CN107018108B - Modulation format identification method for two-dimensional plane of Stokes space - Google Patents

Modulation format identification method for two-dimensional plane of Stokes space Download PDF

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CN107018108B
CN107018108B CN201710324935.9A CN201710324935A CN107018108B CN 107018108 B CN107018108 B CN 107018108B CN 201710324935 A CN201710324935 A CN 201710324935A CN 107018108 B CN107018108 B CN 107018108B
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modulation format
vector
modulation
dimensional plane
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CN107018108A (en
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闫连山
蒋林
盘艳
易安林
潘炜
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Southwest Jiaotong University
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/0012—Modulated-carrier systems arrangements for identifying the type of modulation
    • 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
    • H04B10/614—Coherent receivers comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers

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  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
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Abstract

The invention discloses a modulation format identification method of a Stokes space two-dimensional plane, which comprises the following steps: a receiving end receives digital signals of two polarization states; carrying out dispersion compensation on the digital signal, and mapping the signal after dispersion compensation to a Stokes space for polarization alignment operation; monitoring the Stokes vector S1When the value of the vector appears in one level, the phase modulation signal is judged, and corresponding identification is carried out through a phase modulation format identification method; stokes vector S when monitored1When multiple stages occur, the vector S is further judged1If symmetric, the quadrature amplitude modulation format is used, and if asymmetric, the hybrid modulation format is used. The invention can realize the identification of various modulation formats, improves the flexibility and robustness of the whole transmission system, and makes the transmission system more suitable for a future dynamic backbone network transmission system.

Description

Modulation format identification method for two-dimensional plane of Stokes space
Technical Field
The invention relates to the field of dynamic, large-capacity and multi-service switching transmission networks, in particular to a modulation format identification method of a Stokes space two-dimensional plane.
Background
With the advent of the cloud computing, internet +, internet of things and other big data times, the communication capacity is rapidly increased every year. The traditional single-mode single-core single-wavelength optical fiber transmission mode cannot meet the requirement of transmission capacity. The optical fiber communication transmission capacity is improved by means of wavelength division multiplexing, space division multiplexing (multimode and multicore), polarization multiplexing, time division multiplexing, orbital angular momentum multiplexing, advanced modulation formats and the like, and the optical fiber communication transmission capacity is paid close attention to the majority of researchers.
Among them, the advanced modulation format has become one of the key technologies for realizing a large capacity optical transmission network. At present, an optical communication network approaches to more flexibly self-defining the network, and self-judgment and self-learning are carried out on data in the whole network. An optical transmission network will usually balance the transmission capacity and the transmission channel service quality according to the transmission channel service quality, and then dynamically adjust the transmission debug format to achieve the optimal transmission performance, which is very important for the automatic identification technology of the debug format. Only if the transmission modulation format is correctly identified, the back-end digital signal processing algorithm can correspondingly realize the corresponding data demodulation operation.
In 2012, researchers at hong kong science and technology university propose that the modulation format recognition is realized by using an artificial neural network method, which needs to add an additional modulation format recognition module, although various modulation formats can be recognized, the complexity of a transmission system is increased to a great extent, and the complexity of a neural network algorithm is relatively high. In 2013, researchers at the university of monash, australia, proposed that identification of modulation formats be achieved in stokes space, which requires monitoring the number of cluster points in stokes three-dimensional space. However, the method has certain limitations, firstly, the data volume in the three-dimensional space is relatively large, and the complexity of identification is increased; meanwhile, the method has certain limitation in the identification of a high-order modulation format, and the number of the presented cluster points is exponentially increased after the polarization multiplexing modulation signal enters a Stokes three-dimensional space. In 2014, researchers at hong Kong science and technology university propose that the modulation format identification is realized by using signal power distribution, the method needs to realize the modulation format identification after polarization demultiplexing, and the polarization demultiplexing is usually related to the modulation format, so that the method has certain identification instability; at the same time, the method only works for quadrature amplitude modulation. In 2016, researchers at hong kong chinese university propose that modulation format recognition is achieved by using an image processing method, which requires a certain complexity of performing an early denoising process on an obtained image. Therefore, in order to further improve the real-time performance and sensitivity of modulation format identification, the research on a modulation format identification technology with low complexity has important practical significance and corresponding application prospect.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a modulation format identification method of a Stokes space two-dimensional plane, the polarization, intensity and phase information of a transmission signal are obtained through a coherent receiver, the modulation format identification is realized in a digital signal processing unit, and the flexibility and robustness of the system of the whole transmission network are improved.
In order to solve the technical problems, the invention adopts the technical scheme that:
a modulation format identification method of a Stokes space two-dimensional plane comprises the following steps:
step 1: receiving end receives X polarization state signal ExAnd signal E of polarization state YyNamely:
Ex＝Axexp(jωΔt+jθsx+jθn)
Ey＝Ayexp(jωΔt+jθsy+jθn)
wherein A isx、AyAmplitude values, theta, for the X and Y polarization states, respectivelysx、θsyPhase information, theta, for the X and Y polarization states, respectivelynBeing phase noise of the signal, omegaΔIs the frequency offset of the signal;
step 2: converting the signal into the Stokes space, which is a three-dimensional space, consisting of S1、S2、S3Three mutually perpendicular direction vectors, namely:
s0＝|Ex|2+|Ey|2
s1＝|Ex|2-|Ey|2
wherein s is0、s1、s2、s3Expressed as the total power, vector S, of the two states of polarization, respectively1Specific value of (1), vector S2Specific value of (1), vector S3The specific value of (a) is,a phase difference of two polarization states;
and step 3: aligning the polarized signals mapped to the stokes space;
and 4, step 4: judging signal type
In Stokes space, the aligned polarization multiplexed signal will be perpendicular to the vector S1Direction, while being parallel to the vector S2And S3A plane of composition; different modulation signals in the stokes space will exhibit different characteristics: vector S1When the numerical value of (1) appears, the signal is a phase modulation signal; vector S1When the numerical value of (2) is in multi-level, if positive and negative symmetry occurs, quadrature amplitude modulation is performed; if the positive and negative asymmetry occurs, the signal is a mixed modulation signal;
and 5: according to the vector S1Respectively identify different modulation formats
For phase modulated signals, in a simplified two-dimensional plane S2And S3Identifying the number of cluster points, and judging the type of the phase modulation format;
for orthogonal amplitude modulated signals, in a two-dimensional plane S1And S3Judging the type of the quadrature amplitude modulation format by identifying the number of stages of the modulation format;
for mixed modulation signals, in a two-dimensional plane S1And S3The type of the mixed modulation format is judged by identifying the number of stages of the modulation format.
Compared with the prior art, the invention has the beneficial effects that:
1) identification of multiple modulation formats may be achieved, including multiple phase modulation formats, multiple quadrature amplitude modulation formats, and so on.
2) The complexity is relatively low, and the three-dimensional space data of Stokes is reduced to a two-dimensional space.
3) The modulation format recognition can be realized by directly adopting a coherent receiving processing mode without changing the existing network structure.
4) The method can realize the identification of a plurality of channel modulation formats, improves the flexibility and robustness of the system of the whole transmission network, enables the system to be more suitable for a future dynamic optical transmission network, and has certain research value and application prospect.
Drawings
Fig. 1 is a schematic flow chart of a modulation format identification method of a stokes space two-dimensional plane according to the present invention.
Fig. 2 is a structural block diagram of a modulation format identification method of a stokes space two-dimensional plane.
Fig. 3 is a flowchart of identifying a modulation format of the polarization multiplexing phase modulation signal mPSK.
Fig. 4 is a flowchart of the identification of the modulation format of the polarization-multiplexed quadrature amplitude modulation signal mQAM.
Fig. 5 is a flow chart of polarization multiplexed hybrid modulation format identification.
Fig. 6 is a diagram of multiple modulation format identification performance.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
The invention relates to a modulation format recognition method of a Stokes space two-dimensional plane, which is mainly used for recognizing the modulation format of the Stokes space two-dimensional plane in a digital signal processing unit of a coherent receiver and comprises the following steps: 1) receiving end receives X polarization state signal ExAnd signal E of polarization state YyAnd carrying out corresponding dispersion compensation, mapping the signal subjected to dispersion compensation to a Stokes space from the Jones space, and carrying out polarization alignment operation. 2) In Stokes space, the aligned polarization multiplexed signal will be perpendicular to the vector S1Direction, while being parallel to the vector S2And S3A plane of composition.
Different modulated signals in the stokes space will exhibit different characteristics, such as: the amplitude values of the phase modulated signal (mPSK) are all single constant values, while the phase is multivalued, so that the two-dimensional plane S can be simplified directly2And S3Identifying the number of cluster points, and finally judging the type of the phase modulation format; a multivalued signal in which the amplitude value of the quadrature amplitude modulation signal mQAM is inconstant, vector S1The numerical value of (A) also presents a plurality of values and is symmetrical in positive and negative directions and can be positioned on a two-dimensional plane S1And S3Finally judging the type of the quadrature amplitude modulation format by identifying the number of stages of the modulation format; the mixed modulation signal is a polarization multiplex signal composed of two different modulation formats, vector S1Also present are a plurality of values, however asymmetry will occur, also in the two-dimensional plane S1And S3Finally, the type of the mixed modulation format is judged by identifying the number of stages of the modulation format.
As shown in FIG. 1, the method of the present invention uses one or N wavelengths of polarization multiplexed emission end (101)1～101N) Modulating a polarization-multiplexed phase modulation/quadrature amplitude modulation (m-PSK/m-QAM) signal or two mixed modulation signals with different polarization states, coupling the transmission signals with a plurality of wavelengths together through a wavelength division multiplexer (102), and passing through one section or N sections of optical fiber (103)1～103N) And carrying out transmission. The corresponding transmission loss is provided by one or N fiber optical amplifiers (104)1～104N) Compensation is performed. At the receiving end, the signals of a plurality of wavelengths are processed respectively by a wavelength division demultiplexer (105) and passed through one or N coherent receivers (106)1～106N) Carrying out coherent demodulation on the signals to obtain electric signals with corresponding information such as polarization, intensity, phase and the like; the electrical signal is then passed through a digital to analog converter (107)1～107N) Converting the continuous analog electrical signal into a discrete digital signal; finally, the received digital signal is placed in a digital signal processing unit (108)1～108N) Carrying out treatment; the invention relates to a modulation format identification method of a Stokes space two-dimensional plane, which is implemented in a digital signal processing unit (108)1～108N) In the method, the modulation format of the received digital signal is identified.
Fig. 2 is a structural block diagram of a modulation format identification method of a stokes space two-dimensional plane. The digital signal at the receiving end enters a digital signal processing unit (108)1～108N) And carrying out corresponding signal impairment compensation. The digital signal is firstly subjected to dispersion compensation, and the signal after dispersion compensation is mapped into a Stokes space to be subjected to polarization alignment operation. The aligned polarization multiplexed signal will be perpendicular to the vector S1Direction, while being parallel to the vector S2And S3A plane of composition. Next, the Stokes vector S is monitored1When the value of the vector appears in one level, the phase modulation signal is judged, and corresponding identification is carried out through a phase modulation format identification method; stokes vector S when monitored1When multiple stages occur, the vector S is further judged1If symmetric, the quadrature amplitude modulation format is used, and if asymmetric, the hybrid modulation format is used. And after the identification is finished, carrying out polarization demultiplexing and carrier phase recovery on the signal with the determined modulation format to realize the final demodulation of the signal.
Fig. 3 is a flowchart of identifying a modulation format of the polarization multiplexing phase modulation signal mPSK. First monitor the Stokes vector S1At this time, vector S1The value of (d) is assumed to be in phase modulation format. Next, the Stokes vector S is monitored2And S3The number of the cluster points is monitored through a cluster point identification technology, and when the cluster point is 2, the BPSK modulation format is adopted; when the cluster point is 4, the QPSK modulation format is adopted; the cluster point is 8, and the modulation format is 8 PSK; when the cluster points are m, the modulation format is mPSK; s2And S3Different cluster points appear in the formed two-dimensional plane, and finally the type of the phase modulation format is identified.
Fig. 4 is a flowchart of the identification of the modulation format of the polarization-multiplexed quadrature amplitude modulation signal mQAM. First monitor the Stokes vector S1At this time, vector S1Multiple values are presented, while multiple values are found to exhibit positive and negative symmetry. Monitoring of a two-dimensional plane S by cluster point identification techniques1And S3The number of occurrences. 8QAM has 2-level amplitude values, in this case the two-dimensional plane S1And S33 grades appear; 16QAM has 3 levels of amplitude values, in this case the two-dimensional plane S1And S3Occurrence of grade 5; 32QAM has 5-level amplitude values, in this case the two-dimensional plane S1And S39 stages appeared; similarly, mQAM has n-level amplitude values, which is the two-dimensional plane S1And S3A 2n-1 stage occurs. Aiming at the quadrature amplitude modulation signal, the invention can directly identify in a two-dimensional plane S without identifying in a three-dimensional space1And S3Finally, the type of the qam format is identified by identifying the number of levels in which the qam format appears.
Fig. 5 is a flow chart of polarization multiplexed hybrid modulation format identification. First monitor the Stokes vector S1At this time, vector S1Multiple values are presented while multiple values are found to exhibit asymmetry. Monitoring of a two-dimensional plane S by cluster point identification techniques1And S3The number of occurrences. When QPSK and 8QAM are mixed modulated, two-dimensional plane S1And S32 levels of occurrences where all are non-negative; when QPSK and 16QAM are mixed modulated, two-dimensional plane S1And S33 levels all non-negative appear; when 8QAM and 16QAM are mixed modulated, two-dimensional plane S1And S33 non-negative levels and 1 negative level occur; aiming at the mixed modulation signal, the invention can directly identify in a two-dimensional plane S without identifying in a three-dimensional space1And S3The type of the hybrid modulation format is finally identified by identifying the number of asymmetric levels that the modulation format appears.
Fig. 6 is a diagram of the multiple modulation format identification performance of the present invention. The phase modulation formats QPSK, 8PSK, and 16PSK, and the quadrature amplitude modulation formats 8QAM and 16QAM are taken as examples. The performance test was implemented in a polarization multiplexed coherent transmission system with a symbol rate of 28 GBaud. As can be seen from fig. 6, the present invention can effectively recognize various modulation formats, and at the same time, can still correctly recognize modulation formats under the condition of low noise-to-noise ratio, which indicates that the modulation format recognition technology provided by the present invention can adapt to a dynamic, long-distance, large-capacity transmission system, and has a certain application prospect.

Claims (1)

1. A modulation format identification method of a Stokes space two-dimensional plane is characterized by comprising the following steps:
step 1: receiving end receives X polarization state signal ExAnd signal E of polarization state YyNamely:
Ex＝Axexp(jω△t+jθsx+jθn)
Ey＝Ayexp(jω△t+jθsy+jθn)
wherein A isx、AyAmplitude values, theta, for the X and Y polarization states, respectivelysx、θsyPhase information, theta, for the X and Y polarization states, respectivelynBeing phase noise of the signal, omega△Is the frequency offset of the signal;
step 2: converting the signal into the Stokes space, which is a three-dimensional space, consisting of S1、S2、S3Three mutually perpendicular direction vectors, namely:
s0＝|Ex|2+|Ey|2
s1＝|Ex|2-|Ey|2
wherein s is0、s1、s2、s3Expressed as the total power, vector S, of the two states of polarization, respectively1Specific value of (1), vector S2Specific value of (1), vector S3The specific value of (a) is,a phase difference of two polarization states;
and step 3: aligning the polarized signals mapped to the stokes space;
and 4, step 4: judging signal type
In Stokes space, the aligned polarization multiplexed signal will be perpendicular to the vector S1Direction, while being parallel to the vector S2And S3A plane of composition; different modulation signals in the stokes space will exhibit different characteristics: vector S1When the numerical value of (1) appears, the signal is a phase modulation signal; vector S1When the numerical value of (2) is in multi-level, if positive and negative symmetry occurs, quadrature amplitude modulation is performed; if the positive and negative asymmetry occurs, the signal is a mixed modulation signal;
and 5: according to the vector S1Respectively identify different modulation formats
For phase modulated signals, in a simplified two-dimensional plane S2And S3Identifying the number of cluster points, wherein when the number of the cluster points is m, the modulation format is mPSK, and judging the type of the phase modulation format according to the mPSK;
for orthogonal amplitude modulated signals, in a two-dimensional plane S1And S3By identifying the number of levels occurring in the modulation format, when mQAM has n-level amplitude values, the two-dimensional plane S is now1And S32n-1 level appears, and the type of the quadrature amplitude modulation format is judged according to the level;
for mixed modulation signals, in a two-dimensional plane S1And S3By recognizing the number of stages in which the modulation format appears, the two-dimensional plane S when QPSK and 8QAM are mixed for modulation1And S32 levels of occurrences where all are non-negative; when QPSK and 16QAM are mixed modulated, two-dimensional plane S1And S33 levels all non-negative appear; when 8QAM and 16QAM are mixed modulated, two-dimensional plane S1And S33 non-negative levels and 1 negative level appear, and the type of the mixed modulation format is judged according to the levels.
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