CN-121000308-B - Digital signal optical communication method and system based on single pilot frequency symbol

CN121000308BCN 121000308 BCN121000308 BCN 121000308BCN-121000308-B

Abstract

The invention provides a digital signal optical communication method and system based on single pilot frequency symbol, a transmitting end periodically inserts X/Y polarized pilot frequency symbol pairs, and the quadrature duobinary coding super Nyquist signal is formed, so that each pair of pilot frequency symbols are combined into an equivalent single pilot frequency symbol, phase and amplitude information is reserved and mapped to the outermost ring of a QAM constellation diagram. The receiving end searches an initial pilot frequency symbol sequence based on the characteristic of highest amplitude of the outermost ring of the QAM constellation diagram, a sliding window extraction sequence is constructed in the initial pilot frequency symbol sequence according to the length of the original pilot frequency symbol sequence, the variance of a phase increment is calculated by comparing the sliding window extraction sequence with the original pilot frequency symbol sequence, a frame starting position is determined based on the minimum variance, and the pilot frequency symbol is utilized to provide accurate initial information and periodical guiding decoding for an MLSE algorithm. The method and the device can efficiently utilize pilot frequency symbol resources and remarkably reduce MLSE decoding complexity.

Inventors

LI ZHIPEI
ZHOU SITONG
WANG CHENCHEN
XIN XIANGJUN
GAO RAN
Dong ze
WANG FU
GUO DONG
CHANG HUAN
PAN XIAOLONG

Assignees

北京理工大学

Dates

Publication Date: 20260512
Application Date: 20250619

Claims (8)

1. A digital signal optical communication transmitting method based on single pilot frequency symbol is characterized in that the method comprises the following steps: Generating a pilot frequency symbol sequence based on different X/Y polarization seeds for the quadrature amplitude modulation symbol and sharing the pilot frequency symbol sequence to a receiving end; Inserting a pair of X/Y polarized pilot symbols into a data frame to be transmitted according to a first set number of data symbol periodic intervals based on a preset pilot symbol sequence; Performing super Nyquist signal forming on the data frame through orthogonal duobinary coding and outputting, combining pilot symbols of each pair of X/Y polarization into an equivalent single pilot symbol based on the symmetry of transformation, wherein the single pilot symbol reserves the phase and amplitude information of each pair of pilot symbols for subsequent decoding and guiding, all the single pilot symbols are mapped onto the outermost constellation point in a QAM constellation diagram, the known pilot symbol value of the pilot position is utilized for providing accurate initial information for an MLSE algorithm, and the pilot symbol constraint survival path is utilized for providing periodical guiding and decoding for the MLSE to obtain a target data frame; the method comprises the steps of carrying out super Nyquist signal shaping on the data frame through orthogonal duobinary coding, and further comprising the step of introducing controllable intersymbol interference by using a raised cosine filter or a root raised cosine filter and adjusting a roll-off factor to control the quantity of ISI.
2. The method for optical communication transmission of digital signals based on single pilot symbols according to claim 1, wherein the pseudo random binary sequence is generated by using a linear feedback shift register or is obtained by generating random numbers by using a pseudo random number generator and converting the random numbers into a binary sequence.
3. A digital signal optical communication receiving method based on single pilot symbol, characterized in that the method comprises the following steps: Receiving a signal to be processed obtained by shaping according to the single pilot symbol-based digital signal optical communication transmission method of any one of claims 1 to 2, and performing IQ orthogonalization, time domain equalization, carrier recovery, and DDLSM equalization; traversing all possible frame starting positions, extracting one symbol at a time by taking a first set number of symbols as intervals to obtain candidate sequences, calculating the average amplitude of each candidate sequence, and determining the candidate sequence with the highest average amplitude as an initial pilot frequency symbol sequence; Constructing a sliding window according to a first length of an original pilot frequency symbol sequence inserted by a transmitting end, performing sliding extraction on a symbol-by-symbol basis from a start position of the original pilot frequency symbol sequence to obtain a plurality of window symbols with the first length, performing symbol-by-symbol comparison on each window symbol and the original pilot frequency symbol sequence to obtain a phase increment sequence, calculating a variance of each window symbol corresponding to the phase increment sequence, determining a position of the window symbol with the smallest variance as a frame start position, and finishing frame synchronization; the known pilot symbol values of the pilot positions are used for providing accurate initial information for the MLSE algorithm, and the pilot symbol constraint survival paths are used for providing periodic guided decoding for the MLSE to obtain target data frames.
4. The single pilot symbol based optical communication receiving method of digital signal according to claim 3, wherein providing the MLSE algorithm with accurate initial information using the known pilot symbol values of the pilot positions comprises: in the initialization stage of MLSE decoding, the initial state of the grid graph is determined based on the first known pilot symbol value of the starting position of the received sequence, the path metric corresponding to the initial state is initialized to 0, and the path metrics of other possible states are initialized to infinity.
5. The method of claim 4, wherein providing periodic pilot decoding for the MLSE using pilot constrained survivor paths to obtain the target data frame comprises: when processing to the reception time corresponding to the pilot symbol, only surviving paths with grid states consistent with the known pilot symbol values at the time are reserved, and other unmatched paths are abandoned.
6. A single pilot symbol based digital signal optical communication system, comprising: a transmitting-end digital signal processing module, configured to perform the single pilot symbol-based digital signal optical communication transmitting method according to any one of claims 1 to 2 to obtain a signal to be transmitted; An optical transmitter, comprising: the random waveform generator is used for sampling and outputting the signal to be transmitted according to a first set sampling rate; an external intense laser for generating a continuous wave optical signal of a set wavelength; The coherent optical modulator is used for carrying out IQ modulation on the signal to be transmitted and the optical signal which are sampled and output; A single mode optical fiber for transmitting the optical signal output by the optical transmitter; a coherent optical receiver for mixing an optical signal received from a single-mode optical fiber with a free-running ECL local oscillator to generate an electrical signal; An oscilloscope for capturing the electrical signal at a second set sampling rate; A receiving-end digital signal processing module, configured to perform the single pilot symbol-based digital signal optical communication receiving method according to any one of claims 3 to 5.
7. The single pilot symbol based digital signal optical communication system of claim 6 wherein the receiver digital signal processing module is further configured to perform bit error rate analysis to evaluate system performance.
8. A computer readable storage medium having stored thereon a computer program/instruction which when executed by a processor performs the steps of the method according to any of claims 1 to 5.

Description

Digital signal optical communication method and system based on single pilot frequency symbol Technical Field The present invention relates to the field of optical communications technologies, and in particular, to a digital signal optical communication method and system based on single pilot symbols. Background With the rapid development of cloud computing, internet of things and Data Center (DC) applications, high-bandwidth and low-power optical interconnection technology is a core requirement of modern communication systems. Traditional nyquist rate transmission is limited by spectral efficiency and cannot meet the increasing bandwidth demands. The super-nyquist (FTN) transmission technology introduces controllable inter-symbol interference (ISI) by compressing symbol intervals in a time or frequency domain, breaks through the limitation of the nyquist criterion, and remarkably improves the spectrum utilization rate. However, the shaping and decoding of FTN signals face many challenges, especially in the context of high-order modulation formats (such as 16 QAM) and symbol rate sampling, the complexity of signal processing is high, and the power consumption is high, which limits their application in power sensitive environments such as data centers. In FTN systems, pilot symbols (Pilot symbols) are typically used for frame synchronization, carrier Recovery (CR), and Frequency Offset Estimation (FOE). In the prior art, the Pilot symbol is utilized more singly, and is mainly concentrated on the phase recovery or synchronization function, so that the potential of the Pilot symbol in the decoding stage can not be fully exerted. In addition, the strong correlation between symbols after FTN signal shaping results in an exponential increase in the computational complexity of conventional Maximum Likelihood Sequence Estimation (MLSE) decoding algorithms, particularly when dealing with QDB-16QAM (49 QAM) signals, with a significant increase in the required state space and branch metric computation. In the existing research, the traditional MLSE decoding scheme needs to process complex state transition under the near binary channel response of the QDB signal, and the memory requirement and the processing delay are obviously increased. Some hybrid decoding schemes attempt to combine single symbol detection with simplified MLSE, but due to the inability to precisely locate the error-generating node, frequent MLSE activation is triggered easily in bandwidth-limited scenarios, resulting in reduced decoding efficiency and increased delay. These technical limitations indicate that a solution for efficiently utilizing Pilot symbols, optimizing FTN signal shaping and MLSE decoding is needed to achieve a balance between high performance and low power consumption, and meet the requirements of optical interconnection of the next generation data center. Disclosure of Invention In view of this, the embodiments of the present invention provide a method and a system for optical communication of digital signals based on single pilot symbols, so as to eliminate or improve one or more drawbacks existing in the prior art, and solve the problems of low pilot symbol utilization rate, high complexity of maximum likelihood sequence estimation decoding, and high power consumption in the existing FTN transmission system. One aspect of the present invention provides a method for transmitting optical communication of digital signals based on single pilot symbols, the method comprising the steps of: In a data frame to be transmitted, a pair of X/Y polarized pilot symbols are inserted according to a first set number of data symbol periodic intervals based on a preset pilot symbol sequence; And performing super Nyquist signal forming on the data frame through orthogonal duobinary coding, outputting, combining pilot symbols of each pair of X/Y polarization into an equivalent single pilot symbol based on the symmetry of transformation, wherein the single pilot symbol reserves the phase and amplitude information of each pair of pilot symbols for subsequent decoding guidance, and all the single pilot symbols are mapped to the outermost constellation points in the QAM constellation diagram. In some embodiments, before inserting a pair of X/Y polarized pilot symbols at a first set number of data symbol periodic intervals based on a preset pilot symbol sequence in a data frame to be transmitted, the method further comprises: Generating a pseudo-random binary sequence and mapping the pseudo-random binary sequence to a quadrature amplitude modulation symbol with a set bit number; And generating pilot symbol sequences for the quadrature amplitude modulation symbols based on different X/Y polarization seeds and sharing the pilot symbol sequences to a receiving end. In some embodiments, the pseudo-random binary sequence is generated by using a linear feedback shift register, or is obtained by generating random numbers by using a pseudo-random number genera