;
the DSP chip is connected with the analog-to-digital converter and used for recovering downlink data according to the downlink digital signal and calculating a frequency offset estimation value of the laser, wherein the frequency offset estimation value is used for indicating a difference value of the center frequencies of the local carrier signal and the downlink optical signal;
the DSP chip is also connected with the digital-to-analog converter and is used for performing frequency shift processing on an uplink baseband signal according to the frequency offset estimation value and sending the uplink baseband signal after the frequency shift processing to the digital-to-analog converter, and the digital-to-analog converter is used for converting the uplink baseband signal after the frequency shift processing into an uplink analog signal, wherein the uplink baseband signal is an uplink baseband Frequency Division Multiple Access (FDMA) signal or an uplink baseband Code Division Multiple Access (CDMA) signal;
the modulator is respectively connected with the power divider and the digital-to-analog converter, and is configured to modulate the local carrier signal and the uplink analog signal output by the power divider to obtain an uplink optical signal.
7. The optical communication node of claim 6, wherein the DSP chip comprises a frequency offset estimation unit, a frequency shift unit, and a baseband signal generation unit;
the frequency offset estimation unit is connected with the analog-to-digital converter and used for calculating the frequency offset estimation value;
the frequency shift unit is respectively connected with the frequency offset estimation unit and the baseband signal generation unit and is used for performing frequency shift processing on the uplink baseband signal output by the baseband signal generation unit according to the frequency offset estimation value.
8. The optical communication node of claim 7, wherein the downstream optical signal has a center frequency f0The frequency offset estimation value is delta f, the baseband signal generation unit is an FDMA signal generation unit, and the center frequency of the output uplink baseband FDMA signal is fsub；
The frequency shift unit is used for shifting the center frequency of the uplink baseband FDMA signal to fsub-Δf；
The digital-to-analog converter is used for converting the uplink baseband FDMA signal subjected to frequency shift processing into the uplink analog signal;
the modulator is configured to perform quadrature IQ modulation on the local carrier signal and the uplink analog signal to obtain the uplink optical signal, where a center frequency of the uplink optical signal is f0+fsub。
9. The optical communication node of claim 7, wherein the downstream optical signal has a center frequency f0The estimated frequency offset value is delta f, and the baseband signal generating unit is a CDMA signal generating unit;
the frequency shift unit is used for shifting the central frequency of the uplink baseband CDMA signal to-delta f;
the digital-to-analog converter is used for converting the uplink baseband CDMA signal after frequency shift processing into the uplink analog signal;
the modulator is configured to perform IQ modulation on the local carrier signal and the uplink analog signal to obtain the uplink optical signal, where a center frequency of the uplink optical signal is f0。
10. The optical communication node according to any one of claims 7 to 9, wherein the DSP chip further comprises a channel parameter estimation unit and a channel parameter pre-compensation unit;
the channel parameter estimation unit is connected with the analog-to-digital converter and used for performing channel parameter estimation according to the downlink optical signal and outputting a channel parameter estimation result, wherein the channel parameter estimation result comprises at least one of dispersion estimation or optical fiber dynamic delay estimation;
the channel parameter pre-compensation unit is respectively connected with the channel parameter estimation unit and the baseband signal generation unit and is used for performing channel parameter pre-compensation on the uplink baseband signal according to the channel parameter estimation result.
11. An optical communication system, comprising: the system comprises a central node and n user nodes, wherein the n user nodes are connected with the central node through an optical coupler, n is not less than 2 and is an integer;
the central node is configured to send downlink optical signals to the n user nodes, and the n user nodes are configured to send uplink optical signals to the central node;
each user node comprising an optical communications node according to any one of claims 6 to 10.
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