CN104702377A - LDPC soft decoding method based on frame synchronizing information correction - Google Patents
LDPC soft decoding method based on frame synchronizing information correction Download PDFInfo
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- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
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Abstract
Provided is an LDPC soft decoding method based on frame synchronizing information correction. According to the feature and the frame head length of an LDPC code, a frame head is added to non-coded data after grouping at an emitting end, and an original data frame is obtained. According to the LDPC code feature, an original data frame is subjected to coding. Coded data are subjected to modulation. At a receiving end, received signals are subjected to demodulation, and initial soft information is obtained synchronously. The soft information confidence coefficient corresponding to the frame head in the initial soft information is set to be maximum and is input to an LDPC soft decoding module for soft decoding, and in each iteration process, the middle soft information corresponding to the frame head data is adjusted to the most-credible state. Decoded data are subjected to frame decoding, and estimated data are obtained. The frame synchronizing information is used for carrying out correcting on LDPC soft decoding, the using rate of frame head information is improved, the operation complexity is lowered, the operation process can well be in the right direction, and the bit error rate can be lowered to a certain degree.
Description
Technical field
The invention belongs to the field of channel coding in digital communication, relate to a kind of LDPC soft decoding method based on frame synchronization information correction.
Background technology
1, chnnel coding
Digital signal in transmitting procedure because the impact being subject to interchannel noise and interference is easily erroneously received judgement.Adopt balanced way can correct the intersymbol interference caused by multiplier interference, the impact of addition interference then needs to solve by other ways.If after choose reasonable modulation system, demodulation method and transmitted power, still addition interference declining to a great extent to demodulation performance cannot be resisted, just should consider to adopt error-control technique.
Error-control technique mainly comprises following four kinds: (1) auto repeat require; (2) forward error correction; (3) feedback check; (4) error detection is deleted.This several technology can be combined.Except (3) plant except, its common ground be all in receiving terminal identification with or without error code.Because information symbol sequence is a kind of random sequence, receiving terminal cannot predict the value of code element, and also None-identified is wherein with or without error code.So need to increase some error control code elements in information symbol sequence at transmitting terminal, they are called supervise code element.Have between these supervise code element and information code elements and determine relation, such as certain functional relation, make receiving terminal likely utilize this relation to find or correct the error code that may exist.
Error control coding is often called error correction coding.Different coding methods, has different error detections or error correcting capability.In theory, error control reduces message data rate for cost to improve transmission reliability, and in general, the cost paid is larger, and the wrong ability of inspection (entangling) is stronger.All error correcting codes are all based on a common general principle: redundancy be added in information, so that information of correcting contingent mistake in storage and transmission.Basic form is, redundant symbol is attached to after information symbol and obtains coded sequence or code word.This code is called systematic code.Different according to the mode that redundancy is added in information, error correction coding is divided into two classes: block code and convolution code.These two kinds of encoding schemes all obtain practical application.From in history, people prefer by convolution code, and reason is that it can use floppy disk submissions, and block code is then considered to use efficient Soft decision decoding always for many years.But about theory and the reality of linear block codes Soft decision decoding algorithm, all obtain in recent years and develop on a large scale very much, this contributes to eliminating people's traditional concept on this problem.And best error correction coding known today is long non-rule low density parity check code.
2, low density parity check code (LDPC:Low Density Parity Check Code)
1962, Gallager gave the block code and two kinds of iteration probability decoding algorithms that a class is called low density parity check code.Subsequently, the probability decoding algorithm of Gallager is expanded to more generally situation by Tanner, replaces simple single-parity check equation group to define parity check by subcode.Time more early, proved that the minimum range of LDPC code is with code length linear growth, error correcting capability is suitable with minimum range, and the complexity of decoding algorithm is almost linear.
Research shows, LDPC code can close to shannon limit as turbo code.When block length is very large, the performance of irregular LDPC codes is better than the turbo code with approximate length and code check.Regular LDPC code is linear (N, K) code, and the columns and rows weight of check matrix H is respectively J and K, J and K is all much smaller than code length N, and therefore LDPC code has very sparse check matrix.If select the Hamming weight of columns and rows in H according to certain uneven distribution, just irregular LDPC codes can be obtained.
3, the BP decoding algorithm of LDPC code
Belief propagation (BP:Belief Propagation) decoding algorithm is a kind of iterative decoding algorithm, and this algorithm takes full advantage of the information transmission between variable node and check-node.Each iteration cycle, BP algorithm comprises two parts process: variable node process and code check node processing.For variable node, in each iteration cycle, variable node receives information from the check-node be attached thereto, and then is returned to check-node.Similar, for check-node, in each iteration cycle, check-node receives information from the variable node be attached thereto, and is then being returned to check-node.Last variable node is adjudicated according to the information collected.If each variable node or check-node to be regarded as a processor, the process of so all nodes can be carried out simultaneously.Therefore the parallel organization structure high speed decoder of LDPC code can be utilized.
BP decoding algorithm can be divided into probability belief propagation algorithm and log-likelihood ratio belief propagation algorithm.The essence of two kinds of algorithms is the same, and just the form of expression of message is different.The former message represents with Probability Forms.The message of the latter's algorithm then represents with log-likelihood ratio.On the basis of these two kinds of decoding algorithms, follow-up study personnel propose and much improve BP decoding algorithm, if minimum-sum algorithm etc. is all reach by the Message Transmission formula in innovatory algorithm the object reducing computation complexity or improving performance.
Summary of the invention
For improving the performance of prior art, the present invention aims to provide a kind of LDPC soft decoding method based on frame synchronization information correction, the method can significantly reduce computing and hardware complexity, and improves system demodulation performance performance by mistake, thus effectively increases the reliability of communication system.
For realizing above-mentioned technique effect, the present invention is achieved through the following technical solutions:
Based on a LDPC soft decoding method for frame synchronization information correction, it is characterized in that, comprise the following steps:
Step 1) is at transmitting terminal, and selected by the characteristic sum of selected LDPC code, the length of frame head, divides into groups to uncoded data, obtain grouped data;
Step 2) add described selected frame head for described grouped data and obtain initial data frame;
Step 3), according to the feature of selected LDPC code, is encoded to described initial data frame, is obtained coded data;
Step 4) is modulated described coded data;
Step 5), at receiving terminal, is carried out solution mediation simultaneous operation to the received signal and is obtained initial soft information;
The confidence level of Soft Inform ation corresponding for the frame head in described initial soft information is set to maximum by step 6);
Soft Inform ation after the adjustment that described step 6) obtains by step 7) inputs in the soft decoder module of LDPC and carries out soft decoding, obtains decoded data;
Step 8) carries out the operation of solution frame to described decoded data, obtains the data estimated.
Further, described LDPC code is systematic code.
Further, described initial soft information is finely tuned, Soft Inform ation corresponding for frame head data is set to the most believablely determine state.
Further, the soft decoder module of described LDPC is in the process of work, and the middle Soft Inform ation corresponding in given step adjustment frame head data determines state to the most believable.
Compared with prior art, beneficial effect of the present invention is as follows:
1) improve the utilance of frame originating point information
In existing scheme, frame originating point information is only for synchronously; And the present invention utilizes frame synchronization information to revise the soft decoding of LDPC, thus improve the utilance of frame originating point information, also to a certain degree improve effective code check.
2) computational complexity is reduced
By introducing frame synchronization information, iterative process being revised, effectively can reduce computational complexity; Simulation result shows, the present invention significantly can reduce the maximum operation times under target error rate when large signal to noise ratio.And along with the reduction of computational complexity, the design of the hardware such as circuit area and channel frequency index all has greater flexibility.
3) demodulation performance of system is improved
Introduce the frame synchronization information determined, be conducive to calculating process and carry out towards correct direction, simulation result shows, under little signal to noise ratio condition, the present invention to a certain degree can reduce the error rate.
Above-mentioned explanation is only the general introduction of technical solution of the present invention, in order to better understand technological means of the present invention, and can be implemented according to the content of specification, being modified to embodiment and coordinating accompanying drawing to be described in detail as follows below with sum-product algorithm.The specific embodiment of the present invention is provided in detail by following examples and accompanying drawing thereof.
Accompanying drawing explanation
Accompanying drawing described herein is used to provide a further understanding of the present invention, and form a application's part, schematic description and description of the present invention, for explaining the present invention, does not form inappropriate limitation of the present invention.In the accompanying drawings:
Fig. 1 is former algorithm and innovatory algorithm maximum iteration time comparison diagram under large signal to noise ratio.
Fig. 2 is former algorithm and innovatory algorithm error rate comparison diagram under little signal to noise ratio.
Embodiment
Below in conjunction with embodiment, describe the present invention in detail.Illustration is used to provide a further understanding of the present invention herein, and form a application's part, schematic description and description of the present invention, for explaining the present invention, does not form inappropriate limitation of the present invention.
Embodiment 1:
Based on a LDPC soft decoding method for frame synchronization information correction, comprise the following steps:
Step 1) is at transmitting terminal, and selected by the characteristic sum of selected LDPC code, the length of frame head, divides into groups to uncoded data, obtain grouped data;
Step 2) add described selected frame head for described grouped data and obtain initial data frame;
Step 3), according to the feature of selected LDPC code, is encoded to described initial data frame, is obtained coded data;
Step 4) is modulated described coded data;
Step 5), at receiving terminal, is carried out solution mediation simultaneous operation to the received signal and is obtained initial soft information;
The confidence level of Soft Inform ation corresponding for the frame head in described initial soft information is set to maximum by step 6);
Soft Inform ation after the adjustment that described step 6) obtains by step 7) inputs in the soft decoder module of LDPC and carries out soft decoding, obtains decoded data;
Step 8) carries out the operation of solution frame to described decoded data, obtains the data estimated.
According to the foundation of technique scheme, the LDPC soft decoding method embody rule based on frame synchronization information correction of the present embodiment is as follows:
1, initial sum-product algorithm decoding flow process
Initialization: setting maximum iteration time I, primary iteration number of times
, calculate the probability likelihood ratio message that variable node comes from channel, to each variable node
and the check-node be adjacent
, the initial message that setting variable node transmits to check-node:
（1）
Step 1:
A () horizontal direction, to all check-node j and the variable node be adjacent
.During the l time iteration, calculate the message that variable node is transmitted to check-node:
（2）
B () vertical direction, to all node variables
with the check-node be adjacent
.During the l time iteration, calculation check node is transmitted to the message of variable node:
（3）
Step 2: judgement, and determine whether should finishing iteration decode procedure:
A () adjudicates, if
, then
.Thus obtain the output codons after adjudicating.
If (b)
or
, terminate decoding, go to step 3, otherwise go to step 1.
Step 3: export decode results.
2, based on the sum produce algorithm decoding flow process of frame synchronization information correction
Initialization: setting maximum iteration time I, primary iteration number of times
, calculate the probability likelihood ratio message that variable node comes from channel, to each variable node
and the check-node be adjacent
, the initial message transmitted to check-node according to (1) formula setting variable node:
（4）
And the initial soft information that code element in frame head " 1 " is corresponding is set to-T, the initial soft information of code element " 0 " correspondence is set to T.
Step 1:
A () horizontal direction, to all check-node j and the variable node be adjacent
.During the l time iteration, calculate the message that variable node is transmitted to check-node:
（5）
B () vertical direction, to all node variables
with the check-node be adjacent
.During the l time iteration, calculation check node is transmitted to the message of variable node:
（6）
C () utilizes frame synchronization information to revise two message matrix Q and R.Suppose that framing bit is synchronously effective, so frame head data will be determined, so need not upgrade the confidence level of corresponding message in the process of each iteration.The strategy taked is that the message of fixing aforementioned two matrix respective column is constant, so just can avoid the reduction of effective information and can continue to export update information to other nodes.If a certain position is defined as 0 in frame head, so message is fixed as T, if a certain position is 1, then message is fixed as-T.
Step 2: judgement, and determine whether should finishing iteration decode procedure:
A () adjudicates, if
, then
.Thus obtain the output codons after adjudicating.
If (b)
or
, terminate decoding, go to step 3, otherwise go to step 1.
Step 3: export decode results.
3, based on the sum produce algorithm performance evaluation of frame synchronization information correction
As shown in Figure 1, when signal to noise ratio is 3dB, the maximum iteration time of former algorithm is 67 times, and the maximum iteration time of innovatory algorithm is 26 times.Aforementioned algorism improves the average computation convergence rate of former algorithm, for the multiplexing of hardware resource provides certain theoretical foundation.
As shown in Figure 2, when signal to noise ratio is less than 3dB, innovatory algorithm reduces the error rate.Improve the reliability of communication system.
By introducing frame synchronization information, iterative process being revised, effectively reducing computational complexity.And along with the reduction of computational complexity, the design of the hardware such as circuit area and channel frequency index all has greater flexibility.Introduce the frame synchronization information determined, be conducive to calculating process and carry out towards correct direction, can the error rate be reduced.
Claims (4)
1., based on a LDPC soft decoding method for frame synchronization information correction, it is characterized in that, comprise the following steps:
Step 1) is at transmitting terminal, and selected by the characteristic sum of selected LDPC code, the length of frame head, divides into groups to uncoded data, obtain grouped data;
Step 2) be the described selected frame head of described grouped data interpolation, obtain initial data frame;
Step 3), according to the feature of described selected LDPC code, is encoded to described initial data frame, is obtained coded data;
Step 4) is modulated described coded data;
Step 5), at receiving terminal, is carried out solution mediation simultaneous operation to the received signal and is obtained initial soft information;
The confidence level of Soft Inform ation corresponding for the frame head in described initial soft information is set to maximum by step 6);
Soft Inform ation after the adjustment that described step 6) obtains by step 7) inputs in the soft decoder module of LDPC and carries out soft decoding, obtains decoded data;
Step 8) carries out the operation of solution frame to described decoded data, obtains the data estimated.
2. a kind of LDPC soft decoding method based on frame synchronization information correction according to claim 1, is characterized in that: selected LDPC code is systematic code.
3. a kind of LDPC soft decoding method based on frame synchronization information correction according to claim 1, is characterized in that: finely tune described initial soft information, is set to by Soft Inform ation corresponding for frame head data the most believablely determine state.
4. a kind of LDPC soft decoding method based on frame synchronization information correction according to claim 1, it is characterized in that: the soft decoder module of described LDPC, in the process of work, must adjust middle Soft Inform ation corresponding to frame head data in given step and determine state to the most believable.
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| CN101217355A (en) * | 2008-01-11 | 2008-07-09 | 清华大学 | An iterative timing synchronous method based on low density parity check coding soft decision information |
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| CN101217355A (en) * | 2008-01-11 | 2008-07-09 | 清华大学 | An iterative timing synchronous method based on low density parity check coding soft decision information |
| CN101562456A (en) * | 2009-06-03 | 2009-10-21 | 华北电力大学（保定） | Code assisting frame synchronizing method based on soft decoding information of low-density parity check codes |
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