CN117200897A - High-spectral-efficiency joint channel coding modulation method and optical transmission system - Google Patents
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Abstract
The application discloses a high-spectral-efficiency joint channel coding modulation method and an optical transmission system, which are applied to the technical field of high-speed optical communication. The method comprises the following steps: a data acquisition step, an inter-symbol mathematical association step, a symbol multiplexing step, an optical signal transmission step, a channel equalization step and a bit interleaving iterative symbol demultiplexing step. The application is beneficial to improving the bearing capacity of the high-order modulation symbol and the spectrum efficiency of the system, and improving the capacity of an optical transmission channel; meanwhile, the modulation order of the signals is reduced, the resolution requirement of the signals on photoelectric devices is reduced, the nonlinear tolerance of the optical fibers of the system is improved, and the optical transmission performance and the transmission distance are improved.
Description
Technical Field
The application relates to the technical field of high-speed optical fiber communication, in particular to a high-spectral efficiency joint channel coding modulation method and an optical transmission system.
Background
In order to realize long-distance transmission of a high-speed large-capacity broadband optical fiber communication system, the utilization rate of spectrum resources needs to be improved as much as possible in limited spectrum resources, and the signal-to-noise ratio gain of optical transmission and the system capacity are improved. Under the limit of shannon theory, the high-order modulation and optical multiplexing technology is the main means for solving the transmission capacity bottleneck. But both are susceptible to factors such as system bandwidth bottlenecks, optoelectronic device accuracy limitations, fiber dispersion and nonlinear effects of the fiber optic transmission channel, thereby reducing receiver performance and limiting transmission distance.
In 1968, the low-density parity-check code inventor Gallager taught that "many-to-one" mapping code modulation was conceived, and by mapping a plurality of higher order modulation symbols to the same constellation point, the improvement of the information capacity of the system was achieved, so as to approach the shannon theoretical limit. But limited by the current specifications and the lack of viable demapping and decoding algorithms, this concept has not been appreciated. In recent years, as probability shaping technology is widely studied in the field of high-speed optical fiber communication research, as an alternative to pure bit type probability shaping technology, a "many-to-one" mapping technology is favored by many researchers. The 'many-to-one' mapping technology has great research value for the generation and transmission of high-speed probability shaping signals, and obtains a plurality of research achievements, but the development and application research of the mapping technology meets two bottlenecks at present: 1, limited by the theory of the information carrying capacity of the high-order modulation symbols, the 'many-to-one' mapping is used for realizing the target probability distribution of the high-order modulation signals, and the research is limited to the generation and transmission of probability shaping signals; 2 lack of efficient demapping and channel decoding techniques, most of the current schemes are (1) concatenated extra error correction coding, (2) preset error correction bits as training sequences. Although the 'many-to-one' overlapped symbol demapping can be effectively realized, a great amount of system redundancy is introduced, the complexity of the system is increased, and the effective rate and the spectrum efficiency of the system are reduced.
The forward error correction coding (FEC) is a key technology for controlling the signal receiving error rate by adopting channel coding under the complex channel environments of low reliability, strong noise interference and the like of a transmission channel, and is a main way for effectively obtaining the signal-to-noise ratio gain and breaking through the nonlinear limitation of an optical fiber. The development of FEC technology in the field of optical fiber communication has undergone the process of comprehensively applying hard-decision concatenated codes of interleaving modulation and iterative decoding from the first generation of hard-decision linear block codes to the second generation of hard-decision concatenated codes, and then to the third generation of low-density parity-check codes LDPC based on soft decisions. The cost of the current LDPC code words can be reduced to 15% -20%, the gain of the net coding signal to noise ratio can exceed 11dB, and the LDPC code words are widely applied to the scenes of 100G, 400G, 800G long-distance optical backbone networks, metropolitan area networks, optical interconnections and the like.
Although shannon's theory of information gives a fundamental theoretical relationship between channel capacity and signal-to-noise ratio, application studies of FEC systems and high-order modulation function modules in the current academia and industry are relatively independent, and the inherent mathematical logic association between the FEC systems and the high-order modulation function modules is not clear yet, and the theory and capacity model of optical fiber channel transmission combining the FEC systems and the high-order modulation function modules are not established yet. Therefore, based on a probability shaping mechanism of 'many-to-one' mapping, the method follows the principle of minimum inter-symbol Hamming distance, establishes the internal association between overlapped mapping symbol points of high-order modulation symbols through FEC, realizes relatively simple algorithm of joint channel coding modulation on the premise of not changing forward error correction coding and probability shaping symbol mapping structures, can obtain considerable symbol bearing capacity, and improves channel capacity and system spectrum efficiency.
Therefore, a high-spectrum-efficiency joint channel code modulation method and an optical transmission system are provided to solve the difficulties existing in the prior art, which are the problems to be solved by those skilled in the art.
Disclosure of Invention
In view of this, the present application provides a high-spectrum-efficiency joint channel code modulation method and an optical transmission system, which can improve the channel capacity and the optical fiber transmission distance.
In order to achieve the above object, the present application provides the following technical solutions:
a high-spectrum-efficiency joint channel code modulation method comprises the following steps:
a data acquisition step: acquiring required binary information source data;
inter-symbol mathematical association step: carrying out channel error correction coding on binary source data, and establishing a mathematical association mechanism between coding information bits and high-order modulation signal symbols through forward error correction coding information parameters;
a symbol multiplexing step: establishing an optimal constellation mapping rule of symbol multiplexing by using an intersymbol mathematical association mechanism and taking a maximum likelihood judgment rule and a maximum posterior probability as a criterion and a minimum Hamming distance between symbols as a criterion, and realizing symbol multiplexing of a high-order modulation signal by using 'many-to-one' constellation mapping to obtain a high-spectrum-efficiency symbol multiplexing signal;
an optical signal transmission step: after the high-spectral-efficiency symbol multiplexing signal is subjected to digital-to-analog conversion, the electric-to-optical conversion is realized through modulation of a polarization multiplexing IQ modulator, the generated optical signal is transmitted to an optical receiver through an optical fiber, and then the data is acquired through analog-to-digital conversion, so that the signal after analog-to-digital conversion is obtained;
and (3) a channel equalization step: the signals after analog-digital conversion are subjected to IQ balance, clock recovery, dispersion compensation, polarization demultiplexing, spectrum estimation and phase recovery, so that the equalization and compensation of the signals are realized, and the equalized signals are obtained;
bit interleaved iterative symbol de-multiplexing: the equalized signal is input into a demapper to obtain the code bit information of each symbol in the signal and the symbol demapper outputs soft information, the demapper and the forward error correction FEC decoder are used as one-to-many input-output communication modules, the log likelihood ratio transmitted between the modules is continuously updated through joint iteration, the optimal condition of soft decision channel decoding is satisfied, and symbol demultiplexing and FEC decoding are realized.
In the above method, optionally, in the step of inter-symbol mathematical association, the inter-symbol and inter-symbol bit mathematical association is implemented by the channel coding according to the formula (1), where the formula (1) is expressed as follows:
c＝u·G (1)
wherein u is a binary information source, G is an LDPC forward error correction coding generation matrix, c is a generated code word, the code word is modulated in groups, the formula (2) is a code word required by a 64QAM modulation format, the code word is modulated in groups, each 6 bits of the code word are modulated in a combined mode and mapped into one symbol, and each symbol needs 6 bits to realize all bearing of information:
wherein, gamma is the symbol mapping rule of high-order modulation (64 QAM), v t Is a bit tag.
In the above method, optionally, in the symbol multiplexing step, the core technology "many-to-one" overlap mapping method is implemented according to formula (3), where formula (3) is expressed as follows:
wherein S is i For high order modulation of 64QAM symbols, A i And theta i Is the amplitude and phase of the higher order modulation symbols. Every four 64QAM symbol time domains are mapped to one constellation point in an overlapping mode, and after the symbols are multiplexed, the 64QAM constellation is converted into a 16QAM constellation form.
The above method, optionally, the overlap mapping rule of the overlap mapping method is as follows:
in the above method, optionally, in the symbol multiplexing mapping optimization step, the optimal constellation mapping criteria specifically includes:
1) For different symbols within the same set of multiplexed symbols, minimizing the hamming distance between symbols;
2) The hamming distance between symbols is minimized for different symbols within different groups or adjacent groups of multiplexed symbols.
In the above method, optionally, in the optical signal transmission step, the optical transmitter includes, but is not limited to, a polarization multiplexing IQ modulator; optical receivers include, but are not limited to, integrated coherent receivers.
The method, optionally, in the step of bit interleaving iterative symbol demultiplexing, comprises the following steps:
1): the prior log-likelihood ratio information LLR updated with conditional probability and iteration by calculating Euclidean distance between standard 16QAM constellation points ID Performing first round symbol de-multiplexing on the optical multiplexing signal under the condition of (1);
2): the maximum posterior probability algorithm is adopted, after the first round of symbol de-multiplexing, the code bit information of the multiplexing symbols in each constellation point is aimed at, and the calculated LLR is used as the external information output by a symbol de-mapper;
3): the external information output by the demapper subtracts the prior information from the interleaver, the prior information is input into the forward error correction decoder after the demapping operation, the LLR is output after the internal iterative decoding, the LLR is fed back to the interleaver as the external information, and the LLR is used as the prior information to assist the iterative demultiplexing and demapping operation of the next round after the digital interleaving operation.
The high-spectrum-efficiency combined channel code modulation optical transmission system is characterized by comprising a data acquisition module, an inter-symbol mathematical association module, a symbol multiplexing module, an optical signal transmission module, a channel equalization module and a bit interleaving iterative symbol demultiplexing module which are connected in sequence;
and a data acquisition module: acquiring required binary information source data;
inter-symbol mathematical association module: carrying out channel error correction coding on binary source data, and establishing a mathematical association mechanism between coding information bits and high-order modulation signal symbols through forward error correction coding information parameters;
and a symbol multiplexing module: establishing an optimal constellation mapping rule of symbol multiplexing by using an intersymbol mathematical association mechanism and taking a maximum likelihood judgment rule and a maximum posterior probability as a criterion and a minimum Hamming distance between symbols as a criterion, and realizing symbol multiplexing of a high-order modulation signal by using 'many-to-one' constellation mapping to obtain a high-spectrum-efficiency symbol multiplexing signal;
an optical signal transmission module: after the high-spectral-efficiency symbol multiplexing signal is subjected to digital-to-analog conversion, the electric-to-optical conversion is realized through modulation of a polarization multiplexing IQ modulator, the generated optical signal is transmitted to an optical receiver through an optical fiber, and then the data is acquired through analog-to-digital conversion, so that the signal after analog-to-digital conversion is obtained;
and a channel equalization module: the signals after analog-digital conversion are subjected to IQ balance, clock recovery, dispersion compensation, polarization demultiplexing, spectrum estimation and phase recovery, so that the equalization and compensation of the signals are realized, and the equalized signals are obtained;
bit interleaving iterative symbol demultiplexing module: the equalized signal is input into a demapper to obtain the code bit information of each symbol in the signal and the symbol demapper outputs soft information, the demapper and the forward error correction FEC decoder are used as one-to-many input-output communication modules, the log likelihood ratio transmitted between the modules is continuously updated through joint iteration, the optimal condition of soft decision channel decoding is satisfied, and symbol demultiplexing and FEC decoding are realized.
The system, optionally, the system structure mainly comprises three parts, namely a transmitting end, an optical fiber transmission unit and a receiving end: the transmitting end comprises a laser, a data generation arbitrary waveform generator AWG, an electric drive amplifier, an optical IQ modulator, a polarization multiplexer and a waveform selector WSS; the optical fiber transmission unit is a commercial standard single-mode optical fiber and an erbium-doped optical fiber amplifier; the receiving end consists of a tunable optical filter, a local oscillation signal LO, an integrated coherent receiver comprising a 90-degree optical mixer and a balanced receiver, and a high-speed real-time oscilloscope DAC for realizing data acquisition.
The system, optionally, introduces parallel bit interleaving iterative decoding technology at the receiving end, and combines symbol demodulation and channel decoding technology.
Compared with the prior art, the application provides a high-gain joint channel coding modulation method and an optical transmission system, which have the beneficial effects that:
1) The signal constellation point symbol has the advantage that the channel capacity is improved because the signal constellation point symbol carries more information; compared with the traditional 16QAM, as shown in FIG. 3, the theoretical capacity of the system of the symbol multiplexing 16QAM is improved by 50%; meanwhile, as the symbol multiplexing does not need to consume extra spectrum resources, the spectrum utilization rate of the system can be improved by 50 percent.
2) The number of constellation points required in code modulation is reduced by times by symbol multiplexing, and the modulation format is reduced from the original 64QAM to the optical symbol multiplexing 16QAM, so that the optical symbol multiplexing signal has three advantages in system transmission: (1) the order of a high-order modulation format is effectively reduced, and the average transmission power requirement of the whole signal is reduced; (2) the requirements on the resolution of optical/electrical devices required by signal generation and transmission are effectively reduced, and the system cost is reduced; (3) the influence of the nonlinear effect of the optical fiber on the signal in the optical fiber transmission process is effectively inhibited, the sensitivity of a system receiver is improved, the transmission distance is increased, the optical power loss budget of the system is improved, and the optical transmission performance is improved.
3) The application improves the information carrying capacity of the high-order modulation symbols and improves the frequency spectrum efficiency of the system through the multiplexing of the combined channel coding symbols; the Euclidean distance of signal constellation points is increased, the resolution requirement of a photoelectric device of a system is reduced, the nonlinear tolerance of an optical fiber of the system is improved, and the signal-to-noise ratio gain of optical transmission is obtained; the receiving end introduces parallel bit interleaving iterative decoding technology, combines symbol demodulation and channel decoding technology, and improves signal-to-noise ratio gain.
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In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present application, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for modulating a high-spectral-efficiency joint channel code;
FIG. 2 is a schematic diagram of the generation and transmission of an optical symbol multiplexed 16QAM signal provided by the present application;
fig. 3 is a diagram of theoretical capacity analysis of symbol multiplexing provided by the application;
fig. 4 is a schematic diagram of a symbol demultiplexing technical scheme provided in the present application;
FIG. 5 is a block diagram of a high-spectral-efficiency joint channel code modulation optical transmission system provided by the application;
fig. 6 is a block diagram of a high-spectrum-efficiency joint channel code modulation system provided by the application.
Detailed Description
The following description of the embodiments of the present application 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 application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In the present disclosure, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions, and the terms "comprise," "include," or any other variation thereof, are intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
Referring to fig. 1, the application discloses a high-spectrum-efficiency joint channel coding modulation method, which comprises the following steps:
a data acquisition step: acquiring required binary information source data;
inter-symbol mathematical association step: carrying out channel error correction coding on binary source data, and establishing a mathematical association mechanism between coding information bits and high-order modulation signal symbols through forward error correction coding information parameters;
a symbol multiplexing step: establishing an optimal constellation mapping rule of symbol multiplexing by using an intersymbol mathematical association mechanism and taking a maximum likelihood judgment rule and a maximum posterior probability as a criterion and a minimum Hamming distance between symbols as a criterion, and realizing symbol multiplexing of a high-order modulation signal by using 'many-to-one' constellation mapping to obtain a high-spectrum-efficiency symbol multiplexing signal;
an optical signal transmission step: after the high-spectral-efficiency symbol multiplexing signal is subjected to digital-to-analog conversion, the electric-to-optical conversion is realized through modulation of a polarization multiplexing IQ modulator, the generated optical signal is transmitted to an optical receiver through an optical fiber, and then the data is acquired through analog-to-digital conversion, so that the signal after analog-to-digital conversion is obtained;
and (3) a channel equalization step: the signals after analog-digital conversion are subjected to IQ balance, clock recovery, dispersion compensation, polarization demultiplexing, spectrum estimation and phase recovery, so that the equalization and compensation of the signals are realized, and the equalized signals are obtained;
bit interleaved iterative symbol de-multiplexing: and inputting the equalized signal into a demapper to obtain code bit information of each symbol in the signal and the symbol demapper outputs soft information, using the demapper and an FEC decoder as a one-to-many input-output communication module, continuously updating the log likelihood ratio transferred between the modules through joint iteration, meeting the optimal condition of soft decision channel decoding, and realizing symbol demultiplexing and FEC decoding.
Further, in the inter-symbol mathematical association step, the inter-symbol and inter-symbol bit mathematical association is implemented by the channel coding of formula (1), where formula (1) is expressed as follows:
c＝u·G (1)
wherein u is a binary information source, G is an LDPC forward error correction coding generation matrix, c is a generated code word, the code word is modulated in groups, the formula (2) is a code word required by a 64QAM modulation format, the code word is modulated in groups, each 6 bits of the code word are modulated in a combined mode and mapped into one symbol, and each symbol needs 6 bits to realize all bearing of information:
wherein, gamma is the mapping rule of the high-order modulation 64QAM symbol, v t Is a bit tag.
Further, in the symbol multiplexing step, referring to fig. 2, the core technology "many-to-one" overlap mapping method is implemented according to formula (3), where formula (3) is expressed as follows:
wherein S is i For high order modulation of 64QAM symbols, A i And theta i Is the amplitude and phase of the higher order modulation symbols. Every four 64QAM symbol time domains are mapped to one constellation point in an overlapping mode, and after the symbols are multiplexed, the 64QAM constellation is converted into a 16QAM constellation form. Referring to fig. 3, the capacity is improved by 50% compared to the same baud rate 16QAM signal.
Further, the overlap mapping rule of the overlap mapping method is as follows:
further, in the symbol multiplexing mapping optimization step, the optimal constellation mapping criteria specifically include:
1) For different symbols within the same set of multiplexed symbols, minimizing the hamming distance between symbols;
2) The hamming distance between symbols is minimized for different symbols within different groups or adjacent groups of multiplexed symbols.
Specifically, after symbol multiplexing, 64 constellation points of the original constellation diagram are changed into 16 constellation points, and the characteristics of the 16QAM constellation diagram are presented. Each constellation point of the symbol multiplexed 16QAM signal has 4 higher order modulated 64QAM symbols multiplexed thereon.
Further, in the optical signal transmission step, the optical transmitter includes, but is not limited to, a polarization multiplexing IQ modulator; optical receivers include, but are not limited to, integrated coherent receivers.
Further, in the step of bit interleaving iterative symbol demultiplexing, the method comprises the following steps:
1): the prior log-likelihood ratio information LLR updated with conditional probability and iteration by calculating Euclidean distance between standard 16QAM constellation points ID Performing first round symbol de-multiplexing on the optical multiplexing signal under the condition of (1);
2): the maximum posterior probability algorithm is adopted, after the first round of symbol de-multiplexing, the code bit information of the multiplexing symbols in each constellation point is aimed at, and the calculated LLR is used as the external information output by a symbol de-mapper;
3): the external information output by the demapper subtracts the prior information from the interleaver, the prior information is input into the forward error correction decoder after the demapping operation, the LLR is output after the internal iterative decoding, the LLR is fed back to the interleaver as the external information, and the LLR is used as the prior information to assist the iterative demultiplexing and demapping operation of the next round after the digital interleaving operation.
Specifically, the symbol multiplexed 16QAM signal can be expressed as:
where h (t) represents channel response, including fibre channel impairments, and n (t) represents noise.
Referring to fig. 4, the optical symbol demultiplexing step 2 process can be expressed as:
wherein, psi is -1 Representing the inverse of the symbol multiplexing process. Lambda represents soft decision based on minimum Euclidean distance, LLR ID Representing a priori information of the symbol decisions.
The optical symbol demultiplexing step 3 process can be expressed as:
wherein,sign->Is a probability of (2). />And->Respectively indicate the bit tag +_at time t>And->The code bits at that time.
Specifically, the core of the demultiplexing algorithm is to use a demapper and an FEC decoder as a one-to-many input-multiple output (SISO) communication module, continuously update Log Likelihood Ratios (LLRs) transferred between the modules through joint parallel iteration until the best condition of soft decision is met, and realize forward error correction decoding while finishing symbol demultiplexing.
Specifically, referring to fig. 5, at the optical transmitting end, the source information is encoded and then bit interleaved, and then high-order modulation and symbol multiplexing are performed to obtain a transmission signal. The demapper and the decoder both adopt a SISO information exchange mechanism, the external information output by the demapper and the prior information from the interleaver are deinterleaved and then are sent to the FEC decoder as prior information, and the external information output by the decoder is sent to the demapper after being interleaved to adjust the symbol de-multiplexing and de-mapping results so as to carry out the next iteration. For the demapper and decoder, the extrinsic information refers to the difference between the output bit a priori log likelihood ratio information and the a priori log likelihood ratio information. Both the so-called "outer" and "a priori" are relatively speaking, and the outer information output by the demapper decoder is a priori information to the decoder demapper. In this way, the updating information is continuously exchanged between the demapper and the decoder, the reliability of the exchanged prior information is improved after each iteration process, and the decoder tends to converge after a certain number of iterations.
Corresponding to the method shown in fig. 1, the embodiment of the application also provides a high-spectrum-efficiency joint channel code modulation optical transmission system, which is used for realizing the method in fig. 1, and is shown by referring to fig. 6, and comprises a data acquisition module, an intersymbol mathematical association module, a symbol multiplexing module, an optical signal transmission module, a channel equalization module and a bit interleaving iterative symbol demultiplexing module which are connected in sequence;
inter-symbol mathematical association module: carrying out channel error correction coding on binary source data, and establishing a mathematical association mechanism between coding information bits and high-order modulation signal symbols through forward error correction coding information parameters;
and a symbol multiplexing module: establishing an optimal constellation mapping rule of symbol multiplexing by using an intersymbol mathematical association mechanism and taking a maximum likelihood judgment rule and a maximum posterior probability as a criterion and a minimum Hamming distance between symbols as a criterion, and realizing symbol multiplexing of a high-order modulation signal by using 'many-to-one' constellation mapping to obtain a high-spectrum-efficiency symbol multiplexing signal;
an optical signal transmission module: after the high-spectral-efficiency symbol multiplexing signal is subjected to digital-to-analog conversion, the electric-to-optical conversion is realized through modulation of a polarization multiplexing IQ modulator, the generated optical signal is transmitted to an optical receiver through an optical fiber, and then the data is acquired through analog-to-digital conversion, so that the signal after analog-to-digital conversion is obtained;
and a channel equalization module: the signals after analog-digital conversion are subjected to IQ balance, clock recovery, dispersion compensation, polarization demultiplexing, spectrum estimation and phase recovery, so that the equalization and compensation of the signals are realized, and the equalized signals are obtained;
bit interleaving iterative symbol demultiplexing module: and inputting the equalized signal into a demapper to obtain code bit information of each symbol in the signal and the symbol demapper outputs soft information, using the demapper and an FEC decoder as a one-to-many input-output communication module, continuously updating the log likelihood ratio transferred between the modules through joint iteration, meeting the optimal condition of soft decision channel decoding, and realizing symbol demultiplexing and FEC decoding.
Further, the system structure mainly comprises three parts, namely a transmitting end, an optical fiber transmission unit and a receiving end: the transmitting end comprises a laser, a data generation arbitrary waveform generator AWG, an electric drive amplifier, an optical IQ modulator, a polarization multiplexer and a waveform selector WSS; the optical fiber transmission unit is a commercial standard single-mode optical fiber and an erbium-doped optical fiber amplifier; the receiving end consists of a tunable optical filter, a local oscillation signal LO, an integrated coherent receiver comprising a 90-degree optical mixer and a balanced receiver, and a high-speed real-time oscilloscope DAC for realizing data acquisition.
Specifically, at the transmitting end, a symbol multiplexing signal based on joint code modulation is firstly generated, and the specific process is that after forward error correction coding and bit interleaving with the code rate of 3/4 are carried out on an input binary information source sequence, serial-parallel conversion and packet mapping are carried out on a code word sequence. To generate a single channel 1Tb/s signal, we use a 64QAM signal carrying 6 bits of information per symbol to perform "many-to-one" mapping symbol multiplexing, where every four 64QAM symbols are mapped to the same constellation point, and obtain a symbol multiplexed 16QAM signal as shown in fig. 2. The electric signal is subjected to pre-equalization processing and then a DAC is utilized to generate a 100GBaud symbol multiplexing 16QAM electric signal, and the electric signal is modulated onto an optical carrier generated by a laser through an IQ modulator. And then doubling the total channel rate by polarization multiplexing to obtain an optical symbol multiplexing signal of 1.05Tbit/s of a single channel, and sending the optical symbol multiplexing signal to a single mode fiber link to be transmitted to a receiving end. Meanwhile, the multiple lasers can be used for odd-even grouping to realize IQ modulation respectively, and the waveform selector is adopted for realizing high-density and high-capacity optical transmission after wavelength division multiplexing.
At the receiving end, the local oscillation signal LO and the received optical symbol multiplexing signal are subjected to optical mixing and balanced photoelectric conversion by an integrated coherent receiver comprising a 90-degree optical mixer and a balanced receiver. Then, analog-digital conversion and data acquisition are carried out on two polarized states and four paths of IQ electric signals in total by a high-speed real-time oscilloscope with the sampling rate of 256GSa/s, and finally, the acquired digital signals are sent into an off-line digital signal processing DSP unit, and the processing process mainly comprises the following steps: clock synchronization, 2 times resampling, dispersion compensation, polarization demultiplexing and channel equalization, and frequency offset compensation, phase recovery, symbol demultiplexing, forward error correction decoding and bit error rate calculation are realized.
Furthermore, the receiving end introduces a parallel bit interleaving iterative decoding technology and combines a symbol demodulation and channel decoding technology.
Specifically, by adopting the iterative decoding technology of decision feedback, the system performance of the system under the optical channel is improved. The essence of the method is that the mathematical expectation of the minimum value of the Euclidean distance between symbols in signal judgment is improved through iterative decoding, especially through external iteration, the internal iteration efficiency based on hamming distance judgment is optimized, so that the decoding difficulty of a decoder is reduced, and the internal iteration times of the decoder are reduced. 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 device 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 previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A high spectral efficiency joint channel code modulation method, comprising the steps of:
a data acquisition step: acquiring required binary information source data;
inter-symbol mathematical association step: carrying out channel error correction coding on binary source data, and establishing a mathematical association mechanism between coding information bits and high-order modulation signal symbols through forward error correction coding information parameters;
a symbol multiplexing step: establishing an optimal constellation mapping rule of symbol multiplexing by using an intersymbol mathematical association mechanism and taking a maximum likelihood judgment rule and a maximum posterior probability as a criterion and a minimum Hamming distance between symbols as a criterion, and realizing symbol multiplexing of a high-order modulation signal by using 'many-to-one' constellation mapping to obtain a high-spectrum-efficiency symbol multiplexing signal;
an optical signal transmission step: after the high-spectral-efficiency symbol multiplexing signal is subjected to digital-to-analog conversion, the electric-to-optical conversion is realized through modulation of a polarization multiplexing IQ modulator, the generated optical signal is transmitted to an optical receiver through an optical fiber, and then the data is acquired through analog-to-digital conversion, so that the signal after analog-to-digital conversion is obtained;
and (3) a channel equalization step: the signals after analog-digital conversion are subjected to IQ balance, clock recovery, dispersion compensation, polarization demultiplexing, spectrum estimation and phase recovery, so that the equalization and compensation of the signals are realized, and the equalized signals are obtained;
bit interleaved iterative symbol de-multiplexing: the equalized signal is input into a demapper to obtain the code bit information of each symbol in the signal and the symbol demapper outputs soft information, the demapper and the forward error correction FEC decoder are used as one-to-many input-output communication modules, the log likelihood ratio transmitted between the modules is continuously updated through joint iteration, the optimal condition of soft decision channel decoding is satisfied, and symbol demultiplexing and FEC decoding are realized.
2. The method for modulation and coding of a high spectral efficiency joint channel according to claim 1, wherein:
in the inter-symbol mathematical association step, the inter-symbol and inter-symbol bit mathematical association is realized by the channel coding of the formula (1), and the formula (1) is expressed as follows:
c＝u·G(1)
wherein u is a binary information source, G is an LDPC forward error correction coding generation matrix, c is a generated coding codeword, formula (2) is a coding codeword required by a 64QAM modulation format, the codeword is modulated in groups, each 6 bits are modulated and mapped into a symbol, and each symbol needs 6 bits to realize all bearing of information:
wherein, gamma is the mapping rule of the high-order modulation 64QAM symbol, v t Is a bit tag.
3. The method for modulation and coding of a high spectral efficiency joint channel according to claim 1, wherein:
in the symbol multiplexing step, the core technology 'many-to-one' overlap mapping method is implemented according to a formula (3), and the formula (3) has the following expression:
wherein S is i For high order modulation (64 QAM) symbols, A i And theta i Is the amplitude and phase of the higher order modulation symbols. Every four 64QAM symbol time domains are mapped to one constellation point in an overlapping mode, and after the symbols are multiplexed, the 64QAM constellation is converted into a 16QAM constellation form.
4. A method for efficient joint channel coding modulation as defined in claim 3, wherein,
the overlap mapping rule of the overlap mapping method is as follows:
5. a method of high spectral efficiency joint channel coding modulation as defined in claim 1, wherein,
in the symbol multiplexing mapping optimization step, the optimal constellation mapping criteria specifically include:
1) For different symbols within the same set of multiplexed symbols, minimizing the hamming distance between symbols;
2) The hamming distance between symbols is minimized for different symbols within different groups or adjacent groups of multiplexed symbols.
6. A method of high spectral efficiency joint channel coding modulation as defined in claim 1, wherein,
in the optical signal transmission step, the optical transmitter includes, but is not limited to, a polarization multiplexing IQ modulator; optical receivers include, but are not limited to, integrated coherent receivers.
7. A method of high spectral efficiency joint channel coding modulation as defined in claim 1, wherein,
the bit interleaving iterative symbol demultiplexing step comprises the following steps:
1): the prior log-likelihood ratio information LLR updated with conditional probability and iteration by calculating Euclidean distance between standard 16QAM constellation points ID Performing first round symbol de-multiplexing on the optical multiplexing signal under the condition of (1);
2): the maximum posterior probability algorithm is adopted, after the first round of symbol de-multiplexing, the code bit information of the multiplexing symbols in each constellation point is aimed at, and the calculated LLR is used as the external information output by a symbol de-mapper;
3): the external information output by the demapper subtracts the prior information from the interleaver, the prior information is input into the forward error correction decoder after the demapping operation, the LLR is output after the internal iterative decoding, the LLR is fed back to the interleaver as the external information, and the LLR is used as the prior information to assist the iterative demultiplexing and demapping operation of the next round after the digital interleaving operation.
8. A high-spectrum-efficiency joint channel code modulation optical transmission system, which is characterized in that the high-spectrum-efficiency joint channel code modulation method of any one of claims 1-7 is applied, and the high-spectrum-efficiency joint channel code modulation optical transmission system comprises a data acquisition module, an inter-symbol mathematical association module, a symbol multiplexing module, an optical signal transmission module, a channel equalization module and a bit interleaving iterative symbol demultiplexing module which are connected in sequence;
and a data acquisition module: acquiring required binary information source data;
inter-symbol mathematical association module: carrying out channel error correction coding on binary source data, and establishing a mathematical association mechanism between coding information bits and high-order modulation signal symbols through forward error correction coding information parameters;
and a symbol multiplexing module: establishing an optimal constellation mapping rule of symbol multiplexing by using an intersymbol mathematical association mechanism and taking a maximum likelihood judgment rule and a maximum posterior probability as a criterion and a minimum Hamming distance between symbols as a criterion, and realizing symbol multiplexing of a high-order modulation signal by using 'many-to-one' constellation mapping to obtain a high-spectrum-efficiency symbol multiplexing signal;
an optical signal transmission module: after the high-spectral-efficiency symbol multiplexing signal is subjected to digital-to-analog conversion, the electric-to-optical conversion is realized through modulation of a polarization multiplexing IQ modulator, the generated optical signal is transmitted to an optical receiver through an optical fiber, and then the data is acquired through analog-to-digital conversion, so that the signal after analog-to-digital conversion is obtained;
and a channel equalization module: the signals after analog-digital conversion are subjected to IQ balance, clock recovery, dispersion compensation, polarization demultiplexing, spectrum estimation and phase recovery, so that the equalization and compensation of the signals are realized, and the equalized signals are obtained;
bit interleaving iterative symbol demultiplexing module: and inputting the equalized signal into a demapper to obtain code bit information of each symbol in the signal and the symbol demapper outputs soft information, using the demapper and an FEC decoder as a one-to-many input-output communication module, continuously updating the log likelihood ratio transferred between the modules through joint iteration, meeting the optimal condition of soft decision channel decoding, and realizing symbol demultiplexing and FEC decoding.
9. The spectrally efficient joint channel-code modulated optical transmission system of claim 8 wherein,
the system structure mainly comprises three parts, namely a transmitting end, an optical fiber transmission unit and a receiving end: the transmitting end comprises a laser, a data generation arbitrary waveform generator AWG, an electric drive amplifier, an optical IQ modulator, a polarization multiplexer and a waveform selector WSS; the optical fiber transmission unit is a commercial standard single-mode optical fiber and an erbium-doped optical fiber amplifier; the receiving end consists of a tunable optical filter, a local oscillation signal LO, an integrated coherent receiver comprising a 900 optical mixer and a balance receiver, and a high-speed real-time oscilloscope digital-to-analog conversion DAC for realizing data acquisition.
10. The spectrally efficient joint channel-code modulated optical transmission system of claim 9 wherein,
the receiving end introduces parallel bit interleaving iterative decoding technology and combines symbol demodulation and channel decoding technology.
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