CN102891824B - Based on the noise diffusion suppressing method of radio frequency pilot tone in high-speed light DFT-S OFDM modulation system - Google Patents
Based on the noise diffusion suppressing method of radio frequency pilot tone in high-speed light DFT-S OFDM modulation system Download PDFInfo
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Abstract
The invention belongs to optical fiber communication and optical-fiber network transmission technique field, specially a kind of high-speed light DFT-S? based on the noise diffusion suppressing method of radio frequency pilot tone in OFDM modulation system.Is the method mainly at DFT-S? radio frequency weight of pilot frequency is added in ofdm modulation signal, the approximate characteristic of the distortion in transmission link according to this component and modulation signal, utilize this radio frequency pilot tone to carry out signal equalization, realize nonlinear compensation and phase noise compensation simultaneously.Can the present invention reduce DFT-S? nonlinear distortion and phase noise in ofdm system, thus realize due to DFT-S? the noise diffusion that in OFDM demodulation, inverse Fourier transform causes, raising system, to the resistivity of nonlinear distortion and phase noise, improves transmission performance.
Description
Technical field
The invention belongs to optical fiber communication and optical-fiber network transmission technique field, be specifically related to the noise diffusion suppressing method based on radio frequency pilot tone in a kind of high-speed light DFT-SOFDM modulating system.
Background technology
Optical fiber transmission network is the brace foundation of whole information network.The frequency of light wave of optical fiber communication is 193THz, and its relative bandwidth of 5% is 10THz, thus for high-speed communication provides very large bandwidth resources.The data network service such as the high-speed Internet access day by day increased now, mobile time-frequency voice call, multi-media broadcasting system and application are had higher requirement to the bandwidth of communication system, need optical communication system can support Tb/s and even higher transmission capacity in the transmission range of thousands of miles.According to the prediction of Duo Jia scientific research institution, Future Ten year, backbone traffic was by growth by 100 times, and single channel rate will from 10G to 300G.China's backbone bandwidth in 2009 is 12.7Tbit/s, estimate will reach 110-188Tbit/s in 2014, explore the transmission capacity limits of optical fiber, improve optical communication network bandwidth efficiency, reduce the key point that chromatic dispersion in fiber channel, polarization mode dispersion and nonlinear transport damage are development high-capacity and high-speed optical communication systems.
Realize a technology for high spectrum efficiency optical communication, OFDM (OFDM) technology, causes the extensive concern of people just gradually.This technology has following three advantages: one, because it can effectively solve because the intersymbol interference (ISI) that in optical communication, dispersion causes.Especially, when transmitting quantity and improving, this point becomes more and more important.Because traditional data transmission format is as amplitude modulation(PAM) (OOK) or phase shift keying modulation (BPSK), the code element transmitted in multiple time slot is depended at the signal transmitted sometime, thus can bring very large distorted signals, thus make dispersion compensation need very large cost.But for ofdm system, in the protection prefix that transmitter terminal adds, effectively can resist the intersymbol interference in transmission process, thus improve system to the resistance of dispersion; Its two, order of modulation can be increased flexibly at transmitter, improve further the spectrum efficiency of transmission system, owing to needing at transmitter terminal to carry out digital-to-analogue conversion, in digitally coded process, be easy to realize high order modulation, and the increase of the complexity of system can not be brought; They are three years old, digital signal processing algorithm flexibly can be added, because its transmitting terminal and receiving terminal all need to carry out modulus digital to analog conversion, in these conversion, preequalization and post-equalization algorithm can be increased in the mode of little cost or cost free, the error code of correcting system, thus the performance improving system.Therefore light OFDM modulation is considered to the modulation system of a kind of great potential in Large Copacity height spectrum efficiency optical communication system.
The maximum shortcoming that light ofdm modulation signal exists is that it has larger PAR peak to average ratio, due to the non-linear effects of electrical domain amplifier response limits and fiber channel, light ofdm modulation signal can be subject to larger nonlinear distortion, and the compensating equalization method cost of general nonlinearity distortion is comparatively large, thus transmission performance is subject to certain impact.Thus have already been proposed a lot of scheme to reduce this peak to average, as time domain shearing method, u leads companding method, compound coding etc.Discrete fourier spread spectrum methods, because its effective peak to average reduces performance, arouses attention, and in wireless communications as the up coding standard of next generation mobile communication LTE.
Be illustrated in figure 1 the implementation procedure of DFT-SOFDM modulation.Whole smooth OFDM frequency band is divided into multiple sub-band, first carries out discrete Fourier transform to each sub-band respectively, carries out an inverse Fourier transform, produce time-domain signal after then being arranged by these sub-bands.After this signal is transmitted by light modulation, opto-electronic conversion is carried out at receiver end, in electric demodulating process, first utilize discrete Fourier transform that time-domain signal is transformed to frequency domain, according to the frequency band dividing method of transmitting terminal, receiving terminal frequency band is split again, then inverse Fourier's change is done respectively to individual sub-band and recover transmission data.
Find after deliberation, although DFT-SOFDM modulation scheme can reduce the PAR peak to average ratio of signal to a great extent, but certain complexity cost can be introduced, the more important thing is at receiver end in order to restoring signal, need to carry out once extra inverse Fourier transform.Because Received signal strength is subject to nonlinear distortion in transmitting procedure, laser linewidth, the impact of spontaneous emission noise, can cause certain frequency departure and phase noise.The introducing of extra inverse Fourier transform, due to the characteristic of itself, can reduce signal to noise ratio, and by the noise diffusion of certain subcarrier in whole sub-band, causes the decline of systematic function.
Be illustrated in figure 2 the signal recuperation flow chart of traditional light DFT-OFDM system.The signal received through a digital band-pass filter to reduce out-of-band noise, then Cyclic Prefix is removed, through being fourier transformed into frequency domain, after utilizing check code metasequence to carry out channel estimating, carry out sub-band segmentation, and then carry out phase estimation based on the pilot tone inserted, the data of modulating are obtained finally by decoding.
Finding after deliberation, at least there is following shortcoming in above-mentioned technology:
Although utilize channel estimating and phase estimation can restoring signal to a certain extent, improve transmission performance, but do not consider the distinctive noise diffusion characteristic of DFT-SOFDM system, and the recovery of phase distortion carries out after inverse Fourier transform, do not reduce the noise of the front each subcarrier of conversion.Simultaneously due to the existence of noise diffusion, destroy the continuity of closing on phase noise, no longer applicable based on the phase noise method of estimation inserting pilot tone.In addition, in whole recovery algorithms, do not consider the impact of channel non-linearity distortion, and according to the character of aforementioned OFDM, it is subject to nonlinear interference and can not ignore.
Summary of the invention
The object of the present invention is to provide carry a kind of can make high speed DFT-SOFDM system transfers performance good, to the noise diffusion suppressing method in phase noise and the strong high-speed light DFT-SOFDM modulating system of nonlinear effect resistivity.
Based on the noise diffusion suppressing method of radio frequency pilot tone in the high-speed light DFT-SOFDM modulating system that the present invention proposes, as shown in Figure 3.Signal coding modulating part and signal equalization algorithm is mainly comprised: at transmitter terminal based on the light DFT-SOFDM systems radiate of radio frequency pilot tone and the digital signal modulated of reception and demodulating algorithm flow process, first DFT-SOFDM Signal coding is carried out, then carry out serial to parallel conversion and piecemeal is carried out to signal, sub-band division is carried out to each ofdm signal band and carries out sub-band Fourier transform respectively, again each sub-band is merged into a frequency band and carries out inverse Fourier transform, realize the modulation of DFTS-OFDM signal, after adding Cyclic Prefix, insert radio frequency pilot tone, then the signal of mixing is input in optical fiber link after light modulation transmission, at receiving terminal, after digital band-pass filter selects corresponding signal band, first radio frequency weight of pilot frequency is extracted, this radio frequency pilot tone and signal is utilized to carry out mixing, realize nonlinear distortion compensation and phase noise compensation in DFT-SOFDM system, reach the object of noise suppressed, and then remove Cyclic Prefix and carry out Fourier transform, channel estimating is carried out after converting the signal into frequency domain, in order to realize signal receiving, also need to carry out sub-band inverse Fourier transform, finally carry out parallel serial conversion and decoding, realize the recovery of modulation signal.
Here, DFT-SOFDM is discrete fourier spread-spectrum orthogonal frequency division multiplexing system.
In the present invention, described noise is mainly caused by inverse Fourier transform extra in DFT-SOFDM system.The noise of signal single sub-carrier recovered can be subject to inverse Fourier transform before the impact of each subcarrier noise in this subcarrier place sub-band, therefore the noise of certain subcarrier can be diffused in whole sub-band by inverse Fourier transform, change the distribution of noise, reduce the performance of system.This noise diffusion characteristic is introduced by inverse Fourier transform extra in recovery algorithms, is present in the DFT-SOFDM system of direct detection and coherent reception simultaneously.
In the present invention, described radio frequency pilot tone adds can be determined according to the noise profile actual conditions of ofdm signal band.After transmitter terminal DFT-SOFDM Signal coding adds Cyclic Prefix, add radio frequency pilot tone, both low frequency sub-band can have been utilized as radio frequency pilot tone band, because low frequency sub-band has larger system noise relative to high-frequency sub-band in some systems, also high-frequency sub-band can be utilized as radio frequency pilot tone band, because each bandwidth of a device response limits of system can be subject in some systems, the decline of filter response HFS is larger, the distortion introduced is serious, to reach best laser propagation effect, and for traditional list carrier pilot scheme, the utilance of system for whole frequency band subcarrier can not be reduced.The method inserting radio frequency pilot tone both can be adopt digitally coded scheme to transmit together with modulation signal, also can be a coupling external radio frequency source after modulation signal produces.Then the signal of mixing is input in optical fiber link after light modulation transmission.
In the present invention, the described radio frequency pilot tone that utilizes carries out signal equalization, follow following steps: at receiving terminal, after digital band-pass filter selects corresponding signal band, first utilize digital band-pass filter radio frequency pilot signal to be extracted, then transform to base band, due to this radio frequency and modulation signal distortion identical in transmission link, thus the DFT-SOFDM signal of modulation is multiplied with the conjugate of radiofrequency signal in time domain, realizes the equilibrium of phase noise and nonlinear distortion.
To sum up, first the present invention mainly carries out DFT-SOFDM signal madulation at transmitter terminal, but need a reserved sub-band for insertion radio frequency pilot signal, after adding Cyclic Prefix, add radio frequency pilot tone, the position of pilot tone can be determined according to the noise profile actual conditions of ofdm signal band, as noise is large, the frequency band of frequency response difference is set to radio frequency pilot tone band, and the place responded is as signal band, to reach best laser propagation effect.The method inserting pilot tone both can be adopt digitally coded scheme to transmit together with modulation signal, also can be a coupling external radio frequency source after modulation signal produces.Then the signal of mixing is input in optical fiber link after light modulation transmission.At receiving terminal, after digital band-pass filter selects corresponding signal band, first radio frequency weight of pilot frequency is extracted, due to weight of pilot frequency and modulation signal process is identical channel, be subject to identical phase noise and nonlinear distortion, the approximate characteristic of the distortion in transmission link according to this component and modulation signal, utilize this radio frequency pilot tone to carry out signal equalization, and then carry out channel estimating and decoding, thus realize nonlinear distortion compensation and phase noise compensation in DFT-SOFDM system simultaneously.
The main distinction of modulator approach of the present invention and prior art is, the method of radio frequency pilot tone is adopted to carry out equilibrium to DFT-SOFDM signal, the estimation of phase noise to be put in demodulation flow process before inverse Fourier transform, improve the accuracy that phase noise is estimated, and compensate for nonlinear distortion to a certain extent, thus inhibit noise diffusion, the performance of the system of raising.
As seen from the above technical solution provided by the invention, the present invention utilizes rational radio frequency pilot interposition method and signal equalization algorithm, has following superiority:
1) utilize radio frequency pilot schemes, while estimation phase noise, can compensate nonlinear distortion in optical communication system, improve the resistance of DFT-SOFDM system to nonlinear distortion.
2) radio frequency pilot schemes is utilized, the estimation of phase noise to be put in demodulation flow process before inverse Fourier transform, improve the accuracy that phase noise is estimated, and due to can nonlinear distortion be compensate for, thus each subcarrier noise before reducing inverse Fourier transform, inhibit noise diffusion, the performance of the system of raising.
3) by radio frequency pilot tone frequency band configuration scheme, the sub-band of frequency response difference in DFT-SOFDM system can effectively be avoided, to reach best laser propagation effect.
4) this programme just changes the using method of pilot tone in DFT-SOFDM signal madulation, is concentrated by the pilot frequency carrier wave disperseed and uses, can not reduce the carrier wave utilance of whole frequency band in traditional scheme.
The present invention is applicable to the Signal coding modulation of Large Copacity long distance high speed optical fiber communication and optical-fiber network transmission and digital signal is recovered and demodulation field, can be used for the resistance for channel distortion improving transmission system, raising transmission performance.
Accompanying drawing explanation
Fig. 1 discrete fourier spread-spectrum orthogonal frequency division multiplexing (DFT-SOFDM) signal madulation and demodulation flow chart.
The light DFT-SOFDM system receiver terminal number word signal recuperation algorithm flow chart that Fig. 2 is traditional.
Fig. 3 is based on the light DFT-SOFDM systems radiate of radio frequency pilot tone and the digital signal modulated of reception and demodulating algorithm flow chart.
Amplitude and phase noise diffusion schematic diagram in Fig. 4 DFT-SOFDM inverse Fourier transform process.
The constellation point scatter diagram that Fig. 5 single distortion subcarrier causes in different noise amplitude, (a) 0.25A, (b) 0.33A, (c) 0.5A, the constellation point scatter diagram that (d) two distortion subcarriers cause.(A represents specific distortion amplitudes).
Fig. 6 suppresses the system schematic of noise diffusion scheme in DFT-SOFDM system based on radio frequency pilot frequency system
Fig. 7 is based on the 200Gb/s multiband 16QAMDFT-SOFDM transmission system of two kinds of compensation schemes.
Under Figure 8 shows that different DFT-SOFDM grouping situation, the present invention and prior art are for the resistance figure of system laser live width.
The BER performance of two kinds of different schemes and the relation of launched power is used shown in Fig. 9.
Figure 10 shows that under optimized launched power-1dBm, the BER performance of whole 7 signal bands of transmission 7x80km.
Figure 11 shows that best in two schemes and the poorest BER of signal band and the relation of transmission range.
Number in the figure: 1-low pass filter, 2-low pass filter, 3-digital to analog converter, 4-digital to analog converter, 5-optical band pass filter, 6-light I/Q modulator, 7-cycle controller, 8-erbium-doped fiber amplifier, 9-standard single-mode fiber, 10-local oscillator light source, 11-coherent receiver.
Embodiment
The method suppressing noise diffusion in DFT-SOFDM system based on radio frequency pilot frequency system will proposed according to the present invention below, complete description noise diffusion mechanism and equalization algorithm implementation process.Simultaneously in order to embody the effect of this programme, compare with traditional equalization scheme.
In the light DFT-SOFDM system that the present invention proposes, the mechanism of noise diffusion is described below.
The DFT-SOFDM signal received at receiver place can be expressed as follows:
(1)
Here
,
angular frequency and the phase place of laser in transmitter respectively,
represent time-domain baseband DFT-SOFDM signal,
the impulse response of fiber channel,
represent the noise in transmission link, "
" be convolution symbol.
After opto-electronic conversion, suppose that the linear distortion in DFT-SOFDM system can be balanced, receiver end is by after discrete Fourier transform, and the signal received can be expressed as:
(2)
If the transfer function of channel can be recovered completely by the check code metasequence inserted, DFT-SOFDM signal can be expressed as at frequency domain:
(3)
Here,
,
be illustrated respectively in the signal of a kth sub-carrier transmissions and the signal of distortion in certain DFT-SOFDM code element,
represent the noise in the code element that this is identical on a kth subcarrier, k=1,2 ... L
k.
In order to recover the signal modulated, for DFT-SOFDM system, need that extra inverse Fourier transform is carried out once to each sub-band as follows:
(4)
Here i=1,2 ... L
i, L
irepresent a DFT-SOFDM sub-band number of sub carrier wave.As can be seen from the above equation, the signal finally recovered disturb by the noise item, this noise item is caused by the noise of load code element and the inaccuracy of channel estimating.
This noise is thought to be expressed as:
(5)
The noise of the signal single sub-carrier recovered as can be seen from the above equation can be subject to inverse Fourier transform before the impact of each subcarrier noise in this subcarrier place sub-band, therefore the noise of certain subcarrier can be diffused in whole sub-band by inverse Fourier transform, change the distribution of noise, reduce the performance of system.Fig. 4 is the schematic diagram of this diffusion process.Suppose to only have a sub-carrier distortion, other subcarriers are by correct recovery, and noise diffusion is on the impact of signal constellation (in digital modulation) figure, and the amplitude of diffusion is the amplitude of noise item, and the phase place of diffusion is by the phase place of noise item and coefficient i joint effect.According to conservation of energy principle, the noise item before conversion is equal with the noise item energy after conversion.Used herein is 16QAM(quadrature amplitude modulation) coding.If the subcarrier noise of this distortion is little, then the distortion that causes of noise diffusion is not serious, and signal constellation point can distinguish, as shown in Fig. 5 (a) He (b).If but this sub-carrier distortion is serious, whole sub-band all can be subject to the impact of this subcarrier, signal constellation point is difficult to differentiate, as shown in Fig. 5 (c).Fig. 5 (d) is depicted as the situation of two or more sub-carrier distortion, and the constellation point after diffusion is actually the superposition of multiple circle in Fig. 5 (a).
Therefore, inverse Fourier transform extra DFT-SOFDM system by the noise diffusion of single sub-carrier in whole sub-band, can be changed to the noise profile of system, make system more responsive for Optical Signal To Noise Ratio, reduce the transmission performance of system.It should be noted that this noise diffusion characteristic is introduced by inverse Fourier transform extra in recovery algorithms, be present in the DFT-SOFDM system of direct detection and coherent reception simultaneously.
What the present invention proposed suppresses the scheme of noise diffusion in DFT-SOFDM system to be described below based on radio frequency pilot frequency system.
Its structure as shown in Figure 6 (a), at transmitter terminal, first DFT-SOFDM signal madulation is carried out, a reserved sub-band is for insertion radio frequency pilot signal, after adding Cyclic Prefix, add radio frequency pilot tone, the position of pilot tone can be determined (see Fig. 6 (b)) according to the noise profile actual conditions of ofdm signal band, low frequency sub-band can be utilized as radio frequency pilot tone band, because low frequency sub-band has larger system noise relative to high-frequency sub-band in some systems, also high-frequency sub-band can be utilized as radio frequency pilot tone band, because each bandwidth of a device response limits of system can be subject in some systems, the decline of filter response HFS is larger, the distortion introduced is serious.Arrange to reach best laser propagation effect so flexibly, and for traditional list carrier pilot scheme, the utilance of system for whole frequency band subcarrier can not be reduced.The method inserting radio frequency pilot tone both can be adopt digitally coded scheme to transmit together with modulation signal, also can be a coupling external radio frequency source after modulation signal produces.Then the signal of mixing is input in optical fiber link after light modulation transmission.
At receiving terminal, after digital band-pass filter selects corresponding signal band, first radio frequency weight of pilot frequency is extracted, due to weight of pilot frequency and modulation signal process is identical channel, be subject to identical phase noise and nonlinear distortion, the approximate characteristic of the distortion in transmission link according to this component and modulation signal, utilize this radio frequency pilot tone to carry out signal equalization, idiographic flow is as shown in Fig. 6 (c).First digital band-pass filter is utilized radio frequency pilot signal to be extracted, then base band is transformed to, due to this radio frequency and modulation signal distortion identical in transmission link, thus the DFT-SOFDM signal of modulation is multiplied with the conjugate of radiofrequency signal in time domain, namely the phase noise deducted in signal transmission is equivalent to, this phase noise comes to two aspects, i.e. the phase shift variations of laser linewidth and non-linear introducing.
Finally carry out channel estimating and decoding again, thus realize nonlinear distortion compensation and phase noise compensation in DFT-SOFDM system simultaneously, reach the object of restraint speckle diffusion.
Below for 200Gb/s multi-band DFT-SOFDM transmission system as shown in Figure 7, the equalization performance of the present invention and existing list carrier pilot technology is compared.
Figure 8 shows that the present invention and the prior art resistance figure for system laser live width, and compare the different grouping situation of DFT-SOFDM signal.Can find out that the DFT-SOFDM signal with 4 groupings has better resistance to laser linewidth.In addition, when laser linewidth is lower than 100kHz, these two kinds of compensation schemes have similar performance, this is because when laser linewidth is lower, the noise diffusion caused because of inverse Fourier transform is very little, and when laser linewidth is more than 100kHz, the compensation scheme based on radio frequency pilot tone has better characteristic, because it can suppress the noise diffusion in demodulating process.
The BER performance of two kinds of different schemes and the relation of launched power is used shown in Fig. 9.Transmission link length setting is 7x80km.Can find, scheme based on radio frequency pilot tone has obvious advantage, this is because the scheme of SCPC pilot frequency does not have the ability of balanced nonlinear distortion, and the scheme that the present invention proposes, the phase deviation that can produce because of Self-phase modulation and Cross-phase Modulation in compensated fiber.
Figure 10 shows that under optimized launched power-1dBm, calculate the BER performance of whole 7 signal bands, transmission range is 7x80km.We have studied the scheme based on radio frequency pilot tone of different grouping and different sub-band position, find that the BER of the various scheme based on radio frequency pilot tone is all at 3.8x10
-3(the FEC threshold value of 7%) below, and has the BER of 6 signal bands to exceed this boundary based on the scheme of list carrier pilot.In addition, in 4 grouping situations, low frequency part inserts radio frequency pilot tone, has optimum systematic function.
Figure 11 shows that best in two schemes and the poorest BER of signal band and the relation of transmission range.Optimum launched power is set as-1dBm.The compensation scheme that can find based on radio frequency pilot tone can support the Optical Fiber Transmission of 14x80km, and can only transmit 840km based on its best signal transmission band of scheme of list carrier pilot.
Claims (3)
1. one kind based on noise diffusion suppressing method in the high-speed light DFT-SOFDM modulating system of radio frequency pilot tone, it is characterized in that comprising: Signal coding modulating part and signal equalization algorithm part, at transmitter terminal, first DFT-SOFDM signal madulation is carried out, after adding Cyclic Prefix, insert radio frequency pilot tone, then the signal of mixing is input in optical fiber link after light modulation transmission; At receiving terminal, after digital band-pass filter selects corresponding signal band, first radio frequency weight of pilot frequency is extracted, this radio frequency pilot tone is utilized to carry out signal equalization, and then carry out channel estimating and decoding, thus realize nonlinear distortion compensation and phase noise compensation in DFT-SOFDM system simultaneously, reach the object of noise suppressed; Wherein, described DFT-SOFDM is discrete fourier spread-spectrum orthogonal frequency division multiplexing system; Described utilize this radio frequency pilot tone to carry out signal equalization to follow following steps: at receiving terminal, after digital band-pass filter selects corresponding signal band, first digital band-pass filter is utilized radio frequency pilot signal to be extracted, then base band is transformed to, due to this radio frequency and modulation signal distortion identical in transmission link, thus the DFT-SOFDM signal of modulation is multiplied with the conjugate of radiofrequency signal in time domain, realizes the equilibrium of phase noise and nonlinear distortion.
2. the method for claim 1, is characterized in that described noise diffusion is mainly caused by inverse Fourier transform extra in DFT-SOFDM system; The noise of signal single sub-carrier recovered be subject to inverse Fourier transform before the impact of each subcarrier noise in this subcarrier place sub-band, therefore the noise of certain subcarrier is diffused in whole sub-band by inverse Fourier transform, change the distribution of noise, reduce the performance of system; This noise diffusion characteristic is introduced by inverse Fourier transform extra in recovery algorithms, is present in the DFT-SOFDM system of direct detection and coherent reception simultaneously.
3. the method for claim 1, it is characterized in that described radio frequency pilots insertion, determine according to the noise profile actual conditions of ofdm signal band: after transmitter terminal DFT-SOFDM Signal coding adds Cyclic Prefix, add radio frequency pilot tone, utilize low frequency sub-band as radio frequency pilot tone band, or utilize high-frequency sub-band as radio frequency pilot tone band; The method inserting radio frequency pilot tone adopts digitally coded scheme to transmit together with modulation signal, or the external radio frequency source that is coupled after modulation signal produces, and is then input in optical fiber link after light modulation transmission by the signal of mixing.
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| CN107888530B (en) * | 2016-09-30 | 2021-01-22 | 电信科学技术研究院 | Transmission method, transmitting device and receiving device of phase noise compensation reference signal |
| US10574351B2 (en) * | 2017-10-23 | 2020-02-25 | Huawei Technologies Co., Ltd. | Monitoring performance of optical network equipment using pilot tones |
| CN109962872A (en) * | 2017-12-14 | 2019-07-02 | 中国舰船研究设计中心 | Based on the phase noise inhibition method of iterative algorithm in DFT-S ofdm system |
| CN108400860A (en) * | 2018-05-09 | 2018-08-14 | 浙江赛威通信技术有限公司 | Distributed channel system and method |
| CN109039467A (en) * | 2018-06-26 | 2018-12-18 | 天津师范大学 | The permanent envelope light ofdm signal modulation demodulation system of standard and its modulation-demo-demodulation method based on I/Q modulator |
| CN110808750B (en) * | 2019-11-08 | 2021-03-26 | 电子科技大学 | Method and device for suppressing adjacent channel interference based on inverse filtering |
| CN112822137B (en) * | 2019-11-15 | 2024-06-11 | 华为技术有限公司 | Signal transmission method and device |
| CN111082873B (en) * | 2019-12-17 | 2022-02-11 | 北京邮电大学 | Ultra-long-distance optical fiber high-precision radio frequency signal transmission system and method |
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