Filter device. RU patent 2513044.

FIELD: radio engineering, communication.

SUBSTANCE: invention relates to communication engineering and can be used in optical communication systems. Filter device includes a filter (101) for filtering an input signal using first and second sets of filter coefficients to obtain frequency-domain first and second filtered signals (103) for correlation of a first subset of frequency-domain components of the first filtered signal to obtain a first correlation value, and correlation of a second subset of frequency-domain components of the second filtered signal to obtain a second correlation value, wherein the first subset of correlated frequency-domain components and the second subset of correlated frequency-domain components are respectively located in a given range of correlated signals comprising a clock frequency; and a processor (105) configured to select, for filtration of the input signal, either the first set of filter coefficients or the second set of filter coefficients based on the first correlation value and the second correlation value.

EFFECT: providing frequency-domain filter adaptation.

14 cl, 6 dwg

The level of technology

Modern high-speed communication system uses optical components for information transmission by optical signals. Usually optical transmit signals over fiber optic cable, which, unfortunately, distorts the signal because of the different transmission characteristics for different wavelengths. Distortion may contain the weakening of the signal that depends on the wavelength, or chromatic dispersion that occurs when the components of the signals with different wavelengths propagate at different speeds on the optical channel of communications.

To compensate for the distortions in the receiver can be applied digital filter to improve the quality of the signal and the subsequent detection of the transferred information. In the case of digital filtering, you first perform coherent optical demodulation and, then, optoelectronic conversion using, for example, photodiodes. Finally, analog-to-digital Converter (ADC) outputs a digital signal. However, the resulting digital signal still contains residual distortion, such as chromatic dispersion, which can be reduced by digital filtering.

To filter chromatic dispersion can be applied effective filter, known from the report OUT on OFC 2009 (Exhibition fiber optic communications by Mkurnaloba (.Kuschnerov), Pinasca (F.N. Hauske), Pavanne (.Piyawanno), B. Spindler (.Spinnler), Anapali (A.Napoli) and Blankly (.Lankl), entitled "Adaptive equalization chromatic dispersion for coherent systems with dispersionless control". Described in this case the filter is based on criteria u(t)=|s(t)| 2 - R error output of complex values of the time domain signal s(t), where R denotes the expected capacity. This approach refers to the well-known algorithm based on the criterion of constancy of the module (CMA). For adaptation of the filter in the frequency domain, the signal u(t) error transferred into the frequency domain to update the filter function, i.e. the coefficients of the filter. After many successive updates, filter approximates the ideal function

filter that defines the filter coefficients and represents an inverse function of a function of the channel filter, and introducing chromatic dispersion.

Disclosure of the invention

The present invention is to propose principles of effective adaptation of the filter in the frequency domain, specifically designed to filter chromatic dispersion.

The invention is based on search of the optimal filter that can be derived from the array of filter coefficients from a variety of filter coefficients that are based on an assessment of the filtered signal or autocorrelation sequence of each of the filtered signal in the interval of frequencies near the clock frequency. The input signal is filtered with the use of possible variants of filter coefficients, which can be selected optimal filter coefficients. The input signal may contain or may not contain, dot clock.

According to one aspect of the present invention relates to filtration device for filtering of the input signal and the input signal contains synchronization signal with a given clock frequency. Filtration device contains a filter to filter the input signal using the first set of filter coefficients to obtain the first filtered signal, and filtering of the input signal using the second set of filter coefficients to obtain a second filtered signal, the correlator frequency domain to correlate first subset of the components of the frequency domain of the first filtered signal for first-time correlation values, and to correlate the second subset of the components of the frequency domain of the second filtered signal for the second correlation values, in which the first subset correlated components of the frequency domain and the second subset correlated components frequency domain are in a given range correlated signals that contains the clock speed and the CPU that choose to filter the input signal or the first set of filter coefficients, or the second set of coefficients filter based on the first correlation values and second correlation values. The filter and/or the correlator, and/or the processor can operate in the frequency domain. According to one version of the exercise, the correlator made with the possibility of correlation first subset of the components of the frequency domain to obtain the first correlation sequence to the frequency domain and summing the values of the first correlation sequence for first-time correlation values and correlation of the second subset of the components of the frequency domain to obtain the second correlation sequence to the frequency domain and summation of the values of the second correlation sequence for the second correlation values.

According to one version of the exercise, the processor is made with the possibility of selection of the first set of filter coefficients if the first correlation is greater than or equal to the second correlation to the value of, or the second set of filter coefficients, if the second correlation is greater than or equal to the first correlation value. According to one version of the exercise, the filter is configured to filter the many input signals using the first set of filter coefficients to obtain many first filtered signal, and filter set the input signals using the second set filter to obtain many second filtered signal, the correlator frequency domain is made with the possibility of correlation first subset of the components of the frequency domain for each of the first filtered signals to obtain many of the first correlation values and correlation of the second subset of the components of the frequency domain for each of the second filtered signals to obtain many second correlation of values, where each subset of the components of the frequency domain is located in the given frequency range, contains the clock speed and the CPU is made with the possibility of summarizing many of the first correlation values for first correlative meanings, the summation of many second correlation values for the second correlation values and selection of the first set of filter coefficients if the first correlation is greater than or equal to the second correlation value, or select the second set of filter coefficients, if the second correlation is greater than or equal to the first correlation value.

According to one version of the exercise, the first set of filter coefficients and the second set of filter coefficients contain, respectively, the different characteristics of the filter chromatic dispersion for different filtering of the input signal. According to one version of the exercise, the first set of filter coefficients and the second set of filter coefficients contain, respectively, the characteristics of the filter polarization mode dispersion (PMD), filter rotation of polarization, in particular, to filter rotation of polarization with the same or different corners full of polarization. In this case, the filter PMD can be performed with the possibility of rotation of the polarization that forms a subset of the effects of PMD.

According to one version of the exercise, the first set of filter coefficients contains many first subsets of filter coefficients, many first subsets of filter coefficients contain, respectively, the first characteristic filtering chromatic dispersion and different characteristics of polarization mode dispersion, the second set of filter coefficients contains many second subsets of filter coefficients, many second subsets of coefficients the filter contains hence the second characteristic of the filter chromatic dispersion and different characteristics of polarization mode dispersion, the filter is made with the possibility of filtering of the input signal, with many first subsets of filter coefficients to obtain many first filtered signals and filtering of the input signal using a variety second subsets of filter coefficients to obtain many second filtered signal, the correlator frequency domain is made with the possibility of correlation first subset of the frequency components each of the first filtered signal to obtain the first correlation values and correlation of the second subset of the frequency components of each of the second filtered signals for reception of the second correlation of values, where each subset of the components of the correlation frequency domain is located in the given frequency range that contains the clock speed and the CPU is made with the possibility of summarizing many of the first correlation values for first correlative meanings, the summation of many second correlation values for second the correlation values and selection of the first set of filter coefficients if the first correlation is greater than or equal to the second correlation value, or select the second set of filter coefficients, if the second correlation is greater than or equal to the first correlation values. The sum of the correlation values can be used weights, for example, through the introduction of the factor of forgetting.

According to one version of the exercise, the filter has a filter chromatic dispersion and many filters polarization mode dispersion, located after the filter chromatic dispersion, filter chromatic dispersion made with the possibility of successive filtering of the input signal using the first set of filter coefficients and the second set of filter coefficients to obtain the first filtered signal and the second filtered signal, and in which multiple filters polarization mode dispersion made with the possibility sequential filtering feather filtered signal and the second filtered signal for receiving, respectively, many first filtered signals and second filtered signal.

According to one version of the exercise, the correlator frequency domain is made with the possibility of autocorrelation of the corresponding subsets of the components of the frequency domain. But it can also be performed mutual correlation between different components of the polarization.

According to one version of the exercise, filter device contains Converter Fourier for conversion of the input signal or the appropriate first or second filtered signal in the frequency domain.

According to one version of the exercise, the processor is made with the possibility of increasing the clock frequency for a given increment or decrement the clock frequency on the given decrement to determine a specified frequency range.

According to one version of the exercise, the input signal is a copy of the received signal and the filter is made with the possibility of filtration of received signals by selecting a set of filter coefficients for further processing.

According to one version of the exercise of the input signal contains the first part of the input signal, related to the first optical polarization, and the second part of the input signal that is associated with the second optical polarization.

According to the additional aspect of the present invention relates to a method of filtering of the input signal and the input signal contains synchronization signal with clock frequency. The method contains filtering of the input signal using the first set of filter coefficients to obtain the first filtered signal and filtering of the input signal using the second set of filter coefficients to obtain a second filtered signal, correlation first subset of the components of the frequency domain first filtered signal for first-time correlation values and correlation of the second subset of the components of the frequency domain of the second filtered signal for the second correlation values, where the first subset of the components of the frequency domain and the second subset of the components of the frequency domain are located, respectively, in the given frequency range that contains the clock speed, and a choice of either the first set of filter coefficients, or the second set of filter coefficients on the basis of the first correlation values and second correlation values to filter the input signal.

According to the additional aspect of the present invention relates to a computer program which, when run on the computer will use the above method to filter the input signal.

Brief description of drawings

Further options for the implementation of the present invention will be described with references to the following figures:

figure 1 - block diagram filtering devices under option exercise;

figure 2 - block diagram of filter under option exercise;

figure 3 is a block diagram of filter devices under option exercise;

figure 4 is a block diagram of filter devices under option exercise;

5 is a block diagram of a digital receiver with clearing under option exercise; and

6 - diagram of example assessments under option exercise.

Embodiments of the invention

Figure 2 shows the filter implementation 101, shown in figure 1. Filter the filter contains 201 chromatic dispersion and many filters 203-205 polarization mode dispersion. Filters 203-205 polarization mode dispersion form, for example, a filter SOP (State of Polarization - Polarization) and implemented with the possibility of rotation of the plane of polarization of the signal output from the filter 201 chromatic dispersion at different angles to obtain many of the filtered signal. The correlator 103 can determine, for example, autocorrelation each of the many filtered signals and summarize the correlation sequence associated with the specified frequency range, close to the clock, to obtain the first correlation values. In another moment the filter 201 chromatic dispersion can filter the input signal with other characteristics of the filter chromatic dispersion, so after filtering and correlation can be obtained second correlation value.

Figure 3 shows a filter device contains many filters, 301, 303 and 305 of rotation of polarization. After each filter 301 to 305 provided by the correlators 307, 309 and 311 for determination of the autocorrelation of the corresponding filtered signal. Correlation sequence sent to the processor 313, working, for example, based on a formula shown in figure 3 and is used to select the appropriate set of filter coefficients chromatic dispersion, not shown in figure 3 and located before the filters 301 to 305.

As for 3, then apply a filter group of several filters 203-205 polarization mode dispersion, such as filters, rotation SOP. Stage using filters SOP makes this approach is independent of rotation of polarization.

Each filter 303-305 turn signal on a different angle of rotation of the polarization:

After each filter can be added using ACF (Auto-Correlation function - Function of Autocorrelation) for both deposits from x-polarization and-polarization:

ACF is calculated only for shift Δ versus frequency clock (ARTICLE)that for systems with sampling rate of 2 samples per second is equal FFT size/2. In this respect, the above specified range of frequencies can match Δ or 2?. Not necessarily, but can be calculated average value for each of the ACF and for each filter SOP. As an example, the argument maximum result function

will appreciate CD, where the subscript i denotes the set i of the coefficients of the filter to filter chromatic dispersion and k denotes the input signal k. In particular, the maximum of the above functions associated with a certain set of filter coefficients for filtering chromatic dispersion.

As for the above formulas, values correlation

sequences |U k (CD i ,kl)| summarized calculation

to obtain for each filter CD correlation values that can be used to select the optimal filter CD.

In addition, many of the input signals can be processed in accordance with the formula

to obtain for each filter CD correlation values that can be used to select the optimal filter CD.

In addition, can also be taken into account, for example, the set of filters SOP in accordance with the formula

to obtain for each filter CD correlation values that can be used to select the optimal filter CD, summation of the values are output filters.

According to some variants of implementation, knowing that a set of filter coefficients for chromatic dispersion, the CD can also be evaluated as

The estimated value of the CD, or set of filter coefficients, which reduces the estimated value of the CD, can be applied in the filter FD CD for additional filtering.

Figure 4 shows a filter device for filtering digital optical signal with X-polarization and Y-polarization. Thus, filter device contains highway 401 data X and highway 403 data Y. each tract placed a block 405 series-parallel (S/P) conversion, followed Converter 407 Fourier transform (FFT). Conclusion from the associated inverter 407 Fourier pass filter device 409, based on the principles described in this document. Filter device 409 selects a suitable set of coefficients for the filter 411, which can be a filter chromatic dispersion. Since the operation of the filter for each route is performed in the frequency domain filtering in the frequency domain is reduced to the multiplication that each path can be made on the basis of the corresponding multiplier 413. Output signals of the multiplier 413 transmitted to the respective inverter 415 Fourier transform (IFFT), and, after a series-parallel conversion in the relevant section 417 series-parallel (S/P) conversion receive the filtered signal.

As an example, the structure shown in figure 4, can be applied to filter chromatic dispersion in optical systems.

During propagation in optical fiber, optical signal undergoes chromatic dispersion, which is caused by the difference in speed as a function of frequency, which can be characterized by the transfer function

where L is a long optical fiber, beta 2 is a parameter of the difference of the group velocity, ω is the frequency in radians, which is associated with angular frequency ratio W=2πƒ. Reverse function is

which satisfies the condition

. Up until the optical path is not changed, the residual value of the chromatic dispersion

remains constant over time.

Stages of compensation in the frequency domain can be the following:

Step 1: Perform fast Fourier transform (FFT) to transfer the received signal r(t) in the frequency domain to obtain

Stage 2: the Multiplication of the signal R(*)

for obtaining a

Step 3: Perform the inverse Fourier transform (IFFT) over S(z) for

receiving the representation of s(t) in the time domain signal ω compensated chromatic dispersion.

The structure of the filter, shown in figure 4, can be applied in the slow path management, which can be implemented in the DSP. This simplifies the implementation of high-speed ASICS in the data path. Blocks signal FD "download" in DSP for evaluation CD. Estimated CD generates the appropriate filter function, which loads into the filter compensation CD.

Figure 5 shows the structure of a digital coherent receiver alignment. The receiver contains an optical input cascade 501 containing distributor 503 beam polarization (PBS)with the first conclusion is connected with the first hybrid scheme 505, and the second conclusion, which is connected with the second hybrid scheme 507. Optical input cascade 501 additionally contains a local oscillator 508 (OL), which has two outputs, United, respectively, with corresponding hybrid schemes 505 and 507. Hybrid schemes 505 and 507 may contain circuit to determine if two signals shifted by 90 degrees, on the basis of the respective input signal. Thus, each hybrid scheme 505, 507 contains two conclusions, providing so-called complacency signal, which has components shifted 90 degrees. In particular, the first hybrid scheme 505 contains the first conclusion is connected with the first tool 509 transformation, and the second conclusion, which is connected with the second tool 511 conversion. Similarly, the first conclusion of the second hybrid schemes 507 connected with the first tool 513 transformation, and the second output is connected with the second tool 515 conversion. Each tool 509-515 conversion may contain OPTRON 517 to convert optical signals transmitted from a hybrid 505, 507, into electrical signals. Additionally, each route can be found, the method of balanced detection, a pair of photodiodes, where the received signal is the difference in each diode. In addition, 509-515 may include analog-to-digital Converter 519 (ADC) to convert analog electrical signal received from the respective optocouplers 517, in the digital area. Withdrawals 511-515 conversion can be connected with the tool 521 digital alignment and restore data containing adaptive filter 523, made according to the principles of the present invention.

Adaptive filter 523 accepts input, containing, for example, the four parts of the input signal. The first part of the input signal, Re{r x [n]}, Im{r x [n]}is x-polarization, and the second part of the input signal, Re{r y [n]}, Im{r y [n]}, is u-polarization.

Adaptive filter 523 adapted to the frequency domain on the basis of input signals. After filtering and transformation filtered signals in the time domain, the corresponding filtered signals in the time domain, Re{s x [n]}, Im{s x [n]}, Re{s y [n]}, Im{s y [n]}, pass in an optional blocks signal processing, containing, for example, block 525 recover sync block 527 velocity filter, block 529 recovery carrier and block 531 evaluation of the character, are implemented in accordance with any of the known approaches to the restoration of sync, high-speed filter, restoration the carrier and the assessment of the character.

According to figure 5, the compensation unit variance in the frequency domain is used after analog-digital conversion (ADC) and to the recovery block synchronization. Thus, it softens conditions for requirements for permissible deviation variance in the recovery algorithms synchronization. Compensation of the variance in the frequency domain itself is robust to the frequency of synchronization and deviations phase synchronization. The same filter function is used to navigate to the received signal from x-polarization and y-polarized.

Figure 6 shows an example of the assessment, showing the ratio of high peak to average for the maximum argument associated with a specific index CD.

According to some versions of the implementation of the described approach of the filter selection enables evaluation regardless of the format of modulation and transmission speed and perfect for any coherent optical systems of transfer.

According to some versions of the implementation, when calculating variable assessment directly in the frequency domain, the evaluation procedure can be accelerated and can to achieve faster data retrieval. In addition, there is no need to obtain the expected gain of the ARS.

According to some variants of implementation, can be reduced complexity, which can be increased exercise in which the ratio of the peak-to-average allows an easier implementation even with a reduced precision variables.

According to some variants of implementation, the approaches described in this document can be applied for monitoring of chromatic dispersion in any place of the transmission line by just a low-speed ADC and asynchronous sample rate. As soon as coherent receivers will be integrated, it opens the way for new devices monitoring of optical characteristics.

1. Filter device for filtering of the input signal, containing dot clock with clock frequency, containing: filter (101) to filter the input signal using the first set of filter coefficients to obtain the first filtered signal and filtering of the input signal using the second set of filter coefficients to obtain a second filtered signal; correlator (103) the frequency domain to correlate the first subset of the components in the frequency domain, the first of the filtered signal for first-time correlation values and to correlate the second subset of the components in the frequency domain, the second filtered signal for the second correlation values, the first subset correlated components in the frequency domain, and the second subset correlated components in the frequency domain are located, respectively, in a given range correlated signals that contains the clock speed; and the processor (105), made with the possibility to choose for filtering of the input signal, the first set of filter coefficients or the second set of filter coefficients on the basis of the first correlation values and second correlation values.

2. Filter device according to claim 1 in which the correlator (103) the frequency domain is made with the possibility of correlation specified first subset of the components in the frequency domain to obtain the first correlation sequence to the frequency domain and summation of the values specified for the first correlation sequence to obtain the first correlation values, as well as the possibility correlation specified the second subset of the components in the frequency domain to obtain the second correlation sequence to the frequency domain and summation of the values specified for the second correlation sequence to obtain the second correlation values.

3. Filter device according to claim 1 in which the processor (105) made with the possibility of choice specified in the first set of filter coefficients if the first correlation is greater than or equal to the second correlation value, or select a specified the second set of filter coefficients if the second correlation is greater than or equal to the first correlation value.

4. Filter device of claim 1, wherein: filter (101) executed with the ability to filter the many input signals are specified on the first set of filter coefficients to obtain many first filtered signals and filter multiple input signals using the specified second set of filter coefficients to obtain many second filtered signals; while the correlator (103) made with the possibility of correlation first subset of the components in the frequency domain of each of the first filtered signals to obtain many of the first correlation values and correlation of the second subset of the components in the frequency domain of each of the second filtered signals to obtain many second correlation of values, and each subset correlated components in the frequency domain are located in the given frequency range that contains the clock speed; and the processor (105) made with the possibility of summing a specified multiple of the first correlation values for this first correlative meanings, the summation of the specified set of the second correlation values to obtain the second correlation values and choices specified in the first set of filter coefficients if the first correlation is greater than or equal to the second correlation value, or select a specified the second set of filter coefficients if the second correlation is greater than or equal to the first correlation value.

5. Filter device according to claim 1, wherein said first set of filter coefficients and specified the second set of filter coefficients, respectively, represent different characteristics of the filter chromatic dispersion for filtering of the input signal in different ways.

6. Filter device according to claim 1, wherein said first set of filter coefficients and specified the second set of filter coefficients, respectively, are characteristic of the filter polarization mode dispersion, filter rotation of polarization, in particular, to filter rotation of polarization with the same or different angles of polarization.

7. Filter device according to claim 1 in which: the first set of filter coefficients contains many first subsets of filter coefficients, with a specified set of first subsets of filter coefficients, respectively, constitute the first characteristic filtering chromatic dispersion and different characteristics of polarization mode dispersion, specified the second set of filter coefficients contains many second subsets of filter coefficients, with the specified set of the second subsets of filter coefficients, respectively, are the second characteristic filtering chromatic dispersion and different characteristics of polarization mode dispersion, with the filter (101) are executed with the possibility of filtering the input signal through a specified multiple of the first subsets of filter coefficients to obtain many first filtered signals and filtering the input signal through a specified multiple of the second subsets of filter coefficients to obtain many second filtered signal, the correlator (103) the frequency domain is made with the possibility of correlation first subset of the components in the frequency domain of each of the first filtered signals to obtain many of the first correlation values and correlation of the second subset of the components in the frequency domain of each of the second filtered signals to obtain many second correlation of values, with each subset correlated components in the frequency domain are specified in a given frequency range that contains the clock speed; and the processor (105) made with the possibility of summing a specified multiple of the first correlation values for first correlative meanings, the summation of the specified set of the second correlation values for the second correlation values and choices specified in the first set of filter coefficients if the first correlation is greater than or equal to the second correlation value, or select a specified the second set of filter coefficients if the second correlation is greater than or equal to the first correlation value.

10. Filter device according to claim 1, additionally contains Converter Fourier transform to convert the specified input signal or the relevant specified first or second filtered signal in the frequency domain.

11. Filter device according to claim 1 in which the processor (105) executed with the possibility of increasing the clock frequency for a given increment or decrement the clock frequency on the given decrement for determining specified the given range of frequencies.

12. Filter device according to claim 1, wherein said the input signal is a copy of the received signal, with the specified filter is configured to filter the received signal using the selected set of filter coefficients for further signal processing.

13. Filter device according to claim 1, wherein said input contains the first part of the input signal, related to the first optical polarization, and the second part of the input signal that is associated with the second optical polarization.

14. Way of filtering the input signal containing dot clock with clock frequency, including: filtering of the input signal using the first set of filter coefficients with first filtered signal, and filtering of the input signal using the second set of filter coefficients to obtain a second filtered signal; correlation first subset of the components in the frequency domain is specified first filtered signal with receipt of the first correlation values and correlation of the second subset of the components in the frequency domain specified the second filtered signal to obtain a second correlation values, and specified the first subset correlated components in the frequency domain and the specified second subset correlated components in the frequency domain, respectively, are located in the given frequency range that contains the clock speed, and the choice for filtering the input signal, either specified in the first set of filter coefficients, or the specified second set of filter coefficients based on the first correlation values and specified the second correlation values.