CN103916216A - QC-LDPC coded modulation method based on 8-QAM modulation mode in optical communication system - Google Patents

Abstract

The invention discloses a QC-LDPC coded modulation method based on an 8-QAM modulation mode in an optical communication system. According to the scheme, on the basis of studying the coded modulation scheme of an existing 8-QAM modulation mode, a UP-BP-BP set division mode is adopted, and the Euclidean distance between signals is increased. A nonidentity code protection mode is adopted, a first bit is coded by a QC-LDPC code pattern with low redundancy, and a second bit and a third bit are coded through code patterns with the high code rate. In the decoding process, an MLC/MSD scheme and a multi-stage coding/parallel decoding PDL scheme are combined, and a new QC-LDPC coded modulation scheme is obtained. The calculation complexity of the scheme is 2/3 of that of a traditional scheme. The NCG is higher, and the error correction performance of the scheme is better.

Description

A kind of QC-LDPC code modulating method based on 8-QAM modulation system in optical communication system

Technical field

The invention belongs to signal process field in communication, particularly two stage of the one QC-LDPC coded modulation scheme based on 8-QAM modulation system in optical communication system.

Background technology

Growing along with optical communication technique, also towards the longer distance of larger capacity, more high speed direction is growing thereupon for optical communication system, and the 40Gb/s that single-channel optical communication system capacity develops into 2003 from the 10Gb/s of the nineties, used less than ten years.2010, ITU-T made the relevant criterion of 100Gb/s optical transmission system, and relevant device has entered industrialization test phase.When the global main flow promotion 100Gb/s of producer system global is disposed, also actively carrying out the even beforehand research of 10Tb/s of 400Gb/s, 1Tb/s.Simultaneously, M system amplitude-shift keying (Multiple Amplitude Shift Keying, MASK), M system phase shift keying (Multiple Phase Shift Keying, MPSK), M ary quadrature amplitude (Multilevel Quadrature Amplitude modulation, MQAM) can be brought log ₂the symbol utilance of M, wherein M-ary QAM is a kind of power and all effective transmission meanss of bandwidth, uses in practice at most.In super 100Gb/s scheme, 8-QAM becomes a kind of popular scheme.In the method for various increase power system capacities, M-QAM is also a kind of the jointly control amplitude of sinusoidal carrier and modulation system of phase place at present.8-QAM wherein becomes the popular modulation scheme of optical communication system of future generation.There is experiment report to adopt the system of 8-QAM modulation system to realize the light transmission of single channel speed 114Gb/s.

The present invention is just in this technical background situation, in order to adapt to the growing requirement of optical communication system, the present invention is based on the coded modulation scheme of 8-QAM modulation system, its modulation demodulation system and constellation mapping are furtherd investigate, and the feature of encircling for its planisphere two, propose more efficiently mapping mode, and then propose a kind of optical communication system two more superior stage QC-LDPC coded modulation schemes of combination property of being applicable to.

Summary of the invention

For above deficiency of the prior art, the object of the present invention is to provide the aspect performances such as a kind of net coding gain, frequency efficiency, iterations and complexity all can meet better the code modulating method of the requirement of high speed optical communication system.Technical scheme of the present invention is as follows: a kind of QC-LDPC code modulating method based on 8-QAM modulation system in a kind of optical communication system, is characterized in that comprising the following steps:

101, the signal stream in optical communication system is divided into information bit 1, information bit 2 and information bit 3, the encoder 1 that is then L1 by information bit 1 through redundancy is encoded into the first bit c ₀, and information bit 2 and information bit 3 process redundancy is L2 respectively encoder 2 and encoder 2 are encoded into the second bit c ₁with the 3rd bit c ₂; , wherein L1>L2;

102, the first bit c coding in step 101 being obtained ₀, the second bit c ₁with the 3rd bit c ₂input respectively in 8 ary quadrature amplitude device 8-QAM, respectively to the first bit c ₀, the second bit c ₁with the 3rd bit c ₂adopt UP-BP-BP planisphere split plot design to modulate, be then transferred to decoder;

103, according to the first bit c after the modulation receiving in step 102 ₀, the second bit c ₁with the 3rd bit c ₂, first by the first bit c after modulation ₀carry out soft demodulation, judge the first bit c ₀posterior probability _pif p=0, judges the first bit c ₀for interior ring, calculate the second bit c after modulation ₁with modulation after the 3rd bit c ₂bit log-likelihood ratio LLR, then pass to respectively the first bit c ₀, the second bit c ₁with the 3rd bit c ₂corresponding decoder Decode1, Decode2 and Decode3,

Wherein $\mathrm{LLR}=L\left(c\right)=\log \left(\frac{\mathrm{Pr}(c=0|r=(x,y))}{\mathrm{Pr}(c=1|r=(x,y))}\right),$

Wherein r represents the signal receiving, and r coordinate is (x, y), and c represents transmitted bit the second bit c ₁with the 3rd bit c ₂if p=1, judges the first bit c ₀for outer shroud, repeating step 103 decoding again, completes coded modulation.

Further, the mode that adopts multistage decoding MSD peace row decoding PDL to combine in step 103 is carried out decoding.

Further, in the bit log-likelihood ratio LLR Gaussian white noise channel in step 103, LLR is expressed as:

$L\left(c\right)=\log \left(\frac{{\underset{s\∈S_0}{\mathrm{\Σ}}e}^{\text{-}\frac{1}{{\mathrm{\δ}}^2}({(x-s_x)}^2+{(y-s_y)}^2)}}{{\underset{s\∈S_1}{\mathrm{\Σ}}e}^{-\frac{1}{{\mathrm{\δ}}^2}({(x-s_x)}^2+{(y-s_y)}^2)}}\right)$

Wherein S ₀and S ₁represent respectively the set of the point of bit position bit given in desirable constellation point 0 and 1; s _xand s _yrepresent two quadrature components in desirable coordinate points.δ ²it is the noise in baseband signal.

Advantage of the present invention and beneficial effect are as follows:

The present invention is aspect computation complexity, and the computation complexity of proposed scheme is traditional scheme 2/3.Aspect error-correcting performance, the scheme that not only proposed is compared with the traditional scheme that code check is identical with it, and the net coding gain (NCG) of proposed scheme is higher, and the error-correcting performance of proposed scheme is even better than the traditional scheme that code check is lower.In sum, coded modulation scheme proposed by the invention whole scheme after being combined with QC-LDPC code all can meet the requirement of optical communication system better at aspects such as spectrum efficiency, NCG and complexities.

Accompanying drawing explanation

Fig. 1 is traditional 8-QAM mapping mode

Fig. 2 is that the collection of traditional 8-QAM is cut apart

Fig. 3 is the parallel independent decoder of traditional 8-QAM scheme

Fig. 4 is the UP-BP-BP mixing partitioning scheme that the present invention proposes a plan

Fig. 5 is traditional 8-QAM mapping relations (left side) and mapping relations (right side) proposed by the invention

Fig. 6 is the encoder block diagram of scheme proposed by the invention

Fig. 7 is the decoder block diagram of scheme proposed by the invention

Fig. 8 is the amount of calculation contrast schematic diagram of traditional scheme and scheme proposed by the invention

Fig. 9 tests one: the traditional scheme performance comparison of scheme proposed by the invention and close code check

Figure 10 the present invention tests each scheme performance comparison figure

Figure 11 tests two: the traditional scheme performance comparison of scheme proposed by the invention and close code check

Figure 12 the present invention tests two each scheme performance comparison figure

Figure 13 is scheme proposed by the invention and RS (255,239) performance comparison figure

Table 1 is that the present invention tests QC-LDPC code pattern parameter in

Table 2 is that the present invention tests in one each scheme Performance Ratio

Table 3 is that the present invention tests QC-LDPC code pattern parameter in two

Table 4 is that the present invention tests in two each scheme Performance Ratio.

Embodiment

The invention will be further elaborated to provide the embodiment of an indefiniteness below in conjunction with accompanying drawing.

As shown in Figure 1, plant a kind of QC-LDPC code modulating method based on 8-QAM modulation system in optical communication system, it is characterized in that comprising the following steps:

101, the signal stream in optical communication system is divided into information bit 1, information bit 2 and information bit 3, the encoder 1 that is then L1 by information bit 1 through redundancy is encoded into the first bit c ₀, and information bit 2 and information bit 3 process redundancy is L2 respectively encoder 2 and encoder 2 are encoded into the second bit c ₁with the 3rd bit c ₂; , wherein L1>L2;

102, the first bit c coding in step 101 being obtained ₀, the second bit c ₁with the 3rd bit c ₂input respectively in 8 ary quadrature amplitude device 8-QAM, respectively to the first bit c ₀, the second bit c ₁with the 3rd bit c ₂adopt UP-BP-BP planisphere split plot design to modulate, be then transferred to decoder;

103, according to the first bit c after the modulation receiving in step 102 ₀, the second bit c ₁with the 3rd bit c ₂, first by the first bit c after modulation ₀carry out soft demodulation, judge the first bit c ₀posterior probability p, if p=0 judges the first bit c ₀for interior ring, calculate the second bit c after modulation ₁with modulation after the 3rd bit c ₂bit log-likelihood ratio LLR, then pass to respectively the first bit c ₀, the second bit c ₁with the 3rd bit c ₂corresponding decoder Decode1, Decode2 and Decode3,

Wherein $\mathrm{LLR}=L\left(c\right)=\log \left(\frac{\mathrm{Pr}(c=0|r=(x,y))}{\mathrm{Pr}(c=1|r=(x,y))}\right),$

Wherein, the signal that representative receives, r coordinate is (x, y), c represents transmitted bit the second bit c ₁with the 3rd bit c ₂if p=1, judges the first bit c ₀for outer shroud, repeating step 103 decoding again, completes coded modulation.

The present invention is two stage of the one QC-LDPC coded modulation scheme based on 8-QAM modulation system in optical communication system, comprising:

1. in the method for various increase power system capacities, M-QAM is a kind of the jointly control amplitude of sinusoidal carrier and modulation system of phase place.8-QAM wherein becomes the popular modulation scheme of optical communication of future generation.In the possible signal constellation (in digital modulation) figure of many kinds, a kind of generally acknowledged best 8-QAM signal constellation (in digital modulation) figure and mapping mode are shown in Fig. 1, because it is for the desired power minimum of the minimum range between given signaling point.In Fig. 1 8-QAM signal formed by the signaling point of two amplitudes and signaling point between minimum range be all 2A (coordinate of each signal is by A normalization).A symbol in 8-QAM is made as to c ₀c ₁c ₂number.The constellation point partition mechanism of 8-QAM as shown in Figure 2, because the division of constellation point each time does not all change minimum euclidean distance, the BP collection partitioning scheme that the best 8-QAM planisphere of therefore generally acknowledging adopts.In optical communication, in the time that 8-QAM is applied to coded modulation scheme, in general, adopt Bit Interleave coded modulation (Bit-interweave Coding Modulation, BICM) scheme.In order to contrast with scheme proposed by the invention, BICM scheme is referred to as traditional scheme by unification, or parallel independent decoding scheme.In traditional scheme, three bits adopt same pattern to encode.At receiving terminal, adopt PDL decoding scheme, the process of three bit demodulation and decoding is parallel and independently.As shown in Figure 3.Demod c ₀represent bit c ₀soft demodulating process, LLR (c ₀) expression c ₀bit log-likelihood ratio (Log-likelihood Ratio, LLR).Bit c ₁c ₂in like manner.In traditional scheme, LLR passes to corresponding decoder after being calculated respectively by three demodulators.The LLR of a certain bit c is defined as:

$L\left(c\right)=\log \left(\frac{\mathrm{Pr}(c=0|r=(x,y))}{\mathrm{Pr}(c=1|r=(x,y))}\right)---\left(1\right)$

Wherein r represents the signal receiving, and coordinate is (x, y).C is transmitted bit (in transmission symbol in K bit one), and supposes that all bits are all equiprobability transmission.

In Gaussian white noise channel, LLR can represent with following formula (2):

$L\left(c\right)=\log \left(\frac{{\underset{s\∈S_0}{\mathrm{\Σ}}e}^{\text{-}\frac{1}{{\mathrm{\δ}}^2}({(x-s_x)}^2+{(y-s_y)}^2)}}{{\underset{s\∈S_1}{\mathrm{\Σ}}e}^{-\frac{1}{{\mathrm{\δ}}^2}({(x-s_x)}^2+{(y-s_y)}^2)}}\right)---\left(2\right)$

Wherein S ₀and S ₁represent respectively the set of the point of bit position bit given in desirable constellation point 0 and 1; s _xand s _yrepresent two quadrature components in desirable coordinate points.δ ²it is the noise in baseband signal.

In the present invention, in order to make full use of the feature of 8-QAM annular planisphere, as shown in fig. 1,8-QAM planisphere has 45 ° of QPSK constellation point that differ to be formed by stacking by two, and respectively on the different circle of two radiuses.Thus, the present invention proposes in a kind of new mapping relations, these three relations that bit is no longer equality, and 8-QAM planisphere is divided into two rings, and by first bit decision in symbol, it belongs to interior ring or outer shroud, as shown in Figure 4.From the theory of set-partition, to cut apart for the first time, the Euclidean distance of interior ring each point does not change, but the Euclidean distance between outer shroud obviously increases, and therefore ground floor can be cut apart to regard UP as and cut apart.Take interior ring as example, cut apart for the second time with cutting apart for the third time and all do not make Euclidean distance become large, can regard BP as and cut apart.Therefore, this scheme is UP-BP-BP partitioning scheme.If by mapping mode proposed by the invention and coded modulation scheme combination, coding and decoding mode all can change thereupon.Generally speaking, mapping mode proposed by the invention and the difference of traditional approach are exactly to take full advantage of the planisphere structure that 8-QAM is special, utilize first bit to distinguish interior ring and outer shroud, make the minimum euclidean distance that signal constellation (in digital modulation) figure is shown in become large, as shown in Figure 5.

2. in the scheme proposing in the present invention, three relations that bit is no longer equality in a 8-QAM symbol, c ₀judged result directly affect c ₁and c ₂, c in other words ₁and c ₂to c ₀degree of dependence very large.Given this,, if three identical coded systems that bit adopts, the performance of entirety will allow of no optimist.Be easy to expect, due to c ₀importance, strengthen the protection to it at encoding context, the pattern that selectivity is more excellent, such as the pattern of highly redundant degree.For the redundancy of balance whole system, c ₁and c ₂in same grade, can adopt the pattern that another kind of redundancy is lower.Adopt the encoder block diagram of not reciprocity protection as shown in Figure 6, dash area is c ₀encoder.

3. the present invention program's concrete decoding flow process as shown in Figure 7.First the posterior probability of first bit in compute sign, judges that it is 0 or 1, if 0, calculate c according to the mapping relations of interior ring ₁and c ₂lLR.If 1, be outer shroud.As seen from Figure 7, this kind of effective combination that decoded mode is two kinds of decoded modes in BCM.For c ₀and c ₁c ₂between judgement to belong to MSD be multistage decoding, to c ₁c ₂between judgement to belong to PDL be parallel decoded mode.Two kinds of modes combinations are farthest utilized to the feature of planisphere, effective compromise of the two kinds of decoded mode pluses and minuses of having got back.Generally speaking, traditional scheme, in the time of coding, is all consistent although adopt its code selections of No. three encoder, and scheme proposed by the invention is in the time of coding, by different pattern protection for 3 bits.When decoding, traditional scheme adopts the mode of three parallel decodings of bit, and in scheme proposed by the invention, first obtains the decode results of first bit, judges that this constellation point is at interior ring or outer shroud, then continues decoding.This decoded mode is effective combination of MSD decoding and PDL decoding in BCM.

4. the computation complexity analysis of scheme proposed by the invention

The present invention carrys out the complexity of two schemes of comparison from the calculating of LLR.In traditional scheme, the LLR of each bit can represent with following formula:

$L\left(c\right)=\log \left(\frac{{\underset{s\∈S_0}{\mathrm{\Σ}}e}^{\text{-}\frac{1}{{\mathrm{\δ}}^2}({(x-s_x)}^2+{(y-s_y)}^2)}}{{\underset{s\∈S_1}{\mathrm{\Σ}}e}^{-\frac{1}{{\mathrm{\δ}}^2}({(x-s_x)}^2+{(y-s_y)}^2)}}\right)---\left(3\right)$

S ₀and S ₁represent respectively the set of the point of bit position bit given in desirable constellation point 0 and 1.Owing to being 8 systems modulation, in each symbol, have three bits, each than peculiar 0 and 1 two kind may.Therefore in traditional scheme, in 8-QAM planisphere, there are 8 points, (3) S set in formula ₀s set ₁respectively get four points, therefore when the LLR value of a bit of every calculating, need 8 times computing, the computing that claims such combination in literary composition is a computing collection.Concentrate in such computing, rough calculating, needs 3 sub-additions, 3 multiplication, and 1 power operation.For a symbol of traditional algorithm, there are three bits, altogether need 24 computing collection.In scheme proposed by the invention, as shown in Figure 8.For bit c ₀operation need to carry out equally 8 computing collection.As known c ₀result after, two bits after this calculate according to the LLR value of QPSK, and for c ₁and c ₂, S set ₀s set ₁only have separately two points, that is to say S ₀∪ S ₁no longer 8 points, but 4 points.Therefore each bit only needs 4 computing collection.In proportion, calculation of complex is traditional scheme 2/3.Above analysis is only for the amount of calculation of a symbol.If analyze a frame, take code length as 5000 as example.Propose a plan 5000 × 8 computing collection of minimizing, mean, lacked the computing of 40,000 powers, 120,000 sub-addition computings, 120,000 multiplyings.The reduction of complexity or considerable.As shown in Figure 8, in figure from providing intuitively the required addition number of times of soft demodulation.

5. the performance evaluation of scheme associating finite field QC-LDPC code proposed by the invention

In error control, using LDPC code is to reach at present the most potential coding techniques of shannon limit.In general structurized coded system can produce lower error floor, and this is most important for optical communication.And, adopt cyclic code and quasi-cyclic code can become easy by use shift register in the process of coding.Therefore by scheme proposed by the invention and the combination of two groups of QC-LDPC codes, in conjunction with after can be called QC-LDPC coded modulation scheme.In experiment, adopt two class QC-LDPC codes.Their performance reduces along with the increase of code check.In traditional parallel decoding scheme, three bits all adopt same pattern coding.In scheme proposed by the invention due to c ₁and c ₂value and c ₀judged result have much relations, so the present invention adopts not reciprocity protection (Unequal protection, UEP) coded system, and by c ₀locational bit is strengthened the protection of coding.For the code check of balance whole system, c ₁and c ₂use the higher pattern of code check.In order fully to verify the validity of scheme proposed by the invention.The present invention has carried out two experiments, and in order to have comparativity and to keep unified, three patterns in same experiment all adopt same make, and code length is consistent.For code 1, code check is R1, and the code check of code 2 is R2.Code 3 is R3.For coded modulation scheme proposed by the invention, by code 1 for the protection of c ₀, code 3 is for the protection of c ₁and c ₂.Relation between them is, R ₁<R ₂<R ₃.This relation is description code 1 best performance simultaneously, and secondly, the poorest is code 3 to code 2.And R ₁+ 2R ₃=3R ₂, this relational expression means, the coded modulation scheme of proposition code check is generally with to adopt the traditional scheme of code 2 consistent.According to this principle, following two experiments are carried out.

Experiment one:

In experiment one, adopt based on finite field and add the QC-LDPC code that group constructs.The code length of 3 patterns is consistent, and other parameters are as shown in table 1.Scheme proposed by the invention is combined utilization code 1 and code 3, and its code check is respectively 0.89 and 0.924 pattern, and the code check after it is comprehensive is 0.912, very approaching with the code check 0.918 of code 2.Therefore first the performance that proposes a plan and adopt separately the traditional scheme of code 2 will be analyzed.

In experiment one, the system frequency efficiency of scheme proposed by the invention is 2.74bit/symbol, and the error rate is 10 ^-7in time, is compared with uncoded 8-QAM system, has brought the NCG of 4.85dB.As can be known from Fig. 9, although in low signal-to-noise ratio region, the performance of scheme proposed by the invention a little less than, in the time that EbN0 is greater than 7.75dB, the performance of scheme proposed by the invention starts to be better than traditional scheme, and has brought obvious coding gain.The error rate is 10 ^-7time, the traditional scheme that scheme proposed by the invention is close compared with code check has brought the NCG of 0.2dB.Moreover, can and adopt the traditional scheme of other code check patterns to compare by scheme proposed by the invention, be about to three kinds of codes and be all used in respectively in traditional scheme.Specific performance shows as shown in figure 10.In experiment one, the code check of three kinds of codes is very approaching, and code 1 and code 3 code checks differ only has 3.68%.Therefore in simulation result, three kinds of codes are little at the performance difference of traditional scheme, and performance curve is even overlapping.But still can find out, propose a plan and keeping clear superiority in high s/n ratio region always.In table 2, be given in 10 ^-6the performance parameter of each scheme.Be 10 in the error rate ^-6time, propose a plan and other three kinds of schemes have all been brought to the NCG of 0.12dB left and right.It is worth mentioning that, the performance of scheme proposed by the invention has been better than the lower traditional scheme of code check.

Experiment two:

In experiment two, adopt the QC-LDPC code of constructing based on finite field subgroup, and according to the structure of the subgroup in GF (73) territory one group of QC-LDPC code.Equally, first analyze the performance of two schemes with close code check, adopt propose a plan (code check after comprehensive is 0.881) of code 1 and code 3, and adopt the traditional scheme of code 2 (0.89).As shown in figure 11.

The system frequency efficiency of scheme proposed by the invention is 2.697bit/ symbol, is 10 in the error rate ^-7in time, is compared with uncoded 8-QAM system, has brought 5.45dBNCG.In low signal-to-noise ratio region, the performance of scheme proposed by the invention is slightly not enough, but in the time that EbN0 exceedes 6.8dB, the performance of scheme proposed by the invention starts to occur reversing, and shows obvious advantage after this.Be 10 in the error rate ^-7time, the traditional scheme multi-band that scheme proposed by the invention is close compared with code check has been carried out the net coding gain of 0.45dB.In addition, in order to fully demonstrate the performance of scheme proposed by the invention, these three kinds of patterns are all respectively used in traditional scheme.As can be known from Fig. 12, two stage coding modulation schemes proposed by the invention have been brought obvious coding gain.In table 4, provide the error rate 10 ^-6time, the code check of each scheme and the NCG situation of bringing thereof.Experiment two phenomenons identical with experiment one of same discovery from Figure 12 and in table 4, that is exactly that scheme performance proposed by the invention is not only better than the approaching scheme of code check, is even better than in some situation the traditional scheme that code check is lower.In addition, in experiment two, the code check difference of code 1 and code 3 is slightly large, is 5.89%.Therefore, in experiment two, brought more net coding gain.

6. the combination property analysis of scheme proposed by the invention

Generally speaking, above-mentioned two QC-LDPC codes that experiment is used, code length is different, make difference, performance difference, be combined with coded modulation scheme proposed by the invention, all can be more excellent than the traditional scheme performance with close code check in bit error rate, be even better than the traditional scheme that code check is lower.The broad applicability proposing a plan can be described.And find, when selecting, the code check difference of code word is larger, and scheme proposed by the invention can bring coding gain more.

Next the requirement whether scheme proposed by the invention meets high speed optical communication system is discussed.First the transmission rate that scheme proposed by the invention can reach.Suppose that symbol processing speed is R _sif the single channel speed that adopts the system of palarization multiplexing (Polarization Division Multiplexing, PDM) to reach is 2 × R _s× Rate × logM, wherein Rate is code check, logM is the bit number in each symbol.The character rate R that current level of hardware can be realized _scan reach 40Giga-Symbol/s (GS/s).If use coded modulation scheme proposed by the invention, code check Rate is that 0.918, logM is 3, and single channel speed can reach the speed of 220G/S.In addition, the error floor of 3 LDPC codes in experiment one is verified, all lower than 10 ^-18.Therefore the performance curve in experiment one can be obtained to the estimated value of performance under high s/n ratio according to data of literatures.Then adopt the scheme of RS (255,239) to compare the LDPC code modulation system in experiment one and BPSK modulation.As shown in figure 13.Can see, scheme proposed by the invention is 10 ^-10near performance just starts to be better than RS code, 10 ^-15bring the NCG of 0.65dB.The spectrum efficiency that it is emphasized that scheme proposed by the invention is 2.74bit/symbol, and the RS code plan spectrum efficiency of BPSK modulation is 0.937bit/symbol.That is to say in frequency efficiency Senior Three and doubly in the situation that, still can bring coding gain.In addition, by simulating, verifying, it is 5 times that the present invention tests the QC-LDPC code iterations adopting, and compared with the pattern of other general iteration more than ten time, saves more time and amount of calculation.

In sum, coded modulation scheme proposed by the invention all can meet the requirement of high speed optical communication system better in aspect performances such as net coding gain, frequency efficiency, iterations and complexities.

?	Code length N	Information bit K	Code check R (dB)
				Code 1	5256	4679	0.890
Code 2	5256	4823	0.918
				Code 3	5256	4859	0.924

Table 1 the present invention tests QC-LDPC code pattern parameter in

Table 2 the present invention tests in one each scheme Performance Ratio

?	Code length N	Information bit K	Code check R
				Code 1	2592	2236	0.863
Code 2	2592	2307	0.890
				Code 3	2592	2378	0.917

? table 3 the present invention tests QC-LDPC code pattern parameter in two

Coded modulation scheme	Code check	At 10-6 net coding gain
			Parallel decoding+code 1	86.3％	4.65
Parallel decoding+code 2	89.0％	4.55
			Parallel decoding+code 3	91.7％	4.25
Propose a plan	88.1％	5.10

Table 4 the present invention tests in two each scheme Performance Ratio

These embodiment are interpreted as being only not used in and limiting the scope of the invention for the present invention is described above.After having read the content of record of the present invention, technical staff can make various changes or modifications the present invention, and these equivalences change and modification falls into the inventive method claim limited range equally.

Claims (3)

1. a kind of QC-LDPC code modulating method based on 8-QAM modulation system in optical communication system, is characterized in that comprising the following steps:

101, the signal stream in optical communication system is divided into information bit 1, information bit 2 and information bit 3, the encoder 1 that is then L1 by information bit 1 through redundancy is encoded into the first bit c ₀, and information bit 2 and information bit 3 process redundancy is L2 respectively encoder 2 and encoder 2 are encoded into the second bit c ₁with the 3rd bit c ₂; , wherein L1>L2;

102, the first bit c coding in step 101 being obtained ₀, the second bit c ₁with the 3rd bit c ₂input respectively in 8 ary quadrature amplitude device 8-QAM, respectively to the first bit c ₀, the second bit c ₁with the 3rd bit c ₂adopt UP-BP-BP planisphere split plot design to modulate, be then transferred to decoder;

103, according to the first bit c after the modulation receiving in step 102 ₀, the second bit c ₁with the 3rd bit c ₂, first by the first bit c after modulation ₀carry out soft demodulation, judge the first bit c ₀posterior probability p, if p=0 judges the first bit c ₀for interior ring, calculate the second bit c after modulation ₁with modulation after the 3rd bit c ₂bit log-likelihood ratio LLR, then pass to respectively the first bit c ₀, the second bit c ₁with the 3rd bit c ₂corresponding decoder Decode1, Decode2 and Decode3,

Wherein $\mathrm{LLR}=L\left(c\right)=\log \left(\frac{\mathrm{Pr}(r=0|r=(x,y))}{\mathrm{Pr}(c=1|r=(x,y))}\right)$

Wherein r represents the signal receiving, and r coordinate is (x, y), and c represents transmitted bit the second bit c ₁with the 3rd bit c ₂if p=1, judges the first bit c ₀for outer shroud, repeating step 103 decoding again, completes coded modulation.

2. a kind of QC-LDPC code modulating method based on 8-QAM modulation system in optical communication system according to claim 1, is characterized in that: the mode that adopts multistage decoding MSD peace row decoding PDL to combine in step 103 is carried out decoding.

3. a kind of QC-LDPC code modulating method based on 8-QAM modulation system in optical communication system according to claim 1, is characterized in that: in the bit log-likelihood ratio LLR Gaussian white noise channel in step 103, LLR is expressed as:

$L\left(c\right)=\log \left(\frac{\underset{s\&Element;S_0}{\mathrm{\&Sigma;}}{e}^{-\frac{1}{{\mathrm{\&delta;}}^2}({(x-s_x)}^2+{(y-s_y)}^2)}}{\underset{s\&Element;S_1}{\mathrm{\&Sigma;}}{e}^{-\frac{1}{{\mathrm{\&delta;}}^2}({(x-s_x)}^2+{(y-s_y)}^2)}}\right)$

Wherein S ₀and S ₁represent respectively the set of the point of bit position bit given in desirable constellation point 0 and 1; s _xand s _yrepresent two quadrature components in desirable coordinate points.δ ²it is the noise in baseband signal.