A Polar Code BP Decoding Method Based on Bit Flipping in 5G NTN Scenarios

Abstract

The present invention belongs to the field of communication technologies, and particularly relates to a bit-flipping based belief propagation (BP) decoding method for polar codes in a 5G NTN scenario, which includes: obtaining a received signal through an NTN channel; initializing the log-likelihood ratio of a decoder; performing BP decoding on a polar code information sequence by the decoder after initializing the log-likelihood ratio information to obtain a decoding result; detecting whether the decoding result is successful through CRC; if the decoding fails, constructing a flipping set after multiple bit flips and re-performing the next round of BP decoding until the CRC check passes. The present invention has a significant effect of improving the decoding performance for the performance degradation caused by factors such as Doppler frequency shift and multipath loss in the 5G NTN scenario, and at the same time has a wider practicability in wireless and cellular mobile communication networks in practical scenarios with greater requirements for high throughput, low latency, and error correction performance that are more complex.

Description

Technical Field

[0001] The present invention belongs to the field of communication technologies, and particularly relates to a bit flipping-based belief propagation (BP) decoding method for polar codes in a 5G NTN scenario. Background Art

[0002] In recent years, with the rapid development of terrestrial mobile communications, there have been endless innovations in communication technologies. As the fifth generation of global new-generation mobile communication technology, the 5G has application characteristics such as large bandwidth, low latency, wide connection, and flexible networking, opening the curtain of intelligent Internet of Things. However, with the continuous expansion of scenarios, the 5G communication technology has been further extended to broader air, space, ground, and sea fields, giving rise to the 5G NTN technology. Thereby, there is a need for improving the 5G NTN channel encoding and decoding technologies and the error correction performance in complex scenarios. The channel encoding and decoding technology is directly related to the system bit error rate performance.

[0003] With the integration of 5G and NTN, users have put forward higher requirements for the speed and quality of communication in the 5G NTN scenario. There are many differences between NTN and terrestrial communication systems in terms of deployment environment, channel propagation characteristics, etc., bringing many challenges to the integration of the two and the ability to support 5G services in non-terrestrial networks. The 5G NTN channel is a time-varying channel, and various environments and weather conditions will cause various fades, seriously affecting the transmission reliability of signals. To ensure the reliability of channel transmission, a high-performance BP decoding method suitable for the high-dynamic NTN environment needs to be designed. Summary of the Invention

[0004] To solve the above technical problems, the present invention proposes a bit flipping-based BP decoding method for polar codes in a 5G NTN scenario, including:

[0005] S1. The transmitting end sends the polar code information sequence after encoding and QPSK modulation of k-bit information bits to the receiving end through the NTN channel to obtain a received signal sequence y;

[0006] S2. Initialize the log-likelihood ratio (LLR) of the decoder according to the received signal sequence y;

[0007] S3. Perform BP decoding on the polar code information sequence through the decoder after initializing the log-likelihood ratio information LLR to obtain a decoding result;

[0008] S4. Check whether the decoding result is successful through CRC. If so, end; otherwise, enter step S5;

[0009] S5. Perform multiple rounds of BP decoding and record the LLR values of each information bit in the first S iteration processes, calculate their standard deviations, and select the information bit index values corresponding to the top T largest standard deviations to construct a flip set FS1;

[0010] S6. Calculate the weight values of the information bits transmitted in the polarization channel according to the polarization channel reliability, select the information bits corresponding to the top T largest weight values, compare the channel index values of the selected information bits with the index values of the information bits in the coarse flip set in S5, and delete the same values to obtain the flip set FS.

[0011] S7. Flip each information bit in turn according to the index value of the corresponding information bit in the flip set FS, and re - perform the next round of BP decoding on the flipped polarization code information sequence until the CRC check passes or the number of bit flips is greater than the size of the flip set FS. If the final number of bit flips is greater than the size of the flip set FS and the decoding result fails the CRC check, then execute step S9.

[0012] S8. Combine the bits in the flip set FS into new flip sets with ω (initialize ω = 1) bits in each group, perform multi - bit flips on the new flip sets in units of ω bits, then enter the BP decoder to start a new round of decoding, and perform CRC check on the decoding result until the CRC check passes or ω > T', where T' represents the size of the flip set, and output the decoding result. If the CRC check fails, continue to perform the multi - bit flip process until the CRC check passes or the number of flips reaches the size of the new flip set; if the number of flips reaches the size of the new flip set and the CRC check fails, then set ω = ω + 1, and re - perform the flip decoding and CRC check.

[0013] Advantages of the present invention:

[0014] 1. The present invention takes into account characteristics such as fast time - varying channels in the 5G NTN scenario, and uses the standard deviation of the LLR values in the last S iterations before the end of the iteration to identify error - prone bit information; subsequently, the polarization channel reliability weight values are used to screen out relatively reliable points, and the remaining bit index values are used to construct the flip set.

[0015] 2. By calculating the standard deviation of the LLR in the iterative process, unreliable points can be effectively selected according to the degree of data dispersion, which is more accurate than the previous method of identifying error - prone bits based on the absolute value of the LLR; it can be seen from the polarization channel reliability weight that when the channel weight is large, it means that the information transmission reliability is high, and such points should be excluded. The range of the flip set is reduced by the polarization channel reliability weight, reducing unnecessary flips; it has broad application prospects in wireless and cellular mobile communication networks in practical scenarios with greater and more complex requirements for decoding delay and error - correction performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flowchart for constructing a flip set based on the standard deviation of the log - likelihood ratio and the polarization channel reliability weight of the present invention. Detailed implementation mode

[0017] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0018] A polarization code BP decoding method based on bit flipping in a 5G NTN scenario includes:

[0019] S1. The sending end sends the polarization code information sequence after encoding and QPSK modulation of k-bit information bits to the receiving end through the NTN channel to obtain the received signal sequence y;

[0020] S2. Initialize the log-likelihood ratio LLR of the decoder according to the received signal sequence y;

[0021] S3. Perform BP decoding on the polarization code information sequence through the decoder after initializing the log-likelihood ratio information LLR to obtain the decoding result;

[0022] S4. Check whether the decoding result is successful through CRC. If it is, end; otherwise, enter step S5;

[0023] S5. Perform multiple rounds of BP decoding and record the log-likelihood ratio LLR values of each information bit during the first S iterations, calculate its standard deviation, and select the information bit index values corresponding to the first T largest standard deviations to construct the flip set FS1;

[0024] S6. Calculate the weight values of the information bits transmitted in the polarization channel according to the polarization channel reliability, select the information bits corresponding to the first T largest weight values, compare the channel index values of the selected information bits with the index values of the information bits in the rough flip set in S5, and delete the same values to obtain the flip set FS;

[0025] S7. Flip each information bit in turn according to the index value of the corresponding information bit in the flip set FS, and re-perform the next round of BP decoding on the flipped polarization code information sequence until the CRC check is passed or the number of bit flips is greater than the size of the flip set FS. If the final number of bit flips is greater than the size of the flip set FS and the decoding result fails the CRC check, execute step S9;

[0026] S8. The bits in the flip set FS are combined into ω (initialized ω=1) to form a new flip set. The new flip set is multi-bit flipped in units of ω bits, and then enters the BP decoder to start a new round of decoding. The decoding result is CRC checked until it passes the CRC check or ω>T', where T' represents the size of the flip set. The decoding result is output. If the CRC check fails, the multi-bit flipping process is continued until the CRC check passes or the number of flips reaches the size of the new flip set; if the number of flips reaches the size of the new flip set and the CRC check fails, ω=ω+1 is set, and flip decoding and CRC check are performed again.

[0027] The received signal sequence y comprises:

[0028]

[0029] Among them, y j represents the received signal sequence of the NTN channel at the jth moment, P0 represents the power of the direct component, P1 represents the power of the multipath component, and P i represents the power of the i-th path, x j represents the transmitted signal at time j, g i,j represents the weight of the i-th multipath component at time j i∈[1,5], τ i,j represents the delay of the i-th path relative to the first path at time j, n j represents the noise at time j.

[0030] Initialize the decoder's log-likelihood ratio LLR according to the received signal sequence y, including:

[0031]

[0032] Among them, LLR(y j ) represents the initial log-likelihood ratio of the received signal sequence at time j, y j represents the received signal sequence at time j, and W represents the polarization channel.

[0033] The flip set construction process based on the log-likelihood ratio standard deviation and polarization channel reliability weight is as follows: Figure 1 Shown, including:

[0034] K1, record the left information LLR value of the information bit during the S iterations before the end of the iteration;

[0035] K2, calculate the LLR standard deviation of each information bit during the first S iterations;

[0036] K3, sort the results obtained in K2, and select the first T largest LLR standard deviations to form the index set FS1;

[0037] K4. Calculate the reliability weight value of the polarization channel;

[0038] K5. Sort the results obtained in K4, and select the largest T weight values to form the index set FS2;

[0039] K6. Determine whether there are the same element values in the set FS1 and the set FS2. If there are the same values, execute step K7. If not, let the set FS1 be the flipping set FS;

[0040] K7. Delete the elements with the same index value, and the remaining elements form the precise flipping set FS;

[0041] The descriptions corresponding to each step of constructing the flipping set are as follows:

[0042] First, initialize the left information during the decoding process:

[0043]

[0044] Among them,

[0045]

[0046]

[0047] Among them, y j is the received signal at the j-th moment; σ 2 is the noise variance; v i represents the transmitted signal may take values of 1 or -1; P0 represents the power of the direct component; P1 represents the power of the multipath component; P i represents the power of the i-th path; x j represents the transmitted signal at the j-th moment; g i,j represents the weight value of the i-th multipath component at the j-th moment, where i ∈ [1, 5].

[0048] Then update the left information matrix L. Since the standard deviation can better reflect the stability of a data, we record the left log-likelihood ratio (LLR) of the information bits during the last S iterations before the end of the iteration. First, calculate the average value of each information bit, then calculate the variance of each information bit, and finally calculate the standard deviation of each information bit:

[0049]

[0050]

[0051] Among them, L i,j represents the left LLR value of the node (i, j); Represents the left information LLR value of node (i, j+N / 2); N is the code length; f() represents a statistical function, f(x,y)≈α·sgn(x)sgn(y)min(|x|,|y|); R i,j Is the right information log-likelihood ratio of node (i, j).

[0052]

[0053]

[0054]

[0055] Where S is the number of iterations to be recorded; L S Is the log-likelihood ratio during each iteration. Arrange the results obtained from Equation (5) in descending order, and select the top T (T max =K / 2) largest standard deviation values, and construct the corresponding information bit indices into the coarse flip set FS'.

[0056] During the construction of the polar code, select the information bits to be transmitted on the polar channels according to the reliability of the polar channels. The reliability of the polar channels can be expressed as:

[0057]

[0058] Where:

[0059]

[0060]

[0061]

[0062] Ф(x) is expressed as:

[0063]

[0064] Where P e (u i ) represents the reliability of the i-th polar channel, u i Represents the bit information sequence, Q() represents the symbol error probability function, erfc(x) is the complementary error function, used to solve the bit error rate; Is the expected value of the log-likelihood ratio LLR corresponding to the i-th bit; Represents the log-likelihood ratio of the i-th bit at the n-1 level; Represents the log-likelihood ratio value at the n-th level.

[0065] When the value of a certain information bit is smaller, it proves that the probability of incorrect decoding of this information bit is also smaller. Let Mi Denotes the weight of the reliability of the polarization channel for the \(i\)-th information bit, expressed as:

[0066]

[0067] Where, \(M\) i Denotes the reliability weight value of the polarization channel, \(u\) i Denotes the bit information sequence, \(P\) e (u i ) Denotes the reliability of the polarization channel. When \(P\) e (u i ) is larger, it indicates that the polarization channel is less reliable, that is, the transmitted information bits are prone to errors during the decoding process.

[0068] The reliability weight value of the polarization channel represents a degree of polarization, but the obtained value is relatively large. To further reduce the weight value of \(M\) i , it is further processed as:

[0069]

[0070] Where, \(M\) i Denotes the reliability weight value of the polarization channel, \(u\) i Denotes the bit information sequence, \(P\) e (u i ) Denotes the reliability of the polarization channel. When \(P\) e (u i ) is larger, it indicates that the polarization channel is less reliable, that is, the transmitted information bits are prone to errors during the decoding process.

[0071] Flip each information bit in sequence according to the index value of the corresponding information bit in the fine flip set, including: when \(u\) i > 0, update its right information to \(-\infty\), when \(u\) i < 0, update its right information to \(+\infty\).

[0072] The above right information update includes:

[0073] \(R\) 0,i = (1 - 2u i )×\(\infty\)

[0074] Where, \(R\) 0,i Denotes the information of the first column for initializing the right update matrix, \(u\) i Denotes the information bit sequence, and \(\infty\) denotes the value of infinity.

[0075] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polarization code BP decoding method based on bit flipping in the 5G NTN scenario, characterized in that Including: S1. The sending end encodes k-bit information bits, modulates the encoded bits with QPSK to obtain a polar code information sequence, and sends the polar code information sequence through the NTN channel to the receiving end, obtaining a received signal sequence y. S2. Initialize the log-likelihood ratio LLR of the decoder according to the received signal sequence y. S3. Perform BP decoding on the polar code information sequence through the decoder after initializing the log-likelihood ratio information LLR, obtaining a decoding result. S4. Check whether the decoding result is successful through CRC for the decoding result. If so, end. Otherwise, go to step S5. S5. Perform multiple rounds of BP decoding and record the log-likelihood ratio LLR values of each information bit during the first S iterations, calculate their standard deviations, and select the information bit index values corresponding to the top T largest standard deviations to construct a flip set FS1. S6. Calculate the weight values of the information bits transmitted in the polar channel according to the reliability of the polar channel, select the information bits corresponding to the top T largest weight values, compare the channel index values of the selected information bits with the index values of the information bits in the rough flip set in S5, and delete the same values to obtain a flip set FS. S7. Flip each information bit in turn according to the index value of the corresponding information bit in the flip set FS, re-perform the next round of BP decoding on the flipped polar code information sequence until the CRC check passes or the number of bit flips is greater than the size of the flip set FS. If the final number of bit flips is greater than the size of the flip set FS and the decoding result fails the CRC check, execute step S9. S8. Combine the bits in the flip set FS into new flip sets with ω (initialize ω = 1) bits per set, perform multi-bit flips on the new flip sets in units of ω bits, then enter the BP decoder to start a new round of decoding, and perform CRC check on the decoding result until the CRC check passes or ω > T', where T' represents the size of the flip set, output the decoding result. If the CRC check fails, continue to perform the multi-bit flip process until the CRC check passes or the number of flips reaches the size of the new flip set; if the number of flips reaches the size of the new flip set and the CRC check fails, set ω = ω + 1, and re-perform the flip decoding and CRC check.

2. The polarization code BP decoding method based on bit flipping in a 5G NTN scenario according to claim 1, characterized in that, The received signal sequence y includes: Among them, y j represents the received signal sequence of the NTN channel at the j-th moment, P0 represents the power of the direct component, P1 represents the power of the multipath component, and P i represents the power of the i-th path, x j represents the transmitted signal at the j-th moment, g i,j represents the weight of the i-th multipath component at the j-th moment, i ∈ [1, 5], τ i,j represents the delay of the i-th path relative to the first path at the j-th moment, n j represents the noise at the j-th moment.

3. A polarization code BP decoding method based on bit flipping in a 5G NTN scenario according to claim 1, characterized in that, Initializing the log-likelihood ratio LLR of the decoder according to the received signal sequence y includes: Among them, LLR(y j ) represents the initial log-likelihood ratio of the received signal sequence at the j-th moment, y j represents the received signal sequence at the j-th moment, and W represents the polarization channel.

4. A polarization code BP decoding method based on bit flipping in a 5G NTN scenario according to claim 1, characterized in that, The standard deviation of each information bit during the first S iterations includes: Among them, std i represents the standard deviation of the information bits during the first S iterations, VAR i represents the variance of the information bits during the last S iterations before the end of the iteration, S represents the number of iterations, L s represents the log-likelihood ratio during each iteration, AVE i represents the average value of the information bits during the last S iterations before the end of the iteration, 5. A polarization code BP decoding method based on bit flipping in a 5G NTN scenario according to claim 1, characterized in that, The reliability of the polar channel includes: where, P e (u i ) represents the reliability of the i-th polarization channel, u i represents the bit information sequence, W() represents the symbol error probability function, E{} represents the expectation operation of calculating the log-likelihood ratio, represents the average value of the log-likelihood ratio iterative information, and erfc() is the complementary error function.

6. A polarization code BP decoding method based on bit flipping in a 5G NTN scenario according to claim 1, characterized in that, The weight value of the reliability of the polar channel includes: Among them, M i represents the polarization channel reliability weight value, and u i represents the bit information sequence, and P e (u i ) represents the polarization channel reliability.

7. A polarization code BP decoding method based on bit flipping in a 5G NTN scenario according to claim 1, characterized in that Flip each information bit in sequence according to the index value corresponding to the information bit in the fine flip set, including: when u i > 0, update its right information to -∞, u i < 0, update its right information to +∞.

8. A polarization code BP decoding method based on bit flipping in a 5G NTN scenario according to claim 7, characterized in that The right information update includes: R 0,i = (1 - 2u i ) × ∞ Among them, R 0,i represents the first column information of the right update matrix initialization, and u i represents the information bit sequence, and ∞ represents an infinite value.

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