JP5437205B2 - Optical receiving method, optical receiving apparatus and beat noise estimator - Google Patents

Description

  The present invention relates to an optical receiving method, an optical receiving apparatus, and a beat noise estimator provided in the optical receiving method for reducing the influence of beat noise generated when receiving an optical signal.

  When a plurality of lights are photoelectrically converted at the same time, beat noise that periodically varies depending on the frequency difference (wavelength interval) between the lights is generated. This variation can be expressed in the form of a sine wave with the phase difference of light as a parameter. When three or more light beams are simultaneously photoelectrically converted, a plurality of beat noises are generated according to the optical phase difference. The amplitude of the beat noise may take a value larger than the amplitude of the signal component, and the bit error rate (hereinafter referred to as “BER”) is significantly increased.

  Patent Literature 1 and Non-Patent Literature 1 disclose an optical reception method, an optical reception device, and a beat noise estimator provided therein that can improve determination performance even when a plurality of beat noises are generated simultaneously. FIG. 1 is a block diagram illustrating functions of a conventional optical receiver.

  The optical receiver of FIG. 1 includes a photoelectric converter 11, a beat noise estimator 13, and a maximum likelihood determiner 12. The photoelectric converter 11 photoelectrically converts the received transmission optical signal 90 and outputs a received electrical signal 91. The beat noise estimator 13 estimates beat noise included in the received electrical signal 91 from the photoelectric converter 11 and outputs the estimated beat noise as a beat noise estimated value 93. The maximum likelihood determiner 12 uses the bit pattern of the transmission optical signal 90 as the bit pattern with the maximum posterior probability from the received electrical signal 91 from the photoelectric converter 11 and the beat noise estimation value 93 from the beat noise estimator 13. If there is, the maximum likelihood is determined, and the signal component included in the received electrical signal 91 from the photoelectric converter 11 is estimated and output as the signal component estimated value 92.

  The beat noise estimator 13 estimates the beat noise estimated value 93 from the received electrical signal 91 from the photoelectric converter 11 and the signal component estimated value 92 from the maximum likelihood determiner 12. The beat noise estimator 13 includes a delay element 21, a subtractor 22, and a correlator 23. The delay element 21 gives a time delay to the received electrical signal 91 output from the photoelectric converter 11. The subtracter 22 outputs a noise signal 95 obtained by subtracting the signal component estimation value 92 output from the maximum likelihood determiner 12 from the received electrical signal 91 delayed by the delay element 21 and removing the signal component from the received electrical signal 91. . The correlator 23 estimates beat noise from the correlation between the noise signal 95 output from the subtractor 22 and the signal component estimated value 92 output from the maximum likelihood determiner 12 and outputs the beat noise as an estimated beat noise value 93.

  The correlator 23 includes an arithmetic circuit 31, a signal converter 32, a multiplier 33, and a high frequency component remover (hereinafter referred to as “LPF”) 34. The arithmetic circuit 31 classifies the signal by a predetermined method with respect to the signal component estimation value 92 output from the maximum likelihood determiner 12 in order to extract a specific beat noise component. The signal converter 32 converts the amplitude of the signals classified by the arithmetic circuit 31 under a predetermined condition. The multiplier 33 takes a correlation between the noise signal 95 from the subtracter 22 and the signal output from the signal converter 32. The LPF 34 averages the output of the multiplier 33 to reduce noise components other than the specific beat noise included in the signal output from the multiplier 33.

  Next, the correlator 23 will be described by taking as an example a case where there are three channel signal estimation values determined by the maximum likelihood determiner 12. First, in order to set the output of the correlator 23 to only specific beat noise, the arithmetic circuit 31 classifies the input bit pattern of the signal component estimated value 92 into three types based on the type of generated beat noise. Then, the signal converter 32 sets a coefficient by which the signal is multiplied so that the average of noise components other than the specific beat noise component becomes zero.

  Here, a case where a beat noise component is estimated will be described. Let beat noise generated by channel p and channel q be represented by bpq. For example, b12 indicates beat noise generated from channel 1 and channel 2. Specifically, a case where a specific beat noise component b12 is estimated will be described. In this example, intensity modulation is assumed, and {1} is light and {0} is light. Analyzing the case where beat noise occurs among combinations of 3-bit signals, beat noise occurs when signals of {1} are simultaneously present in two or more channels, so the number of {1} is 2, As the number increases to 3, the number of beat noises also increases to 1 (b12), 3 (b12, b13, b23) due to the mutual relationship. In order to correlate the specific beat noise (b12) to be estimated and the estimated value of the signal component, the following operation rule example is introduced.

(1) If the bit pattern is {1, 1, 0}, the pattern is 1.
(2) If the bit pattern is {1, 1, 1}, the pattern 2 is assumed.
(3) If the bit pattern is other than the above (1) and (2), it is set as pattern 3.
(4) In order to extract only the beat noise component b12, the amplitude values of the patterns 1, 2, and 3 are converted by the signal converter 32 according to the multiplication coefficients 20/3, 4/3, and -4/3, respectively.

  When the above rule example is applied to a 3-bit signal pattern, the outputs of the subtracter 22, the signal converter 32, and the multiplier 33 can be expressed as shown in FIG. x represents noise other than beat noise. Noise other than beat noise is, for example, Gaussian noise. Since the sum of all output patterns of the multiplier 33 is 8b12, when the multiplier outputs are averaged on the assumption that the {0, 1} signal is generated with equal probability, only a specific beat noise component b12 is extracted. All noise components other than b12 are canceled and become zero.

  In this way, the signal including the signal component, the Gaussian noise component, and the beat noise component is converted into a signal having only the beat noise component by the beat noise estimator 13 to achieve beat noise estimation. Although the above description is for the case of three channels, specific beat noise can be estimated by appropriately setting the multiplication coefficient of the signal converter 32 even in the case of n (n ≧ 4) channels. Since the beat noise estimator 13 estimates the beat noise component and uses the estimated value to determine the posterior probability and determine the maximum likelihood, the maximum likelihood determiner 12 calculates a large amount of likelihood information included in the received signal and calculates the posterior probability. And has a high maximum likelihood determination performance.

JP 2009-171274 A

“Maximum likelihood detection with beat noise estimation for minimizing bit error in OCDM-based system”, Optics Express, vol. 17, pp. 12433-12443, 2009.

  The beat noise estimation method by the beat noise estimator 13 of Patent Document 1 and Non-Patent Document 1 is estimated under the assumption that the transmission bit pattern occurrence frequency estimated by the maximum likelihood determiner 12 is the same for all bit patterns. Is the method. Therefore, when the bit pattern occurrence frequency is not always uniform and fluctuates as in the actual system, the correlation may be distorted, which may affect the beat noise estimation error.

  When considering the case where the occurrence frequency of the bit pattern is not necessarily uniform as in the actual system, the time constant in the LPF 34 in the correlator 23 is noticed. The beat noise estimated by the beat noise estimator 13 needs to be estimated including phase noise which is a low frequency, so it is desirable to set the cutoff frequency of the LPF 34 as high as possible, that is, to shorten the time constant. In addition, it is desirable to set the time constant short because the time lag occurs in the output of the beat noise estimator 13 when the time constant is long. On the other hand, if the time constant is shortened, the number of samples at the time of averaging decreases, so that the bit pattern is biased, and the estimation error due to fluctuation increases. These are summarized in FIG. As described above, if the influence of the fluctuation of the bit pattern can be reduced, the estimation error of the beat noise estimator 13 can be reduced even if the time constant of the LPF 34 is set short.

  Therefore, in order to solve the above-described problem, the present invention provides an optical reception method, an optical reception apparatus, and beat noise that can reduce the estimation error of the beat noise estimator by reducing the influence of fluctuation of the bit pattern. An object is to provide an estimator.

  In order to achieve the above object, the beat noise estimator calculates a beat noise estimation value before correction calculated from a noise signal and a signal component estimation value as a signal component estimation value for a plurality of signal components that are beat noise estimation targets. A value corrected with a pseudo beat noise estimated value calculated from the multiplication value of the above is output as a corrected beat noise estimated value.

Specifically, in the present invention, the photoelectric converter photoelectrically converts the received transmission optical signal and outputs a received electrical signal, and the beat noise estimator includes a beat included in the received electrical signal from the photoelectric converter. Estimate noise, output the estimated beat noise as a beat noise estimate, and the maximum likelihood determiner determines the posterior probability from the received electrical signal from the photoelectric converter and the beat noise estimate from the beat noise estimator. A bit pattern that maximizes the bit pattern of the transmitted optical signal, determines the maximum likelihood, estimates the signal component included in the received electrical signal from the photoelectric converter, and outputs the signal component as an estimated value. In the reception method, the beat noise estimator includes a delay element, a subtractor, and a correlator, and the delay element gives a time delay to the received electric signal output from the photoelectric converter, and the subtraction The vessel is in front Retarders outputs a noise signal to remove the maximum likelihood decision unit a signal component from the subtractor to receive the electrical signal a signal component estimation value output from the reception electric signal delay time, the correlator, the maximum likelihood determination Multiplication value of signal component estimation values for a plurality of signal components that are beat noise estimation targets output from the detector, and a coefficient corresponding to the pattern of the bit pattern that the maximum likelihood determination unit determines maximum likelihood The beat noise before correction calculated from the correlation between the noise signal output from the subtractor and the signal component estimated value output from the maximum likelihood determiner using the pseudo beat noise estimated value calculated as the time average of the value obtained correct for the estimated value, an optical receiving method, characterized in that the output as a beat noise estimate after correction.

The present invention also provides a photoelectric converter that photoelectrically converts a received transmission optical signal and outputs a received electrical signal, estimates beat noise included in the received electrical signal from the photoelectric converter, and calculates the estimated beat noise. A beat noise estimator that outputs as a beat noise estimate, a received electrical signal from the photoelectric converter, and a beat noise estimate from the beat noise estimator, a bit pattern that maximizes the posterior probability, And a maximum likelihood determiner that determines a maximum likelihood of the bit pattern and estimates a signal component included in the received electrical signal from the photoelectric converter and outputs the estimated signal component as a signal component estimated value. Then, the beat noise estimator outputs the maximum likelihood determiner from a delay element that gives a time delay to the received electrical signal output from the photoelectric converter, and a received electrical signal that is delayed in time by the delay element. A subtractor for outputting a noise signal obtained by removing the signal component from the received electrical signal by subtracting the signal component estimate to the signal component estimates for a plurality of signal components a beat noise estimation target maximum likelihood decision unit outputs Using the pseudo beat noise estimated value calculated as the time average of the multiplication value of the values and the coefficient according to the bit pattern pattern for which the maximum likelihood determiner determines the maximum likelihood, the subtraction vessel is a value obtained by correct for beat noise estimate before correction calculated from the correlation between the signal component estimate noise signal and the maximum likelihood decision circuit outputs to output, to output as a beat noise estimate after correction And a correlator.

The present invention also provides a delay element that time-delays a received electrical signal output from a photoelectric converter that photoelectrically converts a received transmission optical signal and outputs a received electrical signal, and a received electrical signal that is delayed in time by the delay element. The signal component included in the received electrical signal from the photoelectric converter is estimated and output as a signal component estimated value, and the signal component estimated value output from the maximum likelihood determiner is subtracted to obtain the signal component from the received electrical signal. A subtractor that outputs the removed noise signal, a multiplication value of signal component estimation values for a plurality of signal components that are beat noise estimation targets output from the maximum likelihood determiner, and the maximum likelihood determiner is a maximum likelihood by using the coefficient corresponding to the pattern of the determined bit pattern, the pseudo-beat noise estimate calculated as a time average of the multiplied value, the signal in which the noise signal subtractor outputs said maximum likelihood determination circuit outputs The value obtained correct for beat noise estimate before correction calculated from the correlation between the frequency estimate, be provided with a correlator output as a beat noise estimate the corrected beat noise estimator characterized by is there.

  The beat noise estimated value calculated from the noise signal and the signal component estimated value is a beat noise estimated value before correction. The beat noise estimation value calculated from the multiplication value of the signal component estimation values for a plurality of signal components that are beat noise estimation targets is a pseudo beat noise estimation value. Here, the beat noise estimation value before correction is a multiplication value of a coefficient reflecting the influence of the beat noise estimation value after correction and the fluctuation of the bit pattern. The pseudo beat noise estimation value is a coefficient multiplication value reflecting the influence of beat noise of a known amplitude and fluctuation of the bit pattern. Correcting the beat noise estimate before correction with a pseudo beat noise estimate cancels the coefficient that reflects the effect of bit pattern fluctuations, and the corrected beat noise estimate with beat noise of a known amplitude. To obtain the same result as dividing. An accurate beat noise estimation value can be calculated from the result and the known amplitude, and the estimation error of the beat noise estimator can be reduced. A correlator can be used as the beat noise estimator.

  In the present invention, the transmission optical signal is multiplexed by an optical code division multiplexing method in which transmission data from a transmission side is encoded in a frequency domain, and an optical separator converts the transmission optical signal into a frequency component. The photoelectric converter that is separated into a plurality of optical signals every time, and provided with the number of optical signals separated by the optical separator, photoelectrically converts each separated optical signal and outputs a received electrical signal, In the optical receiving method, the beat noise estimator estimates beat noise of a received electrical signal, and the maximum likelihood determiner performs decoding of the received electrical signal and maximum likelihood determination.

  In the present invention, the transmission optical signal is multiplexed by an optical code division multiplexing method in which transmission data from a transmission side is encoded in a frequency domain, and an optical separator converts the transmission optical signal into a frequency component. The photoelectric converter that is separated into a plurality of optical signals every time, and provided with the number of optical signals separated by the optical separator, photoelectrically converts each separated optical signal and outputs a received electrical signal, The beat noise estimator estimates beat noise of a received electrical signal, and the maximum likelihood determiner performs decoding of the received electrical signal and maximum likelihood determination.

  According to this configuration, it is possible to reduce the influence of beat noise even when optical multiplex transmission is performed by the optical CDM method for encoding in the frequency domain.

  The present invention can provide an optical reception method, an optical reception device, and a beat noise estimator that can reduce the estimation error of the beat noise estimator by reducing the influence of fluctuations in the bit pattern.

It is a block diagram explaining the function of the optical receiver of a prior art. FIG. 3 is a block diagram illustrating functions of the optical receiving device according to the first embodiment. It is the figure which showed the output characteristic of the beat noise estimated value in the optical receiver of FIG. It is the figure which showed the output characteristic of the beat noise estimated value in the optical receiver of FIG. FIG. 6 is a block diagram illustrating functions of an optical receiving device according to a second embodiment. It is the figure which showed the BER characteristic of the data series in the optical receiver of FIG. It is a figure which shows the output of a subtractor, a signal converter, and a multiplier in each bit pattern. It is a figure which shows the various causes of the estimation error of a bit noise estimated value.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 2 is a block diagram illustrating the function of the optical receiving apparatus according to this embodiment. The operation of the optical receiver in FIG. 2 will be described. The transmitted optical signal 90 transmitted from the optical communication path is converted into a received electrical signal 91 by the photoelectric converter 11. For the photoelectric converter 11, a general photodiode (Photo Diode: PD) or the like is applied. The received electrical signal 91 is separated and input to the maximum likelihood determiner 12 and the beat noise estimator 13. The received electrical signal 91 includes Gaussian noise and beat noise in addition to signal components. The maximum likelihood determination unit 12 determines the maximum likelihood so as to extract only the correct signal component from the received electrical signal 91 including these noises using the posterior probability.

  The maximum likelihood determination is a determination method for calculating a posterior probability using a probability density distribution for Gaussian noise and a probability density distribution for beat noise estimated by the beat noise estimator 13 and selecting a bit pattern having the largest posterior probability. It is. The maximum likelihood determiner 12 estimates a signal component included in the received electrical signal 91 based on the selected bit pattern, and outputs a signal component estimated value 92. For example, the maximum likelihood determiner 12 calculates a probability density distribution for Gaussian noise included in the received electrical signal 91 from the photoelectric converter 11 and a probability density distribution for beat noise included in the received electrical signal 91 from the photoelectric converter 11. The posterior probabilities of all the bit patterns may be used to determine the maximum likelihood that the bit pattern having the maximum posterior probability is the bit pattern of the transmission optical signal 90.

  The beat noise estimator 13 estimates beat noise by a predetermined method based on the received electrical signal 91 output from the photoelectric converter 11 and the signal component estimated value 92 output from the maximum likelihood determiner 12. . The optical receiver of FIG. 2 reduces the influence of beat noise on the received electrical signal 91 by combining the maximum likelihood determination of the maximum likelihood determiner 12 and the estimation of the beat noise estimator 13. Note that when a plurality of beat noises are generated, it is necessary to estimate all the generated beat noises. Therefore, the receiving apparatus includes beat noise estimators 13 corresponding to the number of generated beat noises.

  Since the maximum likelihood determiner 12 and the beat noise estimator 13 each use mutual estimation information, the estimation accuracy may be low or diverge in the initial state. Therefore, the maximum likelihood determiner 12 in the initial state outputs a fixed preamble pattern transmitted at the start of communication, and switches to output of the maximum likelihood determination result when the accuracy of the beat noise estimator 13 becomes high. It may be a thing.

  The correlator 23 includes a multiplier 35, an LPF 36, and a fluctuation correction calculator 37 in addition to the arithmetic circuit 31, the signal converter 32, the multiplier 33, and the LPF 34. The arithmetic circuit 31 calculates a multiplication value of the signal component estimation value for a plurality of signal components that are beat noise estimation targets output from the maximum likelihood determiner 12. The multiplier 35 multiplies the multiplication value from the arithmetic circuit 31 and the coefficient from the signal converter 32 in accordance with the bit pattern patterns 1, 2, and 3. The LPF 36 averages the multiplication values from the multiplier 35 and calculates a pseudo beat noise estimation value. The fluctuation correction computing unit 37 outputs a value obtained by correcting the beat noise estimated value before correction from the LPF 34 with the pseudo beat noise estimated value from the LPF 36 as a corrected beat noise estimated value.

A description will be given of how the fluctuation of the bit pattern affects the beat noise estimation value. Α and β are defined as fluctuation components of the occurrence frequency of the bit pattern {1, 1, x} (x is {0} or {1}). When the fluctuation components α and β are used, the occurrence frequency of the bit pattern {1, 1, 0} can be expressed as 1/8 + α, and the occurrence frequency of the bit pattern {1, 1, 1} can be expressed as 1/8 + β. The beat noise estimation value b ^ 12 before correction from the LPF 34 is expressed by Equation (1). However, a = 20 / 3α + 4 / 3β.
b ^ 12 = {20/3 (1/8 + α) +4/3 (1/8 + β)} b12
= {1 + 20 / 3α + 4 / 3β} b12 = (1 + a) b12 (1)

  In other words, if there is no fluctuation of the bit pattern, a = 0 (α = 0, β = 0) even if there is no correction by the multiplier 35, the LPF 36, and the fluctuation correction calculator 37, the fluctuation component of the bit pattern. The estimation error due to is 0, and the beat noise estimation value is b12. However, if the fluctuation of the bit pattern is large, if there is no correction by the multiplier 35, the LPF 36, and the fluctuation correction calculator 37, the estimation error due to the fluctuation component of the bit pattern becomes large, and the beat noise estimated value is different from b12. 12

  Therefore, the beat noise estimator 13 of the first embodiment operates as described below. The arithmetic circuit 31, the signal converter 32, the multiplier 33, and the LPF 34 calculate the beat noise estimation value before correction as in the conventional technique. The arithmetic circuit 31, the signal converter 32, the multiplier 35, and the LPF 36 calculate pseudo beat noise. The fluctuation correction calculator 37 outputs a value obtained by correcting the beat noise estimated value before correction with a pseudo beat noise estimated value as a corrected beat noise estimated value.

  In the bit patterns {1, 1, 0} and {1, 1, 1}, the arithmetic circuit 31 sets 1 as the multiplication value of the signal component estimation value for the signal components of channels 1 and 2 that are beat noise estimation targets. Is calculated. Then, the arithmetic circuit 31 multiplies the signal components of the channels 1 and 2 that are beat noise estimation targets by the signal component estimation values in the bit patterns other than {1, 1, 0} and {1, 1, 1}, respectively. 0 is calculated as a value. In this way, the arithmetic circuit 31 generates a pseudo beat noise signal having an amplitude 1 which is different from the actual one by calculating 1 as a multiplication value of the signal component estimation value.

The original beat noise signal can be expressed as shown in Equation (2). Here, c1 and c2 are transmission bits of channels 1 and 2, A1 and A2 are signal amplitudes of channels 1 and 2, f1 and f2 are optical frequencies of channels 1 and 2, and θ1 and θ2 are channel 1, 2 represents phase noise.
c1 * c2 * A1 * A2 * cos (2 [pi] (f1-f2) t + [theta] 1- [theta] 2) (2)

  The multiplier 35 multiplies 1 that is the multiplication value from the arithmetic circuit 31 and 20/3 that is the coefficient from the signal converter 32 in accordance with the bit pattern of {1, 1, 0}, and obtains 20 as the multiplication value. / 3 is calculated. Then, the multiplier 35 multiplies 1 which is the multiplication value from the arithmetic circuit 31 and 4/3 which is the coefficient from the signal converter 32 in accordance with the bit pattern of {1, 1, 1}. As a result, 4/3 is calculated. Furthermore, the multiplier 35 is a multiplication value 0 from the arithmetic circuit 31 and a coefficient from the signal converter 32 according to a bit pattern other than {1, 1, 0} and {1, 1, 1}. Multiply by (−4/3) to calculate 0 as the multiplication value.

The occurrence frequency of the bit pattern {1, 1, 0} is 1/8 + α, and the occurrence frequency of the bit pattern {1, 1, 1} is 1/8 + β. Therefore, the LPF 36 averages the multiplication values from the multiplier 35 and calculates a pseudo beat noise estimation value as shown in Equation (3).
20/3 (1/8 + α) +4/3 (1/8 + β)
= 1 + 20 / 3α + 4 / 3β = 1 + a (3)

  As described in Expression (1), the beat noise estimation value before correction is (1 + a) b12, and as described in Expression (3), the pseudo beat noise estimation value is 1 + a. Therefore, the fluctuation correction calculator 37 can output the corrected value b12 obtained by dividing the pre-corrected beat noise estimated value by the pseudo beat noise estimated value as the corrected beat noise estimated value.

  In the present embodiment, focusing on the bit pattern in which the absolute value of the corresponding coefficient 20/3 is large and the influence of the fluctuation of the occurrence frequency is dominant, the fluctuation frequency α, {1, 1, x} Only β is targeted for correction. The present embodiment can be extended and applied to fluctuations in the frequency of occurrence of the remaining six patterns {0, 0, 0} to {1, 0, 1}.

When correcting fluctuations in the frequency of occurrence of all the bit patterns, the beat noise estimated value can be expressed as Equation (4). Here, the matrix a is a fluctuation in the occurrence frequency of a bit pattern corresponding to a in Expression (1), and the vector b ^ is a plurality of signal components that are beat noise estimation targets corresponding to b ^ 12 in Expression (1). Beat noise estimated value before correction, vector b is a beat noise estimated value after correction for a plurality of signal components that are beat noise estimation targets corresponding to b12 in Equation (1), and matrix I is a unit matrix. Represent. Therefore, the corrected beat noise estimated value b for a plurality of signal components that are beat noise estimation targets is calculated by performing correction by multiplying both sides of Equation (4) by an inverse matrix of (I + a) ⁻¹ from the left side. can do.
b ^ = (I + a) · b (4)

  FIG. 3 is a diagram showing the output characteristics of the beat noise estimation value in the conventional optical receiver of FIG. 1, and FIG. 4 is the beat noise estimate value of the optical receiver of Embodiment 1 in FIG. It is the figure which showed the output characteristic. The horizontal axis indicates the bit time at a certain time, the vertical axis indicates the magnitude of the beat noise signal, and the time constants of the LPFs 34 and 36 are τ = 40 [bit time]. Since the beat noise signal is usually a sine wave signal as shown in Equation (2), a signal that makes the beat noise signal a sine wave signal is used as the input signal. 3 and 4, the magnitude of the beat noise of the input signal is shown together with the magnitude of the beat noise estimated value.

  In the optical receiving apparatus of the prior art shown in FIG. 1, an estimation error of beat noise occurs, and particularly when the beat noise is large, the estimation error of beat noise is larger. In the optical receiver of Embodiment 1 of FIG. 2, although an estimation error of beat noise occurs, it is clear that the magnitude is very small and the beat noise can be estimated almost regardless of the magnitude of the beat noise. is there.

  With the above operation, beat noise estimation independent of transmission bit pattern fluctuations is achieved. Although the above shows the case of 3 channels, a specific beat noise can be estimated by appropriately setting the coefficient even in the case of n (n ≧ 4) channels.

(Embodiment 2)
FIG. 5 is a block diagram for explaining the functions of the optical receiver according to this embodiment. The optical receiver of FIG. 5 differs from the optical receiver of FIG. 2 in that an optical separator 51 that separates the transmission optical signal 90 into a plurality of optical signals for each frequency component, and an optical signal separated by the optical separator 51. The number of photoelectric converters is provided. In the optical receiver of FIG. 5, the optical separator 51 includes a photoelectric converter 52a, a photoelectric converter 52b, and a photoelectric converter 52c in order to separate the transmission optical signal 90 into three optical signals.

  The optical receiver shown in FIG. 5 is premised on the optical CDM system, and is intended to reduce the influence of beat noise generated by sharing the same frequency between users or channels, especially in the system encoding in the frequency domain.

  Specifically, in the optical reception method of the optical receiver of FIG. 5, the transmission optical signal 90 is multiplexed by an optical code division multiplexing method in which transmission data from the transmission side is encoded in the frequency domain. The separator 51 separates the transmission optical signal 90 into a plurality of optical signals for each frequency component, and the photoelectric converters 52a to 52c provided by the number of optical signals separated by the optical separator 51 are separated light. Each signal is photoelectrically converted to output a received electrical signal 91, the beat noise estimator 13 estimates the beat noise of the received electrical signal 91, and the maximum likelihood determiner 53 decodes the received electrical signal 91 and the maximum likelihood. Make a decision. Here, the beat noise estimator 13 may estimate beat noise of all received electrical signals 91, and the maximum likelihood determiner 53 may perform decoding and maximum likelihood determination of all received electrical signals 91. .

  FIG. 6 is a diagram showing the BER characteristics of the data series when the optical receiver of FIG. 5 is used. In order to show the effect of the invention, the result of signal determination by hard decision which is a conventional optical receiving method is also shown. When the influence of beat noise is not considered, the BER characteristic by the hard decision is as shown by a broken line R1. When the influence of beat noise is taken into consideration, the BER characteristic is as shown by a broken line R2. Compared with the broken line R1, the BER characteristic is deteriorated and the influence of beat noise is very large. On the other hand, when the optical reception method described in the optical reception apparatus of FIG. 5 is applied, a solid line R3 is obtained. The BER characteristic of the solid line R3 is greatly improved, and the influence of beat noise is reduced.

  As described above, the optical receiving apparatus of FIG. 5 can reduce the influence of beat noise even when optical multiplex transmission is performed by the optical CDM method for encoding in the frequency domain. In the present embodiment, the number of users and the number of used frequencies are not limited. Therefore, the number of photoelectric converters 52a to 52c also changes corresponding to the number of operating frequencies.

  Any optical receiver that can simultaneously receive a plurality of optical signals can be applied to a public communication network, a dedicated network, a LAN (Local Area Network), and the like.

11: photoelectric converter 12: maximum likelihood determiner 13: beat noise estimator 21: delay 22: subtractor 23: correlator 31: arithmetic circuit 32: signal converter 33: multiplier 34: LPF
35: Multiplier 36: LPF
37: Fluctuation correction calculator 51: Optical separators 52a, 52b, 52c: Photoelectric converter 53: Maximum likelihood determiner 90: Transmitted light signal 91: Received electric signal 92: Signal component estimated value 93: Beat noise estimated value 95: Noise signal R1, R2: Broken line R3: Solid line

Claims (5)

The photoelectric converter photoelectrically converts the received transmission optical signal and outputs a received electrical signal,
The beat noise estimator estimates beat noise included in the received electrical signal from the photoelectric converter, and outputs the estimated beat noise as a beat noise estimation value.
The maximum likelihood determiner, based on the received electrical signal from the photoelectric converter and the beat noise estimation value from the beat noise estimator, the bit pattern that maximizes the posterior probability is the bit pattern of the transmission optical signal. Judge the likelihood, estimate the signal component included in the received electrical signal from the photoelectric converter and output as a signal component estimated value,
An optical receiving method,
The beat noise estimator includes a delay element, a subtractor, and a correlator.
The delay element gives a time delay to the received electrical signal output by the photoelectric converter,
The subtractor outputs a noise signal obtained by subtracting the signal component estimation value output from the maximum likelihood determiner from the received electrical signal delayed by the delay element and removing the signal component from the received electrical signal;
The correlator includes a multiplication value of signal component estimation values for a plurality of signal components that are beat noise estimation targets output from the maximum likelihood determiner, and a bit pattern pattern that the maximum likelihood determiner determines maximum likelihood. And a correlation between a noise signal output from the subtractor and a signal component estimated value output from the maximum likelihood determiner using a pseudo beat noise estimated value calculated as a time average of a multiplication value of optical receiving method characterized by the value of correct for beat noise estimate before correction calculated from the relationship, and outputs as a beat noise estimate after correction. The transmission optical signal is multiplexed by optical code division multiplexing in which transmission data from the transmission side is encoded in the frequency domain,
An optical separator separates the transmission optical signal into a plurality of optical signals for each frequency component,
The photoelectric converter provided by the number of optical signals separated by the optical separator outputs a received electrical signal by performing photoelectric conversion for each separated optical signal,
The beat noise estimator estimates beat noise of a received electrical signal;
The optical reception method according to claim 1, wherein the maximum likelihood determiner performs decoding of a received electrical signal and maximum likelihood determination. A photoelectric converter that photoelectrically converts the received transmission optical signal and outputs a received electrical signal; and
A beat noise estimator that estimates beat noise included in an electrical signal received from the photoelectric converter and outputs the estimated beat noise as a beat noise estimation value;
From the received electrical signal from the photoelectric converter and the beat noise estimation value from the beat noise estimator, the bit pattern that maximizes the posterior probability is determined to be the maximum likelihood as the bit pattern of the transmission optical signal, A maximum likelihood determiner that estimates a signal component included in the received electrical signal from the photoelectric converter and outputs the signal component as an estimated value;
An optical receiver comprising:
The beat noise estimator is
A delay element that gives a time delay to the received electrical signal output by the photoelectric converter;
A subtractor that outputs a noise signal obtained by subtracting a signal component estimate output by the maximum likelihood determiner from the received electrical signal that is delayed in time by the delay element and removing the signal component from the received electrical signal;
A multiplication value of signal component estimation values for a plurality of signal components that are beat noise estimation targets output by the maximum likelihood determiner, and a coefficient corresponding to a pattern of a bit pattern that the maximum likelihood determiner determines maximum likelihood Correction calculated from the correlation between the noise signal output from the subtractor and the signal component estimated value output from the maximum likelihood determiner using a pseudo beat noise estimated value calculated as the time average of the multiplication values of the value obtained correct for the previous beat noise estimate, a correlator output as a beat noise estimate after correction,
An optical receiver characterized by comprising: The transmission optical signal is multiplexed by optical code division multiplexing in which transmission data from the transmission side is encoded in the frequency domain,
An optical separator separates the transmission optical signal into a plurality of optical signals for each frequency component,
The photoelectric converter provided by the number of optical signals separated by the optical separator outputs a received electrical signal by performing photoelectric conversion for each separated optical signal,
The beat noise estimator estimates beat noise of a received electrical signal;
The optical receiver according to claim 3, wherein the maximum likelihood determiner performs decoding of a received electrical signal and maximum likelihood determination. A delay element that photoelectrically converts the received transmission optical signal and outputs a reception electrical signal, and gives a time delay to the reception electrical signal output by the photoelectric converter;
The signal component estimation value output by the maximum likelihood determiner that estimates the signal component contained in the reception electrical signal from the photoelectric converter and outputs it as the signal component estimation value is subtracted from the reception electrical signal delayed by the delay element. A subtractor that outputs a noise signal obtained by removing the signal component from the received electrical signal;
A multiplication value of signal component estimation values for a plurality of signal components that are beat noise estimation targets output by the maximum likelihood determiner, and a coefficient corresponding to a pattern of a bit pattern that the maximum likelihood determiner determines maximum likelihood Correction calculated from the correlation between the noise signal output from the subtractor and the signal component estimated value output from the maximum likelihood determiner using a pseudo beat noise estimated value calculated as the time average of the multiplication values of the value obtained correct for the previous beat noise estimate, a correlator output as a beat noise estimate after correction,
A beat noise estimator comprising:

Images