A demodulation decoding method based on 16APSK waveform

Abstract

The application discloses a demodulation and decoding method based on 16APSK waveform and belongs to the field of communication signal processing. The method realizes low-complexity receiver construction by approximate processing during demodulation, initializing decoding likelihood ratio information, and converting exponential and logarithmic operations into simple addition and multiplication operations, and specifically comprises the following steps: sequentially performing encoding and modulation processing on an original information sequence, and transmitting the original information sequence into a complex channel; a demodulator receives output symbols from an AWGN channel, and initializes log-likelihood ratio information of a first bit, a second bit, a third bit and a fourth bit by using channel received symbols; an iteration decoding process is completed in an LDPC decoder, and a 16APSK soft demodulation receiver construction based on LDPC code is completed. The application combines LDPC channel coding and high-order 16APSK modulation together, effectively improves the spectrum utilization rate of the system, reduces the complexity of engineering implementation under the condition of ensuring the decoding accuracy, optimizes the engineering structure, and solves relevant engineering problems.

Description

Technical Field

[0001] This invention relates to a demodulation and decoding method based on 16APSK waveform, belonging to the field of communication signal processing. Background Technology

[0002] Digital modulation and channel coding are two commonly used digital signal processing techniques in wireless communication systems, and are key to improving system performance. Employing higher-order modulation techniques can improve system bandwidth utilization. Amplitude Phase Shift Keying (APSK) modulation combines the characteristics of amplitude and phase modulation, representing digital information by changing the amplitude and phase of the signal. Low-Density Parity Check (LDPC) codes possess performance approaching the Shannon limit and the advantage of easy parallel processing. Combining 16APSK modulation and LDPC channel coding can significantly improve data transmission efficiency while maintaining high reliability. To fully maximize channel coding gain and achieve low complexity, LDPC decoding typically employs the min-sum (MS) algorithm in soft-decision decoding. This requires outputting soft information for each bit during constellation-based demodulation. Existing demodulation algorithms involve numerous multiplication, exponentiation, and logarithmic operations, resulting in high complexity and wasted resources in Additive White Gaussian Noise (AWGN) channels. Summary of the Invention

[0003] To address the issue of high complexity in traditional 16APSK soft demodulation algorithms under AWGN channels, requiring numerous multiplication, exponentiation, and logarithmic operations, this invention aims to provide a demodulation and decoding method based on 16APSK waveforms. By approximating the decoding likelihood ratio during demodulation, the exponentiation and logarithmic operations are transformed into simple addition and multiplication operations, enabling the construction of a low-complexity receiver, reducing processing latency, and improving resource utilization.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A demodulation and decoding method based on 16APSK waveforms specifically includes the following steps:

[0006] Step 1: Perform LDPC encoding and 16APSK modulation on the original information sequence in sequence, and then transmit it into the complex AWGN channel;

[0007] The original information sequence u of length k bits is processed by the LDPC coding module to obtain the encoded sequence c = u·G, where G is the generator matrix of the LDPC code and the length of the encoded sequence c is m.

[0008] The encoded information bits are mapped by a constellation mapping function of 16APSK Modulation is performed, and 4 encoded interleaved information bits b3, b2, b1, b0 are mapped into 1 spatial constellation point;

[0009] wherein, is the complete constellation space of the 16APSK mapped symbols, and contains 16 constellation points, the radius of the inner circle constellation point is R1, and the radius of the outer circle constellation point is R2;

[0010] After the encoded sequence c is mapped by 16APSK modulation, a symbol sequence y = φ(c) = {y1, y2,..., y t} is obtained;

[0011] wherein, is the rounding up, that is, if m cannot be divided by 4, 0 is added at the end of the sequence, and after 4 bits are met, mapping is performed again;

[0012] The symbol sequence y is transmitted through a complex AWGN channel;

[0013] Step two, the demodulator receives the output symbol from the AWGN channel, and initializes the log-likelihood ratio information of the first bit using the channel received symbol;

[0014] The symbol sequence output by the channel is z = {z1, z2,..., z t}, z = y + n, n is a complex additive white Gaussian noise sequence with mean 0 and variance ;

[0015] When deriving the soft bit information using the initial symbol information of the received channel, the source is regarded as an equiprobable distribution, that is, the probability of each initial bit being 0 or 1 is equal,

[0016] According to the received symbol z t , the first bit b3 corresponds to the sub-constellation area division diagram, the sub-constellation diagram of the first bit b3 is symmetric about the I-axis and the Q-axis, and the received symbol z t is mapped to the first quadrant as z' t , and the log-likelihood ratio LLR(b3) of the first bit b3 is as shown in formula (1):

[0017]

[0018] wherein, i = 0, 4, 8, 12, is the i-th constellation mapping point, and ||a-b|| is the distance between a and b on the constellation mapping diagram;

[0019] respectively, using a ray D1: ∠θ = π / 6 and a straight line D2: I = D min where max(P0, P4) and max(P8, P 12 ) are determined as shown in equations (2) and (3) respectively:

[0020]

[0021] where (x) I and (x) Q are the real and imaginary parts of a complex signal x respectively;

[0022] Step three, the demodulator receives the output symbols from the AWGN channel and uses the channel received symbols to initialize the log-likelihood ratio information of the second bit b2;

[0023] According to the received symbol z t , the sub-constellation region partitioning diagram of the corresponding second bit b2, the sub-constellation diagram of the second bit b2 is symmetric about the I-axis and the Q-axis, the received symbol is mapped to the first quadrant, and the log-likelihood ratio LLR(b2) of the second bit b2 is shown in equation (4):

[0024]

[0025] respectively, using a ray D3: ∠θ = π / 3 and a straight line D4: I = D min where max(P0, P8) and max(P4, P 12 ) are determined as shown in equations (5) and (6) respectively:

[0026]

[0027] Step four, the demodulator receives the output symbols from the AWGN channel and uses the channel received symbols to initialize the log-likelihood ratio information of the third bit b1;

[0028] According to the received symbol z t , the sub-constellation region partitioning diagram of the corresponding third bit b1, the sub-constellation diagram of the third bit b1 is completely symmetric about the Q-axis, the LLR value of the third bit b1 is only related to the real part (z t ) t of the received symbol z I , and is irrelevant to the imaginary part (z t ) Q , and the LLR(b1) is approximately shown in equation (7):

[0029] LLR(b1) = α × Amp × (z t ) I (7)

[0030] where Amp = (R1*4 + R2*12) / 16 is the average amplitude of the constellation, and a is a weight factor;

[0031] Step five, the demodulator receives the output symbols from the AWGN channel, and uses the channel received symbols to initialize the log-likelihood ratio information of the fourth bit;

[0032] According to the received symbol z t , the sub-constellation region of the fourth bit b0 is divided into two parts, and the sub-constellation of the fourth bit b0 is completely symmetric about the I-axis. The LLR value of the fourth bit b0 is only related to the imaginary part (z t ) t ) Q of the received symbol z t , and is irrelevant to the real part (z I )

[0033] LLR(b0) = a * Amp * (z t ) Q (8)

[0034] where the average amplitude Amp and the weight factor a are the same as in step four;

[0035] Step six, the iteration decoding process is completed in the LDPC decoder, which includes the following sub-steps:

[0036] Step 6.1 updates the information transmitted from the check node to the variable node, as shown in equation (9):

[0037]

[0038] where Lq ij is the initialization, and Lq j\i is the log-likelihood ratio of the i-th bit obtained in steps two to five, and R is the set of positions in the j-th row of the check matrix H except the i-th 1;

[0039] Step 6.2 updates the information transmitted from the variable node to the check node, as shown in equation (10):

[0040]

[0041] where Lp i is the log-likelihood ratio of the i-th bit calculated in steps two to five, and C i\j is the set of positions in the i-th row of the check matrix H except the j-th 1;

[0042] Step 6.3 determines the posterior log-likelihood ratio of each bit as shown in formula (11):

[0043]

[0044] Step 6.4 makes a hard decision of each variable node as 0 or 1 as shown in formula (12):

[0045]

[0046] Step 6.5 determines the stopping condition:

[0047] If the decision result satisfies the check matrix H of the LDPC code, i.e. or reaches the preset maximum iteration number, the decoding iteration is stopped, otherwise, the step 6.1 is returned to update the information again;

[0048] Through the above six steps, the 16APSK soft demodulation receiving mechanism based on the LDPC code is completed;

[0049] It also includes step seven: taking the decision result obtained in step six as the demodulation decoding result of the receiver, judging the position of the received symbol in each bit sub-constellation diagram, simplifying the calculation process of the bit soft information, reducing the exponential processing unit and the logarithmic processing unit in the traditional calculation circuit, reducing the complexity of engineering implementation under the condition of ensuring the decoding accuracy, optimizing the engineering structure, and solving the related engineering problems.

[0050] Beneficial effects:

[0051] 1. The demodulation decoding method based on the 16APSK waveform of the application combines the LDPC channel coding with the high-order 16APSK modulation, effectively improves the spectrum utilization of the system under the condition of ensuring the low bit error rate brought by the channel coding.

[0052] 2. The demodulation decoding method based on the 16APSK waveform of the application converts a large number of exponential operations and logarithmic operations into simple addition operations and comparison operations, simplifies the 16APSK soft demodulation algorithm according to the symmetry characteristics of the constellation diagram, reduces the complexity of the bit soft information operation, and greatly reduces the calculation resource consumption on the basis of the relatively ideal bit error rate performance. DETAILED DESCRIPTION

[0053] Figure 1 It is a flow chart of the demodulation decoding method based on the 16APSK waveform of the application;

[0054] Figure 2 It is a 16APSK constellation diagram of the embodiment;

[0055] Figure 3 4 sub-constellation region partition diagrams obtained by decomposing the 16APSK constellation diagram of the embodiment;

[0056] Figure 4 A decision relationship diagram of the 1st and 2nd bits in the first quadrant of the embodiment;

[0057] Figure 5 A bit error rate simulation comparison curve of a reference code type joint 16APSK modulation receiver of the embodiment. DETAILED DESCRIPTION

[0058] For better illustrating the purposes and advantages of the present application, the following further illustrates the content of the present application in combination with the drawings and examples.

[0059] Embodiment 1:

[0060] The present application is a demodulation and decoding method based on 16APSK waveform, which simplifies the soft demodulation algorithm according to the characteristics of 16APSK constellation diagram, and uses the decision region to approximately calculate the soft information required in the decoding process, as shown in the following formula: Figure 1 The method comprises the following steps:

[0061] In the embodiment, the 16APSK mapping mode is according to the provisions of the DVB-S2 system, and the mapping diagram is as shown in the following figure: Figure 2 The LDPC code selects a π-cyclic code type, and the main parameters are as shown in the following table:

[0062] Parameter Detail Code length 248 Code rate 1 / 2 Modulation method 16 APSK Channel model Gaussian white noise Maximum decoding iteration number 20 Intra-constellation radius ratio 1 / 3

[0063] Step 1: sequentially performing LDPC encoding and 16APSK modulation processing on the original information sequence, and transmitting in a complex AWGN channel;

[0064] The original information sequence u with a length of 124 bits is obtained after the LDPC encoding module, and the encoded sequence c=u·G is obtained, wherein G is the generation matrix of the LDPC code, and the length of the encoded sequence c is 248;

[0065] The encoded information bits are modulated by the 16APSK constellation mapping function Every 4 encoded interleaved information bits b3, b2, b1, b0 are mapped to a constellation point in the space;

[0066] wherein, is the complete constellation space of the 16APSK mapped symbol, which contains 16 constellation points in total, the radius of the inner circle constellation point is R1, and the radius of the outer circle constellation point is R2;

[0067] The encoded sequence c is obtained after the 16APSK modulation mapping, and the symbol sequence y=φ(c)={y1, y2, …, yt}, where t = 248 / 4 = 62;

[0068] The symbol sequence y is transmitted through a complex AWGN channel;

[0069] Step 2: The demodulator receives the output symbols from the AWGN channel and initializes the log-likelihood ratio information of the first bit using the channel received symbols;

[0070] The symbol sequence output by the channel is z = {z1, z2, ..., z} t}, z = y + n, where n is the mean and variance. It is an additive white Gaussian noise sequence;

[0071] When deriving soft bit information using the initial symbol information of the received channel, the source is considered to be of equal probability distribution, meaning that each initial bit has an equal probability of being 0 or 1.

[0072] According to the received symbol z t The corresponding sub-constellation region partitioning diagram for the first bit b3 is as follows: Figure 3 As shown in (a), the sub-constellation diagram of the first bit b3 is symmetrical about the I-axis and Q-axis, and will receive the symbol z. t Mapped to the first quadrant, z t The log-likelihood ratio LLR(b3) of the first bit b3 is shown in equation (1):

[0073]

[0074] in, i = 0, 4, 8, 12, Let a be the i-th constellation mapping point, and ||ab|| be the distance between points a and b on the constellation mapping map;

[0075] like Figure 4 As shown in (a), using ray D1: ∠θ=π / 6 and line D2: Q=D, respectively, we can determine the relationship between ray D1: ∠θ=π / 6 and line D2: Q=D. min ,in Determine max(P0, P4) and max(P8, P... 12 As shown in equations (2) and (3) respectively:

[0076]

[0077] Where, (x) I And (x) Q These are the real and imaginary parts of the complex signal x, respectively.

[0078] Step 3: The demodulator receives the output symbols from the AWGN channel and initializes the log-likelihood ratio information of the second bit using the channel received symbols;

[0079] According to the received symbol z t The corresponding sub-constellation region partitioning diagram for the second bit b2 is as follows: Figure 3 As shown in (b), the sub-constellation diagram of the second bit b2 is symmetric about the I-axis and Q-axis, mapping the received symbol to the first quadrant. The log-likelihood ratio LLR(b2) of the second bit b2 is shown in equation (4).

[0080]

[0081] like Figure 4 As shown in (b), using ray D3: ∠θ=π / 3 and line D4: I=D min ,in Determine max(P0, P8) and max(P4, P8). 12 As shown in equations (5) and (6) respectively:

[0082]

[0083] Step 4: The demodulator receives the output symbols from the AWGN channel and initializes the log-likelihood ratio information of the third bit using the channel received symbols;

[0084] According to the received symbol z t The corresponding sub-constellation region partitioning diagram for the third bit b1 is as follows: Figure 3 As shown in (c), the sub-constellation diagram of the third bit b1 is completely symmetrical about the Q-axis, and the LLR value of the third bit b1 is only related to the received symbol z. t The real part (z) t ) I Related to the imaginary part (z) t ) Q Regardless, LLR(b1) is approximately as shown in equation (7):

[0085] LLR(b1)=α×Amp×(z t ) I (7)

[0086] Where Amp = (R1·4 + R2·12) / 16 is the average amplitude of the constellation diagram, and α is the weighting factor, α = 1.25;

[0087] Step 5: The demodulator receives the output symbols from the AWGN channel and initializes the log-likelihood ratio information of the 4th bit using the channel received symbols;

[0088] According to the received symbol z t The corresponding sub-constellation region partitioning diagram for the 4th bit b0 is as follows: Figure 3(d) as shown, the sub-constellation plot of the 4th bit b0 is completely symmetric about the I-axis, and the LLR value of the 4th bit b0 is only related to the imaginary part (z t ) t ) Q of the received symbol z t ) I , and is independent of the real part (z t ) Q , and the LLR(b0) is approximately as shown in equation (8):

[0089] LLR(b0) = a x Amp x (z ij ) j\i (8)

[0090] wherein the average amplitude Amp and the weight factor a are the same as in step four;

[0091] Step six, the iterative decoding process is completed in the LDPC decoder, and specifically includes the following sub-steps:

[0092] Step 6.1 updates the information transmitted from the check node to the variable node, as shown in equation (9):

[0093]

[0094] wherein Lq ij , is the log-likelihood ratio of the i-th bit obtained in steps two to five, and the set R j\i is the set of positions in the i-th row of the check matrix H except the i-th 1;

[0095] Step 6.2 updates the information transmitted from the variable node to the check node, as shown in equation (10):

[0096]

[0097] wherein Lp i is the log-likelihood ratio of the i-th bit calculated in steps two to five, and the set C i\j is the set of positions in the i-th row of the check matrix H except the j-th 1;

[0098] Step 6.3 determines the posterior log-likelihood ratio of each bit, as shown in equation (11):

[0099]

[0100] Step 6.4 makes a hard decision of each variable node as 0 or 1, as shown in equation (12):

[0101]

[0102] Step 6.5 determines the stopping condition:

[0103] If the decision result satisfies the check matrix H of the LDPC code, i.e. or reaches the preset maximum iteration number, the decoding iteration is stopped, otherwise, the information is renewed in step 6.1 again;

[0104] The embodiment combines the (248, 124) LDPC code and the 16 APSK modulation, improves the frequency band utilization on the basis of ensuring the channel coding gain, and adopts the approximate algorithm in the demodulation and decoding, so that the implementation complexity of the receiver is reduced without losing the system performance;

[0105] The simulation analysis of the bit error rate is carried out for the embodiment, and the simulation result is compared with the traditional demodulation algorithm and the Max-log-MAP algorithm, as shown in the following table: Figure 5 The bit error rate of the soft demodulation approximate method of the application does not have obvious loss, but the implementation complexity is greatly reduced;

[0106] Through the above six steps, the 16 APSK soft demodulation receiver based on the LDPC code is completed;

[0107] And the method further comprises a seventh step of: taking the decision result obtained in the sixth step as the demodulation and decoding result of the receiver, judging the region where the received symbol is located in each bit sub-constellation diagram, simplifying the calculation process of the bit soft information, reducing the exponential processing unit and the logarithmic processing unit in the traditional calculation circuit, and reducing the implementation complexity of the engineering under the condition of ensuring the decoding accuracy, optimizing the engineering structure, and solving the related engineering problems.

[0108] The above specific description further details the purpose, technical scheme and beneficial effects of the application, and it should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application, and any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A demodulation and decoding method based on 16APSK waveform, characterized in that: By approximating the decoding likelihood ratio during demodulation, exponential and logarithmic operations are transformed into simple addition and multiplication operations, thus enabling the construction of a low-complexity receiver, reducing processing latency, and improving resource utilization. Specifically, this includes the following steps: Step 1: Perform LDPC encoding and 16APSK modulation on the original information sequence in sequence, and then transmit it into the complex AWGN channel; The original information sequence u of length k bits is processed by the LDPC coding module to obtain the encoded sequence c = u·G, where G is the generator matrix of the LDPC code and the length of the encoded sequence c is m. The encoded information bits are mapped using a 16APSK constellation mapping function. Modulation is performed, and every four coded and interleaved information bits b3, b2, b1, b0 are mapped to one constellation point in space; in, The complete constellation space after 16APSK mapping contains 16 constellation points, with the radius of the inner constellation points being R1 and the radius of the outer constellation points being R2. After the encoded sequence c is modulated and mapped using 16APSK, the symbol sequence y = φ(c) = {y1, y2, ..., y} is obtained. t }; in, To round up, if m is not divisible by 4, add 0s to the end of the sequence to satisfy 4 bits before mapping. The symbol sequence y is transmitted through a complex AWGN channel; Step 2: The demodulator receives the output symbols from the AWGN channel and initializes the log-likelihood ratio information of the first bit using the channel received symbols; The symbol sequence output by the channel is z = {z1, z2, ..., z} t }, z = y + n, where n is a variable with mean 0 and variance . A sequence of additive white Gaussian noise; When deriving soft bit information using the initial symbol information of the received channel, the source is considered to be of equal probability distribution, meaning that each initial bit has an equal probability of being 0 or 1. According to the received symbol z t The corresponding sub-constellation region partitioning diagram for the first bit b3 is symmetrical about the I-axis and Q-axis, and will receive the symbol z. t Mapped to the first quadrant, z t The log-likelihood ratio LLR(b3) of the first bit b3 is shown in equation (1): in, Let a be the i-th constellation mapping point, and ||ab|| be the distance between points a and b on the constellation mapping map; Using ray D1: ∠θ=π / 6 and line D2: Q=D respectively min ,in Determine max(P0, P4) and max(P8, P... 12 As shown in equations (2) and (3) respectively: Where, (x) I And (x) Q These are the real and imaginary parts of the complex signal x, respectively. Step 3: The demodulator receives the output symbols from the AWGN channel and initializes the log-likelihood ratio information of the second bit using the channel received symbols; According to the received symbol z t The corresponding sub-constellation region partitioning diagram of the second bit b2 is symmetrical about the I-axis and Q-axis, mapping the received symbols to the first quadrant. The log-likelihood ratio LLR(b2) of the second bit b2 is shown in equation (4): Using ray D3: ∠θ=π / 3 and line D4: I=D respectively min ,in Determine max(P0, P8) and max(P4, P8). 12 As shown in equations (5) and (6) respectively: Step 4: The demodulator receives the output symbols from the AWGN channel and initializes the log-likelihood ratio information of the third bit using the channel received symbols; According to the received symbol z t The corresponding sub-constellation region partitioning diagram for the third bit b1 is completely symmetrical about the Q-axis. The LLR value of the third bit b1 is only related to the received symbol z. t The real part (z) t ) I Related to the imaginary part (z) t ) Q Regardless, LLR(b1) is approximately as shown in equation (7): LLR(b1)=α×Amp×(z t ) I (7) Where Amp=(R1·4+R2·12) / 16 is the average amplitude of the constellation diagram, and α is the weighting factor; Step 5: The demodulator receives the output symbols from the AWGN channel and initializes the log-likelihood ratio information of the 4th bit using the channel received symbols; According to the received symbol z t The corresponding sub-constellation region partitioning diagram for the 4th bit b0 is completely symmetrical about the I-axis. The LLR value of the 4th bit b0 is only related to the received symbol z. t The imaginary part (z) t ) Q Related to the real part (z) t ) I Regardless, LLR(b0) is approximately as shown in equation (8): LLR(b0)=α×Amp×(z t ) Q (8) Among them, the average amplitude Amp and the weighting factor α are the same as in step four; Step Six: The iterative decoding process is completed within the LDPC decoder, specifically including the following sub-steps: Step 6.1 Update the information passed from the verification node to the variable node, as shown in equation (9): Among them, initializing Lq ij , Let R be the log-likelihood ratio of the i-th bit obtained in steps two through five. j\i Let H be the set of positions in the j-th row of the verification matrix, excluding the i-th 1. Step 6.2 Update the information passed from the variable node to the verification node, as shown in equation (10): Among them, Lp i Let C be the log-likelihood ratio of the i-th bit calculated in steps two through five. i\j Let H be the set of positions in the i-th row of the verification matrix, excluding the j-th 1. Step 6.3 Determine the posterior log-likelihood ratio for each bit, as shown in Equation (11): Step 6.4 performs a hard decision on each variable node, assigning it either 0 or 1, as shown in equation (12): Step 6.5 Determine the stopping conditions: If the judgment result The parity check matrix H that satisfies the LDPC code is, i.e. If the preset maximum number of iterations is reached, the decoding iteration stops; otherwise, return to step 6.1 to update the information again. By following the above six steps, the 16APSK soft demodulation receiver based on LDPC codes can be constructed.

2. The demodulation and decoding method based on 16APSK waveform as described in claim 1, characterized in that: Step 7: Use the decision result obtained in Step 6 as the demodulation and decoding result of the receiver. By determining the location of the received symbol in each bit sub-constellation diagram, the calculation process of bit soft information is simplified, the exponential processing unit and logarithmic processing unit in the traditional computing circuit are reduced, and the complexity of engineering implementation can be reduced while ensuring the decoding accuracy, optimizing the engineering structure and solving related engineering problems.

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