Satellite communication anti-interference access method based on low-code-rate coding and decoding

Abstract

The invention discloses a satellite communication anti-interference access method based on low-code-rate coding and decoding, and belongs to the field of digital signal processing. The implementation method comprises the following steps: allocating a unique SCMA mapping codebook to each user of a sending end, performing Turbo-Hadamard coding on to-be-sent information by each user at the same code rate, then performing mapping according to the allocated SCMA codebook to obtain a multi-dimensional to-be-sent symbol, and according to a designed frequency hopping pattern, performing frequency hopping on the multi-dimensional to-be-sent symbol according to the multi-dimensional to-be-sent symbol. And modulating the symbol information of each dimension to a corresponding carrier for transmission. All users have the same frequency hopping pattern. And a receiving end effectively identifies the interfered symbol according to the power difference existing in the received signal and performs zero setting on the interfered symbol, and then sends the processed signal to an SCMA multi-user detector to obtain demodulation information of each user. And the decoder obtains the information sent by each user by using the uninterfered part in the demodulation information and the partially interfered information, thereby realizing the satellite communication anti-interference access based on low-code-rate coding and decoding.

Description

Technical Field

[0001] The invention discloses a satellite communication anti-interference access method based on low code rate coding, in particular to an anti-interference method using low code rate coding, and belongs to the field of digital signal processing. Background Art

[0002] Satellite communication systems can provide seamless wireless coverage to complement and extend terrestrial communication networks, and are expected to be incorporated into future wireless networks, especially 6G and other networks, as recent standardization work has done. Low Earth Orbit (LEO) satellite communications, with an orbital altitude of less than 2000 km, have recently gained widespread research interest due to their potential in providing global wireless access. Compared with geostationary orbit communication systems, LEO satellite communication systems have much lower requirements on power consumption and transmission signal delay. Sparse Code Multiple Access (SCMA) is a multiple access technology that can meet the needs of massive access in future communications. Its application in satellite communications can greatly increase the number of users that the system can accommodate and effectively alleviate the pressure on spectrum resources.

[0003] However, the openness of satellite communication links makes them vulnerable to external malicious interference, which will seriously disrupt the normal operation of the system. Traditional frequency hopping technology is an effective anti-interference method, but it can only reduce the probability of signal interference and has limited anti-interference ability. In this regard, based on the ability of low-bitrate coding to utilize coding constraints and effectively restore the interfered signal, an anti-interference method for SCMA-based satellite communication is proposed, which effectively improves the anti-interference ability of the system. This provides strong support for the development of SCMA-based satellite communication. Summary of the invention

[0004] In order to solve the problem that the traditional frequency hopping anti-interference can only reduce the probability of signal interference and has limited anti-interference ability, the purpose of the present invention is to provide a satellite communication anti-interference access method based on low code rate coding. At the transmitting end, the signal to be transmitted is Turbo-Hadamard low code rate encoded, and the encoded sequence is mapped to the SCMA codebook to obtain the symbol sequence to be transmitted, and the symbol sequence to be transmitted is frequency hopping and sent according to the frequency hopping pattern. At the receiving end, the interfered frequency point is set to zero by using a filter, and demapping and decoding are performed to obtain the information sequence sent by each user. Compared with the traditional frequency hopping anti-interference technology, the present invention uses the coding gain provided by the coding to improve the anti-interference performance of the satellite communication system.

[0005] The object of the present invention is achieved through the following technical solutions.

[0006] The present invention discloses a satellite communication anti-interference access method based on low code rate coding, which allocates a unique SCMA mapping codebook to each user at the transmitting end, and each user performs Turbo-Hadamard encoding of the same code rate on the information to be sent, and then maps it according to the allocated SCMA codebook to obtain multi-dimensional symbols to be sent, and modulates the symbol information of each dimension to the corresponding carrier for transmission according to the designed frequency hopping pattern. All users have the same frequency hopping pattern. The receiving end effectively identifies the interfered symbol and sets it to zero based on the power difference in the received signal, and then sends the processed signal to the SCMA multi-user detector to obtain the demodulation information of each user. The Turbo-Hadamard decoder uses the non-interfered part of the demodulated information to recover part of the interfered information to obtain the information sent by each user, thereby realizing satellite communication anti-interference access based on low code rate coding and improving the anti-interference capability of the satellite communication system.

[0007] The present invention discloses a satellite communication anti-interference access method based on low bit rate coding, comprising the following steps:

[0008] Step 1: Determine the total number of users L of the satellite communication system, the length B of the Turbo-Hadamard coded data of each user, the encoder order r and the number M of component encoders, and perform Turbo-Hadamard coding to obtain the coded codeword C.

[0009] Determine the total number of users L in the satellite communication system, the length B of the Turbo-Hadamard coded data of each user, and the coded data of length B of the lth user is represented by b l =[b1,b2,b3,…,b B ], where l = 1, 2, ..., L. l After being interleaved by different interleavers π(m), it is expressed in the form of a matrix of B / r×r, and we get

[0010]

[0011] Among them, all elements b' in D(m) ij ∈b l , m = 1, 2, ..., M represents different component encoders. Parity check is performed on D(m) row by row, and the obtained parity check vector is convolutionally encoded with a code rate of 1 / 2 to obtain a coded check bit vector q(m) = [q1, q2, ..., q B / r ] T . Perform Hadamard coding on [D(m),q(m)] to obtain the check matrix in Represents the real number domain. The encoding results of each component encoder are concatenated to obtain the encoding codeword C = [D', q(1), P(1), q(2), P(2), ..., q(M), P(M)], where D' is the codeword b directly without passing through the interleaver. l =[b1,b2,b3,…,b B ] is expressed as a matrix of B / r×r. Codewords C are sent row by row.

[0012] Step 2: Each user is assigned a unique user codebook x l Perform SCMA mapping to obtain the mapped symbol sequence x l .

[0013] The user codebook x described in step 2 l Expressed as Where K represents the codebook dimension and A represents the modulation base. Based on the modulation base A, log2(A) bits are mapped into a codeword X a ∈χ l , get the mapped symbol sequence where X' i ∈χ l , i=1,2,…,B / R / log2(A), R represents the encoding bit rate.

[0014] Step 3: Translate the symbol sequence x to be sent by each user according to the frequency hopping pattern φ l Each dimension of information is modulated onto the corresponding carrier.

[0015] Each hop in the frequency hopping pattern described in step 3 corresponds to K carriers. For the lth user, the carrier corresponding to the nth hop is represented as {f1,f2,…,f K}, the nth symbol to be sent is Each hop corresponds to a symbol, and the symbol to be sent is modulated onto the corresponding carrier to obtain Each user sends a modulated symbol sequence to the satellite.

[0016] Step 4: The receiving end receives the transmitted signals of L users, and the zth received signal is recorded as

[0017] The zth received signal in step 4 is y z It is expressed by the following formula:

[0018]

[0019] in represents the channel gain coefficient, and diag(·) represents taking the diagonal elements. is subject to the mean of 0 and the variance of σ 2J represents the malicious interference in some frequency bands in the channel. If there is no malicious interference in the signal transmission frequency band, J = 0.

[0020] Step 5: Detect the interfered frequency in the frequency hopping signal based on the power difference between the interfered signal and the non-interfered signal. Use the filter to set the interfered frequency signal to zero and obtain the processed received signal y' z .

[0021] The received signal after processing described in step 5 is expressed as

[0022]

[0023] Step 6: The output signal y' of step 5 z After de-hopping, it is sent to the SCMA multi-user detector, which uses function nodes and variable nodes to iteratively and interactively process the de-hopping processed signal to obtain the demodulated soft information s of each user. l .

[0024] The signal after de-jumping processing described in step 6 is

[0025]

[0026] For the case of J = 0, the MPA algorithm is used to calculate y' z 'Perform SCMA multi-user detection. SCMA multi-user detection includes two steps. The first step is to pass a message from the function node k to the variable node l according to the following formula, denoted as t represents the tth iteration.

[0027]

[0028] where θ k represents the set of all users who use the k-th dimension carrier to transmit messages. k \l means except the lth user.

[0029] The second step is to pass the message from the variable node l to the function node k according to the following formula: t represents the tth iteration.

[0030]

[0031] in Represents the index of all carriers utilized by user l to deliver messages. represents the number of carriers except the kth carrier. W is the normalization factor, which ensures that the sum of the probabilities of the user sending each codeword is 1. After T iterations, the probability of the user corresponding to the codeword is obtained. Substituting the codeword probability into the following formula, we can obtain the bit soft information corresponding to the zth codeword of the lth user:

[0032]

[0033] For the case of J≠0, directly replace s' l,z (o i ) is set to zero, and the demodulated soft information s of each user is obtained l =[s' l,1 ,s' l,2 ,…,s' l,B / R ].

[0034] Step 7: Use the demodulated soft information s of each user l The BCJR algorithm is used for Turbo-Hardamard decoding, and the Turbo-Hardamard decoding gain is used to recover part of the interfered information, and the decoding soft information matrix κ of each user is obtained. l , the user decoding soft information matrix κ l Including the undisturbed information and the restored part of the interfered information, and then using the user decoding soft information matrix κ l Improve the anti-interference capability of satellite communication systems.

[0035] The BCJR algorithm converts the demodulated soft information s of each user into l Substituting the following two formulas, we can obtain the forward and backward recursive metrics α and β respectively.

[0036]

[0037] in Represents branch metric.

[0038] Where: s k represents the state of the convolutional code decoder at time k, h j represents the jth row of the Hadamard matrix, A is a constant related to the channel, and L ak Indicates L a The kth row of P k represents the kth row of P, and The prior extrinsic information matrix representing the information bits, Represents the prior log-likelihood ratio matrix of the check bits. Based on this, the decoding soft information matrix of the k-th row and i-th column information bit in the information matrix D' of the l-th user without interleaving is obtained as follows:

[0039]

[0040] Where k = 1, 2, ..., B / r, i = 1, 2, ..., r.

[0041] User decoding soft information matrix κ l Including the undisturbed information and the restored part of the interfered information, and then using the user decoding soft information matrix κ l Improve the anti-interference capability of satellite communication systems.

[0042] Step 8: Decode the soft information matrix κ of each user obtained in step 7 l Perform bit judgment and obtain the decoded information bits based on the bit judgment results That is to achieve anti-interference access to satellite communications based on low bit rate coding.

[0043] The soft information matrix κ of each user decoder obtained in step 7 is l Make the following judgment to get the decoded information bit

[0044]

[0045] Beneficial effects:

[0046] 1. The present invention discloses a satellite communication anti-interference access method based on low-rate coding. The Turbo-Hadamard low-rate coding can provide high coding gain, thereby correcting the characteristics of the interfered signal. At the transmitting end, the signal to be transmitted is Turbo-Hadamard low-rate coded, and then the coded sequence is mapped to the SCMA codebook to obtain the symbol sequence to be transmitted, and finally the symbol sequence to be transmitted is frequency-hopped and transmitted according to the frequency hopping pattern. At the receiving end, the interfered frequency point is set to zero by using a filter, and demapping and decoding are performed to finally obtain the information sequence sent by each user. The present invention can solve the problem that the traditional frequency hopping anti-interference technology can only reduce the probability of signal interference and has limited anti-interference ability. Improve the anti-interference ability of the satellite communication system.

[0047] 2. The present invention discloses a satellite communication anti-interference access method based on low-code rate coding. At the transmitting end, Turbo-Hadamard low-code rate coding is performed on the signal to be transmitted, and the coded sequence is mapped to the SCMA codebook to obtain the symbol sequence to be transmitted, and the symbol sequence to be transmitted is frequency-hopped and transmitted according to the frequency hopping pattern. At the receiving end, the Turbo-Hadamard decoder uses the non-interfered part of the demodulated information to recover part of the interfered information to obtain the information sent by each user. Compared with the traditional frequency hopping anti-interference technology, the present invention uses the coding gain provided by the coding to improve the anti-interference performance of the satellite communication system.

[0048] 3. The present invention discloses a satellite communication anti-interference access method based on low-code encoding, which allocates a unique SCMA mapping codebook to each user at the transmitting end. Each user performs Turbo-Hadamard encoding of the information to be transmitted at the same code rate and then maps it according to the allocated SCMA codebook to obtain multi-dimensional symbols to be transmitted. According to the designed frequency hopping pattern, the symbol information of each dimension is modulated to the corresponding carrier for transmission. All users have the same frequency hopping pattern. The receiving end effectively identifies the interfered symbol based on the power difference in the received signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the present invention. The drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings without creative work.

[0050] Figure 1 The system block diagram of the SCMA-based satellite communication system.

[0051] Figure 2 A flow chart of an anti-interference method for SCMA-based satellite communications according to the present invention. DETAILED DESCRIPTION

[0052] Embodiment 1:

[0053] like Figure 1 , Figure 2 As shown, the present embodiment discloses an anti-interference method for satellite communication based on SCMA, and the specific implementation steps are as follows:

[0054] Step 1: Determine the total number of satellite communication system users L=6, the length of the Turbo-Hadamard coded data of each user B=200, the encoder order r=5 and the number of component encoders M=3, and perform Turbo-Hadamard coding to obtain the coded codeword C.

[0055] Determine that the total number of users in the satellite communication system is L=6, the length of the coded data of each user's Turbo-Hadamard coding is B=200, and the coded data of length 200 of the lth user is represented by b l =[b1,b2,b3,...,b 200 ], where l = 1, 2, ..., 6. l After being interleaved by different interleavers π(m), it is expressed in the form of a 40×5 matrix, and we get

[0056]

[0057] Among them, all elements b' in D(m) ij ∈b l , m = 1, 2, ..., 3 represent different component encoders. Perform parity check on D(m) row by row, and perform convolutional coding on the obtained parity check vector with a code rate of 1 / 2 to obtain a coded check bit vector q(m) = [q1, q2, ..., q 40 ] T . Then perform Hadamard coding on [D(m),q(m)] to obtain the check matrix in Represents the real number domain. Finally, the encoding results of each component encoder are concatenated to obtain the encoding codeword C = [D', q(1), P(1), q(2), P(2), q(3), P(3)], where D' is the codeword b directly without passing through the interleaver. l =[b1,b2,b3,...,b 200 ] is represented as a 40 × 5 matrix. Codewords C are sent row by row.

[0058] Step 2: Each user is assigned a unique user codebook x l Perform SCMA mapping to obtain the mapped symbol sequence x l .

[0059] The user codebook described in step 2 can be expressed as follows:

[0060]

[0061] The codebook dimension K of the above codebook is 4. According to the modulation number A=4, log2(A)=2 bits are mapped into a codeword X a ∈χ l , get the mapped symbol sequence x l =[X'1,X'2,…,X' 1720 ], where X i '∈χ l , i=1,2,…,1720, Represents the encoding bit rate.

[0062] Step 3: Translate the symbol sequence x to be sent by each user according to the frequency hopping pattern φ l Each dimension of information is modulated onto the corresponding carrier.

[0063] Each hop in the frequency hopping pattern described in step 3 corresponds to 4 carriers. For the first user, the carrier corresponding to the nth hop is represented as {f1,f2,f3,f4}, and the nth symbol to be sent is X' 1,n =[0,-0.1815-1j*0.1318,0,0.7851], each hop corresponds to a symbol, and the symbol to be sent is modulated onto the corresponding carrier to obtain Each user sends a modulated symbol sequence to the satellite.

[0064] Step 4: The receiving end receives the transmitted signals of L users, and the zth received signal is recorded as

[0065] The zth received signal in step 4 is y z It is expressed by the following formula:

[0066]

[0067] in represents the channel gain coefficient, and diag(·) represents taking the diagonal elements. is subject to the mean of 0 and the variance of σ 2 J represents the malicious interference in some frequency bands in the channel. If there is no malicious interference in the signal transmission frequency band, J = 0.

[0068] Step 5: Detect the interfered frequency in the frequency hopping signal based on the power difference between the interfered signal and the non-interfered signal. Use the filter to set the interfered frequency signal to zero and obtain the processed received signal y' z .

[0069] The received signal after processing described in step 5 can be expressed as

[0070]

[0071] Step 6: The output signal y' of step 5 z After de-hopping, it is sent to the SCMA multi-user detector, which uses function nodes and variable nodes to iteratively and interactively process the de-hopping processed signal to obtain the demodulated soft information s of each user. l .

[0072] The signal after de-jumping processing described in step 6 is

[0073]

[0074] For the case of J = 0, the MPA algorithm is used to calculate y' z 'Perform SCMA multi-user detection. SCMA multi-user detection includes two steps. The first step is to pass a message from function node k to variable node l according to the following formula, denoted as t represents the tth iteration.

[0075]

[0076] where θ k represents the set of all users who use the k-th dimension carrier to transmit messages.k \l means except the lth user.

[0077] The second step is to pass the message from the variable node l to the function node k according to the following formula: t represents the tth iteration.

[0078]

[0079] in Represents the index of all carriers utilized by user l to deliver messages. represents the number of carriers except the kth carrier. W is the normalization factor, which ensures that the sum of the probabilities of the user sending each codeword is 1. After T iterations, the probability of the user corresponding to the codeword is obtained. Substituting the codeword probability into the following formula, we can obtain the bit soft information corresponding to the zth codeword of the lth user:

[0080]

[0081] For the case of J≠0, directly replace s' l,z (o i ) is set to zero. Finally, the demodulated soft information s of each user is obtained l =[s' l,1 ,s' l,2 ,…,s' l,3440 ].

[0082] Step 7: Use the demodulated soft information s of each user l The BCJR algorithm is used for Turbo-Hardamard decoding, and the Turbo-Hardamard decoding gain is used to recover part of the interfered information, and the decoding soft information matrix κ of each user is obtained. l , the user decoding soft information matrix κ l Including the undisturbed information and the restored part of the interfered information, and then using the user decoding soft information matrix κ l Improve the anti-interference capability of satellite communication systems.

[0083] The BCJR algorithm converts the demodulated soft information s of each user into l Substituting the following two formulas, we can obtain the forward and backward recursive metrics α and β respectively.

[0084]

[0085] in Represents branch metric.

[0086] Here k represents the state of the convolutional code decoder at time k, h j represents the jth row of the Hadamard matrix, A is a constant related to the channel, and Lak Indicates L a The kth row of P k represents the kth row of P, and The prior extrinsic information matrix representing the information bits, Represents the prior log-likelihood ratio matrix of the check bits. Based on this, the decoding soft information of the k-th row and i-th column information bit in the information matrix D' of the l-th user without interleaving is obtained as follows:

[0087]

[0088] Where k = 1, 2, ..., 40, i = 1, 2, ..., 5.

[0089] User decoding soft information matrix κ l Including the undisturbed information and the restored part of the interfered information, and then using the user decoding soft information matrix κ l Improve the anti-interference capability of satellite communication systems.

[0090] Step 8: Decode the soft information matrix κ of each user obtained in step 7 l The following bit judgment is performed, and the decoded information bits are obtained according to the bit judgment results. That is to achieve anti-interference access to satellite communications based on low bit rate coding.

[0091]

Claims

1. A satellite communication anti-interference access method based on low bit rate coding, characterized in that: The following steps are included: Step 1: Determine the total number of users L of the satellite communication system, the length B of the Turbo-Hadamard coded data of each user, the encoder order r and the number M of component encoders, and perform Turbo-Hadamard coding to obtain a coded codeword C; Step 2: Each user is assigned a unique user codebook x l Perform SCMA mapping to obtain the mapped symbol sequence x l ; Step 3: Translate the symbol sequence x to be sent by each user according to the frequency hopping pattern φ l Each dimension of information is modulated onto the corresponding carrier; Step 4: The receiving end receives the transmitted signals of L users, and the zth received signal is recorded as Step 5: Detect the interfered frequency in the frequency hopping signal based on the power difference between the interfered signal and the non-interfered signal; use the filter to set the signal of the interfered frequency to zero, and obtain the processed received signal y' z ; Step 6: The output signal y' of step 5 z After de-hopping, it is sent to the SCMA multi-user detector, which uses function nodes and variable nodes to iteratively and interactively process the de-hopping processed signal to obtain the demodulated soft information s of each user. l ; Step 7: Use the demodulated soft information s of each user l The BCJR algorithm is used for Turbo-Hardamard decoding, and the Turbo-Hardamard decoding gain is used to recover part of the interfered information, and the decoding soft information matrix κ of each user is obtained. l , the user decoding soft information matrix κ l Including the undisturbed information and the restored part of the interfered information, and then using the user decoding soft information matrix κ l Improve the anti-interference capability of satellite communication systems; Step 8: Decode the soft information matrix κ of each user obtained in step 7 l Perform bit judgment and obtain the decoded information bits based on the bit judgment results That is to achieve anti-interference access to satellite communications based on low bit rate coding.

2. The satellite communication anti-interference access method based on low bit rate coding as claimed in claim 1, characterized in that: The implementation method of step one is: Determine the total number of users L in the satellite communication system, the length B of the Turbo-Hadamard coded data of each user, and the coded data of length B of the lth user is represented by b l =[b1,b2,b3,...,b B ], where l = 1, 2, ..., L; b l After being interleaved by different interleavers π(m), it is expressed in the form of a matrix of B / r×r, and we get Among them, all elements b′ in D(m) ij ∈b l , m = 1, 2, ..., M represents different component encoders; D(m) is parity checked row by row, and the obtained parity check vector is convolutionally encoded with a code rate of 1 / 2 to obtain a coded check bit vector q(m) = [q1, q2, ..., q B / r ] T ; Perform Hadamard coding on [D(m),q(m)] to obtain the check matrix in represents the real number domain; the encoding results of each component encoder are concatenated to obtain the encoding codeword C = [D', q(1), P(1), q(2), P(2), ..., q(M), P(M)], where D' is the codeword b directly without passing through the interleaver. l =[b1,b2,b3,…,b B ] is expressed as a matrix form of B / r×r; codewords C are sent row by row.

3. The satellite communication anti-interference access method based on low bit rate coding as claimed in claim 2, characterized in that: The user codebook x described in step 2 l Expressed as Where K represents the codebook dimension and A represents the modulation number. According to the modulation number A, log2(A) bits are mapped into a codeword X. a ∈χ l , get the mapped symbol sequence where X′ i ∈χ l , i=1,2,…,B / R / log2(A), R represents the encoding bit rate.

4. The satellite communication anti-interference access method based on low bit rate coding as claimed in claim 3, characterized in that: Each hop in the frequency hopping pattern described in step 3 corresponds to K carriers; for the lth user, the carrier corresponding to the nth hop is represented as {f1,f2,…,f K }, the nth symbol to be sent is Each hop corresponds to a symbol, and the symbol to be sent is modulated onto the corresponding carrier to obtain Each user sends a modulated symbol sequence to the satellite.

5. The satellite communication anti-interference access method based on low bit rate coding as claimed in claim 4, characterized in that: The zth received signal in step 4 is y z It is expressed by the following formula: in represents the channel gain coefficient, diag(·) represents taking the diagonal elements; is subject to the mean of 0 and the variance of σ 2 complex Gaussian white noise; J represents the malicious interference in some frequency bands in the channel. If there is no malicious interference in the signal transmission band, J = 0.

6. The satellite communication anti-interference access method based on low bit rate coding as claimed in claim 5, characterized in that: The received signal after processing in step 5 is expressed as 7. The satellite communication anti-interference access method based on low bit rate coding as claimed in claim 6, characterized in that: The signal after de-jumping processing described in step 6 is For the case of J = 0, the MPA algorithm is used to perform SCMA multi-user detection on XX. SCMA multi-user detection includes two steps. The first step is to transfer a message from the function node k to the variable node l according to the following formula: t represents the tth iteration; where θ k represents the set of all users that use the k-th dimension carrier to transmit messages; θ k \l represents all except the lth user; The second step is to pass the message from the variable node l to the function node k according to the following formula: t represents the tth iteration; in The index of all carriers used by user l to deliver messages; represents except the kth carrier; W is the normalization factor, which ensures that the sum of the probabilities of the user sending each codeword is 1; after T iterations, the probability of the user's corresponding codeword is obtained. Substituting the codeword probability into the following formula, we can obtain the bit soft information corresponding to the zth codeword of the lth user: For the case of J≠0, directly replace s′ l,z (o i ) is set to zero, and the demodulated soft information s of each user is obtained l =[s′ l,1 ,s′ l,2 ,...,s′ l,B / R ].

8. The satellite communication anti-interference access method based on low bit rate coding as claimed in claim 7, characterized in that: The implementation method of step seven is: The BCJR algorithm converts each user’s demodulated soft information s l Substitute the following two formulas to obtain the forward and backward recursive metric values ​​α and β respectively; in represents branch metric; Where: s k represents the state of the convolutional code decoder at time k, h j represents the jth row of the Hadamard matrix, A is a constant related to the channel, and L ak Indicates L a The kth row of P k represents the kth row of P, and The prior extrinsic information matrix representing the information bits, represents the prior log-likelihood ratio matrix of the check bits; based on this, the decoding soft information matrix of the k-th row and i-th column information bit in the information matrix D' of the l-th user without interleaving is obtained as follows: Where k = 1, 2, ..., B / r, i = 1, 2, ..., r; User decoding soft information matrix κ l Including the undisturbed information and the restored part of the interfered information, the user decoding soft information matrix κ l Improve the anti-interference capability of satellite communication systems.

9. The satellite communication anti-interference access method based on low bit rate coding as claimed in claim 8, characterized in that: In step eight, The soft information matrix κ of each user decoder obtained in step 7 is l Make the following judgment to get the decoded information bit

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