WO2018232571A1 - 上行光信号调制方法、光通信节点及*** - Google Patents
上行光信号调制方法、光通信节点及*** Download PDFInfo
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- WO2018232571A1 WO2018232571A1 PCT/CN2017/089017 CN2017089017W WO2018232571A1 WO 2018232571 A1 WO2018232571 A1 WO 2018232571A1 CN 2017089017 W CN2017089017 W CN 2017089017W WO 2018232571 A1 WO2018232571 A1 WO 2018232571A1
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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
Definitions
- 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 a system.
- FDMA technology after applying FDMA technology to an optical communication system, a single wavelength in the system is divided into several subcarriers, and each user node in the system flexibly allocates wavelength and channel resources in the wavelength. Each user node is connected through an optical coupler on the link, and finally connected to a central node in the system, thereby performing uplink and downlink optical signal transmission with the central node.
- a frequency guard interval needs to be reserved between each subcarrier.
- the uplink optical signal is separately modulated by each user node using a respective laser, when the laser of a certain user node is frequency-shifted and the frequency offset exceeds the frequency protection interval, the user The subcarriers used by the node will crosstalk with adjacent subcarriers.
- the user node After receiving the downlink optical signal transmitted by the central node, the user node calculates the frequency offset estimation value of the laser according to the downlink optical signal and the local carrier signal generated by the laser. The laser is then feedback adjusted using the frequency offset estimate. Even if the laser is frequency-shifted, the local carrier signal generated by the laser can still be synchronized with the downstream optical signal through the above adjustment mechanism, thereby avoiding crosstalk between the modulated upstream optical signals.
- the embodiment of the present application provides an uplink optical signal modulation method, an optical communication node, and a system.
- the present application provides an uplink optical signal modulation method, where the method includes:
- digital-to-analog conversion is used to convert the digital signal into an analog signal
- the uplink optical signal is modulated according to the local carrier signal and the digital baseband signal processed uplink baseband signal.
- the frequency offset estimation value of the local carrier signal and the downlink optical signal generated by the laser is calculated, and the generated uplink baseband signal is calculated according to the frequency offset estimation value.
- Frequency shift processing and digital-to-analog conversion processing thereby modulating an uplink optical signal according to the local carrier signal and the digital baseband converted uplink baseband signal; since the uplink baseband signal is subjected to frequency shift processing, the frequency offset of the laser is already counted, Therefore, the center frequency of the modulated upstream optical signal is not affected by the laser frequency offset, thereby avoiding crosstalk of the upstream optical signals caused by the frequency shift of the laser; meanwhile, compared to the frequency adjustment of the laser, due to the uplink baseband signal
- the frequency shift processing is faster, so when the downlink optical signal or the laser frequency hopping, the user node can adjust according to the frequency hopping condition in time; and, in the whole modulation process, the frequency adjustment of the laser is not required, even if the user
- the node's laser is not configured with a frequency adjustment interface, user section It can be realized upstream optical signal modulation, to reduce the manufacturing cost of the user node.
- the center frequency of the downlink optical signal is f 0
- the frequency offset estimation value is ⁇ f
- the uplink baseband signal is the uplink baseband FDMA signal
- the center frequency of the uplink baseband FDMA signal is fsub ;
- Performing frequency shifting and digital-to-analog conversion processing on the uplink baseband signal according to the frequency offset estimation value including:
- the center frequency of the baseband uplink FDMA signal to frequency shift f sub - ⁇ f;
- the uplink optical signal is modulated according to the local carrier signal and the digital baseband conversion processed uplink baseband signal, including:
- the local carrier signal and the processed uplink baseband FDMA signal are orthogonal (English: Inphase-Quadrature, referred to as: IQ) modulation to obtain an uplink optical signal, wherein the center frequency of the upstream optical signal is f 0 +f sub .
- the frequency offset estimation value is used to perform frequency shift on the basis of the original center frequency of the uplink baseband FDMA signal, so that the finally modulated uplink optical signal is only downlink.
- the optical signal is related to the center frequency of the original uplink baseband FDMA signal, thereby preventing the upstream optical signal from being affected by the laser frequency offset.
- the center frequency of the downlink optical signal is f 0
- the estimated frequency offset is ⁇ f
- the uplink baseband signal is an uplink baseband CDMA signal
- Performing frequency shifting and digital-to-analog conversion processing on the uplink baseband signal according to the frequency offset estimation value including:
- the center frequency of the uplink baseband FDMA signal is frequency-shifted to - ⁇ f according to the frequency offset estimation value ⁇ f, so that the center frequency of the finally modulated uplink optical signal is The center frequency of the downstream optical signal is kept synchronized, thereby preventing the upstream optical signal from being affected by the laser frequency offset.
- the method further includes:
- Channel parameter pre-compensation is performed on the uplink baseband signal according to the channel parameter estimation result, and the channel parameter estimation result includes At least one of a dispersion estimate or a fiber dynamic delay estimate.
- the downlink optical signal is used according to the downlink optical signal. Estimating the channel parameters to determine the channel quality of the channel with the central node, and performing channel parameter pre-compensation on the uplink baseband signal according to the channel parameter estimation result, thereby reducing the influence of the channel on the uplink optical signal transmission, and further improving the uplink The transmission quality of optical signals.
- the method further includes:
- the present application provides an optical communication node including: a coherent receiver, an analog to digital converter, a laser, a power divider, a digital to analog converter, a modulator, and digital signal processing (English: Digital Signal Processing, referred to as: DSP) chip;
- a coherent receiver an analog to digital converter, a laser, a power divider, a digital to analog converter, a modulator, and digital signal processing (English: Digital Signal Processing, referred to as: DSP) chip;
- DSP Digital Signal Processing
- the power divider is connected to the laser for splitting the local carrier signal generated by the laser into two outputs;
- the coherent receiver is connected to the power divider, and is configured to perform coherent reception on the downlink optical signal according to the local carrier signal output by the power divider, to obtain a downlink analog signal;
- An analog to digital converter is coupled to the coherent receiver for converting the downlink analog signal output by the coherent receiver into a downlink digital signal;
- the DSP chip is connected to the analog-to-digital converter, and is configured to recover downlink data according to the downlink digital signal, and calculate a frequency offset estimation value of the laser, where the frequency offset estimation value is used to indicate a difference between a local carrier signal and a center frequency of the downlink optical signal;
- the DSP chip is further connected to the digital-to-analog converter for frequency-shifting the uplink baseband signal according to the frequency offset estimation value, and transmitting the frequency-shifted uplink baseband signal to the digital-to-analog converter, and the digital-to-analog converter is used for shifting the frequency.
- the processed uplink baseband signal is converted into an uplink analog signal;
- the modulator is respectively connected to the power divider and the digital-to-analog converter, and is configured to obtain an uplink optical signal according to the local carrier signal outputted by the power divider and the uplink analog signal.
- the DSP chip calculates the frequency offset estimation value of the local carrier signal and the downlink optical signal generated by the laser, and generates the generated signal according to the frequency offset estimation value.
- the uplink baseband signal is subjected to frequency shift processing, and the local carrier signal generated by the modulator and the uplink analog signal (generated by the digital-to-analog conversion after the frequency-shifted uplink baseband signal) are modulated by the modulator to obtain an uplink optical signal;
- the frequency shifting process is performed, the frequency offset of the laser is already counted.
- the center frequency of the modulated upstream optical signal is not affected by the laser frequency offset, and the upstream optical signals caused by the frequency offset of the laser are prevented from being crosstalked by each other;
- the digital frequency shift processing of the uplink baseband signal by the DSP chip is faster, so when the downlink optical signal or the laser frequency hopping, the optical communication node can perform the frequency hopping according to the frequency hopping situation. Timely adjustment; and, throughout the modulation process, there is no need to laser Rate adjustment, even if the laser optical communications node is not configured to adjust the frequency of the interface can be realized upstream optical signal modulation, to reduce the manufacturing cost of the optical communication nodes.
- the DSP chip includes a frequency offset estimating unit, a frequency shifting unit, and a baseband signal generating unit;
- the frequency offset estimation unit is connected to the analog to digital converter and is used for calculating the frequency offset estimation value
- the frequency shifting unit is respectively connected to the frequency offset estimating unit and the baseband signal generating unit, and configured to perform frequency shift processing on the uplink baseband signal output by the baseband signal generating unit according to the frequency offset estimation value.
- the center frequency of the downlink optical signal is f 0
- the frequency offset estimation value is ⁇ f
- the baseband signal generating unit is an FDMA signal generating unit
- the center frequency of the output uplink baseband FDMA signal is f sub ;
- Frequency shift unit the center frequency for the baseband uplink FDMA signal to frequency shift f sub - ⁇ f;
- a digital-to-analog converter for converting the uplink baseband FDMA signal after the frequency shift processing into an uplink analog signal
- the modulator is configured to perform IQ modulation 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 f 0 +f sub .
- the frequency shifting unit when the uplink optical signal is modulated based on the uplink baseband FDMA signal, the frequency shifting unit performs frequency shifting on the basis of the original center frequency of the uplink baseband FDMA signal according to the frequency offset estimation value, so that the finally modulated uplink light is obtained.
- the signal is only related to the downstream optical signal and the center frequency of the original uplink baseband FDMA signal, thereby preventing the upstream optical signal from being affected by the laser frequency offset.
- the center frequency of the downlink optical signal is f 0
- the frequency offset estimation value is ⁇ f
- the baseband signal generating unit is a CDMA signal generating unit
- a frequency shifting unit for shifting a center frequency of the uplink baseband CDMA signal to - ⁇ f;
- a digital-to-analog converter for converting the uplink baseband CDMA signal after the frequency shift processing into an uplink analog signal
- the modulator is configured to perform IQ modulation 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 f 0 .
- the frequency shifting unit shifts the center frequency of the uplink baseband FDMA signal to - ⁇ f according to the frequency offset estimation value ⁇ f, so that the final modulation is performed.
- the center frequency of the upstream optical signal is synchronized with the center frequency of the downstream optical signal, thereby preventing the upstream optical signal from being affected by the laser frequency offset.
- the DSP chip further includes a channel parameter estimation unit and a channel parameter pre-compensation unit;
- the channel parameter estimating unit is connected to the analog-to-digital converter, and is 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 a dispersion estimation or a fiber dynamic delay estimation;
- the channel parameter pre-compensation unit is respectively connected to the channel parameter estimation unit and the baseband signal generation unit, and is configured to perform channel parameter pre-compensation on the uplink baseband signal according to the channel parameter estimation result.
- the transmission quality of the optical signal is 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, in this embodiment, after the DSP chip receives the downlink optical signal, the channel parameter is estimated.
- the unit estimates the channel parameters to determine the channel quality of the channel with 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, thereby reducing channel-to-uplink optical signal transmission. The impact is further improved by the transmission quality of the upstream optical signal.
- the present application provides a chip system for implementing a DSP chip in an optical communication node in any of the possible designs of the second aspect or the second aspect.
- the chip system can be composed of chips, and can also include chips and other discrete devices.
- the chip may be an Application-Specific Integrated Circuit (ASIC) or other form of chip.
- the chip system may further include a processor, configured to support the DSP chip to implement the functions involved in the foregoing aspects, for example, acquiring/calculating the signal and/or frequency offset estimation values involved in the foregoing aspects, and performing the foregoing Frequency shifting processing in the aspect, and/or channel parameter pre-compensation processing.
- the chip system further includes a memory for storing necessary program instructions and data of the DSP chip.
- the present application provides an optical communication system including: a central node and n user nodes Point, n user nodes are connected to the central node through an optical coupler, n ⁇ 2, n is an integer;
- the central node is configured to send downlink optical signals to n user nodes, and n user nodes are configured to send uplink optical signals to the central node;
- Each user node comprises an optical communication node as described in the second aspect or any of the possible designs of the second aspect.
- FIG. 1 is 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 of optical signal transmission by a user node using different subcarriers and a central node;
- 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 of a method for modulating an uplink optical signal provided by an embodiment of the present application.
- FIG. 1 is a system architecture diagram of an optical communication system according to an embodiment of the present application.
- the optical communication system includes a central node 110 and n user nodes 120, wherein n user nodes 120 are optically coupled.
- the device 130 (or referred to as a fiber coupler, English: coupler) is coupled to the central node 110.
- the central node 110 is an optical communication node located on the 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 a built-in laser), and pass the user
- the physical channel between the nodes 120 transmits a downlink optical signal to the user node 120, wherein 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 on the user side, and is configured to connect to the user equipment, and modulate the uplink data from the user equipment into an uplink optical signal (modulated by a local carrier signal generated by a built-in laser), and pass through the central node.
- the physical channel between 110 transmits the upstream optical signal to the central node 110.
- the user node 110 is an optical modem (or optical modem, English) connected to the user equipment.
- the FDMA technology or the CDMA technology is applied to the optical communication system shown in FIG.
- a single wavelength in an optical communication system is divided into several subcarriers (different subcarriers correspond to different frequencies), and each user node uses the respective allocated subcarriers for optical signal transmission, and correspondingly, the central node passes Different subcarriers transmit downlink optical signals to different user nodes, and distinguish uplink optical signals sent by different user nodes according to subcarriers.
- the user node 1 performs optical signal transmission with a central node using a subcarrier with a center frequency of f1
- the user node 2 performs optical signal transmission with a central node with a center frequency of f2
- N uses the subcarrier with the center frequency of fN to perform optical signal transmission with the central node, and since the subcarriers are different from each other, the uplink optical signals received by the central node do not cross each other.
- a single wavelength in the optical communication system is divided into multiple spreading code channels (different spreading code channels correspond to different spreading codes), and each user node uses the respective assigned spreading code channel to perform optical signals.
- Transmission, and the central node distinguishes the uplink optical signals sent by different user nodes according to different spreading codes. Since the spreading code channels used by the user nodes are orthogonal to each other, the uplink optical signals received by the central node do not cross each other.
- the frequency accuracy and stability of the laser in the optical communication node will directly affect the transmission quality of the optical signal.
- each user node modulates the upstream optical signal through its own laser.
- the frequency of the laser of a certain user node is shifted, the user
- the uplink optical signal sent by the node will crosstalk with the upstream optical signal sent by other user nodes.
- the uplink optical signal sent by the user node 2 through the sub-carrier 2 will be frequency-shifted, thereby transmitting the uplink light with the user node 1.
- the signal produces crosstalk.
- a single wavelength can only It is divided into a small number of subcarriers (sufficiently set a large frequency guard interval), that is, a single wavelength can only be used by a small number of user nodes, resulting in low wavelength usage.
- a single wavelength is 50 GHz
- the frequency range of each subcarrier is 2.5 GHz
- the frequency offset of the laser is ⁇ 2.5 GHz.
- This wavelength can only be divided into seven 2.5 GHz subcarriers, and frequency protection between each subcarrier.
- the interval is 5Ghz.
- the spreading code channels used by the user node are non-orthogonal, which causes mutual interference between the spreading code channels and affects the normal reception of the uplink optical signal by the central node.
- each user node after receiving the downlink optical signal transmitted by the central node, each user node calculates a frequency offset estimation value of the local carrier signal and the downlink optical signal generated by the laser, so that the laser offset is determined according to the frequency offset estimation value.
- the frequency is feedback adjusted such that the local carrier signal generated by each laser is synchronized with the center frequency of the downstream optical signal.
- the source of the laser needs to be modulated, and the speed of modulating the light source is slow, so that the feedback adjustment of the laser is not timely, and the frequency of the downstream optical signal or the laser jumps (ie, in a short time).
- the frequency changes a lot the laser cannot track the frequency hopping in real time; and the laser must set the corresponding frequency adjustment interface to complete the frequency adjustment, resulting in a smaller application range of the above adjustment method.
- the DSP chip of each user node in the optical communication system has a frequency shifting function, and the DSP chip performs digital frequency shift processing on the generated uplink baseband signal according to the calculated frequency offset estimation value, and The debugger filters the local carrier signal generated by the laser and the digital baseband signal after the digital frequency shift processing, thereby eliminating the influence of the laser frequency offset.
- the user node can perform the frequency shift processing on the uplink baseband signal in time when the downlink optical signal or the laser frequency jumps, and is no longer needed.
- the laser source is adjusted for lasers that are not equipped with a frequency adjustment interface. The following description is made using the illustrative embodiments.
- FIG. 3 is a schematic structural diagram of an optical communication node according to an embodiment of the present application.
- the optical communication section The point can be implemented as a user node 120 in the optical communication system shown in FIG. 1.
- the optical communication node includes: a coherent receiver 310, an analog to digital converter 320, a laser 330, a power divider 340, a digital to analog converter 350, and a modulator. 360 and DSP chip 370.
- the optical communication node shown in FIG. 3 realizes uplink and downlink optical signal transmission by using a single light source, that is, only one laser 330 is included in the optical communication node.
- the laser 330 is connected to the power divider 340, wherein the power divider 340 is a two-way power divider for generating the laser 330.
- the local carrier signal is split into two outputs, and the power of the two local carrier signals output by the power divider 340 is the same.
- the laser 330 During operation, the laser 330 generates a local carrier signal through the local oscillator and inputs a 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 floats within the frequency offset range. For example, when the predetermined frequency of the laser 330 is 20 GHz and the frequency offset range is ⁇ 2.5 GHz, the frequency of the local carrier signal output by the laser 330 fluctuates between 17.5 GHz and 22.5 GHz.
- a first power output of power splitter 340 is coupled to coherent receiver 310 for inputting a local carrier signal generated by laser 330 to 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 can be coherently received by the coherent receiving technology in the field of optical communication, which is not limited by the embodiment of the present application.
- the coherent receiver 310 After receiving the downlink analog signal for the downlink optical signal correlation, the coherent receiver 310 inputs the downlink analog signal into the connected analog-to-digital converter 320 (English: Analog-to-Digital Converter, ADC), which is to be converted by the analog-to-digital converter 320.
- the downlink analog signal is converted into a downlink digital signal.
- the DSP chip 370 is connected to the analog-to-digital converter 320 for receiving the downlink digital signal output by the analog-to-digital converter 320, and performing digital signal processing on the downlink digital signal, thereby restoring the modulation in the downlink optical signal. Downstream data.
- the DSP chip 370 calculates the frequency offset estimation value in real time according to the downlink optical signal and the local carrier signal generated by the laser 330, and the frequency offset estimation value is the difference between the local carrier signal and the center frequency of the downlink optical signal. .
- the DSP chip 370 includes a frequency offset estimation unit 371 connected to the analog-to-digital converter 320 for calculating the frequency offset estimation value.
- the frequency of the local carrier signal generated by the laser 330 is f 0 + ⁇ f.
- the frequency adjustment of the laser 330 is different according to the calculated frequency offset estimation value.
- the uplink baseband signal is digitally shifted according to the frequency offset estimation value. Frequency processing.
- the DSP chip 370 further includes a frequency shifting unit 372 and a baseband signal generating unit 373.
- the frequency shifting unit 372 is connected to the frequency offset estimating unit 371 and the baseband signal generating 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 the uplink data input by the user equipment, where the uplink baseband signal is a digital signal.
- the baseband signal generating unit 373 is an uplink baseband FDMA signal generating unit, configured to generate an uplink baseband FDMA signal;
- the baseband signal generating unit 373 is an uplink baseband CDMA signal generating unit for generating an uplink baseband CDMA signal.
- the frequency shifting unit 372 After receiving the frequency offset estimation value and the uplink baseband signal, the frequency shifting unit 372 performs digital frequency shift processing on the uplink baseband signal, wherein the uplink baseband signal after the digital frequency shift processing is included in the center frequency of the local carrier signal and the downlink signal. Difference. Since the frequency adjustment of the laser 330 is not required, the frequency adjustment interface is provided on the laser 330, which further reduces the manufacturing cost of the laser 330.
- the uplink baseband signal after the frequency shift processing is input to the connected digital-to-analog converter 350 (English: Digital to analog converter, DAC for short), and the digital-to-analog converter 350
- the frequency-shifted uplink baseband signal is converted into an uplink analog signal.
- a modulator 360 which is coupled to the power divider 340 and the digital to analog converter 350, respectively. After receiving the uplink analog signal output by the digital-to-analog converter 350, the modulator 360 modulates the local carrier signal output by the power divider 340 to obtain an uplink optical signal, and finally transmits the upstream light to the central node through the physical channel. signal.
- the modulator 360 is an IQ modulator for performing IQ modulation on the local carrier signal and the uplink analog signal.
- the frequency offset estimation value has been included in the uplink baseband signal after the digital frequency shift processing, when the local carrier signal generated by the laser 330 is used to modulate it, the frequency offset of the laser 330 is eliminated, thereby eliminating the laser frequency offset.
- the effect of shifting on the subcarrier frequency is avoided to avoid crosstalk between adjacent subcarriers.
- the DSP chip calculates the frequency offset estimation value of the local carrier signal and the downlink optical signal generated by the laser, and according to the frequency offset.
- the estimated value is subjected to frequency shift processing on the generated uplink baseband signal, and the local carrier signal generated by the laser and the uplink analog signal (generated by the digital-to-analog conversion after the frequency-shifted uplink baseband signal) are modulated by the modulator to obtain an uplink optical signal; Since the frequency offset of the laser is already counted when the uplink baseband signal is frequency-shifted, the center frequency of the modulated upstream optical signal is not affected by the laser frequency offset, and the upstream light caused by the frequency offset of the laser is avoided.
- the signals are crosstalked at the same time; at the same time, compared with the frequency adjustment of the laser, the digital frequency shift processing of the uplink baseband signal by the DSP chip is faster, so when the downlink optical signal or the laser frequency hopping, the optical communication node can
- the frequency hopping situation is adjusted in time; and, during the entire modulation process, there is no need to Optical frequency adjusting device, even if the laser optical communications node is not configured to adjust the frequency of the interface can be realized upstream optical signal modulation, to reduce the manufacturing cost of the optical communication nodes.
- the baseband signal generating unit 373 in the DSP chip 370 is an FDMA signal generating unit 373a, which is FDMA.
- the signal generating unit 373a is configured to generate an uplink baseband FDMA signal according to the input uplink data, where the center frequency of the uplink baseband FDMA signal is fsub .
- the center frequency of the downlink optical signal received by the optical communication node is f 0 and the frequency offset estimation value calculated by the frequency offset estimation unit 371 is ⁇ f
- the center frequency of the local carrier signal generated by the laser 330 is Is f 0 + ⁇ f.
- the frequency shifting unit 372 performs digital frequency shift processing on the uplink baseband FDMA signal according to the received frequency offset estimation value ⁇ f, and then outputs an uplink baseband FDMA signal with a center frequency of f sub - ⁇ f (ie, after digital frequency shift processing)
- the uplink baseband FDMA signal is transmitted to the digital-to-analog converter 350 to convert the uplink baseband FDMA signal into an uplink analog signal (the center frequency remains unchanged).
- the center frequency of the uplink optical signal finally output by the optical communication node is only related to the center frequency of the downlink optical signal and the uplink baseband FDMA signal, regardless of whether the laser has a frequency offset.
- the downlink optical signals received by different user nodes have the same center frequency (because they are all transmitted by the same central node), and the uplink baseband FDMA signals generated by different user nodes correspond to different subcarriers (that is, different frequencies). Therefore, even if the laser in the user node is frequency-shifted, the uplink optical signals output by different user nodes will not crosstalk, ensuring the transmission quality of the uplink optical signal.
- the baseband signal generating unit 373 in the DSP chip 370 is a CDMA signal generating unit 373b, which is a CDMA signal generating unit 373b.
- the CDMA signal generating unit 373b is configured to generate an uplink baseband CDMA signal according to the input uplink data, wherein the center frequency of the uplink baseband CDMA signal is (near) 0.
- the center frequency of the downlink optical signal received by the optical communication node is f 0 and the frequency offset estimation value calculated by the frequency offset estimation unit 371 is ⁇ f
- the center frequency of the local carrier signal generated by the laser 330 is Is f 0 + ⁇ f.
- the frequency shifting unit 372 performs digital frequency shift processing on the uplink baseband CDMA signal according to the received frequency offset estimation value ⁇ f, and then outputs an uplink baseband CDMA signal with a center frequency of - ⁇ f (ie, uplink after the digital frequency shift processing).
- the baseband CDMA signal is transmitted to the digital-to-analog converter 350 to convert the uplink baseband CDMA signal into an uplink analog signal (the center frequency remains unchanged).
- the above digital frequency shift processing is a frequency shift operation in a mathematical sense.
- the negative center value after the frequency shift processing does not mean that the center frequency is negative, but indicates that the reverse direction is adjusted in the positive frequency direction. .
- the center frequency of the uplink optical signal finally output by the optical communication node is synchronized with the center frequency of the downlink optical signal, regardless of whether the laser has a frequency offset (the laser frequency offset is not correct)
- the spread spectrum code channel has an effect).
- the spreading code channels corresponding to different user nodes are orthogonal to each other, so that the uplink optical signals output by different user nodes do not crosstalk, and the transmission quality of the uplink optical signals is ensured.
- 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, 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 a dispersion estimation or a fiber dynamic delay estimation.
- the channel parameter estimation unit 374 may also output other channel parameters for indicating channel quality, which is not limited by the embodiment of the present application.
- the channel parameter pre-compensation unit 375 is connected to the channel parameter estimation unit 374 and the baseband signal generation unit 373, respectively, for performing channel parameter pre-compensation on the uplink baseband signal according to the channel parameter estimation result.
- the channel parameter pre-compensation unit 375 performs inverse adjustment on the dispersion of the uplink baseband signal according to the dispersion estimation.
- the channel parameter pre-compensation unit 375 adjusts the transmission delay of the uplink baseband signal according to the dynamic delay estimation of the optical fiber, thereby avoiding the optical fiber transmission delay conversion (such as temperature cause)
- the effect of fiber deformation which in turn affects the transmission delay of the light, on the transmission of the upstream optical signal.
- the channel parameter pre-compensation unit 375 is disposed after the frequency shifting unit 372, and is configured to perform channel parameter pre-compensation on the digitally frequency-shifted uplink baseband signal according to the channel parameter estimation result.
- the specific setting position of the parameter pre-compensation unit 375 is defined.
- the DSP chip described in the embodiment of the present application or a component thereof may be a circuit.
- This circuit can be implemented by a chip system.
- the chip system may include: a central processing unit (English: Central Processing, referred to as UnitCPU), a general-purpose processor, a digital signal processor, an application specific integrated circuit (ASIC), and a field programmable gate array (English: Field-Programmable Gate Array) , abbreviated as: FPGA) or other programmable logic device, transistor logic device, discrete device, hardware component or any combination of the above devices. It is possible to implement or carry out the various illustrative logical blocks, modules and circuits described in connection with the present disclosure.
- the DSP chip can also be a combination of computing functions, such as one or more microprocessor combinations, a combination of a DSP and a microprocessor, and the like.
- FIG. 7 is a flowchart of a method for modulating an uplink optical signal according to an embodiment of the present application.
- This embodiment uses the method for modulating the uplink optical signal for each user node 120 in FIG. 1 as an example.
- the method includes the following steps.
- Step 701 Coherently receive the downlink optical signal sent by the central node according to the local carrier signal generated by the laser.
- the user node uses a single light source to implement uplink and downlink optical signal transmission. Therefore, the local carrier signal generated by the laser is input into the two-way power splitter, and the power splitter outputs a local carrier signal to the coherent receiver, so that The coherent receiver coherently receives the downlink optical signal sent by the central node according to the local carrier signal.
- Step 702 Calculate a frequency offset estimation value of the local carrier signal and the downlink optical signal, where the frequency offset estimation value is a difference between a local carrier signal and a center frequency of the downlink optical signal.
- 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 downlink optical signal and the local carrier signal. Center frequency, calculate the frequency offset estimate.
- the built-in analog-to-digital converter performs analog-to-digital conversion on the received downlink optical signal to obtain a downlink digital signal, and performs data signal processing on the downlink digital signal, thereby The downlink data modulated in the downlink optical signal is recovered.
- Step 703 Perform frequency shifting and digital-to-analog conversion processing on the uplink baseband signal according to the frequency offset estimation value, the uplink baseband signal is generated according to the uplink data, and the digital-to-analog conversion is used to convert the digital signal into an analog signal.
- the uplink baseband signal generated by the user node according to the uplink data is an uplink baseband FDMA signal.
- the center frequency of the downlink optical signal is f 0
- the frequency offset estimation value is ⁇ f
- the center frequency of the generated uplink baseband FDMA signal is f sub
- the user node shifts the center frequency of the uplink baseband FDMA signal to f sub - ⁇ f, and converts the frequency-shifted uplink baseband FDMA signal into an analog signal (the center frequency remains unchanged).
- the uplink baseband signal generated by the user node according to the uplink data is an uplink baseband CDMA signal.
- the user node shifts the center frequency of the uplink baseband CDMA signal to - ⁇ f (the center frequency of the original uplink baseband CDMA signal is 0) And converting the up-baseband CDMA signal after the frequency shift processing into an analog signal (the center frequency remains unchanged).
- the transmission quality of the optical signal is also related to the channel quality
- the uplink and downlink optical signals are transmitted through the same channel
- the channel parameter estimation is performed according to the downlink optical signal.
- Step 704 Acquire an uplink optical signal according to the local carrier signal and the digital baseband conversion processed uplink baseband signal.
- the user node performs 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 upstream optical signal is f 0 +f sub .
- the user node performs IQ modulation on the local carrier signal and the processed uplink baseband CDMA signal to obtain an uplink optical signal, wherein the center frequency of the upstream optical signal is f 0 .
- the frequency offset estimation value of the local carrier signal and the downlink optical signal generated by the laser is calculated, and the generated uplink baseband signal is calculated according to the frequency offset estimation value.
- Frequency shift processing and digital-to-analog conversion processing thereby modulating an uplink optical signal according to the local carrier signal and the digital baseband converted uplink baseband signal; since the uplink baseband signal is subjected to frequency shift processing, the frequency offset of the laser is already counted, Therefore, the center frequency of the modulated upstream optical signal is not affected by the laser frequency offset, thereby avoiding crosstalk of the upstream optical signals caused by the frequency shift of the laser; meanwhile, compared to the frequency adjustment of the laser, due to the uplink baseband signal
- the frequency shift processing is faster, so when the downlink optical signal or the laser frequency hopping, the user node can adjust according to the frequency hopping condition in time; and, in the whole modulation process, the frequency adjustment of the laser is not required, even if the user
- the node's laser is not configured with a frequency adjustment interface, user section It can be realized upstream optical signal modulation, to reduce the manufacturing cost of the user node.
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Abstract
本申请公开了一种上行光信号调制方法、光通信节点及***,属于光通信技术领域,所述方法:根据激光器产生的本地载波信号,相干接收中心节点发送的下行光信号;计算本地载波信号与下行光信号的频偏估计值,频偏估计值为本地载波信号与下行光信号的中心频率的差值;根据频偏估计值对上行基带信号进行移频和数模转换处理,上行基带信号根据上行数据生成,数模转换用于将数字信号转换为模拟信号;根据本地载波信号和数模转换处理后的上行基带信号调制得到上行光信号。本申请实施例中,用户节点能够根据频率跳变情况进行及时调节;且无需对激光器进行频率调节,即使用户节点的激光器未配置频率调整接口,也能实现上行光信号调制,降低了用户节点的制造成本。
Description
本申请涉及光通信技术领域,特别涉及一种上行光信号调制方法、光通信节点及***。
随着高清视频以及虚拟现实(英文:Virtual Reality,简称:VR)技术的不断发展,用户对光通信***的通信容量以及延时的需求越来越高。为了提升光通信***的通信容量并降低延时,频分多址(英文:Frequency Division Multiple Access,简称:FDMA)技术和码分多址(英文:Code Division Multiple Access,简称:CDMA)技术被应用于光通信***中。
以FDMA技术为例,将FDMA技术应用到光通信***后,***中单个波长被分割为若干个子载波,且***中各个用户节点灵活分配波长以及波长内的通道资源。各个用户节点通过链路上的光耦合器相连,并最终与***中的中心节点相连,从而与中心节点进行上下行光信号传输。
为了避免各个用户节点使用的子载波之间相互串扰,各个子载波之间需要预留频率保护间隔。然而在上行光信号传输过程中,由于上行光信号由各个用户节点使用各自的激光器分别进行调制,当某一用户节点的激光器发生频率偏移,且频率偏移量超过频率保护间隔时,该用户节点使用的子载波将会与相邻子载波之间发生串扰。
为了避免激光器频率偏移造成的子载波串扰,相关技术中,用户节点接收到中心节点传输的下行光信号后,根据下行光信号和激光器产生的本地载波信号,计算得到激光器的频偏估计值,从而利用该频偏估计值对激光器进行反馈调节。即使激光器发生频率偏移,通过上述调节机制,激光器产生的本地载波信号仍旧能够与下行光信号保持同步,从而避免调制出的上行光信号之间相互串扰。
然而,由于激光器进行反馈调节的速度较慢,当下行光信号或激光器发生频率跳变时,激光器将无法及时进行调节;且当用户节点的激光器未配置相应的频率调整接口时,上述反馈调节将无法执行。
发明内容
为了解决相关技术中,由于激光器进行反馈调节的速度较慢,当下行光信号或激光器发生频率跳变时,激光器将无法及时进行调节;且当用户节点的激光器未配置相应的频率调整接口时,反馈调节将无法执行的问题,本申请实施例提供了一种上行光信号调制方法、光通信节点及***。
第一方面,本申请提供了一种上行光信号调制方法,该方法包括:
根据激光器产生的本地载波信号,相干接收中心节点发送的下行光信号;
计算本地载波信号与下行光信号的频偏估计值,频偏估计值为本地载波信号与下行光信号的中心频率的差值;
根据频偏估计值对上行基带信号进行移频和数模转换处理,上行基带信号根据上行数
据生成,数模转换用于将数字信号转换为模拟信号;
根据本地载波信号和数模转换处理后的上行基带信号调制得到上行光信号。
本实施例中,用户节点相干接收到中心节点发送的下行光信号后,计算激光器产生的本地载波信号与下行光信号的频偏估计值,并根据该频偏估计值对生成的上行基带信号进行移频处理和数模转换处理,从而根据本地载波信号和数模转换处理后的上行基带信号调制出上行光信号;由于对上行基带信号进行移频处理时,已经计入激光器的频率偏移,因此,调制出的上行光信号的中心频率不受激光器频率偏移影响,避免因激光器发生频率偏移造成的上行光信号相互串扰;同时,相较于对激光器进行频率调节,由于对上行基带信号进行移频处理的速度较快,因此在下行光信号或激光器发生频率跳变时,用户节点能够根据频率跳变情况进行及时调节;并且,整个调制过程中,无需对激光器进行频率调节,即使用户节点的激光器未配置频率调整接口,用户节点也能实现上行光信号调制,降低了用户节点的制造成本。
在一种可能的设计中,下行光信号的中心频率为f0,频偏估计值为Δf,上行基带信号为上行基带FDMA信号,且上行基带FDMA信号的中心频率为fsub;
根据频偏估计值对上行基带信号进行移频和数模转换处理,包括:
将上行基带FDMA信号的中心频率移频至fsub-Δf;
将移频处理后的上行基带FDMA信号转换为模拟信号;
根据本地载波信号和数模转换处理后的上行基带信号调制得到上行光信号,包括:
对本地载波信号和处理后的上行基带FDMA信号进行正交(英文:Inphase-Quadrature,简称:IQ)调制,得到上行光信号,其中,上行光信号的中心频率为f0+fsub。
本实施例中,在基于上行基带FDMA信号调制得到上行光信号时,根据频偏估计值在上行基带FDMA信号原有中心频率的基础上进行移频,使得最终调制出的上行光信号仅与下行光信号以及原始上行基带FDMA信号的中心频率有关,从而避免上行光信号受到激光器频率偏移影响。
在一种可能的设计中,下行光信号的中心频率为f0,频偏估计值为Δf,上行基带信号为上行基带CDMA信号;
根据所述频偏估计值对上行基带信号进行移频和数模转换处理,包括:
将上行基带CDMA信号的中心频率移频至-Δf;
将移频处理后的上行基带CDMA信号转换为模拟信号;
根据所述本地载波信号和数模转换处理后的上行基带信号调制得到上行光信号,包括:
对本地载波信号和处理后的上行基带CDMA信号进行IQ调制,得到上行光信号,其中,上行光信号的中心频率为f0。
本实施例中,在基于上行基带CDMA信号调制得到上行光信号时,根据频偏估计值Δf将上行基带FDMA信号的中心频率移频至-Δf,使得最终调制出的上行光信号的中心频率与下行光信号的中心频率保持同步,从而避免上行光信号受到激光器频率偏移影响。
在一种可能的设计中,根据激光器产生的本地载波信号,相干接收中心节点发送的下行光信号之后,还包括:
根据下行光信号进行信道参数估计;
根据信道参数估计结果对上行基带信号进行信道参数预补偿,信道参数估计结果包括
色散估计或光纤动态延时估计中的至少一种。
由于光信号的传输质量与信道质量相关,且上下行光信号通过同一信道传输,因此为了提高上行光信号的传输质量,本实施例中,用户节点相关接收到下行光信号后,根据下行光信号对信道参数进行估计,从而确定与中心节点间信道的信道质量,并根据信道参数估计结果,对上行基带信号进行信道参数预补偿,进而减小信道对上行光信号传输造成的影响,进一步提高上行光信号的传输质量。
在一种可能的设计中,根据激光器产生的本地载波信号,相干接收中心节点发送的下行光信号之后,还包括:
对接收到的下行光信号进行模数转换和数据信号处理,恢复下行数据,模数转换用于将模拟信号转换为数字信号。
第二方面,本申请提供了一种光通信节点,该光通信节点包括:相干接收机、模数转换器、激光器、功分器、数模转换器、调制器和数字信号处理(英文:Digital Signal Processing,简称:DSP)芯片;
功分器与激光器相连,用于将激光器产生的本地载波信号分成两路输出;
相干接收机与功分器相连,用于根据功分器输出的本地载波信号对下行光信号进行相干接收,得到下行模拟信号;
模数转换器与相干接收机相连,用于将相干接收机输出的下行模拟信号转换为下行数字信号;
DSP芯片与模数转换器相连,用于根据下行数字信号恢复下行数据,并计算激光器的频偏估计值,频偏估计值用于指示本地载波信号与下行光信号的中心频率的差值;
DSP芯片还与数模转换器相连,用于根据频偏估计值对上行基带信号进行移频处理,并向数模转换器发送移频处理后的上行基带信号,数模转换器用于将移频处理后的上行基带信号转换为上行模拟信号;
调制器分别与功分器和数模转换器相连,用于根据功分器输出的本地载波信号和上行模拟信号调制得到上行光信号。
本实施例中,光通信节点相干接收到中心节点发送的下行光信号后,通过DSP芯片计算激光器产生的本地载波信号与下行光信号的频偏估计值,并根据该频偏估计值对生成的上行基带信号进行移频处理,交由调制器对激光器产生的本地载波信号和上行模拟信号(移频处理后的上行基带信号经过数模转换后生成)调制得到上行光信号;由于对上行基带信号进行移频处理时,已经计入激光器的频率偏移,因此,调制出的上行光信号的中心频率不受激光器频率偏移影响,避免因激光器发生频率偏移造成的上行光信号相互串扰;同时,相较于对激光器进行频率调节,通过DSP芯片对上行基带信号进行数字移频处理的速度更快,因此在下行光信号或激光器发生频率跳变时,光通信节点能够根据频率跳变情况进行及时调节;并且,整个调制过程中,无需对激光器进行频率调节,即使光通信节点的激光器未配置频率调整接口,也能实现上行光信号调制,降低了光通信节点的制造成本。
在一种可能的设计中,DSP芯片中包括频偏估计单元、移频单元和基带信号生成单元;
频偏估计单元与模数转换器相连,用于计算频偏估计值;
移频单元分别与频偏估计单元和基带信号生成单元相连,用于根据频偏估计值对基带信号生成单元输出的上行基带信号进行移频处理。
在一种可能的设计中,下行光信号的中心频率为f0,频偏估计值为Δf,基带信号生成单元为FDMA信号生成单元,且输出的上行基带FDMA信号的中心频率为fsub;
移频单元,用于将上行基带FDMA信号的中心频率移频至fsub-Δf;
数模转换器,用于将移频处理后的上行基带FDMA信号转换为上行模拟信号;
调制器,用于对本地载波信号和上行模拟信号进行IQ调制,得到上行光信号,其中,上行光信号的中心频率为f0+fsub。
本实施例中,在基于上行基带FDMA信号调制得到上行光信号时,移频单元根据频偏估计值,在上行基带FDMA信号原有中心频率的基础上进行移频,使得最终调制出的上行光信号仅与下行光信号以及原始上行基带FDMA信号的中心频率有关,从而避免上行光信号受到激光器频率偏移影响。
在一种可能的设计中,下行光信号的中心频率为f0,频偏估计值为Δf,基带信号生成单元为CDMA信号生成单元;
移频单元,用于将上行基带CDMA信号的中心频率移频至-Δf;
数模转换器,用于将移频处理后的上行基带CDMA信号转换为上行模拟信号;
调制器,用于对本地载波信号和上行模拟信号进行IQ调制,得到上行光信号,其中,上行光信号的中心频率为f0。
本实施例中,本实施例中,在基于上行基带CDMA信号调制得到上行光信号时,移频单元根据频偏估计值Δf将上行基带FDMA信号的中心频率移频至-Δf,使得最终调制出的上行光信号的中心频率与下行光信号的中心频率保持同步,从而避免上行光信号受到激光器频率偏移影响。
在一种可能的设计中,DSP芯片中还包括信道参数估计单元和信道参数预补偿单元;
信道参数估计单元与模数转换器相连,用于根据下行光信号进行信道参数估计,并输出信道参数估计结果,信道参数估计结果包括色散估计或光纤动态延时估计中的至少一种;
信道参数预补偿单元分别与信道参数估计单元和基带信号生成单元相连,用于根据信道参数估计结果对上行基带信号进行信道参数预补偿。
由于光信号的传输质量与信道质量相关,且上下行光信号通过同一信道传输,因此为了提高上行光信号的传输质量,本实施例中,DSP芯片相关接收到下行光信号后,通过信道参数估计单元对信道参数进行估计,从而确定与中心节点间信道的信道质量,并根据信道参数估计结果,通过信道参数预补偿单元对上行基带信号进行信道参数预补偿,进而减小信道对上行光信号传输造成的影响,进一步提高上行光信号的传输质量。
第三方面,本申请提供了一种芯片***,用于实现第二方面或第二方面任一种可能的设计中所述光通信节点中的DSP芯片。该芯片***可以由芯片构成,也可以包含芯片和其他分立器件。所述芯片,可以是一种专用集成电路(Application-Specific Integrated Circuit,ASIC),也可以是其他形式的芯片。可选的,所述芯片***还可以包含处理器,用于支持DSP芯片实现上述方面中所涉及的功能,例如,获取/计算上述方面中所涉及的信号和/或频偏估计值,进行上述方面中的移频处理,和/或,信道参数预补偿处理过程。在一种可能的设计中,所述芯片***还包括存储器,所述存储器,用于保存DSP芯片必要的程序指令和数据。
第四方面,本申请提供了一种光通信***,光通信***包括:中心节点和n个用户节
点,n个用户节点通过光耦合器与中心节点相连,n≥2,n为整数;
中心节点用于向n个用户节点发送下行光信号,n个用户节点用于向中心节点发送上行光信号;
各个用户节点包括如上述第二方面或第二方面任一种可能的设计中所述的光通信节点。
图1示出了本申请一个实施例提供的光通信***的***架构图;
图2是用户节点采用不同子载波与中心节点进行光信号传输的实施示意图;
图3示出了本申请一个实施例提供的光通信节点的结构示意图;
图4示出了本申请另一个实施例提供的光通信节点的结构示意图;
图5示出了本申请另一个实施例提供的光通信节点的结构示意图;
图6示出了本申请另一个实施例提供的光通信节点的结构示意图;
图7示出了本申请一个实施例提供的上行光信号调制方法的流程图。
下面将结合附图对本申请实施方式作进一步地详细描述。
请参考图1,其示出了本申请一个实施例提供的光通信***的***架构图,该光通信***中包括中心节点110和n个用户节点120,其中,n个用户节点120通过光耦合器130(或称为光纤耦合器,英文:coupler)与中心节点110相连。
中心节点110是位于核心网(英文:core netwok)侧的光通信节点,用于将来自核心网的下行数据调制成下行光信号(通过内置激光器产生的本地载波信号进行调制),并通过与用户节点120之间的物理信道,将下行光信号发送至用户节点120,其中,中心节点110与用户节点120之间的物理信道为光纤。
用户节点120是位于用户侧的光通信节点,用于与用户设备相连,并将来自用户设备的上行数据调制为上行光信号(通过内置激光器产生的本地载波信号进行调制),并通过与中心节点110之间的物理信道,将上行光信号发送至中心节点110。在一种可能的设计中,用户节点110是与用户设备相连的光调制解调器(或称为光猫,英文:Optical modem,)。
为了提升光通信***的容量并降低传输延时,图1所示的光通信***中应用了FDMA技术或CDMA技术。
应用FDMA技术后,光通信***中单个波长被分隔为若干个子载波(不同子载波对应不同的频率),而各个用户节点即利用各自分配的子载波进行光信号传输,相应的,中心节点即通过不同的子载波向不同用户节点传输下行光信号,并根据子载波区分不同用户节点发送的上行光信号。
示意性的,如图2所示,用户节点1利用中心频率为f1的子载波与中心节点进行光信号传输,用户节点2利用中心频率为f2的子载波与中心节点进行光信号传输,用户节点N利用中心频率为fN的子载波与中心节点进行光信号传输,且由于各个子载波之间互不相同,因此中心节点接收到的上行光信号之间互不串扰。
而应用CDMA技术后,光通信***中单个波长被分割为多个扩频码通道(不同扩频码通道对应不同的扩频码),各个用户节点即利用各自分配的扩频码通道进行光信号传输,而中心节点即根据不同的扩频码区分不同用户节点发送的上行光信号。由于各个用户节点使用的扩频码通道相互正交,因此中心节点接收到的上行光信号之间互不串扰。
将FDMA或CDMA技术应用到光通信***后,光通信节点中激光器的频率精度和稳定性将直接影响到光信号的传输质量。
以FDMA为例,在下行光信号传输过程中,由于所有的下行光信号均由中心节点的单个激光器调制发送,因此,当激光器发生频率偏移时,各个子载波的频率均向同一方向偏移,各个子载波之间不会发生串扰;而在上行光信号传输过程中,由于各个用户节点均通过各自的激光器进行上行光信号调制,当某一用户节点的激光器发生频率偏移时,该用户节点发送的上行光信号将与其他用户节点发送的上行光信号产生串扰。示意性的,如图2所示,当用户节点2中的激光器发生频率偏移时,用户节点2通过子载波2发送的上行光信号将发生频率偏移,从而与用户节点1发送的上行光信号产生串扰。
虽然可以通过在子载波间设置频率保护间隔的方式,来降低激光器频率偏移所造成的影响,但是由于目前的商用激光器存在较高的频率偏移(高达±2.5GHz),导致单个波长仅能够被分隔成少量子载波(需要设置足够大的频率保护间隔),即单个波长仅能够被少量用户节点所使用,造成波长的使用率较低。以单个波长为50GHz,每个子载波的频率范围为2.5GHz,激光器的频率偏移为±2.5GHz为例,该波长只能分隔成7个2.5GHz的子载波,每个子载波之间的频率保护间隔为5Ghz。
而在CDMA中,当用户节点中的激光器发生频率偏移时,用户节点使用的扩频码通道间非正交,导致扩频码通道间相互干扰,影响中心节点对上行光信号的正常接收。
为了解决上述问题,相关技术中,各个用户节点接收到中心节点传输的下行光信号后,计算激光器产生的本地载波信号与下行光信号的频偏估计值,从而根据该频偏估计值对激光器的频率进行反馈调节,使得各个激光器产生的本地载波信号与下行光信号的中心频率保持同步。后续利用频率调节后的激光器调制上行光信号时,即不会出现上行光信号串扰的问题。
但是,对激光器进行反馈调节时,由于需要对激光器的光源进行调制,而对光源进行调制的速度较慢,导致激光器反馈调节不及时,在下行光信号或激光器发生频率跳变(即短时间内频率多次变化)时,激光器无法实时跟踪频率跳变;并且,激光器必须设置相应的频率调整接口才能够完成频率调整,导致上述调整方式的适用范围较小。
本申请实施例中,光通信***中各个用户节点的DSP芯片具备移频功能,通过该移频功能,DSP芯片根据计算得到的频偏估计值对产生的上行基带信号进行数字移频处理,并交由调试器对激光器产生的本地载波信号和数字移频处理后的上行基带信号进行调制,从而消除激光器频率偏移造成的影响。同时,由于数字移频处理的速率优于对激光器光源进行调制的速率,因此,用户节点能够在下行光信号或激光器发生频率跳变时,对上行基带信号进行及时移频处理,而不再需要对激光器的光源进行调整,适用于未配置频率调整接口的激光器。下面采用示意性的实施例进行说明。
请参考图3,其示出了本申请一个实施例提供的光通信节点的结构示意图。该光通信节
点可以实现成为图1所示光通信***中的用户节点120,该光通信节点包括:相干接收机310、模数转换器320、激光器330、功分器340、数模转换器350、调制器360和DSP芯片370。
图3所示的光通信节点采用单光源实现上下行光信号传输,即光通信节点中仅包含一个激光器330。为了利用单一激光器产生的本地载波信号实现下行光信号接收和上行光信号调制发送,激光器330与功分器340相连,其中,该功分器340为两路功分器,用于将激光器330产生的本地载波信号分成两路输出,且功分器340输出的两路本地载波信号的功率相同。
激光器330在工作过程中,通过本振产生本地载波信号,并向功分器340输入本地载波信号。由于激光器330存在一定的频率偏移,因此,输出的本地载波信号的频率在频率偏移范围内浮动。比如,激光器330的预定频率为20GHz,且频率偏移范围为±2.5GHz时,激光器330输出的本地载波信号的频率即在17.5GHZ至22.5GHz之间浮动。
功分器340的第一功率输出端与相干接收机310相连,用于向相干接收机310输入激光器330产生的本地载波信号。
相应的,通过物理信道传输的下行光信号达到相干接收机310后,相干接收机31即利用本地载波信号对该下行光信号进行相干接收,从而得到下行模拟信号。其中,相干接收机310可以采用光通信领域成熟的相干接收技术进行相干接收,本申请实施例并不对此进行限定。
对下行光信号相关接收得到下行模拟信号后,相干接收机310将下行模拟信号输入相连的模数转换器320(英文:Analog-to-Digital Converter,简称:ADC),由模数转换器320将下行模拟信号转换为下行数字信号。
作为光通信节点的核心部件,DSP芯片370与模数转换器320相连,用于接收模数转换器320输出的下行数字信号,并对下行数字信号进行数字信号处理,从而恢复下行光信号中调制的下行数据。
在恢复下行数据的同时,DSP芯片370根据下行光信号和激光器330产生的本地载波信号,实时计算频偏估计值,该频偏估计值即为本地载波信号与下行光信号的中心频率的差值。
在一种可能的设计中,如图3所示,DSP芯片370中包括频偏估计单元371,该频偏估计单元371即与模数转换器320相连,用于计算该频偏估计值。
示意性的,当下行光信号的中心频率为f0,且计算得到频偏估计值为Δf时,激光器330产生的本地载波信号的频率则为f0+Δf。
与相关技术中,根据计算得到的频偏估计值对激光器330进行频率调节不同,本实施例中,DSP芯片370计算得到频偏估计值后,根据该频偏估计值对上行基带信号进行数字移频处理。
在一种可能的设计中,如图3所示,DSP芯片370中还包括移频单元372和基带信号生成单元373。其中,移频单元372分别与频偏估计单元371和基带信号生成单元373相连。
基带信号生成单元373与用户设备相连,用于根据用户设备输入的上行数据生成上行基带信号,其中,该上行基带信号为数字信号。可选的,当光通信节点应用FDMA技术时,基带信号生成单元373即为上行基带FDMA信号生成单元,用于生成上行基带FDMA信号;
当光通信节点应用CDMA技术时,基带信号生成单元373即为上行基带CDMA信号生成单元,用于生成上行基带CDMA信号。
移频单元372接收到频偏估计值和上行基带信号后,即对上行基带信号进行数字移频处理,其中,数字移频处理后的上行基带信号计入了本地载波信号与下行信号的中心频率差值。由于无需对激光器330进行频率调整,因此免去了在激光器330上设置频率调整接口,进一步降低了激光器330的制造成本。
DSP芯片370对上行基带信号进行数字移频处理后,即将移频处理后的上行基带信号输入相连的数模转换器350(英文:Digital to analog converter,简称:DAC),由数模转换器350将移频处理后的上行基带信号转换为上行模拟信号。
光通信节点中还设置有调制器360,该调制器360分别与功分器340以及数模转换器350相连。接收到数模转换器350输出的上行模拟信号后,调制器360即利用功分器340输出的本地载波信号对其进行调制,得到上行光信号,并最终通过物理信道向中心节点发送该上行光信号。其中,该调制器360为IQ调制器,用于对本地载波信号和上行模拟信号进行IQ调制。
由于经过数字移频处理后的上行基带信号中已计入频偏估计值,因此,利用激光器330产生的本地载波信号对其进行调制时,激光器330的频率偏移得以消除,从而消除激光器频率偏移对子载波频率的影响,避免相邻子载波之间相互串扰。
综上所述,本实施例中,光通信节点相干接收到中心节点发送的下行光信号后,通过DSP芯片计算激光器产生的本地载波信号与下行光信号的频偏估计值,并根据该频偏估计值对生成的上行基带信号进行移频处理,交由调制器对激光器产生的本地载波信号和上行模拟信号(移频处理后的上行基带信号经过数模转换后生成)调制得到上行光信号;由于对上行基带信号进行移频处理时,已经计入激光器的频率偏移,因此,调制出的上行光信号的中心频率不受激光器频率偏移影响,避免因激光器发生频率偏移造成的上行光信号相互串扰;同时,相较于对激光器进行频率调节,通过DSP芯片对上行基带信号进行数字移频处理的速度更快,因此在下行光信号或激光器发生频率跳变时,光通信节点能够根据频率跳变情况进行及时调节;并且,整个调制过程中,无需对激光器进行频率调节,即使光通信节点的激光器未配置频率调整接口,也能实现上行光信号调制,降低了光通信节点的制造成本。
在一种可能的设计中,将FDMA技术应用到光通信节点时,在图3的基础上,如图4所示,DSP芯片370中的基带信号生成单元373为FDMA信号生成单元373a,该FDMA信号生成单元373a即用于根据输入的上行数据生成上行基带FDMA信号,其中,该上行基带FDMA信号的中心频率为fsub。
如图4所示,光通信节点接收到的下行光信号的中心频率为f0,且频偏估计单元371计算得到的频偏估计值为Δf时,激光器330产生的本地载波信号的中心频率即为f0+Δf。
相应的,移频单元372根据接收到的频偏估计值为Δf,对上行基带FDMA信号进行数字移频处理后,输出中心频率为fsub-Δf的上行基带FDMA信号(即数字移频处理后的上行基带FDMA信号),并交由数模转换器350将该上行基带FDMA信号转换为上行模拟信号(中心频率保持不变)。
调制器360对中心频率为f0+Δf的本地载波信号和中心频率为fsub-Δf的上行模拟信号进行IQ调制后,即输出中心频率为(f0+Δf)+(fsub-Δf)=f0+fsub的上行光信号。
显然,经过上述数字移频处理后,光通信节点最终输出的上行光信号的中心频率仅与下行光信号以及上行基带FDMA信号的中心频率相关,而与激光器是否发生频率偏移无关。由于同一光通信***中,不同用户节点接收到的下行光信号的中心频率相同(因为均由同一中心节点发送),且不同用户节点生成的上行基带FDMA信号对应不同的子载波(即频率不同),因此,即便用户节点中的激光器发生频率偏移,不同用户节点输出的上行光信号也不会发生串扰,确保上行光信号的传输质量。
在另一种可能的设计中,将CDMA技术应用到光通信节点时,在图3的基础上,如图5所示,DSP芯片370中的基带信号生成单元373为CDMA信号生成单元373b,该CDMA信号生成单元373b即用于根据输入的上行数据生成上行基带CDMA信号,其中,该上行基带CDMA信号的中心频率为(趋近于)0。
如图5所示,光通信节点接收到的下行光信号的中心频率为f0,且频偏估计单元371计算得到的频偏估计值为Δf时,激光器330产生的本地载波信号的中心频率即为f0+Δf。
相应的,移频单元372根据接收到的频偏估计值为Δf,对上行基带CDMA信号进行数字移频处理后,输出中心频率为-Δf的上行基带CDMA信号(即数字移频处理后的上行基带CDMA信号),并交由数模转换器350将该上行基带CDMA信号转换为上行模拟信号(中心频率保持不变)。需要说明的是,上述数字移频处理为数学意义上的移频操作,相应的,移频处理后中心频率为负值并非代表中心频率为负,而是指示沿正频率方向的反向进行调节。
调制器360对中心频率为f0+Δf的本地载波信号和中心频率为-Δf的上行模拟信号进行IQ调制后,即输出中心频率为(f0+Δf)+(-Δf)=f0的上行光信号。
显然,经过上述数字移频处理后,光通信节点最终输出的上行光信号的中心频率与下行光信号的中心频率保持同步,而与激光器是否发生频率偏移无关(激光器发生频率偏移不会对扩频码通道产生影响)。由于同一光通信***中,不同用户节点对应的扩频码通道间相互正交,因此不同用户节点输出的上行光信号也不会发生串扰,确保上行光信号的传输质量。
由于光信号的传输质量与信道质量相关,且上下行光信号通过同一信道传输,因此为了提高上行光信号的传输质量,在一种可能的设计中,在图3的基础上,如图6所示,DSP芯片370中还包括信道参数估计单元374和信道参数预补偿单元375。
信道参数估计单元374与模数转换器320相连,用于根据下行光信号进行信道参数估计,并输出信道参数估计结果,其中,信道参数估计结果包括色散估计或光纤动态延时估计中的至少一种。在其他可能的实施方式中,信道参数估计单元374还可以输出其他用于指示信道质量的信道参数,本申请实施例并不对此进行限定。
在一种可能的设计中,信道参数预补偿单元375分别与信道参数估计单元374和基带信号生成单元373相连,用于根据信道参数估计结果对上行基带信号进行信道参数预补偿。可选的,信道参数预补偿单元375根据色散估计,对上行基带信号的色散进行反向调节,
从而避免光纤色散对上行光信号传输所造成的影响;信道参数预补偿单元375根据光纤动态延时估计,对上行基带信号的发送时延进行调节,从而避免光纤传输时延变换(比如温度原因导致光纤形变,进而影响光线传输时延)对上行光信号传输所造成的影响。
在其他可能的设计中,信道参数预补偿单元375设置在移频单元372之后,用于根据信道参数估计结果对数字移频后的上行基带信号进行信道参数预补偿,本申请实施例并不对信道参数预补偿单元375的具体设置位置进行限定。
本申请实施例中所述的DSP芯片或其所包含的组成部分,可以是一种电路。该电路可以由芯片***实现。所述芯片***可以包括:中央处理器(英文:Central Processing,简称:UnitCPU)、通用处理器、数字信号处理器、专用集成电路(ASIC)、现场可编程门阵列(英文:Field-Programmable Gate Array,简称:FPGA)或者其他可编程逻辑器件、晶体管逻辑器件、分立器件、硬件部件或者上述器件的任意组合。其可以实现或执行结合本申请公开内容所描述的各种示例性的逻辑方框,模块和电路。所述DSP芯片也可以是实现计算功能的组合,例如包含一个或多于一个微处理器组合,DSP和微处理器的组合等。
请参考图7,其示出了本申请一个实施例提供的上行光信号调制方法的流程图,本实施例以该上行光信号调制方法用于图1中各个用户节点120为例进行说明,该方法包括如下步骤。
步骤701,根据激光器产生的本地载波信号,相干接收中心节点发送的下行光信号。
本申请实施例中,用户节点采用单光源实现上下行光信号传输,因此,激光器产生的本地载波信号输入两路功分器,由该功分器将一路本地载波信号输出到相干接收机,以便相干接收机根据本地载波信号相干接收中心节点发送的下行光信号。
步骤702,计算本地载波信号与下行光信号的频偏估计值,频偏估计值为本地载波信号与下行光信号的中心频率的差值。
示意性的,当用户节点采用图3所示的光通信节点结构时,DSP芯片中的频偏估计单元接收到模数转换器输入的下行数字信号时,即根据下行光信号以及本地载波信号的中心频率,计算频偏估计值。
可选的,用户节点相干接收到下行光信号后,利用内置的模数转换器对接收到的下行光信号进行模数转换,得到下行数字信号,并对该下行数字信号进行数据信号处理,从而恢复下行光信号中调制的下行数据。
步骤703,根据频偏估计值对上行基带信号进行移频和数模转换处理,上行基带信号根据上行数据生成,数模转换用于将数字信号转换为模拟信号。
在一种可能的设计中,当用户节点应用FDMA技术时,用户节点根据上行数据生成的上行基带信号为上行基带FDMA信号。示意性的,当下行光信号的中心频率为f0,频偏估计值为Δf,且生成的上行基带FDMA信号的中心频率为fsub时,用户节点即将上行基带FDMA信号的中心频率移频至fsub-Δf,并将移频处理后的上行基带FDMA信号转换为模拟信号(中心频率保持不变)。
在另一种可能的设计中,当用户节点应用CDMA技术时,用户节点根据上行数据生成的上行基带信号为上行基带CDMA信号。示意性的,当下行光信号的中心频率为f0,频偏
估计值为Δf时,用户节点将上行基带CDMA信号的中心频率移频至-Δf(原始上行基带CDMA信号的中心频率为0),并将移频处理后的所述上行基带CDMA信号转换为模拟信号(中心频率保持不变)。
由于光信号的传输质量还与信道质量相关,且上下行光信号通过同一信道传输,因此为了提高上行光信号的传输质量,用户节点相关接收到下行光信号后,根据下行光信号进行信道参数估计,并根据信道参数估计结果对上行基带信号进行信道参数预补偿,信道参数估计结果包括色散估计或光纤动态延时估计中的至少一种。
步骤704,根据本地载波信号和数模转换处理后的上行基带信号调制得到上行光信号。
结合步骤703中第一种设计,用户节点对本地载波信号和处理后的上行基带FDMA信号进行IQ调制,得到上行光信号,其中,该上行光信号的中心频率为f0+fsub。
结合步骤703中第二种设计,用户节点对本地载波信号和处理后的上行基带CDMA信号进行IQ调制,得到上行光信号,其中,该上行光信号的中心频率为f0。
本实施例中,用户节点相干接收到中心节点发送的下行光信号后,计算激光器产生的本地载波信号与下行光信号的频偏估计值,并根据该频偏估计值对生成的上行基带信号进行移频处理和数模转换处理,从而根据本地载波信号和数模转换处理后的上行基带信号调制出上行光信号;由于对上行基带信号进行移频处理时,已经计入激光器的频率偏移,因此,调制出的上行光信号的中心频率不受激光器频率偏移影响,避免因激光器发生频率偏移造成的上行光信号相互串扰;同时,相较于对激光器进行频率调节,由于对上行基带信号进行移频处理的速度较快,因此在下行光信号或激光器发生频率跳变时,用户节点能够根据频率跳变情况进行及时调节;并且,整个调制过程中,无需对激光器进行频率调节,即使用户节点的激光器未配置频率调整接口,用户节点也能实现上行光信号调制,降低了用户节点的制造成本。
Claims (11)
- 一种上行光信号调制方法,其特征在于,所述方法包括:根据激光器产生的本地载波信号,相干接收中心节点发送的下行光信号;计算所述本地载波信号与所述下行光信号的频偏估计值,所述频偏估计值为所述本地载波信号与所述下行光信号的中心频率的差值;根据所述频偏估计值对上行基带信号进行移频和数模转换处理,所述上行基带信号根据上行数据生成,所述数模转换用于将数字信号转换为模拟信号;根据所述本地载波信号和数模转换处理后的上行基带信号调制得到上行光信号。
- 根据权利要求1所述的方法,其特征在于,所述下行光信号的中心频率为f0,所述频偏估计值为Δf,所述上行基带信号为上行基带频分多址FDMA信号,且所述上行基带FDMA信号的中心频率为fsub;所述根据所述频偏估计值对上行基带信号进行移频和数模转换处理,包括:将所述上行基带FDMA信号的中心频率移频至fsub-Δf;将移频处理后的所述上行基带FDMA信号转换为模拟信号;所述根据所述本地载波信号和数模转换处理后的上行基带信号调制得到上行光信号,包括:对所述本地载波信号和数模转换处理后的上行基带FDMA信号进行正交IQ调制,得到所述上行光信号,其中,所述上行光信号的中心频率为f0+fsub。
- 根据权利要求1所述的方法,其特征在于,所述下行光信号的中心频率为f0,所述频偏估计值为Δf,所述上行基带信号为上行基带码分多址CDMA信号;所述根据所述频偏估计值对上行基带信号进行移频和数模转换处理,包括:将所述上行基带CDMA信号的中心频率移频至-Δf;将移频处理后的所述上行基带CDMA信号转换为模拟信号;所述根据所述本地载波信号和数模转换处理后的上行基带信号调制得到上行光信号,包括:对所述本地载波信号和数模转换处理后的上行基带CDMA信号进行IQ调制,得到所述上行光信号,其中,所述上行光信号的中心频率为f0。
- 根据权利要求1至3任一所述的方法,其特征在于,所述根据激光器产生的本地载波信号,相干接收中心节点发送的下行光信号之后,还包括:根据所述下行光信号进行信道参数估计;根据信道参数估计结果对所述上行基带信号进行信道参数预补偿,所述信道参数估计结果包括色散估计或光纤动态延时估计中的至少一种。
- 根据权利要求1至3任一所述的方法,其特征在于,所述根据激光器产生的本地载波信号,相干接收中心节点发送的下行光信号之后,还包括:对接收到的所述下行光信号进行模数转换和数据信号处理,恢复下行数据,所述模数转换用于将模拟信号转换为数字信号。
- 一种光通信节点,其特征在于,所述光通信节点包括:相干接收机、模数转换器、激光器、功分器、数模转换器、调制器和数字信号处理DSP芯片;所述功分器与所述激光器相连,用于将所述激光器产生的本地载波信号分成两路输出;所述相干接收机与所述功分器相连,用于根据所述功分器输出的所述本地载波信号对下行光信号进行相干接收,得到下行模拟信号;所述模数转换器与所述相干接收机相连,用于将所述相干接收机输出的下行模拟信号转换为下行数字信号;所述DSP芯片与所述模数转换器相连,用于根据所述下行数字信号恢复下行数据,并计算所述激光器的频偏估计值,所述频偏估计值用于指示所述本地载波信号与所述下行光信号的中心频率的差值;所述DSP芯片还与所述数模转换器相连,用于根据所述频偏估计值对上行基带信号进行移频处理,并向所述数模转换器发送移频处理后的上行基带信号,所述数模转换器用于将移频处理后的上行基带信号转换为上行模拟信号;所述调制器分别与所述功分器和所述数模转换器相连,用于根据所述功分器输出的所述本地载波信号和所述上行模拟信号调制得到上行光信号。
- 根据权利要求6所述的光通信节点,其特征在于,所述DSP芯片中包括频偏估计单元、移频单元和基带信号生成单元;所述频偏估计单元与所述模数转换器相连,用于计算所述频偏估计值;所述移频单元分别与所述频偏估计单元和所述基带信号生成单元相连,用于根据所述频偏估计值对所述基带信号生成单元输出的所述上行基带信号进行移频处理。
- 根据权利要求7所述的光通信节点,其特征在于,所述下行光信号的中心频率为f0,所述频偏估计值为Δf,所述基带信号生成单元为频分多址FDMA信号生成单元,且输出的上行基带FDMA信号的中心频率为fsub;所述移频单元,用于将所述上行基带FDMA信号的中心频率移频至fsub-Δf;所述数模转换器,用于将移频处理后的上行基带FDMA信号转换为所述上行模拟信号;所述调制器,用于对所述本地载波信号和所述上行模拟信号进行正交IQ调制,得到所述上行光信号,其中,所述上行光信号的中心频率为f0+fsub。
- 根据权利要求7所述的光通信节点,其特征在于,所述下行光信号的中心频率为f0,所述频偏估计值为Δf,所述基带信号生成单元为码分多址CDMA信号生成单元;所述移频单元,用于将所述上行基带CDMA信号的中心频率移频至-Δf;所述数模转换器,用于将移频处理后的上行基带CDMA信号转换为所述上行模拟信号;所述调制器,用于对所述本地载波信号和所述上行模拟信号进行IQ调制,得到所述上行光信号,其中,所述上行光信号的中心频率为f0。
- 根据权利要求7至9任一所述的光通信节点,其特征在于,所述DSP芯片中还包括信道参数估计单元和信道参数预补偿单元;所述信道参数估计单元与所述模数转换器相连,用于根据所述下行光信号进行信道参数估计,并输出信道参数估计结果,所述信道参数估计结果包括色散估计或光纤动态延时估计中的至少一种;所述信道参数预补偿单元分别与所述信道参数估计单元和所述基带信号生成单元相连,用于根据所述信道参数估计结果对所述上行基带信号进行信道参数预补偿。
- 一种光通信***,其特征在于,所述光通信***包括:中心节点和n个用户节点,所述n个用户节点通过光耦合器与所述中心节点相连,n≥2,n为整数;所述中心节点用于向所述n个用户节点发送下行光信号,所述n个用户节点用于向所述中心节点发送上行光信号;各个用户节点包括如权利要求6至10任一所述的光通信节点。
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