A signal modulation method, demodulation method, communication method, device and system
By employing chirped weighted discrete Fourier transform and zero-filling mapping techniques, the problem of link quality and data transmission rate compatibility under low signal-to-noise ratio conditions is solved, enabling efficient communication in extreme environments and making it suitable for scenarios such as underground, underwater, and mines.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUAZHONG UNIV OF SCI & TECH
- Filing Date
- 2026-04-20
- Publication Date
- 2026-06-09
AI Technical Summary
Existing technologies cannot maintain link quality and data transmission rate under low signal-to-noise ratio conditions, posing challenges to communication system design, especially in extreme environments such as underground, underwater, and mines.
A digital domain orthogonal chirped subcarrier basis is constructed using chirped weighted discrete Fourier transform. Information symbols are sparsely mapped to the central frequency point of the extended signal space through zero-filling mapping, preserving redundant dimensions to obtain processing gain. Point-by-point phase weighting and inverse Fourier transform are performed during signal modulation and demodulation. Combined with cyclic prefix and frequency domain equalization processing, it can adapt to extreme environments.
It can maintain both link quality and data transmission rate under low signal-to-noise ratio conditions. By adjusting the sparsity ratio, it can achieve a flexible trade-off between processing gain and data rate, adapt to the transmission requirements of different extreme environments, and improve the link survivability and throughput of the system.
Smart Images
Figure CN122179281A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of wireless communication technology, and more specifically, relates to a signal modulation method, demodulation method, communication method, device and system. Background Technology
[0002] With the rapid development of the Internet of Things (IoT) and 6G mobile communication, wireless communication is extending from traditional cellular networks to extreme environments such as underground, underwater, and mines. In these environments, wireless channels suffer from severe path loss, extremely low signal-to-noise ratio (SNR), and non-stationary degradation. The primary task in communication system design is to ensure link survivability; only on this basis does pursuing high speed become practically meaningful.
[0003] Traditional multicarrier modulation methods, such as Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Time-Frequency Space (OTFS), employ a full-carrier multiplexing structure, using all signal dimensions for information transmission without reserving redundant dimensions for processing gain. This results in poor link quality at low signal-to-noise ratios. Solutions designed for extreme environments, such as LoRa, extend a small amount of information across a wide time-frequency range using chirped spread spectrum (CSS). While offering strong robustness, this comes at the cost of data transmission rate, making it difficult to meet the demands of large-scale data backhaul and real-time monitoring. Summary of the Invention
[0004] In view of the above-mentioned defects or improvement needs of the prior art, the present invention provides a signal modulation method, demodulation method, communication method, device and system to solve the technical problem that the prior art cannot be compatible with link quality and data transmission rate under low signal-to-noise ratio conditions.
[0005] To achieve the above objectives, in a first aspect, the present invention provides a signal modulation method, comprising: Mapping the information bits in the target signal to be transmitted to modulation symbols yields a signal containing... Symbol vector of each modulation symbol ; The preset number of subcarriers; For symbol vectors In Multiplexing the modulation symbols into multiple carriers yields the modulation signal. ; in, A chirped weighted diagonal matrix; This is the bandwidth expansion factor; This refers to the total bandwidth of the corresponding communication system; The bandwidth of a single subcarrier; It is the time-bandwidth product; The duration of a single chirp symbol; for The conjugate transpose of ; for OK The normalized discrete Fourier transform matrix of the column; for OK Zero-filled mapping matrix for columns; column index ; ; for A column vector of dimension, whose internal indices are... The element is 1, and all other elements are 0.
[0006] In a second aspect, the present invention provides a communication method applied to a transmitting device, comprising: The signal modulation method provided in the first aspect of the present invention is used to modulate the target signal to be transmitted to obtain a modulated signal; The modulated signal is sequentially subjected to digital-to-analog conversion, low-pass filtering, and up-conversion to obtain the transmitted signal, which is then sent out.
[0007] More preferably, the above communication method further includes: after obtaining the modulated signal and before performing digital-to-analog conversion on the modulated signal, inserting a length of [length missing] before the modulated signal. The cyclic prefix CP is used to update the modulated signal to a modulated signal carrying the cyclic prefix CP; where, Greater than or equal to the maximum channel delay.
[0008] Thirdly, the present invention provides a transmitting end device, comprising: A modulation module is used to modulate the target signal to be transmitted using the signal modulation method provided in the first aspect of the present invention to obtain a modulated signal. The post-processing module is used to sequentially perform digital-to-analog conversion, low-pass filtering, and up-conversion on the modulated signal to obtain the transmitted signal, which is then sent out. The modulation module and post-processing module described above work together to implement the communication method provided in the second aspect of the present invention.
[0009] Fourthly, the present invention provides a signal demodulation method, comprising: Demodulated signal Perform inverse transform processing to obtain the modulation signal estimation result. ; Zero-filled mapping matrix The conjugate transpose of ; Chirped weighted diagonal matrix The conjugate transpose of ; The modulation signal estimation result The modulation symbols in the signal are mapped back to the information bits, thereby recovering the target signal; Among them, the signal to be demodulated The modulated signal is obtained by modulating the target signal using the signal modulation method provided in the first aspect of the present invention; the modulation signal estimation result is then used to obtain the modulated signal. The process of mapping modulation symbols back to information bits is the reverse process of mapping information bits in the target signal to modulation symbols in the signal modulation method provided in the first aspect of the present invention.
[0010] More preferably, the above signal demodulation method further includes: when the signal to be demodulated... Before performing the inverse transformation, the equalization coefficient matrix is used. Demodulated signal Frequency domain equalization is performed to demodulate the signal. Updated to ; Among them, the equilibrium coefficient matrix for OK The diagonal matrix of columns is obtained from the channel frequency response matrix.
[0011] More preferably, the channel frequency response matrix is: OK The diagonal matrix of columns is represented as:
[0012] in, Indicates the first Channel frequency response at each frequency point; ; Diagonal equilibrium coefficient matrix Based on the channel frequency response matrix, the zero-forcing criterion is used to obtain the following: ; ; Alternatively, the diagonal equilibrium coefficient matrix Based on the channel frequency response matrix, the minimum mean square error criterion is used to obtain the following: ; ; for The conjugate of complex numbers; Input signal-to-noise ratio; The signal to be demodulated The power; This represents noise power.
[0013] Fifthly, the present invention provides a communication method for a receiving end device, comprising: The system receives a signal from the transmitting device provided in the third aspect of the present invention to obtain a received signal; it then performs analog-to-digital conversion and serial-to-parallel conversion on the received signal sequentially to obtain a signal to be demodulated. ; Demodulated signal The target signal is recovered by demodulating the signal using the signal demodulation method provided in the fourth aspect of this invention.
[0014] More preferably, when the above-mentioned signal to be demodulated When the signal carries a cyclic prefix (CP), the above communication method further includes: obtaining the signal to be demodulated. Then, and the demodulated signal Remove the signal to be demodulated before demodulation. The cyclic prefix CP carried in it.
[0015] Sixthly, the present invention provides a receiving end device, comprising: The preprocessing module is used to receive the signal sent by the transmitting device provided in the third aspect of the present invention to obtain the received signal; and to perform analog-to-digital conversion and serial-to-parallel conversion on the received signal in sequence to obtain the signal to be demodulated. ; The demodulation module is used to demodulate the signal. The target signal is recovered by demodulating the signal using the signal demodulation method provided in the fourth aspect of the present invention. The aforementioned preprocessing module and demodulation module work together to implement the communication method provided in the fifth aspect of this invention.
[0016] In a seventh aspect, the present invention provides a communication system, including the transmitting end device provided in the third aspect of the present invention and the receiving end device provided in the sixth aspect of the present invention.
[0017] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: 1. This invention provides a signal modulation method, which designs a chirped weighted discrete Fourier transform. Its digital implementation mainly consists of discrete Fourier transform and point-by-point phase weighting, thereby constructing a set of digital domain chirped subcarriers as orthogonal bases to achieve multi-carrier multiplexing during modulation. Due to the sparsity among the chirped subcarriers, the processing gain characteristics can be explicitly preserved and the system complexity reduced. Based on this, the digital domain modulation process can be decomposed into three basic operations: zero-filling mapping, inverse Fourier transform, and point-by-point phase weighting, without introducing complex dedicated transform implementation structures. The chirped weighting matrix used to implement point-by-point phase weighting... The diagonal elements are unit-modulus complex exponents, which apply only a point-by-point phase rotation to the signal without changing its amplitude, thus preserving the orthogonal structure of the Fourier basis. The zero-filling mapping matrix is used to implement the zero-filling mapping. Used to Each information symbol is mapped to A predetermined frequency domain location in the extended signal space, only within which Each dimension carries information, the rest Each dimension is explicitly retained as a redundant dimension, thereby decoupling processing gain from data rate and directly constructing structured sparsity for processing gain in the digital domain. By adjusting... It achieves significant processing gain, enabling multi-carrier transmission while ensuring link quality under low signal-to-noise ratio conditions, thereby improving data transmission rate and achieving compatibility between link quality and data transmission rate under low signal-to-noise ratio conditions.
[0018] 2. The signal modulation method provided by this invention adjusts the sparsity ratio. This invention allows for a flexible trade-off between processing gain and data rate. When the sparsity ratio increases, the redundancy dimension in the extended signal space increases, enhancing the system's processing gain; conversely, when the sparsity ratio decreases, the system's data transmission efficiency improves. Based on this, the invention can adapt to the differentiated requirements for transmission distance and efficiency under various extreme environments, achieving the optimal balance between link survivability and throughput.
[0019] 3. The present invention provides a communication method for use in transmitting devices, which uses the signal modulation method provided in the first aspect of the present invention to perform signal modulation, and can be compatible with link quality and data transmission rate under low signal-to-noise ratio conditions.
[0020] 4. Furthermore, the communication method for transmitting devices provided by the present invention, after obtaining the modulated signal and before performing digital-to-analog conversion on the modulated signal, inserts a length of [length missing] before the modulated signal. The cyclic prefix (CP) is used to copy and insert a segment of sampling points before each symbol and at the end of the symbol to absorb interference between adjacent symbols caused by channel delay spread and maintain the cyclic continuity of the signal within the effective symbol interval. This invention provides a signal demodulation method that decomposes the digital domain modulation process into three basic operations: zero-filling mapping, Fourier transform, and point-by-point phase weighting. This is the inverse process of the signal modulation method provided in the first aspect of this invention, and it can maintain compatibility with link quality and data transmission rate under low signal-to-noise ratio conditions.
[0021] 5. Furthermore, the signal demodulation method provided by the present invention, when the signal to be demodulated... Before performing the inverse transformation, the equalization coefficient matrix is used. Demodulated signal Frequency domain equalization is performed to compensate for the dispersion caused by the frequency-selective channel. Under ideal synchronization and noise-free conditions, this despreading operation can recover the transmitted symbols without distortion. For additive white noise scenarios, this despreading operation is equivalent to... Dimensional received noise projection to This allows for the creation of an effective signal subspace, which is beneficial for further reducing effective noise power and achieving processing gain.
[0022] 6. The signal modulation and demodulation methods provided by this invention do not require the introduction of complex dedicated transformation implementation structures, and their complexity is only [missing information]. This is beneficial for implementation based on existing FFT / IFFT hardware architecture. Attached Figure Description
[0023] Figure 1 A digital implementation diagram of the communication system provided in the embodiments of the present invention under a linear time-invariant (LTI) system; Figure 2 A comparison chart of the bit error rate performance of the communication system and the OCDM system under different sparsity ratios provided in the embodiments of the present invention; Figure 3 The effective throughput performance diagram of the communication system provided in the embodiments of the present invention under different sparsity ratios is shown. Figure 4 A comparison chart of the bit error rate performance of the communication system provided in the embodiments of the present invention under frequency domain equalization conditions. Detailed Implementation
[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.
[0025] To achieve the above objectives, in a first aspect, the present invention provides a signal modulation method, comprising: Mapping the information bits in the target signal to be transmitted to modulation symbols yields a signal containing... Symbol vector of each modulation symbol ; The preset number of subcarriers; For symbol vectors In Multiplexing the modulation symbols into multiple carriers yields the modulation signal. ; in, A chirped weighted diagonal matrix; This is the bandwidth expansion factor; This refers to the total bandwidth of the corresponding communication system; The bandwidth of a single subcarrier; It is the time-bandwidth product; The duration of a single chirp symbol; for The conjugate transpose of ; for OK The discrete Fourier transform matrix of the column; for OK Zero-filled mapping matrix for columns; column index ; ; for A column vector of dimension, whose internal indices are... The element is 1, and all other elements are 0.
[0026] It should be noted that there are various methods for mapping information bits in the target signal to be transmitted as modulation symbols, such as phase shift keying (PSK), quadrature amplitude modulation (QAM), and quadrature phase shift keying (QPSK), etc., which are not limited here.
[0027] In a second aspect, the present invention provides a communication method applied to a transmitting device, comprising: The signal modulation method provided in the first aspect of the present invention is used to modulate the target signal to be transmitted to obtain a modulated signal; The modulated signal is sequentially subjected to digital-to-analog conversion, low-pass filtering, and up-conversion to obtain the transmitted signal, which is then sent out.
[0028] In one optional implementation, the communication method further includes: after obtaining the modulated signal and before performing digital-to-analog conversion on the modulated signal, inserting a length of [length missing] before the modulated signal. The cyclic prefix CP is used to update the modulated signal to a modulated signal carrying the cyclic prefix CP; where, Greater than or equal to the maximum channel delay.
[0029] The related technical solutions are the same as the signal modulation method provided in the first aspect of this invention, and are not limited here.
[0030] Thirdly, the present invention provides a transmitting end device, comprising: A modulation module is used to modulate the target signal to be transmitted using the signal modulation method provided in the first aspect of the present invention to obtain a modulated signal. The post-processing module is used to sequentially perform digital-to-analog conversion, low-pass filtering, and up-conversion on the modulated signal to obtain the transmitted signal, which is then sent out. The modulation module and post-processing module described above work together to implement the communication method provided in the second aspect of the present invention.
[0031] The related technical solutions are the same as the signal modulation method provided in the first aspect of the present invention and the communication method provided in the second aspect of the present invention, and are not limited here.
[0032] Fourthly, the present invention provides a signal demodulation method, comprising: Demodulated signal Perform inverse transform processing to obtain the modulation signal estimation result. ; Zero-filled mapping matrix The conjugate transpose of ; Chirped weighted diagonal matrix The conjugate transpose of ; The modulation signal estimation result The modulation symbols in the signal are mapped back to the information bits, thereby recovering the target signal; Among them, the signal to be demodulated The modulated signal is obtained by modulating the target signal using the signal modulation method provided in the first aspect of the present invention; the modulation signal estimation result is then used to obtain the modulated signal. The process of mapping modulation symbols back to information bits is the reverse process of mapping information bits in the target signal to modulation symbols in the signal modulation method provided in the first aspect of the present invention.
[0033] In one optional implementation, the above signal demodulation method further includes: [the following steps are taken when the signal to be demodulated is...] Before performing the inverse transformation, the equalization coefficient matrix is used. Demodulated signal Frequency domain equalization is performed to demodulate the signal. Updated to ; Among them, the equilibrium coefficient matrix for OK The diagonal matrix of the columns is obtained from the channel frequency response matrix; the channel frequency response matrix is... OK The diagonal matrix of columns is represented as:
[0034] in, Indicates the first Channel frequency response at each frequency point; ; In one alternative implementation, the diagonal equilibrium coefficient matrix Based on the channel frequency response matrix, the zero-forcing criterion is used to obtain the following: ; ; In another alternative implementation, the diagonal equilibrium coefficient matrix Based on the channel frequency response matrix, the minimum mean square error criterion is used to obtain the following: ; ; for The conjugate of complex numbers; Input signal-to-noise ratio; The signal to be demodulated The power; This represents noise power.
[0035] The related technical solutions are the same as the signal modulation method provided in the first aspect of this invention, and are not limited here.
[0036] Fifthly, the present invention provides a communication method for a receiving end device, comprising: The system receives a signal from the transmitting device provided in the third aspect of the present invention to obtain a received signal; it then performs analog-to-digital conversion and serial-to-parallel conversion on the received signal sequentially to obtain a signal to be demodulated. ; Demodulated signal The target signal is recovered by demodulating the signal using the signal demodulation method provided in the fourth aspect of this invention.
[0037] In one alternative implementation, when the above-mentioned signal to be demodulated... When the signal carries a cyclic prefix (CP), the above communication method further includes: obtaining the signal to be demodulated. Then, and the demodulated signal Remove the signal to be demodulated before demodulation. The cyclic prefix CP carried in it.
[0038] The related technical solutions are the same as the transmitting end device provided in the third aspect of the present invention and the signal demodulation method provided in the fourth aspect of the present invention, and are not limited here.
[0039] Sixthly, the present invention provides a receiving end device, comprising: The preprocessing module is used to receive the signal sent by the transmitting device provided in the third aspect of the present invention to obtain the received signal; and to perform analog-to-digital conversion and serial-to-parallel conversion on the received signal in sequence to obtain the signal to be demodulated. ; The demodulation module is used to demodulate the signal. The target signal is recovered by demodulating the signal using the signal demodulation method provided in the fourth aspect of the present invention. The aforementioned preprocessing module and demodulation module work together to implement the communication method provided in the fifth aspect of this invention.
[0040] The related technical solutions are the same as the transmitting end device provided in the third aspect of the present invention and the signal demodulation method provided in the fourth aspect of the present invention, and are not limited here.
[0041] In a seventh aspect, the present invention provides a communication system, including the transmitting end device provided in the third aspect of the present invention and the receiving end device provided in the sixth aspect of the present invention.
[0042] The related technical solutions are the same as the transmitting end device provided in the third aspect of the present invention and the receiving end device provided in the sixth aspect of the present invention, and are not limited here.
[0043] To further illustrate the signal modulation method, demodulation method, communication method, transmitting device, receiving device, and communication system provided in the first aspect of the present invention, a detailed description is provided below with reference to a specific embodiment: Figure 1 This is a digital implementation diagram of the communication system (denoted as OSDM system) proposed in this embodiment under a linear time-invariant (LTI) system.
[0044] In this embodiment, the number of discrete sampling points, the spatial dimension of the extended signal, and the length of the discrete Fourier transform corresponding to a single symbol are all... . P represents the modulation symbol vector; P represents the zero-filling mapping matrix. Represents a chirped weighted diagonal matrix; and They represent Point-normalized discrete Fourier transform matrix and its inverse transform matrix (i.e., conjugate transpose matrix). This represents the modulated signal (i.e., the discrete transmitted signal vector). This represents the received modulated signal (i.e., the received signal vector). This represents the modulation signal estimation result. The core digital implementation link of the system is: the transmitting end, based on... Construct discrete transmission signals, and the receiving end according to... Perform an inverse transformation on the received signal.
[0045] In this embodiment, the digital domain modulation and demodulation process is based on the chirped weighted discrete Fourier transform (CW-DFT) and its inverse transform (ICW-DFT). The CW-DFT essentially applies a point-by-point quadratic phase weighting to the input sequence before the standard discrete Fourier transform; its forward and inverse transforms can be expressed as follows:
[0046]
[0047] in, Indicates the transformation length. This represents the chirp weighting parameter. As defined above, the digital implementation of CW-DFT / ICW-DFT mainly consists of discrete Fourier transform / inverse transform and point-by-point phase weighting. In this embodiment, the transform length is taken as... That is, the number of discrete sampling points corresponding to a single modulation symbol (i.e., an OSDM symbol) in the modulated signal obtained after modulation by the signal modulation method provided in this embodiment is consistent with the number of discrete sampling points corresponding to a single modulation symbol (i.e., an OSDM symbol). Chirp weighting matrix This corresponds to the point-by-point double phase weighting process described above. Therefore, the subsequent modulation and demodulation processes can all be regarded as digital domain modulation and demodulation processes based on CW-DFT / ICW-DFT.
[0048] In this embodiment, based on the transmission distance and data rate requirements of the communication scenario, the total system bandwidth is first set. and configure it as a symmetrical baseband range .
[0049] Furthermore, the bandwidth of a single subcarrier is defined as... And introduce a bandwidth expansion factor It should be noted that, It is a positive integer. When At this time, the system sampling rate equals the subcarrier bandwidth, consistent with the sampling rates of traditional OFDM and OCDM; when At this time, the system operates at a sampling rate higher than the subcarrier bandwidth, providing redundant dimensions for obtaining the subsequent processing gain.
[0050] Furthermore, the time-bandwidth product is defined. ,in The duration of a single chirp symbol. Preferably, Typically, the sampling interval is a power of 2, such as 64, 128, 256, 512, or 1024, to facilitate efficient FFT implementation. In this embodiment, the sampling interval is set to... Therefore, the width is in a single symbol. T The number of discrete sampling points obtained within is Therefore, the discrete Fourier transform length, extended signal space dimension, and number of discrete sampling points corresponding to a single OSDM symbol are all... .
[0051] Furthermore, the number of subcarriers carrying information is set to... (In this embodiment, the value is an even number), satisfying... It should be noted that, The value of directly determines the data transmission rate: rate (bits / second), where To adjust the size of the constellation. Specifically, The smaller the value, the greater the processing gain, but the lower the data rate; conversely, The larger the value, the higher the speed, but the processing gain decreases accordingly.
[0052] In overall bandwidth Under constraints, to construct digital domain chirped subcarriers that satisfy orthogonality, this embodiment adopts a chirping model with a uniform slope. The instantaneous frequency of each subcarrier is defined as:
[0053] Specifically, the first term in the formula For a unified chirped frequency sweep term, the second term The third term is the bandwidth center offset term. This is used to distinguish the initial frequency positions of different subcarriers. This configuration ensures that each subcarrier is symmetrically distributed around zero frequency within the baseband range. Inside.
[0054] Integrating over the instantaneous frequency yields the first... The time-domain waveform of each chirped subcarrier is as follows:
[0055] This yields the set of linear chirped subcarriers.
[0056] It can be proven that this set of waveforms satisfies the orthogonality condition. ,in Let Kronecker function be the Kronecker function. The proof of orthogonality is based on the fact that the difference between the two phases is a linear phase, and that the linear phase change has integer periods within the integration interval.
[0057] This embodiment constructs a digital domain orthogonal chirped subcarrier basis based on chirped weighted discrete Fourier transform. It only requires determining the sampling interval according to the total system bandwidth and completing the digital implementation by combining it with the discrete Fourier transform length, allowing for a bandwidth expansion factor. Flexible configuration eliminates the strict binding relationship between sampling interval and subcarrier bandwidth found in traditional discrete Fresnel transforms, thus enabling more flexible digital implementation. Furthermore, due to this orthogonality and Regardless, the system can freely choose the spread factor without changing the subcarrier orthogonality. This is a significant advantage of this embodiment compared to traditional OCDM.
[0058] For the continuous-time transmitter, the modulation symbols are multiplexed based on the set of linearly chirped subcarriers, that is, the subcarriers are weighted and superimposed according to their corresponding modulation symbols to obtain the continuous-time transmitted signal:
[0059] For index k Modulation symbols; For index k The time-domain wave signal of the chirped subcarrier; t Indicates time; jIt is the symbol for imaginary numbers; Set sampling interval Sampling rate Discretizing the continuous-time transmitted signal yields a discrete transmitted signal sequence:
[0060] The derivation utilizes relations. , ,as well as .
[0061] To facilitate unified representation in the digital domain, a logical subcarrier index is introduced. and define extended symbol sequences Then the discrete transmitted signal sequence can be further rewritten as:
[0062] This formula shows that a discrete transmitted signal can be considered as: first constructing a length of... The sparse frequency domain sequence is then processed by IFFT and point-by-point chirped phase weighting to obtain the time domain transmitted signal.
[0063] Since the number of sampling points in the discrete process is The actual number of information subcarriers loaded is Since the two are usually not equal, this embodiment constructs a zero-filling mapping matrix:
[0064] Mapping matrix The column vector is composed of The standard basis vectors are constructed as follows: , used to A modulation symbol is embedded in In the extended signal space, its mapping position is defined as:
[0065] This mapping method enables Each modulation symbol is continuously mapped to the center frequency position of the extended signal space, and the rest... Each dimension does not carry information and is explicitly reserved as a redundant dimension. The core of this mapping strategy lies in continuously arranging information symbols in the central frequency domain region of the extended signal space; when the mapping position exceeds the boundary, the periodicity of the extended signal space is used to complete the wraparound mapping through modulo operation, thereby ensuring that the mapping position always falls within the boundary. Within the extended signal space.
[0066] Furthermore, construct the chirped weighted diagonal matrix:
[0067] Each diagonal element is a unit modulus complex exponent, which applies a point-by-point phase rotation to the signal without changing its amplitude.
[0068] Therefore, the discrete transmitted signal sequence can be represented in the form of a discrete transmitted signal vector:
[0069] In this expression, Used to implement zero-fill mapping; accomplish Point-normalized inverse discrete Fourier transform; This is used to perform point-by-point chirped phase weighting. The structure shows that the digital domain modulation process of this invention can be decomposed into three basic operations: zero-filling mapping, FFT / IFFT, and point-by-point phase weighting. The structure is regular and easy to implement in engineering.
[0070] After obtaining the above expression, the transmitting device implements signal modulation in the following way: Mapping the information bits in the target signal to be transmitted to modulation symbols yields a signal containing... Symbol vector of each modulation symbol Specifically, phase shift keying (PSK), quadrature amplitude modulation (QAM), and quadrature phase shift keying (QPSK) can be used for mapping. Taking QPSK as an example, every 2 bits are mapped to a complex symbol, with values ranging from 1 to 2. After normalization, a sign vector is formed. .
[0071] For symbol vectors In Multiplexing the modulation symbols into multiple carriers yields the modulation signal. .
[0072] Furthermore, in this embodiment, the modulation signal... The length of the first insertion is The cyclic prefix CP, where The signal delay is greater than or equal to the maximum channel delay. The modulated signal after inserting the cyclic prefix (CP) is transmitted to the communication channel after digital-to-analog conversion, low-pass filtering, and up-conversion. The CP is used to copy and insert a sampling point at the end of each symbol to absorb interference between adjacent symbols caused by channel delay spread, maintaining the cyclic continuity of the signal within the effective symbol interval. Simultaneously, in this embodiment, inserting the CP can also adapt to frequency-selective channels, transforming the channel's linear convolution into a cyclic convolution, facilitating single-tap frequency domain equalization. This allows the channel to exhibit a frequency-point-independent multiplicative relationship in the frequency domain, reducing the complexity of subsequent frequency domain equalization and thus improving its feasibility.
[0073] The receiving end performs down-conversion, low-pass filtering, and analog-to-digital conversion on the received signal, and removes the cyclic prefix at the receiving end to obtain the time-domain received signal vector. In this embodiment, due to the presence of the cyclic prefix, after removing the cyclic prefix at the receiving end, the original linear convolution relationship can be equivalently transformed into a cyclic convolution relationship, providing conditions for subsequent frequency domain single-tap equalization.
[0074] The receiving end performs down-conversion, low-pass filtering, and analog-to-digital conversion on the received signal in sequence, and removes the cyclic prefix (CP) to obtain the time-domain received vector. Assuming the channel is a linear time-invariant (LTI) channel, then ,in The circular convolutional channel matrix, Let be a complex Gaussian white noise vector with zero mean and covariance matrix . .
[0075] The demodulation process is a CW-DFT process:
[0076] in, Chirped weighted diagonal matrix The conjugate transpose matrix is used for inverse transformation at the receiver to recover the transmitted symbol; Used to transform signals to the frequency domain; Zero-filled mapping matrix The conjugate transpose of the vector is used to extract symbols at effective subcarrier positions, thereby recovering the transmitted symbol estimation vector. .
[0077] It should be noted that, due to ,and and All are unitary matrices. Under ideal synchronization and noise-free conditions, the despreading process can recover the transmitted symbols without distortion. For additive white noise scenarios, the despreading operation is equivalent to... Dimensional received noise projection to This allows for the creation of an effective signal subspace, which helps reduce effective noise power and achieve processing gain.
[0078] Furthermore, when the channel is a frequency-selective fading channel, frequency domain equalization is performed before demodulation. Since the linear convolution relationship of the channel can be equivalently transformed into a circular convolution relationship after the transmitting device inserts a cyclic prefix and the receiving device removes the cyclic prefix, a single-tap frequency domain equalization method can be further adopted.
[0079] Specifically, the received signal is first dechirped and subjected to FFT to obtain the frequency domain received vector:
[0080] Since the channel cyclic matrix can be diagonalized after FFT, the channel frequency response matrix is denoted as:
[0081] in, Indicates the first Channel frequency response at each frequency point; ; Perform single-tap frequency domain equalization on the frequency domain received vector to obtain the equalized frequency domain signal:
[0082] Where G is the diagonal equilibrium coefficient matrix.
[0083] After equalization, the frequency domain signal is returned to the time domain via inverse discrete Fourier transform, and then the symbol is recovered via inverse despread transform.
[0084] The equalization-inverse transformation-despreading processing chain is consistent with the digital implementation structure of the transmitting end device of the OSDM system, and the overall structure is unified.
[0085] In this embodiment, the equilibrium coefficient matrix G is: The equilibrium coefficient matrix G can be determined using either the zero-forcing (ZF) criterion or the minimum mean square error (MMSE) criterion.
[0086] When the zero-forcing criterion is used, its diagonal elements are:
[0087] When the minimum mean square error criterion is used, its diagonal elements are:
[0088] in, for The conjugate of complex numbers; Input signal-to-noise ratio; For time-domain receive vector The power; This represents noise power.
[0089] In practical applications, either the ZF criterion or the MMSE criterion can be selected to perform frequency domain equalization based on channel conditions and system requirements. Using the ZF criterion can effectively eliminate channel distortion, but it may introduce noise enhancement at deep fading frequencies. Using the MMSE criterion, a trade-off can be achieved between suppressing noise enhancement and compensating for channel distortion. Therefore, in frequency-selective fading channels, the frequency domain equalization and inverse transform despreading process can work synergistically, thereby improving the symbol recovery performance at the receiver.
[0090] It should be noted that, since the equalization adopts a single-tap diagonal structure in the frequency domain, its processing method is similar to that of traditional OFDM frequency domain equalization, making it easy to integrate with existing digital baseband processing architectures. After equalization, inverse transform despreading can then be used to recover the transmitted symbols.
[0091] This embodiment supports frequency domain equalization processing at the receiving end device. By inserting a cyclic prefix at the transmitting end device and removing the cyclic prefix at the receiving end device, the linear convolution of the channel can be transformed into a cyclic convolution, facilitating single-tap frequency domain equalization. Based on this, the equalized received signal is then combined with inverse transform despreading to recover the transmitted symbols. This receiving processing flow has a unified structure and clear implementation, and can compensate for the dispersion distortion caused by frequency-selective channels, thereby improving the symbol recovery performance of the receiving end device.
[0092] In this embodiment, the system sparsity ratio is defined as:
[0093] By adjusting the sparsity ratio The value of can change the ratio between the redundant dimension and the effective information dimension in the extended signal space, thereby achieving a flexible trade-off between processing gain and data rate.
[0094] when As the size increases, the redundancy dimension in the extended signal space increases, and the system processing gain is enhanced; when When the size is reduced, the proportion of the actual information carried increases, and the system's data transmission efficiency improves accordingly. Therefore, this embodiment can adapt to the differentiated requirements for transmission distance and transmission efficiency under different extreme environments.
[0095] Numerical Example: As a representative set of parameter configurations, we take the discrete block dimension mN=256, the modulation scheme as 16-QAM, and the sparsity ratio mN / M∈{4, 8, 16}. In this case, the corresponding number of loaded subcarriers are M=64, 32, and 16, and the theoretical processing gains are respectively:
[0096]
[0097]
[0098] This shows that, with a fixed discrete block dimension Under these conditions, as the sparsity ratio increases, the system explicitly retains more redundant dimensions, enhancing processing gain, but the actual number of loaded information subcarriers decreases accordingly. Therefore, this embodiment can achieve a trade-off between transmission reliability and effective throughput by adjusting the sparsity ratio. To further illustrate the performance of this embodiment under the above parameter configuration, the following section combines… Figure 2 , Figure 3 and Figure 4 The paper explains the performance from three aspects: bit error rate performance, effective throughput performance, and recovery performance under frequency domain equalization conditions.
[0099] like Figure 2 As shown, under different sparsity ratios, the OSDM system proposed in this embodiment can achieve better bit error rate performance than the OCDM system under lower input signal-to-noise ratio conditions. This indicates that the present embodiment can effectively improve symbol recovery capability under low signal-to-noise ratio conditions through structured sparse mapping and inverse transform despreading.
[0100] like Figure 3 As shown, the system's effective throughput can be characterized by the Goodput metric, which is the number of information bits successfully transmitted per unit time. With varying sparsity ratios, the system can achieve a trade-off between processing gain and effective throughput. Under 16-QAM conditions, the proposed OSDM system can achieve stable effective transmission of approximately 10 Kbps at an input SNR of approximately 10 dB, while the comparative OCDM system typically requires approximately 21 dB to achieve a similar level. Furthermore, in non-stationary channel environments, when mN / M = 8, OSDM can achieve Goodput exceeding 10 Kbps at an input SNR of approximately 8 dB, while OCDM requires approximately 17 dB.
[0101] like Figure 4 As shown, under frequency-selective channel conditions, the receiver employs single-tap frequency domain equalization after removing the cyclic prefix, and combines this with inverse transform despreading to recover the transmitted symbols, which can compensate for distortion caused by channel dispersion. Both ZF and MMSE equalization criteria can be used in the receiver's equalization processing, with the MMSE criterion offering a better trade-off between noise enhancement and channel compensation.
[0102] The numerical results above demonstrate that this embodiment can not only obtain different levels of processing gain by adjusting the sparsity ratio, but also maintain good effective throughput performance under low signal-to-noise ratio conditions, and further improve the symbol recovery performance of the receiver through frequency domain equalization under frequency-selective channel conditions.
[0103] In summary, this invention solves the problem of balancing low signal-to-noise ratio and high data rate in extreme environments. This invention constructs a digital domain orthogonal chirped subcarrier basis based on chirped weighted discrete Fourier transform, and utilizes zero-filling mapping to... A symbolic sparse mapping to The center frequency of the extended signal space is explicitly reserved. The invention employs multiple redundant dimensions to achieve processing gain; the receiving device uses inverse transformation to accumulate signal energy and suppress noise. Simultaneously, it supports frequency domain equalization to compensate for the dispersion effects caused by frequency-selective channels. Compared to existing full-carrier loading systems, this invention improves link survivability under low signal-to-noise ratio conditions and allows for a flexible trade-off between processing gain and data rate by adjusting the sparsity ratio, making it suitable for communication in extreme environments such as underground, underwater, and mines.
[0104] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A signal modulation method, characterized in that, include: Mapping the information bits in the target signal to be transmitted to modulation symbols yields a signal containing... Symbol vector of each modulation symbol ; The preset number of subcarriers; For the symbol vector In Multiplexing the modulation symbols into multiple carriers yields the modulation signal. ; in, A chirped weighted diagonal matrix; This is the bandwidth expansion factor; This refers to the total bandwidth of the corresponding communication system; The bandwidth of a single subcarrier; It is the time-bandwidth product; The duration of a single chirp symbol; for The conjugate transpose of ; for OK The normalized discrete Fourier transform matrix of the column; for OK Zero-filled mapping matrix for columns; column index ; ; for A column vector of dimension, whose internal indices are... The element is 1, and all other elements are 0.
2. A communication method, characterized in that, Applied to transmitting devices, including: The signal modulation method described in claim 1 is used to modulate the target signal to be transmitted to obtain a modulated signal; The modulated signal is sequentially subjected to digital-to-analog conversion, low-pass filtering, and up-conversion to obtain the transmission signal, which is then sent out.
3. The communication method according to claim 2, characterized in that, Also includes: After obtaining the modulated signal and before performing digital-to-analog conversion on the modulated signal, an insertion length of [length missing] is inserted before the modulated signal. The cyclic prefix CP is used to update the modulated signal to a modulated signal carrying the cyclic prefix CP; wherein, Greater than or equal to the maximum channel delay.
4. A transmitting device, characterized in that, include: A modulation module is used to modulate the target signal to be transmitted using the signal modulation method described in claim 1, to obtain a modulated signal; The post-processing module is used to sequentially perform digital-to-analog conversion, low-pass filtering, and up-conversion processing on the modulated signal to obtain the transmission signal and send it out. The modulation module and the post-processing module work together to implement the communication method of claim 2 or 3.
5. A signal demodulation method, characterized in that, include: Demodulated signal Perform inverse transform processing to obtain the modulation signal estimation result. ; Zero-filled mapping matrix The conjugate transpose of ; Chirped weighted diagonal matrix The conjugate transpose of ; The modulation signal estimation result The modulation symbols in the signal are mapped back to the information bits, thereby recovering the target signal; Wherein, the signal to be demodulated The modulated signal is obtained by modulating the target signal using the signal modulation method described in claim 1; the estimation result of the modulated signal is... The process of mapping the modulation symbols back to information bits is the reverse process of mapping the information bits in the target signal to modulation symbols in the signal modulation method of claim 1.
6. The signal demodulation method according to claim 5, characterized in that, Also includes: In the demodulated signal Before performing the inverse transformation, the equalization coefficient matrix is used. For the signal to be demodulated Frequency domain equalization is performed to demodulate the signal. Updated to ; Among them, the equilibrium coefficient matrix for OK The diagonal matrix of columns is obtained from the channel frequency response matrix; The channel frequency response matrix is: OK The diagonal matrix of columns is represented as: Indicates the first Channel frequency response at each frequency point; ; The diagonal balance coefficient matrix Based on the channel frequency response matrix, the zero-forcing criterion is used to obtain the following: ; ; or, The diagonal balance coefficient matrix Based on the channel frequency response matrix, the minimum mean square error criterion is used to obtain the following: ; ; for The conjugate of complex numbers; Input signal-to-noise ratio; The signal to be demodulated The power; This represents noise power.
7. A communication method, characterized in that, For receiving end devices, including: The receiving end device of claim 4 receives the signal sent by the receiving end device to obtain the received signal; the received signal is then subjected to analog-to-digital conversion and serial-to-parallel conversion processes in sequence to obtain the demodulated signal. ; For the signal to be demodulated The target signal is recovered by demodulating the signal using the signal demodulation method described in claim 5 or 6.
8. The communication method according to claim 7, characterized in that, When the signal to be demodulated When the signal carries a cyclic prefix (CP), the communication method further includes: obtaining the signal to be demodulated. Then, for the signal to be demodulated Before demodulation, the signal to be demodulated is removed. The cyclic prefix CP carried in it.
9. A receiving device, characterized in that, include: The preprocessing module is used to receive the signal sent by the transmitting device as described in claim 4 and obtain the received signal; The received signal is sequentially subjected to analog-to-digital conversion and serial-to-parallel conversion to obtain the demodulated signal. ; The demodulation module is used to demodulate the signal to be demodulated. The target signal is recovered by demodulating the signal using the signal demodulation method described in claim 5 or 6. The preprocessing module and the demodulation module work together to implement the communication method of claim 7 or 8.
10. A communication system, characterized in that, It includes the transmitting device as described in claim 4 and the receiving device as described in claim 9.