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

Abstract

The application 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 application realizes the method as follows: a unique SCMA mapping codebook is allocated to each user of a sending end; after each user carries out Turbo-Hadamard coding on to-be-sent information at the same code rate, the user carries out mapping according to the allocated SCMA codebook to obtain multi-dimensional to-be-sent symbols; and according to a designed frequency hopping pattern, the symbol information of each dimension is modulated onto a corresponding carrier to be sent. All users have the same frequency hopping pattern. According to the power difference existing in a received signal, a receiving end effectively identifies the interfered symbols and sets them to zero, and then sends the processed signal into an SCMA multi-user detector to obtain demodulation information of each user. A decoder recovers part of the interfered information by using the non-interfered part in the demodulation information to obtain the sending information of each user, and realizes the satellite communication anti-interference access based on the low code rate coding and decoding.

Description

Technical Field

[0001] This invention discloses a satellite communication anti-interference access method based on low code rate encoding and decoding, and particularly relates to a method for anti-interference using low code rate encoding and decoding, belonging to the field of digital signal processing. Background Technology

[0002] Satellite communication systems can provide seamless wireless coverage to complement and extend terrestrial communication networks, as recent standardization efforts have done, and are expected to be incorporated into future wireless networks, particularly 6G and others. Low Earth Orbit (LEO) satellite communications, orbiting at altitudes less than 2000 km, have recently garnered significant research interest due to their potential to provide global wireless access. Compared to geostationary orbit communication systems, LEO satellite communication systems have much lower requirements regarding power consumption and transmission signal latency. Sparse Code Multiple Access (SCMA), as a multiple access technology, can meet the demands of massive access in future communications; its application in satellite communications can significantly increase the number of users a system can accommodate and effectively alleviate spectrum resource pressures.

[0003] However, the open nature of satellite communication links makes them vulnerable to malicious external interference, which can severely disrupt the normal operation of the system. Traditional frequency hopping technology is an effective anti-interference measure; however, it only reduces the probability of signal interference and has limited anti-interference capability. To address this, based on the ability of low-rate encoding and decoding to effectively recover interfered signals using coding constraints, an anti-interference method for SCMA-based satellite communication is proposed, effectively improving the system's anti-interference capability. This provides strong support for the development of SCMA-based satellite communication. Summary of the Invention

[0004] To address the limitation of traditional frequency-hopping anti-interference methods, which only reduce the probability of signal interference but have limited anti-interference capabilities, this invention aims to provide a satellite communication anti-interference access method based on low-rate encoding and decoding. At the transmitting end, the signal to be transmitted is Turbo-Hadamard low-rate encoded, and the encoded sequence is mapped using SCMA codebooks to obtain the sequence of symbols to be transmitted. This sequence is then transmitted via frequency hopping according to a frequency hopping pattern. At the receiving end, filters are used to zero out the interference frequencies, and demapping and decoding are performed to obtain the information sequences transmitted by each user. Compared to traditional frequency-hopping anti-interference techniques, this invention utilizes the coding gain provided by encoding and decoding to improve the anti-interference performance of the satellite communication system.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] This invention discloses a satellite communication anti-interference access method based on low-rate encoding and decoding. Each user at the transmitting end is assigned a unique SCMA mapping codebook. Each user performs Turbo-Hadamard encoding of the information to be transmitted at the same code rate, and then maps it according to the assigned SCMA codebook to obtain multi-dimensional symbols to be transmitted. Based on a designed frequency hopping pattern, the symbol information of each dimension is modulated onto the corresponding carrier for transmission. All users have the same frequency hopping pattern. At the receiving end, based on the power difference in the received signal, the interfered symbols are effectively identified and zeroed out. The processed signal is then sent to an SCMA multi-user detector to obtain the demodulated information for each user. The Turbo-Hadamard decoder uses the undisturbed portion of the demodulated information to recover some of the interfered information, thus obtaining the transmitted information of each user. This achieves satellite communication anti-interference access based on low-rate encoding and decoding, improving the anti-interference capability of the satellite communication system.

[0007] This invention discloses a satellite communication anti-interference access method based on low code rate encoding and decoding, comprising the following steps:

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

[0009] Given the total number of users L in the satellite communication system, the length B of the Turbo-Hadamard encoded data for each user, and the encoded data of the l-th user of length B represented as b. l =[b1,b2,b3,…,b B ], where l = 1, 2, ..., L. Let b l After being interleaved by different interleavers π(m), it is represented in the form of a matrix B / r×r, which yields...

[0010]

[0011] Where all elements b' in D(m) ij ∈b l Let m = 1, 2, ..., M represent different component encoders. Parity checking is performed row-by-row on D(m), and the resulting parity check vector is convolved at a rate of 1 / 2 to obtain a post-coded check bit vector q(m) = [q1, q2, ..., qm] of length B / r. B / r ] T The parity-check matrix is ​​obtained by performing Hadamard encoding on [D(m), q(m)]. in Represents the real number field. The encoded results of each component encoder are concatenated to obtain the encoded codeword C = [D', q(1), P(1), q(2), P(2), ..., q(M), P(M)], where D' represents the codeword directly encoded without interleaving b. l =[b1,b2,b3,…,b B This is represented as a matrix of B / r×r. Codeword C is sent row by row.

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

[0013] The user codebook χ described in step two l Represented as Where K represents the codebook dimension and A represents the modulation radix. Based on the modulation radix A, log2(A) bits are mapped to a codeword X. a ∈χ l The mapped symbol sequence is obtained. Where X' i ∈χ l , i = 1, 2, ..., B / R / log2(A), where R represents the coding rate.

[0014] Step 3: Based on the frequency hopping pattern φ, determine the symbol sequence x to be transmitted for each user. l Each dimension of information is modulated onto the corresponding carrier.

[0015] Each hop in the frequency hopping pattern described in step three corresponds to K carriers. For the l-th user, the carrier corresponding to the n-th hop is represented as {f1, f2, ..., f...} K The nth symbol to be sent is Each hop corresponds to a symbol. By modulating the symbol to be transmitted onto the corresponding carrier, we can obtain... Each user sends a modulated symbol sequence to the satellite.

[0016] Step 4: The receiving end receives signals from L users, and the z-th received signal is denoted as .

[0017] The z-th received signal mentioned in step four is y z It can be expressed by the following formula:

[0018]

[0019] in This represents the channel gain coefficient, and diag(·) represents taking the diagonal elements. To conform to a mean of 0 and a variance of σ 2The complex Gaussian white noise. J represents the malicious interference in the channel band; if there is no malicious interference in the signal transmission band, then J = 0.

[0020] Step 5: Based on the power difference between the interfered signal and the non-interfering signal, detect the interfered frequency point in the frequency hopping signal. Use a filter to zero out the signal at the interfered frequency point to obtain the processed received signal y'. z .

[0021] The processed received signal described in step five is represented as follows:

[0022]

[0023] Step Six: The signal y' output in Step Five z After de-hopping, the signal is fed into an SCMA multi-user detector. The multi-user detector uses function nodes and variable nodes to iteratively process the de-hopping signal to obtain the demodulated soft information s for each user. l .

[0024] The signal after de-hopping processing described in step six is

[0025]

[0026] For the case where J=0, the MPA algorithm is used to process y' z 'Simultaneous SCMA multi-user detection is performed, which involves 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 t-th iteration.

[0027]

[0028] Where θ k θ represents the set of all users that use the k-th dimension carrier for message passing. k \l represents the number excluding the l-th user.

[0029] The second step is to pass a message from variable node l to function node k according to the following formula, denoted as: t represents the t-th iteration.

[0030]

[0031] in This represents the index of all carriers used by user l to transmit messages. This represents all carriers except the k-th carrier. W is a normalization factor that ensures the sum of the probabilities of each codeword transmitted by the user is 1. After T iterations, the probability of the user's corresponding codeword is obtained. Substituting the codeword probabilities into the following formula yields the bit soft information corresponding to the z-th codeword of the l-th user:

[0032]

[0033] For the case where J≠0, simply use s' l,z (o i Set the value to zero to obtain the demodulation software information s for each user. l =[s' l,1 ,s' l,2 ,…,s' l,B / R ].

[0034] Step 7: Utilize the demodulation software information s of each user l The BCJR algorithm is used for Turbo-Hardamard decoding. The Turbo-Hardamard decoding gain is used to recover some of the interfered information, thus obtaining the decoding soft information matrix κ for each user. l The user-decoded soft information matrix κ l This includes both undisturbed information and partially recovered undisturbed information, which is then used to decode the user's soft information matrix κ. l Improve the anti-interference capability of satellite communication systems.

[0035] The BCJR algorithm demodulates the soft information s of each user. l Substituting into the following two formulas, we obtain the forward and backward recursive metric values ​​α and β, respectively.

[0036]

[0037] in Represents branch metric.

[0038] Where: s k h represents the state of the convolutional code decoder at time k. j This represents the j-th row of the Hadamard matrix, where A is a channel-related constant, and L... ak L represents a The k-th row, P k Let P be the k-th row, and The prior extrinsic information matrix representing information bits. The prior log-likelihood ratio matrix represents the test bits. Based on this, the decoding soft information matrix of the information bits in the k-th row and i-th column of the uninterleaved information matrix D' of the l-th user is obtained according to the following formula:

[0039]

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

[0041] User decoding soft information matrix κ l This includes both undisturbed information and partially recovered undisturbed information, which is then used to decode the user's soft information matrix κ. l Improve the anti-interference capability of satellite communication systems.

[0042] Step 8: Analyze the user decoding soft information matrix κ obtained in Step 7. l Perform bit decision-making, and obtain the decoded information bits based on the bit decision-making results. This enables interference-resistant satellite communication access based on low code rate encoding and decoding.

[0043] The user decoding soft information matrix κ obtained in step seven l The following decision is made to obtain the decoded information bits.

[0044]

[0045] Beneficial effects:

[0046] 1. This invention discloses a satellite communication anti-interference access method based on low-rate encoding and decoding. It utilizes Turbo-Hadamard low-rate encoding to provide high coding gain, thereby correcting the characteristics of interfered signals. At the transmitting end, the signal to be transmitted is encoded using Turbo-Hadamard low-rate encoding. Then, the encoded sequence is mapped using SCMA codebook to obtain the sequence of symbols to be transmitted. Finally, the sequence of symbols to be transmitted is transmitted via frequency hopping according to a frequency hopping pattern. At the receiving end, filters are used to zero out the interfered frequency points, and demapping and decoding are performed to finally obtain the information sequences transmitted by each user. This invention solves the problem that traditional frequency hopping anti-interference techniques can only reduce the probability of signal interference and have limited anti-interference capabilities, thus improving the anti-interference capability of satellite communication systems.

[0047] 2. This invention discloses a satellite communication anti-interference access method based on low-rate encoding and decoding. At the transmitting end, the signal to be transmitted is Turbo-Hadamard low-rate encoded, and the encoded sequence is mapped using SCMA codebook to obtain the symbol sequence to be transmitted. The symbol sequence to be transmitted is then transmitted via frequency hopping according to a frequency hopping pattern. At the receiving end, a Turbo-Hadamard decoder uses the uninterrupted portion of the demodulated information to recover the partially interfered information to obtain the transmitted information of each user. Compared with traditional frequency hopping anti-interference technology, this invention utilizes the coding gain provided by encoding and decoding to improve the anti-interference performance of the satellite communication system.

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

[0049] To more clearly illustrate the technical solutions described in this invention, the accompanying drawings used in this invention will be briefly introduced below. The drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0050] Figure 1 This is a system block diagram for an SCMA-based satellite communication system.

[0051] Figure 2 A flowchart of an anti-interference method for SCMA-based satellite communication according to the present invention. Detailed Implementation

[0052] Example 1:

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

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

[0055] The total number of users in the satellite communication system is L = 6, and the length of the Turbo-Hadamard encoded data for each user is B = 200. The encoded data of the l-th user with a length of 200 is represented as b. l =[b1,b2,b3,...,b 200 ], where l = 1, 2, ..., 6. Let b l After being interleaved by different interleavers π(m), it is represented in a 40×5 matrix form, resulting in

[0056]

[0057] Where all elements b' in D(m) ij ∈b l Let m = 1, 2, ..., 3 represent different component encoders. Parity checking is performed row-by-row on D(m), and the resulting parity check vector is convolved at half the code rate to obtain a coded parity check bit vector q(m) = [q1, q2, ..., qm] of length 40. 40 ] T Then, Hadamard encoding is performed on [D(m), q(m)] to obtain the parity-check matrix. in This represents the real number field. Finally, the encoding results of each component encoder are concatenated to obtain the encoded codeword C = [D', q(1), P(1), q(2), P(2), q(3), P(3)], where D' is the codeword directly encoded without going through an interleaver. l =[b1,b2,b3,...,b 200 This is represented as a 40×5 matrix. Codeword C is sent row by row.

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

[0059] The user codebook mentioned in step two can be represented as follows:

[0060]

[0061] The codebook above has a codebook dimension K = 4. Based on the modulation base A = 4, log2(A) = 2 bits are mapped to a codeword X. a ∈χ l The mapped symbol sequence x is obtained. l =[X'1,X'2,…,X' 1720 ], where X i '∈χ l i = 1, 2, ..., 1720 This represents the encoding bitrate.

[0062] Step 3: Based on the frequency hopping pattern φ, determine the symbol sequence x to be transmitted for each user. l Each dimension of information is modulated onto the corresponding carrier.

[0063] In the frequency hopping pattern described in step three, each hop corresponds to four 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 transmitted is X'. 1,n = [0, -0.1815 - 1j*0.1318, 0, 0.7851], where each hop corresponds to a symbol. Modulating the symbol to be transmitted onto the corresponding carrier yields... Each user sends a modulated symbol sequence to the satellite.

[0064] Step 4: The receiving end receives signals from L users, and the z-th received signal is denoted as .

[0065] The z-th received signal mentioned in step four is y z It can be expressed by the following formula:

[0066]

[0067] in This represents the channel gain coefficient, and diag(·) represents taking the diagonal elements. To conform to a mean of 0 and a variance of σ 2 The complex Gaussian white noise. J represents the malicious interference in the channel band; if there is no malicious interference in the signal transmission band, then J = 0.

[0068] Step 5: Based on the power difference between the interfered signal and the non-interfering signal, detect the interfered frequency point in the frequency hopping signal. Use a filter to zero out the signal at the interfered frequency point to obtain the processed received signal y'. z .

[0069] The processed received signal described in step five can be represented as follows:

[0070]

[0071] Step Six: The signal y' output in Step Five z After de-hopping, the signal is fed into an SCMA multi-user detector. The multi-user detector uses function nodes and variable nodes to iteratively process the de-hopping signal to obtain the demodulated soft information s for each user. l .

[0072] The signal after de-hopping processing described in step six is

[0073]

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

[0075]

[0076] Where θ k θ represents the set of all users that use the k-th dimension carrier for message passing.k \l represents the number excluding the l-th user.

[0077] The second step is to pass a message from variable node l to function node k according to the following formula, denoted as: t represents the t-th iteration.

[0078]

[0079] in This represents the index of all carriers used by user l to transmit messages. This represents all carriers except the k-th carrier. W is a normalization factor that ensures the sum of the probabilities of each codeword transmitted by the user is 1. After T iterations, the probability of the user's corresponding codeword is obtained. Substituting the codeword probabilities into the following formula yields the bit soft information corresponding to the z-th codeword of the l-th user:

[0080]

[0081] For the case where J≠0, simply use s' l,z (o i Set to zero. Finally, obtain the demodulation software information s for each user. l =[s' l,1 ,s' l,2 ,…,s' l,3440 ].

[0082] Step 7: Utilize the demodulation software information s of each user l The BCJR algorithm is used for Turbo-Hardamard decoding. The Turbo-Hardamard decoding gain is used to recover some of the interfered information, thus obtaining the decoding soft information matrix κ for each user. l The user-decoded soft information matrix κ l This includes both undisturbed information and partially recovered undisturbed information, which is then used to decode the user's soft information matrix κ. l Improve the anti-interference capability of satellite communication systems.

[0083] The BCJR algorithm demodulates the soft information s of each user. l Substituting into the following two formulas, we obtain the forward and backward recursive metric values ​​α and β, respectively.

[0084]

[0085] in Represents branch metric.

[0086] Here s k h represents the state of the convolutional code decoder at time k. j This represents the j-th row of the Hadamard matrix, where A is a channel-related constant, and L...ak L represents a The k-th row, P k Let P be the k-th row, and The prior extrinsic information matrix representing information bits. The prior log-likelihood ratio matrix represents the test bits. Based on this, the decoding soft information of the information bits in the k-th row and i-th column of the uninterleaved information matrix D' of the l-th user is obtained according to the following formula:

[0087]

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

[0089] User decoding soft information matrix κ l This includes both undisturbed information and partially recovered undisturbed information, which is then used to decode the user's soft information matrix κ. l Improve the anti-interference capability of satellite communication systems.

[0090] Step 8: Analyze the user decoding soft information matrix κ obtained in Step 7. l Perform the following bit decision, and obtain the decoded information bits based on the bit decision result. This enables interference-resistant satellite communication access based on low code rate encoding and decoding.

[0091]

Claims

1. A satellite communication anti-interference access method based on low code rate encoding and decoding, characterized in that: Includes the following steps, Step 1: Determine the total number of users L of the satellite communication system, the length B of the encoded data for each user's Turbo-Hadamard encoding, the encoder order r, and the number of component encoders M, and perform Turbo-Hadamard encoding to obtain the encoded codeword C; Step 2: Each user uses their assigned unique user codebook χ l Perform SCMA mapping to obtain the mapped symbol sequence x. l ; Step 3: Based on the frequency hopping pattern φ, determine the symbol sequence x to be transmitted for each user. l Each dimension of information is modulated onto the corresponding carrier; Step 4: The receiving end receives signals from L users, and the z-th received signal is denoted as . Step 5: Based on the power difference between the interfered signal and the non-interfering signal, detect the interfered frequency point in the frequency hopping signal; use a filter to zero out the signal at the interfered frequency point to obtain the processed received signal y'. z ; Step Six: The signal y' output in Step Five z After de-hopping, the signal is fed into an SCMA multi-user detector. The multi-user detector uses function nodes and variable nodes to iteratively process the de-hopping signal to obtain the demodulated soft information s for each user. l ; Step 7: Utilize the demodulation software information s of each user l The BCJR algorithm is used for Turbo-Hardamard decoding. The Turbo-Hardamard decoding gain is used to recover some of the interfered information, thus obtaining the decoding soft information matrix κ for each user. l The user-decoded soft information matrix κ l This includes both undisturbed information and partially recovered undisturbed information, which is then used to decode the user's soft information matrix κ. l Improve the anti-interference capability of satellite communication systems; Step 8: Analyze the user decoding soft information matrix κ obtained in Step 7. l Perform bit decision-making, and obtain the decoded information bits based on the bit decision-making results. This enables interference-resistant satellite communication access based on low code rate encoding and decoding.

2. The satellite communication anti-interference access method based on low code rate encoding and decoding as described in claim 1, characterized in that: The implementation method for step one is as follows: Given the total number of users L in the satellite communication system, and the length B of the Turbo-Hadamard encoded data for each user, the encoded data of the l-th user with length B is represented as b. l =[b1,b2,b3,...,b B ], where l = 1, 2, ..., L; b l After being interleaved by different interleavers π(m), it is represented in the form of a matrix B / r×r, which yields... Where all elements b′ in D(m) ij ∈b l Let m = 1, 2, ..., M represent different component encoders; parity check is performed on D(m) row by row, and the resulting parity check vector is convolved with a 1 / 2 bit rate to obtain a post-coded check bit vector q(m) = [q1, q2, ..., qm] of length B / r. B / r ] T ; The parity-check matrix is ​​obtained by performing Hadamard encoding on [D(m),q(m)]. in Represents the real number field; the encoded results of each component encoder are concatenated to obtain the encoded codeword C=[D',q(1),P(1),q(2),P(2),...,q(M),P(M)], where D' is the codeword directly generated without going through an interleaver. l =[b1,b2,b3,...,b B It is represented as a matrix of B / r×r; codewords C are sent row by row.

3. The satellite communication anti-interference access method based on low code rate encoding and decoding as described in claim 2, characterized in that: The user codebook χ described in step two l Represented as Where K represents the codebook dimension and A represents the modulation base; according to the modulation base A, log2(A) bits are mapped to a codeword X. a ∈χ l The mapped symbol sequence is obtained. Where X i '∈χ l , i = 1, 2, ..., B / R / log2(A), where R represents the coding rate.

4. The satellite communication anti-interference access method based on low code rate encoding and decoding as described in claim 3, characterized in that: Each hop in the frequency hopping pattern described in step three corresponds to K carriers; for the l-th user, the carrier corresponding to the n-th hop is represented as {f1, f2, ..., f K The nth symbol to be sent is Each hop corresponds to a symbol. By modulating the symbol to be transmitted onto the corresponding carrier, we can obtain... Each user sends a modulated symbol sequence to the satellite.

5. The satellite communication anti-interference access method based on low code rate encoding and decoding as described in claim 4, characterized in that: The z-th received signal mentioned in step four is y z It can be expressed by the following formula: in This represents the channel gain coefficient, and diag(·) represents taking the diagonal elements; To conform to a mean of 0 and a variance of σ 2 The complex Gaussian white noise; J represents the malicious interference in the channel in part of the frequency band. If there is no malicious interference in the signal transmission frequency band, then J = 0.

6. The satellite communication anti-interference access method based on low code rate encoding and decoding as described in claim 5, characterized in that: The processed received signal described in step five is represented as follows: 。 7. The satellite communication anti-interference access method based on low code rate encoding and decoding as described in claim 6, characterized in that: The signal after de-hopping processing described in step six is For the case where J=0, the MPA algorithm is used to process y. z 'Simultaneous SCMA multi-user detection is performed, which 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 t-th iteration; Where θ k θ represents the set of all users that use the k-th dimension carrier for message passing; k \l represents the user excluding the l-th user; The second step is to pass a message from variable node l to function node k according to the following formula, denoted as: t represents the t-th iteration; in The index of all carriers used by user l to transmit messages; This represents all carriers except the k-th carrier. W is a normalization factor that ensures the sum of the probabilities of each codeword sent by the user is 1; after T iterations, the probability of the user's corresponding codeword is obtained. Substituting the codeword probabilities into the following formula yields the bit soft information corresponding to the z-th codeword of the l-th user: For the case where J≠0, directly use s′ l,z (o i Set the value to zero to obtain the demodulation software information s for each user. l =[s′ l,1 ,s′ l,2 ,…,s′ l,B / R ].

8. The satellite communication anti-interference access method based on low code rate encoding and decoding as described in claim 7, characterized in that: Step seven is implemented as follows: The BCJR algorithm demodulates the soft information s of each user. l Substituting into the following two formulas, we obtain the forward and backward recursive metric values ​​α and β, respectively; in Represents branch metric; Where: s k h represents the state of the convolutional code decoder at time k. j This represents the j-th row of the Hadamard matrix, where A is a channel-related constant, and L... ak L represents a The k-th row, P k Let P be the k-th row, and The prior extrinsic information matrix representing information bits. The prior log-likelihood ratio matrix represents the test bits; based on this, the decoding soft information matrix of the information bits in the k-th row and i-th column of the uninterleaved information matrix D' of the l-th user is obtained according to the following formula: Where k = 1, 2, ..., B / r, i = 1, 2, ..., r; User decoding soft information matrix κ l Including both undisturbed information and partially recovered undisturbed information, using the user-decoded soft information matrix κ l Improve the anti-interference capability of satellite communication systems.

9. A satellite communication anti-interference access method based on low code rate encoding and decoding as described in claim 8, characterized in that: In step eight, The user decoding soft information matrix κ obtained in step seven l The following decision is made to obtain the decoded information bits. 。

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