CN117579170A - Coding modulation method and system based on probability geometry joint shaping - Google Patents
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Abstract
The invention discloses a code modulation method and a system based on probability geometry joint shaping, relating to the field of optical fiber communication; the method comprises the following steps: acquiring a source bit sequence of a signal transmitting end; based on the constellation diagram and the constellation order, probability division is carried out on the source bit sequence to obtain probability distribution of a constellation point set; performing geometric shaping on the source bit sequence based on the constellation diagram and the constellation order to obtain a geometric shaping result; based on constellation order and probability distribution, carrying out serial-parallel conversion on a source bit sequence to obtain a conversion bit sequence; mapping the source bit sequence based on the constellation order and the geometric shaping result to obtain a mapping signal sequence; according to the transformation bit sequence and the mapping signal sequence, adopting a polarization multiplexing and frequency division multiplexing mode to carry out distribution matching code modulation to obtain a modulation signal; the invention can freely adjust the frequency spectrum efficiency and improve the degree of freedom of signals.
Description
Technical Field
The invention relates to the field of optical fiber communication, in particular to a code modulation method and system based on probability geometric joint shaping.
Background
Along with the high-speed development trend of scientific technologies such as the internet of things, artificial intelligence, big data and the like, the informatization degree of each industry is continuously improved, the importance of high-speed data transmission, especially high-speed optical fiber communication serving as a main long-distance transmission mode, is increasingly revealed due to the requirement of mass data transmission, and the improvement of the system transmission capacity of the existing optical communication network is urgent. In recent years, a trellis-coded modulation technique and a constellation shaping technique are receiving more and more attention, and the trellis-coded modulation employs a method of signal set expansion and subset partition mapping, and increases the minimum euclidean distance between adjacent signal points in each signal subset, thereby obtaining corresponding coding gain. Compared with the traditional error correction coding, the method can obtain more remarkable coding gain without increasing bandwidth and reducing effective code rate. Constellation shaping is a technique that improves system performance by changing the probability of transmission and geometry of constellation points. The probability shaping is realized by adjusting the occurrence probability of constellation points in a standard constellation, so that the average power of the constellation points is reduced, and the anti-noise and nonlinear effect resistance of signals is effectively improved; and compared with the traditional rectangular QAM, the geometric shaping uses the non-uniform interval constellation distribution of the symbols, so that the constellation diagram has larger shaping gain, and the transmission rate of the system is more close to the Shannon limit. These techniques have great potential in the context of the current proliferation of information.
However, many studies on constellation shaping alone inevitably reduce the information entropy, so that the amount of information contained in the original sequence is reduced, and as the shaping degree is increased, the degree of freedom of signals is also reduced. In the grid code modulation, a large number of low-dimensional low-order signals are applied, but as the constellation order and the modulation dimension are increased, the minimum Euclidean distance is reduced, the average power of the signals is increased, and the problems of aggravation of nonlinear effects of optical fiber channels, reduction of power efficiency and the like are caused, so that the system performance is seriously affected.
Disclosure of Invention
The invention aims to provide a coding modulation method and a system based on probability geometric joint shaping, which can freely adjust the frequency spectrum efficiency and improve the degree of freedom of signals.
In order to achieve the above object, the present invention provides the following solutions:
a method of code modulation based on probability geometric joint shaping, the method comprising:
acquiring a source bit sequence of a signal transmitting end;
based on a constellation diagram and constellation orders, probability division is carried out on the source bit sequence to obtain probability distribution of a constellation point set; the constellation point set is a set of constellation points scattered on the constellation diagram; the constellation points are signal elements in the source bit sequence; the constellation diagram comprises: a horizontal axis, a vertical axis and an origin;
performing geometric shaping on the source bit sequence based on a constellation diagram and the constellation order to obtain a geometric shaping result;
based on the constellation order and the probability distribution, carrying out serial-parallel conversion on the source bit sequence to obtain a conversion bit sequence;
mapping the source bit sequence based on the constellation order and the geometric shaping result to obtain a mapping signal sequence;
and carrying out distributed matching code modulation by adopting a polarization multiplexing and frequency division multiplexing mode according to the transformation bit sequence and the mapping signal sequence to obtain a modulation signal.
Optionally, probability division is performed on the source bit sequence based on the constellation diagram and the constellation order to obtain probability distribution of a constellation point set, which specifically includes:
dividing the constellation diagram into regions according to the signal energy according to the constellation order to obtain divided regions; the signal energy is determined according to the distance between each constellation point and the origin on the constellation diagram;
dividing the constellation diagram according to the dividing region to obtain a divided subset set; the set of split subsets comprises a plurality of constellation subsets;
and carrying out distribution matching on the segmented subset set based on Maxwell-Boltzmann distribution to obtain probability distribution of the constellation point set.
Optionally, the maxwell-boltzmann distribution has the expression:
wherein X is a constellation point set; p (P) X (x i ) For constellation point x i Is a probability of distribution of (1); v is a probability distribution factor; j is the sequence number of the constellation point; m is the total number of constellation points in the constellation point set; x is x j Is the j-th constellation point.
Optionally, geometric shaping is performed on the source bit sequence based on a constellation diagram and the constellation order to obtain a geometric shaping result, which specifically includes:
based on a constellation diagram and the constellation order, performing geometric position adjustment on constellation points in each constellation subset to obtain an adjustment result;
calculating an adjusted constellation performance index according to the adjustment result;
judging whether the adjusted constellation performance index is larger than the constellation performance index before adjustment;
if yes, the adjustment result is determined to be the geometric shaping result.
Optionally, the calculation formula of the constellation performance index is:
wherein CFM is a constellation performance index;is the square value of the minimum Euclidean distance; />Is the average power of the signal transmitting end.
Optionally, the method further comprises:
and demodulating the modulated signal to obtain the source bit sequence.
Optionally, demodulating the modulated signal to obtain the source bit sequence, which specifically includes:
performing demultiplexing operation on the modulation signal, and performing Viterbi decoding and inverse distribution matching to obtain inverse processing signal data;
and performing data record parallel-serial conversion on the inverse processing signal to obtain the source bit sequence.
A coded modulation system based on probabilistic geometry joint shaping, the system comprising:
the acquisition module is used for acquiring a source bit sequence of the signal transmitting end;
the probability distribution determining module is used for carrying out probability division on the source bit sequence based on the constellation diagram and the constellation order to obtain probability distribution of a constellation point set; the constellation point set is a set of constellation points scattered on the constellation diagram; the constellation points are signal elements in the source bit sequence; the constellation diagram comprises: a horizontal axis, a vertical axis and an origin;
the shaping module is used for geometrically shaping the source bit sequence based on a constellation diagram and the constellation order to obtain a geometric shaping result;
the transformation module is used for carrying out serial-parallel transformation on the source bit sequence based on the constellation order and the probability distribution to obtain a transformation bit sequence;
the mapping module is used for mapping the source bit sequence based on the constellation order and the geometric shaping result to obtain a mapping signal sequence;
and the modulation module is used for carrying out distributed matching code modulation by adopting a polarization multiplexing and frequency division multiplexing mode according to the transformation bit sequence and the mapping signal sequence to obtain a modulation signal.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention provides a code modulation method and a system based on probability geometry joint shaping, which are implemented by acquiring a source bit sequence of a signal transmitting end; based on the constellation diagram and the constellation order, probability division is carried out on the source bit sequence to obtain probability distribution of a constellation point set; performing geometric shaping on the source bit sequence based on the constellation diagram and the constellation order to obtain a geometric shaping result; based on constellation order and probability distribution, carrying out serial-parallel conversion on a source bit sequence to obtain a conversion bit sequence; mapping the source bit sequence based on the constellation order and the geometric shaping result to obtain a mapping signal sequence; according to the transformation bit sequence and the mapping signal sequence, adopting a polarization multiplexing and frequency division multiplexing mode to carry out distribution matching code modulation to obtain a modulation signal; according to the method, the grid coding and the constellation shaping are combined, so that the spectrum efficiency can be freely adjusted, meanwhile, the reduction of signal information entropy caused by the excessively high probability shaping degree is effectively relieved by the spectrum gain brought by the multidimensional constellation, and the signal freedom degree is improved, so that the spectrum efficiency can be freely adjusted, and the signal freedom degree is improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of a coding modulation method based on probability geometry joint shaping according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a modulation and demodulation flow of an eight-dimensional trellis coded signal based on probability geometry joint shaping according to an embodiment of the present invention;
fig. 3 is a schematic diagram of 2D subset partitioning and probability shaping of a basic 2D constellation of 16 QAM;
FIG. 4 is a 2D base constellation effect diagram of an 8D-PS-GS-TCM-16QAM signal;
FIG. 5 is a graph of bit error rate for an 8D-PS-GS-TCM-16QAM signal without probability geometry joint shaping and shaping;
fig. 6 is a block diagram of a coded modulation system based on probability geometry joint shaping.
Symbol description:
the device comprises an acquisition module-1, a probability distribution determination module-2, a shaping module-3, a transformation module-4, a mapping module-5 and a modulation module-6.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a coding modulation method and a system based on probability geometric joint shaping, which can freely adjust the frequency spectrum efficiency and improve the degree of freedom of signals.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1
As shown in fig. 1, an embodiment of the present invention provides a method for code modulation based on probability geometry joint shaping, where the method includes:
step 100: and acquiring a source bit sequence of a signal transmitting end.
Step 200: and carrying out probability division on the source bit sequence based on the constellation diagram and the constellation order to obtain probability distribution of a constellation point set. A constellation point set is a set of constellation points scattered on a constellation; constellation points are signal elements in the source bit sequence; the constellation diagram comprises: a horizontal axis, a vertical axis, and an origin.
The method comprises the steps of carrying out probability division on a source bit sequence based on a constellation diagram and constellation orders to obtain probability distribution of a constellation point set, and specifically comprises the following steps:
dividing the constellation diagram into regions according to the signal energy according to the constellation order to obtain divided regions; the signal energy is determined from the distance of each constellation point from the origin on the constellation.
Dividing the constellation diagram according to the dividing regions to obtain a divided subset set; the set of split subsets includes a plurality of constellation subsets.
And carrying out distribution matching on the subset set based on Maxwell-Boltzmann distribution to obtain probability distribution of the constellation point set.
Specifically, the expression of maxwell-boltzmann distribution is:
wherein X is a constellation point set; p (P) X (x i ) For constellation point x i Is a probability of distribution of (1); v is a probability distribution factor; wherein, the larger v is, the greater the shaping degree is. j is the sequence number of the constellation point; m is the total number of constellation points in the constellation point set; x is x j Is the j-th constellation point.
Step 300: and geometrically shaping the source bit sequence based on the constellation diagram and the constellation order to obtain a geometrical shaping result.
The method comprises the steps of geometrically shaping a source bit sequence based on a constellation diagram and constellation orders to obtain a geometrically shaping result, and specifically comprises the following steps:
and based on the constellation diagram and the constellation order, performing geometric position adjustment on constellation points in each constellation subset to obtain an adjustment result.
And calculating the adjusted constellation performance index according to the adjustment result.
And judging whether the adjusted constellation performance index is larger than the constellation performance index before adjustment.
If yes, the adjustment result is determined to be a geometric shaping result.
Specifically, the calculation formula of the constellation performance index is:
wherein CFM is a constellation performance index;is the square value of the minimum Euclidean distance; />Is the average power of the signal transmitting end.
Step 400: and carrying out serial-parallel conversion on the source bit sequence based on the constellation order and the probability distribution to obtain a conversion bit sequence.
Step 500: and mapping the source bit sequence based on the constellation order and the geometric shaping result to obtain a mapping signal sequence.
Step 600: and carrying out distributed matching code modulation by adopting a polarization multiplexing and frequency division multiplexing mode according to the transformation bit sequence and the mapping signal sequence to obtain a modulation signal.
In one embodiment, the method further comprises: and demodulating the modulated signal to obtain a source bit sequence.
The method for demodulating the modulated signal to obtain a source bit sequence specifically comprises the following steps:
carrying out de-multiplexing operation on the modulated signal, and carrying out Viterbi decoding and inverse distribution matching to obtain inverse processing signal data; and performing parallel-serial conversion on the data of the inverse processing signal to obtain a source bit sequence.
In practical application, the coding modulation method based on probability geometric joint shaping provided by the invention comprises the following specific operation steps:
the coding and decoding of the high-order multidimensional grid coding are combined with the probability geometry joint shaping, so that the coherent optical communication system can freely adjust the frequency spectrum efficiency, improve the degree of freedom of signals and achieve both high efficiency and flexibility.
Specifically, probability division is carried out according to the constellation subsets, and the probability of each part of constellation points is determined; determining the relation between the geometric shaping degree and the subset according to the constellation order; and carrying out distribution matching according to the constellation mapping rule determined by the probability geometry joint shaping to construct the eight-dimensional grid code.
The invention is oriented to a signal transmission method with high frequency spectrum efficiency, high flexibility and high error code performance in a high-speed optical communication system, solves the problem that the nonlinear effect of the optical fiber channel is aggravated due to the smaller minimum Euclidean distance of a high-order multidimensional grid coding constellation, and inevitably reduces the information entropy by singly using constellation shaping, so that the information quantity contained in an original sequence is reduced. The grid coding and constellation shaping are combined, so that the overall scheme can freely adjust the spectrum efficiency, and meanwhile, the spectrum gain brought by the multidimensional constellation effectively relieves the signal information entropy reduction caused by the excessively high probability shaping degree, so that the signal freedom degree is improved, and the method has huge potential in high-speed optical communication.
Firstly, probability division is carried out according to constellation orders and constellation points in the 2D subset, and probability distribution of each part of constellation points is determined, wherein the probability distribution comprises the following steps:
(1) Probability shaping is carried out on the 2D basic constellation, the probability of constellation points being mapped is uneven, the probability of points with smaller energy being mapped is large according to the mapping rule, and the probability of points with larger energy being mapped is small. Firstly, dividing a basic 2D constellation with the order of M into a plurality of proper areas according to the signal energy, so that the selection probability of constellation points close to an origin is high, otherwise, the selection probability of constellation points is low.
(2) And carrying out subset segmentation on the basic 2D constellation to obtain 4 basic 2D subsets A-D, wherein each subset contains M/4 constellation points, the minimum Euclidean distance between adjacent constellation points is equal, and the minimum Euclidean distance is enlarged to be twice before subset segmentation.
(3) An 8D signal is composed of four underlying 2D constellation points, so in order to effectively combine probability shaping with eight-dimensional trellis encoding, in the eight-dimensional trellis encoding architecture, the probabilities of selection of four independent 2D constellation points need to be controlled simultaneously, so that one point is selected from each of four independent 2D constellation subsets, there are (M/4)/(4) possibilities, and the total probability corresponding to each possibility is set according to the probabilities of each of the four points in the 2D constellation determined in (1) in each possibility. The probability distribution of the 8D constellation follows the Maxwell-Boltzmann distribution, expressed as:X＝{x 1 ,x 2 ,…,x m -a }; wherein, here, a specific X is an 8D constellation symbol set, i.e. a constellation point set; p (P) X (x i ) For constellation point x i Is a probability of distribution of (1); v is a probability distribution factor, and the greater v is, the greater the shaping degree is.
The information entropy H of the signal after distribution matching is as follows: this step yields a probability distribution for the eight-dimensional signal. Wherein p is i For eight-dimensional constellation point x i Distribution probability of (i.e. P) X (x i )。
In a second aspect, determining a relationship between the degree of geometric shaping and the subset according to the order of the constellation; the probability geometric joint shaping distribution suitable for eight-dimensional grid coding modulation is obtained by geometrically shaping the 2D constellation diagram according to the grid coding characteristic while obtaining the probability shaping distribution of the 2D constellation points and the corresponding 8D signals, and comprises the following steps:
(1) Geometrically shaping the 2D base constellation. Because the grid coding 2D subset division requires the same number and distribution state of constellation points contained in each subset, the geometric shaping is based on square QAM, and the positions of M/4 constellation points in the 2D subset are adjusted according to the constellation order. The geometric shaping rule is as follows: in each 2D subset, the constellation point closest to the origin is unchanged in position, and the rest constellation points move in a direction away from the origin according to the absolute value of the abscissa and the ordinate of the constellation point and the distance from the origin. The absolute value of the coordinates is larger, the distance from the origin is larger, the moving distance to the corresponding direction is larger, and the moving distance is smaller. Through the operation, the minimum Euclidean distance of adjacent constellation points in the 2D subset can be increased, so that the judgment fault tolerance rate is increased. From the effect of the whole 2D constellation, the points at the outer circle of the 2D constellation are spread outwards.
(2) Calculating constellation information entropy according to the geometric shaping result and constellation performance indexes:i.e. the ratio of the square of the minimum euclidean distance to the average power, the number of constellation values before geometric shaping is larger and the performance is better.
(3) The probability shaping reduces the probability of the outer ring constellation points, so that the power increase caused by the diffusion of the outer ring constellation points in the geometric shaping is relieved, the distance between constellation points with higher selection probability is increased by the geometric shaping, the misjudgment is reduced, and the two complement each other.
In a third aspect, performing distribution matching according to a constellation mapping rule determined by probability geometry joint shaping, and constructing a trellis-coded modulation distribution space and a signal set, thereby constructing an eight-dimensional trellis code, including:
(1) The 2D subsets A1-D1 and A2-D2 subjected to probability geometric shaping are subjected to Cartesian multiplication and then divided to obtain eight 4D subsets A1-h1, the 4D subsets A2-h2 can be obtained by the 2D subsets A3-D3 and A4-D4 in the same way, and then the 4D subsets are subjected to Cartesian multiplication and division to obtain sixteen 8D subsets S0-S15 which serve as the basis of eight-dimensional grid coding.
(2) And generating an equal-probability bit sequence at a transmitting end, and carrying out serial-parallel conversion according to the constellation order. The bits used for constellation point selection pass through a probability shaping distribution matcher to obtain constellation points conforming to the probability distribution in the first aspect, namely the positions of four constellation points in a certain 2D subset respectively. And then performing grid coding modulation on the rest bits, and passing the 3 bits through a convolutional encoder with the code rate of 3/4, wherein the obtained 4 bits are used for selecting one subset from 16 8D subsets. Of the remaining bits, 2 bits are used to determine the cartesian product of a set of 4D subsets and 2 bits are used to select the cartesian product of two sets of 2D subsets, thereby determining the 8D subset, 4D subset, 2D subset selection case of trellis encoding. Combining with constellation points selected by the constellation selection bits, an eight-dimensional trellis coded signal is obtained.
The specific embodiment of the present invention will be described by taking an 8D-PS-GS-TCM-16QAM signal as an example.
In a high-speed optical communication system, constellation shaping can be used for changing probability distribution and geometric distribution of an original signal, so that signal points with lower energy are distributed more densely, the occurrence probability is higher, otherwise, the probability is lower, the average power of a transmitted signal is reduced, the nonlinear effect of an optical fiber channel is reduced, and the constellation shaping with higher degree can cause non-negligible information entropy loss. And the grid coding is used, coded bits are accommodated by expanding a constellation, so that the error code performance of a synchronous data link can be improved under the condition of not sacrificing the data rate or needing more bandwidth, but the minimum Euclidean distance caused by constellation expansion is drastically reduced, the nonlinear effect of a fiber channel can be aggravated, and the power efficiency is reduced. Therefore, by using the grid coding modulation based on constellation shaping, the high-error code performance transmission of the high-spectrum-efficiency signal can be realized, the harm of nonlinear effect to the signal transmission is reduced, the degree of freedom of the signal is increased, and the reduction of the signal information entropy caused by the excessively high probability shaping degree is relieved.
Fig. 2 shows the overall modulation and demodulation scheme for an 8D-PS-GS-TCM-16QAM signal.
As shown in fig. 2-5, a specific algorithm flow is as follows:
1. and carrying out probability division according to the order 16 of the constellation and the constellation points 4 in the 2D subset, and determining probability distribution of each part of constellation points. Probability shaping is performed on the 2D basic constellation, the probability that constellation points are mapped is uneven, the probability that points with smaller energy are mapped according to a mapping rule is high, and the probability that points with larger energy are mapped is low. Firstly, dividing a basic 2D constellation with the order of 16 into three proper areas according to the signal energy, so that the selection probability of constellation points close to an origin is high, and otherwise, the selection probability of constellation points is low. And then carrying out subset segmentation on the basic 2D constellation to obtain 4 basic 2D subsets, wherein each subset contains 4 constellation points, and the minimum Euclidean distance between adjacent constellation points is equal to twice that before subset segmentation. For eight-dimensional trellis encoding, the selection probabilities of four independent 2D constellation points are controlled simultaneously, so that one point is selected from four independent 2D constellation subsets, 256 possibilities are provided, the probability corresponding to each possibility is set, and a corresponding original sequence is generated. The overall probability distribution obeys the Maxwell-Boltzmann distribution, expressed as:
the information entropy H of the signal after distribution matching is as follows: h= - Σ i p i log 2 p i 。
2. At the same time as the probability shaping, the relation between the geometrical shaping degree and the subset is determined according to the order 16 of the constellation. Geometric shaping is carried out on the 2D basic constellation on the basis of probability shaping, the positions of 4 constellation points in the 2D subset are adjusted according to the constellation order 16, and the minimum Euclidean distance between adjacent constellation points is increased. The points at the outer circle of the 2D constellation are spread outwards. Calculating constellation information entropy according to the geometric shaping result and constellation performance indexes:i.e. the ratio of the square of the minimum euclidean distance to the average power, the number of constellation values before geometric shaping is larger and the performance is better.
3. And carrying out distribution matching according to constellation mapping rules determined by probability geometry joint shaping, and constructing a grid code modulation distribution space and a signal set, thereby constructing the eight-dimensional grid code. The 2D subsets A1-D1 and A2-D2 subjected to probability geometric shaping are subjected to Cartesian multiplication and then divided to obtain eight 4D subsets A1-h1, the 4D subsets A2-h2 can be obtained by the 2D subsets A3-D3 and A4-D4 in the same way, and then the 4D subsets are subjected to Cartesian multiplication and division to obtain sixteen 8D subsets S0-S15 which serve as the basis of eight-dimensional grid coding. And generating an equal-probability bit sequence at a transmitting end, and carrying out serial-parallel conversion according to the constellation order. The bits used for constellation point selection pass through a probability shaping distribution matcher to obtain constellation points conforming to the probability distribution in the first aspect, namely the positions of four constellation points in a certain 2D subset respectively. And then performing grid coding modulation on the rest bits, and passing the 3 bits through a convolutional encoder with the code rate of 3/4, wherein the obtained 4 bits are used for selecting one subset from 16 8D subsets. Of the remaining bits, 2 bits are used to determine the cartesian product of a set of 4D subsets and 2 bits are used to select the cartesian product of two sets of 2D subsets, thereby determining the 8D subset, 4D subset, 2D subset selection case of trellis encoding. Combining with constellation points selected by the constellation selection bits, an eight-dimensional trellis coded signal is obtained.
4. And carrying out polarization multiplexing on each two signals of the 2D signals in the 8D signals, and then carrying out frequency division multiplexing on the two signals to a single-mode optical fiber. The signal is transmitted over a fibre channel. At the receiving end, the received signals are demultiplexed and compensated by the DSP, and the functions comprise: dc blocking, normalization, low pass filters, resampling, QI compensation, timing recovery, adaptive equalizer, frequency offset estimation, carrier phase estimation. And then carrying out Viterbi decoding and inverse distribution matching, and obtaining an original bit sequence through parallel-serial conversion, thereby calculating the bit error rate performance.
Example 2
As shown in fig. 6, an embodiment of the present invention provides a coded modulation system based on probability geometry joint shaping, the system including: the device comprises an acquisition module 1, a probability distribution determination module 2, a shaping module 3, a transformation module 4, a mapping module 5 and a modulation module 6.
And the acquisition module 1 is used for acquiring the source bit sequence of the signal transmitting end.
The probability distribution determining module 2 is used for carrying out probability division on the source bit sequence based on the constellation diagram and the constellation order to obtain probability distribution of a constellation point set; a constellation point set is a set of constellation points scattered on a constellation; constellation points are signal elements in the source bit sequence; the constellation diagram comprises: a horizontal axis, a vertical axis, and an origin.
And the shaping module 3 is used for geometrically shaping the source bit sequence based on the constellation diagram and the constellation order to obtain a geometrical shaping result.
And the transformation module 4 is used for carrying out serial-parallel transformation on the source bit sequence based on the constellation order and the probability distribution to obtain a transformation bit sequence.
And the mapping module 5 is used for mapping the source bit sequence based on the constellation order and the geometric shaping result to obtain a mapping signal sequence.
And the modulation module 6 is used for carrying out distributed matching code modulation by adopting a polarization multiplexing and frequency division multiplexing mode according to the transformation bit sequence and the mapping signal sequence to obtain a modulation signal.
In practical application, the code modulation system based on the probability geometry joint shaping can comprise:
(1) And a data generation module: when the original sequence is generated, distribution matching of probabilities corresponding to different entropy values is carried out according to the order of a constellation to be transmitted and the frequency spectrum efficiency, and probability shaping is carried out on the constellation to generate a 01-bit sequence.
(2) Constellation mapping module: the bit sequence is subjected to serial-parallel conversion, geometric shaping is carried out on the selected constellation points, the selected constellation points are mapped into four 2D constellation points of 8D signals, polarization multiplexing is carried out on every two signals, and then the signals are subjected to frequency division multiplexing on a single-mode fiber.
(3) Transmitted over fibre channel.
(4) And a signal demodulation module: the received signals are demultiplexed and compensated by the DSP, the functions of which include: dc blocking, normalization, low pass filters, resampling, QI compensation, timing recovery, adaptive equalizer, frequency offset estimation, carrier phase estimation. And then carrying out the same processing with the unshaped TCM signals, carrying out Viterbi decoding and inverse distribution matching, and obtaining an original bit sequence through parallel-serial conversion, thereby calculating the bit error rate performance.
The invention is based on the modulation and demodulation of the high-speed optical communication system, performs method and performance optimization, adopts the probability shaping based on the high-dimensional constellation subset, the geometric shaping based on the constellation order, and combines the grid coding modulation and demodulation to realize the high-error code performance transmission of the high-frequency spectrum efficiency signal, the application of shaping can effectively reduce the harm of nonlinear effect to the signal transmission, the frequency spectrum gain brought by the multi-dimensional constellation can relieve the signal information entropy reduction caused by the overhigh probability shaping degree while increasing the signal design freedom degree, so that the signal freedom degree is improved, and the invention has great potential in the high-speed optical communication.
The invention can solve the problem of aggravation of nonlinear effect of the optical fiber channel caused by smaller minimum Euclidean distance of the high-order multidimensional grid coding constellation, and the information entropy is inevitably reduced by singly using constellation shaping, so that the information quantity contained in the original sequence is reduced. The grid coding is combined with constellation shaping, so that the overall scheme can freely adjust the spectrum efficiency.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant points refer to the description of the method section.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (8)
1. A method of code modulation based on probability geometry joint shaping, the method comprising:
acquiring a source bit sequence of a signal transmitting end;
based on a constellation diagram and constellation orders, probability division is carried out on the source bit sequence to obtain probability distribution of a constellation point set; the constellation point set is a set of constellation points scattered on the constellation diagram; the constellation points are signal elements in the source bit sequence; the constellation diagram comprises: a horizontal axis, a vertical axis and an origin;
performing geometric shaping on the source bit sequence based on a constellation diagram and the constellation order to obtain a geometric shaping result;
based on the constellation order and the probability distribution, carrying out serial-parallel conversion on the source bit sequence to obtain a conversion bit sequence;
mapping the source bit sequence based on the constellation order and the geometric shaping result to obtain a mapping signal sequence;
and carrying out distributed matching code modulation by adopting a polarization multiplexing and frequency division multiplexing mode according to the transformation bit sequence and the mapping signal sequence to obtain a modulation signal.
2. The method for coded modulation based on probability geometric joint shaping according to claim 1, wherein the probability dividing is performed on the source bit sequence based on a constellation diagram and a constellation order to obtain a probability distribution of a constellation point set, specifically comprising:
dividing the constellation diagram into regions according to the signal energy according to the constellation order to obtain divided regions; the signal energy is determined according to the distance between each constellation point and the origin on the constellation diagram;
dividing the constellation diagram according to the dividing region to obtain a divided subset set; the set of split subsets comprises a plurality of constellation subsets;
and carrying out distribution matching on the segmented subset set based on Maxwell-Boltzmann distribution to obtain probability distribution of the constellation point set.
3. The code modulation method based on probability geometric joint shaping according to claim 2, wherein the expression of maxwell-boltzmann distribution is:
wherein X is a constellation point set; p (P) X (x i ) For constellation point x i Is a probability of distribution of (1); v is a probability distribution factor; j is the sequence number of the constellation point; m is the total number of constellation points in the constellation point set; x is x j Is the j-th constellation point.
4. The method for coded modulation based on probability geometry joint shaping according to claim 2, wherein the geometric shaping is performed on the source bit sequence based on a constellation diagram and the constellation order to obtain a geometric shaping result, specifically comprising:
based on a constellation diagram and the constellation order, performing geometric position adjustment on constellation points in each constellation subset to obtain an adjustment result;
calculating an adjusted constellation performance index according to the adjustment result;
judging whether the adjusted constellation performance index is larger than the constellation performance index before adjustment;
if yes, the adjustment result is determined to be the geometric shaping result.
5. The method for coded modulation based on probability geometric joint shaping as defined in claim 4, wherein the calculation formula of the constellation performance index is:
wherein CFM is a constellation performance index;is the square value of the minimum Euclidean distance; />Is the average power of the signal transmitting end.
6. The probability geometry joint shaping based coded modulation method of claim 1, further comprising:
and demodulating the modulated signal to obtain the source bit sequence.
7. The method for coded modulation based on probability geometric joint shaping according to claim 6, wherein demodulating the modulated signal to obtain the source bit sequence comprises:
performing demultiplexing operation on the modulation signal, and performing Viterbi decoding and inverse distribution matching to obtain inverse processing signal data;
and performing data record parallel-serial conversion on the inverse processing signal to obtain the source bit sequence.
8. A coded modulation system based on probabilistic geometry joint shaping, the system comprising:
the acquisition module is used for acquiring a source bit sequence of the signal transmitting end;
the probability distribution determining module is used for carrying out probability division on the source bit sequence based on the constellation diagram and the constellation order to obtain probability distribution of a constellation point set; the constellation point set is a set of constellation points scattered on the constellation diagram; the constellation points are signal elements in the source bit sequence; the constellation diagram comprises: a horizontal axis, a vertical axis and an origin;
the shaping module is used for geometrically shaping the source bit sequence based on a constellation diagram and the constellation order to obtain a geometric shaping result;
the transformation module is used for carrying out serial-parallel transformation on the source bit sequence based on the constellation order and the probability distribution to obtain a transformation bit sequence;
the mapping module is used for mapping the source bit sequence based on the constellation order and the geometric shaping result to obtain a mapping signal sequence;
and the modulation module is used for carrying out distributed matching code modulation by adopting a polarization multiplexing and frequency division multiplexing mode according to the transformation bit sequence and the mapping signal sequence to obtain a modulation signal.
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