CN109600332B - CO-FBMC/OQAM modulation method and system - Google Patents

CO-FBMC/OQAM modulation method and system Download PDF

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CN109600332B
CN109600332B CN201811394725.8A CN201811394725A CN109600332B CN 109600332 B CN109600332 B CN 109600332B CN 201811394725 A CN201811394725 A CN 201811394725A CN 109600332 B CN109600332 B CN 109600332B
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pilot
signal
pilot frequency
phase noise
frequency
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CN109600332A (en
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罗风光
游璧毓
杨柳
杨帅龙
陈丹慧
倪垚
李斌
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2626—Arrangements specific to the transmitter only
    • H04L27/2627—Modulators
    • H04L27/264—Pulse-shaped multi-carrier, i.e. not using rectangular window
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2602—Signal structure
    • H04L27/261—Details of reference signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2668—Details of algorithms
    • H04L27/2673—Details of algorithms characterised by synchronisation parameters
    • H04L27/2675—Pilot or known symbols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2697—Multicarrier modulation systems in combination with other modulation techniques

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Abstract

The invention discloses a modulation method and a system of CO-FBMC/OQAM, which comprises an interference elimination pilot frequency module and a Kalman filtering compensation module; the interference elimination pilot frequency module comprises a first pilot frequency unit and a second pilot frequency unit which are respectively arranged at two ends of the symbol mapping module and used for removing inherent imaginary part interference at a pilot frequency position and ensuring that each CO-FBMC/OQAM symbol has a pilot frequency symbol to record phase noise superposed on the pilot frequency symbol; and the Kalman filtering compensation module extracts a test pilot frequency symbol of the receiving end, corrects the prediction process of the pilot frequency symbol to obtain a phase noise estimation value of the current moment, and then outputs the estimation value of a receiving end signal. The technical scheme has the capability of eliminating the inherent interference at the pilot frequency position, and meanwhile, the Kalman filtering processing module only needs to adopt one pilot frequency for operation, so that the technical scheme has the capabilities of reducing the calculated amount and reducing the judgment error.

Description

CO-FBMC/OQAM modulation method and system
Technical Field
The invention belongs to the field of optical communication, and particularly relates to a CO-FBMC/OQAM modulation method and system.
Background
Although a traditional Coherent Optical filter bank multi-carrier/offset Quadrature Amplitude Modulation (CO-FBMC/OQAM) system in Optical communication omits a cyclic prefix, which is better than the CO-OFDM system to a certain extent, the transmission performance of the CO-FBMC/OQAM system is susceptible to phase noise due to the longer symbol length and the high peak-to-average power ratio of the CO-FBMC/OQAM system, and the phase noise mainly comes from the laser line width and link nonlinearity, so that the rotation and divergence of a Modulation constellation diagram at a receiving end are generated, thereby increasing the error rate. Therefore, how to efficiently monitor and compensate for the phase noise is a key problem of the CO-FBMC/OQAM system, wherein the imaginary part interference inherent to the system becomes a difficult problem that the phase noise processing algorithm has to solve.
The existing scheme for solving the estimation and compensation of the system phase noise is a Kalman filtering algorithm compensation scheme based on blind decision, the compensation scheme not only has higher calculation complexity, but also is very easy to generate decision errors when the phase noise of a laser is larger due to the influence of system inherent interference superposed on each symbol used for the blind decision, and therefore, the compensation range of the scheme is extremely limited.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to add an interference elimination pilot frequency module at the position of a fixed subcarrier behind a symbol mapping module at the sending end of a system and add a Kalman filtering processing module at the position corresponding to the pilot frequency addition behind an optical domain-frequency domain conversion module at the receiving end of the system, and aims to solve the problems of estimation error caused by the inherent imaginary part interference of the system to the pilot frequency and the compensation of phase noise corresponding to the receiving end.
To achieve the above object, in one aspect, the present invention provides a CO-FBMC/OQAM modulation method, including:
(1) converting a bit signal input by a CO-FBMC/OQAM system into a PAM data symbol;
(2) three rows of subcarriers are accessed to one end of the PAM data symbol, pilot symbols are placed at odd-numbered positions of the subcarriers in the middle row, zero symbols are placed at even-numbered positions of the subcarriers in the middle row, and the other two rows of subcarriers are all set to zero, so that the access of the PAM data symbol and the first pilot unit is completed;
(3) three rows of subcarriers are accessed to the other end of the PAM data symbol, pilot symbols are placed at even-numbered positions of the subcarriers in the middle row, zero symbols are placed at odd-numbered positions of the subcarriers in the middle row, and the other two rows of subcarriers are all set to zero, so that the access of the PAM data symbol and the second pilot unit is completed;
(4) the first pilot frequency unit and the second pilot frequency unit receive the PAM data symbol, eliminate the inherent imaginary part interference of the system and record the phase information of the pilot frequency position;
(5) the frequency domain-time domain conversion module receives the frequency domain signal processed by the pilot frequency unit, performs modulation after the frequency domain signal is subjected to orthogonalization pretreatment, and completes the conversion from the frequency domain signal to the time domain signal;
(6) carrying out IQ modulation on the acquired time domain signal after parallel-serial conversion and training sequence processing so as to transmit the signal to a system receiving end;
(7) the optical domain-frequency domain conversion module receives the received optical domain signals through coherent detection balance to obtain baseband signals;
(8) demodulating the baseband signal after timing synchronization and serial-parallel conversion to obtain a frequency domain signal;
(9) extracting a test pilot signal at the receiving end of the pilot position;
(10) multiplying the pilot signal known by the transmitting end by the phase noise estimation value at the previous moment to obtain the predicted value of the receiving end pilot signal corresponding to the transmitting end pilot signal;
(11) subtracting the predicted value of the test pilot signal and the pilot signal at the receiving end to obtain an error signal between the test pilot signal and the pilot signal;
(12) multiplying the error signal by a fixed Kalman gain to obtain a correction value of the phase noise;
(13) adding the multiplied value and the phase noise estimation value at the previous moment to obtain the phase noise estimation value at the current moment;
(14) performing conjugation processing on the phase noise estimation value at the current moment;
(15) multiplying the conjugate value of the phase noise by the pilot frequency symbol of the receiving end to obtain an estimated value after the phase noise compensation as a signal of the phase noise compensation;
(16) recovering a bit signal after demapping the output signal of the phase compensation;
(17) and performing delay processing on the phase noise estimated value at the current moment to serve as the phase noise estimated value at the previous moment.
On the other hand, the invention provides a CO-FBMC/OQAM system, which comprises a symbol mapping module, a disturbance elimination pilot frequency module, a frequency domain-time domain conversion module, an IQ modulation module, an optical domain-frequency domain conversion module, a Kalman filtering compensation module and a symbol de-mapping module;
the symbol mapping module is used for receiving the bit data after serial-parallel conversion, outputting a signal after the complex number is converted into a real number, and transmitting a real value signal to the interference elimination pilot frequency module;
the interference elimination pilot frequency module is used for receiving the real-value signal transmitted by the symbol mapping module and outputting a frequency domain signal for eliminating the pilot frequency inherent interference, and pilot frequency signals are added at two ends of the symbol mapping module and are used for recording phase information in the pilot frequency signals and acquiring the influence of phase noise on the system;
preferably, the interference elimination pilot module comprises a first pilot unit and a second pilot unit; the first pilot frequency unit and the second pilot frequency unit comprise 3 rows of subcarriers, pilot frequency symbols of the subcarriers positioned in the middle row are alternated with zero setting symbols, the subcarriers of the other two rows are set to be zero, and the pilot frequency symbols of the first pilot frequency unit and the second pilot frequency unit are respectively arranged at the odd number position and the even number position of the corresponding subcarriers;
the frequency domain-time domain conversion module is used for receiving the frequency domain signal transmitted by the pilot frequency module and outputting a time domain signal;
the IQ modulation module is used for receiving a time domain signal and outputting an optical domain signal;
the optical domain-frequency domain conversion module is used for receiving the optical domain signal and outputting a frequency domain signal;
the Kalman filtering compensation module is used for calculating a phase noise value at the position of a pilot frequency symbol based on the state of eliminating the inherent interference of the pilot frequency symbol by the interference elimination pilot frequency module, so as to compensate the phase noise and finally output a frequency domain signal after phase compensation;
preferably, the kalman filter compensation module includes: the pilot frequency extracting unit, the subtracter, the first multiplier, the adder, the delay unit, the second multiplier, the conjugate processing unit and the third multiplier;
the input end of the pilot frequency extraction unit is connected with the optical domain-frequency domain conversion module, and the output end of the pilot frequency extraction unit is connected with the subtracter;
the input end of the subtracter is connected with the output end of the pilot frequency extraction unit and the output end of the second multiplier, and the output end of the subtracter is connected with the input end of the first multiplier;
the input end of the first multiplier is connected with the output end of the subtracter and receives the fixed Kalman gain; the output end is connected with the input end of the adder;
the input end of the adder is connected with the output end of the first multiplier and the output end of the delay unit, and the output end of the adder is connected with the input end of the delay unit and the input end of the conjugate processing unit;
the input end of the delay unit is connected with the output end of the adder, and the output end of the delay unit is connected with the input end of the adder and the input end of the second multiplier;
the input end of the second multiplier is connected with the output end of the delay unit;
the input end of the conjugate processing unit is connected with the output end of the adder, and the output end of the conjugate processing unit is connected with the input end of the third multiplier;
the input end of the third multiplier is connected with the output end of the conjugate processing unit, and the output end of the third multiplier is connected with the real complex number conversion module;
the pilot frequency extracting unit is used for extracting a pilot frequency signal from a receiving end pilot frequency;
the subtracter is used for subtracting the pilot signal at the receiving end from the predicted pilot signal to obtain an error signal between the pilot signal and the predicted pilot signal;
the first multiplier is used for multiplying the error signal by the fixed Kalman gain;
the adder is used for adding the result obtained by the multiplier and the phase noise estimation value at the previous moment to obtain the phase noise estimation value at the current moment;
the delay unit is used for converting the phase noise estimation value of the current moment into the phase noise estimation value of the previous moment;
the second multiplier is used for multiplying the pilot signal of the sending end with the phase noise estimated value at the previous moment to obtain a receiving pilot value corresponding to the predicted pilot symbol;
the conjugation processing unit is used for obtaining a conjugation value of the phase noise at the current moment;
the third multiplier is used for multiplying the conjugate value of the phase noise at the current moment by the pilot frequency symbol at the receiving end to obtain an estimated value after the phase noise is compensated;
the symbol demapping module is used for receiving the frequency domain signal of the frequency domain signal after the real number is converted into the complex number, and outputting bit data.
Through the technical scheme, compared with the prior art, the invention has the following beneficial effects:
(1) the invention adopts the interference elimination pilot frequency module to ensure that the pilot frequency symbol is not influenced by the inherent imaginary part interference in the CO-FBMC/OQAM system, thereby improving the accuracy of the system to the phase noise estimation.
(2) The interference elimination pilot frequency module adopted by the invention can ensure that only one pilot frequency is adopted to record the phase noise for each FBMC symbol, can avoid the defect that the phase noise on each subcarrier needs to be calculated and solved in a blind decision algorithm, and thus can greatly reduce the calculation complexity.
(3) The invention adopts the Kalman filtering algorithm based on the pilot frequency to estimate the phase noise, and can avoid the judgment process required in blind estimation, thereby avoiding the introduction of judgment errors.
Drawings
Fig. 1 is a structural design diagram of a interference cancellation pilot module according to an embodiment of the present invention;
FIG. 2 is a block diagram of a Kalman filtering processing module provided by the present invention;
FIG. 3 is a schematic diagram of a CO-FBMC/OQAM system provided by the present invention;
fig. 4 is a schematic diagram of a 16QAM modulated CO-FBMC/OQAM system provided in this embodiment;
fig. 5 is a simulation result provided by an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and 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.
The invention provides a modulation method of a CO-FBMC/OQAM system, which comprises the following steps:
s1: the symbol mapping module receives the binary input bit signals after serial-parallel conversion, and the output signals are converted into PAM data symbols through complex number to real number conversion;
s2: respectively accessing a first pilot frequency unit and a second pilot frequency unit of a de-interference pilot frequency module at two ends of a PAM data symbol;
s3: the frequency domain-time domain conversion module receives the frequency domain signal processed by the pilot frequency unit, performs modulation after the frequency domain signal is subjected to orthogonalization pretreatment, and completes the conversion from the frequency domain signal to the time domain signal;
s4: the acquired time domain signal is processed by parallel-to-serial conversion and training sequence and then orthogonal (IQ) modulated to transmit the signal to the system receiving end
S5: the optical domain-frequency domain conversion module converts the received optical domain signal into a frequency domain signal, and the phase noise is compensated through the Kalman filtering compensation module;
s6: and recovering the bit signal after the output signal of the phase compensation passes through a symbol demapping module.
Fig. 1 shows a connection relationship between a pilot-interference cancellation module and a Pulse Amplitude Modulation (PAM) data symbol provided by the present invention, and as can be seen from fig. 1, the step S2 specifically includes the following steps:
s2.1: setting three rows of carriers to enable odd-numbered positions of subcarriers in the middle row to be provided with pilot symbols, even-numbered positions to be provided with zero symbols and the rest two rows of subcarriers to be provided with zero symbols, and finishing the setting of a first pilot unit;
s2.2: setting three rows of carriers to enable odd-numbered positions of subcarriers in the middle row to be provided with pilot symbols, even-numbered positions to be provided with zero symbols and the rest two rows of subcarriers to be provided with zero symbols, and finishing the setting of a first pilot unit;
s2.3: the first pilot frequency unit and the second pilot frequency unit are respectively connected to two ends of the PAM data symbol.
Fig. 2 is a schematic diagram of a specific structure calculated by the kalman filter compensation module according to the present invention, where the step S5 specifically includes the following steps according to the kalman phase compensation method shown in fig. 2:
s5.1: the pilot frequency extracting unit extracts a test pilot frequency signal at the pilot frequency position receiving end;
s5.2: multiplying the pilot signal known by the transmitting end by the phase noise estimation value at the previous moment to obtain the predicted value of the receiving end pilot signal corresponding to the transmitting end pilot signal;
s5.3: and subtracting the predicted values of the test pilot signal and the pilot signal at the receiving end to obtain an error signal between the test pilot signal and the pilot signal.
S5.4: multiplying the error signal by a fixed Kalman gain to obtain a correction value of the phase noise;
s5.5: adding the multiplied value and the phase noise estimation value at the previous moment to obtain the phase noise estimation value at the current moment;
s5.6: performing conjugation processing on the phase noise estimation value at the current moment;
s5.7: multiplying the conjugate value of the phase noise by the pilot frequency symbol of the receiving end to obtain an estimated value after the phase noise compensation as a signal of the phase noise compensation;
s5.8: and performing delay processing on the phase noise estimated value at the current moment to serve as the phase noise estimated value at the previous moment.
Fig. 3 is a schematic diagram of a CO-FBMC/OQAM system according to the present invention, and as can be seen from fig. 3, a transmitting end of the CO-FBMC/OQAM system includes a symbol mapping module, an interference cancellation pilot module, and a frequency domain-time domain conversion module, a receiving end includes an optical domain-frequency domain conversion module, a kalman filter compensation module, and a symbol demapping module, and the transmitting end and the receiving end of the system are connected through an IQ modulation module, and convert a time domain signal of the transmitting end into an optical domain signal and transmit the optical domain signal to the receiving end;
preferably, the symbol mapping module is configured to receive bit data subjected to serial-to-parallel conversion, convert an output signal into a real number through a complex number, and transmit a real-valued signal to the interference cancellation pilot module;
the interference elimination pilot frequency module is used for receiving the real-value signal transmitted by the symbol mapping module, outputting a frequency domain signal for eliminating the pilot frequency inherent interference, and simultaneously recording phase information in the pilot frequency signal so as to acquire the influence of phase noise on the system;
the frequency domain-time domain conversion module is used for receiving the frequency domain signal transmitted by the pilot frequency module and outputting a time domain signal;
the IQ modulation module is used for receiving a time domain signal and outputting an optical domain signal;
the optical domain-frequency domain conversion module is used for receiving the optical domain signal and outputting a frequency domain signal;
the Kalman filtering compensation module is used for calculating a phase noise value at the position of a pilot frequency symbol based on the state of eliminating the inherent interference of the pilot frequency symbol by the interference elimination pilot frequency module, so as to compensate the phase noise and finally output a frequency domain signal after phase compensation;
the symbol demapping module is used for receiving the frequency domain signal of the frequency domain signal after the real number is converted into the complex number, and outputting bit data.
Preferably, the structure of the interference cancellation pilot module is as shown in fig. 1, where the interference cancellation pilot module includes a first pilot unit and a second pilot unit;
preferably, the first pilot unit and the second pilot unit each include 3 rows of subcarriers, pilot symbols located in the middle row of subcarriers are alternated with a zero-setting symbol, the pilot symbols of the first pilot unit and the second pilot unit are respectively placed at odd positions and even positions of corresponding subcarriers, and the other two rows of subcarriers are set to zero;
the interference elimination pilot module can effectively remove the inherent imaginary part interference at the pilot frequency position, ensure that the value on the pilot frequency is not influenced by the inherent interference and ensure that each CO-FBMC/OQAM symbol has a pilot frequency symbol for recording the phase noise superposed on the pilot frequency symbol.
The more specific working principle is as follows:
the receive-side demodulation signal of a CO-FBMC/OQAM system considering the presence of phase noise and ASE noise can be written as:
Figure GDA0002443935880000081
Figure GDA0002443935880000082
wherein m is0Denotes the m-th0Sub-carriers,/0Is the first0Individual FBMC/OQAM symbol, LgKM is the filter length, K is the overlap factor, M is the total number of subcarriers, g (n) represents the time domain response function of the filter, gm,lRepresents a time-frequency offset version of the filter,
Figure GDA0002443935880000083
in order to make the ASE noise,
Figure GDA0002443935880000084
represents the Pauli multiphase modulation factor;
order to
Figure GDA0002443935880000085
For superposition of systems carried on
Figure GDA0002443935880000086
The above equation can be simplified to:
Figure GDA0002443935880000087
the above formula shows that the inherent interference is superimposed on the received symbol, which affects the normal determination of the phase noise value, and the inherent interference is a value strongly correlated with the magnitude of the signal itself, and the magnitude of the inherent interference cannot be determined and must be eliminated.
TABLE 1 Pilot Transmission in CO-FBMC/OQAM System
Figure GDA0002443935880000092
As can be seen from table 1, the inherent interference at the pilot location mainly comes from the symbols at the sub-carriers where the pilot is located and at the odd positions spaced from the pilot, and from the symbols at two adjacent rows of the sub-carriers. Therefore, the interference elimination pilot frequency module of the invention can greatly eliminate the influence of the imaginary part interference by the operation of zero setting at the position with large imaginary part interference.
TABLE 1
n-4 n-3 n-2 n-1 n n+1 n+2 n+3 n+4
m-1 0.0054 0.0429j -0.1250 -0.2058j 0.2393 0.2058j -0.1250 -0.0429j 0.0054
m 0 -0.0668 0.0002j 0.5644 1 0.5644 0.0002j -0.0668 0
m+1 0.0054 -0.0429j -0.1250 0.2058j 0.2393 -0.2058j -0.1250 0.0429j 0.0054
According to table 1 and with the designed special pilot structure, equation (3) can be simplified as:
Figure GDA0002443935880000091
preferably, the kalman filter compensation module is configured as shown in fig. 2, and includes: pilot extraction section 1, subtractor 2, first multiplier 3, adder 4, delay section 5, second multiplier 6, conjugate processing section 7, and third multiplier 8.
The input end of the pilot frequency extraction unit 1 is connected with the input end of the optical domain-frequency domain conversion module, and the output end of the pilot frequency extraction unit is connected with the subtracter 2;
the input end of the subtracter 2 is connected with the output end of the pilot frequency extraction unit 1 and the output end of the multiplier 6, and the output end of the subtracter is connected with the input end of the multiplier 3;
the input end of the first multiplier 3 is connected with the output end of the subtracter 2 and receives the fixed Kalman gain; the output end is connected with the input end of the adder 4;
the input end of the adder 4 is connected with the output end of the first multiplier 3 and the output end of the delay unit 5, and the output end of the adder is connected with the input end of the delay unit 5 and the input end of the conjugate processing unit 7;
the input end of the delay unit 5 is connected with the output end of the adder 4, and the output end of the delay unit is connected with the input end of the adder 4 and the input end of the multiplier 6;
the input end of the second multiplier 6 is connected with the output end of the delay unit 5;
the input end of the conjugation processing unit 7 is connected with the output end of the adder 4, and the output end of the conjugation processing unit is connected with the input end of the third multiplier 8;
the input end of the third multiplier 8 is connected with the output end of the conjugate processing unit 7, and the output end is connected with the real complex number conversion module;
preferably, the pilot extracting unit 1 is configured to extract the pilot signal in the receiving end frequency domain signal, that is, to complete:
Figure GDA0002443935880000101
wherein z isnIndicates the nth CO-FBMC/OQAM symbol,
Figure GDA0002443935880000102
indicating the symbol value corresponding to the pilot position p in the nth FBMC/OQAM symbol.
The subtracter 2 is used for actually receiving the pilot symbols received by the receiving end
Figure GDA0002443935880000103
And the predicted receiving end pilot frequency symbol value in the Kalman filtering algorithm
Figure GDA0002443935880000104
Comparing to obtain a prediction error signal enNamely:
Figure GDA0002443935880000105
since the error signal contains unpredictable information, the error signal is also referred to as innovation. The innovation is mainly used for correcting the predicted value of the phase noise;
the first multiplier 3 is used for inputting information enAnd Kalman gain knMultiplication, i.e.: by a suitable factor knWeighting the innovation to obtain a predicted value obtained by the measurement process and the prediction process
Figure GDA0002443935880000106
Correction value k ofnen；、
Preferably;
Figure GDA0002443935880000107
Figure GDA0002443935880000108
wherein the content of the first and second substances,
Figure GDA0002443935880000109
knis the Kalman gain; r is the covariance of the measurement process, which can be obtained by training sequence in the previous period, and is a fixed value, knThe calculated value of (a) can be obtained according to the minimum mean square error criterion of innovation, namely:
Figure GDA00024439358800001010
Figure GDA0002443935880000111
the adder 4 is used for adding the correction value knenAnd the predicted value
Figure GDA0002443935880000112
Adding to obtain an optimal estimation value of the phase noise based on a Kalman filtering algorithm:
Figure GDA0002443935880000113
the delay unit 5 is used for estimating the optimal estimated value based on the Kalman filtering algorithm
Figure GDA0002443935880000114
A time delay is carried out to obtain
Figure GDA0002443935880000115
According to prediction equation (4):
Figure GDA0002443935880000116
it can be known that
Figure GDA0002443935880000117
Finally, the predicted value of the phase noise of the previous moment to the moment is obtained
Figure GDA0002443935880000118
The second multiplier 6 is used for transmitting the known transmitting pilot signal
Figure GDA0002443935880000119
And the predicted value
Figure GDA00024439358800001110
Multiplying to obtain the predicted value of the receiving end pilot signal
Figure GDA00024439358800001111
Figure GDA00024439358800001112
The conjugation processing unit 7 is configured to perform an operation of conjugating the input phase noise:
Figure GDA00024439358800001113
wherein j represents an imaginary number;
the third multiplier 8 is used for the phase noise of the input
Figure GDA00024439358800001114
The conjugate of (a) is multiplied by the frequency domain signal of FBMC/OQAM to obtain the result after phase noise compensation:
Figure GDA00024439358800001115
in summary, the algorithm processing method of the kalman filter compensation module is as follows:
firstly, establishing a prediction equation and a measurement equation required by a Kalman filtering algorithm:
Figure GDA00024439358800001116
Figure GDA00024439358800001117
firstly, the pilot frequency symbol in the receiving end symbol is extracted
Figure GDA00024439358800001118
And its corresponding originating pilot symbols
Figure GDA00024439358800001119
Then initializing phase noise
Figure GDA00024439358800001120
The prediction error covariance P (0) ═ 0.
And for each FBMC/OQAM symbol, sequentially calculating a prediction process and a measurement process:
the equation of the prediction process is as follows:
Figure GDA00024439358800001121
Figure GDA00024439358800001122
wherein Q2 pi Δ vT is the prediction process covariance; Δ v is the combined laser linewidth; t ═ TsFBMC for normalizationOQAM symbol period;
the equation of the measurement process is as follows:
Figure GDA0002443935880000121
Figure GDA0002443935880000122
Figure GDA0002443935880000123
Figure GDA0002443935880000124
Figure GDA0002443935880000125
through the iteration, the corresponding to each one can be obtained
Figure GDA0002443935880000126
According to phase noise of
Figure GDA0002443935880000127
And obtaining a signal after phase compensation.
As shown in fig. 4, for a specific CO-FBMC/OQAM system provided in this embodiment, the total number of subcarriers of the CO-FBMC/OQAM system in this embodiment is 256, the number of effective subcarriers is 250, the symbol rate is 20GS/s, and 16QAM is modulated and carries a pilot signal.
The originating work mechanism of the CO-FBMC/OQAM system is as follows:
the input binary information bits are first converted by serial-to-parallel conversion, 16QAM mapping and complex number to real number processing are carried out, OQAM preprocessing is completed, 250 parallel PAM data symbols are formed, a silencing pilot frequency structure D1 unit and a D2 unit which are designed by the invention are added to two ends of each parallel data symbol, a D1 unit and a D2 unit are used for mixing the 250 parallel PAM data symbols together to form a 256 parallel data structure, then the 256 parallel data structure is subjected to systematic orthogonalization preprocessing by a Poillion multiphase modulation module, each column of the 256 parallel data is loaded on 256 different subcarriers through IFFT conversion and comprehensive filter bank modulation in a comprehensive filter bank module and frequency domain to time domain conversion is completed, finally, FBMC/OQAM baseband signals are formed through parallel-serial conversion and training sequence addition, and then up-conversion from an electrical domain to an optical domain is realized through IQ modulation, and signals which can be transmitted in optical fibers are formed;
the receiving end working mechanism of the CO-FBMC/OQAM system is as follows:
a baseband signal obtained after a transmitting-end FBMC/OQAM signal modulated in an optical domain is received through coherent detection balance is firstly subjected to timing synchronization, serial-parallel conversion, filter bank analysis and channel estimation, and then an obtained frequency domain signal is sent to a filtering compensation module. In the module, a pilot frequency symbol of a receiving end is extracted through an extraction pilot frequency unit 1, a receiving end pilot frequency symbol predicted value obtained by multiplying a phase noise estimated value of the previous moment processed by a delay unit 5 by a pilot frequency symbol of a sending end is extracted, then a test pilot frequency symbol of the receiving end and the receiving end pilot frequency symbol predicted value are subtracted in a subtracter 2 to obtain an error signal between a measured value and the predicted value, a multiplier 3 receives the error signal and multiplies Kalman gain to obtain a correction value of the prediction process in the measurement process, the obtained correction value and the phase noise value of the previous moment are added in an adder 4 to obtain a phase noise estimated value obtained through a Kalman algorithm, and the phase noise estimated value and the phase noise compensated value are processed through a conjugation processing unit 7 to obtain a phase noise compensation value and multiplied by the symbol of the receiving end to obtain a. And the output phase noise compensation signal is subjected to real complex conversion unit, parallel-serial conversion unit and 16QAM constellation demapping to obtain a recovered bit signal and output.
The embodiment respectively performs performance simulation on the signals processed by the CO-FBMC/OQAM system provided by the scheme and the signals processed by the Kalman phase noise compensation device based on blind decision, figure 5 is a graph of BER performance of the system at different laser linewidths for two different methods, wherein, the P-EKF is the CO-FBMC/OQAM system provided by the invention, the total number of the sub-carriers is set to be 256, the number of the effective sub-carriers is set to be 250, wherein 6 sub-carriers close to direct current bias are used for placing a pilot structure proposed by the scheme, B-EKF is a system of a Kalman filtering algorithm structure based on blind decision for performance comparison, the total number of the sub-carriers is 256, the number of effective sub-carriers is 256, the figure shows a comparison of the performance of the two schemes in back-to-back transmission conditions and after 400km of fiber transmission. As can be seen from the figure, under two conditions, the phase noise tolerance of the scheme is improved by about 1000kHz compared with the scheme based on blind decision, and the superiority of the scheme is greatly proved.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (7)

1. A modulation method of CO-FBMC/OQAM is characterized by comprising the following steps:
(1) converting an input bit signal into a PAM data symbol;
(2) eliminating inherent imaginary interference of pilot frequency at two ends of the PAM data symbol and recording phase information of the pilot frequency symbol;
(3) receiving the frequency domain signal processed by the pilot frequency unit, modulating the frequency domain signal after the orthogonalization pretreatment of the frequency domain signal, and completing the conversion from the frequency domain signal to the time domain signal;
(4) carrying out parallel-to-serial conversion and training sequence processing on the acquired time domain signal, and carrying out IQ modulation to transmit the optical domain signal to a system receiving end;
(5) converting the received optical domain signal into a frequency domain signal to perform Kalman filtering phase noise compensation;
(6) recovering a bit signal after demapping the output signal of the phase compensation;
wherein, the specific steps in the step (5) are as follows:
(5.1) receiving the optical domain signal through coherent detection balance to obtain a baseband signal;
(5.2) demodulating the baseband signal after timing synchronization and serial-parallel conversion to obtain a frequency domain signal;
(5.3) subtracting the predicted value of the test pilot signal and the receiving end pilot signal in the frequency domain signal to obtain an error signal;
(5.4) multiplying the received error signal by Kalman gain, and combining the phase noise estimation value at the previous moment to obtain the estimation value of the phase noise at the current moment;
and 5.5, acquiring a phase noise compensation signal according to the estimated value of the phase noise and the pilot frequency symbol.
2. The modulation method according to claim 1, wherein the specific steps in the step (2) are:
(2.1) accessing three rows of subcarriers at one end of the PAM data symbol, placing pilot symbols at odd-numbered positions, placing zero symbols at even-numbered positions and placing zero symbols at the other two rows of subcarriers at zero positions of the middle row of subcarriers, and completing the access of a first pilot unit and the PAM data symbol;
(2.2) accessing three rows of subcarriers at the other end of the PAM data symbol, placing pilot symbols at even positions, placing zero symbols at odd positions and placing zero symbols at the other two rows of subcarriers of the middle row of subcarriers, and completing the access of a second pilot unit and the PAM data symbol;
and (2.3) receiving the PAM data symbols by the first pilot frequency unit and the second pilot frequency unit, eliminating the inherent imaginary part interference of the system and recording the phase information of the pilot frequency position.
3. The modulation method according to claim 1, wherein the step (5.3) comprises the following steps:
(5.3.1) extracting a test pilot signal at the receiving end of the pilot position;
(5.3.2) multiplying the pilot signal known by the transmitting end by the phase noise estimation value at the previous moment to obtain the predicted value of the receiving end pilot signal corresponding to the transmitting end pilot signal;
and (5.3.3) subtracting the predicted values of the test pilot signal and the pilot signal at the receiving end to obtain an error signal between the test pilot signal and the pilot signal.
4. The modulation method according to claim 3, wherein the step (5.4) comprises the following steps:
(5.4.1) multiplying the error signal by a fixed Kalman gain to obtain a correction value of the phase noise;
(5.4.2) adding the multiplied value and the phase noise estimated value of the previous moment to obtain the phase noise estimated value of the current moment.
5. The modulation method according to claim 4, wherein the step (5.5) comprises the following steps:
(5.5.1) performing conjugation processing on the phase noise estimation value at the current moment;
(5.5.2) multiplying the conjugate value of the phase noise by the pilot frequency symbol of the receiving end to obtain an estimated value after the phase noise compensation, and taking the estimated value as a signal of the phase noise compensation;
(5.5.3) the phase noise estimate value at the current time is subjected to delay processing as the phase noise estimate value at the previous time.
6. A CO-FBMC/OQAM system is characterized by comprising a symbol mapping module, a disturbance elimination pilot frequency module, a frequency domain-time domain conversion module, an IQ modulation module, an optical domain-frequency domain conversion module, a Kalman filtering compensation module and a symbol de-mapping module;
the symbol mapping module is used for receiving the bit data after serial-parallel conversion, outputting a signal after the complex number is converted into a real number, and transmitting a real value signal to the interference elimination pilot frequency module;
the interference elimination pilot frequency module receives the real-value signal transmitted by the symbol mapping module, outputs a frequency domain signal for eliminating the inherent interference of the pilot frequency, is used for eliminating the inherent imaginary part interference at the position of the pilot frequency, and is simultaneously used for recording the phase information in the pilot frequency signal so as to acquire the influence of the phase noise on the system;
the frequency domain-time domain conversion module is used for receiving the frequency domain signal transmitted by the interference elimination pilot frequency module and outputting a time domain signal;
the IQ modulation module is used for receiving a time domain signal and outputting an optical domain signal;
the optical domain-frequency domain conversion module is used for receiving an optical domain signal of a time domain signal converted by the IQ modulator and outputting a frequency domain signal;
the Kalman filtering compensation module is used for calculating a phase noise value on a pilot frequency symbol position based on the state of eliminating the inherent interference of the pilot frequency symbol by the interference elimination pilot frequency module, so as to compensate the phase noise and finally output a frequency domain signal after phase compensation;
the symbol demapping module is used for receiving the frequency domain signal of the frequency domain signal after the real number is converted into the complex number, and outputting bit data;
wherein, the Kalman filtering compensation module comprises: the device comprises a pilot frequency extracting unit (1), a subtracter (2), a first multiplier (3), an adder (4), a delay unit (5), a second multiplier (6), a conjugate processing unit (7) and a third multiplier (8);
the input end of the pilot frequency extraction unit (1) is connected with the output end of the optical domain-frequency domain conversion module, and the output end of the pilot frequency extraction unit is connected with the subtracter (2);
the input end of the subtracter (2) is connected with the output end of the pilot frequency extraction unit (1) and the output end of the multiplier (6), and the output end of the subtracter is connected with the input end of the first multiplier (3);
the input end of the first multiplier (3) is connected with the output end of the subtracter (2), and the output end of the first multiplier is connected with the input end of the adder (4);
the input end of the adder (4) is connected with the output end of the first multiplier (3) and the output end of the delay unit (5), and the output end of the adder is connected with the input end of the delay unit (5) and the input end of the conjugate processing unit (7);
the input end of the delay unit (5) is connected with the output end of the adder (4), and the output end of the delay unit is connected with the input end of the adder (4) and the input end of the second multiplier (6);
the input end of the second multiplier (6) is connected with the output end of the delay unit (5);
the input end of the conjugate processing unit (7) is connected with the output end of the adder (4), and the output end of the conjugate processing unit is connected with the input end of the third multiplier (8);
the input end of the third multiplier (8) is connected with the output end of the conjugate processing unit (7), and the output end of the third multiplier is connected with the real complex number conversion module;
the pilot frequency extracting unit (1) is used for extracting a pilot frequency signal from a receiving end pilot frequency;
the subtracter (2) is used for subtracting the pilot signal at the receiving end from the predicted pilot signal to obtain an error signal between the pilot signal and the predicted pilot signal;
-said first multiplier (3) is adapted to multiply the error signal by a fixed kalman gain;
the adder (4) is used for adding the result obtained by the multiplier (3) and the phase noise estimation value at the previous moment to obtain the phase noise estimation value at the current moment;
the delay unit (5) is used for converting the phase noise estimation value of the current moment into the phase noise estimation value of the previous moment;
the second multiplier (6) is used for multiplying the sending pilot signal with the phase noise estimated value at the previous moment to obtain a receiving pilot value corresponding to the predicted pilot symbol;
the conjugation processing unit (7) is used for obtaining a conjugation value of the phase noise at the current moment;
and the third multiplier (8) is used for multiplying the conjugate value of the phase noise at the current moment by the pilot frequency symbol at the receiving end to obtain an estimated value after the phase noise compensation.
7. The CO-FBMC/OQAM system according to claim 6, wherein the interference cancellation pilot module comprises a first pilot unit and a second pilot unit;
the first pilot frequency unit and the second pilot frequency unit respectively comprise 3 rows of subcarriers, pilot frequency symbols of the subcarriers located in the middle row are alternated with zero setting symbols, the subcarriers in the other two rows are set to be zero, and the pilot frequency symbols of the first pilot frequency unit and the second pilot frequency unit are respectively arranged at the odd number position and the even number position of the corresponding subcarriers.
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