CN120567624A - Signal compensation system and method - Google Patents
Signal compensation system and methodInfo
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- CN120567624A CN120567624A CN202510871758.0A CN202510871758A CN120567624A CN 120567624 A CN120567624 A CN 120567624A CN 202510871758 A CN202510871758 A CN 202510871758A CN 120567624 A CN120567624 A CN 120567624A
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Abstract
本申请涉及信号处理技术领域，公开了一种信号补偿系统及方法，系统包括：发送端和接收端，发射端在多个空间维度的数字信号中，通过子载波空分复用在相邻子载波之间插入频域导频信号，获得的发射信号包括导频信号和数据信息信号，接收端接收发射端通过通信信道损伤后的畸变信号，接收端对损伤畸变后导频信号进行下变频操作和低通滤波处理，生成联合信道估计矩阵，进而对损伤畸变后数据信息信号进行补偿，获得补偿后的数据信息信号。本申请通过插入频域导频信号和联合信道估计矩阵对损伤畸变后的数据信息信号进行补偿，从而恢复出高质量的数据信息信号，解决了传统数字信号处理在多维复用系统异步光源场景失效的问题，同时降低了实现复杂度。
The present application relates to the field of signal processing technology and discloses a signal compensation system and method. The system includes: a transmitting end and a receiving end. The transmitting end inserts a frequency domain pilot signal between adjacent subcarriers through subcarrier spatial division multiplexing in a digital signal of multiple spatial dimensions. The obtained transmission signal includes a pilot signal and a data information signal. The receiving end receives the distorted signal after the transmitting end passes through the communication channel damaged. The receiving end performs down-conversion and low-pass filtering on the damaged and distorted pilot signal to generate a joint channel estimation matrix, and then compensates for the damaged and distorted data information signal to obtain a compensated data information signal. The present application compensates for the damaged and distorted data information signal by inserting a frequency domain pilot signal and a joint channel estimation matrix, thereby restoring a high-quality data information signal, solving the problem of failure of traditional digital signal processing in asynchronous light source scenarios of multi-dimensional multiplexing systems, while reducing implementation complexity.
Description
Technical Field
The present application relates to the field of signal processing technologies, and in particular, to a signal compensation system and method.
Background
In space division multiplexed (Space Division Multiplexing, SDM) fiber optic communications, the utilization of the spatial dimensions in multi-core fiber or few-mode fiber optic channels has become critical to breaking through the capacity limits of conventional single-mode fibers. However, as the number of spatial channels increases, system hardware complexity and power consumption increases dramatically.
Although the asynchronous light source (i.e. the lasers of the transmitting end and the receiving end are mutually independent) reduces the complexity of hardware arrangement, the effect is poor and even fails when compensating signal damage due to the independent operation of the light sources of each channel.
Disclosure of Invention
The application mainly aims to provide a signal compensation system and a signal compensation method, which aim to solve the technical problem that the traditional signal processing method compensates signal damage failure in a multidimensional multiplexing system.
In order to achieve the above object, the present application provides a signal compensation system, which includes a transmitting end and a receiving end;
The transmitting terminal is used for inserting a frequency domain pilot signal between adjacent subcarriers through subcarrier space division multiplexing in digital signals with multiple space dimensions to obtain a transmitting signal, and sending the transmitting signal to the receiving terminal through a communication channel, wherein the transmitting signal comprises a pilot signal and a data information signal;
The receiving end is used for receiving the distorted signal damaged by the transmitting end through the communication channel, wherein the distorted signal is the transmitting signal damaged by channel transmission, and the distorted signal comprises a damaged pilot signal and a damaged data information signal;
the receiving end is also used for carrying out down-conversion operation and low-pass filtering treatment on the pilot signal after the damage distortion to generate a joint channel estimation matrix;
The receiving end is further configured to compensate the damaged and distorted data information signal through the joint channel estimation matrix and the distortion signal, so as to obtain a compensated data information signal.
In an embodiment, the receiving end is further configured to perform a down-conversion operation on each of the distorted pilot signals according to the pilot angular frequency corresponding to the transmitting end and the phase offset introduced by the communication channel transmission, so as to obtain a baseband signal;
the receiving end is also used for filtering high-frequency components in the baseband signal through a low-pass filter to obtain a pilot signal after low-pass filtering;
The receiving end is further configured to construct a joint channel estimation matrix based on the low-pass filtered pilot signals in multiple spatial dimensions.
In an embodiment, the transmitting end is further configured to modulate the transmitting signal based on a transmitting end light source phase noise model, and determine a modulated signal, where the transmitting end light source phase noise model is a model constructed according to a transmitting end carrier frequency and phase noise of a transmitting end independent laser;
The receiving end is also used for obtaining distortion signals by beating the modulated signals and local oscillation light of the receiving end based on a channel transmission matrix.
In an embodiment, the transmitting end is further configured to transmit the modulated signal by using an independent laser as a carrier of the transmitting end;
The receiving end is also used for taking another independent laser as receiving end local oscillation light.
In an embodiment, the receiving end is further configured to compensate for the multi-dimensional inter-channel crosstalk, the frequency offset, and the phase noise of the damaged distorted data information signal by multiplying the distorted signal by a joint channel estimation matrix, and the compensated data information signal.
Further, in order to achieve the above object, the present application also provides a signal compensation method, which is applied to the signal compensation system, the system includes a transmitting end and a receiving end, the method includes:
the transmitting terminal inserts frequency domain pilot signals between adjacent subcarriers in digital signals with multiple space dimensions through subcarrier space division multiplexing to obtain transmitting signals, and the transmitting signals are sent to the receiving terminal through a communication channel, wherein the transmitting signals comprise pilot signals and data information signals;
The receiving end receives a distorted signal damaged by the transmitting end through the communication channel, wherein the distorted signal is a transmitted signal damaged by channel transmission, and the distorted signal comprises a damaged pilot signal and a damaged data information signal;
The receiving end performs down-conversion operation and low-pass filtering processing on the pilot signal after the damage distortion to generate a joint channel estimation matrix;
And the receiving end compensates the damaged and distorted data information signals through the joint channel estimation matrix and the distortion signals to obtain compensated data information signals.
In an embodiment, the step of generating the joint channel estimation matrix by the receiving end performing down-conversion operation and low-pass filtering processing on the distorted pilot signal includes:
The receiving end performs down-conversion operation on each damaged and distorted pilot signal according to the corresponding pilot angular frequency of the transmitting end and the phase offset introduced by the communication channel transmission to obtain a baseband signal;
the receiving end filters high-frequency components in the baseband signal through a low-pass filter to obtain a pilot signal after low-pass filtering;
The receiving end builds a joint channel estimation matrix based on the pilot signals after the low-pass filtering of a plurality of space dimensions.
In an embodiment, the receiving end receives a distorted signal after the transmitting end is damaged by the communication channel, where the distorted signal is a transmitted signal after the damage is transmitted by the channel, and the method includes:
The transmitting end modulates the transmitting signal based on a transmitting end light source phase noise model to determine a modulated signal, wherein the transmitting end light source phase noise model is a model constructed according to the transmitting end carrier frequency and the phase noise of the transmitting end independent laser;
The receiving end obtains a distortion signal by beating the modulated signal and the local oscillation light of the receiving end based on a channel transmission matrix.
In an embodiment, before the step of obtaining the distortion signal by beating the modulated signal and the local oscillation light of the receiving terminal, the receiving terminal is based on a channel transmission matrix, the method further includes:
the transmitting end transmits the modulated signal by taking an independent laser as a carrier wave of the transmitting end;
the receiving end takes another independent laser as receiving end local oscillation light.
In an embodiment, the step of the receiving end compensating the damaged distorted data information signal through the joint channel estimation matrix and the distortion signal to obtain a compensated data information signal includes:
The receiving end compensates the multidimensional inter-channel crosstalk, frequency offset and phase noise of the damaged and distorted data information signals by multiplying the combined channel estimation matrix with the distorted signals, and the compensated data information signals.
The application provides a technical scheme and discloses a signal compensation system and a method, wherein the system comprises a transmitting end and a receiving end, wherein the transmitting end inserts frequency domain pilot signals between adjacent subcarriers in digital signals with multiple space dimensions through subcarrier space division multiplexing to obtain transmitting signals, the transmitting signals are transmitted to the receiving end through communication channels, the transmitting signals comprise pilot signals and data information signals, the receiving end receives distorted signals damaged by the transmitting end through the communication channels, the distorted signals are transmitted to the damaged transmitting signals through the channels, the distorted signals comprise damaged pilot signals and damaged data information signals, the receiving end performs down-conversion operation and low-pass filtering processing on the damaged pilot signals to generate a joint channel estimation matrix, and the receiving end compensates the damaged data information signals through the joint channel estimation matrix and the distorted signals to obtain compensated data information signals. The application compensates the damaged data information signal by inserting the frequency domain pilot signal and the joint channel estimation matrix, thereby recovering the high-quality data information signal, solving the problem of asynchronous light source scene failure of the traditional digital signal processing in the multidimensional multiplexing system, and reducing the realization complexity.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and together with the description, serve to explain the principles of the application.
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required to be used in the description of the embodiments or the prior art will be briefly described below, and it will be obvious to those skilled in the art that other drawings can be obtained from these drawings without inventive effort.
FIG. 1 is a block diagram of a first embodiment of a signal compensation system according to the present application;
FIG. 2 is a schematic diagram of a two-mode system (four-dimensional multiplexing) asynchronous light source digital signal processing flow;
FIG. 3 is a flowchart of a signal compensation method according to a first embodiment of the present application;
Fig. 4 is a flowchart of a second embodiment of the signal compensation method of the present application.
The achievement of the objects, functional features and advantages of the present application will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
It should be understood that the specific embodiments described herein are merely illustrative of the technical solution of the present application and are not intended to limit the present application.
For a better understanding of the technical solution of the present application, the following detailed description will be given with reference to the drawings and the specific embodiments.
Although the asynchronous light source reduces the complexity of hardware arrangement, the effect is poor and even fails when compensating signal damage due to the independent operation of the light sources of each channel.
Therefore, in order to overcome the defects, the application provides a solution to compensate the damaged data information signals by inserting the frequency domain pilot signals and the joint channel estimation matrix, thereby recovering the high-quality data information signals, solving the problem that the traditional digital signal processing fails in the asynchronous light source scene of the multi-dimensional multiplexing system, and reducing the implementation complexity.
Based on this, an embodiment of the present application provides a signal compensation system, referring to fig. 1, fig. 1 is a block diagram of a first embodiment of the signal compensation system according to the present application. The signal compensation system comprises a transmitting end 10 and a receiving end 20.
The transmitting end 10 is configured to insert a frequency domain pilot signal between adjacent subcarriers through subcarrier space division multiplexing in digital signals in multiple spatial dimensions, obtain a transmitting signal, and send the transmitting signal to the receiving end through a communication channel, where the transmitting signal includes a pilot signal and a data information signal.
In SDM fiber optic communications, the utilization of spatial dimensions in multi-core fiber or few-mode fiber optic channels is critical to breaking through the capacity limits of conventional single-mode fibers. However, as the number of spatial channels increases, system hardware complexity and power consumption rise dramatically, and especially the requirement for laser synchronization becomes a bottleneck for large-scale deployment.
Asynchronous light sources can effectively reduce the complexity of hardware arrangement, but the resulting multi-channel independent phase noise and multi-frequency offset problems present new challenges for signal processing, and such asynchronous phase noise will significantly weaken or even fail the performance of a Multiple-Input Multiple-Output (MIMO) equalizer conventionally used to compensate for inter-channel crosstalk. In the prior art, an extended Kalman filter is adopted for equalization and carrier phase recovery, but the implementation complexity is high, and the method is not suitable for practical scenes. And a pilot frequency auxiliary phase and channel joint estimation algorithm is adopted, so that the frequency offset difference problem caused by an asynchronous light source is not considered. In addition, the scheme based on unscented Kalman filtering reduces complexity, but still does not solve the problem of asynchronous frequency offset.
In order to solve the problem that the conventional signal processing method fails in compensating signal damage under the asynchronous scene of carrier light source phase and local oscillator light phase in a multidimensional multiplexing system, the problem that MIMO equalization and carrier recovery are respectively and independently carried out in a conventional algorithm must be avoided, and a proper technical path is to carry out collaborative recovery on the MIMO equalization and phase noise. Based on the thought, the application provides a multi-dimensional inter-channel crosstalk, frequency offset and phase noise collaborative recovery scheme based on frequency domain pilot signals, frequency domain pilot signals are respectively inserted into each dimension signal of a transmitting end, a receiving end extracts a joint channel estimation matrix for estimating the multi-dimensional inter-channel crosstalk, frequency offset and phase noise by the pilot signals after damage distortion, the joint channel estimation matrix is used for compensating signal damage, and the calculation complexity is reduced to a linear level.
The method can solve the problem that the traditional equalization algorithm under the asynchronous light source fails, successfully realize decoupling among multidimensional channels under asynchronous phase noise, realize decoupling among multidimensional channels under asynchronous frequency offset, and further reduce the overall implementation complexity through multi-damage cooperative recovery. In addition, the existing scheme only considers the asynchronous phase noise problem brought by an asynchronous light source in an asynchronous light source scene, and does not consider asynchronous frequency offset, the method can realize decoupling among multidimensional channels even under the asynchronous frequency offset, has high dimensional expandability, and can be applied only by inserting a new frequency domain pilot signal into a new multiplexing dimensional signal when the system expands to a higher spatial dimension, so that the method can be easily expanded to any dimensional multiplexing system.
When the signal compensation method is realized, the transmitting end firstly distributes digital signals to a plurality of space dimensions, in the signals of each space dimension, a frequency domain pilot signal is inserted between adjacent subcarriers through a subcarrier space division multiplexing technology, and finally, the transmitting signals containing the pilot signal and the data information signal are transmitted to the receiving end through a communication channel. In SDM optical fiber communication, multiple subcarriers are distributed to different space dimensions to increase capacity of communication system, and frequency domain pilot signal is known reference signal inserted in frequency domain for channel estimation and signal compensation at receiving end.
It should be appreciated that in order to improve the transmission quality and reliability of the signal, symbol mapping and pulse shaping are also performed before the frequency domain pilot signal is inserted. Symbol mapping is the mapping of input data bits onto specific modulation symbols, which typically have specific amplitudes and phases, that better adapt to the characteristics of the fibre channel. Through symbol mapping, the data bits can be converted into a signal format suitable for transmission in an optical fiber.
The pulse shaping is to further process the symbol mapped by the symbol to optimize the spectrum characteristic of the signal, and by the pulse shaping, the inter-symbol interference of the signal in the transmission process can be reduced and the spectrum efficiency of the signal can be improved. Pulse shaping may be achieved by using a special filter, for example a root raised cosine filter, to shape the signal for better performance during transmission.
The receiving end 20 is configured to receive a distorted signal after the transmitting end is damaged by the communication channel, where the distorted signal is a transmitting signal after the damage is transmitted through the channel, and the distorted signal includes a damaged distorted pilot signal and a damaged distorted data information signal.
The distorted signal refers to a signal whose characteristics such as amplitude and phase change due to channel impairment (impairment due to factors such as inherent characteristics of an optical fiber, splice impairment, or nonlinear effects in an optical fiber) after transmission through a communication channel, the distorted pilot signal refers to a pilot signal after channel transmission impairment, and the distorted data information signal refers to a data information signal after channel transmission impairment.
The receiving end 20 is further configured to perform a down-conversion operation and a low-pass filtering process on the distorted pilot signal, so as to generate a joint channel estimation matrix.
It should be noted that the down-conversion operation is a process of converting a high-frequency signal into a low-frequency signal, the low-pass filtering process is to filter out a high-frequency component by a low-pass filter, the low-pass filter is a signal processing tool that allows the low-frequency signal to pass through and attenuates the high-frequency signal, and based on the frequency characteristic of the signal, the unnecessary high-frequency component can be effectively removed by selecting a proper filter parameter, and the joint channel estimation matrix is constructed based on the pilot signals after the low-pass filtering of multiple spatial dimensions and is used for describing the transmission characteristic of the channel.
In the specific implementation, the receiving end performs down-conversion operation on the pilot signal after the damage distortion, converts the pilot signal into a baseband signal, then filters high-frequency components in the baseband signal through a low-pass filter, obtains a pilot signal after the low-pass filtering, and further constructs a joint channel estimation matrix based on the pilot signal after the low-pass filtering of a plurality of spatial dimensions.
The receiving end 20 is further configured to compensate the damaged and distorted data information signal by using the joint channel estimation matrix and the distortion signal, so as to obtain a compensated data information signal.
The joint channel estimation matrix quantization reflects the damage degree suffered by the signal in the transmission process, and the receiving end can accurately identify the specific damage suffered by the signal in the transmission process by combining the joint channel estimation matrix with the distorted signal. For example, if the joint channel estimation matrix shows that the amplitude of a signal with a specific frequency has significant attenuation, the receiving end can perform corresponding gain adjustment on the damaged signal to recover the original amplitude of the signal according to the amplitude, and if the joint channel estimation matrix reveals phase offset or frequency offset, the receiving end can correct the offset through proper phase correction or frequency adjustment to recover the phase and frequency characteristics of the signal.
In addition, by analyzing the channel estimation matrix, the receiving end can recognize the existence of multi-dimensional inter-channel crosstalk and take corresponding measures to eliminate or reduce the interference. For example, through matrix operation, the receiving end can design a compensation matrix to counteract the influence of crosstalk, so that the independence and the integrity of the signals in each dimension can be recovered.
As an embodiment, the receiving end 20 is further configured to compensate for the multi-dimensional inter-channel crosstalk, the frequency offset, and the phase noise of the distorted data information signal by multiplying the distorted signal by a joint channel estimation matrix, and the compensated data information signal.
It should be noted that, the crosstalk between multidimensional channels refers to a phenomenon that signals between different channels (such as different optical fiber cores or modes) interfere with each other to cause signal distortion, the frequency offset refers to a difference between an actual frequency and a theoretical frequency of a signal, which is mainly derived from frequency mismatch of lasers at a transmitting end and a receiving end, and a nonlinear effect in a channel transmission process, and the phase noise is random fluctuation of a signal phase, which is usually caused by insufficient phase stability of the lasers, and causes phase distortion of the signal.
In the specific implementation, the system can compensate the multi-dimensional inter-channel crosstalk, frequency offset and phase noise of the damaged and distorted data information signals by multiplying the joint channel estimation matrix with the distorted signals. In addition, other mathematical operations or signal processing techniques, such as addition, subtraction, convolution, etc., may be used to compensate, depending on the nature of the channel impairments and the requirements of the system design. The recovered impairment may also cover other types of channel impairments such as amplitude attenuation, delay spread, nonlinear distortion, etc.
According to the method and the device, the damaged data information signals are compensated by inserting the frequency domain pilot signals and the joint channel estimation matrix, so that high-quality data information signals are recovered, the problem that the traditional digital signal processing fails in an asynchronous light source scene of a multi-dimensional multiplexing system is solved, and meanwhile, the implementation complexity is reduced.
In the second embodiment of the present application, the same or similar content as in the first embodiment of the present application may be referred to the description above, and will not be repeated. Based on the embodiment shown in fig. 1 described above, a second embodiment of the signal compensation system of the present application is presented.
In this embodiment, the receiving end 20 is further configured to perform a down-conversion operation on each of the distorted pilot signals according to the corresponding pilot angular frequency of the transmitting end and the phase offset introduced by the transmission of the communication channel, so as to obtain a baseband signal.
It should be noted that, the frequency domain pilot signal inserted by the transmitting end has specific independent angular frequencies, which are preset, and provide an accurate reference for the receiving end to estimate and compensate various impairments in the channel. In addition, when a signal is transmitted through a communication channel, the characteristics of the channel may cause a phase shift of the signal, reflecting the environmental impact the signal is subjected to during transmission.
The receiving end performs down-conversion operation on the damaged pilot signal by accurately measuring the phase offsets and combining the known pilot angular frequency, and converts the high-frequency pilot signal into a baseband signal, which may be achieved by multiplying the received signal (i.e., the damaged distorted pilot signal) with a local oscillation signal, the frequency of which matches the frequency of the pilot signal.
The receiving end 20 is further configured to filter the high frequency component in the baseband signal by using a low-pass filter, so as to obtain a low-pass filtered pilot signal.
In this process, the receiving end passes the baseband signal through a low pass filter, which attenuates signal components above that frequency according to its preset cut-off frequency, thereby preserving the main characteristics of the signal. After the processing of the low-pass filter, purer signals are obtained, and key information of pilot signals is reserved.
The receiving end 20 is further configured to construct a joint channel estimation matrix based on the low-pass filtered pilot signals in multiple spatial dimensions.
In a space division multiplexing system, signals are transmitted in multiple spatial dimensions, with signals in each dimension potentially being affected by different channels. Therefore, in order to accurately describe the transmission characteristics of the whole channel, the receiving end needs to comprehensively consider information from different spatial dimensions, namely, the construction of a joint channel estimation matrix involves analyzing and processing pilot signals after low-pass filtering of a plurality of spatial dimensions, and the receiving end calculates a matrix capable of reflecting the transmission characteristics of the whole channel according to the characteristics of the amplitude, the phase and the like of the pilot signals, wherein the matrix not only comprises the characteristics of channels of each spatial dimension, but also reflects the mutual influence of signals among different dimensions.
According to the embodiment, through down-conversion and filtering processing, the receiving end can accurately extract key information of the pilot signal from the complex distortion signal, and then a comprehensive and accurate joint channel estimation matrix is constructed, based on the matrix, the receiving end can realize cooperative compensation of multi-dimensional inter-channel crosstalk, frequency offset and phase noise, and the recovery quality of the signal and the overall performance of the system are effectively improved.
As an implementation manner, the transmitting end 10 is further configured to modulate the transmitting signal based on a transmitting end light source phase noise model, and determine a modulated signal, where the transmitting end light source phase noise model is a model constructed according to a transmitting end carrier frequency and a phase noise of a transmitting end independent laser.
In fiber optic communications, a laser acts as a carrier source for a signal, and its phase noise is a random fluctuation in the phase of the laser output signal. The emitting end light source phase noise model is built to accurately describe the influence of laser phase noise on signals, and is built based on the carrier frequency of the emitting end (namely the center frequency of the laser emitting signal) and the phase noise characteristic of the emitting end independent laser.
In the modulation process, the transmitting end carries out preprocessing on the transmitting signal, including coding and modulation format selection, then calculates the predicted value of phase noise according to the phase noise model of the transmitting end light source, and introduces opposite phase adjustment in the signal to pre-compensate the influence of the phase noise. Further, the modulated signal is converted into an optical signal by an electro-optical modulator and sent to a receiving end through a fiber channel.
The receiving end 20 is further configured to obtain a distortion signal by beating the modulated signal and a local oscillation light of the receiving end based on a channel transmission matrix.
It should be noted that the channel transmission matrix is a mathematical model for describing the transmission characteristics of signals in a communication channel, including attenuation, phase change, etc., and beat frequency refers to the generation of a new signal (i.e., a distorted signal) by mixing a received signal with a signal generated by a local oscillator (local oscillator light), where the frequency of the new signal is the difference between the frequencies of the two signals.
As an implementation manner, the transmitting end 10 is further configured to transmit the modulated signal by using a separate laser as a carrier of the transmitting end.
The receiving end 20 is further configured to use another independent laser as a receiving end local oscillation light.
In the signal compensation system, a transmitting end and a receiving end respectively use independent lasers to complete the transmitting and receiving processes of signals. The transmitting end generates a transmitting end carrier wave through an independent laser, the carrier wave is a carrier for signal transmission, the frequency and phase characteristics of the carrier wave directly influence the quality and transmission performance of signals, the transmitting end loads the modulated signals on the carrier wave and then transmits the modulated signals through an optical fiber channel, so that the transmitting end can flexibly control the transmitting characteristics of the signals, and meanwhile, the modulating and processing of the signals are facilitated. The receiving end can accurately control the beat frequency process by using an independent laser as local oscillation light, so as to ensure correct demodulation and recovery of signals.
According to the embodiment, the signal is modulated based on the transmitting end light source phase noise model at the transmitting end, so that signal distortion caused by the transmitting end laser phase noise can be compensated in advance, the phase and frequency characteristics of the signal are more stable after the signal is transmitted through the optical fiber channel, and the error rate and the signal distortion caused by the phase noise are reduced. Meanwhile, the receiving end can recover the original signal more accurately through beat frequency operation with the local oscillation light, and demodulation performance of the signal can be effectively improved even if channel damage and interference exist.
For ease of understanding, reference is made to FIG. 2, which is not intended to be limiting of the signal compensation system of the present application. Fig. 2 is a schematic diagram of a two-mode system (four-dimensional multiplexing) asynchronous light source digital signal processing flow, and as shown in fig. 2, the system adopts a 16-QAM (quadrature amplitude modulation) technology to modulate and demodulate signals. At the transmitting end, pseudo-random binary sequences are first generated and then converted into corresponding modulation symbols by 16-QAM mapping. The symbols are then processed using nyquist pulse shaping techniques to optimize the spectral characteristics of the signal and reduce inter-symbol interference. And then, carrying out subcarrier multiplexing, and multiplexing the processed signals onto different subcarriers so as to improve the frequency spectrum efficiency. In addition, a frequency domain pilot signal is inserted into the signal, and the signal is transmitted to a receiving end through an optical fiber after being modulated and processed.
At the receiving end, the signal first passes through a mode demultiplexer and then is received by a polarization diversity coherent receiver. The received signal is processed by two polarization diversity coherent receivers respectively after polarization separation to improve the receiving quality and reliability of the signal, then the received modulation symbols are converted back into binary data through 16-QAM demapping, the signal is further recovered and the influence of noise is reduced through matched filtering and subcarrier demultiplexing, and finally pilot frequency damage compensation and resampling are carried out to compensate the damage possibly suffered by the signal in the transmission process. By comparing the power spectrums of the transmitting end and the receiving end, the quality of signal recovery can be evaluated, and in an ideal case, the power spectrum of the receiving end is as close to the power spectrum of the transmitting end as possible, which indicates that the signal recovery is good.
Further specific description is as follows:
The application uses the frequency domain pilot frequency sequence to carry out the cooperative compensation of the multi-dimensional inter-channel crosstalk, the frequency offset and the phase noise on the transmission signal of the space division multiplexing system, thereby solving the problem of the failure of the traditional equalization scheme under the asynchronous light source and achieving the aim of simplifying the digital signal processing (DIGITAL SIGNAL Processors, DSP) algorithm. Taking a four-dimensional multiplexed (i.e., a system that uses four independent dimensions to transmit and process signals) fiber optic transmission for a two-mode (i.e., two modes of transmission in an optical fiber) system as an example, the following is described:
in the transmitting end DSP, the signals are subjected to subcarrier multiplexing, frequency domain pilot signals are inserted between adjacent subcarriers, and the transmitting end signals can be expressed as:
It is known that the pilot signal and the data information signal are independent. In the formula, A dual polarized digital domain transmit signal representing two modes; A dual polarized data information signal representing two modes; An angular frequency representing the inserted pilot signal; Representing the amplitude of the inserted pilot signal, the amplitude of the pilot signal being determined by the Carrier-to-Signal Power Ratio, PSR, ,AndRespectively representing data information signalsPower and pilot signal of (2)Is set, is provided.
The transmitting end can use two independent lasers as signal carriers, the receiving end uses another two independent lasers as local oscillation light, and the transmitting end light source phase noise model and the receiving end local oscillation light phase noise modelAndExpressed as:
in the formula, Representing the frequencies of two carrier light sources at the transmitting end; Is the corresponding phase noise; Representing the frequency of the local oscillation light; is the corresponding phase noise.
Modulated signal by modulatorCan be expressed as:
the modulated signal is transmitted by space division multiplexing optical fiber, and the channel transmission matrix Can be expressed as:
The signal reaches the receiving end and the beat frequency of the local oscillator light obtains the receiving signal (I.e., distorted signal):
in the formula, The damaged and distorted pilot signal at the receiving end is represented by, for example, a pilot signal on a first polarization in a first mode, and after the damage is transmitted through a channel, the received damaged and distorted pilot signal is represented as:
wherein, the Representing the frequency offset of the optical carrier and the local oscillator light; representing phase noise.
In the receiving end DSP, the pilot signal estimation joint channel estimation matrix after damage distortion is utilized. Because the pilot signals of the transmitting end are known, the four polarized pilot signals are respectively down-converted to the baseband, and the pilot signals after the damage distortion are extracted by adopting a low-pass filter and are used for estimating the crosstalk, the frequency offset and the phase noise among the multidimensional channels. The joint channel estimation matrix may represent:
in the formula, The low-pass filtering is represented, and the calculation formula of each element is shown as the formula by using a first behavior example:
Joint channel estimation matrix Other elements of (c) are similarly available. From equation (9), it can be seen that the joint channel estimation matrix contains multi-dimensional inter-channel crosstalk, frequency offset and phase noise, so that the joint channel estimation matrix is multiplied by the signal to be processed (distorted signal) to obtain a recovered signal, and thus, the crosstalk, frequency offset and phase noise in the system can be compensated simultaneously under an asynchronous light source scene.
The key point of the signal compensation system is that the application discloses a space division multiplexing optical fiber communication digital signal processing technology based on a frequency domain pilot signal, which can realize the coordinated compensation of crosstalk, frequency offset and phase noise among multidimensional channels under the influence of asynchronous phase noise and asynchronous frequency offset of an asynchronous light source; the method comprises the steps of adding frequency domain pilot signals into digital signals of a transmitting end, extracting damaged frequency domain pilot signals by a receiving end through digital signal processing, estimating a joint channel estimation matrix of crosstalk, frequency offset and phase noise in a channel by the extracted frequency domain pilot signals, respectively carrying out down-conversion on each damaged and distorted pilot signal to a baseband in the process of estimating the joint channel estimation matrix, and then extracting by a low-pass filter, thereby constructing a synthetic joint channel estimation matrix.
It should be noted that, in the above embodiment, the pilot is inserted into the gap between adjacent subcarriers to avoid interference between the pilot and the signal by using subcarrier multiplexing technology, and besides the above manner, it is also possible to separate the pilot and the signal in the time domain, so that even in a single carrier system, it is possible to insert a pilot sequence before a signal sequence, and furthermore, it is also possible to insert a frequency domain pilot outside the signal spectrum of a single carrier. Another possible modification is to modify the means of extracting the frequency domain pilot, in the above embodiment, the pilot is down-converted by digital signal processing technology and then extracted by low-pass filtering, and the process can directly extract the damaged pilot signal by means of analog signal processing. Furthermore, when pilots exist in a time domain sequence, pilot information may be extracted directly through frame synchronization.
Referring to fig. 3, the signal compensation system of the present application provides a signal compensation method, and fig. 3 is a flow chart of a first embodiment of the signal compensation method of the present application, where the signal compensation system includes a transmitting end and a receiving end, and the signal compensation method includes steps S10 to S40:
step S10, the transmitting end inserts a frequency domain pilot signal between adjacent subcarriers through subcarrier space division multiplexing in a plurality of digital signals with spatial dimensions, obtains a transmitting signal, and sends the transmitting signal to the receiving end through a communication channel, where the transmitting signal includes a pilot signal and a data information signal.
When the signal compensation method is realized, the transmitting end firstly distributes digital signals to a plurality of space dimensions, in the signals of each space dimension, a frequency domain pilot signal is inserted between adjacent subcarriers through a subcarrier space division multiplexing technology, and finally, the transmitting signals containing the pilot signal and the data information signal are transmitted to the receiving end through a communication channel. In SDM optical fiber communication, multiple subcarriers are distributed to different space dimensions to increase capacity of communication system, and frequency domain pilot signal is known reference signal inserted in frequency domain for channel estimation and signal compensation at receiving end.
It should be appreciated that in order to improve the transmission quality and reliability of the signal, symbol mapping and pulse shaping are also performed before the frequency domain pilot signal is inserted. Symbol mapping is the mapping of input data bits onto specific modulation symbols, which typically have specific amplitudes and phases, that better adapt to the characteristics of the fibre channel. Through symbol mapping, the data bits can be converted into a signal format suitable for transmission in an optical fiber.
The pulse shaping is to further process the symbol mapped by the symbol to optimize the spectrum characteristic of the signal, and by the pulse shaping, the inter-symbol interference of the signal in the transmission process can be reduced and the spectrum efficiency of the signal can be improved. Pulse shaping may be achieved by using a special filter, for example a root raised cosine filter, to shape the signal for better performance during transmission.
Step S20, the receiving end receives a distorted signal after the transmitting end is damaged by the communication channel, where the distorted signal is a transmitted signal after the damage is transmitted by the channel, and the distorted signal includes a damaged and distorted pilot signal and a damaged and distorted data information signal.
The distorted signal refers to a signal whose characteristics such as amplitude and phase change due to channel impairment (impairment due to factors such as inherent characteristics of an optical fiber, splice impairment, or nonlinear effects in an optical fiber) after transmission through a communication channel, the distorted pilot signal refers to a pilot signal after channel transmission impairment, and the distorted data information signal refers to a data information signal after channel transmission impairment.
And step S30, the receiving end performs down-conversion operation and low-pass filtering processing on the distorted pilot signals to generate a joint channel estimation matrix.
It should be noted that the down-conversion operation is a process of converting a high-frequency signal into a low-frequency signal, the low-pass filtering process is to filter out a high-frequency component by a low-pass filter, the low-pass filter is a signal processing tool that allows the low-frequency signal to pass through and attenuates the high-frequency signal, and based on the frequency characteristic of the signal, the unnecessary high-frequency component can be effectively removed by selecting a proper filter parameter, and the joint channel estimation matrix is constructed based on the pilot signals after the low-pass filtering of multiple spatial dimensions and is used for describing the transmission characteristic of the channel.
In the specific implementation, the receiving end performs down-conversion operation on the pilot signal after the damage distortion, converts the pilot signal into a baseband signal, then filters high-frequency components in the baseband signal through a low-pass filter, obtains a pilot signal after the low-pass filtering, and further constructs a joint channel estimation matrix based on the pilot signal after the low-pass filtering of a plurality of spatial dimensions.
And step S40, the receiving end compensates the damaged and distorted data information signals through the joint channel estimation matrix and the distortion signals to obtain compensated data information signals.
The joint channel estimation matrix quantization reflects the damage degree suffered by the signal in the transmission process, and the receiving end can accurately identify the specific damage suffered by the signal in the transmission process by combining the joint channel estimation matrix with the distorted signal. For example, if the joint channel estimation matrix shows that the amplitude of a signal with a specific frequency has significant attenuation, the receiving end can perform corresponding gain adjustment on the damaged signal to recover the original amplitude of the signal according to the amplitude, and if the joint channel estimation matrix reveals phase offset or frequency offset, the receiving end can correct the offset through proper phase correction or frequency adjustment to recover the phase and frequency characteristics of the signal.
In addition, by analyzing the channel estimation matrix, the receiving end can recognize the existence of multi-dimensional inter-channel crosstalk and take corresponding measures to eliminate or reduce the interference. For example, through matrix operation, the receiving end can design a compensation matrix to counteract the influence of crosstalk, so that the independence and the integrity of the signals in each dimension can be recovered.
In one implementation manner, the step S40 in this embodiment may include the receiving end compensating for the multi-dimensional inter-channel crosstalk, the frequency offset, and the phase noise of the damaged distorted data information signal by multiplying the distorted signal by a joint channel estimation matrix, where the compensated data information signal is obtained by the receiving end.
It should be noted that, the crosstalk between multidimensional channels refers to a phenomenon that signals between different channels (such as different optical fiber cores or modes) interfere with each other to cause signal distortion, the frequency offset refers to a difference between an actual frequency and a theoretical frequency of a signal, which is mainly derived from frequency mismatch of lasers at a transmitting end and a receiving end, and a nonlinear effect in a channel transmission process, and the phase noise is random fluctuation of a signal phase, which is usually caused by insufficient phase stability of the lasers, and causes phase distortion of the signal.
In the specific implementation, the system can compensate the multi-dimensional inter-channel crosstalk, frequency offset and phase noise of the damaged and distorted data information signals by multiplying the joint channel estimation matrix with the distorted signals. In addition, other mathematical operations or signal processing techniques, such as addition, subtraction, convolution, etc., may be used to compensate, depending on the nature of the channel impairments and the requirements of the system design. The recovered impairment may also cover other types of channel impairments such as amplitude attenuation, delay spread, nonlinear distortion, etc.
According to the method and the device, the damaged data information signals are compensated by inserting the frequency domain pilot signals and the joint channel estimation matrix, so that high-quality data information signals are recovered, the problem that the traditional digital signal processing fails in an asynchronous light source scene of a multi-dimensional multiplexing system is solved, and meanwhile, the implementation complexity is reduced.
In the second embodiment of the present application, the same or similar content as in the first embodiment of the present application may be referred to the description above, and will not be repeated. On this basis, a second embodiment of the signal compensation method of the present application is proposed with reference to the embodiment shown in fig. 4.
In this embodiment, the step S30 may include steps S301 to S303:
in step S301, the receiving end performs a down-conversion operation on each damaged and distorted pilot signal according to the pilot angular frequency corresponding to the transmitting end and the phase offset introduced by the communication channel transmission, so as to obtain a baseband signal.
It should be noted that, the frequency domain pilot signal inserted by the transmitting end has specific independent angular frequencies, which are preset, and provide an accurate reference for the receiving end to estimate and compensate various impairments in the channel. In addition, when a signal is transmitted through a communication channel, the characteristics of the channel may cause a phase shift of the signal, reflecting the environmental impact the signal is subjected to during transmission.
The receiving end performs down-conversion operation on the damaged pilot signal by accurately measuring the phase offsets and combining the known pilot angular frequency, and converts the high-frequency pilot signal into a baseband signal, which may be achieved by multiplying the received signal (i.e., the damaged distorted pilot signal) with a local oscillation signal, the frequency of which matches the frequency of the pilot signal.
In step S302, the receiving end filters out the high frequency component in the baseband signal through a low-pass filter, and obtains a low-pass filtered pilot signal.
In this process, the receiving end passes the baseband signal through a low pass filter, which attenuates signal components above that frequency according to its preset cut-off frequency, thereby preserving the main characteristics of the signal. After the processing of the low-pass filter, purer signals are obtained, and key information of pilot signals is reserved.
In step S303, the receiving constructs a joint channel estimation matrix based on the low-pass filtered pilot signals with multiple spatial dimensions.
In a space division multiplexing system, signals are transmitted in multiple spatial dimensions, with signals in each dimension potentially being affected by different channels. Therefore, in order to accurately describe the transmission characteristics of the whole channel, the receiving end needs to comprehensively consider information from different spatial dimensions, namely, the construction of a joint channel estimation matrix involves analyzing and processing pilot signals after low-pass filtering of a plurality of spatial dimensions, and the receiving end calculates a matrix capable of reflecting the transmission characteristics of the whole channel according to the characteristics of the amplitude, the phase and the like of the pilot signals, wherein the matrix not only comprises the characteristics of channels of each spatial dimension, but also reflects the mutual influence of signals among different dimensions.
According to the embodiment, through down-conversion and filtering processing, the receiving end can accurately extract key information of the pilot signal from the complex distortion signal, and then a comprehensive and accurate joint channel estimation matrix is constructed, based on the matrix, the receiving end can realize cooperative compensation of multi-dimensional inter-channel crosstalk, frequency offset and phase noise, and the recovery quality of the signal and the overall performance of the system are effectively improved.
In one implementation, the step S20 may include that the transmitting end modulates the transmitting signal based on a transmitting end light source phase noise model, and determines a modulated signal, where the transmitting end light source phase noise model is a model constructed according to a transmitting end carrier frequency and a phase noise of a transmitting end independent laser, and the receiving end obtains a distortion signal by beating the modulated signal and a receiving end local oscillation light based on a channel transmission matrix.
In fiber optic communications, a laser acts as a carrier source for a signal, and its phase noise is a random fluctuation in the phase of the laser output signal. The emitting end light source phase noise model is built to accurately describe the influence of laser phase noise on signals, and is built based on the carrier frequency of the emitting end (namely the center frequency of the laser emitting signal) and the phase noise characteristic of the emitting end independent laser.
In the modulation process, the transmitting end carries out preprocessing on the transmitting signal, including coding and modulation format selection, then calculates the predicted value of phase noise according to the phase noise model of the transmitting end light source, and introduces opposite phase adjustment in the signal to pre-compensate the influence of the phase noise. Further, the modulated signal is converted into an optical signal by an electro-optical modulator and sent to a receiving end through a fiber channel.
It should be noted that the channel transmission matrix is a mathematical model for describing the transmission characteristics of signals in a communication channel, including attenuation, phase change, etc., and beat frequency refers to the generation of a new signal (i.e., a distorted signal) by mixing a received signal with a signal generated by a local oscillator (local oscillator light), where the frequency of the new signal is the difference between the frequencies of the two signals.
In one embodiment, before the step of obtaining the distortion signal by beating the modulated signal and the local oscillation light of the receiving end based on the channel transmission matrix, the receiving end may further include the transmitting end transmitting the modulated signal by using an independent laser as a carrier of the transmitting end, where the receiving end uses another independent laser as the local oscillation light of the receiving end.
In the signal compensation system, a transmitting end and a receiving end respectively use independent lasers to complete the transmitting and receiving processes of signals. The transmitting end generates a transmitting end carrier wave through an independent laser, the carrier wave is a carrier for signal transmission, the frequency and phase characteristics of the carrier wave directly influence the quality and transmission performance of signals, the transmitting end loads the modulated signals on the carrier wave and then transmits the modulated signals through an optical fiber channel, so that the transmitting end can flexibly control the transmitting characteristics of the signals, and meanwhile, the modulating and processing of the signals are facilitated. The receiving end can accurately control the beat frequency process by using an independent laser as local oscillation light, so as to ensure correct demodulation and recovery of signals.
According to the embodiment, the signal is modulated based on the transmitting end light source phase noise model at the transmitting end, so that signal distortion caused by the transmitting end laser phase noise can be compensated in advance, the phase and frequency characteristics of the signal are more stable after the signal is transmitted through the optical fiber channel, and the error rate and the signal distortion caused by the phase noise are reduced. Meanwhile, the receiving end can recover the original signal more accurately through beat frequency operation with the local oscillation light, and demodulation performance of the signal can be effectively improved even if channel damage and interference exist.
It should be noted that the foregoing examples are only for understanding the present application, and are not meant to limit the signal compensation method of the present application, and more forms of simple transformation based on the technical concept are all within the scope of the present application.
The foregoing is only a part of embodiments of the present application, and is not intended to limit the scope of the present application, and all equivalent structural changes made by the description of the present application and the accompanying drawings or direct/indirect application in other related technical fields are included in the scope of the present application.
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