CN110266322B - Iterative decoding method for very high frequency data exchange system - Google Patents

Iterative decoding method for very high frequency data exchange system Download PDF

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CN110266322B
CN110266322B CN201910552357.3A CN201910552357A CN110266322B CN 110266322 B CN110266322 B CN 110266322B CN 201910552357 A CN201910552357 A CN 201910552357A CN 110266322 B CN110266322 B CN 110266322B
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likelihood ratio
probability log
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CN110266322A (en
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周昊苏
刘柳
周雷
郭颖
左惠文
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Shanghai Spaceflight Institute of TT&C and Telecommunication
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/03—Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words
    • H03M13/05—Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words using block codes, i.e. a predetermined number of check bits joined to a predetermined number of information bits
    • H03M13/11—Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words using block codes, i.e. a predetermined number of check bits joined to a predetermined number of information bits using multiple parity bits
    • H03M13/1102—Codes on graphs and decoding on graphs, e.g. low-density parity check [LDPC] codes
    • H03M13/1105—Decoding
    • H03M13/1111—Soft-decision decoding, e.g. by means of message passing or belief propagation algorithms
    • H03M13/1125—Soft-decision decoding, e.g. by means of message passing or belief propagation algorithms using different domains for check node and bit node processing, wherein the different domains include probabilities, likelihood ratios, likelihood differences, log-likelihood ratios or log-likelihood difference pairs
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/27—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes using interleaving techniques
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/29—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes combining two or more codes or code structures, e.g. product codes, generalised product codes, concatenated codes, inner and outer codes
    • H03M13/2948—Iterative decoding

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Abstract

The invention discloses an iterative decoding method of a very high frequency data exchange system, which comprises the following steps: a posterior probability log-likelihood ratio sequence l according to the obtained information sequence a 2 De-interleaving and judging to obtain information estimation sequence
Figure DDA0002104882320000011
The invention has the technical characteristics of strong compatibility between the coding rate and the modulation mode and excellent decoding performance.

Description

Iterative decoding method for very high frequency data exchange system
Technical Field
The invention belongs to the technical field of ship satellite communication, and particularly relates to an iterative decoding method of a very high frequency data exchange system.
Background
With the great success of the application of Automatic Identification Systems (AIS) for ships and the continuous development of AIS functions, the network load of AIS is getting larger and larger to impair the initial concept of AIS collision avoidance. In order to guarantee the performance of the AIS, the international telecommunication union WP5B group and the international navigation aid and navigation association E-NAV group hold a conference to discuss the technical scheme and the development direction of the next generation AIS, namely a very high frequency data exchange system (VDES). On the basis of ensuring the highest priority of the AIS, the international maritime organization, the international telecommunication union and other organizations separate the application-specific messages in the AIS and allocate new channels (CH 2027 and CH 2028) and modulation schemes (QPSK) for the application-specific messages. Meanwhile, a new VHF band (CH 24, CH25, CH26, CH84, CH85, and CH 86) and a new modulation scheme (QPSK, 8PSK, 16QAM, 16APSK, etc.) are allocated to the VDE, and a forward error correction coding technique, a continuous phase modulation spread spectrum technique, etc. are introduced into the VDE.
The modulation mode diversification (MPSK/MQAM/MAPSK modulation) brings a new problem to the decoding work of forward error correction coding, and at present, no unified solution exists.
Disclosure of Invention
The technical purpose of the invention is to provide an iterative decoding method of a very high frequency data exchange system, which has the technical characteristics of strong compatibility of coding rate and modulation mode and excellent decoding performance.
In order to solve the problems, the technical scheme of the invention is as follows:
the invention provides an iterative decoding method of a very high frequency data exchange system, which comprises the following steps:
s1: the prior probability log likelihood ratio sequence l in,a 、
Figure GDA0003985646730000011
Sending the received signal sequence r into a modulation inverse mapping module, combining the forward error correction coding rate with the system number of the multi-system modulation code element, and calculating the posterior probability log-likelihood ratio sequence l out,a 、
Figure GDA0003985646730000021
And
Figure GDA0003985646730000022
s2: the posterior probability log-likelihood ratio sequence l out,a And
Figure GDA0003985646730000023
sending the information sequence a into a first BCJR decoder, and simultaneously sending a priori probability log-likelihood ratio sequence l of the information sequence a in,a Inputting the first BCJR decoder to obtain a posterior probability log-likelihood ratio sequence l of the information sequence a 1 Subtracting the prior probability log-likelihood ratio sequence l in,a Obtaining the sequence l out,1 While obtaining the sequence
Figure GDA0003985646730000024
S3: for the sequence l out,1 Interweaving to obtain sequence l in,2 Then the sequence l is added in,2 And a posteriori probability log-likelihood ratio sequence
Figure GDA0003985646730000025
Sending the data to a second BCJR decoder to obtain a posterior probability log-likelihood ratio sequence l of the information sequence a 2 Sequence of subtractionColumn l in,2 To obtain the sequence l out,2 To the sequence l out,2 Performing inverse interleaving to obtain a sequence l in,1 While obtaining the sequence
Figure GDA0003985646730000026
S4: judging whether iteration is carried out, if so, repeating S1-S3 to carry out preset corresponding times of iteration;
s5: according to the posterior probability log-likelihood ratio sequence l of the information sequence a obtained after the iteration of S3 or S4 2 De-interleaving and judging to obtain information estimation sequence
Figure GDA0003985646730000027
Further, in the iterative decoding method of the vhf data exchange system, the S1 includes:
s11: a priori probability log-likelihood ratio sequence
Figure GDA0003985646730000028
Figure GDA0003985646730000029
And
Figure GDA00039856467300000210
performing digital conversion according to the system number of 16QAM modulation symbols
Figure GDA00039856467300000211
Figure GDA00039856467300000212
And
Figure GDA00039856467300000213
s12: log-likelihood ratio sequence based on prior probability
Figure GDA00039856467300000214
Figure GDA00039856467300000215
Figure GDA00039856467300000216
And calculating the posterior probability log-likelihood ratio sequence of the 16QAM modulation code element by the received signal sequence r
Figure GDA00039856467300000217
Figure GDA0003985646730000031
And
Figure GDA0003985646730000032
s13: posterior probability log-likelihood ratio sequence
Figure GDA0003985646730000033
Figure GDA0003985646730000034
And
Figure GDA0003985646730000035
conversion to digital according to the carry of 16QAM modulation symbols
Figure GDA0003985646730000036
And
Figure GDA0003985646730000037
further, in the iterative decoding method of the vhf data exchange system, the S2 includes:
s21: forward iteration for first BCJR decoder
Figure GDA0003985646730000038
And backward iteration
Figure GDA0003985646730000039
Carrying out initialization;
s22: the sequence l out,a And
Figure GDA00039856467300000310
sending the data into a first BCJR decoder, and simultaneously sending a prior probability log-likelihood ratio sequence l of the information sequence a in,a Inputting a first BCJR decoder;
s23: calculate each time n and each state
Figure GDA00039856467300000311
Corresponding forward iteration
Figure GDA00039856467300000312
And backward iteration
Figure GDA00039856467300000313
S24: by using
Figure GDA00039856467300000314
And a probability distribution function for calculating a posterior probability log-likelihood ratio l 1 And
Figure GDA00039856467300000315
s25: posterior probability log-likelihood ratio sequence l of information sequence a 1 Subtracting a sequence of prior probability log-likelihood ratios l in,a Obtaining the sequence l out,1 While obtaining the sequence
Figure GDA00039856467300000316
Further, in the iterative decoding method of the vhf data exchange system, the S3 includes:
s30: for the sequence l out,1 Interweaving to obtain sequence l in,2 ；
S31: forward iteration for second BCJR decoder
Figure GDA00039856467300000317
And backward iteration
Figure GDA00039856467300000318
Carrying out initialization;
s32: the sequence l in,2 And with
Figure GDA0003985646730000041
Sending to a second BCJR decoder to calculate each time n and each state
Figure GDA0003985646730000042
Corresponding forward iteration
Figure GDA0003985646730000043
And backward iteration
Figure GDA0003985646730000044
S33: by using
Figure GDA0003985646730000045
And a probability distribution function for calculating a posterior probability log-likelihood ratio l 2 And
Figure GDA0003985646730000046
s34: a posteriori probability log-likelihood ratio l for information sequence a 2 Subtracting a prior probability log-likelihood ratio sequence l in,2 Obtaining the sequence l out,2 To the sequence l out,2 De-interleaving to obtain a sequence l in,1 While obtaining the sequence
Figure GDA0003985646730000047
The invention obtains the posterior probability log-likelihood ratio sequence l of the information sequence a according to 2 De-interleaving and judging to obtain information estimation sequence
Figure GDA0003985646730000048
The invention has strong compatibility of coding rate and modulation mode and decoding performanceExcellent technical characteristics.
Drawings
FIG. 1 is a block diagram of a forward error correction encoder of a very high frequency data switching system;
FIG. 2 is a block diagram of a recursive systematic convolutional encoder;
FIG. 3 is a diagram of a structure of information transmission in a Gaussian white noise channel;
FIG. 4 is a factor graph of the joint posterior probability function P (a, c, u | r);
FIG. 5 is a graph of the n-time joint posterior probability function P (a, c) 1 ,c 2 ,c,u 1 ,u 2 Factor graph of r);
FIG. 6 is a third coding rate MPSK/MQAM/MAPSK modulation decoding structure diagram of the present invention;
FIG. 7 is a diagram of a modulation inverse mapping module;
FIG. 8 is a diagram of a transform module;
fig. 9 is an inverse transform block diagram.
Detailed Description
The iterative decoding method and the iterative decoder for a very high frequency data switching system according to the present invention will be described in detail with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following.
The invention provides an iterative decoding method of a very high frequency data exchange system, which takes one third of coding rate 16QAM modulation as an example and is characterized by comprising the following steps:
s1: the prior probability log likelihood ratio sequence l in,a 、
Figure GDA0003985646730000051
And the received signal sequence r is sent to a modulation inverse mapping module, and a posterior probability log-likelihood ratio sequence l is calculated by combining the forward error correction coding rate and the system number of the multi-system modulation code elements out,a 、
Figure GDA0003985646730000052
And
Figure GDA0003985646730000053
s2: the posterior probability log-likelihood ratio sequence l out,a And
Figure GDA0003985646730000054
sending the data into a first BCJR decoder, and simultaneously sending a prior probability log-likelihood ratio sequence l of the information sequence a in,a Inputting the first BCJR decoder to obtain a posterior probability log-likelihood ratio sequence l of the information sequence a 1 Subtracting the prior probability log-likelihood ratio sequence l in,a Obtaining the sequence l out,1 While obtaining the sequence
Figure GDA0003985646730000055
S3: for the sequence l out,1 Interweaving to obtain sequence l in,2 Then the sequence l is added in,2 And a posteriori probability log-likelihood ratio sequence
Figure GDA0003985646730000056
Sending the data to a second BCJR decoder to obtain a posterior probability log-likelihood ratio sequence l of the information sequence a 2 Subtracting the sequence l in,2 Obtaining the sequence l out,2 For sequence l out,2 Carrying out reverse interleaving processing to obtain a sequence l in,1 While obtaining the sequence
Figure GDA0003985646730000057
S4: judging whether iteration is carried out, if so, repeating S1-S3 to carry out iteration of preset corresponding times;
s5: according to the posterior probability log-likelihood ratio sequence l of the information sequence a obtained after the iteration of S3 or S4 2 De-interleaving and judging to obtain information estimation sequence
Figure GDA0003985646730000058
The invention further researches a factor graph and a BCJR algorithm and provides an iterative decoding method suitable for forward error correction coding of a VDES system.
In an embodiment of the iterative decoding method for a very high frequency data exchange system of the present invention, taking one third of the encoding rate 16QAM modulation as an example, the step S1 specifically includes the following steps:
s11: a priori probability log-likelihood ratio sequence
Figure GDA0003985646730000059
Figure GDA00039856467300000510
And
Figure GDA00039856467300000511
performing digital conversion according to the system number of 16QAM modulation symbols
Figure GDA00039856467300000512
Figure GDA0003985646730000061
And
Figure GDA0003985646730000062
s12: log-likelihood ratio sequence based on prior probability
Figure GDA0003985646730000063
Figure GDA0003985646730000064
Figure GDA00039856467300000619
And calculating the posterior probability log-likelihood ratio sequence of the 16QAM modulation code element by the received signal sequence r
Figure GDA0003985646730000065
Figure GDA0003985646730000066
And
Figure GDA0003985646730000067
s13: posterior probability log-likelihood ratio sequence
Figure GDA0003985646730000068
Figure GDA0003985646730000069
And
Figure GDA00039856467300000610
performing digital conversion according to the system number of 16QAM modulation symbols
Figure GDA00039856467300000611
And
Figure GDA00039856467300000612
in an embodiment of the iterative decoding method for a very high frequency data exchange system of the present invention, the one-third coding rate 16QAM modulation is taken as an example, and the step S2 specifically includes the following steps:
s21: forward iteration for first BCJR decoder
Figure GDA00039856467300000613
And backward iteration
Figure GDA00039856467300000614
Carrying out initialization;
s22: the sequence l out,a And
Figure GDA00039856467300000615
sending the data into a first BCJR decoder, and simultaneously sending a prior probability log-likelihood ratio sequence l of the information sequence a in,a Inputting a first BCJR decoder;
s23: calculate each time n and each state
Figure GDA00039856467300000616
Corresponding forward stackSubstitute for Chinese traditional medicine
Figure GDA00039856467300000617
And backward iteration
Figure GDA00039856467300000618
S24: by using
Figure GDA0003985646730000071
And a probability distribution function for calculating a posterior probability log-likelihood ratio l 1 And with
Figure GDA0003985646730000072
S25: posterior probability log-likelihood ratio sequence l of information sequence a 1 Subtracting a prior probability log-likelihood ratio sequence l in,a Obtaining the sequence l out,1 While obtaining the sequence
Figure GDA0003985646730000073
In an embodiment of the iterative decoding method for the vhf data exchange system of the present invention, a one-third coding rate 16QAM modulation is taken as an example, and the step S3 specifically includes the following steps:
s30: for the sequence l out,1 Interweaving to obtain sequence l in,2 ；
S31: forward iteration for second BCJR decoder
Figure GDA0003985646730000074
And backward iteration
Figure GDA0003985646730000075
Initializing;
s32: the sequence l in,2 And with
Figure GDA0003985646730000076
Sending to a second BCJR decoder to calculate each time n and each state
Figure GDA0003985646730000077
Corresponding forward iteration
Figure GDA0003985646730000078
And backward iteration
Figure GDA0003985646730000079
S33: by using
Figure GDA00039856467300000710
And probability distribution function, calculating posterior probability log-likelihood ratio 2 And with
Figure GDA00039856467300000711
S34: a posteriori probability log-likelihood ratio l for information sequence a 2 Subtracting a sequence of prior probability log-likelihood ratios l in,2 Obtaining the sequence l out,2 For sequence l out,2 De-interleaving to obtain a sequence l in,1 While obtaining the sequence
Figure GDA00039856467300000712
Here, the iterative decoder of the present invention may include the following modules: the device comprises a modulation reverse mapping module, a BCJR module, an interleaver module and a deinterleaver module. The modulation reverse mapping module utilizes the soft decision output result of the BCJR module to perform reverse mapping processing on the modulation signals such as MPSK, MQAM and MAPSK
The general structure of the forward error correction encoder on the satellite and terrestrial components of a VDES system is shown in fig. 1, wherein the recursive systematic convolutional encoder structure is shown in fig. 2. The component code transfer function is as follows
Figure GDA00039856467300000713
Wherein n is 0 (D)＝1+D+D 3 ，n 1 (D)＝1+D+D 2 +D 3 ，d(D)＝1+D 2 +D 3 。
Rate matching is achieved by puncturing the encoder output. Table 1 gives the data bit puncturing pattern.
Figure GDA0003985646730000081
TABLE 1 puncturing pattern for data bit periods
Note: for each rate, the erasure table should first be read from left to right, then from top to bottom. A 0 indicates that the symbol should be deleted and a 1 indicates that the symbol should be passed.
Figure GDA0003985646730000091
Figure GDA0003985646730000101
TABLE 2 puncturing pattern for the last six bit periods
Note: for each rate, the erasure table should first be read from left to right, then from top to bottom. 0 indicates that the symbol should be deleted, and 1 indicates that the symbol should pass, 2 or 3 indicates that the symbol should pass and be copied 2 or 3 times.
The interleaver specification is as follows: first, decompose k = k 1 k 2 Here, the parameter k 1 And k 2 Depending on the choice of the respective information length and code rate, k is the information block length and the values are given in table 3.
Figure GDA0003985646730000111
Figure GDA0003985646730000121
TABLE 3 interleaver and puncturing parameters for different information lengths/code rates
Note: * Indicating that the suggested settings have not been supported by data, indicates no tail puncturing.
The following operation obtains a conversion number pi(s), s ∈ (1,. Eta., k):
Π(s)＝2(t+ck 1 /2+1)-m
wherein t = (19i + 1) mod (k) 1 /2)，
Figure GDA0003985646730000122
c＝(p q j+21m)mod k 2 ，q＝tmod8+1，
Figure GDA0003985646730000123
m = (s-1) mod2, amodb represents the remainder of a divided by b,
Figure GDA0003985646730000124
denotes rounding down x, p q Representing a prime number, q ∈ {1, 2.., 8}, selected from a set of prime numbers. After interleaving, the s-th bit data of the second encoder corresponds to the pi(s) -th bit data inputted by the first encoder.
The BCJR algorithm and factor graph are described below. The information transmission structure is shown in fig. 3, and the channel is a gaussian white noise channel, where a = (a =) 1 ,a 2 ,...,a k ) Representing a sequence of transmitted information, a n E.g., a = {0,1}, k denotes the information sequence length, c = (c =) (c) 1 ,c 2 ,...,c k ) Represents an output sequence of the information sequence encoded by the encoder, w = (w) 1 ,w 2 ,...,w k ) Is a Gaussian white noise sequence (mean 0, variance σ) 2 )，r＝(r 1 ,r 2 ,...,r k ) Representing the received signal sequence. Modeling an encoder with a finite state machine
c n ＝g 1 (a n ,u n )
u n+1 ＝g 2 (a n ,u n )
Wherein u is n Indicating the state of the encoder at time n. Function g 1 Representing a signal a n The entry state is u n The encoder obtains an encoded signal c n . Function g 2 Representing a signal a n Entry state u n The encoder changes the encoder state to u n+1 . The signal received by the receiver is denoted r n ＝c n +w n
a n Maximum a posteriori probability estimation of
Figure GDA0003985646730000131
Is composed of
Figure GDA0003985646730000132
a n And u n Determining a unique symbol c n Thus, a probability distribution function can be obtained
Figure GDA0003985646730000133
Posterior probability P (a) n R) can be obtained by calculating the marginal function of P (a r)
Figure GDA0003985646730000134
Since the initial state of the encoder is fixed, the transmission sequence a can determine a unique code sequence c and a state sequence u. Thus, P (a | r) = P (a, c, u | r)
The joint posterior probability function P (a, c, u | r) for sequences a, c, u is expressed as:
Figure GDA0003985646730000135
p (c, u | a) is an indication function, when a, c, u correspond one by one, P (c, u | a) =1, otherwise,
p (c, u | a) =0.P (c, u | a) can be expressed as the product of all trellis section index functions (Wiberg diagram)
Figure GDA0003985646730000141
Wherein when a n ,c n ,u n ,u n+1 When a state transition exists, I Tn (a n ,c n ,u n ,u n+1 ) =1, otherwise I Tn (a n ,c n ,u n ,u n+1 ) And =0. Thus, the device
Figure GDA0003985646730000142
The factor graph corresponding to the joint posterior probability function P (a, c, u | r) is shown in fig. 4. According to a factor graph, a forward iteration expression of the BCJR algorithm is as follows:
Figure GDA0003985646730000143
the reverse iteration expression of the BCJR algorithm is
Figure GDA0003985646730000144
a n Is estimated as
Figure GDA0003985646730000145
For binary symbols, the log-likelihood ratio is taken as a soft decision basis. The log-likelihood ratio is calculated as follows
Figure GDA0003985646730000146
l n For deciding a n If l is n A is more than or equal to 0, then a n =0, otherwise, a n And =1. In general l n The larger the modulus value, the higher the reliability of the decision. Hypothetical encoderInitial state of
Figure GDA0003985646730000147
Known to then
Figure GDA0003985646730000148
Since the termination state of the encoder is unknown, initialization of the reverse iteration is
Figure GDA0003985646730000151
μ k Is in any state
S represents the number of states of the encoder. The BCJR algorithm is organized as follows:
(1) And initializing the forward iteration and the backward iteration.
(2) Calculate each time n and each state u n Corresponding forward iteration alpha n+1 (u n+1 ) And backward iteration of beta n (u n )。
(3) Using alpha n+1 (u n+1 )、β n (u n ) And a probability distribution function P (r) n |c n ) Calculating the posterior probability P (a) n |r)。
(4) Log-likelihood ratios are calculated and symbols are decided.
An iterative decoder scheme for solving the MPSK/MQAM/MAPSK modulation mode is introduced below. Assuming that the communication system adopts a 1/3 coding rate, the corresponding puncturing pattern is [1;1;0;0;1;0]. The transmission channel is a white gaussian noise channel. The information sequence is a = (a) 1 ,a 2 ,...,a k )。
Sequences a, c 1 ,c 2 ,c,u 1 ,u 2 Of the joint a posteriori probability functions P (a, c) 1 ,c 2 ,c,u 1 ,u 2 | r) is expressed as
Figure GDA0003985646730000152
Wherein the content of the first and second substances,
Figure GDA0003985646730000153
r＝(r 1 ,r 2 ,...,r k )，c＝(c 1 ,c 2 ,...,c k )，
Figure GDA0003985646730000154
Figure GDA0003985646730000155
wherein, a n′ Representing the symbol entering the second RSC encoder at time n. Further, the posterior probability functions P (a, c) are combined 1 ,c 2 ,c,u 1 ,u 2 | r) is expressed as
Figure GDA0003985646730000156
n moments joint posterior probability function P (a, c) 1 ,c 2 ,c,u 1 ,u 2 R) is shown in fig. 5. In the drawings
Figure GDA0003985646730000161
Figure GDA0003985646730000162
Figure GDA0003985646730000163
Will sequence P O (a) And P O (c 1 ) Sending into the first BCJR decoder to calculate forward iteration and backward iteration respectively
Figure GDA00039856467300001615
Figure GDA0003985646730000164
Thus, the sequence P can be obtained I (a) And P I (c 1 )
Figure GDA0003985646730000165
Figure GDA0003985646730000166
For sequence P I (a) Interweaving to obtain a sequence
Figure GDA0003985646730000167
Will be sequenced
Figure GDA0003985646730000168
And P O (c 2 ) Sending to a second BCJR decoder to calculate forward iteration and backward iteration respectively
Figure GDA0003985646730000169
Figure GDA00039856467300001610
Further, a sequence was obtained
Figure GDA00039856467300001611
And P I (c 2 )
Figure GDA00039856467300001612
Figure GDA00039856467300001613
To the sequence
Figure GDA00039856467300001614
De-interleaving to obtain a sequence P I (a) In that respect Thus, an MPSK/MQAM/MAPSK modulation iterative decoding structure is obtained as shown in fig. 6.
The modulation demapping module will be described by taking 16QAM modulation as an example, as shown in fig. 7. In the figure, the position of the upper end of the main shaft,
Figure GDA0003985646730000171
representing the input sequence of the modulation inverse map.
Figure GDA0003985646730000172
Figure GDA0003985646730000173
Representing the output sequence of the modulation inverse map. The transformation module in the figure transforms the sequence l in,a 、
Figure GDA0003985646730000174
And
Figure GDA0003985646730000175
is converted into a sequence
Figure GDA0003985646730000176
Figure GDA0003985646730000177
And
Figure GDA0003985646730000178
as shown in fig. 8.
Sequence of
Figure GDA0003985646730000179
And
Figure GDA00039856467300001710
the elements in (1) respectively represent a sequence
Figure GDA00039856467300001711
And
Figure GDA00039856467300001712
likelihood ratio of the medium bit.
The input signal of the 16QAM inverse mapping module is
Figure GDA00039856467300001713
Figure GDA00039856467300001714
The output signal of the 16QAM inverse mapping module is
Figure GDA00039856467300001715
Figure GDA00039856467300001716
Figure GDA0003985646730000181
Figure GDA0003985646730000182
Wherein the content of the first and second substances,
Figure GDA0003985646730000183
representing a bit combination as b n Whether or not a path exists, if a path exists
Figure GDA0003985646730000184
If not, then,
Figure GDA0003985646730000185
inverse transformation module transforms the sequence
Figure GDA0003985646730000186
Figure GDA0003985646730000187
And
Figure GDA0003985646730000188
transformation into a sequence l out,a 、
Figure GDA0003985646730000189
And
Figure GDA00039856467300001810
as shown in fig. 9.
The sequence l out,a And
Figure GDA00039856467300001811
sending into the first BCJR decoder to calculate forward iteration and backward iteration respectively
Figure GDA00039856467300001812
Figure GDA00039856467300001813
Thereby obtaining the sequence
Figure GDA00039856467300001814
And
Figure GDA00039856467300001815
Figure GDA0003985646730000191
Figure GDA0003985646730000192
Figure GDA0003985646730000193
for the sequence l out,1 Interweaving to obtain sequence l in,2 . Will be sequenced
Figure GDA0003985646730000194
And l in,2 Sending to a second BCJR decoder to calculate forward iteration and backward iteration respectively
Figure GDA0003985646730000195
Figure GDA0003985646730000196
Figure GDA0003985646730000197
Thereby obtaining a sequence
Figure GDA0003985646730000198
And
Figure GDA0003985646730000199
Figure GDA00039856467300001910
Figure GDA00039856467300001911
Figure GDA00039856467300001912
for the sequence l out,2 Interweaving to obtain sequence l in,a . For the sequence l 2 De-interleaving and judging to obtain information estimation sequence
Figure GDA00039856467300001913
The decoding steps are as follows:
(1) The sequence l out,a And
Figure GDA00039856467300001914
sending the data into a first BCJR decoder, and simultaneously sending the prior probability log-likelihood ratio l of the information sequence a in,a Inputting the first BCJR decoder to obtain the posterior probability log-likelihood ratio l of the information sequence a 1 Subtracting the prior probability log-likelihood ratio l in,a To obtain l out,1 . Obtaining sequences simultaneously
Figure GDA00039856467300001915
(2) For the sequence l out,1 Interweaving to obtain sequence l in,2 Then the sequence l is added in,2 And
Figure GDA0003985646730000201
sending the data to a second BCJR decoder to obtain the posterior probability log-likelihood ratio l of the information sequence a 2 Subtracting the prior probability log-likelihood ratio l in,2 To obtain l out,2 . For the sequence l out,2 Carrying out reverse interleaving processing to obtain a sequence l in,1 . Obtaining sequences simultaneously
Figure GDA0003985646730000202
(3) And (4) repeating the steps (1) to (2) for corresponding iteration times if iteration is needed.
According to the posterior probability log-likelihood ratio sequence l of the information sequence a obtained in the step (2) 2 De-interleaving and judging to obtain information estimation sequence
Figure GDA0003985646730000203
For other coded modulation modes, the mapping relationship between the input and output of the log-likelihood ratio sequence, the transformation module, the inverse mapping module, and the inverse transformation module in fig. 6 and 7 may be modified according to the coding rate, the puncturing pattern, and the number of the modulated signal symbols.
The embodiments of the present invention have been described in detail with reference to the drawings, but the present invention is not limited to the embodiments. Even if various changes are made to the present invention, it is still within the scope of the present invention if they fall within the scope of the claims of the present invention and their equivalents.

Claims (4)

1. An iterative decoding method for a very high frequency data exchange system, comprising the steps of:
s1: the prior probability log-likelihood ratio sequence l in,a 、
Figure FDA0003985646720000011
Figure FDA0003985646720000012
And the received signal sequence r is sent to a modulation inverse mapping module, and a posterior probability log-likelihood ratio sequence l is calculated by combining the forward error correction coding rate and the system number of the multi-system modulation code elements out,a 、
Figure FDA0003985646720000013
And
Figure FDA0003985646720000014
s2: the posterior probability log-likelihood ratio sequence l out,a And
Figure FDA0003985646720000015
sending into the first BCJR decoderSequence l of prior probability log-likelihood ratios of time-varying information sequence a in,a Inputting the first BCJR decoder to obtain a posterior probability log-likelihood ratio sequence l of the information sequence a 1 Subtracting the prior probability log-likelihood ratio sequence l in,a Obtaining the sequence l out,1 While obtaining the sequence
Figure FDA0003985646720000016
S3: for the sequence l out,1 Interweaving to obtain sequence l in,2 Then the sequence l is added in,2 And posterior probability log-likelihood ratio sequence
Figure FDA0003985646720000017
Sending the data to a second BCJR decoder to obtain a posterior probability log-likelihood ratio sequence l of the information sequence a 2 Subtracting the sequence l in,2 Obtaining the sequence l out,2 To the sequence l out,2 Carrying out reverse interleaving processing to obtain a sequence l in,1 While obtaining the sequence
Figure FDA0003985646720000018
S4: judging whether iteration is carried out, if so, repeating S1-S3 to carry out iteration of preset corresponding times;
s5: according to the posterior probability log-likelihood ratio sequence l of the information sequence a obtained after the iteration of S3 or S4 2 De-interleaving and judging to obtain information estimation sequence
Figure FDA0003985646720000019
2. The iterative decoding method for vhf data exchange system according to claim 1, wherein said S1 comprises:
s11: a priori probability log-likelihood ratio sequence
Figure FDA00039856467200000110
Figure FDA00039856467200000111
And
Figure FDA00039856467200000112
conversion to digital according to the carry of 16QAM modulation symbols
Figure FDA00039856467200000113
Figure FDA00039856467200000114
And
Figure FDA00039856467200000115
s12: log-likelihood ratio sequence based on prior probability
Figure FDA0003985646720000021
Figure FDA0003985646720000022
Figure FDA0003985646720000023
And calculating the posterior probability log-likelihood ratio sequence of the 16QAM modulation code element by the received signal sequence r
Figure FDA0003985646720000024
Figure FDA0003985646720000025
And
Figure FDA0003985646720000026
s13: posterior probability log-likelihood ratio sequence
Figure FDA0003985646720000027
Figure FDA0003985646720000028
And
Figure FDA0003985646720000029
conversion to digital according to the carry of 16QAM modulation symbols
Figure FDA00039856467200000210
And
Figure FDA00039856467200000211
3. the iterative decoding method for vhf data exchange system according to claim 1, wherein said S2 comprises:
s21: forward iteration for first BCJR decoder
Figure FDA00039856467200000212
And backward iteration
Figure FDA00039856467200000213
Carrying out initialization;
s22: the sequence l out,a And
Figure FDA00039856467200000214
sending the data into a first BCJR decoder, and simultaneously sending a prior probability log-likelihood ratio sequence l of the information sequence a in,a Inputting a first BCJR decoder;
s23: calculate each time n and each state
Figure FDA00039856467200000215
Corresponding forward iteration
Figure FDA00039856467200000216
And backward iteration
Figure FDA00039856467200000217
S24: by using
Figure FDA00039856467200000218
Figure FDA00039856467200000219
And a probability distribution function for calculating a posterior probability log-likelihood ratio l 1 And
Figure FDA00039856467200000220
s25: posterior probability log-likelihood ratio sequence l of information sequence a 1 Subtracting a prior probability log-likelihood ratio sequence l in,a Obtaining the sequence l out,1 While obtaining the sequence
Figure FDA0003985646720000031
4. The iterative decoding method for vhf data exchange system according to claim 1, wherein said S3 comprises:
s30: for the sequence l out,1 Interweaving to obtain sequence l in,2 ；
S31: forward iteration for second BCJR decoder
Figure FDA0003985646720000032
And backward iteration
Figure FDA0003985646720000033
Carrying out initialization;
s32: the sequence l in,2 And with
Figure FDA0003985646720000034
Sending to a second BCJR decoder to calculate each time n and each state
Figure FDA0003985646720000035
Corresponding forward iteration
Figure FDA0003985646720000036
And backward iteration
Figure FDA0003985646720000037
S33: by using
Figure FDA0003985646720000038
Figure FDA0003985646720000039
And a probability distribution function for calculating a posterior probability log-likelihood ratio l 2 And
Figure FDA00039856467200000310
s34: a posteriori probability log-likelihood ratio l for information sequence a 2 Subtracting a prior probability log-likelihood ratio sequence l in,2 Obtaining the sequence l out,2 For sequence l out,2 De-interleaving to obtain a sequence l in,1 While obtaining the sequence
Figure FDA00039856467200000311
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