16-7 probability forming method and device based on symbol-level labels

Abstract

The invention discloses a 16-7 probability forming method and device based on symbol-level labels, and the method comprises the steps: S1, carrying out the serial-to-parallel conversion of original data, and obtaining parallel bit data; s2, symbol-level label mapping is carried out on the parallel bit data, and parallel frequency domain signals are obtained; s3, carrying out IFFT (Inverse Fast Fourier Transform) on the parallel frequency domain signal to obtain a parallel time domain signal; and S4, shaping and filtering the real part and the imaginary part of the parallel time domain signal to obtain a symbol-level label probability shaping signal. The space utilization rate of the constellation is improved, the signal transmission power is remarkably reduced, and the transmission rate and channel capacity of the system are improved.

Description

Technical Field

[0001] The present application belongs to the field of optical transmission communication technology, and specifically relates to a 16-7 probability shaping method and device based on symbol-level labels. Background Art

[0002] In terms of access network, passive optical network (PON) has been proven to be an effective and future-oriented network architecture. Compared with traditional cable modems or x-digital subscriber lines (xDSL), it has unparalleled advantages such as lower power consumption, higher data transmission rate and wider access coverage. In the construction of the next generation of passive optical network transmission systems, considering factors such as network operation costs and the simplicity of user-side signal transceiver design, intensity modulation / direct detection (IM / DD) technology has a wide range of and efficient application scenarios in access networks due to its simple transceiver structure, good signal transmission quality and economical construction cost. In addition, carrier-free amplitude phase modulation technology (CAP) as a signal generation scheme has the advantages of high spectrum efficiency, economic cost and low computational complexity, and has unparalleled competitiveness in short-distance communications in access networks.

[0003] Therefore, in order to adapt to the exponentially growing traffic generated by emerging network technologies and applications, the existing network must be upgraded to a higher level to have higher speed, longer transmission distance and greater capacity, and to improve the data transmission rate and channel capacity of the passive optical network. Summary of the invention

[0004] Purpose: In view of at least one of the above technical problems, in order to improve the data transmission rate and channel capacity of a passive optical fiber network, the present application provides a 16-7 probability shaping method and device based on symbol-level labels, which can improve the spatial utilization of the constellation and significantly reduce the signal transmission power, thereby improving the transmission rate and channel capacity of the system.

[0005] The technical solution adopted in this application is:

[0006] In a first aspect, the present application provides a 16-7 probability shaping method based on symbol-level labels, comprising:

[0007] S1, converting the original data into serial-to-parallel data to obtain parallel bit data;

[0008] S2. Perform symbol-level label mapping on the parallel bit data respectively to obtain parallel frequency domain signals;

[0009] S3, performing IFFT transformation on the parallel frequency domain signals to obtain parallel time domain signals;

[0010] S4. Perform shaping filtering on the real part and the imaginary part of the parallel time domain signal to obtain a symbol-level label probability shaped signal.

[0011] In some embodiments, S2, respectively performing symbol-level label mapping on the parallel bit data to obtain parallel frequency domain signals, including:

[0012] S21, mapping 16 signal points of 4 bits of parallel bit data into 3 bits of 7 formed signal points through constellation mapping;

[0013] S22, respectively calculating the probabilities of the seven signal points after forming, and determining the label of each signal point according to the probabilities of the seven signal points;

[0014] S23. Combining high and low bits according to the 3 bits of each signal point and the corresponding label to form 5 output bits of 7 signal points, thereby forming a parallel frequency domain signal.

[0015] Further, in some embodiments, S21, mapping 16 signal points of 4 bits of parallel bit data into 3 bits of 7 shaped signal points through a constellation, includes:

[0016] Mapping the first 4 bits 0000, the corresponding coordinates are (-1, -1),

[0017] Mapping the first 4 bits 0011, the corresponding coordinates are (3, -1),

[0018] Mapping the first 4 bits 1111, the corresponding coordinates are (3,3),

[0019] These three signal points are mapped into three bits 000 through the constellation, and the corresponding coordinates are (0,0);

[0020] Mapping the first 4 bits 0001, the corresponding coordinates are (1, -1),

[0021] Mapping the first 4 bits 1110, the corresponding coordinates are (-3,3),

[0022] Mapping the first 4 bits 1100, the corresponding coordinates are (-1,3),

[0023] These three signal points are mapped into three bits 001 through the constellation, and the corresponding coordinates are (1, 1.73205);

[0024] Mapping the first 4 bits 0010, the corresponding coordinates are (-3, -1),

[0025] Mapping the first 4 bits 1101, the corresponding coordinates are (1,3),

[0026] These two signal points are mapped into 3 bits 010 through the constellation, and the corresponding coordinates are (1, -1.73205);

[0027] Mapping the first 4 bits 1001, the corresponding coordinates are (1,1),

[0028] Mapping the first 4 bits 1011, the corresponding coordinates are (3,1),

[0029] These two signal points are mapped into 3 bits 100 through the constellation, and the corresponding coordinates are (-2,0);

[0030] Map the first 4 bits 1000, the corresponding coordinates are (-1,1),

[0031] Mapping the first 4 bits 0111, the corresponding coordinates are (3, -3),

[0032] These two signal points are mapped into 3 bits 110 through the constellation, and the corresponding coordinates are (-1, -1.73205);

[0033] Mapping the first 4 bits 0100, the corresponding coordinates are (-1, -3),

[0034] Mapping the first 4 bits 0101, the corresponding coordinates are (1, -3),

[0035] These two signal points are mapped into 3 bits 101 through the constellation, and the corresponding coordinates are (-1, 1.73205);

[0036] Mapping the first 4 bits 0110, the corresponding coordinates are (-3,-3),

[0037] Mapping the first 4 bits 1010, the corresponding coordinates are (-3,1),

[0038] These two signal points are mapped into three bits 011 through the constellation, and the corresponding coordinates are (2,0).

[0039] In a second aspect, the present application provides a 16-7 probability shaping device based on symbol-level labels, including a processor and a storage medium;

[0040] The storage medium is used to store instructions;

[0041] The processor is configured to operate according to the instructions to execute the method according to the first aspect.

[0042] In a third aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the method described in the first aspect when executed by a processor.

[0043] In a fourth aspect, the present application provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the method of the first aspect when executing the computer program.

[0044] In a fifth aspect, the present application provides a computer program product, comprising a computer program, which implements the method described in the first aspect when executed by a processor.

[0045] Beneficial effects: The 16-7 probability shaping method and device based on symbol-level labels provided in the present application have the following advantages: using carrier-free amplitude phase modulation, the original input signal point first performs signal format recognition to determine the encoding form, and then performs probability calculation of each signal point, and notifies the calculation result to the symbol-level label generator, thereby determining the best label for each signal point in the probability shaping. Finally, in the probability distribution mapper, each signal point and its corresponding pre-set label together constitute the final output signal point. By using probability shaping technology, the spatial utilization of the new constellation is improved, thereby improving the transmission rate and capacity of the system. The spatial utilization is improved, and compared with conventional modulation formats, it has better performance, expands the channel capacity, thereby improving the data transmission rate, and by adjusting the signal point distribution, the average transmission power can be reduced, thereby improving the bit error rate (BER) performance / scalability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 1 is a flow chart of a 16-7 probability shaping method based on symbol-level labels according to an embodiment of the present application;

[0047] Figure 2 Schematic diagram of a 16-7 signal point probability shaping mapping scheme according to an embodiment of the present application;

[0048] Figure 3 Schematic diagram of coordinates corresponding to 3 bits of 7 signal points after shaping according to an embodiment of the present application;

[0049] Figure 4 Schematic diagram of 7 signal point constellation points after symbol-level label probability shaping according to an embodiment of the present application;

[0050] Figure 5 Schematic diagram of a 16-7 WDM-PON transmission system based on symbol-level labels according to an embodiment of the present application. DETAILED DESCRIPTION

[0051] The present application is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and cannot be used to limit the protection scope of the present application.

[0052] In the description of this application, "several" means more than one, "more" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, and "above", "below", "within", etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0053] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0054] The term "and / or" is only a description of the association relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " generally indicates that the related objects are in an "or" relationship.

[0055] Embodiment 1: This embodiment provides a 16-7 probability shaping method based on symbol-level labels, such as Figure 1 As shown, at the transmitting end, the method includes:

[0056] S1, converting the original data into serial-to-parallel data to obtain parallel bit data;

[0057] S2. Perform symbol-level label mapping on the parallel bit data respectively to obtain parallel frequency domain signals;

[0058] S3, performing IFFT transformation on the parallel frequency domain signals to obtain parallel time domain signals;

[0059] S4. Perform shaping filtering on the real part and the imaginary part of the parallel time domain signal to obtain a symbol-level label probability shaped signal.

[0060] In some embodiments, S2, respectively performing symbol-level label mapping on the parallel bit data to obtain parallel frequency domain signals, including:

[0061] S21, mapping 16 signal points of 4 bits of parallel bit data into 3 bits of 7 formed signal points through constellation mapping;

[0062] S22, respectively calculating the probabilities of the seven signal points after forming, and determining the label of each signal point according to the probabilities of the seven signal points;

[0063] S23. Combining high and low bits according to the 3 bits of each signal point and the corresponding label to form 5 output bits of 7 signal points, thereby forming a parallel frequency domain signal.

[0064] Further, in some embodiments, S21, mapping 16 signal points of 4 bits of parallel bit data into 3 bits of 7 shaped signal points through a constellation, includes:

[0065] Mapping the first 4 bits 0000, the corresponding coordinates are (-1, -1),

[0066] Mapping the first 4 bits 0011, the corresponding coordinates are (3, -1),

[0067] Mapping the first 4 bits 1111, the corresponding coordinates are (3,3),

[0068] These three signal points are mapped into three bits 000 through the constellation, and the corresponding coordinates are (0,0);

[0069] Mapping the first 4 bits 0001, the corresponding coordinates are (1, -1),

[0070] Mapping the first 4 bits 1110, the corresponding coordinates are (-3,3),

[0071] Mapping the first 4 bits 1100, the corresponding coordinates are (-1,3),

[0072] These three signal points are mapped into three bits 001 through the constellation, and the corresponding coordinates are (1, 1.73205);

[0073] Mapping the first 4 bits 0010, the corresponding coordinates are (-3, -1),

[0074] Mapping the first 4 bits 1101, the corresponding coordinates are (1,3),

[0075] These two signal points are mapped into 3 bits 010 through the constellation, and the corresponding coordinates are (1, -1.73205);

[0076] Mapping the first 4 bits 1001, the corresponding coordinates are (1,1),

[0077] Mapping the first 4 bits 1011, the corresponding coordinates are (3,1),

[0078] These two signal points are mapped into 3 bits 100 through the constellation, and the corresponding coordinates are (-2,0);

[0079] Map the first 4 bits 1000, the corresponding coordinates are (-1,1),

[0080] Mapping the first 4 bits 0111, the corresponding coordinates are (3, -3),

[0081] These two signal points are mapped into 3 bits 110 through the constellation, and the corresponding coordinates are (-1, -1.73205);

[0082] Mapping the first 4 bits 0100, the corresponding coordinates are (-1, -3),

[0083] Mapping the first 4 bits 0101, the corresponding coordinates are (1, -3),

[0084] These two signal points are mapped into 3 bits 101 through the constellation, and the corresponding coordinates are (-1, 1.73205);

[0085] Mapping the first 4 bits 0110, the corresponding coordinates are (-3,-3),

[0086] Mapping the first 4 bits 1010, the corresponding coordinates are (-3,1),

[0087] These two signal points are mapped into 3 bits 011 through the constellation, and the corresponding coordinates are (2,0). The coordinates corresponding to the 3 bits of the 7 signal points are as follows Figure 3 The coordinates and bits before and after mapping are shown in Table 1.

[0088] Table 1

[0089]

[0090] Assume that the distribution mapping of probability shaping is a matrix of M0×L0, where M0 is the number of signal points after probability shaping, and L0 is the maximum overlap number of signal point divisions. For the signal points in each row of the matrix, a specific symbol-level label is used as a marker and attached to the modulation symbol pre-determined at the beginning to form a newly generated signal point. Generally speaking, information representation composed of "0" or "1", if it is a modulation format of bit input and m-bit output (n>m), will form 2 on the constellation diagram respectively. m and 2 n signal points. However, in order to achieve the reversible demapping operation at the receiving end, for the original 2 m input information points, only 2 n Therefore, the symbol-level label is used to determine and distinguish the overlap of the original signal points, making the decoding in the receiver accurate and effective. When it is not an integer (2 n>M0), the bit information does not have the completeness to describe M0, so the traditional It is not suitable for labeling. At this time, the coded bit information in M0 needs to be considered as a mapping scheme.

[0091] Since the number of signal points output in the end is 7, 3 bits of original information are needed for shaping operations. At the same time, in order to distinguish the original 16 signal points, a part of the output 7 signal points is selected as overlapping mapping. Therefore, in this embodiment, the label uses 2-bit labels "00", "01", and "10" to uniquely distinguish the original 16 signal points. It should be noted that "11" is not selected here because its code weight is 2, which is larger than the code weight of other labels. Specifically, when the code weight is 0, the symbol "000" is used; when the code weight is 1, the symbols "100", "010", and "001" are used; when the code weight is 2, "101" and "110" are used. Moreover, the signal points covered by the label "00" have a greater probability of constellation mapping and are placed in the inner area with the lowest energy in the constellation diagram.

[0092] In this way, the original valid information, which was originally uniformly distributed, undergoes the dual effects of bit-level ontological label encoding, and the formed information is correspondingly probabilized. This scheme maps 16 signal points into 7 signal points in the constellation, divides the long bit information, and forms a 3-bit signal. In the demodulation process, the redundancy is used to form its own overall mark as a bit-level mark to distinguish the signal points. In order to be able to reasonably calculate the probability of each signal point after forming, according to the corresponding combination arrangement of the forming scheme, combined with the Bayesian formula of probability theory. Further, in some embodiments, in S22, the probability of the 7 signal points after forming is calculated, including:

[0093] ,

[0094] in, Indicates the index of the 7 signal points after shaping, Indicates the first The probability of a signal point, Represents a set of consecutive 3 bits transmitted during the shaped coding process, , Represents all composable sets The set of different combinations of all the 7 signal points after forming; Representing a collection The probability of the i-th element in the 5-bit output bit; Indicates the type of 5-bit output bits, Representing a collection The probability of the jth element in the 5-bit output bit; Representing a collection The probability of the kth element in the 5-bit output bit is, Representing a collection With Collection Combine into a collection The type of element in .

[0095] Further, in some embodiments, in S22, a label of each signal point is determined using a symbol-level label generator according to the probability of the seven signal points.

[0096] Figure 2 A schematic diagram of the probability mapping of 16-7 signal points is given. The constellation points after symbol-level label probability shaping are as follows: Figure 4 As shown, CFM(C) is the overall gain of the constellation. The CFM of the 7-signal point constellation using symbol-level label probability shaping is:

[0097]

[0098] It is known that the CFM of the traditional 16CAP is 0.4, and the CFM of the 7 signal points using symbol-level label probability shaping is increased by 0.77.

[0099] In some embodiments, a 16-7 WDM-PON transmission system based on symbol-level labels is as follows: Figure 5 As shown in the figure, at the transmitting end, the DSP module implements the CAP modulation technology offline. Specifically, the original input bit stream (serial bit data) is converted from serial to parallel to generate 4 channels of bit data for parallel transmission; then, the 4 channels of parallel bit data are probability shaped based on symbol-level labels to form corresponding information symbols for up-conversion of CAP modulation. The real and imaginary parts of the signal are then separated and corresponding shaping filters are performed respectively. Finally, the signal waveform in the electrical domain is formed through the AWG and amplified by an electrical amplifier. In the optical path, the generated waveform is loaded on the Mach-Zehnder modulator, and the generated optical signal is amplified by the erbium-doped fiber amplifier and injected into the standard single-mode optical fiber to realize the transmission of the optical fiber channel.

[0100] At the receiving end, the amplified spontaneous emission noise is suppressed by the fiber filter. In addition, a variable optical attenuator is applied to adjust the received optical power value before the photodiode detection. The mixed signal oscilloscope with a sampling rate of 100Gs / s resamples the received signal, then divides it into real and imaginary parts, and performs matched filtering and down-conversion. Finally, through the symbol-level label decoding corresponding to the transmitting end, the signal is reconverted into serial bit data for further system performance analysis.

[0101] Embodiment 2: Based on embodiment 1, this embodiment provides a 16-7 probability shaping device based on symbol-level labels, including a processor and a storage medium;

[0102] The storage medium is used to store instructions;

[0103] The processor is used to operate according to the instruction to execute the method according to embodiment 1.

[0104] Embodiment 3: Based on Embodiment 1, this embodiment provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the method described in Embodiment 1 is implemented.

[0105] Embodiment 4: Based on Embodiment 1, this embodiment provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor implements the method described in Embodiment 1 when executing the computer program.

[0106] Embodiment 5: Based on Embodiment 1, this embodiment provides a computer program product, including a computer program, which implements the method described in Embodiment 1 when executed by a processor.

[0107] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems or computer program products. Therefore, the present application may take the form of a complete hardware embodiment, a complete software embodiment or an embodiment combining software and hardware. Moreover, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0108] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems) and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram and the combination of the processes and / or blocks in the flowchart and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0109] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0110] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0111] The above is only a preferred implementation of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A 16-7 probability shaping method based on symbol-level labels, characterized in that: include: S1, converting the original data into serial-to-parallel data to obtain parallel bit data; S2. Perform symbol-level label mapping on the parallel bit data respectively to obtain parallel frequency domain signals; S3, performing IFFT transformation on the parallel frequency domain signals to obtain parallel time domain signals; S4. Perform shaping filtering on the real part and the imaginary part of the parallel time domain signal to obtain a symbol-level label probability shaped signal.

2. The method according to claim 1, characterized in that S2, performing symbol-level label mapping on the parallel bit data respectively to obtain parallel frequency domain signals, including: S21, mapping 16 signal points of 4 bits of parallel bit data into 3 bits of 7 formed signal points through constellation mapping; S22, respectively calculating the probabilities of the seven signal points after forming, and determining the label of each signal point according to the probabilities of the seven signal points; S23. Combining high and low bits according to the 3 bits of each signal point and the corresponding label to form 5 output bits of 7 signal points, thereby forming a parallel frequency domain signal.

3. The method according to claim 2, characterized in that S21, mapping 16 signal points of 4 bits of parallel bit data into 3 bits of 7 formed signal points through constellation, including: Mapping the first 4 bits 0000, the corresponding coordinates are (-1, -1), Mapping the first 4 bits 0011, the corresponding coordinates are (3, -1), Mapping the first 4 bits 1111, the corresponding coordinates are (3,3), These three signal points are mapped into three bits 000 through the constellation, and the corresponding coordinates are (0,0); Mapping the first 4 bits 0001, the corresponding coordinates are (1, -1), Mapping the first 4 bits 1110, the corresponding coordinates are (-3,3), Mapping the first 4 bits 1100, the corresponding coordinates are (-1,3), These three signal points are mapped into three bits 001 through the constellation, and the corresponding coordinates are (1, 1.73205); Mapping the first 4 bits 0010, the corresponding coordinates are (-3, -1), Mapping the first 4 bits 1101, the corresponding coordinates are (1,3), These two signal points are mapped into 3 bits 010 through the constellation, and the corresponding coordinates are (1, -1.73205); Mapping the first 4 bits 1001, the corresponding coordinates are (1,1), Mapping the first 4 bits 1011, the corresponding coordinates are (3,1), These two signal points are mapped into 3 bits 100 through the constellation, and the corresponding coordinates are (-2,0); Map the first 4 bits 1000, the corresponding coordinates are (-1,1), Mapping the first 4 bits 0111, the corresponding coordinates are (3, -3), These two signal points are mapped into 3 bits 110 through the constellation, and the corresponding coordinates are (-1, -1.73205); Mapping the first 4 bits 0100, the corresponding coordinates are (-1, -3), Mapping the first 4 bits 0101, the corresponding coordinates are (1, -3), These two signal points are mapped into 3 bits 101 through the constellation, and the corresponding coordinates are (-1, 1.73205); Mapping the first 4 bits 0110, the corresponding coordinates are (-3,-3), Mapping the first 4 bits 1010, the corresponding coordinates are (-3,1), These two signal points are mapped into three bits 011 through the constellation, and the corresponding coordinates are (2,0).

4. The method according to claim 2, characterized in that: The label uses 2-bit labels "00", "01", and "10".

5. The method according to claim 2, characterized in that: In S22, the probabilities of the seven signal points after forming are calculated, including: ， in, Indicates the index of the 7 signal points after shaping, Indicates the first The probability of a signal point, Represents a set of consecutive 3 bits transmitted during the shaped coding process, , Represents all composable sets The set of different combinations of all the 7 signal points after forming; Representing a collection The probability of the i-th element in the 5-bit output bit; Indicates the type of 5-bit output bits, Representing a collection The probability of the jth element in the 5-bit output bit; Representing a collection The probability of the kth element in the 5-bit output bit is, Representing a collection With Collection Combine into a collection The type of element in .

6. The method according to claim 2, characterized in that In S22, a label of each signal point is determined using a symbol-level label generator according to the probabilities of the seven signal points.

7. A 16-7 probability shaping device based on symbol-level labels, characterized in that: including processor and storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to execute the method according to any one of claims 1 to 6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the method according to any one of claims 1 to 6 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method according to any one of claims 1 to 6 is implemented.

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