CN111884661B - Method of LDPC coding combined with 16DAPSK modulation and demodulation - Google Patents

Abstract

The utility model discloses a method for combining 16DAPSK time domain differential modulation and demodulation based on LDPC channel coding of an OFDM system, which is characterized by comprising the following steps: 1) Generating data; 2) Generating (512, 256) an LDPC channel coding matrix; 3) Generating a check matrix; 4) Channel coding is carried out on the data; 5) 16DAPSK digital modulation; 6) OFDM is orthogonal frequency division multiplexing; 7) Adding noise to pass through a channel; 8) Solving OFDM; 9) DIFTIME_16DAPSK joint LDPC channel decoding demodulation; 10 LDPC minimum sum decoding output data information. The method has the advantages of easy hardware realization, good adaptability, capability of resisting the error code performance reduction caused by a multipath fading channel, capability of improving the effectiveness of the channel and the utilization rate of subcarriers, and capability of improving the fault tolerance of the channel to the carrier phase, namely, demodulating correct corresponding data under the condition of large carrier phase deviation.

Description

Method of LDPC coding combined with 16DAPSK modulation and demodulation

technical field

The invention relates to communication technology, in particular to a method for LDPC coding combined with 16DAPSK modulation and demodulation.

Background technique

With the development of communication technology and the requirements of practical applications, the rapid growth of wireless multimedia mobile access communication applications leads to the rapid increase of high bit rate wireless access. OFDM+MQAM is currently the most commonly used channel coding multi-carrier digital modulation technology. Using the good performance of OFDM multi-carrier in multi-path channels combined with the advantages of MQAM's good bit error rate performance and MQAM's high frequency band utilization, it is widely used in all aspects of people's lives.

However, if MQAM digital modulation and demodulation technology is used, coherent demodulation must be used, which requires channel estimation to understand the channel distortion on each OFDM subcarrier, but the channel estimation of coherent demodulation requires a large amount of calculation and needs to add long and short training sequences , which increases the complexity of implementation and reduces the effectiveness of the channel. Moreover, the low bit error rate performance of MQAM digital modulation is not ideal in multipath fading channels.

Contents of the invention

The purpose of the present invention is to provide a method for LDPC coding combined with 16DAPSK modulation and demodulation to address the deficiencies of the prior art. This method is easy to implement in hardware, has good adaptability, can resist the error performance reduction caused by multipath fading channels, can improve the effectiveness of the channel and the utilization rate of subcarriers, and can improve the error tolerance of the channel to the carrier phase, that is, the carrier phase offset. In a large case, the correct corresponding data can still be demodulated.

The technical scheme that realizes the object of the present invention is:

A method for LDPC coding joint 16DAPSK modulation and demodulation, comprising the steps:

1) Generated data: The generated data includes 256 symbols, and each symbol includes 48 subcarriers. The generated data is regarded as information bits, and the mathematical representation is a [48,256] matrix, and the matrix [48,256] is an all-zero matrix. Demodulation It must be all zeros when it comes out, which has no effect on error correction performance and bit error performance;

β的上标表示第几个循环子矩阵的种子、下标表示循环行向量所在的行数，如表1所示，每一个种子由64个16进制表示，将16进制转换为4比特二进制表示，变为256个二进制表示，将此256二进制表示的数据，循环右移一位产生新的一行，依次循环右移63次产生63行256个二进制数据，加上种子一行，总共组成64行256个二进制数据，数学表示为[64,256]的子矩阵，总共有4个种子β即/>

那么生成矩的阵数学表示为[256,256]的矩阵，依据公式(1)产生信道编码矩阵，其中I_64×64代表一个64阶单位矩阵，0表示全零矩阵，最后的编码矩阵数学表示为[512,256]：2) Generate (512,256) LDPC channel coding matrix: According to formula (1), the generated matrix is composed of two parts: identity matrix I and cyclic sub-matrix β, wherein the cyclic row vector seed of cyclic sub-matrix is

The superscript of β indicates the seed of the cyclic submatrix, and the subscript indicates the number of rows where the cyclic row vector is located. As shown in Table 1, each seed is represented by 64 hexadecimals, and the hexadecimals are converted into 4 bits The binary representation becomes 256 binary representations. The 256 binary representations of data are shifted to the right by one bit to generate a new row, and then shifted to the right 63 times in turn to generate 63 rows of 256 binary data, plus a seed row to form a total of 64 256 rows of binary data, mathematically expressed as a sub-matrix of [64,256], there are a total of 4 seeds β that />

Then the mathematical representation of the generating matrix is a [256,256] matrix, and the channel coding matrix is generated according to formula (1), where I _64×64 represents a 64-order unit matrix, 0 represents an all-zero matrix, and the final coding matrix is mathematically represented as [ 512,256]:

Table 1: Cyclic row vector seeds for generating matrices

代表模2运算，将公式(2)转换为向量的种子，如表2所示，表2中总共有32个种子，每个种子都是长度为64的行向量，表中的坐标表示元素“1”所在行向量的位置，每个通过1的位置产生每个子矩阵第一行的行向量，每个子矩阵都是64x64的大小，所以循环右移63次，产生63个新的行向量与原来的行向量组成一个校验子矩阵，故校验矩阵的数学表示为[256,512]的矩阵：3) Generation of parity check matrix: parity check matrix is as shown in formula (2), and wherein I represents the unit matrix that size is P, and P=64, and 0 represents that size is the all-zero matrix of P, and Φ represents that by unit matrix I _{64 ×64} The matrix obtained by circular right shifting,

Represents the modulo 2 operation, transforming the formula (2) into the seed of the vector, as shown in Table 2, there are a total of 32 seeds in Table 2, each seed is a row vector with a length of 64, and the coordinates in the table represent elements " The position of the row vector where 1" is located, each passing through the position of 1 generates the row vector of the first row of each sub-matrix, each sub-matrix is 64x64 in size, so the cycle is shifted to the right 63 times, and 63 new row vectors are generated that are the same as the original The row vectors form a syndrome matrix, so the mathematical representation of the check matrix is a matrix of [256,512]:

Table 2: Circular row vector seeds for parity check matrix

1 2 3 4 5 6 7 8 1 (64,62) (9) (49) (twenty four) NALL (42) (61) (64) 2 (55) (64,60) (49) (twenty two) (64) NALL (36) (25) 3 (15) (64) (64,54) (26) (55) (64) NALL (42) 4 (34) (55) (61) (64,10) (57) (2) (64) NALL

,

4) Perform channel coding on the data: take the data generated in step 1) as the data source, let the data source be X, expressed as shown in formula (3), assume that the coded data is represented by Y, according to the channel coding formula ( 4) Encode the data source, and the encoded data can be expressed as shown in formula (5), where y ₁ y ₂ ... y ₂₅₆ represents valid information, and c ₁ c ₂ ... c ₂₅₆ represents is the check digit, and the encoded data is expressed as a matrix of [48,512]:

X＝[x ₁ x ₂ x ₃ x ₄ ... x ₂₅₄ x ₂₅₅ x ₂₅₆ ] (3),

Y=X*G (4),

Y=[y ₁ y ₂ ... y ₂₅₆ c ₁ c ₂ ... c ₂₅₆ ] (5),

5) 16DAPSK digital modulation: convert the data matrix of [48,512] in step 3) into a format suitable for 16DAPSK modulation, that is, convert it into a matrix of [4,6144], and then each column is regarded as a 4-bit binary number, assuming It is [b3b2b1b0], the highest bit b3 is used as the amplitude for amplitude differential encoding, and then the encoded data 0 is mapped to 0.5, and 1 is mapped to 1, and the input lower 3 bits b2b1b0 are generated according to formula (6) and formula (7) Differential phase Δθ _i , where I _i and Q _i represent the horizontal and vertical coordinates of the mapping, and Δθ _i represents the phase difference between the current data and the previous data. The specific mapping relationship divides a circle into 8 equal parts, that is, {π/8,3π One of /8,5π/8,7π/8,9π/8,11π/8,13π/8,15π/8}, 16 coordinate points in the modulated 16DAPSK constellation diagram are "o", and the other 16 coordinates For "*", the signal can only jump alternately between "*" and "o", avoiding 180° phase jump:

I _i =I _i-1 cos(Δθ _i )-Q _i-1 sin(Δθ _i ) (6),

Q _i ＝I _i-1 sin(Δθ _i )+Q _i-1 cos(Δθ _i ) (7);

6) OFDM is Orthogonal Frequency Division Multiplexing: The system subcarrier spacing of OFDM is 312.5KHz, and the standard uses 48 parallel subcarriers for data transmission. After step 4), it becomes 128+1 symbols after modulation, and each symbol has 48 subcarriers. Carrier, adding 16 empty carriers, each symbol becomes 64 subcarriers, and then undergoes 64-point IFFT for time domain change, then adds 16 subcarrier cyclic prefixes, and finally performs serial conversion and parallelization. The data format from OFDM is Complex signal of [1,10320];

7) Noise-added over-channel: Noise-added over-channel includes:

7-1) Gaussian additive white noise channel, wherein the noise variance is σ ² , and each SNR point has 100 data frames;

7-2) In the hilly area of the COST207 channel, the channel propagation delay Delay=[0 1 2 3 4 5], the path power decibel value PowerdB=[0 -4 -8 -12 -16 -20], and the noise variance is also σ ² , 100 data frames for each SNR point;

8) Solution to OFDM: convert the 10320 complex signals after passing through the channel into a matrix of [80,129] first, then remove the cyclic prefix of 16 subcarriers and convert them into a matrix of [64,129], and then undergo FFT changes, Then remove 16 empty carriers, and transform the data format into a matrix of [48,129];

然后依据公式(8)进行归一化：9) DIFTIME_16DAPSK joint LDPC channel decoding and demodulation: set the i-th data demodulated in step 7) as G _i , let

Then normalize according to formula (8):

After normalization, it is equivalent to only extracting the phase information of b ₂ b ₁ b _0. The logarithmic likelihood ratio of a single bit, that is, the soft information LLR, is defined as shown in formula (9), where k is 0, 1, 2. It means the kth bit in the phase modulation, S represents the data point after π/8-8DPSK modulation, and Gdn _i represents the normalized information:

对应相位调制中第i个数据的(b₂b₁b₀)：According to the distribution characteristics of the normalized constellation diagram, the formula (9) is simplified as (10), where E _s represents the bit signal energy, N ₀ represents the noise power with a mean of 1 and a variance of σ ² , because LDPC The decoding uses the minimum sum decoding algorithm that is not affected by the same scale factor of the input information, so formula (10) can be simplified to formula (11), the soft information

Corresponding to (b ₂ b ₁ b ₀ ) of the i-th data in phase modulation:

The ratio Gd _i of two adjacent signals is distributed around circles with radii of 0.5, 1, and 2. If Gd _i is less than 1, then the amplitude soft information corresponding to b ₃ is shown in formula (12):

If Gd _i is less than 1, then the amplitude soft information corresponding to b ₃ is shown in formula (13):

Among them, α is the ratio of high level to low level of amplitude modulation. In 16DAPSK, α=2, the soft bit information of one data (b ₃ b ₂ b ₁ b ₀ ), so 16DAPSK is like the demodulated data format is [48,512];

10) LDPC minimum sum decoding output data information: the 16DAPSK in step 8) such as the demodulated data [48,512] utilizes the check matrix generated in step 2) to decode and output through the minimum sum decoding algorithm, and each output symbol to remove its 256 parity bits, and the final output data format is [48,256] which is the final demodulation output.

In view of the deficiencies and related defects of the traditional OFDM+MQAM system, this technical solution converts the 10320 complex signals after passing through the channel into a matrix of [80,129], and then removes the cyclic prefix of 16 subcarriers Convert to the matrix of [64,129], and then undergo FFT changes, then remove 16 empty carriers, and transform the data format into a matrix of [48,129]; use the powerful channel error correction capability of LDPC, the anti-multipath performance of OFDM, in the digital modulation On the one hand, it adopts the digital modulation and demodulation technology of time-domain difference 16DAPSK, and non-coherent demodulation can be used at the demodulation end, without channel estimation, which reduces the complexity of the system. The corresponding data can be correctly demodulated, and DIFTIME_16DAPSK can weaken the performance degradation caused by the fading channel in the multipath fading channel.

Compared with the prior art, this technical solution has the following characteristics:

1. The data length is more suitable for processing by related computing equipment: the LDPC encoding method of the ultra-short code (256,512) in CCSDS is adopted, the encoding efficiency is 1/2, the length of the error correction code is 256, and the length of the information code is 256. Both 256 and 512 are 16 , 32, and 64 multiples, so it is more suitable for the processing of current computing equipment;

2. OFDM uses 48 effective subcarriers, 16 inserted pilots, and 64 subcarriers to form an OFDM symbol, which is more suitable for IFFFT and computing processing equipment;

3. Using DIFTIME_16DAPSK technology, no channel estimation is required, which greatly reduces the complexity of implementation, and at the same time, DIFTIME_16DAPSK can effectively resist performance degradation caused by multipath fading;

4. DIFTIME_16DAPSK modulation is divided into 2DASK amplitude differential and 8DPSK. In 8DPSK modulation, this technical solution uses π/8-8DPSK so that the phase modulation can only jump between two adjacent points, eliminating the phase modulation The phenomenon of phase ambiguity;

5. The bit error performance of different bits of a symbol in high-order modulation and demodulation is different. The utility model adopts a soft demodulation method to calculate the probability that each bit is 0 and 1. Separate the probability value of the amplitude and the probability value of the phase into 4 groups of sub-data, send each group of data to the minimum sum decoding algorithm Min_sum for decoding, and finally perform data reorganization.

This method is easy to implement in hardware, has good adaptability, can resist the error performance reduction caused by multipath fading channels, can improve the effectiveness of the channel and the utilization rate of subcarriers, and can improve the error tolerance of the channel to the carrier phase, that is, the carrier phase offset. In a large case, the correct corresponding data can still be demodulated.

Description of drawings

Fig. 1 is a schematic block diagram of DIFTIME_16DAPSK modulation in an embodiment;

Fig. 2 is a schematic diagram of the mapping relationship between differential phase Δθ _i and b ₂ b ₁ b ₀ in an embodiment;

Fig. 3 is the DIFTIME_16DAPSK constellation diagram in the embodiment;

Fig. 4 is a schematic block diagram of DIFTIME_16DAPSK joint LDPC channel decoding soft demodulation in the embodiment;

Fig. 5 is a schematic diagram of BER performance curves of 16DAPSK soft demodulation LDPC coding Min_Sum decoding and high-order soft demodulation convolutional channel coding Viterbi decoding under the AWGN channel in the embodiment;

Fig. 6 is a schematic diagram of BER performance curves of 16DAPSK soft demodulation LDPC encoding Min_Sum decoding and 16DAPSK hard demodulation LDPC encoding Min_Sum decoding under the AWGN channel in the embodiment;

Fig. 7 is a schematic diagram of the bit error rate performance curves of 16DAPSK soft demodulation LDPC encoding Min_Sum decoding, 16DAPSK hard demodulation LDPC encoding Min_Sum decoding and 16ADQAM demodulation LDPC encoding Min_Sum decoding under the COST207 hilly area channel in the embodiment.

Detailed ways

The content of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited.

Example:

A method for LDPC coding joint 16DAPSK modulation and demodulation, comprising the steps:

1) Generated data: The generated data includes 256 symbols, and each symbol includes 48 subcarriers. The generated data is regarded as information bits, and the mathematical representation is a [48,256] matrix, and the matrix [48,256] is an all-zero matrix. Demodulation It must be all zeros when it comes out, which has no effect on error correction performance and bit error performance;

β的上标表示第几个循环子矩阵的种子、下标表示循环行向量所在的行数，如表1所示，每一个种子由64个16进制表示，将16进制转换为4比特二进制表示，变为256个二进制表示，将此256二进制表示的数据，循环右移一位产生新的一行，依次循环右移63次产生63行256个二进制数据，加上种子一行，总共组成64行256个二进制数据，数学表示为[64,256]的子矩阵，总共有4个种子β即/>

那么生成矩的阵数学表示为[256,256]的矩阵，依据公式(1)产生信道编码矩阵，其中I_64×64代表一个64阶单位矩阵，0表示全零矩阵，最后的编码矩阵数学表示为[512,256]：2) Generate (512,256) LDPC channel coding matrix: According to formula (1), the generated matrix is composed of two parts: identity matrix I and cyclic sub-matrix β, wherein the cyclic row vector seed of cyclic sub-matrix is

The superscript of β indicates the seed of the cyclic submatrix, and the subscript indicates the number of rows where the cyclic row vector is located. As shown in Table 1, each seed is represented by 64 hexadecimals, and the hexadecimals are converted into 4 bits The binary representation becomes 256 binary representations. The 256 binary representations of data are shifted to the right by one bit to generate a new row, and then shifted to the right 63 times in turn to generate 63 rows of 256 binary data, plus a seed row to form a total of 64 256 rows of binary data, mathematically expressed as a sub-matrix of [64,256], there are a total of 4 seeds β that />

Then the mathematical representation of the generating matrix is a [256,256] matrix, and the channel coding matrix is generated according to formula (1), where I _64×64 represents a 64-order unit matrix, 0 represents an all-zero matrix, and the final coding matrix is mathematically represented as [ 512,256]:

Table 1: Circular row vector seeds for generating matrix from submatrix

代表模2运算，将公式(2)转换为向量的种子，如表2所示，表2中总共有32个种子，每个种子都是长度为64的行向量，表中的坐标表示元素“1”所在行向量的位置，每个通过1的位置产生每个子矩阵第一行的行向量，每个子矩阵都是64x64的大小，所以循环右移63次，产生63个新的行向量与原来的行向量组成一个校验子矩阵，故校验矩阵的数学表示为[256,512]的矩阵：3) Generation of parity check matrix: parity check matrix is as shown in formula (2), and wherein I represents the unit matrix that size is P, and P=64, and 0 represents that size is the all-zero matrix of P, and Φ represents that by unit matrix I _{64 ×64} The matrix obtained by circular right shifting,

Represents the modulo 2 operation, transforming the formula (2) into the seed of the vector, as shown in Table 2, there are a total of 32 seeds in Table 2, each seed is a row vector with a length of 64, and the coordinates in the table represent elements " The position of the row vector where 1" is located, each passing through the position of 1 generates the row vector of the first row of each sub-matrix, each sub-matrix is 64x64 in size, so the cycle is shifted to the right 63 times, and 63 new row vectors are generated that are the same as the original The row vectors form a syndrome matrix, so the mathematical representation of the check matrix is a matrix of [256,512]:

Table 2: Circular row vector seeds for parity check matrix

1 2 3 4 5 6 7 8 1 (64,62) (9) (49) (twenty four) NALL (42) (61) (64) 2 (55) (64,60) (49) (twenty two) (64) NALL (36) (25) 3 (15) (64) (64,54) (26) (55) (64) NALL (42) 4 (34) (55) (61) (64,10) (57) (2) (64) NALL

,

4) Perform channel coding on the data: take the data generated in step 1) as the data source, let the data source be X, expressed as shown in formula (3), assume that the coded data is represented by Y, according to the channel coding formula ( 4) Encode the data source, and the encoded data can be expressed as shown in formula (5), where y ₁ y ₂ ... y ₂₅₆ represents valid information, and c ₁ c ₂ ... c ₂₅₆ represents is the check digit, and the encoded data is expressed as a matrix of [48,512]:

X＝[x ₁ x ₂ x ₃ x ₄ ... x ₂₅₄ x ₂₅₅ x ₂₅₆ ] (3),

Y=X*G (4),

Y=[y ₁ y ₂ ... y ₂₅₆ c ₁ c ₂ ... c ₂₅₆ ] (5),

5) 16DAPSK digital modulation: convert the data matrix of [48,512] in step 3) into a format suitable for 16DAPSK modulation, that is, convert it into a matrix of [4,6144], and then each column is regarded as a 4-bit binary number, assuming It is [b3b2b1b0], the highest bit b3 is used as the amplitude for amplitude differential encoding, and then the encoded data 0 is mapped to 0.5, and 1 is mapped to 1, and the input lower 3 bits b2b1b0 are generated according to formula (6) and formula (7) Differential phase Δθ _i , where I _i and Q _i represent the horizontal and vertical coordinates of the mapping, and Δθ _i represents the phase difference between the current data and the previous data. The specific mapping relationship divides a circle into 8 equal parts, that is, {π/8,3π One of /8,5π/8,7π/8,9π/8,11π/8,13π/8,15π/8}, 16 coordinate points in the modulated 16DAPSK constellation diagram are "o", and the other 16 coordinates For "*", the signal can only jump alternately between "*" and "o", avoiding 180° phase jump:

I _i =I _i-1 cos(Δθ _i )-Q _i-1 sin(Δθ _i ) (6),

Q _i ＝I _i-1 sin(Δθ _i )+Q _i-1 cos(Δθ _i ) (7);

6) OFDM is Orthogonal Frequency Division Multiplexing: The system subcarrier spacing of OFDM is 312.5KHz, and the standard uses 48 parallel subcarriers for data transmission. After step 4), it becomes 128+1 symbols after modulation, and each symbol has 48 subcarriers. Carrier, adding 16 empty carriers, each symbol becomes 64 subcarriers, and then undergoes 64-point IFFT for time domain change, then adds 16 subcarrier cyclic prefixes, and finally performs serial conversion and parallelization. The data format from OFDM is Complex signal of [1,10320];

7) Noise-added over-channel: Noise-added over-channel includes:

7-1) Gaussian additive white noise channel, wherein the noise variance is σ ² , and each SNR point has 100 data frames;

7-2) Delay in channel propagation in hilly areas in COST207 channel Delay=[0 1 2 3 4 5], path power decibel value PowerdB=[0 -4-8 -12 -16 -20], noise variance is also σ ² , 100 data frames for each SNR point;

8) Solution to OFDM: convert the 10320 complex signals after passing through the channel into a matrix of [80,129] first, then remove the cyclic prefix of 16 subcarriers and convert them into a matrix of [64,129], and then undergo FFT changes, Then remove 16 empty carriers, and transform the data format into a matrix of [48,129];

然后依据公式(8)进行归一化：9) DIFTIME_16DAPSK joint LDPC channel decoding and demodulation: set the i-th data demodulated in step 7) as G _i , let

Then normalize according to formula (8):

After normalization, it is equivalent to only extracting the phase information of b ₂ b ₁ b _0. The logarithmic likelihood ratio of a single bit, that is, the soft information LLR, is defined as shown in formula (9), where k is 0, 1, 2. It means the kth bit in the phase modulation, S represents the data point after π/8-8DPSK modulation, and Gdn _i represents the normalized information:

对应相位调制中第i个数据的(b₂b₁b₀)：According to the distribution characteristics of the normalized constellation diagram, the formula (9) is simplified as (10), where E _s represents the bit signal energy, N ₀ represents the noise power with a mean of 1 and a variance of σ ² , because LDPC The decoding uses the minimum sum decoding algorithm that is not affected by the same scale factor of the input information, so formula (10) can be simplified to formula (11), the soft information

Corresponding to (b ₂ b ₁ b ₀ ) of the i-th data in phase modulation:

The ratio Gd _i of two adjacent signals is distributed around circles with radii of 0.5, 1, and 2. If Gd _i is less than 1, then the amplitude soft information corresponding to b ₃ is shown in formula (12):

If Gd _i is less than 1, then the amplitude soft information corresponding to b ₃ is shown in formula (13):

Among them, α is the ratio of high level to low level of amplitude modulation. In 16DAPSK, α=2, the soft bit information of one data (b ₃ b ₂ b ₁ b ₀ ), so 16DAPSK is like the demodulated data format is [48,512];

10) LDPC minimum sum decoding output data information: the 16DAPSK in step 8) such as the demodulated data [48,512] utilizes the check matrix generated in step 2) to decode and output through the minimum sum decoding algorithm, and each output symbol to remove its 256 parity bits, and the final output data format is [48,256] which is the final demodulation output.

Bit error rate analysis: As shown in Figure 5, under the AWGN channel, the time domain difference 16DAPSK is maintained, the OFDM system parameters and the method of soft demodulation are changed, and only the channel coding is changed. Compared with the same bit error rate of 10 ^-3 The bit error performance of the convolutional channel coding and Viterbi decoding scheme is improved by about 2-2.5dB; as shown in Figure 6, the time domain difference 16DAPSK is kept, the OFDM system parameters and the LDPC coding and decoding scheme are unchanged, only changing 16DAPSK demodulation method, as shown in Figure 7, when the bit error rate is 10 ^-3 , the bit error rate using soft demodulation is about 10-11dB higher than the bit error performance using hard demodulation, and the hills in the COST207 model The regional (HL) channel is also a multipath channel. Under the condition that OFDM parameters and LDPC structure remain unchanged, as shown in Figures 5, 6, and 7, it is better than the hard demodulation scheme and 16ADQAM when the bit error rate is 10 ^-2 The bit error rate performance of the solution is improved by about 8-9dB.

Claims (1)

1. The method for combining the 16DAPSK time domain differential modulation and demodulation based on the LDPC channel coding of the OFDM system is characterized by comprising the following steps:

1) Generating data: the generated data comprises 256 symbols, each symbol comprises 48 sub-carriers, the generated data is used as information bits and is expressed as a matrix [48,256] mathematically, the matrix [48,256] is an all-zero matrix, and the demodulated data also needs to be all-zero;

2) Generating (512, 256) an LDPC channel coding matrix: the generating matrix consists of an identity matrix I and a cyclic submatrix beta according to the formula (1), wherein the cyclic row vector seeds of the cyclic submatrix are as follows

The upper index of beta indicates what number of seeds of the cyclic submatrix and the lower index indicates the number of rows where the cyclic vector is located, as shown in table 1, each seed is represented by 64 16-ary, 16-ary is converted into 4-bit binary, 256-ary is converted into 256-ary, the data of the 256-ary is circularly shifted right by one bit to generate a new row, 63 rows of 256-ary data are circularly shifted right in turn, and the total of 64 rows of 256-ary data are formed by adding one seed row, which is mathematically represented as [64,256 ]]In total 4 seeds beta, i.e. +.>

Then the matrix mathematical representation of the generated moment is [256,256 ]]Generates a channel coding matrix according to equation (1), wherein I _64×64 Representing a 64-order identity matrix, 0 representing an all-zero matrix, and the final code matrix being mathematically represented as [512,256 ]]：

Table 1: generating cyclic row vector seeds for matrix submatrices

3) Generating a check matrix: the check matrix is shown in formula (2), wherein I represents an identity matrix with the size of P, P=64, 0 represents an all-zero matrix with the size of P, and phi represents a matrix I formed by the identity matrix _64×64 Cycle right shiftThe resulting matrix is then used to determine,

representing the modulo-2 operation, the seed of the formula (2) is converted into a vector, as shown in Table 2, there are 32 seeds in total in Table 2, each seed is a row vector with the length of 64, the coordinates in the table represent the position of the row vector where the element '1' is located, each row vector of the first row of each submatrix is generated through the position of 1, each submatrix is 64x64 in size, so the seed is circularly shifted right 63 times, 63 new row vectors and the original row vector form a check submatrix, and the mathematical representation of the check matrix is [256,512 ]]Is a matrix of (a): table 2: cyclic row vector seed for check matrix

1 2 3 4 5 6 7 8 1 (64,62) (9) (49) (24) NALL (42) (61) (64) 2 (55) (64,60) (49) (22) (64) NALL (36) (25) 3 (15) (64) (64,54) (26) (55) (64) NALL (42) 4 (34) (55) (61) (64,10) (57) (2) (64) NALL

，

4) Channel coding the data: taking the data generated in the step 1) as a data source, enabling the data source to be X and expressed as shown in a formula (3), assuming that the encoded data is expressed by Y, encoding the data source according to a channel encoding formula (4), and enabling the encoded data to be expressed as shown in a formula (5), wherein Y is ₁ y ₂ ... y ₂₅₆ Representing the effective information, c ₁ c ₂ ... c ₂₅₆ Representing check bits, the encoded data is represented as [48,512]]Is a matrix of (a):

X＝[x ₁ x ₂ x ₃ x ₄ ... x ₂₅₄ x ₂₅₅ x ₂₅₆ ] (3)，

Y＝X*G (4)，

Y＝[y ₁ y ₂ ... y ₂₅₆ c ₁ c ₂ ... c ₂₅₆ ] (5)，

5) 16DAPSK digital modulation: step 3) [48,512]]Is converted into a format suitable for 16DAPSK modulation, i.e. [4,6144 ]]Then each column is considered as a 4-bit represented binary number, assumed to be [ b3b2b1b 0]]The highest b3 is used as amplitude to carry out amplitude differential coding, the coded data 0 is mapped to 0.5,1 is mapped to 1, and the input low 3 bits b2b1b0 are mapped according to the formula (6) and the formula (7) to generate differential phase delta theta _i Wherein I _i ，Q _i Represents the abscissa, Δθ, of the map _i Representing the phase difference between the current data and the last data, dividing a circle 8 equally by a specific mapping relation, namely taking one of { pi/8, 3 pi/8, 5 pi/8, 7 pi/8, 9 pi/8, 11 pi/8, 13 pi/8, 15 pi/8 }, wherein 16 coordinate points in the modulated 16DAPSK constellation diagram are 'o', and the other 16 coordinate points areThe coordinates are "×", the signal can only alternate between "×" and "o", avoiding 180 ° phase jumps:

I _i ＝I _i-1 cos(Δθ _i )-Q _i-1 sin(Δθ _i ) (6)，

Q _i ＝I _i-1 sin(Δθ _i )+Q _i-1 cos(Δθ _i ) (7)；

6) OFDM is orthogonal frequency division multiplexing: the system subcarrier interval of OFDM is 312.5KHz, the standard adopts 48 parallel subcarriers to carry out data transmission, the modulation in step 4) is changed into 128+1 symbols, each symbol 48 subcarriers is added with 16 empty carriers, each symbol is changed into 64 subcarriers, then the time domain change is carried out through 64-point IFFT, then the cyclic prefix of 16 subcarriers is added, finally the serial-to-parallel conversion is carried out, and the data format from OFDM is the complex signal of [1,10320 ];

7) Noise-adding over-channel: the noise-plus-channel includes:

7-1) Gaussian additive white noise channel, where the noise variance is σ ² 100 data frames per SNR point;

7-2) Delay of channel propagation in hilly region in COST207 channel = [0 12 3 4 5 ]]Path power decibel value powerdb= [ 0-4-8-12-16-20 ]]The noise variance is also sigma ² 100 data frames per SNR point;

8) Solving OFDM: the 10320 complex signals after the channel are subjected to serial-parallel conversion and are converted into a matrix of [80,129], cyclic prefixes of 16 sub-carriers are removed and are converted into a matrix of [64,129], FFT is carried out to change, 16 empty carriers are removed, and the data format is converted into a matrix of [48,129 ];

9) DIFTIME_16DAPSK joint LDPC channel decoding demodulation: setting the ith data demodulated in the step 7) as G _i Order-making

Normalization is then performed according to equation (8):

after normalization, the composition b is extracted ₂ b ₁ b ₀ The definition of the phase information, the log-likelihood ratio of a single bit, i.e., soft information LLR, is shown in equation (9), where k is 0,1,2, representing the kth bit in the phase modulation, S represents the data point after pi/8-8 DPSK modulation, gdn _i Representing normalized information:

according to the distribution characteristics of the normalized constellation diagram, the formula (9) is simplified to be (10), wherein E _s Representative is bit signal energy, N ₀ Representing a mean of 1 and a variance of sigma ² Since LDPC decoding employs a minimum sum decoding algorithm that is not affected by the input information and the scale factor, equation (10) can be simplified to equation (11), soft information

(b) corresponding to the ith data in phase modulation ₂ b ₁ b ₀ )：

Ratio Gd of two adjacent signals _i Distributed in the vicinity of circles of radii 0.5,1 and 2, if Gd _i Less than 1, then b ₃ The corresponding amplitude soft information is shown in formula (12):

if Gd _i Less than 1, then b ₃ The corresponding magnitude soft information is shown in equation (13):

where α is the ratio of the high level to the low level of the amplitude modulation, α=2 in 16DAPSK, soft bit information (b ₃ b ₂ b ₁ b ₀ ) Thus, the 16DAPSK has a data format of [48,512]]；

10 LDPC minimum and decoded output data information: decoding and outputting the 16DAPSK in the step 8) as the demodulated data [48,512] by utilizing the check matrix generated in the step 2) through a minimum sum decoding algorithm, removing 256 check bits of each output symbol, and finally outputting the data with the data format of [48,256] as the final demodulated output.

Images