OFDM (Orthogonal Frequency Division Multiplexing) signal transmission and processing method based on affine transform domain pilot frequency

Abstract

The invention provides an OFDM (Orthogonal Frequency Division Multiplexing) signal transmission and processing method based on affine transform domain pilot frequency, which belongs to the field of wireless communication, and comprises the following steps: generating an affine transform domain pilot frequency symbol and a data symbol by a transmitting end, splicing the affine transform domain pilot frequency symbol and the data symbol in a time domain and then transmitting through a high Doppler multipath channel; the receiving end processes the received signal to obtain a time domain received symbol, and predicts a predicted pilot symbol corresponding to a data symbol in the time domain received symbol by using a pilot symbol in the time domain received symbol; and estimating an affine transform domain channel matrix corresponding to the data symbol according to the predicted pilot symbol, converting the affine transform domain channel matrix to a frequency domain to obtain a frequency domain channel matrix, and performing frequency domain equalization on frequency domain data corresponding to the data symbol in the received signal by using the frequency domain channel matrix to obtain a final transmission result. According to the method, robustness and low complexity can be achieved, and the balance performance and Doppler interference resistance of the OFDM system are remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of wireless communication, and in particular to an OFDM signal transmission and processing method based on affine transform domain pilots. Background Technology

[0002] With the continuous evolution of information technology, sixth-generation mobile communication aims to support richer service models and application scenarios, especially to achieve highly reliable and high-speed data transmission in high-mobility environments. However, the current mainstream communication waveform—Orthogonal Frequency Division Multiplexing (OFDM)—is extremely sensitive to the Doppler effect. When the Doppler frequency shift is too large, it will destroy the orthogonality between subcarriers, thereby causing significant inter-carrier interference (ICI) and seriously affecting link quality.

[0003] In recent years, affine radio frequency division multiplexing (AFDM) technology has been proposed to address the transmission challenges in high Doppler channels. AFDM introduces inverse affine Fourier transform modulation at the transmitter and flexibly sets frequency modulation parameters based on prior channel information, mapping the Doppler frequency shift and time delay effects in the traditional time domain to cyclic shifts in the affine transform domain. Within this transform domain, channel effects are completely separated, thus fully utilizing multipath diversity gain. This gives AFDM good robustness and potential advantages in high-speed mobile scenarios.

[0004] However, AFDM's channel matrix has a two-dimensional structure, requiring highly complex matrix inversion during equalization, which contradicts the stringent low-latency requirements of 6G. Furthermore, compared to OFDM, AFDM's flexibility in physical resource mapping and multiple access remains limited, making it still quite far from practical commercial application.

[0005] In summary, OFDM and AFDM each have their own advantages and disadvantages. How to effectively integrate the advantages of both to build a communication system that is both robust and low-complexity in high Doppler scenarios remains an important direction that urgently needs in-depth research. Summary of the Invention

[0006] The main objective of this invention is to propose an OFDM signal transmission and processing method based on affine transform domain pilots, which can combine robustness and low complexity, and significantly improve the equalization performance and anti-Doppler interference capability of OFDM systems.

[0007] This invention is achieved through the following technical solution:

[0008] The OFDM signal transmission and processing method based on affine transform domain pilots includes the following steps:

[0009] Step S1: The transmitter of the OFDM system generates affine transform domain pilot symbols and data symbols, and then concatenates the affine transform domain pilot symbols and data symbols in the time domain and transmits them to the receiver through a high Doppler multipath channel.

[0010] Step S2: The receiving end processes the received signal to obtain the time-domain received symbol, and uses the pilot symbol in the time-domain received symbol to predict the predicted pilot symbol corresponding to the data symbol in the time-domain received symbol;

[0011] Step S3: Based on the predicted pilot symbols obtained in step S2, estimate the affine transform domain channel matrix corresponding to the data symbols using the affine transform domain channel characteristics. Transform the affine transform domain channel matrix to the frequency domain to obtain the frequency domain channel matrix. Use the frequency domain channel matrix to perform frequency domain equalization on the frequency domain data corresponding to the data symbols in the received signal to obtain the final transmission result.

[0012] Furthermore, step S1 includes the following steps:

[0013] Step S11: The transmitter of the OFDM system generates affine transform domain pilot symbols, performs discrete inverse affine Fourier transform on the affine transform domain pilot symbols, and transforms them to the time domain to obtain pilot symbols. Where N is the number of subcarriers, , This is the pilot generation core, where c1 and c2 are the set frequency modulation parameters;

[0014] Step S12: The transmitting end concatenates the pilot symbols and data symbols in the time domain. The concatenated signal frame is represented as follows: ,in, These are pilot symbols transmitted by the transmitter. K is the total number of pilot symbols in a frame. For data symbols transmitted by the transmitter, S is the total number of data symbols in a frame. This represents the total number of transmitted symbols within a frame.

[0015] Step S13: The transmitter transmits the spliced ​​time-domain signal and transmits it to the receiver via a high Doppler multipath channel.

[0016] Furthermore, step S2 includes the following steps:

[0017] Step S21: The receiving end processes the received signal to obtain the time-domain received symbol, and processes the pilot symbol in the time-domain received symbol. Perform a discrete affine Fourier transform to obtain K receive pilot symbols in the affine transform domain. ,in, , ;

[0018] Step S22: Based on the correlation between the channel matrix corresponding to the data symbols and the channel matrix corresponding to the pilot symbols, and according to the K received pilot symbols obtained in step S21, use an LSTM network to predict the subsequent S predicted pilot symbols corresponding to the data symbols. ,in, , , For LSTM networks based The predicted real pilot symbol, To perform the real part operation, This is an operation to extract the imaginary part.

[0019] Furthermore, step S3 includes the following steps:

[0020] Step S31: The receiver estimates the affine transform domain channel matrix corresponding to the data symbols based on the predicted pilot symbols and by utilizing the sparsity characteristics of the affine transform domain channel response. ;

[0021] Step S32: Perform a similar unitary transform on the affine transform domain channel to obtain the frequency domain channel matrix. ,in, , k'=1,2 This is the normalized discrete Fourier transform matrix;

[0022] Step S33: Perform Discrete Fourier Transform on the data symbols in the time-domain received symbols to the frequency domain to obtain frequency domain data. Based on the frequency domain channel matrix, perform frequency domain equalization on the frequency domain data to obtain the final transmission result.

[0023] Furthermore, in step S11, the pilot generation kernel is represented as... , where T is the index of the non-zero element of the pilot generation kernel, which is set by the transmitter.

[0024] Furthermore, in step S13, the transmitting end processes the spliced ​​time-domain signal before transmitting it. This processing includes adding CP, parallel-to-serial conversion, digital-to-analog conversion, and RF up-conversion. In step S21, the receiving end processes the received signal, including RF down-conversion, digital-to-analog conversion, serial-to-parallel conversion, and CP removal.

[0025] Furthermore, in step S22, the correlation between the channel matrices refers to the fact that when a frame of transmitted symbols is within a relevant time period, the channel matrix corresponding to the data symbol and the channel matrix corresponding to the pilot symbol exhibit autoregressive properties.

[0026] Furthermore, in step S22, the... Input a multi-layer LSTM network and output a feature vector containing the correlation information between received pilot symbols. , to feature vector Input a linear network, reconstruct its dimensions, and output real pilot symbols. ,in, This is the analytical mapping function for the LSTM network.

[0027] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention generates affine transform domain pilot symbols and data symbols at the transmitter of an OFDM system. The affine transform domain pilot symbols and data symbols are concatenated in the time domain and transmitted to the receiver via a high-Doppler multipath channel. At the receiver, the received signal is processed to obtain time-domain received symbols. Predicted pilot symbols corresponding to the data symbols in the time-domain received symbols are predicted using the pilot symbols in the time-domain received symbols. Based on the predicted pilot symbols, the affine transform domain channel matrix corresponding to the data symbols is estimated using the affine transform domain channel characteristics. The affine transform domain channel matrix is ​​transformed to the frequency domain to obtain the frequency-domain channel matrix. Frequency-domain equalization is performed on the frequency-domain data corresponding to the data symbols in the received signal using the frequency-domain channel matrix to obtain the final transmission result. By introducing affine transform domain pilots and utilizing AFDM channel estimation, a complete two-dimensional frequency-domain channel response can be reconstructed, thereby significantly improving equalization performance and anti-Doppler interference capability.

[0029] 2. Compared to AFDM systems, this invention utilizes the conversion relationship between the affine domain and the frequency domain to transform the complex two-dimensional equalization problem into traditional frequency domain equalization, significantly reducing hardware and computational overhead. This invention retains the flexibility of OFDM in resource mapping and system implementation, as well as the low complexity of equalization, while fully utilizing the robust characteristics of AFDM in high Doppler scenarios, achieving a deep integration of the advantages of AFDM and OFDM technologies, making the system more suitable for 6G high-speed mobile communication scenarios.

[0030] 3. This invention addresses the problem of large interpolation errors in high-speed scenarios. The LSTM-based channel prediction network can utilize the autoregressive structure of the channel to effectively track rapidly changing channels, improving channel prediction accuracy and outperforming traditional interpolation methods.

[0031] 4. The pilot symbols proposed in this invention have constant mode characteristics and good peak-to-average power ratio characteristics, which are beneficial to improving the efficiency of the transmitting power amplifier and enhancing the overall stability and feasibility of the system. Attached Figure Description

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Figure 1 This is a flowchart of the present invention.

[0034] Figure 2 This is a detailed flowchart of the entire invention.

[0035] Figure 3 This is a flowchart of the transmitter processing of the present invention.

[0036] Figure 4 This is a schematic diagram of the LSTM network structure of the present invention.

[0037] Figure 5 This is a flowchart of the receiving end processing of the present invention.

[0038] Figure 6 The figure shows the comparison results of the bit error rate performance of the present invention and the comparative scheme under high Doppler channels.

[0039] Figure 7 The figure shows the comparison results of the bit error rate performance of the present invention under different pilot symbol ratios.

[0040] Figure 8 The graph shows the comparison results of the bit error rate performance of the present invention and the comparative scheme under static channel conditions. Detailed Implementation

[0041] The present invention will be further described below through specific embodiments.

[0042] like Figure 1 and Figure 2 As shown, the OFDM signal transmission and processing method based on affine transform domain pilots includes the following steps:

[0043] Step S1: The transmitter of the OFDM system generates affine transform domain pilot symbols and data symbols, and then concatenates the affine transform domain pilot symbols and data symbols in the time domain and transmits them to the receiver through a high Doppler multipath channel.

[0044] like Figure 3 As shown, the specific steps include the following:

[0045] Step S11: The transmitter of the OFDM system generates pilot symbols in the affine transform domain. A discrete inverse affine Fourier transform is performed on each single pilot symbol in the affine transform domain to obtain the pilot symbol in the time domain. Where N is the number of subcarriers, , Here, c1 and c2 are frequency modulation parameters set by the transmitter, and T is the index of the non-zero element of the pilot generation kernel set by the transmitter, which can generally be set to 0.

[0046] Simultaneously, the data symbols are processed, that is, the inverse discrete Fourier transform is performed on the frequency domain data symbols to obtain the time domain data symbols.

[0047] In this embodiment, , , , .

[0048] Step S12: Each frame of transmitted signal is transmitted within a relevant time window; that is, the Channel State Information (CSI) corresponding to the data symbols within a frame can be inferred from the CSI of the pilot symbols. The transmitter concatenates the pilot symbols and data symbols in the time domain, and the concatenated frame signal is represented as follows: ,in, These are pilot symbols transmitted by the transmitter. K is the total number of pilot symbols in a frame. For data symbols transmitted by the transmitter, S is the total number of data symbols in a frame. This represents the total number of transmitted symbols within a frame.

[0049] In this embodiment, K=4 and S=8.

[0050] Step S13: The transmitter transmits the spliced ​​time-domain signal and transmits it to the receiver via a high Doppler multipath channel.

[0051] Both the transmitter and receiver are equipped with a single antenna, forming a single-input single-output communication system. The transmitter transmits signals using a conventional OFDM signal transmission procedure. This process includes adding a cyclic prefix (CP), parallel-to-serial conversion, digital-to-analog conversion, and RF up-conversion. This process is existing technology.

[0052] Step S2: The receiving end processes the received signal to obtain the time-domain received symbol, and uses the pilot symbol in the time-domain received symbol to predict the predicted pilot symbol corresponding to the data symbol in the time-domain received symbol;

[0053] The processing flow at the receiving end is as follows: Figure 4 As shown. To address the issues of low channel estimation accuracy and large interpolation errors in OFDM systems under high dynamic conditions, an AFDM channel estimation method is introduced, and LSTM neural networks are used for pilot symbol prediction to achieve robust transmission under high Doppler conditions.

[0054] Specifically, the steps include the following:

[0055] Step S21: The receiving end processes the received signal to obtain the time-domain received symbol, and processes the pilot symbol in the time-domain received symbol. Perform a discrete affine Fourier transform to obtain K receive pilot symbols in the affine transform domain. ,in, , ;

[0056] The receiving end processes the received signal, including RF down-conversion, digital-to-analog conversion, serial-to-parallel conversion, and CP removal. This process is existing technology.

[0057] Step S22: Since the transmitted frame of symbols is within the correlation time, the channel matrix corresponding to the data symbols and the channel matrix corresponding to the pilot symbols are correlated, specifically exhibiting autoregressive behavior. Therefore, by using the K received pilot symbols arranged in the header of each frame to predict the received pilot symbols corresponding to the following S data symbols, and using the predicted pilot symbols to estimate the CSI corresponding to the data symbols, where, The total number of multipath paths in a high-Doppler multipath channel. These are the autoregressive coefficients. ;

[0058] In this embodiment, P=3;

[0059] Based on the correlation between the channel matrix corresponding to the data symbols and the channel matrix corresponding to the pilot symbols, and according to the K received pilot symbols obtained in step S21, a Long Short-Time Memory (LSTM) network is used to predict the subsequent S predicted pilot symbols corresponding to the data symbols. The structure of the LSTM network is as follows: Figure 5 As shown.

[0060] Specifically, before The received pilot symbols in the affine transform domain are reassembled into a real vector. ,Will Input a multi-layer LSTM network and output a feature vector containing the correlation information between received pilot symbols. Then the feature vector A linear network connected to the input and output of an LSTM network is used for dimension reconstruction, and the output is the predicted real pilot symbol. The predicted real pilot symbols are reconstructed into complex pilot symbols, thus obtaining the prediction result. ,in, To perform the real part operation, To perform the imaginary part operation, , , For the analytic mapping function of the LSTM network, For the mapping and reconstruction function of a linear network, For LSTM networks based The predicted real pilot symbols. Both LSTM networks and linear networks are existing technologies.

[0061] Thus, accurate pilot prediction under high Doppler conditions was achieved using an LSTM prediction network, reducing interpolation errors.

[0062] Step S3: Based on the predicted pilot symbols obtained in step S2, estimate the affine transform domain channel matrix corresponding to the data symbols using the affine transform domain channel characteristics. Transform the affine transform domain channel matrix to the frequency domain to obtain the frequency domain channel matrix. Use the frequency domain channel matrix to perform frequency domain equalization on the frequency domain data corresponding to the data symbols in the received signal to obtain the final transmission result.

[0063] By introducing the AFDM channel estimation method, channel estimation is performed in the affine transform domain. The frequency domain channel of the data symbols is obtained by utilizing the conversion relationship between the affine transform domain and the frequency domain. Finally, channel equalization with lower complexity is performed in the frequency domain, realizing the integration of the advantages of AFDM and OFDM.

[0064] Specifically, the steps include the following:

[0065] Step S31: Based on the predicted pilot symbols, the receiver uses the sparsity property of the affine transform domain channel response and employs the sparse Bayesian algorithm in AFDM channel estimation to estimate the affine transform domain channel matrix corresponding to the data symbols. ,in, Using the sparse Bayesian algorithm to estimate The process is existing technology;

[0066] Step S32: Perform a similar unitary transform on the affine transform domain channel to obtain the frequency domain channel matrix. ,in, , k'=1,2 This is the normalized discrete Fourier transform matrix;

[0067] Step S33: Perform a discrete Fourier transform on the data symbols in the time-domain received symbols to the frequency domain to obtain frequency domain data. Based on the frequency domain channel matrix, perform frequency domain equalization on the frequency domain data to obtain the final transmission result. At this time, the frequency domain channel matrix is ​​strictly diagonally dominant, and the inversion operation has lower complexity than the inversion operation in the affine transform domain.

[0068] Figure 6 The x-axis represents the receiver's signal-to-noise ratio (SNR), and the y-axis represents the transmission bit error rate (BER). Simulation experiments compare the BER performance of the traditional transmission scheme and the present invention (affine transform domain pilot, LSTM prediction) in a high-Doppler channel under interpolation and LTSM network prediction conditions, respectively. Figure 6 It can be seen that the bit error rate performance of this invention is significantly lower than that of traditional transmission schemes. This is because this method can obtain a more accurate and complete CSI under high Doppler conditions, resulting in superior performance after equalization. With LTSM network prediction, the bit error plateau phenomenon under high signal-to-noise ratio is reduced, demonstrating that this invention can effectively alleviate interpolation errors under high Doppler conditions.

[0069] Figure 7 The x-axis represents the receiver's signal-to-noise ratio (SNR), and the y-axis represents the transmission bit error rate (BER). Simulation experiments compare the BER performance under different pilot / data symbol ratios. Figure 7 It can be seen that the larger the pilot / data symbol ratio, the better the bit error rate performance, but the lower the transmission efficiency, reflecting the trade-off between communication reliability and effectiveness.

[0070] Figure 8 The x-axis represents the receiver's signal-to-noise ratio (SNR), and the y-axis represents the transmission bit error rate (BER). Simulation experiments compare the BER performance of traditional transmission schemes and the present invention (affine transform domain pilot) in static channels. Figure 8 It can be seen that the bit error rate performance of the present invention is significantly lower than that of the traditional transmission scheme. This is because it uses a single pilot in the affine transform domain. Under the same symbol energy conditions, the present invention has a higher pilot signal-to-noise ratio, which reflects the channel estimation accuracy advantage of the present invention.

[0071] In this invention, the terms "first," "second," and "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. The use of terms such as "upper," "lower," "left," "right," "front," and "rear" to indicate orientation or positional relationships is based on the orientation or positional relationships shown in the accompanying drawings and is only for the convenience of describing the invention, not to indicate or imply that the device referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation on the scope of protection of this invention. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0072] Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0073] The above are merely specific embodiments of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing upon the protection scope of the present invention.

Claims

1. A method for OFDM signal transmission and processing based on affine transform domain pilots, characterized in that: Includes the following steps: Step S1: The transmitter of the OFDM system generates affine transform domain pilot symbols and data symbols, and then concatenates the affine transform domain pilot symbols and data symbols in the time domain and transmits them to the receiver through a high Doppler multipath channel. Step S2: The receiving end processes the received signal to obtain the time-domain received symbol, and uses the pilot symbol in the time-domain received symbol to predict the predicted pilot symbol corresponding to the data symbol in the time-domain received symbol; Step S3: Based on the predicted pilot symbols obtained in step S2, estimate the affine transform domain channel matrix corresponding to the data symbols using the affine transform domain channel characteristics. Transform the affine transform domain channel matrix to the frequency domain to obtain the frequency domain channel matrix. Use the frequency domain channel matrix to perform frequency domain equalization on the frequency domain data corresponding to the data symbols in the received signal to obtain the final transmission result.

2. The OFDM signal transmission and processing method based on affine transform domain pilots according to claim 1, characterized in that: Step S1 includes the following steps: Step S11: The transmitter of the OFDM system generates affine transform domain pilot symbols, performs discrete inverse affine Fourier transform on the affine transform domain pilot symbols, and transforms them to the time domain to obtain pilot symbols. Where N is the number of subcarriers, , This is the pilot generation core, where c1 and c2 are the set frequency modulation parameters; Step S12: The transmitting end concatenates the pilot symbols and data symbols in the time domain. The concatenated signal frame is represented as follows: ,in, These are pilot symbols transmitted by the transmitter. K is the total number of pilot symbols in a frame. For data symbols transmitted by the transmitter, S is the total number of data symbols in a frame. This represents the total number of transmitted symbols within a frame. Step S13: The transmitter transmits the spliced ​​time-domain signal and transmits it to the receiver via a high Doppler multipath channel.

3. The OFDM signal transmission and processing method based on affine transform domain pilots according to claim 2, characterized in that: Step S2 includes the following steps: Step S21: The receiving end processes the received signal to obtain the time-domain received symbol, and processes the pilot symbol in the time-domain received symbol. Perform a discrete affine Fourier transform to obtain K receive pilot symbols in the affine transform domain. ,in, , ; Step S22: Based on the correlation between the channel matrix corresponding to the data symbols and the channel matrix corresponding to the pilot symbols, and according to the K received pilot symbols obtained in step S21, use an LSTM network to predict the subsequent S predicted pilot symbols corresponding to the data symbols. ,in, , , For LSTM networks based The predicted real pilot symbol, To perform the real part operation, This is an operation to extract the imaginary part.

4. The OFDM signal transmission and processing method based on affine transform domain pilots according to claim 3, characterized in that: Step S3 includes the following steps: Step S31: The receiver estimates the affine transform domain channel matrix corresponding to the data symbols based on the predicted pilot symbols and by utilizing the sparsity characteristics of the affine transform domain channel response. ; Step S32: Perform a similar unitary transform on the affine transform domain channel to obtain the frequency domain channel matrix. ,in, , k'=1,2 This is the normalized discrete Fourier transform matrix; Step S33: Perform Discrete Fourier Transform on the data symbols in the time-domain received symbols to the frequency domain to obtain frequency domain data. Based on the frequency domain channel matrix, perform frequency domain equalization on the frequency domain data to obtain the final transmission result.

5. The OFDM signal transmission and processing method based on affine transform domain pilots according to claim 2, 3, or 4, characterized in that: In step S11, the pilot generation kernel is represented as , where T is the index of the non-zero element of the pilot generation kernel, which is set by the transmitter.

6. The OFDM signal transmission and processing method based on affine transform domain pilots according to claim 3 or 4, characterized in that: In step S13, the transmitting end processes the spliced ​​time-domain signal and then transmits it. This processing includes adding CP, parallel-to-serial conversion, digital-to-analog conversion, and radio frequency up-conversion. In step S21, the receiving end processes the received signal, including radio frequency down-conversion, digital-to-analog conversion, serial-to-parallel conversion, and CP removal.

7. The OFDM signal transmission and processing method based on affine transform domain pilots according to claim 3 or 4, characterized in that: In step S22, the correlation between the channel matrices refers to the fact that when a frame of symbols is transmitted within a relevant time period, the channel matrix corresponding to the data symbol and the channel matrix corresponding to the pilot symbol exhibit autoregressive properties.

8. The OFDM signal transmission and processing method based on affine transform domain pilots according to claim 3 or 4, characterized in that: In step S22, Input a multi-layer LSTM network and output a feature vector containing the correlation information between received pilot symbols. , to feature vector Input a linear network, reconstruct its dimensions, and output real pilot symbols. ,in, This is the analytical mapping function for the LSTM network.

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