CN111865428A - Coherent optical wireless optical communication transmission method, system, storage medium, and device - Google Patents

Coherent optical wireless optical communication transmission method, system, storage medium, and device Download PDF

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CN111865428A
CN111865428A CN202010725745.XA CN202010725745A CN111865428A CN 111865428 A CN111865428 A CN 111865428A CN 202010725745 A CN202010725745 A CN 202010725745A CN 111865428 A CN111865428 A CN 111865428A
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symbol
polarization state
time slot
bit
phase
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朱敏
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Xijing University
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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
    • H04B10/50—Transmitters
    • H04B10/516—Details of coding or modulation
    • H04B10/548—Phase or frequency modulation
    • H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
    • 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
    • H04B10/612—Coherent receivers for optical signals modulated with a format different from binary or higher-order PSK [X-PSK], e.g. QAM, DPSK, FSK, MSK, ASK
    • 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
    • H04B10/613—Coherent receivers including phase diversity, e.g., having in-phase and quadrature branches, as in QPSK coherent receivers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B15/00—Suppression or limitation of noise or interference
    • H04B15/005—Reducing noise, e.g. humm, from the supply

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Abstract

The invention belongs to the technical field of free space optical communication, and discloses a coherent optical wireless optical communication transmission method, a system, a storage medium and equipment, wherein three variables of phase, polarization state and data sign bit are utilized to carry out data sign mapping so as to generate baseband sign streams on X and Y polarization states; the four paths of baseband signals are subjected to I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two paths of symbol data streams corresponding to the generated baseband signals. The invention can effectively inhibit phase noise caused by atmospheric turbulence, and can effectively avoid crosstalk between polarization states in the same symbol time slot period by cross-modulating symbol information in two adjacent symbol periods in orthogonal polarization states. Therefore, the invention can effectively improve the performance of the traditional atmosphere coherent optical communication system based on the PSK or QAM modulation mode, and the transmission distance of the atmosphere laser communication system is expanded.

Description

Coherent optical wireless optical communication transmission method, system, storage medium, and device
Technical Field
The invention belongs to the technical field of free space optical communication, and particularly relates to a coherent optical wireless optical communication transmission method, a coherent optical wireless optical communication transmission system, a coherent optical wireless optical communication storage medium and coherent optical wireless optical communication equipment.
Background
Currently, free space optical communication technology is a key technology for developing rapid deployment systems, security systems, communication systems, real-time monitoring and surveillance systems. Free-space optical communication systems have many advantages, such as short deployment times, relatively inexpensive devices, resistance to electromagnetic interference, and freedom from radio licenses, especially with high bandwidths that radio frequency communications are not comparable. The system can provide broadband wireless extension for an Internet backbone network in the commercial field, and provides a high-bandwidth link for delay-free web page browsing, database access, electronic commerce, access and transmission of big data, real-time audio and video, video conference, real-time medical image transmission and rapid development of enterprise networks; in the field of national defense, high-bandwidth instruments required by the current satellite, such as a hyper-spectral imager, a Synthetic Aperture Radar (SAR) and the like, and real-time video communication in the future interplanetary manned space need to be realized, and a large amount of high-resolution high-definition images and video information transmission need to be carried out. For example, taking the Mars Global Survey (MGS) mission by NASA in the United states, which has returned hundreds of Tbits of data, throughout the main mission phase, limited by the capacity of the communication, the mission can only map a small portion of the Mars' surface at high resolution. The real-time transmission capacity of the existing synthetic aperture radar data also reaches several Gbps. Under the influence of space irradiation, the storage and processing capacity of the satellite data is very limited at present, and the large-capacity high-definition image information and measurement and control data obtained in space application can be returned in real time by utilizing a space coherent laser communication technology with high spectral efficiency, so that the design pressure of satellite data storage and processing is favorably reduced. In addition, networking of future relay satellites and construction of a space-ground integrated network need to provide high-bandwidth communication links by using a spatial coherent laser communication technology. Therefore, the spatial coherent optical communication technology with high spectral efficiency and high sensitivity has wide application prospect in the civil and military fields. However, in the satellite-ground laser communication link, the phase noise caused by the atmospheric turbulence is still a main factor hindering the development of the high-spectrum-efficiency free-space coherent optical communication system, and the traditional coherent optical communication based on the PSK or QAM modulation method must use expensive adaptive optical equipment to overcome the phase noise caused by the atmospheric turbulence, so that the popularization and the popularity of the free-space coherent optical communication are limited.
The existing coherent optical communication technology based on PSK or QAM modulation mode simultaneously utilizes X and Y orthogonal polarization states to transmit information so as to increase the transmission rate, so that the two polarization states are respectively modulatedIndependent and irrelevant information symbols, symbol S1、S2、…、SnIndependent of each other. After being transmitted through an atmospheric turbulence channel, the X polarization state and the Y polarization state are independently demodulated at a receiving end respectively so as to recover the transmitted symbols. Since the transmitted symbols are independent of each other, even if correlated phase noise is introduced to the symbols, the noise suppression cannot be performed on the receiving end by using the noise correlation. And crosstalk is easily generated between two polarization states in the same symbol time slot period, so that the performance of the system is further reduced. Therefore, the existing coherent optical communication technology based on the PSK or QAM modulation method has the disadvantages that the phase noise caused by the atmospheric turbulence cannot be effectively inhibited, and the crosstalk between the two polarization states can be generated.
Through the above analysis, the problems and defects of the prior art are as follows: the existing coherent optical communication technology based on PSK or QAM cannot effectively inhibit phase noise caused by atmospheric turbulence, and crosstalk can be generated between two polarization states.
The difficulty in solving the above problems and defects is: in order to effectively suppress phase noise caused by atmospheric turbulence, the existing coherent optical communication technology based on the PSK or QAM modulation scheme has to use a complex and expensive adaptive optical system, which is effective, but the system cost increase caused by the system cost even exceeds the cost of the communication system itself, and cannot be borne by a commercial communication system sensitive to the cost.
The significance of solving the problems and the defects is as follows: the invention can effectively inhibit phase noise caused by atmospheric turbulence, brings little system cost increase, reduces the commercial popularization difficulty of atmospheric coherent laser communication, and has important significance for 5G forwarding and future 6G communication by utilizing a free space optical communication system.
Disclosure of Invention
The invention provides a coherent optical wireless optical communication transmission method, a system, a storage medium and equipment, aiming at the problems in the prior art.
The present invention is achieved as such, in a coherent optical wireless optical communication transmission method, including:
performing symbol mapping of data using three variables, namely phase, polarization state and data symbol bit, to generate baseband symbol streams in X and Y polarization states;
the four paths of baseband signals are subjected to I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two paths of symbol data streams corresponding to the generated baseband signals.
Further, the symbol mapping of data using three variables, i.e., phase, polarization state and data symbol bit, to generate baseband symbol streams in X and Y polarization states includes:
firstly, information mapping is carried out on binary data streams to be transmitted, wherein bit 0 is mapped to-1, and bit 1 is mapped to + 1;
secondly, grouping the data streams generated by the information mapping in the first step, wherein every four adjacent bits form a group;
thirdly, symbol mapping is carried out on each group grouped in the second step; wherein the first two bits of each group are mapped to QPSK symbols SiThe third bit is mapped to the X/Y polarization state, i.e. the symbol S mapped by the first two bits when the third bit is +1iWill be in time slot TiThe information is sent in the X or Y polarization state, and no information is sent in the Y or X polarization state; symbol S mapped by the first two bits when the third bit is-1iWill be in time slot TiThe information is sent in a Y or X polarization state, and no information is sent in the X or Y polarization state; the fourth bit of each group is mapped to the symbol b × (S)i)*Wherein b is the value of the fourth bit, and is +1 or-1; (S)i)*QPSK symbols S representing the mapping of the first two bits in each groupiComplex conjugation of (c) (. 1)*Representing a complex conjugate calculation; symbol b x (S) of the fourth bit mapi)*In the following time slot TiThen Ti *Time slot transmission, and the polarization state occupied by it and time slot TiTransmitted symbol SiThe occupied polarization states are mutually exclusive, i.e. if SiTransmitting in X polarization state, then b × (S)i)*In the Y polarization stateOtherwise, if SiTransmitting in Y polarization state, then b × (S)i)*Transmitting in an X polarization state; the four bits of each group are mapped to produce a stream of baseband symbols in the X and Y polarization states.
Further, the obtaining of the two symbol data streams corresponding to the generated baseband signals after the four baseband signals are sequentially subjected to I/Q imbalance compensation, channel equalization, timing recovery, carrier frequency offset compensation, and carrier phase offset compensation includes: one of the paths is the symbol data stream 0 in the X polarization state,
Figure BDA0002601600690000041
0，0，
Figure BDA0002601600690000042
and the other is a symbol data stream in the Y polarization state
Figure BDA0002601600690000043
Figure BDA0002601600690000043
Figure BDA0002601600690000043
Figure BDA0002601600690000043
0，0，
Figure BDA0002601600690000044
0; errors exist between the two paths of symbol data which are influenced by noise after being transmitted and the symbol data of a transmitting end; after the front-end processing of the baseband signals, the two baseband signal symbol streams corresponding to the X and Y polarization states are synchronized, and the two data streams are aligned with the symbols on each time slot; and performing decision recovery on the two aligned symbol data streams.
Further, the decision recovery of the two aligned symbol data streams includes:
1) at TiTaking two symbols in X and Y polarization states during time slot
Figure BDA0002601600690000045
And
Figure BDA0002601600690000046
die of
Figure BDA0002601600690000047
And
Figure BDA0002601600690000048
if it is
Figure BDA0002601600690000049
Or
Figure BDA00026016006900000410
Wherein Threshold is the selected Threshold, the symbol is declared
Figure BDA00026016006900000411
In the X polarization state, the information recovered by the third bit is + 1; on the contrary, if
Figure BDA00026016006900000412
Or
Figure BDA00026016006900000413
Then explain the symbol
Figure BDA00026016006900000414
In the Y polarization state, the information recovered by the third bit is-1;
2) at TiTime slot, symbol
Figure BDA00026016006900000415
The quadrant in which the phase angle is 0-pi is M; at Ti *Time slot, to and symbol
Figure BDA00026016006900000416
Sign-up on mutually exclusive states of polarization
Figure BDA00026016006900000417
Or
Figure BDA00026016006900000418
The phase angle of 0-pi is located in a quadrant N; if N is in the conjugate quadrant of M, then Ti *Symbol and T on a time slotiSymbols on a time slot
Figure BDA00026016006900000419
Of the same sign, i.e. Ti *Symbols on time slots
Figure BDA00026016006900000420
At this time, the fourth bit is judged to be + 1; if N is in the diagonal quadrant of M, then Ti *Symbol and T on a time slotiSymbols on a time slot
Figure BDA00026016006900000421
Opposite sign, i.e. Ti *Symbols on time slots
Figure BDA00026016006900000422
At this time, the fourth bit is judged to be-1;
3) according to the result of the decision in 2), if Ti *Symbols on a time slot are
Figure BDA00026016006900000423
Then is equal to TiSymbols on a time slot
Figure BDA00026016006900000424
The following operations are performed:
Figure BDA00026016006900000425
if T isi *Symbols on a time slot are
Figure BDA00026016006900000426
Then is equal to TiSymbols on a time slot
Figure BDA00026016006900000427
The following operations are performed:
Figure BDA00026016006900000428
to pair
Figure BDA0002601600690000051
And carrying out QPSK symbol judgment to recover the first two bits.
Further, the coherent optical wireless optical communication transmission method includes electro-optical modulation of a baseband signal, the baseband symbol stream generated in the X and Y polarization states is modulated by an electro-optical modulator to generate an optical signal for transmission, and the generated baseband signal stream in the X and Y polarization states may include an in-phase component IXAnd IYAnd a quadrature component QXAnd QYThe four paths of baseband signals are respectively modulated by two optical I/Q modulators; or the baseband signal flow in the X and Y polarization states can also be directly two paths of phase information, and the two paths of phase information are respectively corresponding to IX+j·QXAnd IY+j·QYAnd the two paths of phase information are obtained by calculating the phase angle, and are modulated by a phase modulator.
Further, the coherent optical wireless optical communication transmission method includes splitting an optical signal output by a laser through a polarization beam splitter to generate an optical signal in an X polarization state and an optical signal in a Y polarization state, modulating the two optical signals through a modulator, combining the optical signals through a polarization beam combiner, optically amplifying the optical signals, and transmitting the optical signals to a free space channel through an optical antenna.
Further, the coherent optical wireless optical communication transmission method is characterized in that after coherent reception of free space optical signals and free space transmission of optical signals sent by a transmitting end, the optical signals are received by an optical antenna at a receiving end, amplified by an optical amplifier and then enter an optical mixer together with a local oscillator laser for frequency mixing, the optical signals after frequency mixing are converted into four paths of analog electric signals through four balance detectors, and the four paths of analog electric signals are in-phase components I in an X polarization state respectivelyXAnd quadrature component QXAnd the in-phase component I in the Y polarization stateYAnd quadrature component QY(ii) a The four analog electric signals are converted into digital signals after analog/digital conversion, and the digital signals are processed by a baseband signal processing and demodulating module.
It is a further object of the invention to provide a computer device comprising a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to perform the steps of:
performing symbol mapping of data using three variables, namely phase, polarization state and data symbol bit, to generate baseband symbol streams in X and Y polarization states;
the four paths of baseband signals are subjected to I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two paths of symbol data streams corresponding to the generated baseband signals.
It is another object of the present invention to provide a computer-readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the steps of:
performing symbol mapping of data using three variables, namely phase, polarization state and data symbol bit, to generate baseband symbol streams in X and Y polarization states;
the four paths of baseband signals are subjected to I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two paths of symbol data streams corresponding to the generated baseband signals.
Another object of the present invention is to provide a coherent optical wireless optical communication transmission system implementing the coherent optical wireless optical communication transmission method, the coherent optical wireless optical communication transmission system including:
the electro-optical modulation module of the baseband signal is used for carrying out symbol mapping on data by utilizing three variables of phase, polarization state and data symbol bit so as to generate baseband symbol streams on X and Y polarization states;
and the baseband signal processing module is used for realizing that the four paths of baseband signals sequentially undergo I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation to obtain two paths of symbol data streams corresponding to the generated baseband signals.
By combining all the technical schemes, the invention has the advantages and positive effects that: the present invention is based on PSThe invention has the advantages that the information symbols with phase conjugate relation are cross-modulated in two adjacent symbol periods in the orthogonal polarization state, the phase noise introduced in the two polarization states after passing through an atmospheric turbulence channel has correlation, the influence of the phase noise can be eliminated at a receiving end by utilizing the correlation, the crosstalk between the polarization states in the same symbol period can be avoided, and the defects in the traditional technology are overcome. In order to verify the effectiveness of the technical scheme, the effect of the technical scheme is simulated under strong air turbulence, and is compared with the effect of the traditional scheme. The atmospheric structure constant of the simulated medium-intensity turbulence is
Figure BDA0002601600690000061
The bit error rate of the present invention and the prior art under the strong turbulence is shown in fig. 8. As can be seen from the graph, the solution of the present invention can bring about a significant bit error rate improvement compared to the prior art solutions.
The invention firstly introduces the symbol information with phase conjugation relation on the orthogonal polarization state, can effectively inhibit phase noise caused by atmospheric turbulence, and can effectively avoid crosstalk between the polarization states in the same symbol time slot period by cross-modulating the symbol information in two adjacent symbol periods on the orthogonal polarization state. Therefore, the invention can effectively improve the performance of the traditional atmosphere coherent optical communication system based on the PSK or QAM modulation mode, and the transmission distance of the atmosphere laser communication system is expanded.
The invention introduces the phase conjugation modulation format in the orthogonal polarization modulation, improves the defect that the traditional coherent optical communication based on PSK or QAM modulation mode can not directly overcome the phase noise caused by the atmospheric turbulence, reduces the system cost, and leads the application of the coherent laser communication in the free space in the atmosphere to be popularized and popularized.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained from the drawings without creative efforts.
Fig. 1 is a flowchart of a coherent optical wireless optical communication transmission method according to an embodiment of the present invention.
Fig. 2 is a schematic structural diagram of a coherent optical wireless optical communication transmission system provided by an embodiment of the present invention;
in the figure: 1. an electro-optical modulation module of a baseband signal; 2. and a baseband signal processing module.
Fig. 3 is a flow chart of information symbol mapping according to an embodiment of the present invention.
Fig. 4 is a flowchart of front-end processing of baseband signals according to an embodiment of the present invention.
Fig. 5 is a schematic block diagram 1 of an electro-optical modulation of a baseband signal according to an embodiment of the present invention.
Fig. 6 is a schematic block diagram 2 of an electro-optical modulation of a baseband signal according to an embodiment of the present invention.
Fig. 7 is a schematic block diagram of coherent reception of free-space optical signals according to an embodiment of the present invention.
FIG. 8 is a diagram illustrating the distribution of the received light field intensity at different atmospheric structure constants according to an embodiment of the present invention; in fig. 8: (a)
Figure BDA0002601600690000071
(b)
Figure BDA0002601600690000072
FIG. 9 is a strong turbulent flow provided by embodiments of the present invention
Figure BDA0002601600690000073
The error rate comparison schematic diagram of the technical scheme of the invention and the prior art is shown below.
FIG. 10 is a weak turbulence provided by embodiments of the present invention
Figure BDA0002601600690000081
The error rate comparison schematic diagram of the technical scheme of the invention and the prior art is shown below.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In view of the problems in the prior art, the present invention provides a coherent optical wireless optical communication transmission method, system, storage medium, and device, and the present invention is described in detail below with reference to the accompanying drawings.
As shown in fig. 1, the coherent optical wireless optical communication transmission method provided by the present invention includes the following steps:
s101: symbol mapping of the data is performed using three variables, phase, polarization state and data symbol bit, to produce a baseband symbol stream in the X and Y polarization states.
S102: the four paths of baseband signals are subjected to I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two paths of symbol data streams corresponding to the generated baseband signals.
Those skilled in the art can also implement the coherent optical wireless optical communication transmission method provided by the present invention by using other steps, and the coherent optical wireless optical communication transmission method provided by the present invention in fig. 1 is only one specific embodiment.
As shown in fig. 2, the coherent optical wireless optical communication transmission system provided by the present invention includes:
the electro-optical modulation module 1 of the baseband signal is used for carrying out symbol mapping of data by using three variables of phase, polarization state and data symbol bit so as to generate baseband symbol streams on X and Y polarization states.
And the baseband signal processing module 2 is used for realizing that the four paths of baseband signals sequentially undergo I/Q imbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation to obtain two paths of symbol data streams corresponding to the generated baseband signals.
The technical solution of the present invention is further described below with reference to the accompanying drawings.
1. Baseband signal generation
The invention fully utilizes three variables of phase, polarization state and data sign bit to carry out data sign mapping so as to generate baseband symbol streams on X and Y polarization states. Here, the symbol mapping method is specifically described by taking QPSK as an example, as shown in fig. 3.
The first step is as follows: a binary data stream (consisting of 0 and 1) to be transmitted is information mapped, where bit 0 is mapped to-1 and bit 1 is mapped to + 1. Assuming the binary bit stream is 010100101100 in FIG. 1, the mapping becomes-1, +1, -1, +1, -1, -1.
The second step is that: the data streams (consisting of +1 and-1) resulting from the mapping of information in the first step are grouped, with every four adjacent bits grouped. As shown in the figure, the-1, +1, -1, +1, -1, -1, +1, -1, +1, +1, -1, -1 data streams are divided into three groups, the first group being +1, -1, +1, -1; the second group is-1, +1, -1, + 1; the third group is +1, +1, -1, -1.
The third step: and carrying out symbol mapping on each group after the grouping in the second step. Wherein the first two bits of each group are mapped to QPSK symbols SiThe third bit is mapped to the X/Y polarization state, i.e. the symbol S mapped by the first two bits when the third bit is +1iWill be in time slot TiThe polarization state of the X (or Y) is transmitted, and no information is transmitted in the polarization state of the Y (or X); symbol S mapped by the first two bits when the third bit is-1iWill be in time slot TiIt is transmitted in the Y (or X) polarization state, and no information is transmitted in the X (or Y) polarization state. The fourth bit of each group is mapped to the symbol b × (S)i)*Where b is the value of the fourth bit, either +1 or-1. (S)i)*QPSK symbols S representing the mapping of the first two bits in each groupiComplex conjugation of (c) (. 1)*Indicating a complex conjugate calculation. Symbol of fourth bit mappingb×(Si)*In the following time slot TiThen Ti *Time slot transmission, and the polarization state occupied by it and time slot TiTransmitted symbol SiThe occupied polarization states are mutually exclusive, i.e. if SiTransmitting in X polarization state, then b × (S)i)*Transmitting in the Y polarization state, otherwise, if SiTransmitting in Y polarization state, then b × (S)i)*Transmitting in the X polarization state. Thus, four bits of each group are mapped to produce a baseband symbol stream in both the X and Y polarization states. For example, the first group of data-1, +1, -1, +1 after the second step of grouping in fig. 1, where the first two bits-1, +1 are mapped to QPSK symbol S1The third bit-1 is mapped to the Y polarization state, i.e. the first two bits-1, +1 are mapped to the symbol S1Will be in time slot T1It is transmitted in the Y polarization state, and no information is transmitted in the X polarization state, which is indicated by 0. The fourth bit +1 is mapped to a symbol
Figure BDA0002601600690000091
And is
Figure BDA0002601600690000092
Will follow the time slot T1Then T1 *The time slot is transmitted, and the time slot transmits in the X polarization state, and no information is transmitted in the Y polarization state at the time, and the time slot is indicated by 0; after the-1, -1, +1, -1 of the second group is mapped according to the same mapping method, the time slot T is used2Transmitting the symbol S in the X polarization state2In time slot T2 *Transmitting symbols in the Y polarization state
Figure BDA0002601600690000101
After the +1, +1, -1, -1 mapping of the third group, in time slot T3Transmitting symbols S in the Y polarization state3In time slot T2 *Transmitting symbols in the X polarization state
Figure BDA0002601600690000102
The resulting baseband symbol stream in the X polarization state is 0,
Figure BDA0002601600690000103
S2，0，0，
Figure BDA0002601600690000104
the baseband symbol stream in the Y polarization state is S1，0，0，
Figure BDA0002601600690000105
S3，0。
2. Baseband signal processing
The baseband signal front-end processing flow is shown in fig. 4. The four baseband signals are subjected to I/Q imbalance compensation, channel equalization, timing recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two symbol data streams corresponding to the baseband signals generated in the figure 1. One of the paths is the symbol data stream 0 in the X polarization state,
Figure BDA0002601600690000106
0，0，
Figure BDA0002601600690000107
and the other is a symbol data stream in the Y polarization state
Figure BDA0002601600690000108
Figure BDA0002601600690000108
Figure BDA0002601600690000108
Figure BDA0002601600690000108
0，0，
Figure BDA0002601600690000109
Figure BDA00026016006900001010
0. The two paths of symbol data are influenced by noise after being transmitted, and errors exist between the two paths of symbol data and the symbol data of a transmitting end. Despite the various signal processing procedures in fig. 5, there is still a large noise between the two paths of symbol data and the transmitted symbol data. After the front-end processing of the baseband signals, the two baseband signal symbol streams corresponding to the X and Y polarization states are synchronized, and the two data streams are aligned with each other on each time slot. And at the moment, the two paths of aligned symbol data streams are judged and restored through the following steps:
1) at TiTaking two symbols in X and Y polarization states during time slot
Figure BDA00026016006900001011
And
Figure BDA00026016006900001012
die of
Figure BDA00026016006900001013
And
Figure BDA00026016006900001014
if it is
Figure BDA00026016006900001015
Or
Figure BDA00026016006900001016
Wherein Threshold is the selected Threshold, the symbol is declared
Figure BDA00026016006900001017
In the X polarization state, the information recovered by the third bit is + 1; on the contrary, if
Figure BDA00026016006900001018
Or
Figure BDA00026016006900001019
Then explain the symbol
Figure BDA00026016006900001020
In the Y polarization state, the information recovered by the third bit at this time is-1.
2) At TiTime slot, symbol
Figure BDA00026016006900001021
The quadrant in which the phase angle (range: 0-pi) is located is M; at Ti *Time slot, to and symbol
Figure BDA00026016006900001022
Sign-up on mutually exclusive states of polarization
Figure BDA00026016006900001023
Or
Figure BDA00026016006900001024
Quadrant N in which the phase angle (range: 0-pi) of (A) is located; if N is in the conjugate quadrant of M, then Ti *Symbol and T on a time slotiSymbols on a time slot
Figure BDA00026016006900001025
Of the same sign, i.e. Ti *Symbols on time slots
Figure BDA00026016006900001026
At this time, the fourth bit is judged to be + 1; if N is in the diagonal quadrant of M, then Ti *Symbol and T on a time slotiSymbols on a time slot
Figure BDA00026016006900001027
Opposite sign, i.e. Ti *Symbols on time slots
Figure BDA0002601600690000111
The fourth bit is now decided to be-1.
3) According to the result of the decision in 2), if Ti *Symbols on a time slot are
Figure BDA0002601600690000112
Then is equal to TiSymbols on a time slot
Figure BDA0002601600690000113
The following operations are performed:
Figure BDA0002601600690000114
if T isi *Symbols on a time slot are
Figure BDA0002601600690000115
Then is equal to TiSymbols on a time slot
Figure BDA0002601600690000116
The following operations are performed:
Figure BDA0002601600690000117
to pair
Figure BDA0002601600690000118
And carrying out QPSK symbol judgment to recover the first two bits.
The technical solution of the present invention is further described with reference to the following specific examples.
The coherent optical wireless optical communication transmission method provided by the embodiment of the invention comprises the following steps:
1. electro-optical modulation of baseband signals
The baseband symbol streams produced at the X and Y polarization states are modulated by an electro-optic modulator to produce an optical signal for transmission. The whole modulation system is composed into a block diagram as shown in fig. 5 or fig. 6. The baseband signal streams at the X and Y polarization states produced by the flow of fig. 3 may contain in-phase components IXAnd IYAnd a quadrature component QXAnd QYThe four baseband signals are modulated by two optical I/Q modulators, respectively, as shown in fig. 5. Or the baseband signal flow in the X and Y polarization states can also be directly two paths of phase information, and the two paths of phase information are respectively corresponding to IX+j·QXAnd IY+j·QYThe two paths of phase information obtained by calculating the phase angle are modulated by the phase modulator, as shown in fig. 6.
In fig. 5 and 6, an optical signal output by a laser is split by a polarization beam splitter to generate one path of optical signal in an X polarization state and one path of optical signal in a Y polarization state, and the two paths of optical signals are modulated by a modulator (an optical I/Q modulator in fig. 5, a phase modulator in fig. 6), combined by a polarization beam combiner, optically amplified, and transmitted to a free space channel (an atmospheric channel or a vacuum channel) through an optical antenna.
2. Coherent reception of free-space optical signals
After the optical signal sent by the transmitting end is transmitted in free space, the optical signal is received by an optical antenna at the receiving end, amplified by an optical amplifier and then enters an optical mixer together with a local oscillator laser for frequency mixing, the optical signal after frequency mixing is converted into four paths of analog electric signals through four balance detectors, and the four paths of analog electric signals are in-phase components I on X polarization states respectivelyXAnd quadrature component QXAnd the in-phase component I in the Y polarization stateYAnd quadrature component QY. The four analog electric signals are converted into digital signals after analog/digital conversion, and the digital signals are processed by a baseband signal processing and demodulating module.
The technical effects of the present invention will be described in detail with reference to experiments.
In order to verify the effectiveness of the technical scheme, the effect of the technical scheme is simulated under the atmospheric turbulence with different strengths, and compared with the effect of the traditional scheme. The atmospheric structure constant of the simulated medium-intensity turbulence is
Figure BDA0002601600690000121
The atmospheric structure constant of weak turbulence is
Figure BDA0002601600690000122
The light intensity distribution obtained at the receiving end under strong turbulence and weak turbulence is shown in fig. 8.
Fig. 9 and 10 show the bit error rate obtained by processing the optical signal received in the above diagram according to the technical solutions of the present invention and the prior art. As can be seen from the graphs in fig. 9 and 10, the solution of the present invention can bring about a significant bit error rate improvement compared to the prior art solution.
It should be noted that the embodiments of the present invention can be realized by hardware, software, or a combination of software and hardware. The hardware portion may be implemented using dedicated logic; the software portions may be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or specially designed hardware. Those skilled in the art will appreciate that the apparatus and methods described above may be implemented using computer executable instructions and/or embodied in processor control code, such code being provided on a carrier medium such as a disk, CD-or DVD-ROM, programmable memory such as read only memory (firmware), or a data carrier such as an optical or electronic signal carrier, for example. The apparatus and its modules of the present invention may be implemented by hardware circuits such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., or by software executed by various types of processors, or by a combination of hardware circuits and software, e.g., firmware.
The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.

Claims (10)

1. A coherent optical wireless optical communication transmission method, comprising:
performing symbol mapping of data using three variables, namely phase, polarization state and data symbol bit, to generate baseband symbol streams in X and Y polarization states;
the four paths of baseband signals are subjected to I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two paths of symbol data streams corresponding to the generated baseband signals.
2. The coherent optical wireless optical communication transmission method of claim 1, wherein said symbol mapping of data using three variables, phase, polarization state and data symbol bit, to generate baseband symbol streams in X and Y polarization states comprises:
firstly, information mapping is carried out on binary data streams to be transmitted, wherein bit 0 is mapped to-1, and bit 1 is mapped to + 1;
secondly, grouping the data streams generated by the information mapping in the first step, wherein every four adjacent bits form a group;
thirdly, symbol mapping is carried out on each group grouped in the second step; wherein the first two bits of each group are mapped to QPSK symbols SiThe third bit is mapped to the X/Y polarization state, i.e. the symbol S mapped by the first two bits when the third bit is +1iWill be in time slot TiThe information is sent in the X or Y polarization state, and no information is sent in the Y or X polarization state; symbol S mapped by the first two bits when the third bit is-1iWill be in time slot TiThe information is sent in a Y or X polarization state, and no information is sent in the X or Y polarization state; the fourth bit of each group is mapped to the symbol b × (S)i)*Wherein b is the value of the fourth bit, and is +1 or-1; (S)i)*QPSK symbols S representing the mapping of the first two bits in each groupiComplex conjugation of (c) (. 1)*Representing a complex conjugate calculation; symbol b x (S) of the fourth bit mapi)*In the following time slot TiThen Ti *Time slot transmission, and the polarization state occupied by it and time slot TiTransmitted symbol SiThe occupied polarization states are mutually exclusive, i.e. if SiTransmitting in X polarization state, then b × (S)i)*Transmitting in the Y polarization state, otherwise, if SiTransmitting in Y polarization state, then b × (S)i)*Transmitting in an X polarization state; the four bits of each group are mapped to produce a stream of baseband symbols in the X and Y polarization states.
3. The coherent optical wireless optical communication transmission method according to claim 1, wherein obtaining two symbol data streams corresponding to the generated baseband signals after the four baseband signals are sequentially subjected to I/Q imbalance compensation, channel equalization, timing recovery, carrier frequency offset compensation, and carrier phase offset compensation comprises: one of the paths is the symbol data stream 0 in the X polarization state,
Figure FDA0002601600680000021
0，0，
Figure FDA0002601600680000022
and the other is a symbol data stream in the Y polarization state
Figure FDA0002601600680000023
0，0，
Figure FDA0002601600680000024
0; errors exist between the two paths of symbol data which are influenced by noise after being transmitted and the symbol data of a transmitting end; after the front-end processing of the baseband signals, the two baseband signal symbol streams corresponding to the X and Y polarization states are synchronized, and the two data streams are aligned with the symbols on each time slot; and performing decision recovery on the two aligned symbol data streams.
4. The coherent optical wireless optical communication transmission method according to claim 3, wherein said decision recovery of the two aligned symbol data streams comprises:
1) at TiTaking two symbols in X and Y polarization states during time slot
Figure FDA0002601600680000025
And
Figure FDA0002601600680000026
die of
Figure FDA0002601600680000027
And
Figure FDA0002601600680000028
if it is
Figure FDA0002601600680000029
Or
Figure FDA00026016006800000210
Wherein Threshold is the selected Threshold, the symbol is declared
Figure FDA00026016006800000211
In the X polarization state, the information recovered by the third bit is + 1; on the contrary, if
Figure FDA00026016006800000212
Or
Figure FDA00026016006800000213
Then explain the symbol
Figure FDA00026016006800000214
In the Y polarization state, the information recovered by the third bit is-1;
2) at TiTime slot, symbol
Figure FDA00026016006800000215
The quadrant in which the phase angle is 0-pi is M; at Ti *Time slot, to and symbol
Figure FDA00026016006800000216
Sign-up on mutually exclusive states of polarization
Figure FDA00026016006800000217
Or
Figure FDA00026016006800000218
The phase angle of 0-pi is located in a quadrant N; if N is in the conjugate quadrant of M, then Ti *Symbol and T on a time slotiSymbols on a time slot
Figure FDA00026016006800000219
Of the same sign, i.e. Ti *Symbols on time slots
Figure FDA00026016006800000220
At this time, the fourth bit is judged to be + 1; if N is in the diagonal quadrant of M, then Ti *Symbol and T on a time slotiSymbols on a time slot
Figure FDA00026016006800000227
Opposite sign, i.e. Ti *Symbols on time slots
Figure FDA00026016006800000221
At this time, the fourth bit is judged to be-1;
3) according to the result of the decision in 2), if Ti *Symbols on a time slot are
Figure FDA00026016006800000222
Then is equal to TiSymbols on a time slot
Figure FDA00026016006800000223
The following operations are performed:
Figure FDA00026016006800000224
if T isi *Symbols on a time slot are
Figure FDA00026016006800000225
Then is equal to TiSymbols on a time slot
Figure FDA00026016006800000226
The following operations are performed:
Figure FDA0002601600680000031
to pair
Figure FDA0002601600680000032
And carrying out QPSK symbol judgment to recover the first two bits.
5. The coherent optical wireless optical communication transmission method according to claim 1, wherein the coherent optical wireless optical communication transmission method comprises electro-optical modulation of a baseband signal, the baseband symbol streams generated in the X and Y polarization states are modulated by an electro-optical modulator to generate an optical signal for transmission, and the generated baseband symbol streams in the X and Y polarization states may contain an in-phase component IXAnd IYAnd a quadrature component QXAnd QYThe four paths of baseband signals are respectively modulated by two optical I/Q modulators; or the baseband signal flow in the X and Y polarization states can also be directly two paths of phase information, and the two paths of phase information are respectively corresponding to IX+j·QXAnd IY+j·QYAnd the two paths of phase information are obtained by calculating the phase angle, and are modulated by a phase modulator.
6. The coherent optical wireless optical communication transmission method according to claim 1, wherein an optical signal output by the laser is split by a polarization beam splitter to generate an optical signal in an X polarization state and an optical signal in a Y polarization state, and the two optical signals are modulated by a modulator, combined by the polarization beam combiner, optically amplified, and transmitted to a free space channel through an optical antenna.
7. The coherent optical wireless optical communication transmission method according to claim 1, wherein coherent reception of the free-space optical signal in the coherent optical wireless optical communication transmission method is performed by receiving the optical signal transmitted from the transmitting end by the optical antenna at the receiving end after free-space transmission, amplifying the optical signal by the optical amplifier, and then mixing the amplified optical signal with the local oscillator laser in the optical mixer, and the mixed optical signal is converted into four analog electrical signals by four balanced detectors, wherein the four analog electrical signals are the in-phase component I in the X polarization stateXAnd quadrature component QXAnd Y polarizationIn-phase component I in phaseYAnd quadrature component QY(ii) a The four analog electric signals are converted into digital signals after analog/digital conversion, and the digital signals are processed by a baseband signal processing and demodulating module.
8. A computer device, characterized in that the computer device comprises a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to carry out the steps of:
performing symbol mapping of data using three variables, namely phase, polarization state and data symbol bit, to generate baseband symbol streams in X and Y polarization states;
the four paths of baseband signals are subjected to I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two paths of symbol data streams corresponding to the generated baseband signals.
9. A computer-readable storage medium storing a computer program which, when executed by a processor, causes the processor to perform the steps of:
performing symbol mapping of data using three variables, namely phase, polarization state and data symbol bit, to generate baseband symbol streams in X and Y polarization states;
the four paths of baseband signals are subjected to I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation in sequence to obtain two paths of symbol data streams corresponding to the generated baseband signals.
10. A coherent optical wireless optical communication transmission system for implementing the coherent optical wireless optical communication transmission method according to any one of claims 1 to 7, the coherent optical wireless optical communication transmission system comprising:
the electro-optical modulation module of the baseband signal is used for carrying out symbol mapping on data by utilizing three variables of phase, polarization state and data symbol bit so as to generate baseband symbol streams on X and Y polarization states;
and the baseband signal processing module is used for realizing that the four paths of baseband signals sequentially undergo I/Q unbalance compensation, channel equalization, time sequence recovery, carrier frequency offset compensation and carrier phase offset compensation to obtain two paths of symbol data streams corresponding to the generated baseband signals.
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CN113938624A (en) * 2021-10-15 2022-01-14 北京邮电大学 Carrier crosstalk and polarization crosstalk combined compensation method in multi-carrier system
CN114111852A (en) * 2021-11-11 2022-03-01 中国电信股份有限公司 Method, device and system for generating two-way coherent optical signal and storage medium
CN114244435A (en) * 2021-12-20 2022-03-25 北京大学 Optical communication device and method based on polarization direction domain orthogonality
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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113938624A (en) * 2021-10-15 2022-01-14 北京邮电大学 Carrier crosstalk and polarization crosstalk combined compensation method in multi-carrier system
CN113938624B (en) * 2021-10-15 2022-06-07 北京邮电大学 Carrier crosstalk and polarization crosstalk combined compensation method in multi-carrier system
CN114111852A (en) * 2021-11-11 2022-03-01 中国电信股份有限公司 Method, device and system for generating two-way coherent optical signal and storage medium
CN114111852B (en) * 2021-11-11 2023-09-12 中国电信股份有限公司 Dual-path coherent optical signal generation method, device and system and storage medium
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CN117176259A (en) * 2023-11-02 2023-12-05 众瑞速联（武汉）科技有限公司 Four-way multiplexing optical communication method and device based on self-coherence
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