CN116318427A - Low-power-consumption and originating damage tolerant Digital Signal Processor (DSP) system - Google Patents

Low-power-consumption and originating damage tolerant Digital Signal Processor (DSP) system Download PDF

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CN116318427A
CN116318427A CN202310228423.8A CN202310228423A CN116318427A CN 116318427 A CN116318427 A CN 116318427A CN 202310228423 A CN202310228423 A CN 202310228423A CN 116318427 A CN116318427 A CN 116318427A
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杨彦甫
范林生
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Shenzhen Graduate School Harbin Institute of Technology
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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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/614—Coherent receivers comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers
    • 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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/616—Details of the electronic signal processing in coherent optical receivers
    • H04B10/6162—Compensation of polarization related effects, e.g., PMD, PDL
    • 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
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/616—Details of the electronic signal processing in coherent optical receivers
    • H04B10/6165—Estimation of the phase of the received optical signal, phase error estimation or phase error correction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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Abstract

The invention provides a low-power consumption and originating damage tolerant Digital Signal Processor (DSP) system, which comprises a transmitting end and a receiving end, wherein the transmitting end comprises a transmitting end DSP module, a digital-to-analog conversion module and a dual-polarization optical IQ modulator, and the receiving end comprises a dual-polarization coherent optical receiver, an analog-to-digital conversion module and a digital signal processing module which are sequentially connected. The beneficial effects of the invention are as follows: the invention has the characteristics of low power consumption, tolerance of IQ damage at the originating end and low complexity, and can quickly track polarization.

Description

Low-power-consumption and originating damage tolerant Digital Signal Processor (DSP) system
Technical Field
The invention relates to the field of optical communication, in particular to a low-power-consumption and originating damage tolerant DSP system.
Background
With the advent of various emerging technologies such as edge computing, internet of things, mesh audio, 5/6G, etc., the rate of increase of IP data traffic for metropolitan area networks and access networks exceeds that of backbone networks. The direct alignment (IM-DD) and Time Division Multiplexing (TDM) technologies commonly used in metropolitan area networks and access networks do not meet the increasing traffic demands, which makes coherent reception schemes sink towards metropolitan area networks and access networks. Star topology is commonly used in metropolitan area networks and access networks to implement point-to-multipoint (P2 MP) network architecture, thereby simplifying network design and maintenance. In this context, the recently proposed coherent optical communication scheme based on digital subcarrier multiplexing (DSCM) can increase transmission capacity while implementing a flexible P2PM structure, which well matches the evolution direction of the requirements of the metropolitan area network and the access network. However, the characteristics of high complexity and high power consumption of the traditional coherent DSP algorithm make the traditional coherent DSP algorithm not directly applicable to a DSCM coherent system. Aiming at a demand background, a new optical communication technology research which combines transmission capacity and power consumption is necessary to be developed to meet the industrial development demand.
In DSCM systems, to compensate for channel impairments, each subcarrier signal is typically treated as a single carrier signal after subcarrier demultiplexing, and the subcarriers are individually processed using conventional DSP algorithms, including equalization, frequency offset estimation, and carrier phase recovery. However, since each subcarrier is similarly processed, this brings about serious computational redundancy, and increases DSP power consumption. Before we have proposed a scheme (Yang Yanfu, fan Linsheng) that utilizes frequency domain FPT, a low complexity polarization rotation and carrier phase co-recovery method [ P ]. Guangdong province: CN114915350a,2022-08-16 ], the co-recovery of frequency offset, polarization aliasing and carrier phase for all subcarriers is achieved before subcarrier demultiplexing, greatly reducing the computational complexity of DSP.
However, DSCM systems are significantly more sensitive to imperfections in the transceiver-side opto-electronic devices than Single Carrier (SC) systems. The non-ideal nature of these opto-electronic devices introduces in-phase quadrature component (IQ) impairments, mainly including IQ amplitude and phase imbalance and IQ delay. These IQ impairments are particularly severe in DSCM systems, which can cause each subcarrier to generate a conjugate symmetric component, thereby interfering with the frequency symmetric subcarriers. For damage of a receiving end device, compensation is only needed immediately after analog-to-digital conversion (ADC); but for originating impairments compensation can only be done after polarization demultiplexing and carrier recovery. However, the IQ impairments can severely affect the demultiplexing and carrier phase recovery of DSCM signals, degrading system performance. Aiming at the problem of IQ damage of an originating terminal, one feasible scheme is to use an 8 multiplied by 8 real-valued butterfly equalizer or a 4 multiplied by 4 complex wide linear butterfly equalizer to balance four subcarrier signals of two polarized symmetrical subcarriers simultaneously, so as to realize polarization demultiplexing and compensate the IQ damage of the originating terminal. However, this scheme has little tolerance to phase noise, slow polarization tracking rate, and very high complexity, and the computational complexity of these two equalizers is not acceptable for power and energy sensitive application scenarios. In view of the foregoing, it is desirable to find DSP techniques that are suitable for DSCM signals with low complexity and high tolerance to originating impairments.
Disclosure of Invention
The invention provides a low-power consumption and originating damage tolerant DSP system, which is characterized by comprising a transmitting end and a receiving end, wherein the transmitting end comprises a transmitting end DSP module, a digital-to-analog conversion module and a dual-polarization optical IQ modulator, the transmitting end DSP module generates loaded mutually independent random bit sequences of all subcarriers, the loaded mutually independent random bit sequences are respectively mapped into signals with required modulation formats, a root raised cosine filter is used for respectively shaping the signals, the shaped signals are multiplexed by the subcarriers to obtain SCM signals, a protection bandwidth is reserved between adjacent subcarriers of the SCM signals, 1 FPT is respectively inserted into the protection bandwidth of the two polarization signals, the FPT represents pilot signals of a frequency domain, and the frequencies of the FPT of the two polarizations are different and asymmetric; then converting the signal into an analog signal through a digital-to-analog conversion module, driving a dual-polarization optical IQ modulator, and loading the modulated signal into a standard single-mode fiber to be transmitted to a receiving end;
the receiving end comprises a dual-polarization coherent optical receiver, an analog-to-digital converter and a digital signal processing module which are sequentially connected, wherein the dual-polarization coherent optical receiver is used for receiving signal light and local oscillator light, the received signal is converted into a digital signal by the analog-to-digital converter, and the obtained electrical signal is processed by the digital signal processing module.
As a further improvement of the present invention, mapping to the desired modulation format signal includes, but is not limited to, QPSK, 16QAM, 64QAM.
As a further development of the invention, in the transmitting-end DSP module, each polarized signal is composed of an even number of carriers.
As a further improvement of the invention, a guard bandwidth is reserved between adjacent subcarriers of the SCM signal, and the guard bandwidth needs to ensure that adjacent subcarrier spectrums do not overlap. 5. The DSP system of claim 1 wherein the digital signal processing module first compensates for IQ delays and imbalances of the receiver devices, then estimates frequency offset by calculating the offset between the FPT frequencies of the frequency emissions of the two FPTs, then downconverts the two FPTs to 0 frequency, extracts the amplitude and phase of the FPTs by a low pass filter, and obtains an estimated signal polarization rotation and phase noise matrix; compensating for frequency offset, polarization and carrier phase noise simultaneously by combining the estimated matrix with the frequency offset;
after compensating frequency deviation, phase noise and polarization rotation, carrying out subcarrier demultiplexing on the signals, respectively equalizing the signals with two polarization states, and simultaneously equalizing the two symmetrical subcarriers by adopting an equalizer to compensate the originating damage, and respectively equalizing the signals with two polarization states; finally, the bit error rate is calculated.
As a further improvement of the invention, in the digital signal processing module, the FPT is extracted by the low pass filter according to the following formula,
Figure BDA0004119335400000031
Figure BDA0004119335400000032
wherein H {. Cndot. } denotes the low-pass filter operation, wherein R x/y (t) represents the received X/Y polarized signal, ω 1 And omega 2 Angular frequencies, Δω and Y polarization FPT, respectively
Figure BDA0004119335400000033
Respectively representing frequency offset between the laser of the transmitting end and local oscillation light, carrier phase noise and additive Gaussian white noise, < ->
Figure BDA0004119335400000034
And->
Figure BDA0004119335400000035
The FPTs extracted by the low pass filters, respectively.
As a further development of the invention, the low-pass filter is implemented using a sliding window averaging.
As a further improvement of the invention, in the digital signal processing module, the equalizer is a complex MIMO of 2×2 or a real MIMO of 4*4.
As a further improvement of the invention, in the digital signal processing module, the tap coefficients of the filter are updated according to a decision-directed minimum mean algorithm, so that residual phase noise can be compensated.
The beneficial effects of the invention are as follows: the invention has the characteristics of low power consumption, tolerance of IQ damage at the originating end and low complexity, and can quickly track polarization.
Drawings
FIG. 1 is a spectrum of a transmitted signal, wherein (a) is an X-polarized signal spectrum and (b) is a Y-polarized signal spectrum;
FIG. 2 is a power spectrum of signals under different impairments, wherein (a) there is no impairment; (b) IQ delay 20ps; (c) amplitude imbalance: 3dB, phase imbalance: 20 °; (d) IQ delay 20ps, amplitude imbalance: 3dB, phase imbalance: 20 °;
fig. 3 is a 2 x 2 complex MIMO;
FIG. 4 is a system schematic of the present invention;
FIG. 5 is a process flow diagram of a digital signal processing module;
fig. 6 is a block diagram of an algorithm for frequency offset, polarization and carrier phase noise recovery.
Detailed Description
The invention discloses a low-power-consumption and originating-end damage tolerant DSP system, which is a DSCM coherent system-oriented DSP scheme with low power consumption, originating-end IQ damage tolerance and fast polarization tracking capability.
System model and principle:
fig. 1 (a) and (b) show a spectrum diagram of a transmission signal according to one embodiment of the present invention, in which a guard bandwidth is provided between each subcarrier in an SCM signal. In both polarization directions, a pilot signal (FPT) in the frequency domain is inserted in the guard bandwidth. To avoid crosstalk of the FPTs caused by originating impairments, the frequencies of the two FPTs cannot be symmetrical to each other. The transmit signal may be expressed as:
Figure BDA0004119335400000041
wherein E is x/y (t),S x/y (t) represents the X/Y polarized transmit signal and the SCM signal, respectively, A, ω represents the amplitude and angular frequency of the FPT, respectively. The power of the added FPT depends on the pilot signal power ratio (PSR), defined as PSR (dB) =10log 10 (P pilot /P signal ). Under the influence of the originating IQ impairment effect, the output signal of Tx can be expressed as:
Figure BDA0004119335400000042
wherein k is ij And K ij (i ε {1,2}, j ε {1,2 }) is the transfer function of IQ impairments. It can be seen that under the influence of IQ impairment effects, new conjugate components are generated.
Neglecting polarization mode dispersion and polarization dependent loss, the received signal can be expressed as:
Figure BDA0004119335400000043
wherein R is x/y (t),J(t),Δω,
Figure BDA0004119335400000044
Respectively representing the received X/Y polarized signals, a time-varying Jones matrix caused by random birefringence in the optical fiber, frequency offset between the laser of a transmitting end and local oscillation light, carrier phase noise and additive Gaussian white noise. The frequency offset Δω is estimated by comparing the frequency difference of the receive signal FPT and the transmit signal FPT. After estimating the frequency offset, the frequency of the FPT is shifted to zero frequency, and the FPT is extracted by using a low-pass filter, so that a matrix M can be obtained as follows:
Figure BDA0004119335400000051
Figure BDA0004119335400000052
Figure BDA0004119335400000053
considering frequency offset, the inverse matrix of the signal compensation can be obtained as: t (T) =conj { W T }e -jΔωt
Where H { · } represents the low pass filter operation, conj { · } represents the conjugate operation, { · } T Representing the transpose of the matrix.
To further reduce the computational complexity, the low pass filter may be implemented by means of block averaging. Wherein the constant AK 1x (ω 1 ) And AK (alkyl ketene dimer) 1y (ω 2 ) Elimination by normalization: i J xx | 2 +|J yx | 2 =1 and |j xy | 2 +|J yy | 2 ＝1。
Through the process, even if the originating damage and the phase noise exist, the estimation and compensation of frequency offset, phase noise and polarization rotation can be realized at the same time, the calculation complexity of the coherent DSP is greatly reduced, and the robustness of the algorithm to the originating damage is ensured.
After compensating frequency offset, phase noise and polarization rotation, the signals are demultiplexed by subcarriers, then the signals with two polarizations are respectively balanced, and two symmetrical subcarriers are simultaneously balanced by adopting 2 x 2 complex MIMO to compensate the originating damage. The structure of the equalizer is shown in fig. 3. Wherein E is Ain And E is Bin Are subcarriers with two frequencies symmetrical to each other.
Specific examples:
the DSP system is suitable for the digital subcarrier multiplexing situation and can be used for a point-to-multipoint (PTMP) scene in an aggregation convergence network.
As shown in fig. 4, the transmitting DSP module generates the loaded mutually independent random bit sequences of each subcarrier, which are mapped to the required modulation format signals, such as QPSK, 16QAM, 64QAM, etc., using root risingThe cosine filters shape the signals respectively. The shaped signals are subjected to subcarrier multiplexing (SCM), and each polarized signal is composed of 4 carriers (the number of subcarriers can be changed to be even according to the requirement). The SCM signal reserves protection bandwidth (more than 500 MHz) between adjacent subcarriers, 1 FPT is inserted into the protection bandwidth of two polarized signals respectively, and the frequencies of the two polarized FPTs are different from each other and are asymmetric. The spectrum of the generated signal is shown in fig. 1. The signal is then converted to an analog signal by a digital-to-analog conversion module and drives a dual-polarization optical IQ modulator. The modulated signal is loaded into a standard single mode fiber and transmitted to a receiving end. The signal light and the local oscillation light are received by a dual-polarization coherent optical receiver, the received signals are converted into digital signals by an analog-to-digital converter, and the obtained electrical signals pass through a subsequent off-line digital signal processing module. The flow of the digital signal processing module is shown in fig. 5, and the digital signal processing module compensates IQ delay and imbalance of the receiving end device first. The frequency offset is then estimated by calculating the deviation between the FPT frequencies of the frequency emissions of the two FPTs. Subsequently, the two FPTs are downconverted to 0 frequency according to the following formula
Figure BDA0004119335400000061
Figure BDA0004119335400000062
The amplitude and phase of the FPT are extracted by a low pass filter to obtain an estimated signal polarization rotation and phase noise matrix. And combining the frequency offset by the estimated matrix to simultaneously compensate the frequency offset, polarization and carrier phase noise. A block diagram of the algorithm for frequency offset, polarization and carrier phase noise recovery is shown in fig. 6.
After compensating frequency offset, phase noise and polarization rotation, the signals are demultiplexed by subcarriers, then the signals with two polarizations are respectively balanced, two symmetrical subcarriers are simultaneously balanced by complex MIMO with the frequency of 2 x 2 to compensate the originating damage, and the signals with two polarizations are respectively balanced. The tap coefficients of the filter are updated according to a decision directed minimum mean algorithm to compensate for residual phase noise. The structure of the equalizer is shown in fig. 3. Finally, the Bit Error Rate (BER) is calculated.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.

Claims (9)

1. The DSP system is characterized by comprising a transmitting end and a receiving end, wherein the transmitting end comprises a transmitting end DSP module, a digital-to-analog conversion module and a dual-polarization optical IQ modulator, the transmitting end DSP module generates loaded mutually independent random bit sequences of subcarriers, the loaded mutually independent random bit sequences are mapped into signals with required modulation formats respectively, a root raised cosine filter is used for shaping the signals respectively, the shaped signals are multiplexed by the subcarriers to obtain SCM signals, a protection bandwidth is reserved between adjacent subcarriers of the SCM signals, 1 FPT is inserted into the protection bandwidth of the two polarization signals respectively, the FPT represents pilot signals of a frequency domain, and the frequencies of the FPTs of the two polarizations are different and asymmetric; then converting the signal into an analog signal through a digital-to-analog conversion module, driving a dual-polarization optical IQ modulator, and loading the modulated signal into a standard single-mode fiber to be transmitted to a receiving end;
the receiving end comprises a dual-polarization coherent optical receiver, an analog-to-digital converter and a digital signal processing module which are sequentially connected, wherein the dual-polarization coherent optical receiver is used for receiving signal light and local oscillator light, the received signal is converted into a digital signal by the analog-to-digital converter, and the obtained electrical signal is processed by the digital signal processing module.
2. The DSP system of claim 1, wherein mapping to the desired modulation format signal includes, but is not limited to, QPSK, 16QAM, 64QAM.
3. The DSP system of claim 1, wherein in the transmit side DSP module, each polarized signal is comprised of an even number of carriers.
4. The DSP system of claim 1, wherein a guard bandwidth is reserved between adjacent subcarriers of the SCM signal, the guard bandwidth being required to ensure that adjacent subcarriers do not overlap in frequency spectrum.
5. The DSP system of claim 1 wherein the digital signal processing module first compensates for IQ delays and imbalances of the receiver devices, then estimates frequency offset by calculating the offset between the FPT frequencies of the frequency emissions of the two FPTs, then downconverts the two FPTs to 0 frequency, extracts the amplitude and phase of the FPTs by a low pass filter, and obtains an estimated signal polarization rotation and phase noise matrix; compensating for frequency offset, polarization and carrier phase noise simultaneously by combining the estimated matrix with the frequency offset;
after compensating frequency deviation, phase noise and polarization rotation, carrying out subcarrier demultiplexing on the signals, respectively equalizing the signals with two polarization states, and simultaneously equalizing the two symmetrical subcarriers by adopting an equalizer to compensate the originating damage, and respectively equalizing the signals with two polarization states; finally, the bit error rate is calculated.
6. The DSP system of claim 5, wherein in said digital signal processing module, the FPT is extracted by a low pass filter according to the following formula,
Figure FDA0004119335380000021
Figure FDA0004119335380000022
wherein H {. Cndot. } denotes the low-pass filter operation, wherein R x/y (t) represents the received X/Y polarized signal, ω 1 And omega 2 Angular frequencies, Δω and Y polarization FPT, respectively
Figure FDA0004119335380000023
Respectively representing frequency offset between the laser of the transmitting end and local oscillation light, carrier phase noise and additive Gaussian white noise, < ->
Figure FDA0004119335380000024
And->
Figure FDA0004119335380000025
The FPTs extracted by the low pass filters, respectively.
7. The DSP system of claim 6 wherein the low pass filter is implemented using a sliding window averaging.
8. The DSP system of claim 6 wherein in the digital signal processing module, the equalizer is a complex MIMO of 2 x 2 or a real MIMO of 4*4.
9. The DSP system of claim 6, wherein in the digital signal processing module, the tap coefficients of the filter are updated according to a decision-directed minimum mean algorithm to compensate for residual phase noise.
CN202310228423.8A 2023-02-28 2023-02-28 Low-power-consumption and originating damage tolerant Digital Signal Processor (DSP) system Pending CN116318427A (en)

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