CN-121984594-A - IQ amplitude imbalance estimation method for coherent optical communication

CN121984594ACN 121984594 ACN121984594 ACN 121984594ACN-121984594-A

Abstract

The invention relates to an IQ amplitude imbalance estimation method for coherent optical communication, belonging to the technical field of coherent optical communication. The method solves the problems that the constellation diagram is distorted and the traditional algorithm has high calculation complexity due to the imbalance of the IQ amplitude of the receiving end under the condition of frequency offset and carrier phase noise. The technical scheme includes that preprocessing compensation such as dispersion compensation and channel equalization is carried out on coherent demodulation signals at a receiving end, average value removal processing is carried out after a training sequence is extracted, covariance matrix is calculated, eigenvalue decomposition is carried out, the amplitude unbalance is accurately estimated by utilizing the ratio of the maximum eigenvalue to the minimum eigenvalue, and finally, the signals are compensated. The invention can realize high-precision estimation, obviously reduce the calculation complexity and simultaneously maintain excellent error rate performance.

Inventors

GONG XIAOXUE
Xiao Menling
ZHANG YUKUN
ZHANG XU
GUO LEI

Assignees

重庆邮电大学

Dates

Publication Date: 20260505
Application Date: 20260122

Claims (6)

1. An IQ amplitude imbalance estimation method for coherent optical communication is characterized by comprising the following steps: Carrying out transmitting-end Digital Signal Processing (DSP) on the original data at a transmitting end, modulating the data processed by the transmitting-end DSP by adopting an IQ modulator, and generating a coherent optical signal; transmitting the coherent optical signal in a fiber channel and compensating optical power; receiving the coherent optical signal at a receiving end and performing coherent demodulation on the signal; carrying out receiving end DSP processing on the signals after coherent demodulation to obtain restored signals; the receiving end DSP processing comprises preprocessing, compensating and optimizing the signals after coherent demodulation to obtain optimized signals, calculating training sequences in the optimized signals, performing principal component analysis processing on the training sequences to obtain amplitude imbalance estimated values, and compensating the signals according to the amplitude imbalance estimated values.
2. The IQ amplitude imbalance estimation method for coherent optical communication according to claim 1, wherein the preprocessing compensation comprises performing dispersion compensation, polarization mode dispersion compensation, clock recovery and channel equalization processing on the signal after coherent demodulation.
3. The IQ amplitude imbalance estimation method for coherent optical communication according to claim 1, wherein the principal component analysis processing comprises extracting received training sequence data, performing a de-averaging processing on the training sequence, calculating a covariance matrix of the de-averaged training sequence, performing eigenvalue decomposition on the covariance matrix, and performing calculation of an IQ amplitude imbalance amount.
4. The IQ amplitude imbalance estimation method for coherent optical communication according to claim 3, wherein the de-averaging process comprises: extracting the received training sequence data and recording the column vector form as ; Calculating training sequence data Mean of (2) The expression is ; Training sequence data And its average value Subtracting to obtain the training sequence after removing the mean value The expression is , Meets the zero-mean condition, i.e 。
5. The IQ amplitude imbalance estimation method for coherent optical communication according to claim 3, wherein the covariance matrix The expression of (2) is: Wherein, the In the form of column vectors of the received training sequence after the mean removal process, Representing the conjugate-transpose operation, Representing mathematical expectations.
6. The IQ amplitude imbalance estimation method for coherent optical communication according to claim 3, wherein the eigenvalue decomposition and calculation of IQ amplitude imbalance amount comprises: For covariance matrix Decomposing the maximum eigenvalue And minimum characteristic value Is good at Calculating the estimated value of IQ amplitude imbalance of receiving end The expression is: Wherein, the Corresponding to the square of the principal component of the constellation of the signal in the complex plane, Corresponding to the square of the minor component.

Description

IQ amplitude imbalance estimation method for coherent optical communication Technical Field The invention belongs to the technical field of coherent optical communication, and relates to an IQ amplitude imbalance estimation method for coherent optical communication. Background The invention belongs to the technical field of coherent optical communication. With the rapid growth of global data traffic, fiber optic transmission systems face the fundamental requirements of long distance, high rate, and large capacity. The coherent optical communication technology is a key solution for realizing high-speed transmission because of its high receiving sensitivity and supporting high-order modulation formats such as Quadrature phase shift keying (Quadrature PHASE SHIFT KEYING, QPSK) and hexadecimal Quadrature amplitude modulation (16-Quadrature Amplitude Modulation, 16-QAM). However, in actual hardware, due to factors such as manufacturing defects of transceiver equipment and inconsistent response of a photoelectric detector, IQ amplitude imbalance problem often occurs at a receiving end. This imbalance causes the signal constellation to lose circular symmetry and distort from a perfect circular shape to an elliptical shape, severely degrading system performance, especially at high baud rates. In addition, carrier frequency offset and phase noise introduced by the transceiver laser can cause the constellation diagram to rotate on a complex plane, so that distorted ellipses are no longer aligned with coordinate axes, and the difficulty of estimation and compensation is further increased. Currently, various algorithms are dedicated to estimation and compensation of IQ amplitude imbalance. For example, one method implements compensation by inserting a frequency domain training sequence and utilizing the phase rotation effect between frames, but the method needs to perform time domain to frequency domain conversion, and has high computational complexity. Another common method is the glamer-schmitt orthogonalization algorithm (Gram-Schmidt Orthogonalization Procedure, GSOP), which forces the recovery of orthogonality by calculating the correlation coefficients of the I-and Q-path signals, while compensating for the impairments effectively, the computational burden is large due to the need to process all the data. The existing methods have insufficient precision or high complexity when frequency offset and phase noise exist, and are difficult to meet the real-time requirement of a modern high-speed coherent optical communication system. Aiming at the problems, the invention provides an IQ amplitude imbalance estimation method based on a training sequence, which utilizes the rotation invariant characteristic of principal component analysis to accurately extract elliptical long and short axis characteristics from a rotating constellation diagram, thereby realizing high-precision estimation with low computational complexity and remarkably improving the robustness and performance of a system. Disclosure of Invention In view of the above, an object of the present invention is to provide an IQ amplitude imbalance estimation method for coherent optical communication. In order to achieve the above purpose, the present invention provides the following technical solutions: An IQ amplitude imbalance estimation method for coherent optical communication, comprising: carrying out transmitting-end digital signal Processing (DIGITAL SIGNAL Processing, DSP) on the original data at a transmitting end, and modulating the data processed by the transmitting-end DSP by adopting an IQ modulator to generate a coherent optical signal; transmitting the coherent optical signal in a fiber channel and compensating optical power; receiving the coherent optical signal at a receiving end and performing coherent demodulation on the signal; carrying out receiving end DSP processing on the signals after coherent demodulation to obtain restored signals; the receiving end DSP processing comprises preprocessing, compensating and optimizing the signals after coherent demodulation to obtain optimized signals, calculating training sequences in the optimized signals, performing principal component analysis processing on the training sequences to obtain amplitude imbalance estimated values, and compensating the signals according to the amplitude imbalance estimated values. Further, the preprocessing compensation comprises dispersion compensation, polarization mode dispersion compensation, clock recovery and channel equalization processing on the signals after coherent demodulation. Further, the principal component analysis processing includes extracting received training sequence data, performing an average value removal processing on the training sequence, calculating a covariance matrix of the training sequence after the average value removal, performing eigenvalue decomposition on the covariance matrix, and performing calculation of IQ amplitude imbalance. Furt