CN116865909A - Physical layer processing method combining SFBC space frequency coding and Polar channel code - Google Patents
Physical layer processing method combining SFBC space frequency coding and Polar channel code Download PDFInfo
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Abstract
The invention discloses a physical layer processing method combining SFBC space frequency coding and Polar channel code, which comprises the following steps: firstly, a signal passes through a processing module of a transmitting end to generate an OFDM symbol, wherein Polar channel coding and SFBC space-frequency coding are introduced into the transmitting end; the signal then enters a processing module of the receiving end through a channel, and is demodulated through a series of demodulation processes, wherein SFBC space frequency decoding and Polar decoding are introduced into the receiving end. The technical problems to be solved by the invention are as follows: in a complex channel environment, the MIMO-OFDM system has the problem of high error rate, and by adopting a joint method based on SFBC and Polar codes, the system can jointly improve the channel estimation performance under the condition of low signal to noise ratio, thereby further reducing the error rate and improving the reliability of the system.
Description
Technical Field
The invention relates to the technical field of bit error rate performance in the communication field, in particular to a physical layer processing method combining SFBC space frequency coding and Polar channel code.
Background
In the field of wireless communications, diversity techniques are used to mitigate the effects of fading to improve the reliability of the link. Space-frequency block coding (Space Frequency Block Code, SFBC) is used as a transmit diversity technique, and a joint coding technique combining transmit diversity in the spatial domain and channel coding in the frequency domain has the advantages of high spectrum utilization and better communication quality. Multiple input multiple output (Multiple Input Multiple Output, MIMO) technology employs multiple antennas at a transmitting end and a receiving end, respectively, to simultaneously transmit and receive signals, thereby improving capacity and spectrum utilization of a communication system. The orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) technology has the advantages of strong multipath interference resistance and frequency selective fading capability. By combining MIMO technology with OFDM technology, higher data transmission rates and better anti-fading characteristics can be obtained. Based on MIMO-OFDM, space Frequency Block Coding (SFBC) is introduced, so that space diversity and frequency diversity are obtained simultaneously, and compared with space time block coding (Space Time Block Code, STBC), the space time block coding (SFBC) has higher diversity gain, so that the error rate of a channel can be further reduced, and the reliability of the channel is improved.
In a communication system, channel coding is used to increase the reliability of signal transmission, thereby improving the transmission quality of the system. With the continuous complexity of communication systems, the requirements for channel coding performance become very high. In 2009, turkish Arikan teaches a Polar Code (Polar Code) coding method based on the channel polarization phenomenon, and the channel coding method is strictly proved to reach the channel capacity, and when the polarization Code length is long, the coding and decoding structure is simple, has good error correction performance, and has better applicability compared with other channel coding schemes.
Disclosure of Invention
The invention aims to: SFBC and Polar coding algorithm have excellent performance in reducing error rate, polar code adopts recursive coding mode, make it have lower coding calculation complexity, therefore, in MIMO-OFDM system, through will not increase the scheme of the two combination under the precondition of complexity, under the lower signal-to-noise ratio, obtain the better error rate performance, make the reliability of the communication system promoted.
In order to achieve the above purpose, the present invention provides the following technical solutions:
a physical layer processing method combining SFBC space frequency coding and Polar channel code comprises the following steps:
firstly, a signal passes through a processing module of a transmitting end to generate an OFDM symbol, wherein Polar channel coding and SFBC space-frequency coding are introduced into the transmitting end; the signal then enters a processing module of the receiving end through a channel, and is demodulated through a series of demodulation processes, wherein SFBC space frequency decoding and Polar decoding are introduced into the receiving end.
The method belongs to an algorithm for receiving and transmitting information sequences in a communication system, and can be realized on an FPGA.
The first step: the signal transmission processing module:
1) Adding CRC syndrome modules
2) Polar channel coding module
3) QPSK modulation module
4) Spread spectrum scrambling module
5) SFBC space frequency coding module
6) An OFDM mapping module;
and a second step of: signal receiving processing procedure
1) OFDM demapping module
2) SFBC space frequency decoding module
3) Despreading and descrambling module
4) QPSK demodulation module
5) Polar decoding module
6) And receiving a CRC check module.
Preferably, in the first step: the signal sending and processing process comprises the following steps:
adding CRC syndrome modules
Cyclic Redundancy Check (CRC) is used as a channel error detection technology to ensure the correctness and the integrity of data transmission; adding CRC check bit at the tail of the bit data information, and then sending the bit data added with CRC check to a Polar coding module;
polar channel coding module
Carrying out channel coding on the input bit data added with CRC, and outputting the coded bits to a quadrature phase shift keying QPSK modulation module;
polar codes can be encoded by generating a matrix
wherein ,for the original bit sequence, < > for>G is the coded bit sequence N Generating a matrix with a code length of n=2 n ；
Generating matrix G N Represented as
wherein ,for matrix->Is of the order of n Cronecker products (recursive +)>)；B N For ordering matrix to complete bit reverse order rearrangement operation, ">I 2 Is a 2-dimensional unit array, B 2 ＝I 2 Matrix R N For replacing the matrix, separating odd-order elements and even-order elements from the input sequence;
the module adopts a rate-adaptive puncturing polarization RCPP code scheme, and defines the coding rate as R=K/M; at a transmitting end, inputting K information bit sequences into a CRC unit, adding m check bits, and outputting the number of bits as K=k+m; then the K bit source sequence outputs a coding sequence of N bits through a Polar encoder; then, a puncturing method is adopted, the method does not need to change the coding and decoding structure, the code length and the coding rate can be adaptively adjusted, the coding sequences of N bits are input into a puncturing unit, and after N-M bits are punctured, puncturing polarization codes of M bits are output;
QPSK modulation module
The QPSK modulation module finishes the mapping process from the bit to the complex value data and then sends the complex value data to the spread spectrum scrambling module;
spread spectrum scrambling module
Spread spectrum scrambling is carried out on complex value data, and then the complex value data is sent to an SFBC module;
SFBC space frequency coding module
SFBC space-frequency coding is carried out on the data after the spread spectrum scrambling;
let the received symbol of the j (j=1, 2) th receiving antenna on the kth subcarrier of a certain OFDM symbol beNoise is->The channel coefficient of the ith (i=1, 2) transmitting antenna and the jth receiving antenna is +.>When the transmitting end and the receiving end are two antennas, the transmitted SFBC coding matrix can be expressed as +.>
The reception symbol of the j (j=1, 2) th reception antenna is expressed as:
by combiningTaking a conjugate construction equivalent transmission equation:
is available in the form of
Equivalent channel transmission matrixDetecting the same by adopting a detection algorithm to obtain the equivalent transmitted symbol vector +.>Is a function of the estimated value of (2);
OFDM mapping module
And performing Inverse Fast Fourier Transform (IFFT) and Cyclic Prefix (CP) processing to complete the transformation of complex-valued data from a frequency domain to a time domain, and generating an OFDM symbol.
Preferably, in the second step, the signal receiving process, the core algorithm is:
OFDM demapping module
The process is the inverse process of the IFFT mapping processing, the CP removal processing is completed, and the transformation from the time domain to the frequency domain is realized through the IFFT;
SFBC space frequency decoding module
Performing space-frequency decoding on 1280 complex-valued data from two antennas and a channel estimation result of a channel estimation module; definition of the definitionFor complex value data of antenna 1, +.>Complex value data for the antenna 2; h 11 (0)，…，H 11 (N) is channel estimation between the transmitting antenna 1 and the receiving antenna 1, H 12 (0)，…，H 12 (N) is channel estimation between the transmitting antenna 1 and the receiving antenna 2, H 21 (0)，…，H 21 (N) is channel estimation between the transmitting antenna 2 and the receiving antenna 1, H 22 (0)，…，H 22 (N) is a channel estimate between the transmit antenna 2 and the receive antenna 2; />Complex-valued data after space-frequency decoding, where n=1280;
the SFBC space-frequency coding result may be expressed as:
wherein i=1, 2, …,640; r is (r) 11 ＝d 1 (n 1 )，n 1 ＝1，3，…，1279；r 12 ＝d 1 (n 2 )，n 2 ＝2，4，…，1280；r 21 ＝d 2 (n 1 )，n 1 ＝1，3，…，1279；r 22 ＝d 2 (n 2 )，n 2 ＝2，4，…，1280；
Despreading and descrambling module
Performing despreading and descrambling processing on the complex-valued data decoded by the SFBC, and transmitting the complex-valued data to a QPSK demodulation module;
QPSK demodulation module
QPSK demodulation processing is carried out on the complex value data to obtain soft bit information;
polar decoding module
Inputting the soft symbol to a decoder, and transmitting the decoded output bits to a CRC (cyclic redundancy check) module;
the continuous cancellation list SCL is provided on the basis of continuously canceling the SC, and when decoding is completed, a bit sequence with highest reliability is selected from the L reserved candidate paths to be used as decoding output so as to improve decoding performance;
the Polar decoding module adopts a CRC-assisted continuous offset list decoding algorithm, L decoding results are obtained by using an SCL decoding algorithm, then CRC check is carried out on the L decoding results, and the decoding result which is checked by the CRC and has the minimum path metric value is output as the optimal decoding result; CA-SCL decoding flow chart;
receive CRC check module
And comparing the obtained bit check bit with the original bit check bit, if the bit check bit is the same as the original bit check bit, checking the bit, and if the bit check bit is not the original bit check bit, checking the bit is failed.
The invention has the technical effects and advantages that:
the invention solves the problem of high error rate of the MIMO-OFDM system in a complex channel environment; by adopting the combined method based on SFBC and Polar codes, the system can be ensured to jointly improve the channel estimation performance under the condition of low signal-to-noise ratio, thereby further reducing the error rate and improving the reliability of the system.
Drawings
FIG. 1 is a flow chart of a transceiving processing algorithm;
FIG. 2 is a rate adaptation polarization code (RCPP) and CA-SCL decoding;
fig. 3 is a comparison of BER performance for different methods under a rayleigh Li Duojing fading channel.
Detailed Description
The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
Firstly, a signal passes through a processing module of a transmitting end to generate an OFDM symbol, wherein Polar channel coding and SFBC space-frequency coding are introduced into the transmitting end; the signal then enters a processing module of the receiving end through a channel, and is demodulated through a series of demodulation processes, wherein SFBC space frequency decoding and Polar decoding are introduced into the receiving end. Fig. 1 is a flowchart of an algorithm for transmitting and receiving information sequences.
Example two
The core algorithm is as follows:
the first step: signal transmission processing procedure
1) Adding CRC syndrome modules
Cyclic redundancy check (Cyclic redundancy check, CRC) is used as a channel error detection technique to ensure the correctness and integrity of data transmissions. And adding CRC check bit at the tail part of the bit data information, and then sending the bit data added with CRC check to a Polar coding module.
2) Polar channel coding module
The input bit data (CRC check added) is channel-coded, and the coded bits are output to a quadrature phase shift keying (Quadrature Phase Shift Keying, QPSK) modulation module.
Polar codes can be encoded by generating a matrix
wherein ,for the original bit sequence, < > for>G is the coded bit sequence N Generating a matrix with a code length of n=2 n 。
Generating matrix G N Expressed as:
wherein ,for matrix->Is of the order of n Cronecker products (recursive +)>)；B N For ordering matrix to complete bit reverse order rearrangement operation, ">I 2 Is a 2-dimensional unit array, B 2 ＝I 2 Matrix R N To replace the matrix, the separation of odd-order elements and even-order elements is done for the input sequence.
The module adopts a rate-adaptive puncturing polarization (RCPP) code scheme, and defines the coding rate as r=k/M. At the transmitting end, K information bit sequences are input into the CRC unit, m check bits are added, and the output bit number is k=k+m. The K-bit source sequence then passes through a Polar encoder to output a coded sequence of N bits. Then, a puncturing method is adopted, the method does not need to change the coding and decoding structure, the code length and the coding rate can be adaptively adjusted, the coding sequences of N bits are input into a puncturing unit, and after N-M bits are punctured, the puncturing polarization codes of M bits are output. Rate adaptation punctured polarization (RCPP) code schemes, as shown in fig. 2.
3) QPSK modulation module
The QPSK modulation module completes the mapping process from the bit to the complex value data and then sends the complex value data to the spread spectrum scrambling module.
4) Spread spectrum scrambling module
And after the complex-valued data are subjected to spread spectrum scrambling, the complex-valued data are sent to an SFBC module.
5) SFBC space frequency coding module
And carrying out SFBC space-frequency coding on the data after the spread spectrum scrambling.
Let the received symbol of the j (j=1, 2) th receiving antenna on the kth subcarrier of a certain OFDM symbol beNoise is->The channel coefficient of the ith (i=1, 2) transmitting antenna and the jth receiving antenna is +.>When the transmitting end and the receiving end are two antennas, the transmitted SFBC coding matrix can be expressed as +.>
The reception symbol of the j (j=1, 2) th reception antenna is expressed as:
by combiningTaking a conjugate construction equivalent transmission equation:
is available in the form of
Equivalent channel transmission matrixDetecting the same by adopting a detection algorithm to obtain the equivalent transmitted symbol vector +.>Is used for the estimation of the estimated value of (a).
6) OFDM mapping module
The conversion of complex-valued data from the frequency domain to the time domain is completed by inverse fast fourier transform (Inverse Fast Fourier Transform, IFFT) and Cyclic Prefix (CP) processing, and an OFDM symbol is generated.
And a second step of: signal receiving processing procedure
1) OFDM demapping module
The process is the inverse of the IFFT mapping process, the CP removal process is completed, and the transformation from the time domain to the frequency domain is realized through the IFFT.
2) SFBC space frequency decoding module
The 1280 complex-valued data from the two antennas and the channel estimation result of the channel estimation module are space-frequency decoded. Definition of the definitionFor complex value data of antenna 1, +.>Complex value data for the antenna 2; h 11 (0)，…，H 11 (N) is channel estimation between the transmitting antenna 1 and the receiving antenna 1, H 12 (0)，…，H 12 (N) is channel estimation between the transmitting antenna 1 and the receiving antenna 2, H 21 (0)，…，H 21 (N) is channel estimation between the transmitting antenna 2 and the receiving antenna 1, H 22 (0)，…，H 22 (N) is a channel estimate between the transmit antenna 2 and the receive antenna 2; />Is complex-valued data after space-frequency decoding, where n=1280.
The SFBC space-frequency coding result may be expressed as:
wherein i=1, 2, …,640; r is (r) 11 ＝d 1 (n 1 )，n 1 ＝1，3，…，1279；r 12 ＝d 1 (n 2 )，n 2 ＝2，4，…，1280；r 21 ＝d 2 (n 1 )，n 1 ＝1，3，…，1279；r 22 ＝d 2 (n 2 )，n 2 ＝2，4，…，1280。
3) Despreading and descrambling module
And performing despreading and descrambling processing on the complex-valued data decoded by the SFBC, and transmitting the complex-valued data to a QPSK demodulation module.
4) QPSK demodulation module
And carrying out QPSK demodulation processing on the complex-valued data to obtain soft bit information.
5) Polar decoding module
The soft symbol is input to a decoder, and the decoded bits are sent to a CRC check module.
The successive cancellation list (Successive Cancellation List, SCL) proposes that, based on successive cancellation (Successive Cancellation, SC), when decoding is completed, a bit sequence with highest reliability is selected from the retained L candidate paths as a decoding output, so as to improve decoding performance.
The Polar decoding module adopts a CRC-assisted continuous cancellation list (CRC-insulated SCL, CA-SCL) decoding algorithm, L decoding results are obtained by the SCL decoding algorithm, then CRC check is carried out on the L decoding results, and the decoding result which passes the CRC check and has the minimum path metric value is output as the optimal decoding result. CA-SCL decoding flow chart, as shown in figure 2.
6) Receive CRC check module
And comparing the obtained bit check bit with the original bit check bit, if the bit check bit is the same as the original bit check bit, checking the bit, and if the bit check bit is not the original bit check bit, checking the bit is failed.
Simulation analysis
In order to effectively evaluate the performance of the method provided by the invention, the following simulation verification is performed. In the simulation, an SFBC-based MIMO-OFDM wireless communication system is adopted, the modulation type is QPSK, the simulation is carried out under a Rayleigh Li Duojing fading channel, and the simulation result takes an average value of 5000 times. The relevant parameters in the simulation experiment are set as follows: the number of transmitting antennas is 2, the number of receiving antennas is 2, the number of subcarriers is 1280, the number of IFFT/FFT points is 2048, the CP length is 512, the spreading factor SF=5, the number of information bits K=36, the length M=512 after rate adaptation, the decoding list length in a CA-SCL (CRC-assisted continuous cancellation list decoding) algorithm is 8, the code rate R=the information bit length/the coding code length=K/M=36/512=9/128, the CRC check bit is 24, the signal-to-noise ratio SNR= -10:1:10, and simulation comparison analysis is shown in fig. 3.
As can be seen from fig. 3, the BER performance of the method of the present invention is similar to that of the SFBC method when snr=6db when snr= -5 dB. Compared with SFBC method, the method has more excellent performance when SNR is more than or equal to-8 dB, and BER=7.5X10 when SNR is more than or equal to-5 dB -5 . Simulation analysis shows that the performance of the method is more superior than that of the SFBC method under the condition of low signal-to-noise ratio.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (4)
1. A physical layer processing method combining SFBC space frequency coding and Polar channel code is characterized by comprising the following steps:
firstly, a signal passes through a processing module of a transmitting end to generate an OFDM symbol, wherein Polar channel coding and SFBC space-frequency coding are introduced into the transmitting end;
the signal then enters a processing module of the receiving end through a channel, and is demodulated through a series of demodulation processes, wherein SFBC space frequency decoding and Polar decoding are introduced into the receiving end.
2. The physical layer processing method combining SFBC space-frequency coding and Polar channel codes according to claim 1, wherein: the method belongs to an algorithm for receiving and transmitting information sequences in a communication system, and can be realized on an FPGA, and comprises the following specific steps:
the first step: a signal transmission processing module comprising:
1) Adding CRC syndrome modules
2) Polar channel coding module
3) QPSK modulation module
4) Spread spectrum scrambling module
5) SFBC space frequency coding module
6) An OFDM mapping module;
and a second step of: signal receiving process comprising
1) OFDM demapping module
2) SFBC space frequency decoding module
3) Despreading and descrambling module
4) QPSK demodulation module
5) Polar decoding module
6) And receiving a CRC check module.
3. The physical layer processing method combining SFBC space-frequency coding and Polar channel codes according to claim 2, wherein:
wherein, in the first step: the signal sending and processing process comprises the following steps:
1) Adding CRC syndrome modules
Cyclic Redundancy Check (CRC) is used as a channel error detection technology to ensure the correctness and the integrity of data transmission; adding CRC check bit at the tail of the bit data information, and then sending the bit data added with CRC check to a Polar coding module;
2) Polar channel coding module
Carrying out channel coding on the input bit data added with CRC, and outputting the coded bits to a quadrature phase shift keying QPSK modulation module;
polar codes can be encoded by generating a matrix
wherein ,for the original bit sequence, < > for>G is the coded bit sequence N Generating a matrix with a code length of n=2 n ；
Generating matrix G N Expressed as:
wherein ,for matrix->Is of the order of n Cronecker products (recursive +)>)；B N For ordering matrix to complete bit reverse order rearrangement operation, ">I 2 Is a 2-dimensional unit array, B 2 ＝I 2 Matrix R N For replacing the matrix, separating odd-order elements and even-order elements from the input sequence;
the module adopts a rate-adaptive puncturing polarization RCPP code scheme, and defines the coding rate as R=K/M; at a transmitting end, inputting K information bit sequences into a CRC unit, adding m check bits, and outputting the number of bits as K=k+m; then the K bit source sequence outputs a coding sequence of N bits through a Polar encoder; then, a puncturing method is adopted, the method does not need to change the coding and decoding structure, the code length and the coding rate can be adaptively adjusted, the coding sequences of N bits are input into a puncturing unit, and after N-M bits are punctured, puncturing polarization codes of M bits are output;
3) QPSK modulation module
The QPSK modulation module finishes the mapping process from the bit to the complex value data and then sends the complex value data to the spread spectrum scrambling module;
4) Spread spectrum scrambling module
Spread spectrum scrambling is carried out on complex value data, and then the complex value data is sent to an SFBC module;
5) SFBC space frequency coding module
SFBC space-frequency coding is carried out on the data after the spread spectrum scrambling;
let the received symbol of the j (j=1, 2) th receiving antenna on the kth subcarrier of a certain OFDM symbol be r j (k) Noise isThe channel coefficient of the ith (i=1, 2) transmitting antenna and the jth receiving antenna is +.>When the transmitting end and the receiving end are two antennas, the transmitted SFBC coding matrix can be expressed as +.>
The reception symbol of the j (j=1, 2) th reception antenna is expressed as:
by combining r j (k+1) Taking a conjugate construction equivalent transmission equation:
is available in the form of
Equivalent channel transmission matrixDetecting the same by adopting a detection algorithm to obtain the equivalent transmitted symbol vector +.>Is a function of the estimated value of (2);
6) OFDM mapping module
And performing Inverse Fast Fourier Transform (IFFT) and Cyclic Prefix (CP) processing to complete the transformation of complex-valued data from a frequency domain to a time domain, and generating an OFDM symbol.
4. The physical layer processing method combining SFBC space-frequency coding and Polar channel codes according to claim 2, wherein:
in the second step, the signal receiving processing process, the core algorithm is:
1) OFDM demapping module
The process is the inverse process of the IFFT mapping processing, the CP removal processing is completed, and the transformation from the time domain to the frequency domain is realized through the IFFT;
2) SFBC space frequency decoding module
Performing space-frequency decoding on 1280 complex-valued data from two antennas and a channel estimation result of a channel estimation module; definition of the definitionFor complex value data of antenna 1, +.>Complex value data for the antenna 2; h 11 (0),…,H 11 (N) is channel estimation between the transmitting antenna 1 and the receiving antenna 1, H 12 (0),…,H 12 (N) is channel estimation between the transmitting antenna 1 and the receiving antenna 2, H 21 (0),…,H 21 (N) is channel estimation between the transmitting antenna 2 and the receiving antenna 1, H 22 (0),…,H 22 (N) is a channel estimate between the transmit antenna 2 and the receive antenna 2; />Complex-valued data after space-frequency decoding, where n=1280;
the SFBC space-frequency coding result may be expressed as:
wherein i=1, 2, …,640; r is (r) 11 ＝d 1 (n 1 ),n 1 ＝1,3,…,1279；r 12 ＝d 1 (n 2 ),n 2 ＝2,4,…,1280；r 21 ＝d 2 (n 1 ),n 1 ＝1,3,…,1279；r 22 ＝d 2 (n 2 ),n 2 ＝2,4,…,1280；
3) Despreading and descrambling module
Performing despreading and descrambling processing on the complex-valued data decoded by the SFBC, and transmitting the complex-valued data to a QPSK demodulation module;
4) QPSK demodulation module
QPSK demodulation processing is carried out on the complex value data to obtain soft bit information;
5) Polar decoding module
Inputting the soft symbol to a decoder, and transmitting the decoded output bits to a CRC (cyclic redundancy check) module;
the continuous cancellation list SCL is provided on the basis of continuously canceling the SC, and when decoding is completed, a bit sequence with highest reliability is selected from the L reserved candidate paths to be used as decoding output so as to improve decoding performance;
the Polar decoding module adopts a CRC-assisted continuous offset list decoding algorithm, L decoding results are obtained by using an SCL decoding algorithm, then CRC check is carried out on the L decoding results, and the decoding result which is checked by the CRC and has the minimum path metric value is output as the optimal decoding result; CA-SCL decoding flow chart;
6) Receive CRC check module
And comparing the obtained bit check bit with the original bit check bit, if the bit check bit is the same as the original bit check bit, checking the bit, and if the bit check bit is not the original bit check bit, checking the bit is failed.
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