CN113364717B - 32APSK soft information calculation method suitable for DVBS2 modulation - Google Patents
32APSK soft information calculation method suitable for DVBS2 modulation Download PDFInfo
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Abstract
The invention relates to a 32APSK soft information calculation method suitable for DVBS2 modulation, belonging to wireless digital transmissionThe technical field of high-order demodulation decoding in a system; the method comprises the following steps: a low complexity demodulation soft information calculation method for a specific 32APSK modulation format is proposed, which is capable of calculating corresponding 5 bits b from received symbols 1 b 2 b 3 b 4 b 5 Soft information for subsequent decoding. The method for calculating the demodulation soft information can obviously reduce the complexity of soft information calculation, improve the realizability of high-speed digital transmission hardware, and does not cause obvious loss of channel capacity and error code performance by the simplified calculation method.
Description
Technical Field
The invention belongs to the technical field of high-order demodulation decoding in a wireless digital transmission system, and particularly relates to a 32APSK soft information calculation method suitable for DVBS2 modulation.
Background
At present, the high-order Amplitude Phase Shift Keying (APSK) technology has high spectrum efficiency and can save bandwidth resources, so that the method has a wide application prospect. The second generation satellite digital broadcasting (DVBS 2) standard in europe and the standard of the space data system Counseling Committee (CCSDS) entitled "variable advanced coding and modulation methods for high speed telemetry applications" (CCSDS 131.2-R-1) both specify a 32APSK modulation scheme.
The general calculation formula for the soft information for the received signal y = I + jQ is as follows:
where y = I + jQ is the received symbol, I is the real part of the signal, Q is the imaginary part of the signal,
are respectively b n Constellation point set with hard bit decision of '0' and '1', gamma = gamma re +jγ im Is composed of
Or
Point of middle, σ 2 Is the variance of an additive white gaussian noise channel. As can be seen from fig. 1, the decision domain is asymmetric with respect to the complex plane coordinate axis, and the region where the received symbol is located cannot be simply determined by numerical value positive-negative or polar coordinate transformation. Therefore, when the method is used for calculating soft information, gamma in the formula re 、γ im The value is complex, the soft information calculation formula comprises a large number of exponential operations, square operations and division operations, the operation complexity is high, and the method is not suitable for hardware to realize high-speed digital transmission.
Therefore, at present, a 32APSK soft information calculation method suitable for DVBS2 modulation needs to be designed to solve the above problems.
Disclosure of Invention
The present invention aims to provide a 32APSK soft information calculation method suitable for DVBS2 modulation, which is used to solve the technical problems existing in the prior art, such as: in the prior art method, when soft information calculation is carried out, gamma in a formula re 、γ im The value is complex, the soft information calculation formula comprises a large number of exponential operations, square operations and division operations, the operation complexity is high, and the method is not suitable for hardware to realize high-speed digital transmission.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a32 APSK soft information calculation method suitable for DVBS2 modulation comprises the following steps:
(1) Properly rotating the outer ring of the 32APSK constellation diagram to form a new 32APSK constellation diagram;
(2) Decomposing the constellation diagram of 32APSK into 5 amplitude sub-constellation diagrams in sequence, wherein the code element value of the constellation point of each amplitude sub-constellation diagram is the code element of the corresponding position of the code element sequence of the constellation point corresponding to the original constellation diagram;
(3) Respectively calculating the decision threshold in the 5 sub-constellation diagrams, and judging the received signal to be a binary signal 0 or 1;
(4) Respectively mapping the modulation signal values received by the 32APSK demodulator to a coordinate system of 5 amplitude sub-constellation maps, and respectively calculating soft information of the 5 amplitude sub-constellation maps according to a decision threshold of each amplitude sub-constellation map;
(5) And combining the soft information of the 5-amplitude sub-constellation diagram obtained by calculation in sequence to obtain a soft information sequence required by the decoder.
Further, the signal received by the receiving end is y = I + jQ, σ 2 Is the AWGN channel noise variance;
wherein the step (1) is to rotate the outer ring symbol constellation diagram by pi/16 counterclockwise, i.e. multiply by e jπ/16 ；
The step (3) is specifically to calculate the decision threshold in 5 sub-constellations respectively, and calculate according to the following formula:
the threshold calculation formula of the 1 st amplitude sub-constellation diagram is as follows:
the threshold calculation formula of the 2 nd sub-constellation diagram is as follows: w 2 ＝0.5*R 1 (γ 1 +γ 2 )；
The threshold calculation formula of the 3 rd graph sub-constellation is as follows: w 3 ＝0；
The threshold calculation formula of the 4 th graph sub-constellation is as follows: w 4 ＝0；
The threshold calculation formula of the sub-constellation diagram of the 5 th diagram is as follows:
further, the step (4) is specifically to calculate the soft information of the 5 sub-constellations respectively according to the following formula:
the soft information calculation formula of the 1 st sub-constellation diagram is as follows:
the soft information calculation formula of the 2 nd sub-constellation diagram is as follows: LLR (b) 2 )≈|y|-W 2 ；
The soft information calculation formula of the 3 rd sub-constellation diagram is as follows: LLR (b) 3 )≈W 3 -I；
The soft information calculation formula of the 4 th sub-constellation diagram is as follows: LLR (b) 4 )≈W 4 -Q；
The soft information calculation formula of the 5 th sub-constellation diagram is as follows:
further, the step (5) specifically combines the calculated 5-bit demodulation soft information in order, and arranges the combined soft information into (b) according to the order of the decomposed sub-constellations 1 b 2 b 3 b 4 b 5 ) And (4) sequencing.
Compared with the prior art, the invention has the beneficial effects that:
(1) When the soft information is calculated, the bit decision area has certain symmetry, so that the corresponding formula can be efficiently and approximately simplified, and a complex operation process is not included any more;
(2) The invention decomposes the 32APSK constellation diagram of 5 bits into 5 amplitude sub-constellation diagrams, which is convenient for rapidly determining the decision threshold and reduces the mutual interference among the bits;
(3) It was verified by simulation that the algorithm did not cause significant loss of performance.
Drawings
Fig. 1 is a 32APSK constellation diagram in the DVBS2 standard;
FIG. 2 is a schematic diagram of the calculation process of the soft demodulation information according to the present invention;
FIG. 3 is a 32APSK constellation diagram after the outer ring symbol is rotated in the present invention;
FIG. 4 is the 1 st sub-constellation obtained by decomposing the constellation diagram shown in FIG. 3 according to the present invention;
FIG. 5 is a 2 nd amplitude sub-constellation obtained by decomposing the constellation diagram shown in FIG. 3 according to the present invention;
FIG. 6 is a 3 rd amplitude sub-constellation obtained by decomposing the constellation diagram shown in FIG. 3 according to the present invention;
FIG. 7 is a 4 th sub-constellation obtained by decomposing the constellation diagram shown in FIG. 3 according to the present invention;
FIG. 8 is a 5 th amplitude sub-constellation obtained by decomposing the constellation diagram shown in FIG. 3 according to the present invention;
FIG. 9 is a block diagram of an exemplary digital communication system architecture;
fig. 10 is a simulation graph of bit error rate for demodulating soft information according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to fig. 1 to 10 of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
The embodiment is as follows:
as shown in fig. 2, a 32APSK soft information calculation method suitable for DVBS2 modulation is therefore proposed.
The method comprises the following specific steps:
and step 1, carrying out angle rotation of pi/16 anticlockwise on an outer ring of a constellation diagram of the 32APSK signal.
And 2, decomposing the 32APSK constellation diagram into 5 amplitude sub-constellation diagrams in sequence.
The constellation of the rotated 32APSK is shown in fig. 3. And (3) disassembling and constructing 5 new constellations according to the constellation structure of the graph in fig. 3, so that the new constellations have the same constellation point number as that of the graph in fig. 3, and the position of each constellation point is the same as that of the graph in fig. 3, thereby obtaining 5 sub-constellations, as shown in fig. 4-8. Wherein:
fig. 4 is a 1 st sub-constellation diagram, and the corresponding symbol value of each constellation point is the 1 st symbol in the corresponding symbol sequence of each constellation point in the constellation diagram of fig. 3;
fig. 5 is a 2 nd sub-constellation diagram, in which the symbol value corresponding to each constellation point is the 2 nd symbol in the symbol sequence corresponding to each constellation point in the constellation diagram of fig. 3;
fig. 6 is a 3 rd sub-constellation diagram, in which the symbol value corresponding to each constellation point is the 3 rd symbol in the symbol sequence corresponding to each constellation point in the constellation diagram of fig. 3;
fig. 7 is a 4 th sub-constellation diagram, in which the corresponding symbol value of each constellation point is the 4 th symbol in the corresponding symbol sequence of each constellation point in the constellation diagram of fig. 3;
fig. 8 is a 5 th sub-constellation diagram, in which the corresponding symbol value of each constellation point is the 5 th symbol in the corresponding symbol sequence of each constellation point in the constellation diagram of fig. 3;
and 3, respectively calculating the decision threshold in the 5 sub-constellation diagrams of the figures 4-8.
(3.1) calculating the decision threshold W in the 1 st amplitude sub-constellation diagram 1
Referring to fig. 4, for signals of an outer ring, the invention uses straight lines L2 and L5 to distinguish the inner side and the outer side, the outer side signal selects a decision threshold as a central line of constellation points corresponding to 0 symbol values and 1 symbol values whose real parts are closest to each other, that is, two straight lines L1 and L6 in fig. 4, and the decision threshold value is:
the decision threshold of the inner signal is selected as a central line of constellation points corresponding to the 0 code element value and the 1 code element value, namely two straight lines L3 and L4 in fig. 4, and the decision threshold value is as follows:
for signals of the inner middle ring, the invention selects the decision threshold as the sum of 0 code element values with the imaginary parts being nearest to each otherThe central line of the constellation point corresponding to the 1-symbol value is two straight lines L7 and L8 in fig. 4, and the decision threshold value is:
(3.2) calculating the decision threshold W in the 2 nd sub-constellation diagram 2
Referring to fig. 5, all constellation points with code element value of 1 are distributed in the outer ring, all constellation points with code element value of 0 are distributed in the inner and middle rings, the present invention uses the average value of the radii of the outer ring and the middle ring as the decision threshold, which is the dashed ring in fig. 5, and the decision threshold value is: w 2 ＝0.5*R 1 (γ 1 +γ 2 )。
(3.3) calculating the decision threshold W in the 3 rd amplitude sub-constellation diagram 3
Referring to fig. 6, all constellation points with symbol values of 1 are distributed on the left side of the Y axis, and all constellation points with symbol values of 0 are distributed on the right side of the Y axis, and the Y axis is used as a decision threshold, and the decision threshold value is: w is a group of 3 ＝0。
(3.4) calculating the decision threshold W in the 4 th sub-constellation diagram 4
Referring to fig. 7, all constellation points with symbol values of 1 are distributed on the lower side of the X axis, and all constellation points with symbol values of 0 are distributed on the upper side of the X axis, and the present invention uses the X axis as a decision threshold, and the decision threshold value is: w is a group of 4 ＝0。
(3.5) calculating the decision threshold W in the 5 th sub-constellation diagram 5
Referring to fig. 8, for signals of the outer ring, the present invention selects the decision threshold as a central line of constellation points corresponding to 0 symbol value and 1 symbol value whose real parts are closest to each other, that is, two straight lines H1 and H2 in fig. 8, where the decision threshold is:
for the inner ring signal, the invention selects the decision threshold as the median of the constellation points corresponding to the 0 code element value and the 1 code element value whose real parts are nearest, i.e. two straight lines H3 and H4 in fig. 8, and the decision threshold value is:
and 4, respectively calculating the soft information of each bit according to the decision threshold.
Assuming that the input modulation signal y = I + jQ, the signal value is mapped in the coordinate system of each sub-constellation and the respective soft information is calculated.
(4.1) the invention compares the signal y with a decision threshold W 1 And obtaining the 1 st bit soft information as follows:
(4.2) the invention compares the signal y with a decision threshold W 2 And obtaining the 2 nd bit soft information as follows:
LLR(b 2 )≈|y|-W 2
(4.3) the invention compares the signal y with a decision threshold W 2 And obtaining the 3 rd bit soft information as follows:
LLR(b 3 )≈W 3 -I
(4.4) the invention compares the signal y with a decision threshold W 2 And obtaining the 4 th bit soft information as follows:
LLR(b 4 )≈W 4 -Q
(4.5) the invention compares the signal y with a decision threshold W 2 And obtaining the 5 th bit soft information as follows:
and 5, combining the soft information to obtain a soft information sequence.
Arranging the 5 bits of soft information obtained by calculation in sequence to obtain the soft information sequence (b) required by the decoder 1 b 2 b 3 b 4 b 5 )。
Specifically, the method comprises the following steps:
(1) With reference to fig. 9, the user performs TPC (11/16 ) coding on the source at the transmitting end to obtain a coded sequence 1010010010011 \8230;, this embodiment takes the first 5-bit coded sequence 10100 for the description of the calculation method for demodulating soft information.
(2) 32APSK modulation format based on DVBS2 standard, reference R, according to fig. 1 and the following table 1 ＝0.242，γ 1 ＝2.84，γ 2 =5.27, select coded sequence 10100 modulation to symbol (-0.6639 + j01779).
Labeling: different code rates and inner ring radius R of 32APSK constellation diagram in DVBS2 standard 1 And the ratio of the radii of the middle ring and the outer ring gamma 1 And gamma 2
(3) After the signal is transmitted through an additive white gaussian noise channel, the receiving end obtains a received signal:
(-0.7060+j0.2441)。
(4) The soft information of 5 bits is calculated in sequence by the expression given by the invention according to the received information:
(4.1) calculating the sub-constellation diagram decision thresholds of fig. 4-8 respectively:
the decision threshold of the 1 st bit code element is:
the decision threshold of the 2 nd bit code element is: w 2 ＝0.9813；
The decision threshold of the 3 rd bit code element is: w 3 ＝0；
The decision threshold of the 4 th bit code element is: w 4 ＝0；
The decision threshold of the 5 th bit code element is:
(4.2) mapping the received signal (-0.7060 + j0.2441) to the sub-constellation diagram respectively to calculate each bit of soft information:
the soft information of the 1 st bit code element is: LLR (b) 1 )≈W 1 (inner middle ring) - |0.2441| =0.0878
The soft information of the 2 nd bit symbol is: LLR (b) 2 )≈|-0.7060+j0.2441|-W 2 ＝-0.2343；
The soft information of the 3 rd bit code element is: LLR (b) 3 )≈W 3 -(-0.7060)＝0.7060；
The soft information of the 4 th bit symbol is: LLR (b) 4 )≈W 4 -(0.2441)＝-0.2441；
The soft information of the 5 th bit code element is:
LLR(b 5 )≈W 5 (inner middle ring) - | 0.7060| = -0.3741
(4.3) combining the 5 bits of soft information in sequence to obtain the demodulated soft information sequence (0.0878, -0.2343,0.7060, -0.2441, -0.3741) of the symbol (-0.7060 + j0.2441).
(5) The obtained soft information is used for decoding judgment by a decoder at the rear end, so that the calculation complexity of the soft information is reduced and the communication function is completed at the same time.
The above are preferred embodiments of the present invention, and all changes made according to the technical scheme of the present invention that produce functional effects do not exceed the scope of the technical scheme of the present invention belong to the protection scope of the present invention.
Claims (1)
1. A32 APSK soft information calculation method suitable for DVBS2 modulation is characterized by comprising the following steps:
(1) Rotating the outer ring of the 32APSK constellation diagram by pi/16 counterclockwise to form a new 32APSK constellation diagram;
(2) Decomposing 5 code element values of each constellation point in the 32APSK constellation diagram into 5 amplitude sub-constellation diagrams one by one from left to right, wherein the code element value of the constellation point of each amplitude sub-constellation diagram is a code element at a position corresponding to a code element sequence of the constellation point corresponding to the original constellation diagram;
(3) Respectively calculating the decision threshold in the 5 sub-constellation diagrams, and judging the received signal to be a binary signal 0 or 1;
(4) Respectively mapping the modulation signal values received by the 32APSK demodulator to a coordinate system of 5 amplitude sub-constellation maps, and respectively calculating soft information of the 5 amplitude sub-constellation maps according to a decision threshold of each amplitude sub-constellation map;
(5) Combining the soft information of the 5-amplitude sub-constellation diagram obtained by calculation in sequence to obtain a soft information sequence required by a decoder;
the signal received by the receiving end is y = I + jQ, I is a real part of the signal, and Q is an imaginary part of the signal;
wherein the step (1) is to rotate the outer ring symbol constellation diagram by pi/16 counterclockwise, i.e. multiply by e jπ/16 ；
The step (3) is specifically to calculate the decision threshold in 5 sub-constellations respectively, and calculate according to the following formula:
the threshold calculation formula of the 1 st amplitude sub-constellation diagram is as follows:
the threshold calculation formula of the 2 nd sub-constellation diagram is as follows: w 2 ＝0.5*R 1 (γ 1 +γ 2 )；
The threshold calculation formula of the 3 rd graph sub-constellation is as follows: w is a group of 3 ＝0；
The threshold calculation formula of the 4 th graph sub-constellation is as follows: w is a group of 4 ＝0；
The threshold calculation formula of the sub-constellation diagram of the 5 th diagram is as follows:
wherein, the step (4) is to calculate the soft information of 5 sub-constellation maps respectively according to the following formula:
the soft information calculation formula of the 1 st sub-constellation diagram is as follows:
the soft information calculation formula of the 2 nd sub-constellation diagram is as follows: LLR (b) 2 )≈|y|-W 2 ；
The soft information calculation formula of the 3 rd amplitude sub-constellation diagram is as follows: LLR (b) 3 )≈W 3 -I；
The soft information calculation formula of the 4 th sub-constellation diagram is as follows: LLR (b) 4 )≈W 4 -Q；
The soft information calculation formula of the 5 th sub-constellation diagram is as follows:
wherein, the step (5) is to combine the 5-bit demodulation soft information obtained by calculation in sequence, and arrange the combined soft information into (b) according to the sequence of the decomposed sub-constellation diagrams 1 b 2 b 3 b 4 b 5 ) And (4) sequencing.
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