Digital signal processing apparatus and digital signal processing method

Abstract

To provide a digital signal processor and a digital signal processing method for reducing an operation amount of adaptive filter processing.SOLUTION: In the digital signal processing device 10, the adaptive filter 12 includes the first filter that adaptively performs the wavelength dispersion compensation filter processing on the received reception signal and the second filter that adaptively performs the polarization separation filter processing on the received reception signal, and updates the filter coefficient of the second filter in the learning phase, which is an operation phase (for example, initial setting, maintenance, and the like) in which normal communication is not performed, at a higher frequency than the update of the filter coefficient of the second filter in the operation phase, which is an operation phase executed to actually communicate the user signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a digital signal processing device and a digital signal processing method. [Background technology]

[0002] Figure 6 is a diagram showing an outline of a conventional hardware implementation of adaptive filtering. As shown in Figure 6, in a real-time hardware implementation of adaptive filtering, the filter coefficients are updated based on the results of filtering input data. On the other hand, in a real-time software implementation of Digital Signal Processing (DSP), high-frequency data transfers are avoided compared to hardware implementations. For this reason, long input data is buffered and processed in batches.

[0003] FIG. 7 is a diagram showing an outline of conventional adaptive filter processing for polarization multiplexed signals. In conventional adaptive filter processing for polarization multiplexed signals, in order to deal with cases where the optimal filter coefficients fluctuate over time, filter processing is performed after updating the filter coefficients for each data in the buffer. Furthermore, it has also been proposed to divide the buffer into multiple regions (for example, Non-Patent Document 1). Specifically, a common filter coefficient is used within each divided region. Within each region, filter coefficients are calculated using multiple threads. With this configuration, a method has been proposed that achieves high-speed adaptive filter processing.

[0004] More specifically, it is as follows. Figure 8 is a diagram showing an outline of a configuration that realizes high-speed processing of an adaptive filter. As shown in Figure 8, the signal is divided into regions of L symbols, and a filter coefficient h is calculated based on the results of performing filter processing on P symbols. A value obtained by averaging multiple calculated filter coefficients is used to perform filter processing on all L symbols.

[0005] As a reference technique, Non-Patent Document 2 discloses a technique for reducing the number of hardware resources required for hardware implementation of filter processing. Specifically, it discloses a technique for separating one adaptive filter process into adaptive filter process for chromatic dispersion compensation and adaptive filter process for polarization separation. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] T. Suzuki, S.- Y. Kim, J.- i. Kani, and T. Yoshida, “Real-Time Polarization Demultiplexing by Multi-Thread Constant Modulus Algorithm for Fully Softwarized Access Networks,” IEEE / OSA Journal of Lightwave Technology, vol. 41, no. 5, pp. 1346-1356, Nov. 2022. [Non-patent document 2] K. Matsuda and N. Suzuki, “Hardware-Efficient Signal Processing Technologies for Coherent PON Systems,” Journal of Lightwave Technology, vol. 37, no. 6, pp. 1614-1620, 2018. Summary of the Invention [Problem to be solved by the invention]

[0007] When chromatic dispersion is large, such as in long-distance or high-speed transmission, it is necessary to perform appropriate waveform equalization. Therefore, in the conventional technology described above, it was necessary to increase the number of taps in the filter that compensates for chromatic dispersion. This increases the amount of calculation required for adaptive filter processing.

[0008] The present invention has been made in view of the above circumstances, and provides a technique that makes it possible to reduce the amount of calculation required for adaptive filter processing. [Means for solving the problem]

[0009] One aspect of the present invention is a digital signal processing device comprising a first filter that adaptively performs a first filter process on a received signal, and a second filter that adaptively performs a second filter process on a received signal, and which updates the filter coefficients of the second filter in a first operating phase more frequently than updates the filter coefficients of the second filter in a second operating phase.

[0010] One aspect of the present invention is a digital signal processing method that adaptively performs a first filter process on a received signal, adaptively performs a second filter process on a received signal, and updates the filter coefficients of the second filter process in a first operation phase more frequently than updates the filter coefficients of the second filter process in a second operation phase. [Effects of the Invention]

[0011] According to the present invention, it is possible to reduce the amount of calculation required for adaptive filtering. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic block diagram showing the functional configuration of a digital signal processing device 10 according to the present invention. [Figure 2] FIG. 2 is a diagram illustrating an outline of the functional configuration of an adaptive filter 12. [Figure 3] 10 is a flowchart showing a specific example of the flow of operations of the adaptive filter 12 in the learning phase. [Figure 4] 10 is a flowchart showing a specific example of the flow of operations of the adaptive filter 12 in the operation phase. [Figure 5]FIG. 2 is a diagram illustrating an outline of an example of the hardware configuration of an information processing device 90 applied to the present embodiment. [Figure 6] FIG. 1 is a diagram illustrating an outline of a hardware implementation of conventional adaptive filtering. [Figure 7] FIG. 1 is a diagram illustrating an outline of conventional adaptive filter processing for a polarization multiplexed signal. [Figure 8] FIG. 1 is a diagram illustrating an outline of a configuration that realizes high-speed processing of an adaptive filter. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Summary] A digital signal processing device of the present invention will be described. The digital signal processing device of the present invention is a device used in optical communications. The present invention utilizes the fact that chromatic dispersion changes little over time in optical communications. In the digital signal processing device of the present invention, adaptive filtering is divided into multiple types of filtering. For example, the adaptive filtering is divided into first filtering and second filtering. In a specific example of this embodiment, chromatic dispersion compensation filtering is applied as the first filtering, and polarization separation filtering is applied as the second filtering. Note that, as another specific example of the filters, the adaptive filtering can be divided into three filtering. For example, timing recovery filtering may be applied as the first filtering, chromatic dispersion compensation filtering may be applied as the second filtering, and polarization separation filtering may be applied as the third filtering.

[0014] Furthermore, the update of the filter coefficients used in each filter process is divided into a learning phase and an operation phase. In the learning phase, the filter coefficient update process is performed relatively more frequently than in the operation phase. For example, the filter coefficients of the chromatic dispersion compensation filter are updated in the learning phase, while the filter coefficients of the chromatic dispersion filter are updated relatively less frequently than in the operation phase. Performing the update less frequently also includes not performing the update at all. This configuration makes it possible to reduce the frequency of the filter coefficient update process in the operation phase and reduce the amount of calculation required for the update process, thereby reducing the time required.

[0015] [detail] 1 is a schematic block diagram showing the functional configuration of a digital signal processing device 10 of the present invention. The digital signal processing device 10 is applied to, for example, an optical coherent receiver. In this case, the digital signal processing device 10 processes a received signal received by a receiving unit 1 provided in the optical coherent receiver.

[0016] The digital signal processing device 10 is configured using a processor such as a CPU (Central Processing Unit) and a memory (main storage device). The digital signal processing device 10 functions as a sampling phase synchronization unit 11, an adaptive filter 12, a frequency offset compensation unit 13, a carrier phase compensation unit 14, a code determination unit 15, and a decoding unit 16 by the processor executing a program.

[0017] Note that all or part of the functions of the digital signal processing device 10 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The above program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, and semiconductor storage devices (e.g., SSDs: Solid State Drives), as well as storage devices such as hard disks and semiconductor storage devices built into computer systems. The above program may be transmitted via a telecommunications line.

[0018] The sampling phase synchronization unit 11 performs sampling synchronized with the phase of the received signal. The adaptive filter 12 compensates for waveform degradation of the received signal due to polarization fluctuations and chromatic dispersion through filtering. The frequency offset compensation unit 13 compensates for the frequency offset of the received signal. The carrier phase compensation unit 14 compensates for phase noise contained in the received signal. The code determination unit 15 determines the code from the signal waveform of the received signal. The decoding unit 16 decodes the received signal by performing any decoding process such as differential decoding, Gray decoding, or error correction decoding.

[0019] FIG. 2 is a diagram showing an outline of the functional configuration of the adaptive filter 12. The adaptive filter 12 includes a polarization separation filter 121, a chromatic dispersion filter 122, and an update control unit 123. The adaptive filter 12 is configured to be able to perform the functions of a conventional adaptive filter, and has a novel configuration with regard to the frequency of execution of update processing. That is, the processing performed by the polarization separation filter 121 and the chromatic dispersion filter 122 may each be conventional processing. The polarization separation filter 121 performs filtering for polarization separation. The chromatic dispersion filter 122 performs filtering for chromatic dispersion compensation.

[0020] The update control unit 123 controls the update timing of the filter coefficients of the polarization separation filter 121 and the chromatic dispersion filter 122. For example, the update control unit 123 controls the update timing of the filter coefficient of the polarization separation filter 121 at a frequency relatively higher than the update timing of the filter coefficient of the chromatic dispersion filter 122. The update control unit 123 is also configured to be able to set a learning phase and an operation phase as the operating phase of the adaptive filter 12. The update control unit 123 controls the update timing at different frequencies depending on each phase.

[0021] The learning phase is a phase in which communication is possible with lower optical communication performance than in the operation phase, or in which communication is not necessary at all. The learning phase may be, for example, a state in which optical communication is not actually being performed. More specifically, the learning phase may be an operation phase that is set when the optical coherent receiver is initially connected to the communication path. This is an operation phase that is executed to converge the filter coefficients of each filter to a certain extent.

[0022] The operation phase is an operation phase executed to actually communicate user signals. For example, the operation phase may be an operation phase in which normal communication is performed, and the learning phase may be an operation phase in which normal communication is not performed (e.g., initial setup, maintenance, etc.).

[0023] For example, the update timing of the polarization separation filter 121 in the learning phase is called the first update timing, the update timing of the wavelength dispersion filter 122 in the learning phase is called the second update timing, the update timing of the polarization separation filter 121 in the operation phase is called the third update timing, and the update timing of the wavelength dispersion filter 122 in the operation phase is called the fourth update timing.

[0024] The second update timing occurs relatively more frequently than the fourth update timing, i.e., the filter coefficient of the chromatic dispersion filter 122 in the learning phase is updated more frequently than the filter coefficient of the chromatic dispersion filter 122 in the operation phase.

[0025] The first update timing may be configured to occur relatively more frequently than the third update timing, i.e., the filter coefficients of the polarization separation filter 121 in the learning phase may be updated more frequently than the filter coefficients of the polarization separation filter 121 in the operation phase.

[0026] The first update timing occurs relatively more frequently than the second update timing, i.e., in the learning phase, the filter coefficients of the polarization separation filter 121 are updated more frequently than the filter coefficients of the chromatic dispersion filter 122.

[0027] The third update timing occurs relatively more frequently than the fourth update timing. That is, in the operation phase, the filter coefficient of the polarization separation filter 121 is updated more frequently than the filter coefficient of the chromatic dispersion filter 122.

[0028] 3 is a flowchart showing a specific example of the operation flow of the adaptive filter 12 in the learning phase. The update control unit 123 determines whether the first update timing has arrived (step S101). If the first update timing has arrived (step S101—YES), the update control unit 123 instructs the polarization separation filter 121 to update the filter coefficients. The polarization separation filter 121 updates the filter coefficients (step S102). Thereafter, the polarization separation filter 121 performs filtering on the received signal (step S103). If the first update timing has not arrived (step S101—NO), the update control unit 123 instructs the polarization separation filter 121 not to update the filter coefficients. In response to this instruction, the polarization separation filter 121 performs filtering on the received signal (step S103).

[0029] The update control unit 123 determines whether the second update timing has arrived (step S104). If the second update timing has arrived (step S104-YES), the update control unit 123 instructs the chromatic dispersion filter 122 to update the filter coefficient. The chromatic dispersion filter 122 updates the filter coefficient (step S105). Thereafter, the chromatic dispersion filter 122 performs filtering on the received signal (step S106). If the second update timing has not arrived (step S104-NO), the update control unit 123 instructs the chromatic dispersion filter 122 not to update the filter coefficient. In response to this instruction, the chromatic dispersion filter 122 performs filtering on the received signal (step S106).

[0030] 4 is a flowchart showing a specific example of the operation flow of the adaptive filter 12 in the operation phase. The update control unit 123 determines whether the third update timing has arrived (step S201). If the third update timing has arrived (step S201-YES), the update control unit 123 instructs the polarization separation filter 121 to update the filter coefficients. The polarization separation filter 121 updates the filter coefficients (step S202). Thereafter, the polarization separation filter 121 performs filtering on the received signal (step S203). If the third update timing has not arrived (step S201-NO), the update control unit 123 instructs the polarization separation filter 121 not to update the filter coefficients. In response to this instruction, the polarization separation filter 121 performs filtering on the received signal (step S203).

[0031] The update control unit 123 determines whether the fourth update timing has arrived (step S204). If the fourth update timing has arrived (step S204-YES), the update control unit 123 instructs the chromatic dispersion filter 122 to update the filter coefficient. The chromatic dispersion filter 122 updates the filter coefficient (step S205). Thereafter, the chromatic dispersion filter 122 performs filtering on the received signal (step S206). If the fourth update timing has not arrived (step S204-NO), the update control unit 123 instructs the chromatic dispersion filter 122 not to update the filter coefficient. In response to this instruction, the chromatic dispersion filter 122 performs filtering on the received signal (step S206).

[0032] 5 is a diagram showing an outline of an example of the hardware configuration of an information processing device 90 applied to this embodiment. The information processing device 90 includes a processor 91, a main memory device 92, an auxiliary memory device 93, an input / output interface 94, and an internal bus 95. The processor 91, the main memory device 92, the auxiliary memory device 93, and the input / output interface 94 are connected to each other via the internal bus 95 so as to be able to communicate with each other. The information processing device 90 may be applied to, for example, a digital signal processing device 10.

[0033] In the digital signal processing device 10 configured in this manner, the filter coefficients are updated relatively less frequently in the operation phase than in the learning phase. For example, the filter coefficients of the chromatic dispersion filter are updated relatively less frequently in the operation phase than the filter coefficients of the chromatic dispersion filter 122 in the learning phase. In this case, it is possible to suppress a decrease in processing accuracy while updating the filter coefficients of the chromatic dispersion filter less frequently than conventionally performed in the operation phase. In other words, by relatively increasing the update frequency in the learning phase, the filter coefficients of the chromatic dispersion filter 122 can be converged to a certain extent during the learning phase. Therefore, it is possible to suppress a decrease in accuracy even with less frequent updates during the operation phase. As a result, it is possible to reduce the amount of calculation required for the update process of adaptive filter processing during the operation phase, thereby reducing the time required. For example, it is possible to achieve high-speed implementation of adaptive filter processing in software during the operation phase.

[0034] In particular, the change over time in the filter coefficients of the chromatic dispersion filter 122 is smaller than that of the polarization separation filter 121. For this reason, as in the present invention, the adaptive filter 12 is configured separately into the polarization separation filter 121 and the chromatic dispersion filter 122, and the update process for the filter coefficients of the chromatic dispersion filter 122 is performed less frequently in the operation phase than in the learning phase, thereby reducing the amount of calculation required for the update process and enabling a reduction in processing time.

[0035] (Variation) The filter coefficients may be updated in the learning phase by offline processing. The filter coefficients of the chromatic dispersion filter may be updated in the learning phase at any predetermined update frequency until the chromatic dispersion filter coefficients converge to a level that satisfies a predetermined criterion.

[0036] The adaptive filter 12 does not necessarily have to include the update control unit 123. As a result, as long as the polarization separation filter 121 and the chromatic dispersion filter 122 are configured to update the filter coefficients at the update frequency as described above, this may be realized by any configuration.

[0037] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention. [Explanation of symbols]

[0038] 10... digital signal processing device, 1... receiving unit, 11... sampling phase synchronization unit, 12... adaptive filter, 13... frequency offset compensation unit, 14... carrier phase compensation unit, 15... code determination unit, 16... decoding unit, 121... polarization separation filter, 122... wavelength dispersion filter, 123... update control unit

Claims

1. a first filter that adaptively performs a first filtering process on a received signal; a second filter that adaptively performs a second filtering process on the received signal; A digital signal processing apparatus configured to update the filter coefficients of the second filter in a first operation phase more frequently than to update the filter coefficients of the second filter in a second operation phase.

2. the second operation phase is an operation phase in which normal communication is performed, 2. The digital signal processing device according to claim 1, wherein the first operation phase is an operation phase in which normal communication is not performed.

3. The digital signal processing device of claim 1 , wherein the second filter performs chromatic dispersion compensation filtering.

4. adaptively performing a first filtering process on the received signal; adaptively performing a second filtering process on the received signal; A digital signal processing method, comprising updating the filter coefficients of the second filtering process in a first operation phase more frequently than updating the filter coefficients of the second filtering process in a second operation phase.

Images