WO2017198111A1 - 一种频偏估计方法、装置及计算机存储介质 - Google Patents

一种频偏估计方法、装置及计算机存储介质 Download PDF

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WO2017198111A1
WO2017198111A1 PCT/CN2017/084082 CN2017084082W WO2017198111A1 WO 2017198111 A1 WO2017198111 A1 WO 2017198111A1 CN 2017084082 W CN2017084082 W CN 2017084082W WO 2017198111 A1 WO2017198111 A1 WO 2017198111A1
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signal
value
index
unit
frequency offset
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PCT/CN2017/084082
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English (en)
French (fr)
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姚扬中
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深圳市中兴微电子技术有限公司
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/60—Receivers
    • H04B10/61—Coherent receivers
    • H04B10/616—Details of the electronic signal processing in coherent optical receivers
    • H04B10/6164—Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
    • H04L27/22—Demodulator circuits; Receiver circuits
    • H04L27/223—Demodulation in the optical domain

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  • the present invention relates to frequency offset processing techniques in optical communications, and more particularly to a frequency offset estimation method and apparatus and computer storage medium.
  • digital coherence technology is generally used to solve the above problems.
  • digital coherence technology can tolerate lower optical signal-to-noise ratio, such as: optical signal-to-noise ratio gain of about 3dB; electrical equalization technology can be used to cope with channel changes, which can reduce costs, etc.; Modulation technology and polarization multiplexing technology to increase transmission capacity. Since these advantages of digital coherence technology can meet the needs of next-generation optical communication networks for higher single-wavelength rates and higher spectral efficiency, digital coherence technology is considered to be a key technology for high-speed optical communication systems.
  • the received optical signal is mixed with the optical signal generated by the local oscillator laser, and then photoelectrically converted to obtain a baseband electrical signal, the baseband electrical signal reflecting the signal optical field envelope; thereafter, the baseband The electrical signal is sampled and quantized and digitally processed to recover The original send signal.
  • the frequency of the laser in the transmitter cannot be completely consistent with the frequency of the laser in the receiver. Therefore, the baseband electrical signal may have a non-zero intermediate frequency, that is, a frequency difference or a frequency offset. Therefore, the frequency offset in the coherent optical receiver must be estimated and then controlled or compensated.
  • Figure 1 shows a typical correlation frequency offset estimation device that estimates the existing frequency offset based on a correlation method.
  • the complex signal entering the frequency difference monitor is divided into two paths, which are respectively connected to a register and a multiplier, wherein the register and the complex conjugater delay and conjugate the complex signal to obtain a delay. a subsequent conjugate signal, and outputting the delayed conjugate signal to the other input of the multiplier; after that, the multiplier multiplies the complex signal by the delayed conjugate signal and outputs the result to the fourth power square This process removes the effect of signal phase noise on frequency offset monitoring.
  • the fourth power is used to perform a quadratic operation on the signal output from the multiplier, and the result is output to the summer; wherein the summer acts as an averager, which can reduce the additive noise to estimate the frequency offset. Impact.
  • the output of the summer is operated by a quarter-angler to take a quarter-amplitude operation, and a frequency offset estimation signal is output; the frequency offset estimation signal is a signal phase increment caused by the frequency offset in one sampling period. .
  • the magnitude of the register delay amount D affects the measurement result of the frequency offset estimation, and when D is equal to 1, it is large.
  • the D value is switched from small to large, which will result in a frequency offset estimation blur, resulting in an output error frequency offset estimation result. It can be seen that the switching control of the D value is complicated, and it is difficult to achieve both large-scale and high-precision frequency offset estimation.
  • embodiments of the present invention are expected to provide a frequency offset estimation method, apparatus, and computer storage medium, which can effectively solve the problem of large range and high precision of frequency offset estimation.
  • An embodiment of the present invention provides a frequency offset estimation method, where the method includes:
  • the method before performing the Fourier transform on the input signal, the method further comprises: performing a fourth power operation on the input signal to convert the input signal into a fourth power signal.
  • the input signal is a signal obtained by equalizing and filtering the digital baseband electrical signal.
  • the performing low pass filtering comprises: performing low pass filtering by using a weighted average filter or a first order Infinite Impulse Response (IIR) digital filter.
  • IIR Infinite Impulse Response
  • the processing operation comprises: a modulo square operation, or an absolute value operation; and correspondingly, the processed signal is a modulo squared signal, or an absolute value signal.
  • the method further comprises dividing the corrected maximum value index value by four times the value of the Fourier transform point number as a signal phase increment caused by the frequency offset in one sampling period.
  • An embodiment of the present invention further provides a frequency offset estimation apparatus, where the apparatus includes: a Fourier transform unit, a processing unit, a low pass filtering unit, a maximum index calculation unit, and an interpolation unit;
  • the Fourier transform unit is configured to perform a Fourier transform on the input signal to obtain a frequency domain signal, and output the signal to the processing unit;
  • the processing unit is configured to perform processing on the frequency domain signal to obtain a processed signal, and output the signal to the low pass filtering unit;
  • the low pass filtering unit is configured to perform low pass filtering on the processed signal to obtain a filtered signal, and output the signal to the maximum value index calculating unit and the interpolation unit;
  • the maximum value index calculation unit is configured to calculate an index of a frequency point corresponding to a maximum value of the filtered signal, and output the index to the interpolation unit;
  • the interpolation unit is configured to obtain a value of a neighboring position of the maximum value index according to the value of the maximum index position, and perform interpolation operation on all the obtained values to obtain a corrected maximum value index value.
  • the apparatus further includes: a signal quadratic unit configured to perform a fourth power operation on the input signal before the Fourier transform unit performs a Fourier transform on the input signal, the input signal Transform to a fourth power signal.
  • the input signal is a signal obtained by equalizing and filtering the digital baseband electrical signal.
  • the performing low pass filtering comprises: performing low pass filtering using a weighted average filter, or a first order IIR digital filter.
  • the processing operation comprises: a modulo square operation, or an absolute value operation; and correspondingly, the processed signal is a modulo squared signal, or an absolute value signal.
  • the interpolation unit is further configured to divide the corrected maximum value index value by four times the value of the Fourier transform point number as a signal phase increment caused by the frequency offset in one sampling period.
  • the embodiment of the present invention further provides a computer storage medium, where the computer storage medium stores computer executable instructions, and the computer executable instructions are used to execute the embodiment of the present invention.
  • the frequency offset estimation method is a method that uses computer executable instructions to calculate the frequency offset of the present invention.
  • the frequency offset estimation method and device and the computer storage medium provided by the embodiments of the present invention obtain a frequency domain signal after performing Fourier transform on the input signal; processing the frequency domain signal to obtain a processed signal, and obtaining the processed signal
  • the processed signal is subjected to low-pass filtering; the index of the frequency point corresponding to the maximum value of the filtered signal is calculated, and the value of the adjacent position of the maximum index is obtained according to the value of the maximum index position; and all the obtained values are interpolated to obtain The corrected maximum index value.
  • the frequency domain method can effectively solve the large-scale and high-precision problem of the frequency offset estimation; in addition, the frequency offset estimation method, device, and computer storage medium in the embodiment of the present invention do not include any complex multiplication operation, thereby greatly reducing the algorithm. the complexity.
  • FIG. 1 is a schematic structural diagram of a conventional correlation frequency offset estimation apparatus
  • FIG. 2 is a schematic flowchart of an implementation process of a frequency offset estimation method according to an embodiment of the present invention
  • FIG. 3 is a schematic flowchart of a specific implementation process of a frequency offset estimation method according to an embodiment of the present invention
  • FIG. 4 is a schematic structural diagram of a frequency offset estimation apparatus according to an embodiment of the present invention.
  • the signals received by the digital coherent optical receiver can be modulated by various modulation methods, for example, Binary Phase Shift Keying (BPSK) modulation, quadrature phase shift keying (QPSK). , Quadrature Phase Shift Keying) modulation, eight phase shift keying (8-PSK, 8 Phase Shift Keying) modulation.
  • BPSK Binary Phase Shift Keying
  • QPSK quadrature phase shift keying
  • 8-PSK 8 Phase Shift Keying
  • the present invention is applicable to all of the above modulation methods.
  • the embodiments of the present invention are directed to a digital coherent optical receiver using only polarization multiplexing-quadrature phase shift keying (PM-QPSK, Polarization) in QPSK modulation.
  • the modulation method of Multiplexing four Phase Shift Keying is described in detail at a rate of 128 Gb/s.
  • the optical signal received by the digital coherent optical receiver is photoelectrically converted to obtain a baseband electrical signal, and after equalization and polarization demultiplexing of the baseband electrical signal, two signals appear: an x-polarized signal and a y-polarized signal.
  • the frequency of the laser in the transmitter cannot be completely consistent with the frequency of the laser in the receiver, so that the two polarization signals output by the equalizer may have a certain frequency offset. Therefore, it is necessary to separately perform frequency offset estimation on the x-polarization and y-polarization signals, or perform frequency offset estimation on only one of the polarization signals, and then supply the frequency offset estimation result of the path to another polarization signal.
  • the embodiment of the present invention describes frequency offset estimation of any one of the polarized signals.
  • the implementation process of the frequency offset estimation method in the embodiment of the present invention includes the following steps:
  • Step 201 After performing a Fourier transform on the input signal, obtaining a frequency domain signal;
  • the method further includes: performing a fourth power operation on the input signal to convert the input signal into a fourth power signal.
  • the input signal is a signal obtained by equalizing and filtering the digital baseband electrical signal, and the parallelism of the equalized filtered signal is 64; the quadratic operation of the input signal is performed to remove the original modulation phase information of the data.
  • the frequency offset of the complex signal has also become four times the original.
  • the equalized filtered input signal belongs to the time domain signal
  • the signal is analyzed directly in the time domain.
  • time domain analysis sometimes the time domain parameters of some signals are the same, but these signals cannot be explained. It's exactly the same.
  • the signal changes not only with time, but also with parameters such as frequency and phase, it is necessary to transform the time domain signal into a frequency domain signal and further analyze the signal through the spectrogram.
  • FFT Fast Fourier Transform
  • DFT Discrete Fourier Transform
  • Step 202 Perform processing operations on the frequency domain signal to obtain a processed signal, and perform low-pass filtering on the processed signal.
  • the processing operation includes: a modulo square operation, or an absolute value operation; correspondingly, the processed signal is a modulo square signal, or an absolute value signal.
  • the value of the multiple inputs of each frequency point of the processed signal is low-pass filtered to obtain a filtered signal, which is output to the maximum value index calculation unit, and the filtered signal is also output to the interpolation unit.
  • the purpose of performing low-pass filtering on the processed signal is to smooth filter the values of multiple inputs, thereby reducing the influence of noise on the frequency offset estimation.
  • a simple weighted averaging filter or a first order IIR digital filter can be used for low pass filtering.
  • Step 203 Calculate an index of a frequency point corresponding to a maximum value of the filtered signal, and obtain a value of a position adjacent to the maximum index according to a value of the maximum index position;
  • Step 204 Perform interpolation on all the obtained values to obtain a corrected maximum index value.
  • two values of the adjacent positions of the maximum value index may be obtained according to the value of the maximum index position, and then the obtained three values are interpolated to obtain the corrected maximum index value.
  • the present invention does not specifically limit the method for obtaining the corrected maximum index value.
  • the method further comprises: dividing the corrected maximum value index value by four times the value of the Fourier transform point number as the signal phase increment caused by the frequency offset in one sampling period.
  • a specific implementation process of the frequency offset estimation method in the embodiment of the present invention includes the following steps:
  • Step 301 performing a fourth power operation on the input signal to obtain a fourth power signal
  • Step 302 After performing FFT on the fourth power signal, obtaining a frequency domain signal
  • time domain signal can be transformed into a frequency domain signal by the following Fourier transform formula:
  • k is the frequency domain variable after two-dimensional discrete Fourier transform of the signal image
  • x(n) is the input signal
  • X(k) For the Fourier transform results.
  • w N recorded as w N is a simplified method for the corresponding parameters in the two-dimensional discrete Fourier transform formula
  • J is the imaginary unit
  • j 2 -1.
  • Step 303 Perform a modulo square operation on the frequency domain signal X(k) to obtain a modular squared signal S(k), and perform low-pass filtering on the modular squared signal S(k);
  • the modular squared signal S(k) can be obtained by using the following modular squared operation formula:
  • k is the frequency domain variable after two-dimensional discrete Fourier transform of the signal image
  • X(k) is the result of Fourier transform, which is a complex
  • the signal, real(X(k)) 2 is the result of squaring the real part of the complex signal, imag(X(k)) 2 is the result of squaring the imaginary part of the complex signal, and S(k) is the modulo squared signal.
  • N is a positive integer representing the number of Fourier transform points
  • k is the frequency domain variable after the two-dimensional discrete Fourier transform of the signal image.
  • Step 304 Calculate an index of a frequency point corresponding to a maximum value of the filtered modular square signal, according to The value of the maximum index position, and obtain the value of the adjacent position of the maximum index;
  • Step 305 Perform interpolation operations on all the obtained values to obtain a corrected maximum index value
  • the k 'value is adjusted to max range [-N / 2, N / 2 ) can, if k' max ⁇ N / 2, then k 'max subtracting the maximum value of the index N is corrected.
  • Step 306 Dividing the corrected maximum value index value by four times the value of the Fourier transform point number as a signal phase increment caused by the frequency offset in one sampling period.
  • the method does not include any complex multiplication operation, which greatly reduces the complexity of the algorithm.
  • this method can achieve the monitoring of any large frequency offset.
  • the existing method based on correlation method for frequency offset estimation in order to simultaneously consider large-scale frequency offset estimation and high-precision frequency offset estimation, it is not necessary to gradually switch the correlation interval D value, but adopt the frequency domain method to perform frequency domain frequency.
  • the partial estimation not only simplifies the complexity of the algorithm, but also achieves a large range of frequency offset estimation, and at the same time, can accurately estimate the frequency offset.
  • an embodiment of the present invention further provides a frequency offset estimating apparatus.
  • the apparatus includes a Fourier transform unit 41, a processing unit 42, a low pass filtering unit 43, and a maximum index calculating unit 44.
  • Interpolation unit 45 As shown in FIG. 4, the apparatus includes a Fourier transform unit 41, a processing unit 42, a low pass filtering unit 43, and a maximum index calculating unit 44. Interpolation unit 45; wherein
  • the Fourier transform unit 41 is configured to perform a Fourier transform on the input signal to obtain a frequency domain signal, and output the signal to the processing unit 42;
  • the processing unit 42 is configured to perform a processing operation on the frequency domain signal to obtain a processed signal, and output the signal to the low pass filtering unit 43;
  • the low pass filtering unit 43 is configured to perform low pass filtering on the processed signal to obtain a filtered signal, and output the signal to the maximum value index calculating unit 44 and the interpolation unit 45;
  • the maximum value index calculation unit 44 is configured to calculate an index of the frequency point corresponding to the maximum value of the filtered signal, and output to the interpolation unit 45;
  • the interpolation unit 45 is configured to acquire the value of the adjacent position of the maximum value index according to the value of the maximum index position, and perform interpolation operation on all the obtained values to obtain the corrected maximum index value.
  • the interpolation unit 45 is further configured to divide the corrected maximum value index value by four times the value of the Fourier transform point number as the signal phase increment caused by the frequency offset in one sampling period.
  • the apparatus further includes: a signal quadratic unit 46 configured to perform a fourth power operation on the input signal before the Fourier transform unit 41 performs Fourier transform on the input signal, and convert the input signal into Fourth power signal.
  • a signal quadratic unit 46 configured to perform a fourth power operation on the input signal before the Fourier transform unit 41 performs Fourier transform on the input signal, and convert the input signal into Fourth power signal.
  • the input signal is a signal obtained by equalizing and filtering the digital baseband electrical signal.
  • a weighted averaging filter, or a first-order IIR digital filter may be used for low-pass filtering; the processing operation includes: a modulo square operation, or an absolute value operation; accordingly, the processed signal is a modulo square signal, Or absolute value signal.
  • the Fourier transform unit 41, the processing unit 42, the low pass filtering unit 43, the maximum value index calculating unit 44, the interpolation unit 45, and the signal quadratic unit 46 may all be located by the frequency offset estimating device or the frequency.
  • a frequency domain signal is obtained; the frequency domain signal is processed and processed to obtain a processed signal, and the processed signal is low-passed. Filtering; calculating an index of a frequency point corresponding to the maximum value of the filtered signal, obtaining a value of a position adjacent to the maximum index according to the value of the maximum index position; performing interpolation on all the obtained values to obtain a corrected maximum index value.
  • the frequency domain method can effectively solve the large-scale and high-precision problem of the frequency offset estimation.
  • the frequency offset estimation method and apparatus in the embodiment of the present invention does not include any complex multiplication operation, thereby greatly reducing the algorithm complexity.
  • Embodiments of the present invention also describe a computer storage medium storing one or more programs, the one or more programs being executable by one or more processors to implement the following steps:
  • the one or more programs may be executed by the one or more processors to implement the following steps:
  • the input signal is subjected to a quadratic operation to convert the input signal into a fourth power signal.
  • the input signal is a signal obtained by equalizing and filtering the digital baseband electrical signal.
  • performing the low pass filtering comprises: performing low pass filtering by using a weighted average filter or a first order infinite impulse response IIR digital filter.
  • the processing operation includes: a modulo square operation, or an absolute value operation; correspondingly, the processed signal is a modulo square signal, or an absolute value signal.
  • the one or more programs may also be executed by the one or more processors to implement the following steps:
  • the corrected maximum value index value is divided by four times the value of the Fourier transform point number as the signal phase increment caused by the frequency offset in one sampling period.
  • embodiments of the present invention can be provided as a method, system, or computer program product. Accordingly, the present invention can take the form of a hardware embodiment, a software embodiment, or a combination of software and hardware. Moreover, the invention can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage and optical storage, etc.) including computer usable program code.
  • the computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture comprising the instruction device.
  • the apparatus implements the functions specified in one or more blocks of a flow or a flow and/or block diagram of the flowchart.
  • These computer program instructions can also be loaded onto a computer or other programmable data processing device such that a series of operational steps are performed on a computer or other programmable device to produce computer-implemented processing for execution on a computer or other programmable device.
  • the instructions are provided to implement the work specified in one or more blocks of a flow or a flow and/or a block diagram of the flowchart The steps that can be made.
  • the technical solution of the embodiment of the present invention performs a Fourier transform on the input signal to obtain a frequency domain signal; performs processing on the frequency domain signal to obtain a processed signal, and performs low-pass filtering on the processed signal;
  • the index of the frequency point corresponding to the maximum value of the signal is obtained according to the value of the maximum index position, and the value of the adjacent position of the maximum value index is obtained; and all the obtained values are interpolated to obtain the corrected maximum index value.
  • the frequency domain method can effectively solve the problem of large-scale and high-precision frequency offset estimation.
  • the technical solution of the embodiment of the present invention does not include any complex multiplication operation, thereby greatly reducing the algorithm complexity.

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Abstract

本发明实施例公开了一种频偏估计方法，包括：对输入信号进行傅立叶变换后，得到频域信号；将所述频域信号进行处理运算，得到处理后信号，并对所述处理后信号进行低通滤波；计算滤波后信号的最大值所对应频点的索引，根据最大值索引位置的值，获取最大值索引相邻位置的值；对获取的所有值进行插值运算，得到修正后的最大值索引值。本发明实施例还同时公开了一种频偏估计装置及计算机存储介质。

Description

一种频偏估计方法、装置及计算机存储介质
相关申请的交叉引用
本申请基于申请号为201610324172.3、申请日为2016年05月16日的中国专利申请提出，并要求该中国专利申请的优先权，该中国专利申请的全部内容在此引入本申请作为参考。
技术领域
本发明涉及光通信中的频偏处理技术，尤其涉及一种频偏估计方法和装置及计算机存储介质。
背景技术
随着互联网流量的不断增加，在干线光通信系统中需要更大的容量。然而，当载波以每波长比特率增加时，在传输路径上的色度色散、偏振色散、以及各种非线性效应的波形失真，会导致信息质量的退化变得更加严重。
目前，一般采用数字相干技术来解决上述问题。与非相干技术相比，数字相干技术可以容忍更低的光信噪比，比如：3dB左右的光信噪比增益；可采用电均衡技术来应对信道变化，可降低成本等；可采用更高效的调制技术、以及偏振复用技术来提高传输容量。由于数字相干技术的这些优点能够满足下一代光通信网对更高单波长速率和更高频谱效率的需求，因此，数字相干技术被认为是高速光通信系统的关键技术。
在相干光接收机中，接收到的光信号与本振激光器产生的光信号进行混频，然后经光电变换得到基带电信号，该基带电信号可反映信号光电场包络；之后，对该基带电信号进行采样量化和数字信号处理，最终可恢复 出原始发送信号。但在实际应用中，发射机中激光器的频率与接收机中激光器的频率不能保持完全一致，因而，基带电信号会存在非零中频，即频差或称为频偏。因此，必须对相干光接收机中的频偏进行估计，进而对其进行控制或补偿。
图1给出了一种典型的相关法频偏估计装置，该装置是基于相关的方法，对现有频偏进行估计。如图1所示，将进入频差监测器的复信号分成两路，分别连接到寄存器和乘法器，其中，寄存器和取复共轭器对复信号进行延时、共轭处理后，得到延迟后的共轭信号，并将延迟后的共轭信号输出至乘法器的另一个输入端；之后，乘法器将复信号与延迟后的共轭信号相乘，并将结果输出给四次方器，这个过程去除了信号相位噪声对频偏监测的影响。接着，四次方器将对乘法器输出的信号进行四次方运算，并将结果输出给求和器；其中，求和器的作用相当于平均器，可以减小加性噪声对频偏估计的影响。最后，由1/4辐角器对求和器的输出结果进行取1/4辐角操作，并输出频偏估计信号；该频偏估计信号为频偏在一个采样周期内引起的信号相位增量。
上述现有的频偏估计方法，虽然能在一定程度上对载波频偏进行估计，但尚且存在一些问题：寄存器延迟量D的大小影响频偏估计的测量结果，当D等于1时，为大的相关间隔，此时频偏估计范围大，但估计精度较低；当D增大时，为小的相关间隔，此时估计精度有所提高，但频偏估计范围变小。因此，为了同时兼顾大范围与高精度频偏估计，通常先以D＝1开始工作，当频偏估计收敛到一定精度时，增大D的值。若频偏估计精度达不到预设精度值时，则将D值由小切换到大，这样会带来频偏估计模糊，导致输出错误的频偏估计结果。可见，D值的切换控制比较复杂，进而实现同时兼顾大范围与高精度频偏估计较为困难。
发明内容
有鉴于此，本发明实施例期望提供一种频偏估计方法、装置及计算机存储介质，能够有效解决频偏估计的大范围与高精度问题。
为达到上述目的，本发明实施例的技术方案是这样实现的：
本发明实施例提供一种频偏估计方法，所述方法包括：
对输入信号进行傅立叶变换后，得到频域信号；
将所述频域信号进行处理运算，得到处理后信号，并对所述处理后信号进行低通滤波；
计算滤波后信号的最大值所对应频点的索引，根据最大值索引位置的值，获取最大值索引相邻位置的值；
对获取的所有值进行插值运算，得到修正后的最大值索引值。
在一实施例中，在所述对输入信号进行傅立叶变换之前，所述方法还包括：对所述输入信号进行四次方运算，将所述输入信号变换为四次方信号。
在一实施例中，所述输入信号为将数字基带电信号进行均衡滤波后的信号。
在一实施例中，所述进行低通滤波包括：采用加权平均滤波器、或一阶无限脉冲响应(IIR，Infinite Impulse Response)数字滤波器进行低通滤波。
在一实施例中，所述处理运算包括：模平方运算、或取绝对值运算；相应地，所述处理后信号为模平方信号、或绝对值信号。
在一实施例中，所述方法还包括：将所述修正后的最大值索引值除以四倍的傅立叶变换点数的值，作为频偏在一个采样周期内引起的信号相位增量。
本发明实施例还提供一种频偏估计装置，所述装置包括：傅立叶变换单元、处理单元、低通滤波单元、最大值索引计算单元、插值单元；其中，
所述傅立叶变换单元，配置为对输入信号进行傅立叶变换后，得到频域信号，并输出给所述处理单元；
所述处理单元，配置为将所述频域信号进行处理运算，得到处理后信号，并输出给所述低通滤波单元；
所述低通滤波单元，配置为对所述处理后信号进行低通滤波，得到滤波后信号，并输出给所述最大值索引计算单元和所述插值单元；
所述最大值索引计算单元，配置为计算所述滤波后信号的最大值所对应频点的索引，并输出给所述插值单元；
所述插值单元，配置为根据最大值索引位置的值，获取最大值索引相邻位置的值，并对获取的所有值进行插值运算，得到修正后的最大值索引值。
在一实施例中，所述装置还包括：信号四次方单元，配置为在所述傅立叶变换单元对输入信号进行傅立叶变换之前，对所述输入信号进行四次方运算，将所述输入信号变换为四次方信号。
在一实施例中，所述输入信号为将数字基带电信号进行均衡滤波后的信号。
在一实施例中，所述进行低通滤波包括：采用加权平均滤波器、或一阶IIR数字滤波器进行低通滤波。
在一实施例中，所述处理运算包括：模平方运算、或取绝对值运算；相应地，所述处理后信号为模平方信号、或绝对值信号。
在一实施例中，所述插值单元还配置为：将所述修正后的最大值索引值除以四倍的傅立叶变换点数的值，作为频偏在一个采样周期内引起的信号相位增量。
本发明实施例还提供了一种计算机存储介质，所述计算机存储介质中存储有计算机可执行指令，所述计算机可执行指令用于执行本发明实施例 所述的频偏估计方法。
本发明实施例所提供的频偏估计方法、装置及计算机存储介质，对输入信号进行傅立叶变换后，得到频域信号；将所述频域信号进行处理运算，得到处理后信号，并对所述处理后信号进行低通滤波；计算滤波后信号的最大值所对应频点的索引，根据最大值索引位置的值，获取最大值索引相邻位置的值；对获取的所有值进行插值运算，得到修正后的最大值索引值。如此，采用频域方式能够有效解决频偏估计的大范围与高精度问题；另外，本发明实施例的频偏估计方法、装置及计算机存储介质中不包含任何复数乘法运算，进而大大降低了算法复杂度。
附图说明
图1为现有典型的相关法频偏估计装置的组成结构示意图；
图2为本发明实施例频偏估计方法的实现流程示意图；
图3为本发明实施例频偏估计方法的具体实现流程示意图；
图4为本发明实施例频偏估计装置的组成结构示意图。
具体实施方式
为了能够更加详尽地了解本发明实施例的特点与技术内容，下面结合附图对本发明实施例的实现进行详细阐述，所附附图仅供参考说明之用，并非用来限定本发明。
需要说明的是：对于数字相干光接收机接收到的信号，可以采用各种调制方式进行调制，例如：二进制相移键控(BPSK，Binary Phase Shift Keying)调制、正交相移键控(QPSK，Quadrature Phase Shift Keying)调制、八移相键控(8-PSK，8 Phase Shift Keying)调制等。本发明适用于上述所有的调制方式。为了简便，本发明实施例是针对数字相干光接收机仅采用QPSK调制中的偏振复用-四相相移键控(PM-QPSK，Polarization  Multiplexing four Phase Shift Keying)的调制方式进行详细说明，其速率为128Gb/s。
将数字相干光接收机接收到的光信号经过光电变换得到基带电信号，对该基带电信号进行均衡和偏振解复用之后，会出现两路信号：x偏振信号和y偏振信号。由于在实际应用中，发射机中激光器的频率与接收机中激光器的频率不能保持完全一致，从而导致均衡器输出的两路偏振信号都有可能存在一定的频偏。因此，需要对x偏振和y偏振两路信号分别进行频偏估计，或者只对其中任意一路偏振信号进行频偏估计，然后将该路的频偏估计结果供给另一路偏振信号使用。为了方便，本发明实施例描述的是对其中任意一路偏振信号的频偏估计。
如图2所示，本发明实施例中频偏估计方法的实现流程，包括以下步骤：
步骤201：对输入信号进行傅立叶变换后，得到频域信号；
在执行本步骤之前，所述方法还包括：对所述输入信号进行四次方运算，将所述输入信号变换为四次方信号。
其中，所述输入信号为将数字基带电信号进行均衡滤波后的信号，且该均衡滤波后的信号的并行度为64；对输入信号进行四次方运算，是为了去除数据原始调制相位信息，不过与此同时复信号的频偏也变为了原来的4倍。
这里，由于均衡滤波后的输入信号属于时域信号，是直接在时间域内对信号进行分析，然而，对信号进行时域分析时，有时一些信号的时域参数相同，但并不能说明这些信号就完全相同。因为信号不仅随时间进行变化，还与频率、相位等参数有关，这就需要将时域信号变换为频域信号，通过频谱图进一步分析该信号。可采用快速傅立叶变换(FFT，Fast Fourier Transform)或离散傅立叶变换(DFT，Discrete Fourier Transform)等方式， 将时域信号变换为频域信号。
步骤202：将所述频域信号进行处理运算，得到处理后信号，并对所述处理后信号进行低通滤波；
其中，所述处理运算包括：模平方运算、或取绝对值运算；相应地，所述处理后信号为模平方信号、或绝对值信号。
这里，对所述处理后信号的每个频点的多次输入的值进行低通滤波，得到滤波后信号，并输出给最大值索引计算单元，同时还将滤波后信号输出给插值单元。
其中，对所述处理后信号进行低通滤波的目的在于：对多次输入的值进行平滑滤波，从而减小噪声对频偏估计的影响。
这里，可选用简单的加权平均滤波器、或一阶IIR数字滤波器进行低通滤波。
步骤203：计算滤波后信号的最大值所对应频点的索引，根据最大值索引位置的值，获取最大值索引相邻位置的值；
这里，具体如何计算滤波后信号的最大值所对应频点的索引属于现有技术，这里不再一一赘述。
步骤204：对获取的所有值进行插值运算，得到修正后的最大值索引值。
这里，可以根据最大值索引位置的值，获取最大值索引相邻位置的两个值，然后对获取的三个值进行插值运算，以得到修正后的最大值索引值。当然，对于采取哪种方式获得修正后的最大值索引值，本发明不做具体限定。
具体如何进行插值运算属于现有技术，这里不再一一赘述。
在执行本步骤之后，所述方法还包括：将所述修正后的最大值索引值除以四倍的傅立叶变换点数的值，作为频偏在一个采样周期内引起的信号相位增量。
下面对本发明提供的采用频域方式进行频偏估计的具体实现过程作进一步详细介绍：
如图3所示，本发明实施例中频偏估计方法的具体实现流程，包括以下步骤：
步骤301：对输入信号进行四次方运算，得到四次方信号；
步骤302：对所述四次方信号进行FFT后，得到频域信号；
其中，可以通过如下傅立叶变换公式将时域信号变换为频域信号：
Figure PCTCN2017084082-appb-000001
其中，k＝0，…，N-1，N为正整数，表示傅立叶变换点数，k为信号图像进行二维离散傅立叶变换后的频域变量，x(n)为输入信号，X(k)为傅立叶变换结果。另外，
Figure PCTCN2017084082-appb-000002
可用wN来表示，记为
Figure PCTCN2017084082-appb-000003
wN为二维离散傅立叶变换公式中对应参数的简化写法，
Figure PCTCN2017084082-appb-000004
中的j为虚单位，j2＝-1。
步骤303：将所述频域信号X(k)进行模平方运算，得到模平方信号S(k)，并对所述模平方信号S(k)进行低通滤波；
这里，可采用如下的模平方运算公式得到模平方信号S(k)：
S(k)＝real(X(k))2+imag(X(k))2
其中，k＝0，…，N-1，N为正整数，表示傅立叶变换点数，k为信号图像进行二维离散傅立叶变换后的频域变量，X(k)为傅立叶变换结果，是一复信号，real(X(k))2为对复信号的实部进行平方的结果，imag(X(k))2为对复信号的虚部进行平方的结果，S(k)为模平方信号。
这里，可选用简单的加权平均滤波器、或一阶IIR数字滤波器进行低通滤波。将低通滤波后的结果记为：
Figure PCTCN2017084082-appb-000005
N为正整数，表示傅立叶变换点数，k为信号图像进行二维离散傅立叶变换后的频域变量。
步骤304：计算滤波后的模平方信号的最大值所对应频点的索引，根据 最大值索引位置的值，获取最大值索引相邻位置的值；
这里，将最大值索引记为kmax，则
Figure PCTCN2017084082-appb-000006
步骤305：对获取的所有值进行插值运算，得到修正后的最大值索引值；
为方便描述，假设获取最大值索引相邻位置的两个值，然后对获取的三个值进行插值运算，将修正后的最大值索引值记为k'max，具体可通过如下公式计算得到k'max：
Figure PCTCN2017084082-appb-000007
这里，将k'max的值调整到区间[-N/2，N/2)即可，若k'max≥N/2，则将k'max减去N得到修正后的最大值索引值。
步骤306：将所述修正后的最大值索引值除以四倍的傅立叶变换点数的值，作为频偏在一个采样周期内引起的信号相位增量。
通过上述本发明实施例中频偏估计方法的实现流程可以看出，该方法不包含任何复数乘法运算，大大降低了算法复杂度。从理论上而言，该方法能够实现任意大频偏的监测。相比现有的基于相关法进行频偏估计的方法，为同时兼顾大范围频偏估计与高精度频偏估计，不需要逐步切换相关间隔D值，而是采用频域方法，进行频域频偏估计，不仅简化了算法的复杂度，还达到了频偏估计范围大，同时又能高精度估计频偏的效果。
为实现上述方法，本发明实施例还提供了一种频偏估计装置，如图4所示，该装置包括傅立叶变换单元41、处理单元42、低通滤波单元43、最大值索引计算单元44、插值单元45；其中，
所述傅立叶变换单元41，配置为对输入信号进行傅立叶变换后，得到频域信号，并输出给所述处理单元42；
所述处理单元42，配置为将所述频域信号进行处理运算，得到处理后信号，并输出给所述低通滤波单元43；
所述低通滤波单元43，配置为对所述处理后信号进行低通滤波，得到滤波后信号，并输出给所述最大值索引计算单元44和所述插值单元45；
所述最大值索引计算单元44，配置为计算所述滤波后信号的最大值所对应频点的索引，并输出给所述插值单元45；
所述插值单元45，配置为根据最大值索引位置的值，获取最大值索引相邻位置的值，并对获取的所有值进行插值运算，得到修正后的最大值索引值。
其中，所述插值单元45还配置为：将所述修正后的最大值索引值除以四倍的傅立叶变换点数的值，作为频偏在一个采样周期内引起的信号相位增量。
这里，所述装置还包括：信号四次方单元46，配置为在所述傅立叶变换单元41对输入信号进行傅立叶变换之前，对所述输入信号进行四次方运算，将所述输入信号变换为四次方信号。
其中，所述输入信号为将数字基带电信号进行均衡滤波后的信号。
这里，可采用加权平均滤波器、或一阶IIR数字滤波器进行低通滤波；所述处理运算包括：模平方运算、或取绝对值运算；相应地，所述处理后信号为模平方信号、或绝对值信号。
在实际应用中，所述傅立叶变换单元41、处理单元42、低通滤波单元43、最大值索引计算单元44、插值单元45、信号四次方单元46均可由位于频偏估计装置或所述频偏估计装置所属设备中的中央处理器(CPU，Central Processing Unit)、微处理器(MPU，Micro Processor Unit)、数字信号处理器(DSP，Digital Signal Processor)、或现场可编程门阵列(FPGA，Field Programmable Gate Array)等实现。
本发明实施例对输入信号进行傅立叶变换后，得到频域信号；将所述频域信号进行处理运算，得到处理后信号，并对所述处理后信号进行低通 滤波；计算滤波后信号的最大值所对应频点的索引，根据最大值索引位置的值，获取最大值索引相邻位置的值；对获取的所有值进行插值运算，得到修正后的最大值索引值。如此，采用频域方式能够有效解决频偏估计的大范围与高精度问题；另外，本发明实施例的频偏估计方法和装置中不包含任何复数乘法运算，进而大大降低了算法复杂度。
本发明实施例还记载了一种计算机存储介质，所述计算机存储介质存储有一个或者多个程序，所述一个或者多个程序可被一个或者多个处理器执行，以实现以下步骤：
对输入信号进行傅立叶变换后，得到频域信号；
将所述频域信号进行处理运算，得到处理后信号，并对所述处理后信号进行低通滤波；
计算滤波后信号的最大值所对应频点的索引，根据最大值索引位置的值，获取最大值索引相邻位置的值；
对获取的所有值进行插值运算，得到修正后的最大值索引值。
作为一种实施方式，在所述对输入信号进行傅立叶变换的步骤之前，所述一个或者多个程序还可被所述一个或者多个处理器执行，以实现以下步骤：
对所述输入信号进行四次方运算，将所述输入信号变换为四次方信号。
其中，所述输入信号为将数字基带电信号进行均衡滤波后的信号。
其中，所述进行低通滤波包括：采用加权平均滤波器、或一阶无限脉冲响应IIR数字滤波器进行低通滤波。
其中，所述处理运算包括：模平方运算、或取绝对值运算；相应地，所述处理后信号为模平方信号、或绝对值信号。
作为一种实施方式，所述一个或者多个程序还可被所述一个或者多个处理器执行，以实现以下步骤：
将所述修正后的最大值索引值除以四倍的傅立叶变换点数的值，作为频偏在一个采样周期内引起的信号相位增量。
本领域技术人员应当理解，本实施例的计算机存储介质的功能，可参照前述频偏估计方法的相关描述而理解。
本领域内的技术人员应明白，本发明的实施例可提供为方法、系统、或计算机程序产品。因此，本发明可采用硬件实施例、软件实施例、或结合软件和硬件方面的实施例的形式。而且，本发明可采用在一个或多个其中包含有计算机可用程序代码的计算机可用存储介质(包括但不限于磁盘存储器和光学存储器等)上实施的计算机程序产品的形式。
本发明是参照根据本发明实施例的方法、设备(系统)、和计算机程序产品的流程图和/或方框图来描述的。应理解可由计算机程序指令实现流程图和/或方框图中的每一流程和/或方框、以及流程图和/或方框图中的流程和/或方框的结合。可提供这些计算机程序指令到通用计算机、专用计算机、嵌入式处理机或其他可编程数据处理设备的处理器以产生一个机器，使得通过计算机或其他可编程数据处理设备的处理器执行的指令产生用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能的装置。
这些计算机程序指令也可存储在能引导计算机或其他可编程数据处理设备以特定方式工作的计算机可读存储器中，使得存储在该计算机可读存储器中的指令产生包括指令装置的制造品，该指令装置实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功能。
这些计算机程序指令也可装载到计算机或其他可编程数据处理设备上，使得在计算机或其他可编程设备上执行一系列操作步骤以产生计算机实现的处理，从而在计算机或其他可编程设备上执行的指令提供用于实现在流程图一个流程或多个流程和/或方框图一个方框或多个方框中指定的功 能的步骤。
以上所述，仅为本发明的较佳实施例而已，并非用于限定本发明的保护范围，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。
工业实用性
本发明实施例的技术方案对输入信号进行傅立叶变换后，得到频域信号；将所述频域信号进行处理运算，得到处理后信号，并对所述处理后信号进行低通滤波；计算滤波后信号的最大值所对应频点的索引，根据最大值索引位置的值，获取最大值索引相邻位置的值；对获取的所有值进行插值运算，得到修正后的最大值索引值。如此，采用频域方式能够有效解决频偏估计的大范围与高精度问题；另外，本发明实施例的技术方案不包含任何复数乘法运算，进而大大降低了算法复杂度。

Claims (13)

  1. 一种频偏估计方法，所述方法包括：
    对输入信号进行傅立叶变换后，得到频域信号；
    将所述频域信号进行处理运算，得到处理后信号，并对所述处理后信号进行低通滤波；
    计算滤波后信号的最大值所对应频点的索引，根据最大值索引位置的值，获取最大值索引相邻位置的值；
    对获取的所有值进行插值运算，得到修正后的最大值索引值。
  2. 根据权利要求1所述的方法，其中，在所述对输入信号进行傅立叶变换之前，所述方法还包括：对所述输入信号进行四次方运算，将所述输入信号变换为四次方信号。
  3. 根据权利要求2所述的方法，其中，所述输入信号为将数字基带电信号进行均衡滤波后的信号。
  4. 根据权利要求1所述的方法，其中，所述进行低通滤波包括：采用加权平均滤波器、或一阶无限脉冲响应IIR数字滤波器进行低通滤波。
  5. 根据权利要求1所述的方法，其中，所述处理运算包括：模平方运算、或取绝对值运算；相应地，所述处理后信号为模平方信号、或绝对值信号。
  6. 根据权利要求1至5任一项所述的方法，其中，所述方法还包括：将所述修正后的最大值索引值除以四倍的傅立叶变换点数的值，作为频偏在一个采样周期内引起的信号相位增量。
  7. 一种频偏估计装置，所述装置包括：傅立叶变换单元、处理单元、低通滤波单元、最大值索引计算单元、插值单元；其中，
    所述傅立叶变换单元，配置为对输入信号进行傅立叶变换后，得到频域信号，并输出给所述处理单元；
    所述处理单元，配置为将所述频域信号进行处理运算，得到处理后信号，并输出给所述低通滤波单元；
    所述低通滤波单元，配置为对所述处理后信号进行低通滤波，得到滤波后信号，并输出给所述最大值索引计算单元和所述插值单元；
    所述最大值索引计算单元，配置为计算所述滤波后信号的最大值所对应频点的索引，并输出给所述插值单元；
    所述插值单元，配置为根据最大值索引位置的值，获取最大值索引相邻位置的值，并对获取的所有值进行插值运算，得到修正后的最大值索引值。
  8. 根据权利要求7所述的装置，其中，所述装置还包括：信号四次方单元，配置为在所述傅立叶变换单元对输入信号进行傅立叶变换之前，对所述输入信号进行四次方运算，将所述输入信号变换为四次方信号。
  9. 根据权利要求8所述的装置，其中，所述输入信号为将数字基带电信号进行均衡滤波后的信号。
  10. 根据权利要求7所述的装置，其中，所述进行低通滤波包括：采用加权平均滤波器、或一阶IIR数字滤波器进行低通滤波。
  11. 根据权利要求7所述的装置，其中，所述处理运算包括：模平方运算、或取绝对值运算；相应地，所述处理后信号为模平方信号、或绝对值信号。
  12. 根据权利要求7至11任一项所述的装置，其中，所述插值单元还配置为：将所述修正后的最大值索引值除以四倍的傅立叶变换点数的值，作为频偏在一个采样周期内引起的信号相位增量。
  13. 一种计算机存储介质，所述计算机存储介质中存储有计算机可执行指令，所述计算机可执行指令用于执行权利要求1至6任一项所述的频偏估计方法。
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