JP5993042B2 - Optical transmission system and transmission line compensation method - Google Patents

Description

  The present invention relates to an optical transmission system and a transmission path compensation method used for characteristic compensation of such an optical transmission system.

  In recent years, with the spread of multimedia services and the expansion of the use of information and communication technology (ICT) services, Internet traffic flowing through the backbone network has been increasing year by year. In recent years, digital coherent signal processing technology has been attracting attention as a next-generation optical communication technology that will drive the ever-increasing traffic.

  In a 100-Gbps wavelength division multiplexing (WDM) system that has already been commercialized, compensation by signal processing is widely performed in the digital domain in order to correct distortion of an optical signal generated in a transmission path. The distortion of the optical signal to be compensated includes hardware other than optical fiber, such as a digital analog converter (DAC), an IQ modulator (IQ modulator), an optical filter, a wavelength selective switch (Wavelength Selective). Switch: WSS), analog digital converter (ADC), etc., transfer function amplitude distortion that occurs. Further, there is chromatic dispersion (CD) that is loaded by transmitting an optical fiber.

  It is known that the system characteristics can be improved by compensating the waveform distortion accompanying the transmission at the transmitting end as compared with the case of compensating only at the receiving end. According to Non-Patent Document 1, a filtering penalty is reduced by measuring a transfer function of an optical filter that passes at the time of transmission with a network analyzer in advance and compensating the acquired coefficient at a transmission end. Further, according to Non-Patent Document 2, the amplitude characteristic of the transfer function of a transmitter / receiver such as a D / A conversion circuit or an A / D conversion circuit is obtained by signal processing at a receiving unit during non-transmission, and the obtained coefficient Is applied to the transmitting end to improve the transmission characteristics.

T. Sugihara et al., “43 Gb / s DQPSK Pre-equalization controlling 6-bit, 43GS / s DAC Integrated LSI for Cascaded ROADM Filtering,” OFC / NFOEC 2010, PDPB6, (2010). J. Zhang et al., “Transmission of 480-Gb / s Dual-carrier PM-8QAM over 2550km SMF-28 Using Adaptive Pre-equalization,” in OFC / NFOEC 2014, Th4F. 6, (2014).

  However, these methods are complicated and difficult to implement in an actual transmission system. In order to execute Non-Patent Document 1, it is necessary to measure all transfer functions of a device passing through a transmission line with a network analyzer in advance. However, the number of hardware in the transmission path becomes enormous, and it is difficult to obtain in advance the transfer functions of all devices passing through the transmission path. In order to execute Non-Patent Document 2, it is necessary to estimate the transfer function in the non-transmission state and apply it to the transmission unit before the transmission / reception apparatus is incorporated into the actual transmission system. However, in consideration of the possibility that the route is switched in the middle, it is not realistic to estimate the transfer function in advance in all the transmitters / receivers that may become a transmission / reception pair. In the method of Non-Patent Document 2, the coefficient estimated by the receiving unit is physically fed back to the transmission end using a path different from the transmission path. However, in an actual transmission system, it is difficult to provide a new transmission channel for transmitting the compensation coefficient. Therefore, without passing through the process of measuring the transfer function of the device in advance, and easily estimating the transfer function at the receiving unit without changing the transmission system configuration, the information is transmitted to the transmitting unit without newly providing a transmission channel, A system that performs compensation at the transmitter is required.

  In view of the above-described problems, the present invention can estimate a transfer function of a transmission line without performing complicated processing, and can perform characteristic compensation at a transmission end without using a special transmission channel. It is another object of the present invention to provide a transmission path compensation method.

  The present invention is an optical transmission system comprising a first transceiver and a second transceiver for transmitting and receiving an optical signal, and an optical transmission path between the first transceiver and the second transceiver. The first transceiver and the second transceiver each include a transmission unit having a signal multiplexing circuit that time-multiplexes a known signal sequence into a data signal sequence, a characteristic compensation circuit that performs characteristic compensation of a transmission signal, and a received signal A reception unit having a known signal extraction circuit for extracting a known signal from the signal and a transfer function information generation circuit for estimating a transfer function from the received known signal sequence, wherein the first transceiver is configured by the signal multiplexing circuit. A data signal sequence and a known signal sequence are time-multiplexed and transferred to the second transceiver, and the second transceiver estimates a transfer function from the known signal sequence received by the transfer function information generation circuit, Estimated transfer function To the first transmitter / receiver using a known signal, and the first transmitter / receiver performs characteristic compensation at a transmission end using the transfer function returned by the characteristic compensation circuit. To do.

  The present invention is characterized in that the second transmitter / receiver modulates the polarization of an alternating signal sequence, which is a known signal sequence, with the estimated transfer function, and returns the modulated signal sequence to the first transmitter / receiver.

  The present invention is characterized in that the first transmitter / receiver time-multiplexes a known signal sequence for estimating an amplitude characteristic of a transfer function and a known signal sequence for estimating a variance alternately into a data signal sequence.

  The present invention is characterized in that a pseudo-random sequence is used as a known signal sequence for estimating the amplitude characteristic of the transfer function.

  The present invention is characterized in that a CAZAC (Constant Amplitude Zero Auto-Correlation) sequence is used as the known signal sequence for estimating the amplitude characteristic of the transfer function.

  The present invention relates to a transmission path of an optical transmission system comprising a first transceiver and a second transceiver for transmitting and receiving an optical signal, and an optical transmission path between the first transceiver and the second transceiver. In the compensation method, the first transmitter / receiver time-multiplexes a data signal sequence and a known signal sequence and transfers the data signal sequence to the second transmitter / receiver, and the second transmitter / receiver receives the received known signal sequence. And the estimated transfer function is returned to the first transmitter / receiver using a known signal, and the first transmitter / receiver performs characteristic compensation at the transmitting end using the returned transfer function. It is characterized by performing.

  According to the present invention, it is possible to estimate the transfer function of the transmission path without performing complicated processing, and to obtain the effect of performing characteristic compensation at the transmission end without using a special transmission channel.

1 is a block diagram showing an outline of an optical transmission / reception system according to a first embodiment of the present invention. It is a block diagram which shows the structure of the transmission part in the optical transmission / reception system which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the receiving part in the optical transmission / reception system which concerns on the 1st Embodiment of this invention. It is explanatory drawing of an example of the transmission frame in the optical transmission / reception system which concerns on the 1st Embodiment of this invention. It is explanatory drawing of the other example of the transmission frame in the optical transmission / reception system which concerns on the 1st Embodiment of this invention. It is explanatory drawing of the further another example of the transmission frame in the optical transmission / reception system which concerns on the 1st Embodiment of this invention. It is explanatory drawing of an example of the modulation system of the known signal in the optical transmission / reception system which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the characteristic compensation process of the optical transmission / reception system in the 1st Embodiment of this invention. It is a graph which shows the measurement result of the reception spectrum before and behind the characteristic compensation in a transmission end.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an optical transmission / reception system 1 according to a first embodiment of the present invention. As shown in FIG. 1, an optical transmission / reception system 1 to which the present invention can be applied includes transceivers 10 and 20 and transmission paths 30 and 40 between the transceiver 10 and the transceiver 20.

  The transceiver 10 includes a transmission unit 11 and a reception unit 12. The transceiver 20 includes a transmission unit 21 and a reception unit 22. The transmission path 30 is a transmission path for signals transmitted from the transceiver 10 side to the transceiver 20 side. The transmission path 40 is a transmission path for signals transmitted from the transceiver 20 side to the transceiver 10 side. The transmission lines 30 and 40 are optical fiber transmission lines.

  In this embodiment, when a data signal is transmitted from the transceiver 10 to the transceiver 20, the known signal sequence is time-multiplexed with the transmission frame by the transmission unit 11. Then, the transmission unit 11 converts the signal of the transmission frame into an optical signal, and transmits the optical signal toward the transceiver 20 via the transmission path 30.

  The optical signal transmitted through the transmission path 30 is received by the receiving unit 22 of the transceiver 20. As described above, a known signal sequence is time-multiplexed in the signal transferred from the transceiver 10 to the transceiver 20. In the present embodiment, when receiving a signal from the transceiver 10, the receiving unit 22 extracts a known signal sequence from the transmission frame, and uses this known signal sequence to transmit a transmission path from the transceiver 10 to the transceiver 20. Estimate the transfer function. This estimated transfer function is sent from the receiver 22 to the transmitter 21.

  The transmission unit 21 returns information on the estimated transfer function to the transceiver 10. At this time, in the present embodiment, information on the estimated transfer function is transferred to the transceiver 10 using a known signal sequence.

  That is, as in the case of transmitting a data signal from the transmitter / receiver 10 to the transmitter / receiver 20, a known signal sequence is time-multiplexed in the signal transmitting the data signal from the transmitter / receiver 20 to the transmitter / receiver 10. In the present embodiment, the transfer function information of the transmission path from the transceiver 10 to the transceiver 20 estimated by the receiver 22 is modulated into the known signal sequence sent from the transceiver 20 to the transceiver 10. The signal of this transmission frame is converted into an optical signal and transmitted to the transceiver 10 via the transmission path 40.

  The optical signal transmitted through the transmission path 40 is received by the receiving unit 12 of the transceiver 10. At this time, in the present embodiment, a known signal sequence portion is extracted from the transmission frame. As described above, the transfer function information of the transmission path from the transceiver 10 to the transceiver 20 is modulated in this known signal series. Information on this transfer function is demodulated by the receiver 12 and sent from the receiver 12 to the transmitter 11.

  Upon receiving the transfer function information, the transmission unit 11 applies the inverse function of the transfer function to the transmission signal sequence. As a result, the characteristics of the signal transmitted from the transceiver 10 to the transceiver 20 are compensated at the transmission end.

  Thus, in the first embodiment of the present invention, characteristic compensation is performed at the transmission end. As characteristic compensation, in particular, compensation for chromatic dispersion and amplitude characteristics of the transfer function is performed. By compensating for chromatic dispersion at the transmitting end, the signal spreads in the time slot direction and is transmitted in a state where the amplitude of each symbol is smoothed, so the effect of nonlinear phase rotation that occurs in proportion to the instantaneous power is reduced, The transmission characteristics can be improved.

  FIG. 2 is a block diagram illustrating the configuration of the transmission units 11 and 21. As shown in FIG. 2, the transmission units 11 and 21 include data signal sequence generation circuits 51a and 51b, known signal sequence generation circuits 52a and 52b, signal multiplexing circuits 53a and 53b, and transfer function information acquisition circuits 54a and 54b. Characteristic compensation circuits 55a and 55b, D / A converters 56a and 56b, electrical / optical conversion circuits 57a and 57b, and a polarization multiplexing circuit 58.

  The data signal sequence generation circuits 51a and 51b generate X polarization and Y polarization data signal sequences. Known signal sequence generation circuits 52a and 52b generate known signal sequences for estimating a transfer function. The signal multiplexing circuits 53a and 53b time-multiplex the data signal sequence and the known signal sequence to generate a transmission frame. The transfer function information acquisition circuits 54a and 54b acquire transfer function information from the signal fed back from the receiving unit. The characteristic compensation circuits 55a and 55b apply the inverse function of the acquired transfer function to the transmission signal sequence to perform characteristic compensation of the transmission signal. The D / A converters 56a and 56b convert the transmission signal sequence from a digital signal to an analog signal. The electrical / optical conversion circuits 57a and 57b convert the transmission analog signal sequence into an optical signal. The polarization multiplexing circuit 58 multiplexes the X polarization and the Y polarization that are orthogonal to each other and transmits the multiplexed light to the optical fiber transmission line.

  FIG. 3 is a block diagram showing the configuration of the receiving units 12 and 22. As shown in FIG. 3, the receiving units 12 and 22 include a polarization separation circuit 71, optical / electrical conversion circuits 72a and 72b, A / D conversion circuits 73a and 73b, main signal demodulation circuits 74a and 74b, It comprises known signal extraction circuits 75a and 75b, a differential decoding circuit 76, and a transfer function information generation circuit 77.

  The polarization separation circuit 71 separates orthogonal X polarization and Y polarization from the optical signal received via the optical fiber transmission line. The optical / electrical conversion circuits 72a and 72b convert optical signals into electrical signals. The A / D conversion circuits 73a and 73b convert analog signals into digital signals. The main signal demodulation circuits 74a and 74b demodulate the data signal series that becomes the main signal. The known signal extraction circuits 75a and 75b extract a known signal sequence for estimating a transfer function from the digital signal sequence. The differential decoding circuit 76 performs differential decoding of the extracted known signal series. The transfer function information generation circuit 77 generates transfer function information from the differentially decoded signal.

  FIG. 4 shows an example of a transmission frame used in the optical transmission / reception system 1 according to the first embodiment of the present invention. As shown in FIG. 4, the transmission frame includes a known signal sequence 81 and a data signal sequence 82. The known signal sequence 81 is used to obtain a transfer function of the transmission path. Factors that cause distortion of the transfer function include a D / A converter, an A / D converter, an IQ modulator, a band narrowing filter, wavelength dispersion, polarization mode dispersion, and a nonlinear optical effect. The known signal series 81 is preferably one that can estimate these factors as a transfer function.

  FIG. 5 shows another example of a transmission frame. In this example, a known signal sequence 81a for dispersion estimation is added to the first frame as a known signal sequence that is time-multiplexed with the transmission frame, and a known signal sequence 81b for transfer function amplitude characteristic estimation is added to the second frame. . Thus, in this example, the known signal sequence 81a for variance estimation and the known signal sequence 81b for transfer function amplitude characteristic estimation are alternately added for each frame.

  FIG. 6 shows still another example of the transmission frame. In this example, a known signal sequence 81c for estimating dispersion and a known signal sequence 81d for estimating transfer function amplitude characteristics are added to each frame.

  As a known signal sequence for dispersion estimation added to a transmission frame, an alternating pattern that repeats (S, S, -S, -S), (S, -S, S, -S), etc. as a complex signal S is used. Can be used. Also, alternating patterns with different periods and patterns that are not the same between X and Y can be used. The known signal sequence for estimating the amplitude characteristic of the transfer function is preferably a sequence having a high autocorrelation peak and a broad spectrum. For example, a maximum length shift register sequence used as a pseudo noise sequence, a bulk code used as a spreading code, and the like can be given. Also, a Zadaoff-Chu sequence, which is a Constant Amplitude Zero Auto-Correlation (CAZAC) sequence in which the amplitude is constant at all times and the autocorrelation is a delta function, can be used. However, the present invention is not limited to these, and any signal sequence having a spectrum in the same band as the data signal component can be used.

  FIG. 7 is an example of a known signal modulation method that can be used when returning information on the transfer function to the transmitting end in the optical transmission / reception system 1 according to the first embodiment of the present invention. In this example, by modulating the polarization of an alternating signal sequence, which is a known signal sequence used for dispersion estimation, transfer function estimation information can be fed back to the transmission side without using a special channel. In the case of this pattern, the phase of the alternating signal sequence of Y polarization is shifted by 180 degrees in order to generate the orthogonal polarization state. At this time, by performing differential demodulation on the front and rear frames, 1 in the parallel polarization state (FIG. 7A) and 1 in the orthogonal polarization state (FIG. 7B) “0”. Bit information can be transmitted.

  FIG. 8 is a flowchart showing the characteristic compensation process of the optical transmission / reception system 1 according to the first embodiment of the present invention. Here, it is assumed that characteristic compensation is performed when data is transferred from the transceiver 10 to the transceiver 20.

  As illustrated in FIG. 8, the transmission unit 11 of the transceiver 10 transmits a data signal sequence by time-multiplexing a known signal sequence. That is, the known signal sequence 81 as shown in FIGS. 4 to 6 is added to one frame of the transmission signal. In this way, a signal in which a known signal sequence is time-multiplexed is transmitted from the transmitter / receiver 10 to the transmitter / receiver 20 via the transmission path 30 (step S1).

  The signal transmitted through the transmission path 30 is received by the receiving unit 22 of the transceiver 20. The receiving unit 22 extracts a known signal sequence from this signal, and estimates the transfer function of the transmission path from the transceiver 10 to the transceiver 20 using this known signal sequence (step S2).

  Information on the transfer function of the transmission path from the transceiver 10 to the transceiver 20 is sent from the receiver 22 to the transmitter 21. The transmission unit 21 modulates a known signal sequence using information on the transfer function of the transmission path from the transceiver 10 to the transceiver 20 and returns the modulated signal sequence to the transceiver 10. That is, using the modulation method shown in FIG. 7, the information of the transfer function is included in the known signal sequence and transferred to the transceiver 10 via the transmission path 40 (step S3).

  The signal transmitted via the transmission path 40 is received by the receiving unit 12 of the transceiver 10. The receiving unit 12 extracts a known signal sequence from this signal. Then, from this known signal sequence, information on the transfer function of the transmission path from the transceiver 10 to the transceiver 20 is acquired and demodulated. In other words, when the modulation method shown in FIG. 7 is used and transfer information including transfer function information is transferred to a known signal sequence, the transfer function information can be demodulated by performing differential demodulation on the preceding and following frames. Information on the transfer function of the transmission path from the transceiver 10 to the transceiver 20 is sent from the receiver 12 to the transmitter 11 (step S4).

  Based on the transfer function information acquired from the reception unit 12, the transmission unit 11 performs characteristic compensation of the data signal sequence to be transmitted. That is, the transmission unit 11 performs characteristic compensation at the transmission end by applying the obtained inverse function of the transfer function to the transmission signal sequence (step S5).

  As described above, in the first embodiment of the present invention, the data signal sequence and the known signal sequence are time-multiplexed by the transceiver 10 and transferred to the transceiver 20, and the known signal sequence received by the transceiver 20 is used. The transfer function is estimated. Then, the transmitter / receiver 20 returns the estimated transfer function to the transmitter / receiver 10 using a known signal, and the transmitter / receiver 10 performs characteristic compensation at the transmission end using the returned transfer function. As a result, the characteristics can be compensated at the transmission end without using complicated equipment.

  FIG. 9 shows a comparison of received spectra when the characteristic compensation at the transmission end is performed and when the characteristic compensation is not performed. FIG. 9A shows a reception spectrum before the characteristic compensation at the transmission end, and FIG. 9B shows a reception spectrum after the characteristic compensation at the transmission end. In FIG. 9, the horizontal axis indicates the frequency, and the vertical axis indicates the power.

  When the characteristic compensation is not performed, the pass characteristic deteriorates as the frequency becomes higher due to the transfer function of the device that passes during transmission. For this reason, the reception spectrum before performing transmission end compensation has a spectrum shape in which the vicinity of the direct current rises and the power decreases as the frequency increases, as shown in FIG.

  On the other hand, as shown in the first embodiment of the present invention, when transmission end compensation is performed using the inverse characteristic of the transfer function, as shown in FIG. The power on the high frequency side is increased to obtain a flat frequency characteristic. When the reception unit compensates the transfer function and raises the high frequency band, not only the signal component but also the noise component is raised, so the characteristics deteriorate. However, by performing compensation at the transmission end, the transfer function can be compensated without a noise enhancement effect.

  In the above-described embodiment, when the transfer function is returned to the transmission end, the known signal sequence is modulated with the estimated transfer function information so that the transfer function information is included in the known signal sequence. However, the present invention is not limited to this, and a channel may be provided separately from the transmission path between the transmitter and the receiver to transmit the transfer function information. As an example, another dedicated transmission line can be provided or communicated by telephone. Also, the transmission path used between the transceivers can be used as it is. For example, the transfer function information can be transmitted by time division multiplexing or frequency multiplexing with respect to the data signal sequence, or transmitted using subcarriers of the OFDM signal. Furthermore, transmission can be performed using amplitude modulation, phase modulation, quadrature amplitude modulation, polarization modulation, or the like.

  As described above, the reception unit receives the known signal, estimates the transfer function, returns the transfer function to the transmission unit using the known signal, and performs characteristic compensation at the transmission end. As a result, the characteristics can be compensated at the transmission end without using complicated equipment. Transmission end compensation compensates for chromatic dispersion at the transmission end, so that the signal spreads in the time slot direction and is transmitted with the amplitude of each symbol smoothed. Therefore, nonlinear phase rotation that occurs in proportion to the instantaneous power The transmission characteristics can be improved. Further, by performing signal processing performed in the receiving unit in the transmitting unit, it is possible to suppress an increase in power consumption in the receiving unit and perform averaging in transmission and reception. By performing characteristic compensation at the transmission end in advance, it is possible to avoid the noise enhancement effect that occurs when compensation is performed only by the reception unit, and transmission characteristics can be improved. Further, by performing compensation in the transmission unit, it is possible to reduce the signal processing load of the reception unit. In addition, by transmitting the transfer function estimation information back to the transmission unit using the known signal, a special channel for feeding back the transfer function estimation information becomes unnecessary.

  A program for realizing all or part of the functions of the optical transmission / reception system 1 is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into the computer system and executed. You may perform the process of each part. Here, the “computer system” includes an OS and hardware such as peripheral devices. Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used. The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case, and a program that holds a program for a certain period of time are also included. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design changes and the like without departing from the gist of the present invention.

1: optical transmission / reception system 10, 20: transmitter / receiver 11, 21: transmission unit 12, 22: reception unit 30, 40: optical fiber transmission line 51a, 51b: data signal sequence generation circuit 52a, 52b: known signal sequence generation circuit 53a 53b: signal multiplexing circuits 54a, 54b: transfer function information acquisition circuits 55a, 55b: characteristic compensation circuits 56a, 56b: D / A converters 57a, 57b: electrical / optical conversion circuit 58: polarization multiplexing circuit 71: polarization Separation circuits 72a, 72b: optical / electrical conversion circuits 73a, 72b: A / D conversion circuits 74a, 74b: main signal demodulation circuits 75a, 75b: known signal extraction circuit 76: differential decoding circuit 77: transfer function information generation circuit

Claims (4)

An optical transmission system comprising a first transceiver and a second transceiver for transmitting and receiving an optical signal, and an optical transmission path between the first transceiver and the second transceiver,
The first transceiver and the second transceiver are:
A transmission unit having a signal multiplexing circuit for time-multiplexing a known signal sequence to a data signal sequence, and a characteristic compensation circuit for performing characteristic compensation of a transmission signal;
A reception unit having a known signal extraction circuit that extracts a known signal from a received signal and a transfer function information generation circuit that estimates a transfer function from the received known signal sequence;
The first transmitter / receiver time-multiplexes a data signal sequence and a known signal sequence by the signal multiplexing circuit, and transfers them to the second transmitter / receiver. The second transmitter / receiver transmits the transfer function information generation circuit. The transfer function is estimated from the known signal sequence received by the step S1, the estimated transfer function is returned to the first transceiver using the known signal, and the first transceiver is returned by the characteristic compensation circuit. Compensation at the transmitting end using the transfer function
The first transmitter / receiver time-multiplexes a known signal sequence for estimating an amplitude characteristic of a transfer function and a known signal sequence for estimating a variance alternately into a data signal sequence. The optical transmission system according to claim 1, characterized in that for use as a known signal sequence for estimation of the amplitude characteristic of the transfer function, the pseudo random sequence. The optical transmission system according to claim 1 as a known signal sequence for estimation of the amplitude characteristic of the transfer function, characterized by the use of CAZAC (Constant Amplitude Zero Auto-Correlation ) sequence. A transmission path compensation method for an optical transmission system, comprising: a first transceiver and a second transceiver that transmit and receive optical signals; and an optical transmission path between the first transceiver and the second transceiver. And
The first transmitter / receiver time-multiplexes a data signal sequence and a known signal sequence and transfers them to the second transmitter / receiver,
The second transceiver estimates a transfer function from the received known signal sequence, and returns the estimated transfer function to the first transceiver using the known signal;
The first transceiver performs characteristic compensation at a transmission end using the returned transfer function,
The transmission / reception compensation method, wherein the first transmitter / receiver alternately time-multiplexes a known signal sequence for estimating an amplitude characteristic of a transfer function and a known signal sequence for estimating a dispersion into a data signal sequence.

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