CN113783623B - Method and system for reducing eight-level pulse amplitude modulation error rate in optical fiber communication - Google Patents
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Abstract
The invention discloses a method for reducing eight-level pulse amplitude modulation error rate in optical fiber communication, which comprises the following steps: adjusting a probability distribution of a four-level pulse amplitude modulation symbol to increase and decrease occurrence probabilities of a middle-low level and a high level of the four-level pulse amplitude modulation symbol, respectively; demapping the four-level pulse amplitude modulation symbols after the probability distribution is adjusted to obtain a bit sequence, and sequentially performing forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain eight-level pulse amplitude modulation symbols for a transmitting end to send; and after the eight-level pulse amplitude modulation symbol is received by a receiving end, sequentially carrying out demapping, binary system mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence. The invention improves the error rate of eight-level pulse amplitude modulation and reduces the requirement on the signal-to-noise ratio by the inter-symbol probability distribution adjustment technology.
Description
Technical Field
The invention belongs to the field of optical fiber communication, and particularly relates to a method for reducing eight-level pulse amplitude modulation error rate in optical fiber communication.
Background
Today, the bandwidth requirements of data center interconnects are rapidly increasing, and such systems need to provide high bit rates, while at the same time being of lower complexity and cost, which drives the need for intensity modulation/direct detection fiber transmission links. Pulse amplitude modulation is generally considered for data center interconnect systems.
In an optical fiber communication system, pulse amplitude modulation refers to a modulation method of a signal, which is a modulation method that a series of analog signals are modulated by pulse signal sampling, thereby intercepting the amplitude of an original signal. Theoretically, in analog pulse amplitude modulation, there is no upper limit to the number of levels of pulse amplitude, while in digital pulse amplitude modulation the number of levels of pulse amplitude is reduced to the power of 2. For example, in four-level pulse amplitude modulation, there are four possible discrete pulse amplitudes; in eight-level pulse amplitude modulation there are eight possible discrete pulse amplitudes. For pulse amplitude modulation, only one directly modulated laser, or one external cavity laser and one external modulator are needed to realize the transmission of the pulse amplitude modulated optical signal at the transmitting end of the optical fiber communication system, and only one photoelectric detector is needed to complete the reception of the pulse amplitude modulated optical signal at the receiving end.
However, according to the theoretical relationship between the bit error rate and the signal-to-noise ratio, the signal-to-noise ratio required by the pulse amplitude modulation formats with different orders can be obtained. It is assumed that the signal-to-noise ratios required for four-level pulse amplitude modulation and eight-level pulse amplitude modulation are a and b respectively, where a < b, the signal-to-noise ratio for a certain communication system (considering a baud rate and under a given distance) is between a and b, if the four-level pulse amplitude modulation is transmitted, the signal-to-noise ratio is wasted, if the eight-level pulse amplitude modulation is transmitted, the performance is poor, and the requirement of error-free code transmission cannot be met, in the previous system, in this case, the four-level pulse amplitude modulation signal is generally transmitted, and the redundant signal-to-noise ratio is left as a system margin. Clearly this wastes signal to noise ratio resources. Meanwhile, for the pulse amplitude modulation of a specific order, the amount of information carried by each symbol is an integer, and the adjustment of the baud rate is very limited when a given line rate is designed. To ensure higher spectral efficiency, the baud rate should be adjusted to fill the smallest possible channel spacing. Therefore, while the pulse amplitude modulation wastes the signal-to-noise ratio resource, it is inconvenient for system design and optimization due to the discrete baud rate.
Disclosure of Invention
In view of the above defects or improvement requirements of the prior art, the present invention provides a method for reducing the error rate of eight-level pulse amplitude modulation in optical fiber communication, thereby solving the technical problem of high error rate of the existing pulse amplitude modulation.
To achieve the above object, according to a first aspect of the present invention, there is provided a method for reducing an eight-level pulse amplitude modulation error rate in optical fiber communication, comprising:
s1, adjusting the probability distribution of the four-level pulse amplitude modulation symbol to respectively increase and decrease the occurrence probability of the middle-low level and the high level of the four-level pulse amplitude modulation symbol;
s2, demapping the four-level pulse amplitude modulation symbol after probability distribution adjustment to obtain a bit sequence, and sequentially performing forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain an eight-level pulse amplitude modulation symbol for a transmitting end to send;
and after the eight-level pulse amplitude modulation symbol is received by a receiving end, sequentially carrying out demapping, binary system mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence.
Preferably, the probability distribution after the four-level pulse amplitude modulation symbol adjustment obeys the following formula:
wherein i is four level values of a four-level pulse amplitude modulation symbol, i is 0,1,2, 3; v is the scaling factor.
Preferably, the probability distribution after the four-level pulse amplitude modulation symbol adjustment obeys the following formula:
wherein i is four level values of the four-level pulse amplitude modulation symbol, and i is 0,1,2, 3; v is the scaling factor.
Preferably, before the transmitting end transmits the eight-level pulse amplitude modulation symbol, the method further includes:
and adjusting the power of the eight-level pulse amplitude modulation symbol to ensure that the average power of the eight-level pulse amplitude modulation symbol is the same as the average power before adjustment.
Preferably, the four-level pulse amplitude modulation and the eight-level pulse amplitude modulation both follow a gray code mapping relationship.
Preferably, the forward error correction coding adopts DVB-S2 standard, including BCH outer code and LDPC inner code.
Preferably, the coding rate of the LDPC outer code is 3/4, and the binary flag includes uniformly distributed bit interpolation without information, so that the ratio of the bit sequence length after probability distribution adjustment to the uniformly distributed bit sequence length after forward error correction coding is 2: 1.
preferably, before the eight-level pulse amplitude modulation is performed on the bit sequence, the method further includes:
reordering the bit sequence to make the bit sequence adjusted by the probability distribution be located at the highest position and the middle position of the three bits, and the bit sequence with uniform distribution be located at the lowest position of the three bits;
after demapping the eight-level pulse amplitude modulation symbol, the method further includes:
the demapped bit sequence is reordered to correspond to the forward error correction encoded bit sequence.
According to a second aspect of the present invention, there is provided an apparatus for reducing eight-level pulse amplitude modulation error rate in optical fiber communication, comprising:
the probability distribution adjusting module is used for adjusting the probability distribution of the four-level pulse amplitude modulation symbol so as to respectively increase and decrease the occurrence probability of the middle-low level and the high level of the four-level pulse amplitude modulation symbol;
the modulation module is used for demapping the four-level pulse amplitude modulation symbol after the probability distribution is adjusted to obtain a bit sequence, and sequentially performing forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain an eight-level pulse amplitude modulation symbol for a transmitting end to transmit;
and after the eight-level pulse amplitude modulation symbol is received by a receiving end, sequentially carrying out demapping, binary system mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence.
According to a third aspect of the present invention, there is provided a system for reducing eight-level pulse amplitude modulation error rate in optical fiber communication, comprising:
the processing module is used for adjusting the probability distribution of the four-level pulse amplitude modulation symbol so as to respectively increase and decrease the occurrence probability of the middle-low level and the high level of the four-level pulse amplitude modulation symbol; demapping the four-level pulse amplitude modulation symbols after the probability distribution is adjusted to obtain a bit sequence, and sequentially carrying out forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain eight-level pulse amplitude modulation symbols;
a transmitting end for transmitting the eight-level pulse amplitude modulation symbol
And the receiving end is used for receiving the eight-level pulse amplitude modulation symbol and sequentially carrying out demapping, binary mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
1. the invention provides a method for reducing eight-level pulse amplitude modulation error rate in optical fiber communication, which comprises the steps of adjusting probability distribution among four-level pulse amplitude modulation symbols in a four-level pulse amplitude modulation symbol generation stage, sequentially carrying out forward error correction coding, binary marking and eight-level pulse amplitude modulation on a bit sequence obtained after demapping to obtain eight-level pulse amplitude modulation signals after the probability distribution is adjusted, and transmitting the eight-level pulse amplitude modulation signals by a transmitting end; and the receiving end performs demapping, binary mark recovery and decoding of forward error correction coding on the received eight-level pulse amplitude modulation symbol to obtain an original ratio sequence. By adjusting the probability distribution among symbols of the eight-level pulse amplitude modulation signal, the requirement on the signal to noise ratio is reduced while the error rate is improved, and the eight-level pulse amplitude modulation signal can be used for reducing the error rate of eight-level pulse amplitude modulation in an optical fiber data communication system, particularly a short-distance data communication system.
2. The method for reducing the eight-level pulse amplitude modulation error rate in optical fiber communication provided by the invention considers that in the process of adjusting the probability distribution, because the probability of the occurrence of the signal with small amplitude is increased and the probability of the occurrence of the signal with large amplitude is reduced, before the transmitting end transmits the eight-level pulse amplitude modulation symbol, the method further comprises the following steps: the power of the eight-level pulse amplitude modulation symbol is adjusted to make the average power of the eight-level pulse amplitude modulation symbol the same as the average power before adjustment, namely the average power of the eight-level pulse amplitude modulation symbol after power adjustment is the same as the average power of the eight-level pulse amplitude modulation symbol before power adjustment, so that the distance between the levels is increased, and the error rate can be further reduced due to the fact that the distance between the levels is increased under the same signal to noise ratio.
3. According to the method for reducing the error rate of eight-level pulse amplitude modulation in optical fiber communication, both four-level pulse amplitude modulation and eight-level pulse amplitude modulation follow a Gray code mapping relation. Since the gray coding mode is defined as that only one bit changes when the adjacent bits are switched, the possibility of error can be reduced, thereby improving reliability and stability.
Drawings
FIG. 1 is a schematic flow chart of a method for reducing an eight-level pulse amplitude modulation error rate in optical fiber communication according to the present invention;
FIG. 2 is a schematic diagram of probability distribution of four-level pulse amplitude modulation symbols after adjusting probability distribution according to the present invention;
FIG. 3 is a schematic diagram of the probability distribution of eight-level pulse amplitude modulation symbols after adjusting the probability distribution of the symbols according to the present invention;
FIG. 4 is a schematic diagram of a bit sequence after forward error correction coding according to the present invention;
fig. 5 is a diagram of the position relationship between the bits with the adjusted probability distribution and the uniformly distributed bits in the three bits of the eight-level pulse amplitude modulation provided by the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The embodiment of the present invention provides a method for reducing an eight-level pulse amplitude modulation error rate in optical fiber communication, as shown in fig. 1, including:
s1, adjusting the probability distribution of the four-level pulse amplitude modulation symbol to increase and decrease the occurrence probability of the middle and low levels and the high level of the four-level pulse amplitude modulation symbol, respectively.
Specifically, four-level pulse amplitude modulation symbols are generated, and probability distribution among the symbols is adjusted so that the probability of occurrence of low levels is increased and the probability of occurrence of high levels is decreased.
Preferably, in the process of adjusting the probability distribution between symbols by using quaternary pulse amplitudes, the probability distribution after the adjustment of the four-level pulse amplitude modulation symbols obeys the following formula:
wherein i is four level values of a four-level pulse amplitude modulation symbol, i is 0,1,2, 3; v is the scaling factor.
In equation (1), the denominator term represents the sum of the probability values of the four levels, normalizing the total probability. v is a scaling factor, which may represent the degree of inter-symbol probability distribution, and takes on a value between 0 and 1. The larger v represents the probability difference between symbols, the larger v is determined by the signal-to-noise ratio, and theoretically, each signal-to-noise ratio can be matched with an optimal v to maximize mutual information.
In a practical optical fiber communication transmission system, the current signal-to-noise ratio needs to be confirmed to correspond to the optimal v parameter. The symbol probability diagram of the four-level pulse amplitude modulation after the inter-symbol probability adjustment is shown in fig. 2. Where the curves refer to a continuous form of the expression and the histogram represents the relative probability magnitudes of the symbols.
Further, the formula for calculating mutual information is:
I(X:Y)＝H(X)-H(X|Y) (2)
in the formula, X is a transmission symbol and Y is a reception symbol. H (X) represents the source entropy, and H (X | Y) represents the uncertainty of X after Y is received due to various interferences, which is the reduction of the amount of information obtained by the receiving end due to the interferences. The amount of mutual information may represent the information capacity of the communication system, and the optimization of adjusting the probability distribution between symbols for a particular optical fiber communication system may be measured by the mutual information.
Preferably, in the process of adjusting the probability distribution between symbols by using quaternary pulse amplitudes, the probability distribution after the adjustment of the four-level pulse amplitude modulation symbols obeys the following formula:
wherein i is four level values of a four-level pulse amplitude modulation symbol, i is 0,1,2, 3; v is the scaling factor.
S2, demapping the four-level pulse amplitude modulation symbol after probability distribution adjustment to obtain a bit sequence, and sequentially performing forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain an eight-level pulse amplitude modulation symbol for a transmitting end to transmit;
and after the eight-level pulse amplitude modulation symbol is received by a receiving end, sequentially carrying out demapping, binary system mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence.
Specifically, a four-level pulse amplitude modulation symbol sequence is subjected to demapping to obtain a bit sequence, after forward error correction coding and binary marking are sequentially performed on the bit sequence, eight-level pulse amplitude modulation is realized on the bit sequence, the eight-level pulse amplitude modulation is sent to a transmitting end, and the transmitting end sends the eight-level pulse amplitude modulation to a receiving end;
the receiving end sequentially performs demapping, binary mark recovery and decoding of forward error correction coding on the received eight-level pulse amplitude modulation symbol sequence to obtain an original sequence (namely an original bit sequence) and calculate the error rate.
The eight-level pulse amplitude modulation follows gray code mapping relationship, and after the mapping is completed, the probability distribution of each symbol of the eight-level pulse amplitude modulation is shown in fig. 3.
Preferably, before the transmitting end transmits the eight-level pulse amplitude modulation symbol, the method further includes:
and adjusting the power of the eight-level pulse amplitude modulation symbol to ensure that the average power of the eight-level pulse amplitude modulation symbol is the same as the average power before adjustment.
Specifically, in the process of adjusting the probability distribution between symbols, the probability of the occurrence of a signal with a small amplitude is increased, and the probability of the occurrence of a signal with a large amplitude is decreased, so that the average power of the signal is reduced. In order to make the average power of the signal after the probability distribution adjustment the same as that of the original signal, it is necessary to perform power adjustment so that the average power of the eight-level pwm symbol after the power adjustment is the same as the average power of the eight-level pwm symbol before the power adjustment.
Preferably, both the four-level pulse amplitude modulation and the eight-level pulse amplitude modulation follow a gray code mapping relationship.
Specifically, the gray coding mode is defined as that only one bit changes when adjacent bits are converted, so that the possibility of errors can be reduced, and the system stability is improved.
Preferably, the forward error correction coding is based on DVB-S2 standard, and comprises BCH outer code and LDPC inner code.
The BCH code is a multi-level, cyclic, error correcting, variable length digital code used to correct multiple random error patterns; the LDPC code is one of linear block codes, and is used to correct an encoding mode in which an error occurs during a transmission process.
Accordingly, the decoding part of the forward error correction coding comprises two parts of decoding BCH coding and decoding LDPC coding.
Preferably, the coding rate of the LDPC outer code is 3/4, and the binary flag in step S2 includes uniformly distributed bit interpolation without information, so that the ratio of the bit sequence length after probability distribution adjustment to the uniformly distributed bit sequence length after forward error correction coding is 2: 1.
the current error correction coding adopts DVB-S2 standard, which includes BCH outer code and LDPC inner code. After the quaternary pulse amplitude modulation symbols realize the probability distribution adjustment among symbols, because the error correction coding frame length of the standard DVB-S2 is 64800, and different BCH codes and LDPC codes can obtain a plurality of coding rates, in order to meet the bit sequence length requirement of the octal pulse amplitude modulation, the coding rate of the LDPC codes is preferably 3/4.
When the coding rate of the LDPC code is 3/4, the length of the demapped bit sequence is 43200 (multiplied by 64800), the length of the net information bit is 48600, which is greater than the length of the demapped bit 43200, at this time, it is necessary to insert bits with no information and uniform distribution into the positions where the net information bit sequence is located at 43201 and 48408, so as to ensure that the ratio of the length of the bit sequence for achieving the probability distribution adjustment to the length of the bit sequence for uniform distribution after the forward error correction coding is 2: 1. the position relationship among the bit sequence for realizing the inter-symbol probability adjustment, the interpolated bit sequence and the forward error correction coding bit sequence is shown in FIG. 4, wherein the length of the bit sequence for the probability distribution adjustment is within the interval of 1-43200, the length of the bit sequence for the interpolated non-information uniform distribution is within the interval of 43201-48408, the interval of BCH code is 48409-48600, and the interval of LDPC is 48601-64800.
Thus, the binary marking process involves information-free uniformly distributed bit interpolation of the net information bit sequence, ensuring that the ratio of the length of the bit sequence that achieves probability distribution adjustment to the length of the uniformly distributed bit sequence after forward error correction coding is 2: 1.
preferably, before the eight-level pulse amplitude modulation is performed on the bit sequence, the method further includes:
reordering the bit sequence to make the bit sequence adjusted by the probability distribution be located at the highest position and the middle position of the three bits, and the bit sequence with uniform distribution be located at the lowest position of the three bits;
after demapping the eight-level pulse amplitude modulation symbol, the method further includes:
the demapped bit sequence is reordered to correspond to the forward error correction encoded bit sequence.
Specifically, before the eight-level pulse amplitude modulation is implemented, the bit sequence needs to be reordered, and since three bits are mapped into eight-level pulse amplitude modulation symbols, the bit sequence after probability distribution adjustment is distributed in the highest bit and the middle bit of the three bits, and the bit sequence with uniform distribution is located in the lowest bit. The positional relationship of the bits for realizing the inter-symbol probability adjustment and the uniformly distributed bits in the three bits of the eight-level pulse amplitude modulation is shown in fig. 5.
After the received signal is demapped, the highest bit and the middle of the three bits corresponding to each symbol are bits corresponding to the adjusted probability distribution, and the lowest bit corresponds to a bit with uniform distribution, and the bit sequence needs to be reordered.
It is understood that the bit error rate is calculated by comparing the first 43200 bits of the received bit sequence with the bit sequence in S1 bit by bit.
That is, after the receiving end de-maps the eight-level pulse amplitude modulation signal, the highest bit and the middle bit of the three bits corresponding to each symbol correspond to the bit for realizing the inter-symbol probability adjustment, the lowest bit corresponds to the uniformly distributed bit, the bit sequence needs to be reordered to correspond to the bit position relationship after the forward error correction coding of the transmitting end, and the decoding part of the forward error correction coding includes the decoding part of the BCH coding and the decoding part of the LDPC coding. And finally, carrying out bit-by-bit detection on the first 43200 bits after forward error correction coding and decoding and the bit sequence after demapping, and calculating to obtain the bit error rate.
The following describes the apparatus for reducing the error rate of eight-level pulse amplitude modulation according to the present invention, and the apparatus for reducing the error rate of eight-level pulse amplitude modulation described below and the method for reducing the error rate of eight-level pulse amplitude modulation described above may be referred to correspondingly.
The embodiment of the invention provides a device for reducing eight-level pulse amplitude modulation error rate in optical fiber communication, which is characterized by comprising the following components:
the probability distribution adjusting module is used for adjusting the probability distribution of the four-level pulse amplitude modulation symbol so as to respectively increase and decrease the occurrence probability of the middle-low level and the high level of the four-level pulse amplitude modulation symbol;
the modulation module is used for demapping the four-level pulse amplitude modulation symbol after the probability distribution is adjusted to obtain a bit sequence, and sequentially performing forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain an eight-level pulse amplitude modulation symbol for a transmitting end to transmit;
and after the eight-level pulse amplitude modulation symbol is received by a receiving end, sequentially carrying out demapping, binary system mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence.
The embodiment of the invention provides a system for reducing eight-level pulse amplitude modulation error rate in optical fiber communication, which is characterized by comprising the following steps:
the processing module is used for adjusting the probability distribution of the four-level pulse amplitude modulation symbol so as to respectively increase and decrease the occurrence probability of the middle-low level and the high level of the four-level pulse amplitude modulation symbol; demapping the four-level pulse amplitude modulation symbols after the probability distribution is adjusted to obtain a bit sequence, and sequentially carrying out forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain eight-level pulse amplitude modulation symbols;
a transmitting end for transmitting the eight-level pulse amplitude modulation symbol
And the receiving end is used for receiving the eight-level pulse amplitude modulation symbol and sequentially carrying out demapping, binary mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (8)
1. A method for reducing eight-level pulse amplitude modulation error rate in optical fiber communication, comprising:
s1, adjusting the probability distribution of the four-level pulse amplitude modulation symbol to respectively increase and decrease the occurrence probability of the middle-low level and the high level of the four-level pulse amplitude modulation symbol;
s2, demapping the four-level pulse amplitude modulation symbol after probability distribution adjustment to obtain a bit sequence, and sequentially performing forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain an eight-level pulse amplitude modulation symbol for a transmitting end to transmit;
after the eight-level pulse amplitude modulation symbol is received by a receiving end, sequentially carrying out demapping, binary system mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence;
the forward error correction coding adopts DVB-S2 standard, and comprises BCH outer code and LDPC inner code;
the code rate of the LDPC inner code is 3/4, and the binary flag comprises uniformly distributed bit interpolation without information, so that the ratio of the bit sequence length after probability distribution adjustment to the bit sequence length uniformly distributed after forward error correction coding is 2: 1;
wherein, the bit sequence which is uniformly distributed after the forward error correction coding comprises an interpolated bit sequence which is uniformly distributed without information, a BCH outer code and an LDPC inner code; the interval of the bit sequence after the probability distribution adjustment is 1-43200, the interval of the interpolated uniformly distributed bit sequence without information is 43201-48408, the interval of the BCH outer code is 48409-48600, and the interval of the LDPC inner code is 48601-64800.
2. The method for reducing error rates of eight-level pulse amplitude modulation in optical fiber communication according to claim 1, wherein the adjusted probability distribution of the four-level pulse amplitude modulation symbols obeys the following equation:
wherein,
four level values for a four-level pulse amplitude modulation symbol,
；
is a scaling factor.
3. The method of reducing eight-level pulse amplitude modulation error rate in optical fiber communication according to claim 1, wherein the adjusted probability distribution of the four-level pulse amplitude modulation symbols obeys the following formula:
wherein,
four level values for a four-level pulse amplitude modulation symbol,
；
is a scaling factor.
4. The method for reducing the error rate of eight-level pulse amplitude modulation in optical fiber communication according to claim 1, wherein before the transmitting end transmits the eight-level pulse amplitude modulation symbols, the method further comprises:
and adjusting the power of the eight-level pulse amplitude modulation symbol to ensure that the average power of the eight-level pulse amplitude modulation symbol is the same as the average power before adjustment.
5. The method of reducing bit error rate of eight-level pulse amplitude modulation in optical fiber communication according to claim 1, wherein the four-level pulse amplitude modulation and the eight-level pulse amplitude modulation both follow gray code mapping.
6. The method of reducing an eight-level pulse amplitude modulation error rate in optical fiber communication according to claim 1, further comprising, before eight-level pulse amplitude modulating the bit sequence:
reordering the bit sequence so that the bit sequence adjusted by the probability distribution is positioned at the highest position and the middle position of the three bits, and the bit sequence uniformly distributed is positioned at the lowest position of the three bits;
after demapping the eight-level pulse amplitude modulation symbol, the method further includes:
the demapped bit sequence is reordered to correspond to the forward error correction encoded bit sequence.
7. An apparatus for reducing eight-level pulse amplitude modulation error rate in optical fiber communication, comprising:
the probability distribution adjusting module is used for adjusting the probability distribution of the four-level pulse amplitude modulation symbol so as to respectively increase and decrease the occurrence probability of the middle-low level and the high level of the four-level pulse amplitude modulation symbol;
the modulation module is used for demapping the four-level pulse amplitude modulation symbol after the probability distribution is adjusted to obtain a bit sequence, and sequentially performing forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain an eight-level pulse amplitude modulation symbol for a transmitting end to transmit;
after the eight-level pulse amplitude modulation symbol is received by a receiving end, sequentially carrying out demapping, binary system mark recovery and forward error correction coding decoding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence;
the forward error correction coding adopts DVB-S2 standard, and comprises BCH outer code and LDPC inner code;
the code rate of the LDPC inner code is 3/4, and the binary flag comprises uniformly distributed bit interpolation without information, so that the ratio of the bit sequence length after probability distribution adjustment to the bit sequence length uniformly distributed after forward error correction coding is 2: 1;
wherein, the bit sequence which is uniformly distributed after the forward error correction coding comprises an interpolated bit sequence which is uniformly distributed without information, a BCH outer code and an LDPC inner code; the interval of the bit sequence after the adjustment of probability distribution is 1-43200, the interval of the interpolated uniformly distributed bit sequence without information is 43201-.
8. A system for reducing eight-level pulse amplitude modulation error rate in optical fiber communications, comprising:
the processing module is used for adjusting the probability distribution of the four-level pulse amplitude modulation symbol so as to respectively increase and decrease the occurrence probability of the middle-low level and the high level of the four-level pulse amplitude modulation symbol; demapping the four-level pulse amplitude modulation symbols after the probability distribution is adjusted to obtain a bit sequence, and sequentially carrying out forward error correction coding, binary marking and eight-level pulse amplitude modulation on the bit sequence to obtain eight-level pulse amplitude modulation symbols;
the transmitting end is used for transmitting the eight-level pulse amplitude modulation symbol;
a receiving end, configured to receive the eight-level pulse amplitude modulation symbol, and sequentially perform demapping, binary flag recovery, and decoding of forward error correction coding on the eight-level pulse amplitude modulation symbol to obtain the bit sequence;
the forward error correction coding adopts DVB-S2 standard, and comprises BCH outer code and LDPC inner code;
the code rate of the LDPC inner code is 3/4, and the binary flag comprises uniformly distributed bit interpolation without information, so that the ratio of the bit sequence length after probability distribution adjustment to the bit sequence length uniformly distributed after forward error correction coding is 2: 1;
wherein, the uniformly distributed bit sequence after the forward error correction coding comprises an interpolated non-information uniformly distributed bit sequence, a BCH outer code and an LDPC inner code; the interval of the bit sequence after the adjustment of probability distribution is 1-43200, the interval of the interpolated uniformly distributed bit sequence without information is 43201-.
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| US10091046B1 (en) * | 2017-11-20 | 2018-10-02 | Nokia Technologies Oy | Joint use of probabilistic signal shaping and forward error correction |
| CN109286431A (en) * | 2018-09-21 | 2019-01-29 | 复旦大学 | A kind of equiprobability method for precoding for receiving system based on the hair of pulse amplitude modulation two one |
| CN110574309A (en) * | 2017-06-27 | 2019-12-13 | 华为技术有限公司 | optimization and equalization of pulse amplitude modulation levels in optical systems |
| CN111049586A (en) * | 2019-12-25 | 2020-04-21 | 南京信息工程大学 | Pulse amplitude position modulation system based on amplitude reduction type probability forming |
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| CN110574309A (en) * | 2017-06-27 | 2019-12-13 | 华为技术有限公司 | optimization and equalization of pulse amplitude modulation levels in optical systems |
| US10091046B1 (en) * | 2017-11-20 | 2018-10-02 | Nokia Technologies Oy | Joint use of probabilistic signal shaping and forward error correction |
| CN109286431A (en) * | 2018-09-21 | 2019-01-29 | 复旦大学 | A kind of equiprobability method for precoding for receiving system based on the hair of pulse amplitude modulation two one |
| CN111049586A (en) * | 2019-12-25 | 2020-04-21 | 南京信息工程大学 | Pulse amplitude position modulation system based on amplitude reduction type probability forming |
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