Polarization mode dispersion compensation method and system adopting weighted constant modulus

Abstract

The invention belongs to the technical field of communication, and particularly relates to a polarization mode dispersion compensation method and system with low complexity and rapid convergence, and the method comprises the steps: obtaining the normalized amplitude weight of a signal through normalization processing according to the characteristic of a signal constellation point module value; a signal passes through a butterfly filter, and depolarization division multiplexing and polarization mode dispersion compensation are carried out; calculating a difference value between a symbol after equalization and a signal constant modulus constant so as to determine an equalizer vector updating direction and scale; according to the method, the normalized amplitude weight of the signal constellation point is calculated, the butterfly filter is used for filtering the signal, then the filter tap matrix is guided to be updated and iterated according to the normalized amplitude weight, and finally the polarization mode dispersion compensation and depolarization multiplexing are realized. Therefore, convergence of the tap matrix is accelerated, a reliable and stable communication system can be provided, and the method has great potential and application prospects in the communication field.

Description

Technical Field

[0001] This invention relates to the field of optical communication, and specifically to a polarization mode dispersion compensation method and system using weighted constant mode. Background Technology

[0002] To meet the rapidly growing network demands, the development of high-speed, high-capacity communication technologies is an inevitable trend in information and communication research. Since high-order QAM signals and probabilistic shaping (PS) techniques increase the peak value of the signal source, the polarization mode dispersion compensation effect is greatly affected. Therefore, polarization mode dispersion compensation is the key to improving the capacity and performance of optical communication systems. In recent years, due to advancements in optical communication technology, computer processing speed, digital signal processing (DSP), and high-speed analog-to-digital converter (ADC) chips, optical signal digital equalization technology has developed rapidly. These equalization techniques can effectively compensate for signal impairments by estimating the characteristics of the transmission system, so as to accurately recover signals affected by noise in complex environments.

[0003] Low-complexity and fast-convergence polarization mode dispersion compensation methods are crucial for long-distance transmission in extended optical communication systems. Currently, many traditional DSP algorithms are well-known in related fields, such as the Constant Mode Aspect (CMA) algorithm and the Concatenated Multimode Aspect (CMMA) algorithm. CMA is a commonly used polarization mode dispersion compensation and demultiplexing algorithm in the communication field, and it has been widely applied in the field of polarization mode dispersion compensation. The CMMA algorithm is a polarization mode dispersion compensation algorithm based on CMA with multiple reference radii cascaded, often used for polarization mode impairment compensation of high-order QAM signals. However, these traditional algorithms all have their own imperfections. The CMA algorithm can achieve blind equalization, but it suffers from slow and insufficient convergence when dealing with high-source peak values ​​of high-order QAM and PS signals. The CMMA algorithm can achieve fast convergence for high-order QAM signals, but it requires prior experience with the transmission signal modulation format and cannot achieve blind equalization. Furthermore, the algorithm complexity increases with the signal modulation order. Currently, a low-complexity polarization mode dispersion compensation method that can achieve blind equalization and fast convergence is still lacking. Summary of the Invention

[0004] This invention provides a polarization mode dispersion compensation method for weighted constant mode. This invention is a low-complexity and fast-converging polarization mode dispersion compensation and de-multiplexing method that can effectively compensate for signal impairments during transmission in coherent communication systems without increasing complexity.

[0005] This invention relates to a signal compensation method and system for optical communication systems. By processing signals using a butterfly filter, calculating the normalized amplitude weight of the signal, and performing tap matrix iteration based on the normalized amplitude weight and the steepest descent method, the polarization mode dispersion of the signal can be effectively compensated and the partial multiplexing can be de-multiplexed. This provides a reliable and stable communication system with great potential and application prospects in the field of communication.

[0006] A weighted mode-constant polarization mode dispersion compensation method for optical communication systems includes:

[0007] 1. The specific steps for polarization mode dispersion compensation and depolarization multiplexing of signals based on butterfly filters are as follows:

[0008] (1) Set the initial values ​​of the butterfly filter tap matrix , , and The initial operation matrix of the butterfly filter is obtained. , No. Operation matrix The calculation method is as follows:

[0009]

[0010] (2) Calculate the convergence radius of the input signal The calculation method is as follows:

[0011]

[0012] in To calculate the average, For the input signal amplitude, the first Amplitude information of each input signal The calculation method is as follows:

[0013]

[0014] in For the first The complex value of an input signal, To perform the operation of taking the real part, For operations involving the imaginary part;

[0015] (3) Polarization mode dispersion compensation and depolarization multiplexing of the input signal are performed. The calculation method is as follows:

[0016]

[0017] in , For the first Complex values ​​of input x-polarized and y-polarized signals, , The first output of the butterfly filter Complex values ​​of x-polarized and y-polarized signals, For the butterfly filter A set of operation matrices.

[0018] 2. Based on the input signal and the signal output by the butterfly filter, calculate the normalized amplitude weight of the signal. The specific steps are as follows:

[0019] (1) Calculate the amplitude information of the output signal of each butterfly filter respectively. The calculation method is as follows:

[0020]

[0021] in The first output of the butterfly filter The complex value of a signal;

[0022] (2) Calculate the normalized amplitude weight for each signal. The calculation method is as follows:

[0023]

[0024] in The length of the input signal sequence.

[0025] 3. Iteration of the tap matrix based on normalized magnitude weights and the steepest descent method, the specific steps are as follows:

[0026] (1) Calculate the error factor. The calculation method is as follows:

[0027]

[0028] (2) Update the butterfly filter tap matrix. The calculation method is as follows:

[0029]

[0030]

[0031]

[0032]

[0033] in To perform conjugate operations, This is the iteration step size;

[0034] (3) Repeat steps 1 (3), 2, 3 (1) and 3 (2) until the error factor is less than the set threshold.

[0035] This method is mainly designed for the DSP module of optical communication receivers. It focuses on introducing a weight factor containing signal amplitude information to guide the iteration of filter taps, and combining it with the steepest descent method to enable the rapid convergence of the butterfly filter taps, thereby achieving polarization mode dispersion compensation while demultiplexing. Attached Figure Description

[0036] Figure 1 This is a block diagram of a digital signal processing system employing the weighted constant mode polarization mode dispersion compensation method of this invention.

[0037] Figure 2 This is a flowchart of the steps of the weighted constant mode polarization mode dispersion compensation method in this invention.

[0038] Figure 3 This is a diagram showing the effect of processing the PM-PS-64QAM signal in Example 1 using a weighted constant mode polarization mode dispersion compensation method.

[0039] Figure 4 The bit error rate curves of PM-PS-64QAM signals under different optical signal-to-noise ratios in Example 1 are shown after processing by the weighted constant modulus polarization mode dispersion compensation method and the constant modulus algorithm-based polarization mode dispersion compensation method. Detailed Implementation

[0040] Referring to the accompanying drawings, the foregoing and other features of the embodiments of the present invention will become apparent from the following description. These embodiments are merely exemplary and not intended to limit the invention. To enable those skilled in the art to readily understand the principles and implementation methods of the present invention, the embodiments of the present invention are described below. Figure 1 The working principle of this invention will be explained using the digital signal processing system shown as an example.

[0041] The specific embodiments of the present invention will be described below with reference to the accompanying drawings, taking the PM-PS-64QAM signal as an example.

[0042] Example 1:

[0043] Coherent optical communication systems can simultaneously achieve high spectral efficiency and long-distance transmission. Probabilistic shaping techniques can improve spectral efficiency and transmission capacity. However, increasing the modulation order of QAM signals and using probabilistic shaping techniques can increase the source kurtosis of the signal, which can reduce the polarization mode dispersion compensation effect and thus affect the signal decision. Therefore, system polarization mode dispersion compensation is considered a key technology for improving the capacity and performance of optical communication systems.

[0044] This invention designs a DSP module for a polarization mode dispersion compensation method employing weighted constant mode. Figure 1 The DSP module signal, after being received by a zero-difference coherent receiver, is output from an analog-to-digital converter to an IQ quadrature module for quadrature balancing, and then input to a clock recovery module to eliminate the influence of chromatic dispersion and polarization mode dispersion introduced during fiber transmission on the clock information. Next, a dispersion compensation module compensates for the dispersion of the I and Q signals in the x and y polarization states that are affected by dispersion interference in the channel. The dispersion-compensated signal is then connected to a polarization mode dispersion compensation module to perform polarization mode dispersion compensation and demultiplexing on the x and y polarization state signals affected by polarization mode dispersion interference during transmission. The signal output from the polarization mode dispersion compensation module is then sent to a carrier phase recovery module to remove interference caused by frequency offset and phase noise. A nonlinear compensation module eliminates interference caused by signal phase offset and laser phase noise, thus achieving signal compensation. The specific algorithm flow under the polarization mode dispersion compensation module is as follows:

[0045] 1. Initialize the butterfly filter taps, where and Set to , and Set to The initial tap matrix of the butterfly filter is obtained. ; Calculate the amplitudes of the x-biased and y-biased signals. and ; Calculate the convergence radius of the x-biased signal and the y-biased signal. and .

[0046] 2. The PM-PS-64QAM signal, after undergoing orthogonal balancing, dispersion compensation, and clock recovery, is processed using a butterfly filter. Calculate the amplitudes of the x-biased and y-biased signals output by the filter. and ;Calculate the normalized amplitude weights of the x-biased and y-biased signals. and .

[0047] 3. Calculate the error factors for the x-biased and y-biased signals. and Update the butterfly filter tap matrix. , , and .

[0048] Repeat steps 2 and 3 until the error factor is less than the set threshold to achieve polarization mode dispersion compensation and depolarization multiplexing of the PM-PS-64QAM signal.

Claims

1. A polarization mode dispersion compensation method using weighted constant modulus for high-speed communication systems, characterized by, Comprise: (1) based on the signal polarization mode dispersion compensation and demultiplexing butterfly filter; (2) extraction signal amplitude, calculate the normalized amplitude weight of signal constellation point; (3) based on the normalized amplitude weight and the tap matrix iteration of steepest descent method.

2. The polarization mode dispersion compensation and demultiplexing butterfly filter based on signal according to claim 1, the specific steps are as follows: (1) Set the initial value of the butterfly filter tap matrix , , and , get the initial operation matrix of the butterfly filter , the th operation matrix is calculated as follows: (2) Calculate the convergence radius of the input signal The calculation method is as follows: wherein is the mean value operation, is the input signal amplitude, the amplitude information of the input signal The calculation method is as follows: wherein is the complex value of the input signal, is the real part operation, is the imaginary part operation; (3) polarization mode dispersion compensation and demultiplexing butterfly filter based on signal, the calculation method is as follows: in , For the first Complex values ​​of input x-polarized and y-polarized signals, , The first output of the butterfly filter Complex values ​​of x-polarized and y-polarized signals, For the butterfly filter A set of operation matrices.

3. The normalized amplitude weight calculation according to claim 1, the specific steps are as follows: (1) Calculate the amplitude information of each output signal of the butterfly filter respectively The calculation method is as follows: wherein is a complex value of the output of the 2nd butterfly filter for the kth signal; (2) Calculate the normalized amplitude weight of each signal respectively The calculation method is as follows: wherein is the sequence length of the input signal.

4. The tap matrix iteration of steepest descent method based on normalized amplitude weight according to claim 1, the specific steps are as follows: (1) calculate the error factor, the calculation method is as follows: (2) update the tap matrix of butterfly filter, the calculation method is as follows: wherein is a conjugate operation, is an iteration step. (3) repeat 2(3), 3, 4(1) and 4(2) until the error factor is less than the set threshold.

5. The polarization mode dispersion compensation method based on weighted constant modulus according to claim 1, the proposed DSP module comprises: (1) IQ quadrature module: the module is connected with the analog-to-digital converter of received signal, mainly for the quadrature imbalance phenomenon caused by receiving equipment, to ensure the orthogonality of I, Q two-way, to ensure the system performance; (2) clock recovery module: the module is connected with the IQ quadrature module, mainly to eliminate the influence of chromatic dispersion and polarization mode dispersion introduced in the transmission process on the clock information; (3) dispersion compensation module: the module is connected with the clock recovery module, mainly for the dispersion compensation of I, Q road signal of X, Y polarization state disturbed by dispersion in the channel; (4) polarization mode dispersion compensation module: the module is connected with the dispersion compensation module, the algorithm implementation part of claim 1, mainly to eliminate the influence of polarization mode dispersion on the signal in the transmission process and realize demultiplexing; (5) carrier frequency compensation module: the module is connected with the polarization mode dispersion compensation module, mainly for the frequency compensation of frequency offset generated in the transmission process of signal; (6) carrier phase recovery module: the module is connected with the carrier frequency compensation module, mainly to remove the frequency offset interference and laser phase noise; (7) nonlinear compensation module: the module is connected with the carrier phase recovery module, mainly to eliminate the nonlinear effect of signal and realize the nonlinear compensation of signal.

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