A dispersion and nonlinear compensation method for data center optical interconnection

Abstract

The present invention discloses a method for compensating for dispersion and nonlinearity in data center optical interconnects, belonging to the field of optical fiber communication technology. The method comprises: pruning tap coefficients of a decision feedback equalizer in a second feedforward-decision feedback equalizer based on an absolute value kernel, constructing a Tomlinson-Halassima precoding based on an absolute value kernel using the pruned tap coefficients, and compensating for a pulse amplitude modulated signal to be transmitted using the Tomlinson-Halassima precoding based on the absolute value kernel. The present invention uses absolute value as a nonlinear kernel function, reducing the number of multipliers by half compared to traditional nonlinear kernels, while introducing a threshold pruning step to further reduce the number of multipliers required. Therefore, the method can compensate for dispersion and nonlinear damage incurred during medium and long-distance transmission with low computational complexity, thereby improving the quality of the received signal. The method is suitable for cost- and power-sensitive data center optical interconnects and other application scenarios.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communications, and more specifically, relates to a dispersion and nonlinearity compensation method for optical interconnection in a data center. Background Art

[0002] With the surge in bandwidth-intensive services such as video streaming, cloud computing, the Internet of Things, and virtual and augmented reality, the continued growth of data center traffic is driving the demand for medium- and long-haul Ethernet exceeding 100 Gb / s / λ for data center interconnects. The cost and power sensitivity of data center scenarios makes intensity modulation with direct detection (IM / DD) systems based on the 4-level pulse amplitude modulation (PAM-4) format the preferred choice. Double-sideband (DSB) signals can be easily generated using Mach-Zehnder modulators or intensity modulation of directly modulated lasers. However, the power fading effects caused by dispersion in C-band transmission can cause severe distortion of DSB signals. Using optical compensation methods such as optical bandpass filters or dispersion-compensating fiber increases link attenuation and reduces transmission distance. Therefore, applying dispersion and nonlinearity compensation algorithms in the digital signal processing of transmitters and receivers is a better option.

[0003] In existing technologies, dispersion precompensation algorithms based on Tomlinson-Halassima precoding (THP) can effectively compensate for dispersion impairments and extend transmission distances. Due to the nonlinear impairments introduced by dispersive channel responses and components such as modulator amplifiers, adding a nonlinear kernel to the THP feedback loop transfer function, resulting in nonlinear THP, can enhance dispersion and nonlinearity compensation capabilities, thereby improving system performance. Traditional nonlinear THP uses a nonlinear kernel based on the Volterra series. Compared to linear THP, this significantly increases the number of multipliers required for algorithm implementation, significantly increasing the hardware resource cost and energy consumption required for digital signal processing.

[0004] In summary, there is an urgent need for a low-computational-complexity dispersion and nonlinearity compensation method for IM / DD systems used in medium- and long-distance data center optical interconnects. Summary of the Invention

[0005] In response to the above-mentioned defects or improvement needs of the prior art, the present invention provides a method for dispersion and nonlinear compensation for data center optical interconnection, which aims to solve the technical problem of high computational complexity of dispersion and nonlinear compensation for medium and long-distance data center optical interconnection in the prior art.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for compensating for dispersion and nonlinearity in data center optical interconnection is provided, comprising:

[0007] S1: Using an initial pulse amplitude modulation signal sequence sent by a signal transmitting end as a reference signal and a target pulse amplitude modulation signal sequence recovered by a signal receiving end as an input signal, an adaptive algorithm is used to adjust the equalizer tap coefficients to train a first feedforward-decision feedback equalizer based on an absolute value kernel, thereby obtaining a second feedforward-decision feedback equalizer based on an absolute value kernel with optimal equalization performance in a transmission link between the signal transmitting end and the signal receiving end;

[0008] S2: Pruning tap coefficients of a decision feedback equalizer in the second feedforward-decision feedback equalizer based on the absolute value kernel, and constructing a Tomlinson-Halassima precoding based on the absolute value kernel using the pruned tap coefficients;

[0009] S3: Compensating the pulse amplitude modulation signal to be transmitted by using the absolute value kernel-based Tomlinson-Halassima precoding to eliminate the dispersion and nonlinear damage caused by the transmission link to the transmission signal.

[0010] In one embodiment, the S2 includes:

[0011] The nonlinear feedback tap coefficients of the decision feedback equalizer in the second feedforward-decision feedback equalizer based on the absolute value kernel are pruned, and the nonlinear feedback tap coefficients greater than a threshold are selected to construct Tomlinson-Halassima precoding based on the absolute value kernel.

[0012] In one embodiment, the second feedforward-decision feedback equalizer based on the absolute value kernel includes a second feedforward equalizer and a second decision feedback equalizer, and the second feedforward-decision feedback equalizer based on the absolute value kernel is expressed as:

[0013]

[0014] Wherein, n is the ordinal number of the output signal, k and q both represent the ordinal numbers of the input signals, y(n) represents the nth output signal of the second feedforward-decision feedback equalizer based on the absolute value kernel, w1(k) represents the linear feedforward tap coefficient of the second feedforward equalizer when the kth input signal is input, w2(k,q) represents the nonlinear feedforward tap coefficient of the second feedforward equalizer when the kth input signal and the qth input signal are input, r(·) represents the equalizer input signal sequence, h1(k) represents the linear feedback tap coefficient of the second decision feedback equalizer, h2(k,q) represents the nonlinear feedback tap coefficient of the second decision feedback equalizer, d(·) represents the decision symbol sequence corresponding to the output signal sequence y(n); N1 represents the linear feedforward memory length, N2 represents the nonlinear feedforward memory length, D1 represents the linear feedback memory length, and D2 represents the nonlinear feedback memory length. Indicates a floor operation.

[0015] In one embodiment, the absolute value kernel-based Tomlinson-Halassima precoding constructed in S2 is expressed as:

[0016]

[0017] x(n)=mod 2M (x'(n));

[0018] Wherein, x(n), x(nk), and x(nq) represent the nth, nkth, and nqth output signals of the second-step output sequence of the encoder, x′(n) represents the nth output signal of the first-step output sequence of the encoder, s(n) represents the nth input symbol of the first-step output sequence of the encoder, h′2 represents the nonlinear feedback tap coefficient after pruning, mod represents modular operation, and M is the number of levels of the pulse amplitude modulation signal.

[0019] In one embodiment, the S2 includes:

[0020] The linear feedback tap coefficients and the nonlinear feedback tap coefficients of the second feedforward-decision feedback equalizer based on the absolute value kernel are pruned, and the linear feedback tap coefficients whose absolute values ​​are greater than a first threshold and the nonlinear feedback tap coefficients whose absolute values ​​are greater than a second threshold are selected to construct Tomlinson-Halassima precoding based on the absolute value kernel.

[0021] In one embodiment, before S1, the method further includes:

[0022] Generate an original pulse amplitude modulation signal sequence using the signal transmitting end, and perform upsampling and pulse shaping on the original pulse amplitude modulation signal sequence to obtain the initial pulse amplitude modulation signal sequence; modulate the initial pulse amplitude modulation signal sequence onto an optical carrier through intensity modulation and transmit the signal via the transmission link;

[0023] The signal receiving end is used to convert the received optical signal into an electrical signal, and then down-sampling, clock recovery and matched filtering are performed to obtain the target pulse amplitude modulation signal.

[0024] According to another aspect of the present invention, a communication method for data center optical interconnection is provided, comprising:

[0025] A1: At the signal transmitting end, the pulse amplitude modulation signal to be transmitted is compensated using the dispersion and nonlinearity compensation method for data center optical interconnection, and then modulated onto an optical carrier for transmission;

[0026] A2: At the signal receiving end, the received optical signal is converted into an initial electrical signal, which is then down-sampled, clock recovered, and matched filtered to obtain a target electrical signal. The target electrical signal is then decoded to restore the original pulse amplitude modulation signal.

[0027] In one embodiment, the A2 includes: at the signal receiving end: converting the received optical signal into an initial electrical signal, and then performing downsampling, clock recovery, and matched filtering to obtain a target electrical signal; using a third feedforward equalizer based on an absolute value kernel and a modular operation to perform Tomlinson-Harasima precoding decoding based on an absolute value kernel on the target electrical signal to restore the original pulse amplitude modulation signal; and demapping the pulse amplitude modulation signal;

[0028] The third feedforward equalizer based on the absolute value kernel is obtained by training the original pulse amplitude modulation signal s(n) and the first and second step output sequences x′(n) and x(n) after Tomlinson-Halassima precoding based on the absolute value kernel, and performing the operation s(n)+x′(n)-x(n) as reference signals, and using the target pulse amplitude modulation signal sequence recovered at the signal receiving end as the input signal, by adjusting the tap coefficients of the second feedforward equalizer based on the absolute value kernel through an adaptive algorithm.

[0029] In one embodiment, the third feedforward equalizer based on the absolute value kernel is expressed as:

[0030]

[0031] Wherein, k and q both represent the ordinal numbers of the input signals, y(n) represents the n-th output signal of the third feedforward-decision feedback equalizer based on the absolute value kernel, w1(k) represents the linear feedforward tap coefficient of the third feedforward equalizer when the k-th input signal is input, w2(k,q) represents the nonlinear feedforward tap coefficient of the third feedforward equalizer when the k-th input signal and the q-th input signal are input, r(·) represents the equalizer input signal sequence, N1 represents the linear feedforward memory length, N2 represents the nonlinear feedforward memory length, Indicates a floor operation.

[0032] According to another aspect of the present invention, a data center optical interconnection system is provided, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0033] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0034] (1) The present invention provides a method for compensating for dispersion and nonlinearity in data center optical interconnection, which prunes the tap coefficients of the decision feedback equalizer in the second feedforward-decision feedback equalizer based on the absolute value kernel, and uses the pruned tap coefficients to construct a Tomlinson-Halassima precoding based on the absolute value kernel. The present invention uses the absolute value as the nonlinear kernel function, which reduces the number of multipliers by half compared with the traditional nonlinear kernel based on the Volterra series. At the same time, the introduction of the threshold pruning step further reduces the required number of multipliers. Therefore, the dispersion and nonlinear damage suffered during the medium and long-distance transmission process can be compensated with lower computational complexity, thereby improving the quality of the received signal. The method is suitable for application scenarios such as data center optical interconnection that are sensitive to cost and power consumption.

[0035] (2) This scheme prunes the nonlinear feedback tap coefficients of the decision feedback equalizer in the second feedforward-decision feedback equalizer based on the absolute value kernel, selects nonlinear feedback tap coefficients greater than a threshold and complete linear feedback tap coefficients to construct Tomlinson-Halassima precoding based on the absolute value kernel, so that the computational complexity of the subsequent compensation algorithm is lower.

[0036] (3) The second feedforward-decision feedback equalizer based on the absolute value kernel described in this solution is expressed as:

[0037]

[0038] It takes into account the linear and nonlinear signal impairments caused by dispersion and nonlinear effects in the IM / DD transmission system, realizes adaptive modeling of nonlinear channels, and provides the coefficients of the absolute value kernel-based Tomlinson-Halassima precoding.

[0039] (4) The Tomlinson-Halassima precoding based on the absolute value kernel in this scheme is:

[0040]

[0041] It takes into account the linear and nonlinear signal impairments caused by dispersion and nonlinear effects in the IM / DD transmission system, and realizes pre-compensation of the feedback part of the linear and nonlinear signal impairments.

[0042] (5) This scheme selects nonlinear feedback tap coefficients whose absolute values ​​are greater than the first threshold and linear feedback tap coefficients whose absolute values ​​are greater than the second threshold to construct Tomlinson-Halassima precoding based on the absolute value kernel, so that the computational complexity of the subsequent compensation algorithm is lower.

[0043] (6) This solution generates an original pulse amplitude modulation signal sequence at the signal transmitting end and performs up-sampling and pulse shaping on the original pulse amplitude modulation signal sequence to obtain the initial pulse amplitude modulation signal sequence, thereby removing redundant signals.

[0044] (7) The present invention also provides a communication method for optical interconnection in a data center, which uses pruned tap coefficients to construct a Tomlinson-Halassima precoding based on an absolute value kernel; the Tomlinson-Halassima precoding based on an absolute value kernel is used to compensate for the pulse amplitude modulation signal to be transmitted, so as to eliminate the dispersion and nonlinear damage caused by the transmission link to the transmission signal, and modulate it to an optical carrier for transmission. The dispersion and nonlinear damage suffered during the medium and long distance transmission process can be compensated with lower computational complexity, thereby improving communication efficiency.

[0045] (8) This scheme uses a third feedforward equalizer based on an absolute value kernel and modular operation to perform absolute value kernel-based Tomlinson-Halassima precoding and decoding on the target electrical signal, which takes into account the linear and nonlinear feedforward signal impairments in the IM / DD transmission system and realizes channel equalization and decoding of the absolute value kernel-based Tomlinson-Halassima precoded signal.

[0046] (9) The third feedforward-decision feedback equalizer based on the absolute value kernel described in this solution is expressed as:

[0047] It takes into account the linear and nonlinear feedforward signal impairments in the IM / DD transmission system and realizes post-compensation of the feedforward part of the linear and nonlinear signal impairments. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a flow chart of a dispersion and nonlinearity compensation method for data center optical interconnection provided by Example 1 of the present invention;

[0049] Figure 2 2 is a schematic diagram of the structure of Tomlinson-Halassima precoding based on absolute value kernel provided in Example 1 of the present invention;

[0050] Figure 3 1 is a schematic structural diagram of an intensity modulation / direct detection transmission system provided in Example 1 of the present invention;

[0051] Figure 4 This is a flow chart of a communication method for data center optical interconnection provided by Example 2 of the present invention;

[0052] Figure 5 This is a flow chart of another communication method for data center optical interconnection provided by Example 2 of the present invention;

[0053] Figure 6 This is a comparison chart of bit error rates of the communication method for data center optical interconnection provided by the present invention under different received optical powers, provided by Example 2 of the present invention. DETAILED DESCRIPTION

[0054] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0055] Example 1

[0056] like Figure 1 As shown, this embodiment provides a dispersion and nonlinearity compensation method for data center optical interconnection, including: S1-S3. S1: using the initial pulse amplitude modulation signal sequence sent by the signal transmitting end as the reference signal, and the target pulse amplitude modulation signal sequence recovered by the signal receiving end as the input signal, the equalizer tap coefficients are adjusted by an adaptive algorithm to train the first feedforward-decision feedback equalizer based on the absolute value kernel, and the second feedforward-decision feedback equalizer based on the absolute value kernel with the best equalization performance under the transmission link between the signal transmitting end and the signal receiving end is obtained; S2: pruning the tap coefficients of the decision feedback equalizer in the second feedforward-decision feedback equalizer based on the absolute value kernel, and using the pruned tap coefficients to construct the Tomlinson-Halassima precoding based on the absolute value kernel, as shown Figure 2 As shown; S3: Tomlinson-Halassima precoding based on absolute value kernel is used to compensate the pulse amplitude modulation signal to be transmitted to eliminate the dispersion and nonlinear damage caused by the transmission link to the transmission signal.

[0057] It should be understood that although Figure 1 The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. In addition, Figure 1 At least part of the steps may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily executed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least part of the sub-steps or stages of other steps.

[0058] As a preferred implementation, S2 includes: pruning the nonlinear feedback tap coefficients of the decision feedback equalizer in the second feedforward-decision feedback equalizer based on the absolute value kernel, and selecting nonlinear feedback tap coefficients greater than a threshold to construct Tomlinson-Halassima precoding based on the absolute value kernel.

[0059] As a preferred embodiment, the second feedforward-decision feedback equalizer based on the absolute value kernel includes a second feedforward equalizer and a second decision feedback equalizer. The second feedforward-decision feedback equalizer based on the absolute value kernel is expressed as:

[0060]

[0061] Wherein, n is the ordinal number of the output signal, k and q both represent the ordinal numbers of the input signals, y(n) represents the nth output signal of the second feedforward-decision feedback equalizer based on the absolute value kernel, w1(k) represents the linear feedforward tap coefficient of the second feedforward equalizer when the kth input signal is input, w2(k,q) represents the nonlinear feedforward tap coefficient of the second feedforward equalizer when the kth input signal and the qth input signal are input, r(·) represents the equalizer input signal sequence, h(k) represents the linear feedback tap coefficient of the second decision feedback equalizer, h2(k,q) represents the nonlinear feedback tap coefficient of the second decision feedback equalizer, d(·) represents the decision symbol sequence corresponding to the output signal sequence y(n); N1 represents the linear feedforward memory length, N2 represents the nonlinear feedforward memory length, D1 represents the linear feedback memory length, and D2 represents the nonlinear feedback memory length. Indicates a floor operation.

[0062] For example, r is the received signal sampled at twice the baud rate, d is the symbol after decision, and y is the equalizer output; h and w are the decision feedback tap and feedforward tap coefficients; N1=51, N2=35, D1=25, and D2=15 are the linear feedforward memory length, nonlinear feedforward memory length, linear feedback memory length, and nonlinear feedback memory length of the channel, respectively; The tap coefficients can be trained using the Least Mean Square (LMS) algorithm.

[0063] For example, threshold pruning is performed on the obtained nonlinear decision feedback taps h2, discarding nonlinear terms h2(k,q)|x(nk)+x(nq)| where the absolute value of the tap coefficients |h2(k,q)| is less than a threshold value T = 0.006. The pruned decision feedback taps are then used to construct Tomlinson-Halassima precoding based on an absolute value kernel.

[0064] As a preferred embodiment, the absolute value kernel-based Tomlinson-Halassima precoding constructed in S2 is expressed as:

[0065]

[0066] x(n)=mod 2M (x′(n));

[0067] Wherein, x(n), x(nk), and x(nq) represent the nth, nkth, and nqth output signals of the second-step output sequence of the encoder, x′(n) represents the nth output signal of the first-step output sequence of the encoder, and s(n) represents the nth input symbol of the first-step output sequence of the encoder; h1′ represents the linear feedback tap coefficient after pruned, h2′ represents the nonlinear feedback tap coefficient after pruned, mod represents the modular operation, and M is the number of levels of the pulse amplitude modulation signal.

[0068] As a preferred implementation, S2 includes: pruning the linear feedback tap coefficients and nonlinear feedback tap coefficients of the second feedforward-decision feedback equalizer based on the absolute value kernel, selecting the linear feedback tap coefficients whose absolute values ​​are greater than the first threshold and the nonlinear feedback tap coefficients whose absolute values ​​are greater than the second threshold to construct Tomlinson-Halassima precoding based on the absolute value kernel.

[0069] The pruning operation is expressed as:

[0070]

[0071] Where T1 is the first threshold, T2 为 The second threshold. After the pruning operation, the product terms h′1(k)x(nk) and h′2(k)|x(nk)+x(nq)|, where the tap coefficients h′1 and h′2 are assigned zero, are directly discarded in the absolute value kernel-based Tomlinson-Halassima precoding and do not participate in the coding calculation. The corresponding constructed absolute value kernel-based Tomlinson-Halassima precoding can be expressed as:

[0072]

[0073] x(n)=mod 2M (x'(n)).

[0074] As a preferred embodiment, before S1, it also includes: using a signal transmitting end to generate an original pulse amplitude modulation signal sequence, and up-sampling and pulse shaping the original pulse amplitude modulation signal sequence to obtain an initial pulse amplitude modulation signal sequence; modulating the initial pulse amplitude modulation signal sequence onto an optical carrier through intensity and transmitting it through a transmission link; using a signal receiving end to convert the received optical signal into an electrical signal, and then down-sampling, clock recovery and matched filtering are performed to obtain a target pulse amplitude modulation signal.

[0075] Specifically, the dispersion and nonlinearity compensation method based on the absolute value kernel Tomlinson-Halassima precoding is divided into two stages. The first stage is the pre-training stage: the pulse amplitude modulation received signal of the optical channel is used to train the feedforward-decision feedback equalizer based on the absolute value kernel, and the tap coefficients of the trained decision feedback equalizer are pruned as the feedback loop tap coefficients of the absolute value kernel Tomlinson-Halassima precoding; the second stage is the transmission stage: the constructed absolute value kernel-based Tomlinson-Halassima precoding is used to process the transmitted pulse amplitude modulation data of the optical channel to achieve pre-compensation for the dispersion and nonlinear damage of the optical channel. The specific steps are as follows:

[0076] Step 1: During the pre-training phase, the signal transmitter generates a pulse amplitude modulation (PAM) training sequence; upsamples and pulse shapes the PAM signal; specifically, the binary training sequence is mapped to generate a 40 Gbaud 4-level PAM sequence; the 40 Gbaud 4-level PAM sequence is upsampled by a factor of 2 and pulse shaped using a root raised cosine filter with a roll-off factor of 0.6; and the sequence is resampled to the transmitter's required sampling rate of 60 GSa / s.

[0077] Step 2: The processed pulse amplitude modulation signal is modulated onto a C-band optical carrier through intensity modulation and transmitted through a standard single-mode optical fiber link. The optical intensity signal is converted into an electrical signal by sampling and direct reception at the signal receiving end. The intensity modulation / direct detection transmission system includes a signal transmitting end and a signal receiving end, such as Figure 3 It is also equipped with: an intensity modulation unit using a Mach Zehnder modulator (MZM) to modulate the electrical signal onto the intensity variation of the optical carrier. The laser wavelength is 1550nm, and the Mach Zehnder modulator is used to achieve optical intensity modulation; a standard single-mode fiber link for long-distance optical signal transmission, using G.652 standard single-mode fiber with a length of 70km; an optical amplifier unit using an erbium-doped fiber amplifier (EDFA) to compensate for the power loss of the long-distance optical transmission signal; a direct detection unit for receiving the optical signal and converting it into an electrical signal, implemented using a 40GHz bandwidth photodiode device and sampled by an 80GSa / s ADC.

[0078] Step 3: Downsample, recover the clock, and perform matched filtering on the received signal at the receiving end. Downsample, recover the clock, and perform matched filtering on the received signal at the receiving end. The downsampling process reduces the sampling rate of the received signal to 2 times the baud rate. Clock recovery corrects the sampling clock deviation using the Gardner algorithm. Matched filtering is implemented using a root-raised cosine filter with a roll-off factor of 0.6.

[0079] Step 4: Use the signal to train the tap coefficients of the feedforward-decision feedback equalizer based on the absolute value kernel; perform threshold pruning on the tap coefficients (h1) of the linear part and the tap coefficients (h2) of the nonlinear part of the obtained decision feedback equalizer part and use them as the tap coefficients of the Tomlinson-Halassima precoding based on the absolute value kernel.

[0080] Step 5: During the transmission phase, the data at the signal transmitter is mapped into a pulse amplitude modulated signal; dispersion and nonlinear impairments are pre-compensated through Tomlinson-Halassima precoding based on an absolute value kernel.

[0081] Example 2

[0082] This embodiment provides a communication method for data center optical interconnection, such as Figure 4 and Figure 5 As shown, the process includes the following.

[0083] A1: At the signal transmitter, the dispersion and nonlinearity compensation method for data center optical interconnects described above is used to compensate for the pulse amplitude modulated signal to be transmitted and modulate it onto an optical carrier for transmission. For example, the data at the signal transmitter is mapped into a pulse amplitude modulated signal; the 4-level pulse amplitude modulated signal is pre-compensated for dispersion and nonlinear impairments by using the absolute value kernel-based Tomlinson-Halassima precoding constructed in step S4; the signal after the absolute value kernel-based Tomlinson-Halassima precoding is upsampled by a factor of 2 and pulse shaped using a root-raised cosine filter with a roll-off factor of 0.6; and the signal is resampled to the transmitter's required sampling rate of 60GSa / s.

[0084] A2: At the signal receiving end, the received optical signal is converted into an initial electrical signal, which is then downsampled, clock recovered, and matched filtered to obtain the target electrical signal. This target electrical signal is then decoded and restored to the original pulse amplitude modulation signal. For example, at the receiving end, the received signal undergoes downsampling, clock recovery, and matched filtering. The downsampling process reduces the received signal sampling rate to 2 times the baud rate. Clock recovery corrects sampling clock deviation using the Gardner algorithm. Matched filtering is implemented using a root-raised cosine filter with a roll-off factor of 0.6.

[0085] As a preferred embodiment, A2 includes: at the signal receiving end: converting the received optical signal into an initial electrical signal, and then performing downsampling, clock recovery, and matched filtering to obtain a target electrical signal; using a third feedforward equalizer based on an absolute value kernel and a modular operation to perform Tomlinson-Harasima precoding decoding based on an absolute value kernel on the target electrical signal to restore the original pulse amplitude modulation signal; and demapping the pulse amplitude modulation signal;

[0086] The third feedforward equalizer based on the absolute value kernel is obtained by using the original pulse amplitude modulation signal s(n) and the first and second step output sequences x′(n) and x(n) after Tomlinson-Halassima precoding based on the absolute value kernel, and the result of the s(n)+x′(n)-x(n) operation as the reference signal, and using the target pulse amplitude modulation signal sequence recovered at the signal receiving end as the input signal, and adjusting the tap coefficients of the second feedforward equalizer based on the absolute value kernel through an adaptive algorithm for training. As a preferred embodiment, the third feedforward equalizer based on the absolute value kernel is expressed as:

[0087]

[0088] Wherein, k and q both represent the ordinal number of the input signal, y(n) represents the nth output signal of the third feedforward equalizer based on the absolute value kernel, w1(k) represents the linear feedforward tap coefficient of the third feedforward equalizer when the kth input signal is input, w2(k,q) represents the nonlinear feedforward tap coefficient of the third feedforward equalizer when the kth input signal and the qth input signal are input, r(·) represents the equalizer input signal sequence, N1 represents the linear feedforward memory length, N2 represents the nonlinear feedforward memory length, Indicates a floor operation.

[0089] The Tomlinson-Halassima precoder decoder based on the absolute value kernel uses a feedforward equalizer based on the absolute value kernel to perform channel equalization on the signal, then performs a modulo-8 operation on the signal to restore the original 4-level pulse amplitude modulation signal; finally, the 4-level pulse amplitude modulation signal is demapped. The feedforward equalizer based on the absolute value kernel can be expressed as:

[0090]

[0091] This embodiment provides a method for improving the performance of an inter-data center optical interconnection transmission system, which can effectively compensate for optical fiber dispersion damage and nonlinear damage caused by optoelectronic devices.

[0092] Compared with the prior art, this application has the following beneficial effects:

[0093] In the C-band intensity modulation / direct detection system, the direct detection signal after transmission is expressed as:

[0094]

[0095] c(t) is the DC bias of the signal, and s(t) is the original signal. -1 is the inverse Fourier transform. h(t) and H(f) are the dispersion-related transfer functions:

[0096] Re(H(f))=cos(2π 2β2Lf 2 );

[0097] β2 is the group velocity dispersion, and L is the fiber length. Signal-to-signal beat frequency interference introduces dispersion-related nonlinear distortion to the signal. Furthermore, nonlinear responses in devices such as modulators and amplifiers can cause signal distortion. Therefore, compared to traditional algorithms, nonlinear algorithms based on the absolute value kernel function enhance nonlinear impairment compensation capabilities and can better compensate for dispersive channel responses and device nonlinear impairments.

[0098] The use of absolute value as the nonlinear kernel function in this invention reduces the number of multipliers by half compared to traditional Volterra series-based nonlinear kernels. The introduction of a threshold pruning step further reduces the number of required multipliers. Therefore, the method of this invention can compensate for the dispersion and nonlinear impairments experienced by C-band systems during medium- and long-distance transmission with low computational complexity, improving received signal quality and making it suitable for cost- and power-sensitive data center optical interconnect applications.

[0099] Figure 6 The bit error rate performance of the absolute value kernel-based Tomlinson-Halassima precoding method of the present invention is compared with that of the traditional linear Tomlinson-Halassima precoding method, the feedforward-decision feedback equalizer post-compensation method, and the Volterra-based Tomlinson-Halassima precoding method.

[0100] The mathematical models of the three schemes used for comparison are as follows:

[0101] 1. Linear Tomlinson-Halassima precoding can be expressed as:

[0102]

[0103] x(n)=mod 2M (x'(n))

[0104] The channel equalization of the decoder can be expressed as:

[0105] 2. Volterra-based Tomlinson-Halassima precoding can be expressed as:

[0106]

[0107] x(n)=mod 2M (x'(n))

[0108] The channel equalization of the decoder can be expressed as:

[0109]

[0110] 3. The feedforward-decision feedback equalizer is expressed as:

[0111]

[0112] The traditional V-Tomlinson-Halassima precoding method and the linear Tomlinson-Halassima precoding method differ only in the Tomlinson-Halassima precoder construction formulas in step S3 and the decoder construction formulas in step S8 at the transmitter. Both traditional methods do not include the coefficient pruning process in step S4. The traditional feedforward-decision-feedback equalizer post-compensation method does not pre-compensate at the transmitter, but only uses feedforward-decision-feedback equalizer channel equalization to compensate for signal impairments at the receiver. The remaining signal processing components of the four experimental schemes are identical.

[0113] Figure 5 The graph shows the relationship between the bit error rate and the received optical power using the above four schemes in a 70km 40Gbaud pulse amplitude modulation-4 intensity modulation / direct detection transmission experiment. The received optical power is defined as Figure 3 The optical power before entering the EDFA module is controlled by the variable optical attenuator. The parameters of the above four dispersion and nonlinear compensation methods are shown in Table 1.

[0114] Table 1

[0115]

[0116] The Tomlinson-Harasima precoding method based on the absolute value kernel of the present invention achieves 9.08×10 -3 , which is lower than the soft decision forward error correction threshold of 1×10 -2 . The performance of the Tomlinson-Halassima precoding based on the absolute value kernel is almost the same as that of the Tomlinson-Halassima precoding method based on Volterra, and is significantly higher than the feedforward-decision feedback equalizer post-compensation scheme. Compared with the linear Tomlinson-Halassima precoding method, the Tomlinson-Halassima precoding method based on the absolute value kernel of the present invention significantly improves the performance of the Tomlinson-Halassima precoding by adding an absolute value term nonlinear kernel in the transfer function. Table 2 shows the number of multipliers required per symbol for the dispersion and nonlinear compensation algorithm parts of several schemes. Compared with the Tomlinson-Halassima precoding method based on Volterra, the present invention reduces the number of multipliers by approximately 90% in the transmitter encoder and receiver decoder parts while maintaining almost the same performance.

[0117] Table 2

[0118]

[0119] Example 3

[0120] This embodiment provides a data center optical interconnection system, including a memory and a processor. The memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0121] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A dispersion and nonlinearity compensation method for data center optical interconnection, characterized in that: include: S1: Using an initial pulse amplitude modulation signal sequence sent by a signal transmitting end as a reference signal and a target pulse amplitude modulation signal sequence recovered by a signal receiving end as an input signal, an adaptive algorithm is used to adjust the equalizer tap coefficients to train a first feedforward-decision feedback equalizer based on an absolute value kernel, thereby obtaining a second feedforward-decision feedback equalizer based on an absolute value kernel with optimal equalization performance in a transmission link between the signal transmitting end and the signal receiving end; S2: Pruning tap coefficients of a decision feedback equalizer in the second feedforward-decision feedback equalizer based on the absolute value kernel, and constructing a Tomlinson-Halassima precoding based on the absolute value kernel using the pruned tap coefficients; S3: Compensating the pulse amplitude modulation signal to be transmitted by using the absolute value kernel-based Tomlinson-Halassima precoding to eliminate the dispersion and nonlinear damage caused by the transmission link to the transmission signal.

2. The dispersion and nonlinearity compensation method for data center optical interconnection according to claim 1, wherein: The S2 includes: The nonlinear feedback tap coefficients of the decision feedback equalizer in the second feedforward-decision feedback equalizer based on the absolute value kernel are pruned, and the nonlinear feedback tap coefficients greater than a threshold are selected to construct Tomlinson-Halassima precoding based on the absolute value kernel.

3. The dispersion and nonlinearity compensation method for data center optical interconnection according to claim 2, wherein: The second feedforward-decision feedback equalizer based on the absolute value kernel includes a second feedforward equalizer and a second decision feedback equalizer. The second feedforward-decision feedback equalizer based on the absolute value kernel is expressed as: Wherein, n is the ordinal number of the output signal, k and q both represent the ordinal numbers of the input signals, y(n) represents the nth output signal of the second feedforward-decision feedback equalizer based on the absolute value kernel, w1(k) represents the linear feedforward tap coefficient of the second feedforward equalizer when the kth input signal is input, w2(k,q) represents the nonlinear feedforward tap coefficient of the second feedforward equalizer when the kth input signal and the qth input signal are input, r(·) represents the equalizer input signal sequence, h1(k) represents the linear feedback tap coefficient of the second decision feedback equalizer, h2(k,q) represents the nonlinear feedback tap coefficient of the second decision feedback equalizer, d(·) represents the decision symbol sequence corresponding to the output signal sequence y(n); N1 represents the linear feedforward memory length, N2 represents the nonlinear feedforward memory length, D1 represents the linear feedback memory length, and D2 represents the nonlinear feedback memory length. Indicates a floor operation.

4. The dispersion and nonlinearity compensation method for data center optical interconnection according to claim 3, wherein: The absolute value kernel-based Tomlinson-Halassima precoding constructed in S2 is expressed as: x(n)=mod 2M (x'(n)); Wherein, x(n), x(nk), and x(nq) represent the nth, nkth, and nqth output signals of the second-step output sequence of the encoder, x′(n) represents the nth output signal of the first-step output sequence of the encoder, s(n) represents the nth input symbol of the first-step output sequence of the encoder, h′2 represents the nonlinear feedback tap coefficient after pruning, mod represents modular operation, and M is the number of levels of the pulse amplitude modulation signal.

5. The dispersion and nonlinearity compensation method for data center optical interconnection according to claim 1, wherein: The S2 includes: The linear feedback tap coefficients and the nonlinear feedback tap coefficients of the second feedforward-decision feedback equalizer based on the absolute value kernel are pruned, and the linear feedback tap coefficients whose absolute values ​​are greater than a first threshold and the nonlinear feedback tap coefficients whose absolute values ​​are greater than a second threshold are selected to construct Tomlinson-Halassima precoding based on the absolute value kernel.

6. The dispersion and nonlinearity compensation method for data center optical interconnection according to claim 1, wherein: Before S1, it also includes: Generate an original pulse amplitude modulation signal sequence using the signal transmitting end, and perform upsampling and pulse shaping on the original pulse amplitude modulation signal sequence to obtain the initial pulse amplitude modulation signal sequence; modulate the initial pulse amplitude modulation signal sequence onto an optical carrier through intensity modulation and transmit the signal via the transmission link; The signal receiving end is used to convert the received optical signal into an electrical signal, and then down-sampling, clock recovery and matched filtering are performed to obtain the target pulse amplitude modulation signal.

7. A communication method for optical interconnection in a data center, characterized in that: include: A1: At the signal transmitting end, the dispersion and nonlinearity compensation method for data center optical interconnection according to any one of claims 1 to 6 is used to compensate the pulse amplitude modulated signal to be transmitted, and then modulate it onto an optical carrier for transmission; A2: At the signal receiving end, the received optical signal is converted into an initial electrical signal, which is then down-sampled, clock recovered, and matched filtered to obtain a target electrical signal. The target electrical signal is decoded to restore the original pulse amplitude modulation signal.

8. The communication method for data center optical interconnection according to claim 7, wherein: The step A2 of decoding and restoring the target electrical signal to obtain the original pulse amplitude modulation signal includes: performing Tomlinson-Halassima precoding and decoding based on an absolute value kernel on the target electrical signal using a third feedforward equalizer based on an absolute value kernel and a modular operation to restore the original pulse amplitude modulation signal; The third feedforward equalizer based on the absolute value kernel is obtained by training the original pulse amplitude modulation signal s(n) and the first and second step output sequences x′(n) and x(n) after Tomlinson-Halassima precoding based on the absolute value kernel, and performing the operation s(n)+x′(n)-x(n) as reference signals, and using the target pulse amplitude modulation signal sequence recovered at the signal receiving end as the input signal, by adjusting the tap coefficients of the second feedforward equalizer based on the absolute value kernel through an adaptive algorithm.

9. The communication method for data center optical interconnection according to claim 8, wherein: The third feedforward equalizer based on the absolute value kernel is expressed as: Wherein, k and q both represent the ordinal number of the input signal, y(n) represents the nth output signal of the third feedforward equalizer based on the absolute value kernel, w1(k) represents the linear feedforward tap coefficient of the third feedforward equalizer when the kth input signal is input, w2(k,q) represents the nonlinear feedforward tap coefficient of the third feedforward equalizer when the kth input signal and the qth input signal are input, r(·) represents the equalizer input signal sequence, N1 represents the linear feedforward memory length, N2 represents the nonlinear feedforward memory length, Indicates a floor operation.

10. A data center optical interconnection communication system, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 7 to 9 are implemented.

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