A coding method of polarization coded cascaded space-time coding for MIMO-PLC system

Abstract

The present invention relates to the technical field of power line carrier communication, and in particular to a coding method of polarization coding cascade space-time coding for MIMO-PLC systems. The method comprises: S1. polarization coding is performed on a transmitting end information source by Gaussian approximation; S2. the polarization code is modulated by binary phase keying to obtain modulated symbols; S3. the modulated symbols are passed through a space-time encoder, so that polarization coding and space-time coding are cascaded to construct PC-STBC coding; S4. the PC-STBC-coded information is sent to a receiving end through a transmitting end, and the receiving end decodes after receiving the PC-STBC coding. The method of the present invention brings diversity gain to the system through space-time coding, and brings coding gain to the system through the excellent error correction capability of polarization codes, so that the error performance of the MIMO-PLC system is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power line carrier communication, and in particular to a coding method of polarization coding cascade space-time coding for a MIMO-PLC system. Background Art

[0002] Power line communication is a transmission method that uses existing power transmission lines as the transmission medium to transmit data. With the development of smart grids, power line communication has the advantages of not requiring any infrastructure and a wider coverage of power networks compared to typical wireless infrastructure, making power line communication one of the main communication methods. In home networks, walls between different rooms have a strong blocking effect on wireless signals. Power line communication can effectively make up for the shortcomings of wireless communication in home networks and accelerate the development of power line communication in home networks. However, power lines are designed to transmit power without considering communication. Due to the constantly changing load on the power lines, there is serious multipath fading and noise interference in the power line channel.

[0003] With the advent of the 5G era, the traditional single-input single-output power line communication system can no longer meet the development needs. Introducing the MIMO system of wireless communication into the power line system can increase the channel capacity and transmission efficiency of the power line. In the low-voltage power distribution system, the power line is mainly composed of phase line, neutral line, and ground line. The combination of each wire can form a multiple input multiple output power line carrier communication (MIMO-PLC) system. In order to effectively combat the harsh PLC channel environment and improve the error performance of the PLC system, channel coding technology is particularly important. The literature (Chen Guo, Peng Xiaofeng, Cao Yang, et al. Research on Raptor cascade coding scheme in power line communication [J]. Journal of Chongqing University of Technology (Natural Science), 2019, 33(3): 169-173+179), (Chen Guo, Cao Yang, Peng Xiaofeng, et al. Research on fountain code cascade in power line communication [J]. Laser Journal, 2020, 41(6): 111–115) studied the impact of fountain coding on the bit error performance of PLC system. The proposed CRC-Raptor cascade coding scheme is better than the traditional one. Raptor CodingThe error code performance of the PLC system is greatly improved. The literature (Jianqi L, Zhe Z, Chuanyuan Z, et al. A Code Scheme for G3-PLCPhysical Layer Specification Based on Turbo Code [A]. 2021 2nd Information Communication Technologies Conference (ICTC) [C]. 2021: 11–15) replaces the RS coding in the G3-PLC physical layer specification with LDPC coding. The results show that under the same code length, LDPC coding has better system error code performance in Gaussian white noise channels and colored background noise channels. The literature (Wang X, Hong H, Wang K, et al. Performance of LDPC and Turbo Coded Power Line Communication over Multipath Channel and Narrowband Noise [A]. 2022 2nd Asia-Pacific Conference on Communications Technology and Computer Science (ACCTCS) [C]. 2022: 263–269) studied the bit error performance of turbo coding and LDPC coding in PLC systems. Through simulation analysis, it is found that the bit error performance of turbo coding and LDPC coding is better as the code length increases. The literature (Hadi A, Rabie KM, Alsusa E. Polar codes based OFDM-PLC systems in the presence of middleton class-A noise [A]. 2016 10th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP) [C]. 2016: 1–6) analyzes the impact of different code lengths of polar coding and LDPC coding on the bit error performance of PLC systems. The simulation shows that the bit error performance of PLC systems using polar coding is better.The literature (Liu J, Dai X, Ge H, et al. On the SCL Decoding of Polar Codes in Power Line Communications [A]. 2022 IEEE / ACIS 22nd International Conference on Computer and Information Science (ICIS) [C]. 2022: 137–139) studied the impact of the polar code SCL decoding algorithm on the bit error performance of the PLC system. The study showed that the proposed SCL algorithm can improve the decoding capability of the system, thereby improving the bit error performance of the system.

[0004] As a typical channel coding of MIMO-PLC system, space-time coding can improve the reliability of MIMO system through spatial diversity and spatial multiplexing. Spatial multiplexing is to divide the data to be transmitted into multiple sub-data streams and send them on different transmission ports, so as to increase the transmission rate of MIMO system. In the research of MIMO-PLC transmission environment, the low-complexity singular value decomposition precoding algorithm proposed in the literature (Lin Huan, Li Xiang. Bilateral Jacobi SVD precoding method for MIMO PLC system [J]. Application of Electronic Technology, 2018, 44(9): 121–124) reduces the complexity of inverse operation in traditional precoding algorithm and effectively improves the system's bit error performance. Literature (Li Mingwei, Zhang Chuanyuan, Xie Shiyin, et al. Analysis of broadband power line carrier channel coding and diversity technology [J]. Electric Power Information and Communication Technology, 2019, 17(3): 61–66), (Cao Wangbin, Yin Chengqun, Xie Zhiyuan, et al. Research on multi-input multi-output broadband power line carrier communication channel model [J]. Proceedings of the CSEE, 2017, 37(4): 1136–1142) In order to overcome the problem that a large amount of measured data is required to establish a top-down channel model, a MIMO-PLC hybrid model is proposed by combining top-down and bottom-up modeling methods and introducing MIMO channel correlation, which improves the system performance indicators. Reference (ZhiQuan, Moises Vidal Ribeiro. A low cost STBC-OFDM system with improved reliability for power line communications [A]. 2011 IEEE International Symposium on Power Line Communications and Its Applications [C]. Udine, Italy: IEEE, 2011: 261–266) uses cyclic shift to construct OFDM symbols to increase symbol diversity to combat the damage of pulse noise in order to solve the problem of frequency selectivity and strong impulse noise in MIMO-PLC channels. Reference (Cao Wangbin, Kang Hui, Xie Zhiyuan, et al. Research on Coding Methods for MIMO-PLC Direct Sequence Spread Spectrum System [J]. Proceedings of the CSEE, 2021, 41(S1): 121–129) proposes a MIMO-PLC direct spread spectrum sequence system scheme, which can effectively reduce the bit error rate of the spatial diversity system using Alamouti coding and effectively improve the system's anti-interference capability.Reference (Aono K, Zheng B, Sawahashi M, et al. Performance of FDE Using Partial LDPC Coding with Double Gray Mapping for Single-Carrier LOS-MIMO [A]. 2020 IEEE 91st Vehicular Technology Conference (VTC2020-Spring) [C]. 2020: 1–6) uses low-density parity-check (LDPC) coding for frequency domain equalization in MIMO-PLC systems. Simulation results show that the use of LDPC coding can improve the channel gain by 6.6 dB.

[0005] In combination with the above prior art, in order to resist pulse interference in the MIMO-PLC system channel and further improve the system error performance, polar code is selected as channel coding. Combined with space-time coding and applied in the MIMO-PLC system, we propose the polar code cascaded space-time coding (Polar code cascaded space-time coding PC-STBC) method of the present invention. Summary of the invention

[0006] The object of the present invention is to provide a coding method of polarization coding cascade space-time coding for a MIMO-PLC system, which is used to resist pulse interference in the MIMO-PLC system channel and further improve the system error performance.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a coding method for polarization coding cascade space-time coding for a MIMO-PLC system, comprising the following steps:

[0009] S1. Polarization encoding of the information source at the transmitting end is performed by Gaussian approximation;

[0010] S2. Modulating the polarization code by binary phase keying to obtain a modulated symbol;

[0011] S3. The modulated symbols are passed through a space-time encoder, so that the polarization coding and the space-time coding are cascaded to construct a PC-STBC code;

[0012] S4. The PC-STBC encoded information is sent to the receiving end through the sending end, and the receiving end decodes the PC-STBC encoding after receiving it.

[0013] Further, the performing polarization coding on the information source of the transmitting end by Gaussian approximation includes:

[0014] By the bit permutation matrix B N With the kernel matrix The n-th Kronecker product gives the generator matrix G N , expressed as follows:

[0015]

[0016]

[0017] set up is the input vector of the channel, generated by the matrix G N Polarization coding is available The polarization coding structure relationship is expressed as:

[0018]

[0019] Further, the modulating the polarization code by binary phase keying includes:

[0020] Constructing a factor graph, the polar code adopts a BP decoding algorithm and relies on the factor graph for implementation;

[0021] The method for constructing the factor graph is as follows: for a factor graph with a length of N=2 n The leftmost 2×2 module of the polar code is the first column, and so on, the rightmost is the nth column. Each column is composed of N / 2 2×2 modules from top to bottom. The formed module can be represented by (i, j), 1≤i≤n, 1≤j≤N, where i and j represent the number of columns and rows.

[0022] The operation process of the BP decoding algorithm is to perform the operation through the log-likelihood ratio: γij,j Indicates information transmitted to the right, L γij,j Represents the information transmitted to the left. The leftward propagation and the rightward propagation are collectively called an iterative process, and the expression is as follows:

[0023]

[0024] f(x,y)=sign(x)sign(y)min{|x|,|y|}

[0025]

[0026] In the formula, mod(a,b) represents the remainder of a divided by b, and |x| represents rounding down;

[0027] After reaching the maximum number of iterations, the source sequence and codeword sequence Make a judgment, the judgment formula is:

[0028]

[0029]

[0030] Furthermore, the encoding method of the space-time encoder includes:

[0031] The space-time coding uses Alamouti code to convert two continuous signals x 1 ,x 2 Construct a complex orthogonal matrix, expressed as follows:

[0032]

[0033] In the formula, x 1 ,x 2 Two symbols sent from different ports in the first cycle, Two symbols sent from different ports for the second cycle;

[0034] The signal received by the receiver can be expressed as:

[0035]

[0036] In the formula, r 1,1 ,r 1,2 are the signals received in the first cycle of port 1 and port 2 respectively, r 2,1 ,r 2,2 They are the signals received in the second cycle of port 1 and port 2 respectively;

[0037] Under the condition that the channel gain H and noise z are known, the signal at receiving port 1 can be expressed as:

[0038]

[0039] The received signal r 1,2 Taking the complex conjugate, the signal matrix of receiving port 1 can be changed to:

[0040]

[0041] again:

[0042] R 1 =H 1 x+z

[0043]

[0044] Merged data available The expression is as follows:

[0045]

[0046] After the data is merged, the judgment result is drawn through judgment. The expression is as follows:

[0047]

[0048] The code is modulated by bit keying, and the modulated code is directly cascaded with the space-time block code; the method of the present invention brings diversity gain to the system through space-time coding, and brings coding gain to the system through the excellent error correction capability of the polarization code, so that the error performance of the MIMO-PLC system is effectively improved.

[0049] The present invention obtains the result through simulation: when the system bit error rate is 10 -4 The cascade coding method proposed in the present invention has a gain of about 7.4dB compared with space-time coding; under different fading paths and overlapping factors, the cascade coding scheme improves the system bit error performance more significantly, with a coding gain of about 6 to 6.3dB; the cascade coding scheme shows better suppression of multipath fading and pulse noise, and improves the bit error performance of the multi-input and multi-output power line carrier communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0051] Figure 1 Schematic diagram of MIMO-PLC channel model;

[0052] Figure 2 Schematic diagram of MIMO-PLC channel transfer function;

[0053] Figure 3 Schematic diagram of MIMO-PLC noise classification;

[0054] Figure 4 N = 8, polar code factor graph;

[0055] Figure 5 It is a schematic diagram of the operation process of 2×2 modules;

[0056] Figure 6 Schematic diagram of the Alamouti space-time encoder;

[0057] Figure 7 The principle of Alamouti coded receiver;

[0058] Figure 8 This is the framework diagram of the MIMO-PLC polar code cascade STBC coding transmitter;

[0059] Fig. 9 This is the framework diagram of the MIMO-PLC polar code cascade STBC coding receiver;

[0060] Fig.10 Schematic diagram of bit error rate performance of MIMO-PLC system under different bit rate PC-STBC coding and STBC coding;

[0061] Fig.11 The BER performance of MIMO-PLC system under different code lengths for PC-STBC coding;

[0062] Fig.12 Schematic diagram of bit error rate of MIMO-PLC system under different paths with PC-STBC coding and STBC coding;

[0063] Fig.13 Schematic diagram of the bit error rate performance of the MIMO-PLC system under different overlapping factors of PC-STBC coding;

[0064] Fig.14 Schematic diagram of the method of the present invention. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0066] See also Fig.14 , the main steps of the method of the present invention are:

[0067] S1. Polarization encoding of the information source at the transmitting end is performed by Gaussian approximation;

[0068] S2. Modulating the polarization code by binary phase keying to obtain a modulated symbol;

[0069] S3. The modulated symbols are passed through a space-time encoder, so that the polarization coding and the space-time coding are cascaded to construct a PC-STBC code;

[0070] S4. The PC-STBC encoded information is sent to the receiving end through the sending end, and the receiving end decodes the PC-STBC encoding after receiving it.

[0071] Specifically, the details are as follows:

[0072] 1. MIMO-PLC system model

[0073] The three-wire power line is generally composed of a phase line, a neutral line, and a ground line. Any two wires are combined to form a power line transmission channel. Based on the limitation of Kirchhoff's law, when the transmitting end has three ports, the sum of the injected voltage is zero. Therefore, the MIMO-PLC system has at most two transmitting ports; in addition to the three differential circuits that can send signals at the receiving end, there are also common-mode signals caused by capacitance and electric coupling, which can form 2×2, 2×3, and 2×4 MIMO-PLC systems.

[0074] This embodiment mainly takes the 2×2 MIMO system as the research object, and its channel model is as follows: Figure 1 shown.

[0075] The 2×2 MIMO system consists of two transmitting ports and two receiving ports. It can be regarded as two SISO channels with interference from the channel correlation coefficient transmitting signals at the same carrier frequency. The calculation formula of the carrier channel frequency response in the SISO channel is:

[0076]

[0077] Where A represents the channel middle gain, which is 1; α 0 ,α 1 is the attenuation factor, which is related to the resistance, inductance, capacitance and conductivity of the power line; g n is the path reflection and transmission factor, and its value is [-1,1] Uniform distribution; d n is the path length, which is uniformly distributed in [0,200]; N is the total number of signal transmission paths, which is Poisson distribution with a value of 0.2L; V is the path rate per unit length, which is 0.2.

[0078] In a 2×2 MIMO system, there is correlation between channels. To ensure the accuracy of channel transmission, the present invention constructs a channel correlation matrix R t and R r , expressed as follows:

[0079]

[0080] In the formula, γ r ,γ t is the correlation coefficient between channels, which is 0.9. Combining the above formula, it can be inferred that the frequency response expression of the multi-input multi-output power line channel is:

[0081]

[0082] Formula (3) is further calculated and expressed as follows:

[0083]

[0084] In this matrix h 11 (f), h 22 (f) represents the common channel, h 12 (f), h 21 (f) represents the mutual channel. In formula (3), T represents the transposition operation. This model reflects the correlation between different paths of the MIMO channel. The co-channel and mutual channel attenuation characteristics are simulated as follows: Figure 2 shown.

[0085] 2. Noise Model

[0086] Power line channel noise can be divided into two categories according to the power characteristics and time-varying properties of the noise: one is background noise and the other is impulse noise. Figure 3 As shown in the figure, background noise is divided into colored background noise, narrowband power line noise, and periodic pulse noise asynchronous to the power frequency. The characteristics of these three types of noise can remain unchanged for a long time, but their power is low, their time-varying property is small, and their impact on signal transmission is small. Pulse noise is divided into periodic pulse noise synchronized to the power frequency and random noise. These two types of noise have short duration, large RMS amplitude, strong randomness and high power, and have a great impact on signal transmission.

[0087] Many noise models have been established for the non-Gaussian noise in the power line channel environment. Among the numerous noise models, Middleton's class-A noise model is the most widely used. The probability density function expression of this model is as follows:

[0088]

[0089]

[0090]

[0091]

[0092] Where m is the number of impulse noise sources, is the mth pulse noise power, Γ is the ratio of Gaussian noise power to pulse noise power, and P is the sum of Gaussian noise power and pulse noise. A represents the overlap factor, which is generally between 0.00001 and 0.35. The larger the value, the smaller the pulse intensity and the closer the noise is to Gaussian noise; the smaller the value, the larger the pulse intensity and the closer the noise is to pulse noise.

[0093] 3. PC-STBC solution in MIMO-PLC communication system

[0094] 3.1 Construction of polar codes

[0095] Polar code was proposed by Turkish professor Arikan. It is the first coding method that can be mathematically proven to reach the Shannon limit. The polar code of the present invention adopts Gaussian structure, which is composed of bit permutation matrix B N With the kernel matrix The n-th Kronecker product gives the generator matrix G N , the expression is as follows:

[0096]

[0097]

[0098] Assumptions is the input vector of the channel, and the polarization coding can be obtained by generating the matrix The polarization coding construction relationship is:

[0099]

[0100] 3.2 Polar Code BP Decoding Algorithm

[0101] The BP decoding algorithm relies on the factor graph of polar codes to be implemented. For a factor graph of length N = 2 n The leftmost 2×2 module of polar coding is the first column, and so on, the rightmost is the nth column. Each column is composed of N / 2 2×2 modules from top to bottom. The formed modules can be represented by (i, j), 1≤i≤n, 1≤j≤N, where i and j represent the number of columns and rows. Figure 4 express.

[0102] The operation process of BP decoding algorithm 2×2 module is as follows Figure 5 As shown, the operation process is performed through the log-likelihood ratio. Among them, Represents the information transmitted to the right, which is the known LLR value. Represents the information transmitted to the left, which is the calculated LLR value.

[0103] Figure 5 The leftward propagation and the rightward propagation are collectively called an iterative process, and the specific expression is as follows:

[0104]

[0105] f(x,y)=sign(x)sign(y)min{|x|,|y|} (13)

[0106]

[0107] In the formula, mod(a,b) represents the remainder when a is divided by b, and |x| represents rounding down.

[0108] After reaching the maximum number of iterations, the source sequence and codeword sequence Make a judgment, the judgment formula is:

[0109]

[0110]

[0111] 3.3 MIMO-PLC Space-Time Coding Scheme

[0112] MIMO space-time coding is divided into two coding methods: spatial diversity and spatial multiplexing.

[0113] Spatial diversity can increase the channel capacity by sending signals at multiple transmitting ends, and spatial multiplexing is to send the same signal at multiple transmitting ends to improve the channel reliability. Since the MIMO-PLC channel environment is very harsh, choosing spatial diversity can effectively improve the transmission performance of the system and reduce the system bit error rate. Alamouti code is a typical STBC code, which converts two continuous signals x 1 ,x 2 Construct a complex orthogonal matrix:

[0114]

[0115] In the formula, x 1 ,x 2 Two symbols sent from different ports in the first cycle, These are two symbols sent by different ports in the second cycle. Therefore, the signal sent by 2×2MIMO-PLC in two cycles is the same as the signal sent by SISO-PLC in the same cycle, and the channel capacity has not increased. The transmission process is as follows: Figure 6 shown.

[0116] After signal X passes through the MIMO-PLC channel, the receiving end combines the received signals. The receiving end principle block diagram is as follows: Figure 7 shown.

[0117] The signal received by the receiver can be expressed as:

[0118]

[0119] In the formula, r 1,1 ,r 1,2 are the signals received by port 1 and port 2 in the first cycle, r 2,1 ,r 2,2 They are the signals received by port 1 and port 2 in the second cycle respectively.

[0120] Under the condition that the channel gain H and noise z are known, the signal at the receiving end 1 can be expressed as:

[0121]

[0122] The received signal r 1,2 Taking the complex conjugate, the signal matrix of receiving port 1 can be changed to:

[0123]

[0124] Formula (15) can be simplified as:

[0125] R 1 =H 1 x+z(21)

[0126] Multiplying both sides of the matrix by the transpose of the transmission parameter matrix, equation (16) becomes:

[0127]

[0128] Further simplifying formula (17) to obtain the merged data

[0129]

[0130] After the data is merged, the decision result is obtained through ML judgment.

[0131]

[0132] 3.4 PC-STBC Coding Scheme for MIMO-PLC System

[0133] The system simulation process is mainly divided into three parts: encoding, signal merging, and decoding.

[0134] The coding is divided into polar coding and STBC coding. STBC coding uses Alamouti coding to increase system reliability. First, the information source x at the sending end is 0 ,x 1 ,x 2 ...x n-1 Polarization coding is performed, and then the polarization coding is modulated into symbols through binary phase shift keying modulation (BPSK). The symbols arrive at the space-time encoder to construct PC-STBC coding, and then the coding is sent through the MIMO-PLC channel by two ports. The sending end process is as follows Figure 8 shown.

[0135] The receiving end receives and combines the codes after passing through the channel, restores the transmitted symbols for BPSK demodulation, and finally enters the polar codec for belief propagation (BP) decoding, and calculates the bit error rate to reflect the system error performance. The receiving end flow chart is as follows Fig. 9 shown.

[0136] 4. Simulation results and analysis

[0137] In order to further verify the performance of polar code concatenated space-time coding, PC-STBC coding and STBC coding were simulated in MIMO-PLC system with different fading paths and overlapping factors, and the influence of PC-STBC coding on the bit error rate of MIMO-PLC system with different code lengths and code rates was analyzed. The system simulation experiment parameters are shown in Table 1:

[0138] Table 1 Simulation parameter settings of MIMO-PLC polar code cascade space-time coding system

[0139]

[0140] Fig.10 This is a simulation analysis of different code rate PC-STBC coding and STBC coding in MIMO-PLC system, where code length N = 1024, path L = 4, and the horizontal axis "SNR (dB)" represents the signal-to-noise ratio.

[0141] It can be seen from the simulation diagram that cascade coding with R≤3 / 4 can effectively reduce the system bit error rate. As the bit rate decreases, the system bit error performance improves more significantly. In addition, when cascade coding R=1, the system bit error performance is better than the STBC coding system performance when BER≥12dB. Compared with STBC coding, the lower the bit rate, the lower the signal-to-noise ratio required for the cascade coding system BER to exceed the STBC coding system BER, and when the STBC coding BER=10 -2 When R≤3 / 4, the PC-STBC coding BER value remains at 10 -4 The following is equivalent to STBC coding needing to be improved by at least 5dB. It can be seen that under the same signal-to-noise ratio conditions, the lower the PC-STBC coding bit rate, the lower the BER reduction. This shows that low-bit-rate PC-STBC coding has a significant effect on MIMO-PLC systems against harsh noise environments.

[0142] Fig.11 To explore the impact of different code lengths on the system bit error rate performance. Under the conditions of R = 1 / 2 and L = 4, simulations were performed for N = 256, 512, 1024, and 2048, respectively. As can be seen from the figure, the longer the PC-STBC code length, the more complete the sub-channel polarization, and the better the system bit error performance as the signal-to-noise ratio increases. When the signal-to-noise ratio is lower than 2dB, the code length has no significant improvement on the system performance, but when the signal-to-noise ratio is greater than 2dB, as the code length increases, the system BER value decreases more. When BER = 10 -4When N=512, N=1024, and N=2048 are compared with N=256, the signal-to-noise ratio is improved by about 0.3dB, 0.5dB, and 0.2dB respectively. PC-STBC coding has learned the advantage that the longer the code length of polar coding, the better the system error performance. Therefore, the increase Figure 8 The longer code length of PC-STBC can make the MIMO-PLC system more resistant to noise.

[0143] Fig.12 The influence of PC-STBC coding and STBC coding on the system bit error rate performance under different paths in the MIMO-PLC system is analyzed. The simulation results show that the path using the cascade coding scheme has a more obvious impact on the system BER value, and the system BER value decreases more significantly as the number of paths decreases. Compared with the two schemes with L=5, when the bit error rate is 10 -4 When the bit error rate is 10 -4 When 4 attenuated paths have a signal-to-noise ratio of about 0.1 dB higher than that of 5 attenuated paths, and 6 attenuated paths have a signal-to-noise ratio of about 0.2 dB higher than that of 5 attenuated paths. In the MIMO-PLC system, the number of attenuated paths has little effect on the system bit error performance. When the signal-to-noise ratio is greater than 10.5 dB, a more obvious difference in the system bit error rate appears. For example, when SNR = 10.5 dB, the fewer the number of paths, the better the system bit error performance.

[0144] Fig.13 This is a simulation analysis of the system bit error rate performance under different overlapping factors of MIMO-PC-STBC. The figure simulates the MIMO-PLC system with A = 0.1, 0.2, 0.3, L = 4, and R = 1 / 2. It can be seen from the figure that the overlapping factor has a greater impact on the PC-STBC coding scheme than the STBC coding scheme. The larger the A value, the stronger the pulse noise. For both coding schemes, the system bit error performance worsens as the pulse interference intensity increases. When the system bit error rate is 10 -3 When the MIMO-PC-STBC system is 10, the signal-to-noise ratio of the MIMO-STBC system is improved by about 6 to 6.3 dB. In addition, the overlap factor has a more obvious impact on the PC-STBC coding scheme system. Specifically, in the MIMO-PLC-STBC coding scheme system, when the system bit error rate is 10 -3 When A=0.2 is compared with A=0.3, the signal-to-noise ratio is improved by about 1dB, and when A=0.2 is compared with A=0.1, the signal-to-noise ratio is improved by about 1.2dB. In the system using STBC coding scheme, when the system bit error rate is 10 -3When A=0.2 is compared with A=0.3, the signal-to-noise ratio is improved by about 1dB, and the signal-to-noise ratio is improved by about 1.3dB compared with A=0.1. It can be seen that the cascade scheme proposed in the present invention still has good anti-noise ability in the MIMO-PLC channel environment with large pulse intensity.

[0145] 5. Conclusion

[0146] The present invention applies polarization codes in MIMO systems and completes the construction of polarization code cascade space-time coding. This coding combines the error correction performance of polarization coding and the space-time diversity gain of STBC coding to reduce the impact of pulse noise on the system's bit error performance. This paper compares the impact of different paths and overlapping factors of PC-STBC coding and STBC coding on the bit error performance of the MIMO-PLC system through simulation. The simulation analysis results show that when the PC-STBC coding scheme is compared with the STBC coding scheme, when the path L=4, 5, and 6, the PC-STBC coding scheme gain is approximately 7 to 7.4dB; when the overlapping factor A=0.1, 0.2, and 0.3, the PC-STBC coding scheme gain is approximately 6 to 6.3dB. In addition, due to the characteristics of polarization codes, as the PC-STBC coding code length increases and the code rate decreases, the bit error performance of the MIMO-PLC system can be effectively improved.

[0147] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A coding method for polarization coding cascade space-time coding for MIMO-PLC system, characterized in that: The following steps are involved: S1. Polarization encoding of the information source at the transmitting end is performed by Gaussian approximation; S2. Modulating the polarization code by binary phase keying to obtain a modulated symbol; S3. The modulated symbols are passed through a space-time encoder, so that the polarization coding and the space-time coding are cascaded to construct a PC-STBC code; S4 PC-STBC encoded information is sent to the receiving end through the transmitting end, and the receiving end decodes after receiving the PC-STBC encoding; The performing polarization encoding on the information source of the transmitting end by Gaussian approximation includes: By the bit permutation matrix B N With the kernel matrix The n-th Kronecker product gives the generator matrix G N , expressed as follows: set up is the input vector of the channel, generated by the matrix G N Polarization coding is available The polarization coding structure relationship is expressed as: The step of modulating the polarization code by binary phase keying comprises: Constructing a factor graph, the polar code adopts a BP decoding algorithm and relies on the factor graph for implementation; The method for constructing the factor graph is as follows: for a factor graph with a length of N=2 n The leftmost 2×2 module of the polar code is the first column, and so on, the rightmost is the nth column. Each column is composed of N / 2 2×2 modules from top to bottom. The formed module can be represented by (i, j), 1≤i≤n, 1≤j≤N, where i and j represent the number of columns and rows. The operation process of the BP decoding algorithm is to perform operations through log-likelihood ratio: Indicates information transmitted to the right. Represents the information transmitted to the left. The leftward propagation and the rightward propagation are collectively called an iterative process, and the expression is as follows: f(x,y)=sign(x)sign(y)min{|x|,|y|} In the formula, mod(a,b) represents the remainder of a divided by b, and |x| represents rounding down; After reaching the maximum number of iterations, the source sequence and codeword sequence Make a judgment, the judgment formula is: The encoding method of the space-time encoder comprises: The space-time coding adopts Alamouti code, and two continuous signals x1 and x2 are formed into a complex orthogonal matrix, which is expressed as follows: Where x1 and x2 are two symbols sent by different ports in the first cycle. Two symbols sent from different ports for the second cycle; The signal received by the receiver can be expressed as: In the formula, r 1,1 ,r 1,2 are the signals received by port 1 at different periods, r 2,1 ,r 2,2 They are the signals received by port 2 at different periods respectively; Under the condition that the channel gain H and noise z are known, the signal at receiving port 1 can be expressed as: The received signal r 1,2 Taking the complex conjugate, the signal matrix of receiving port 1 can be changed to: again: R1=H1x+z Merged data available The expression is as follows: After the data is merged, the judgment result is drawn through judgment. The expression is as follows:

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