阅读说明：本技术 解决脉冲幅度调制信号频偏混叠的方法及系统 (Method and system for solving frequency offset aliasing of pulse amplitude modulation signal ) 是由 范芸芸 诸葛群碧 胡卫生 于 2021-05-31 设计创作，主要内容包括：本发明提供了一种解决脉冲幅度调制信号频偏混叠的方法及系统,涉及脉冲幅度调制的混叠信号的频偏估计补偿和相位恢复技术领域,该方法包括：在发射端及脉冲幅度调制信号的载波频谱边缘插入频域导频信号；各载波频谱被调制到不同频段的光域上,载波频谱在光域上耦合复用；在接收端对子载波复用信号解复用,分开处理各个子载波信号,对分开的子载波分别做色散补偿,利用频域导频信号进行频偏估计以及频偏补偿,从分开后的数据里提取出导频信号；对信号进行相位恢复；再对信号进行频域共轭,并镜像翻转恢复混叠受损的信号；对信号进行均衡模块的运算,并解调均衡后的信号。本发明能够易于实现,且使用方便,节省成本,能够克服现有技术的缺陷。(The invention provides a method and a system for solving the frequency offset aliasing of a pulse amplitude modulation signal, which relate to the technical field of frequency offset estimation compensation and phase recovery of the pulse amplitude modulation aliasing signal, and the method comprises the following steps: inserting frequency domain pilot signals at the transmitting end and the edge of a carrier frequency spectrum of the pulse amplitude modulation signal; each carrier spectrum is modulated to an optical domain of different frequency bands, and the carrier spectrums are coupled and multiplexed on the optical domain; demultiplexing the subcarrier multiplexing signals at a receiving end, separately processing each subcarrier signal, respectively performing dispersion compensation on the separated subcarriers, performing frequency offset estimation and compensation by using frequency domain pilot signals, and extracting the pilot signals from the separated data; performing phase recovery on the signal; then, carrying out frequency domain conjugation on the signals, and carrying out mirror image overturning to recover the aliasing damaged signals; and carrying out operation of an equalization module on the signal, and demodulating the equalized signal. The invention is easy to realize, convenient to use, cost-saving and capable of overcoming the defects of the prior art.)

1. A method for resolving frequency offset aliasing of a pulse amplitude modulated signal, comprising:

step S1: inserting frequency domain pilot signals at the transmitting end and the edge of a carrier frequency spectrum of the pulse amplitude modulation signal;

step S2: modulating each carrier spectrum to an optical domain of different frequency bands, uniformly selecting a frequency band at a right side or a left side pilot frequency position between adjacent carrier spectrums to leave a gap which is larger than the maximum frequency offset of the device, and coupling and multiplexing the carrier spectrums on the optical domain;

step S3: demultiplexing the subcarrier multiplexing signals at a receiving end, separately processing each subcarrier signal, respectively performing dispersion compensation on the separated subcarriers, performing frequency offset estimation and compensation by using frequency domain pilot signals, and extracting the pilot signals from the separated data;

step S4: performing phase recovery on the signal by using the phase information of the frequency domain pilot frequency; then, carrying out frequency domain conjugation on the signals, and carrying out mirror image overturning to recover the aliasing damaged signals;

step S5: and carrying out operation of an equalization module on the signal, and demodulating the equalized signal.

2. The method for resolving aliasing in frequency offset of pulse amplitude modulated signal according to claim 1, wherein said step S1 comprises:

step S1.1: the data sent by the sending end is mapped into a pulse amplitude modulation signal by a bit sequence, and root raised cosine pulse shaping is carried out.

3. The method for resolving aliasing in frequency offset of pulse amplitude modulated signal according to claim 1, wherein said step S1 further comprises:

step S1.2: two frequency domain pilot signals are inserted at the two edges, the left edge and the right edge, of the carrier spectrum of the pulse amplitude modulation signal, and the frequency domain pilot signals are expressed as follows:

wherein, C is a constant matrix and represents the amplitude of the frequency domain pilot frequency; Δ f_pThe frequency domain distance from the center of the carrier wave of the frequency domain pilot signal is the frequency domain distance, and the frequency domain pilot frequency is positioned in the frequency spectrum gap at the edge of the carrier wave; fs is the sampling rate; j represents the imaginary symbol; t represents a time series.

4. The method for resolving aliasing in frequency offset of pulse amplitude modulated signal according to claim 1, wherein said step S2 comprises: different transmitting end signals are photoelectrically converted into optical signals for transmission, adjacent optical carriers form a group, the frequency interval of each group needs to ensure that the gap of the frequency domain pilot signal at the opposite side is greater than the maximum frequency offset value of the laser, and the maximum frequency offset value of the laser is recorded as FO_maxThe signals are coupled and multiplexed in the optical domain.

5. The method for resolving aliasing in frequency offset of pulse amplitude modulated signal according to claim 1, wherein said step S3 comprises:

step S3.1: at the receiving end, the individual subcarrier signals are processed separately and are to be processedDown-converting the carrier wave to base frequency, demultiplexing the carrier wave by low-pass filtering, the filtering bandwidth is more than delta f_p+FO_maxAnd performing dispersion compensation on the filtered signal.

6. The method for resolving aliasing in frequency offset of pulse amplitude modulated signal according to claim 1, wherein said step S3 further comprises:

step S3.2: performing FFT (fast Fourier transform) on the subcarrier signals after dispersion compensation, finding a peak value, namely the position of a frequency point where the frequency domain pilot frequency is located, and comparing the position difference of the positions of the frequency domain pilot frequency points inserted into a transmitting end to obtain an estimated value of frequency offset;

carrying out frequency shift and frequency offset recovery on the signal;

extracting frequency domain pilot frequency in carrier wave, wherein the center frequency of filtering is delta f_pThe bandwidth of the filtering is about 300MHz, and the frequency domain pilot frequency energy can not be damaged and the subcarrier signal can not be contained.

7. The method for resolving aliasing in frequency offset of pulse amplitude modulated signal according to claim 1, wherein said step S4 comprises:

step S4.1: the phase noise at the transmitting and receiving ends of the laser represents the sub-carrier after demultiplexing as follows:

wherein S is_tRepresents a modulated baseband signal; t represents a time series; phi (t) represents phase noise; calculating frequency domain pilot signal Pe obtained by shifting frequency after filtering to fundamental frequency^φ(t)And extracting information of the phase noise, and compensating the phase noise for the signal.

8. The method for resolving aliasing in frequency offset of pulse amplitude modulated signal according to claim 1, wherein said step S4 further comprises:

step S4.2: let the time domain of the signal after pulse amplitude modulation be x, and represent it on the frequency domain as:

real part of the frequency domain pulse amplitude modulation signal:

Re(-ω)＝Re(ω)

imaginary part of frequency domain pulse amplitude modulation signal:

Im(-ω)＝-Im(ω)

wherein t represents a time series; j represents the imaginary symbol; ω represents a frequency sequence; the pulse amplitude modulated signal is symmetric about the 0-frequency conjugate in the frequency domain. The conjugate mirror inversion is performed using the unaliased side of the phase recovered signal.

9. The method for resolving aliasing in frequency offset of pulse amplitude modulated signal according to claim 1, wherein said step S5 comprises: for each subcarrier signal, the signal is recovered by an equalization algorithm, and then the pulse amplitude modulation signal symbols are demapped into bit sequences.

10. A system for resolving frequency offset aliasing of a pulse amplitude modulated signal, comprising: a sending end and a receiving end;

wherein, the sending end includes:

the bit mapping module is used for mapping a bit sequence to be sent into a pulse amplitude modulation symbol;

the pulse shaping module is used for shaping the symbol root raised cosine pulse to generate each subcarrier;

the frequency domain pilot frequency inserting module is used for respectively inserting frequency domain pilot frequency signals at the spectrum intervals at two sides of the subcarrier;

the subcarrier multiplexing module is used for multiplexing subcarriers;

and the receiving end includes:

the subcarrier demultiplexing module is used for demultiplexing the subcarriers;

the dispersion compensation module is used for compensating dispersion accumulated by the optical fiber in the transmission process;

the frequency offset estimation compensation module is used for frequency offset estimation and compensation and carrying out frequency offset estimation by using the frequency domain pilot frequency signal;

the frequency domain pilot signal extracting module is used for estimating phase noise;

the frequency domain pilot frequency recovery signal phase module is used for extracting the phase noise of the pilot frequency signal and carrying out phase recovery on the signal;

the conjugate mirror image turning module is used for turning and recovering the mixed and overlapped signal conjugate mirror image;

the equalizing module is used for equalizing the signal by the minimum mean square error equalizer;

and the symbol demapping module is used for demapping the symbols into bit sequences.

Technical Field

The invention relates to the technical field of frequency offset estimation compensation and phase recovery of aliasing signals of pulse amplitude modulation, in particular to a method for solving frequency offset aliasing of the pulse amplitude modulation signals.

Background

The point-to-multipoint coherent architecture provides a superior scheme for upgrading a future aggregation network, a point-to-point architecture is adopted in a traditional optical network, even if each link in the aggregation network needs a pair of transceivers, the adoption of the point-to-multipoint architecture can save the quantity requirement of the whole network on the transceivers, greatly save the construction, operation and maintenance cost of the network, perform combined processing and allocation of multiple subcarriers and fully utilize the resources of the links. Compared with direct alignment detection, coherent detection has high receiving sensitivity, can realize dual-polarization transmission, is a key technology for realizing high-capacity and high-frequency spectrum utilization, and more importantly, by utilizing a natural transmission demodulation mode, each subcarrier can be directly demodulated in a beat frequency mode without additionally using an optical filter to separate each subcarrier. The XR technology (infiner Corporation, "XR Optics: door-Changing Innovation for Next-Generation Networks," https:// www.infinera.com/Innovation/XR-Optics ") proposed by infiner Corporation is a typical case where a single-wavelength high-bandwidth signal is divided into multiple low-bandwidth subcarriers by digital subcarrier multiplexing technology and a large-capacity coherent transceiver, and then transmitted to different users through different links.

The point-to-multipoint coherent architecture has the following advantages: the method has the advantages of flexibility, low cost and low power consumption, and the application scenes of the method are point-to-multipoint access systems, such as a forward transmission system, a middle transmission system and a backward transmission system in 5G, a next generation access network and the like. Due to the requirement of cost control, especially in a short-distance access scene, a laser with high frequency offset precision cannot be adopted, so that the frequency offset problem is a key problem in point-to-multipoint uplink transmission, because the frequency offset can cause signal aliasing among carriers, clean carrier signals are difficult to extract, and accordingly frequency offset estimation and signal recovery follow-up algorithms fail.

The invention patent with publication number CN110535532A discloses a coherent receiving method and system for polarization-independent pulse amplitude modulation signals, the method includes the following steps: and performing bipolar precoding and polarization time coding on the pulse amplitude modulation PAM signal at a sending end to obtain two orthogonal polarization signals. And converting the two orthogonal polarization signals into two polarization optical signals, and coupling to obtain a coupled optical signal. The coupled optical signal is directly mixed with local oscillation light in an optical mixer, and the two signals are converted by two balance detectors to obtain I, Q two paths of current signals. I, Q two paths of current signals are converted into digital signals and then are subjected to digital signal processing to obtain synchronous receiving signals. And performing channel equalization, polarization time decoding and bipolar decoding on the synchronous received signal to recover the PAM signal at the transmitting end. The invention can simplify the structure of the coherent receiving system and reduce the cost of the coherent receiving system.

For frequency offset aliasing, the processing scheme is mainly to prevent frequency offset aliasing, and there is no aliasing when the frequency spectrum interval between carriers is left to be enough maximum frequency offset, but the fatal defect of the scheme is to sacrifice bandwidth, and with the continuous update of communication technology, the future frequency spectrum resources are inevitably scarce, and the adoption of the scheme essentially also sacrifices a potential rate promotion space. When there is a scheme for processing frequency offset aliasing, a data preprocessing algorithm is adopted at the transmitting end, and some advanced data compression algorithms and spectrum shaping algorithms are also used for preventing aliasing. Or some of them adopt anti-aliasing filters to resist and alleviate part of the damage caused by aliasing, and these algorithms have no capability of recovering signals when aliasing is serious, and the complexity of the algorithms is high.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method and a system for solving the frequency offset aliasing of a pulse amplitude modulation signal.

According to the method and the system for solving the frequency offset aliasing of the pulse amplitude modulation signal, the scheme is as follows:

in a first aspect, a method for resolving frequency offset aliasing of a pulse amplitude modulation signal is provided, the method comprising:

step S1: inserting frequency domain pilot signals at the transmitting end and the edge of a carrier frequency spectrum of the pulse amplitude modulation signal;

step S2: modulating each carrier spectrum to an optical domain of different frequency bands, uniformly selecting a frequency band at a right side or a left side pilot frequency position between adjacent carrier spectrums to leave a gap which is larger than the maximum frequency offset of the device, and coupling and multiplexing the carrier spectrums on the optical domain;

step S3: demultiplexing the subcarrier multiplexing signals at a receiving end, separately processing each subcarrier signal, respectively performing dispersion compensation on the separated subcarriers, performing frequency offset estimation and compensation by using frequency domain pilot signals, and extracting the pilot signals from the separated data;

step S4: performing phase recovery on the signal by using the phase information of the frequency domain pilot frequency; then, carrying out frequency domain conjugation on the signals, and carrying out mirror image overturning to recover the aliasing damaged signals;

step S5: and carrying out operation of an equalization module on the signal, and demodulating the equalized signal.

Preferably, the step S1 includes:

the data sent by the sending end is mapped into a pulse amplitude modulation signal by a bit sequence, and root raised cosine pulse shaping is carried out.

Preferably, the step S1 further includes:

two frequency domain pilot signals are inserted at the two edges, the left edge and the right edge, of the carrier spectrum of the pulse amplitude modulation signal, and the frequency domain pilot signals are expressed as follows:

wherein, C is a constant matrix and represents the amplitude of the frequency domain pilot frequency; Δ f_pThe frequency domain distance from the center of the carrier wave of the frequency domain pilot signal is the frequency domain distance, and the frequency domain pilot frequency is positioned in the frequency spectrum gap at the edge of the carrier wave; fs is the sampling rate; j represents virtualA part symbol; t represents a time sequence.

Preferably, the step S2 includes: different transmitting end signals are photoelectrically converted into optical signals for transmission, adjacent optical carriers form a group, the frequency interval of each group needs to ensure that the gap of the frequency domain pilot signal at the opposite side is greater than the maximum frequency deviation value of the laser, and the maximum frequency deviation value of the laser is recorded as FO_maxThe signals are coupled and multiplexed in the optical domain.

Preferably, the step S3 includes:

separately processing each sub-carrier signal at a receiving end, down-converting the carrier to be processed to a base frequency, demultiplexing the carrier by low-pass filtering, the filtering bandwidth being greater than deltaf_p+FO_maxAnd performing dispersion compensation on the filtered signal.

Preferably, the step S3 further includes:

performing FFT (fast Fourier transform) on the subcarrier signals after dispersion compensation, finding a peak value, namely the position of a frequency point where the frequency domain pilot frequency is located, and comparing the position difference between the positions of the frequency domain pilot frequency points inserted into a transmitting end to obtain an estimated value of frequency offset;

carrying out frequency shift and frequency offset recovery on the signal;

extracting frequency domain pilot frequency in carrier wave, wherein the center frequency of filtering is delta f_pThe bandwidth of the filtering is about 300MHz, and the frequency domain pilot frequency energy can not be damaged and the subcarrier signal can not be contained.

Preferably, the step S4 includes:

the phase noise at the transmitting and receiving ends of the laser represents the sub-carrier after demultiplexing as follows:

wherein S is_tRepresents a modulated baseband signal; t represents a time series; phi (t) represents phase noise; calculating frequency domain pilot signal Pe obtained by frequency shifting to fundamental frequency after filtering^φ(t)And extracting information of the phase noise, and compensating the phase noise for the signal.

Preferably, the step S4 further includes:

let the time domain of the signal after pulse amplitude modulation be x, and represent it on the frequency domain as:

real part of the frequency domain pulse amplitude modulation signal:

Re(-ω)＝Re(ω)

imaginary part of frequency domain pulse amplitude modulation signal:

Im(-ω)＝-Im(ω)

wherein t represents a time series; j represents the imaginary symbol; ω represents a frequency sequence; the pulse amplitude modulated signal is symmetric about the 0-frequency conjugate in the frequency domain. The conjugate image inversion is therefore performed using the unaliased side of the phase recovered signal.

Preferably, the step S5 includes: for each subcarrier signal, the signal is recovered by an equalization algorithm and the pulse amplitude modulation signal symbols are de-mapped into bit sequences.

In a second aspect, a system for resolving frequency offset aliasing of a pulse amplitude modulated signal is provided, the system comprising:

a sending end and a receiving end;

wherein, the sending end includes:

the bit mapping module is used for mapping a bit sequence to be sent into a pulse amplitude modulation symbol;

the pulse shaping module is used for shaping the symbol root raised cosine pulse to generate each subcarrier;

the frequency domain pilot frequency inserting module is used for respectively inserting frequency domain pilot frequency signals at the spectrum intervals at two sides of the subcarrier;

the subcarrier multiplexing module is used for multiplexing subcarriers;

and the receiving end includes:

the subcarrier demultiplexing module is used for demultiplexing the subcarriers;

the dispersion compensation module is used for compensating dispersion accumulated by the optical fiber in the transmission process;

the frequency offset estimation compensation module is used for frequency offset estimation and compensation and carrying out frequency offset estimation by using the frequency domain pilot frequency signal;

the frequency domain pilot signal extracting module is used for estimating phase noise;

the frequency domain pilot frequency recovery signal phase module is used for extracting the phase noise of the pilot frequency signal and carrying out phase recovery on the signal;

the conjugate mirror image turning module is used for turning and recovering the mixed and overlapped signal conjugate mirror image;

the equalizing module is used for equalizing the signal by the minimum mean square error equalizer;

and the symbol demapping module is used for demapping the symbols into bit sequences.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention relates to the field of optical communication application, and has the capability of recovering an aliasing half signal spectrum;

2. the invention makes full use of the information of the frequency domain pilot signal at the receiving end to carry out frequency offset estimation and compensation; performing phase recovery on the signal by using the frequency domain pilot signal; the conjugate mirror image turning is realized without bringing extra algorithm complexity cost;

3. the invention is easy to realize, convenient to use, cost-saving and capable of overcoming the defects of the prior art.

Drawings

Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:

FIG. 1 is a schematic diagram of signal processing at a transmitting end and a receiving end based on a frequency domain pilot signal solution high-speed polarization rotation and phase recovery algorithm according to the present invention;

FIG. 2 is a schematic diagram of the frequency offset recovery performance of the simulation system according to the method of the present invention.

Detailed Description

The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.

The embodiment of the invention provides a method for solving frequency offset aliasing of a pulse amplitude modulation signal, which specifically comprises the following steps: at a sending end, mapping sent data into a pulse amplitude modulation signal by a bit sequence, and carrying out root raised cosine pulse shaping; two frequency domain pilot signals are inserted at the two edges, the left edge and the right edge, of the carrier spectrum of the pulse amplitude modulation signal, and the frequency domain pilot signals are expressed as follows:

where C is a constant matrix representing the amplitude of the frequency domain pilot, Δ f_pThe frequency domain distance from the center of the carrier wave of the frequency domain pilot signal is shown, the frequency domain pilot frequency is positioned in the frequency spectrum gap at the edge of the carrier wave, and fs is the sampling rate; j represents the imaginary symbol; t represents a time sequence. Different transmitting end signals are photoelectrically converted into optical signals for transmission, adjacent optical carriers form a group, the frequency interval of each group needs to ensure that the gap of the frequency domain pilot signal at the opposite side is greater than the maximum frequency deviation value of the laser, and the maximum frequency deviation value of the laser is recorded as FO_max(ii) a The signals are coupled and multiplexed in the optical domain.

At the receiving end, the individual subcarrier signals are processed separately, the carrier to be processed is down-converted to the base frequency, the carrier is demultiplexed by low-pass filteringWith a filter bandwidth greater than Δ f_p+FO_max(ii) a Carrying out dispersion compensation on the filtered signal; performing FFT (fast Fourier transform) on the subcarrier signals after dispersion compensation, finding a peak value, namely the position of a frequency point where the frequency domain pilot frequency is located, and comparing the position difference of the positions of the frequency domain pilot frequency points inserted into a transmitting terminal to obtain an estimated value of frequency offset; carrying out frequency shift on the signal and recovering the frequency offset; extracting frequency domain pilot frequency in carrier wave, wherein the center frequency of filtering is delta f_pThe bandwidth of the filtering is about 300MHz, the frequency domain pilot frequency energy can not be damaged, and the subcarrier signal can not be contained; the phase noise at the transceiving end of the laser represents the demultiplexed subcarrier as:

wherein S is_tRepresents a modulated baseband signal; t represents a time series; phi (t) represents phase noise; calculating frequency domain pilot signal Pe obtained by frequency shifting to fundamental frequency after filtering^φ(t)And extracting information of the phase noise, and compensating the phase noise for the signal. The pulse amplitude modulated signal is symmetric about the 0-frequency conjugate in the frequency domain. Therefore, conjugate image inversion is carried out by using the unaliased side of the signal after phase recovery; for each subcarrier signal, recovering the signal by using an equalization algorithm; and then demapping the pulse amplitude modulation signal symbols into bit sequences.

The principle of the invention is as follows:

let the time domain of the signal after pulse amplitude modulation be x, and represent it on the frequency domain as:

real part of the frequency domain pulse amplitude modulation signal:

Re(-ω)＝Re(ω)

imaginary part of frequency domain pulse amplitude modulation signal:

Im(-ω)＝-Im(ω)

wherein t represents a time series; j represents the imaginary symbol; ω represents a frequency sequence; the pulse amplitude modulated signal is symmetric about the 0-frequency conjugate in the frequency domain. After frequency offset and phase noise are compensated, the influence of additive noise on conjugate symmetry can be ignored, so that the unaliased side of the signal after phase recovery is used for conjugate mirror inversion.

The invention also provides a system for solving the frequency offset aliasing of the pulse amplitude modulation signal, which comprises a sending end and a receiving end, and is shown in the figure 1.

The transmitting end includes:

the bit mapping module is used for mapping a bit sequence to be sent into a pulse amplitude modulation symbol;

the pulse shaping module is used for shaping the symbol root raised cosine pulse to generate each subcarrier;

the frequency domain pilot frequency inserting module is used for respectively inserting frequency domain pilot frequency signals at the spectrum intervals at two sides of the subcarrier;

and the subcarrier multiplexing module is used for multiplexing subcarriers.

The receiving end includes:

the subcarrier demultiplexing module is used for demultiplexing the subcarriers;

the dispersion compensation module is used for compensating dispersion accumulated by the optical fiber in the transmission process;

the frequency offset estimation compensation module is used for frequency offset estimation and compensation and carrying out frequency offset estimation by using the frequency domain pilot frequency signal;

the frequency domain pilot signal extracting module is used for estimating phase noise;

the frequency domain pilot frequency recovery signal phase module is used for extracting the phase noise of the pilot frequency signal and carrying out phase recovery on the signal;

the conjugate mirror image turning module is used for turning and recovering the mixed and overlapped signal conjugate mirror image;

the equalizing module is used for equalizing the signal by the minimum mean square error equalizer;

and the symbol demapping module is used for demapping the symbols into bit sequences.

Referring to fig. 2, the algorithm designed by the present invention is applied to a subcarrier multiplexing simulation system to obtain the error rate performance. The Modulation format of the subcarrier is dual-polarization PAM4(Pulse Amplitude Modulation), the Baud rate is 15G Baud, G is unit giga, Baud is unit Baud, 6 subcarriers are provided in total, the roll-off coefficient is 0.1, the frequency domain pilot frequency filtering bandwidth is set to be 200MHz, M is unit mega, Hz is unit Hz, the power ratio of the inserted frequency domain pilot frequency signal and the signal is-20 dB, dB is unit decibel, the line width of the laser at the transmitting and receiving end is 500kHz, and k is unit thousand. The frequency offset aliasing part is up to 7GHz, the recovery is not carried out by adopting a mirror image inversion algorithm, the system is invalid, signals cannot be demodulated, and information cannot be transmitted. The method of the invention can better recover the signal and efficiently solve the problem of frequency offset aliasing.

The embodiment of the invention provides a method for solving frequency offset aliasing of a pulse amplitude modulation signal, which relates to the field of optical communication application and has the capability of recovering an aliasing half signal spectrum; the information of the frequency domain pilot signal is fully utilized at the receiving end to carry out frequency offset estimation and compensation; performing phase recovery on the signal by using the frequency domain pilot signal; the conjugate mirror image turning is realized without bringing extra algorithm complexity cost; meanwhile, the invention is easy to realize, convenient to use, cost-saving and capable of overcoming the defects of the prior art.

Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, units provided by the present invention as pure computer readable program code, the system and its various devices, modules, units provided by the present invention can be fully implemented by logically programming method steps in such a manner as to implement the same functions in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Therefore, the system and various devices, modules and units thereof provided by the invention can be regarded as a hardware component, and the devices, modules and units included in the system for realizing various functions can also be regarded as structures in the hardware component; means, modules, units for performing the various functions may also be regarded as structures within both software modules and hardware components for performing the method.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.