Communication method and system based on delay doppler alignment modulation and orthogonal time frequency space modulation

Abstract

The application relates to a communication method and system based on time-delay Doppler alignment modulation and orthogonal time-frequency-space modulation, which comprises the following steps: S1, screening out a grid unit needing time-delay Doppler alignment modulation processing according to an equivalent channel impulse response of a communication channel in a time-delay-Doppler domain; S2, a transmitting end carries data symbols to be transmitted in the time-delay-Doppler domain and performs orthogonal time-frequency-space modulation; S3, the transmitting end uses time-delay and Doppler frequency shift modules consistent with the number of units to be aligned, introduces corresponding time-delay compensation and Doppler frequency shift compensation for a symbol string needed to be transmitted on each branch, and performs beam forming design based on the grid unit by using multiple antennas; and S4, a receiving end performs orthogonal time-frequency-space demodulation on a received signal and outputs a time-delay-Doppler domain symbol. Compared with the prior art, the application has the advantages of greatly reducing the time-delay and Doppler spread of the equivalent channel and releasing the performance potential of the OTFS system.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a communication method and system based on time-delay Doppler aligned modulation (DDAM) and orthogonal time-frequency-space (OTFS) modulation, applicable to high-frequency bands such as millimeter waves and terahertz waves and high-speed mobile scenarios. Background Technology

[0002] The sixth-generation (6G) mobile communication network will be widely used in ultra-high mobility scenarios such as high-speed railways, vehicle-mounted communications, and drone communications. In such scenarios, wireless signal propagation undergoes complex multipath effects, and the relatively high-speed motion of the transmitting and receiving ends introduces significant Doppler frequency shift, resulting in the channel exhibiting time-selective fading and frequency-selective fading, which poses a severe challenge to the physical layer waveform design.

[0003] Orthogonal Time-Frequency-Space (OTFS) modulation, as an emerging waveform technology, directly modulates information symbols in the delay-Doppler domain instead of the traditional time-frequency domain. This transforms the complex response of time-varying, frequency-selective channels in the time-frequency domain into a quasi-static channel in the delay-Doppler domain. In high-mobility environments, OTFS exhibits stronger robustness to Doppler spread and better bit error rate performance compared to mainstream Orthogonal Frequency Division Multiplexing (OFDM) modulation. However, the performance potential of OTFS systems is constrained by channel delay spread and Doppler spread. To avoid aliasing distortion in the delay-Doppler domain, the delay period and Doppler period of the OTFS frame must be greater than the maximum delay spread and maximum Doppler spread of the channel, respectively. Furthermore, the pursuit of high spectral efficiency and low peak-to-average power ratio (PAPR) also imposes additional constraints on the design of OTFS frame parameters. Therefore, when channel delay and Doppler spread are large, multiple constraints conflict, often resulting in an empty feasible domain for OTFS system parameter design, severely impacting the performance of traditional OTFS systems.

[0004] On the other hand, the combination of millimeter-wave / terahertz bands with very large-scale MIMO (XL-MIMO) provides high spatial resolution, making precise manipulation of independent propagation paths in sparse channels possible. Against this backdrop, Delay-Doppler Aligned Modulation (DDAM) technology was proposed. Its core idea is to design beamforming vectors for each significant multipath component after acquiring channel state information at the transmitter, and apply pre-compensation to the signal carried on it with a value opposite to the path delay and Doppler value. Through this processing, all multipath signals, after propagating through the actual channel, can achieve synchronous arrival in the time domain and frequency offset alignment in the Doppler domain at the receiver, thus actively "reshaping" the originally time-frequency dual-selective channel into an equivalent channel with significantly reduced or even nearly flat delay and Doppler spread. This fundamentally suppresses inter-symbol interference (ISI) and inter-carrier interference (ICI) in broadband communication.

[0005] A search of Chinese Patent Publication No. CN116155662A reveals a channel estimation method for a multi-input multi-output orthogonal time-frequency spatial modulation system based on fractional Doppler frequency shift. This method involves transmitting the transmitted signal using a time-delayed Doppler equivalent channel containing inter-Doppler interference (IDI), and then using the LDAMP algorithm at the receiver to perform fractional Doppler channel estimation to obtain the estimated channel value. This means that the proposed scheme still exhibits superior estimation performance even in the presence of IDI and effectively compensates for the performance loss caused by fractional Doppler interference. However, this existing patent uses the LDAMP algorithm at the receiver to estimate the channel with IDI. Regardless of the accuracy of the estimation, IDI itself destroys the orthogonality of OTFS symbols, and the performance loss is intrinsic and cannot be completely eliminated. Furthermore, the LDAMP algorithm requires training multiple DnCNN denoisers, performing multi-layer iterations, and calculating Onsager correction terms, which leads to high computational complexity and processing latency at the receiver, making it unfriendly to terminals with limited power consumption and computing power. Therefore, how to overcome the frame parameter design conflict (limited feasible domain) caused by excessive channel delay spread and Doppler spread in the traditional Orthogonal Time-Frequency-Space (OTFS) system under the Cluster Delay Line (CDL) channel model, and thus unleash the performance potential of the OTFS system in terms of spectral efficiency and peak-to-average power ratio, has become a technical problem that needs to be solved.

[0006] DDAM's powerful channel reshaping capability provides a novel approach for OTFS systems to overcome the aforementioned parameter constraints. Combining DDAM with OTFS is expected to significantly expand the feasible design area of ​​OTFS frame parameters and unleash its performance potential by pre-compressing channel extension through DDAM. This is primarily based on the ideal Discrete Tap Delay Line (TDL) channel model, which assumes that each propagation path is discrete and non-dispersion-free, meaning that a scatterer generates only one path with a single delay, Doppler effect, and angle. In contrast, the Cluster Delay Line (CDL) channel model is closer to the actual physical propagation environment. For the more realistic CDL channel model, the design methodology of DDAM still requires further research. Therefore, for high-speed mobile communication scenarios, a joint DDAM-OTFS communication architecture suitable for CDL channels needs to be designed. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a communication method and system based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation. By screening key grid cells in the time-delay-Doppler domain for alignment, the multi-cluster scattering channel is actively reshaped into an approximate single-cluster channel, thereby significantly reducing the time delay and Doppler spread of the equivalent channel and releasing the performance potential of the OTFS system.

[0008] The objective of this invention can be achieved through the following technical solutions: According to one aspect of the present invention, a communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation is provided, the method comprising the following steps: Step S1: Based on the equivalent channel impulse response of the communication channel in the time-delay-Doppler domain, select the grid cells that need to undergo time-delay-Doppler alignment modulation processing, and obtain the number of cells to be aligned, as well as the time delay, Doppler frequency shift and channel response vector of the corresponding grid cells. Step S2: The transmitting end carries the data symbols to be transmitted in the time-delay-Doppler domain and performs orthogonal time-frequency conditioning to obtain the time domain signal; Step S3: The transmitter uses a delay and Doppler shift module that matches the number of cells to be aligned to introduce corresponding delay compensation and Doppler shift compensation for the symbol string to be transmitted on each branch. It also uses multiple antennas to perform beamforming design based on grid cells so that the signal can reach the receiver simultaneously without frequency shift after passing through multiple clustered scattering path channels. Step S4: The receiver performs orthogonal time-frequency space demodulation on the received signal and outputs a time-delay-Doppler domain symbol.

[0009] As a preferred technical solution, the communication channel in step S1 is a time-frequency dual-selection millimeter wave or terahertz channel, and the scattering paths in the channel are distributed in a cluster.

[0010] As a preferred technical solution, the specific steps in step S1 for selecting the grid cells that need to undergo time-delay Doppler alignment modulation processing are as follows: based on the equivalent channel impulse response, determine the channel response intensity of each grid cell in the time-delay-Doppler domain, and select grid cells with intensity exceeding a preset threshold as the cells that need to be aligned.

[0011] As a preferred technical solution, the channel response vectors on the grid cells to be aligned in step S1 are spatially weakly correlated and are dominated by different scattering clusters.

[0012] As a preferred technical solution, the delay compensation introduced for the symbol string on each branch in step S3 is equal to the maximum delay value among all grid cells to be aligned minus the delay value of the corresponding grid cell of that branch.

[0013] As a preferred technical solution, the Doppler frequency shift compensation amount introduced into the symbol string of each branch in step S3 is equal to the negative number of the Doppler frequency shift value of the corresponding grid cell of that branch.

[0014] As a preferred technical solution, the beamforming vector design in step S3 is based on the minimum mean square error criterion to maximize the signal-to-interference-plus-noise ratio at the receiver.

[0015] As a preferred technical solution, in step S3, the signal after time delay Doppler alignment modulation and beamforming design is propagated through the actual multi-cluster channel and arrives at the receiving end simultaneously. The receiving end receives the time delay aligned and Doppler frequency shift compensated multipath signal, whose time delay is equal to the maximum time delay among all grid cells to be aligned.

[0016] According to another aspect of the present invention, a communication system based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation is provided, comprising: The grid cell filtering module is used to filter out the grid cells that need to undergo time-delay Doppler alignment modulation processing based on the equivalent channel impulse response of the communication channel in the time-delay-Doppler domain, and obtain the number of cells to be aligned, as well as the time delay, Doppler frequency shift and channel response vector of the corresponding grid cells. The orthogonal time-frequency modulation module is used to carry the data symbols to be transmitted in the time-delay-Doppler domain and perform orthogonal time-frequency modulation to obtain the time domain signal; The delay-Doppler alignment modulation module is used to introduce corresponding delay compensation and Doppler frequency shift compensation for the symbol string to be transmitted on each branch using a delay and Doppler frequency shift module that is consistent with the number of units to be aligned. It also uses multiple antennas to perform beamforming design based on grid units so that the signal can reach the receiver simultaneously without frequency shift after passing through multiple clustered scattering path channels. The orthogonal time-frequency space demodulation module is used to perform orthogonal time-frequency space demodulation on the received signal and output delay-Doppler domain symbols.

[0017] As a preferred technical solution, the time-delay Doppler alignment modulation module includes multiple parallel processing branches, each branch being provided with a time-delay compensation module, a Doppler compensation module and a beamforming module in sequence; The delay compensation applied to the signal by the delay compensation module is equal to the maximum delay value in all critical grid cells minus the delay value of the corresponding grid cell of the branch. The Doppler frequency shift compensation amount applied to the signal by the Doppler compensation module is equal to the negative number of the Doppler frequency shift value of the corresponding grid cell of the branch. The beamforming vector of the beamforming module is designed based on the minimum mean square error criterion to maximize the signal-to-interference-plus-noise ratio at the receiver.

[0018] Compared with the prior art, the present invention has the following advantages: 1) This invention can use the introduced DDAM to perform timing and frequency deviation compensation at the transmitting end, thereby reshaping the channel characteristics; 2) This invention fully exploits the sparse characteristics of millimeter-wave / terahertz communication channels and the rich spatial dimensions brought by large-scale antenna arrays. By combining time-delay Doppler alignment modulation with OTFS, the characteristics of the channel are reshaped. Compared with traditional systems, it suppresses the interference problem between data symbols through signal processing with lower complexity. 3) This invention reduces the system's guard interval (CP) overhead by reducing channel delay spread. To avoid signal interference between different time slots and reduce the complexity of signal detection at the receiver, traditional OTFS systems typically require adding a guard interval between each time slot. The CP length must be greater than the channel delay spread. After DDAM processing, the channel delay spread is greatly reduced, thus saving CP overhead and improving the system's spectral efficiency performance. 4) This invention allows for more flexible selection of the number of time slots due to the reduction in channel Doppler spread. To avoid aliasing in the delay-Doppler domain of the OTFS system, the number of time slots in the OTFS is constrained by the channel Doppler spread. After DDAM processing, the channel Doppler spread is greatly reduced, thus allowing for the selection of a lower number of time slots, thereby reducing the system's PAPR. Attached Figure Description

[0019] Figure 1 A schematic diagram of the DDAM-OTFS communication system provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the DDAM-OTFS transmitter and receiver architecture provided in an embodiment of the present invention; Figure 3This is a schematic diagram of the time-delay-Doppler domain channel response before and after DDAM operation; Figure 4 A flowchart of the DDAM-OTFS communication method provided in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0021] Example 1 This invention provides a communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation. After acquiring channel state information, the transmitter selects key grid cells in the time-delay-Doppler domain, applies targeted time delay and Doppler frequency shift pre-compensation, and combines it with grid cell-based beamforming design. This enables all signals to achieve time-domain synchronization and Doppler domain alignment at the receiver after passing through actual multi-cluster channels. This actively reshapes the frequency-selective and time-selective channels into an approximately flat equivalent channel, significantly reducing the constraints of the OTFS system on guard interval and frame parameter design.

[0022] like Figure 4 As shown, the method includes the following main components (details of specific implementations are provided in the following detailed description and exemplary embodiments): Step S1: Based on the equivalent channel impulse response of the communication channel in the time-delay-Doppler domain, select the grid cells that need to be processed by DDAM, and obtain the number of cells that need to be aligned, as well as the time delay, Doppler frequency shift and channel response vector of the corresponding grid cells; Step S2: The transmitting end performs orthogonal time-frequency conditioning on the data symbols to be transmitted to obtain a time-domain signal; Step S3: The transmitter uses a delay and Doppler shift module that matches the number of packets to introduce corresponding delay and Doppler shift compensation for the signal of each processing branch (corresponding to one packet), and uses multiple antennas to perform beamforming design based on grid cells. Step S4: The receiver performs orthogonal time-frequency space demodulation on the received signal and outputs a time-delay-Doppler domain symbol.

[0023] in: Delay-Doppler aligned modulation exploits the sparsity of millimeter-wave terahertz communication channels and the rich spatial dimensions provided by large-scale antenna arrays. When the spatial design freedom of the transmitter is much greater than the number of grid cells required for alignment, grid cell-based compensation can be performed, enabling the signal to reach the receiver simultaneously and without frequency offset after passing through multiple clustered scattering path channels.

[0024] Based on the channel impulse response in the time-delay-Doppler domain, the transmitter first selects the trellis cells to be aligned. The time-delay-Doppler alignment adjustment method employs a time-delay module, a Doppler frequency shift module, and a beamforming module, matching the number of trellis cells to be aligned. The signal is carried in the time-delay-Doppler domain, and the conversion between the time domain and the time-delay-Doppler domain is completed through the OTFS modulation and demodulation module. The time-delay-Doppler alignment method processes the time-domain signal, outputting a superimposed signal after beamforming corresponding to the time-delay and Doppler frequency shift compensation signals of each path.

[0025] The screening process in step S1) can be carried out by combining the characteristics of the energy and spatial angle of the channel response on each grid cell in the time delay-Doppler domain, and a key grid cell dominated by different scattering clusters can be selected.

[0026] In step S2), the orthogonal time-frequency control can be implemented using methods such as inverse discrete Zak (IDZT) to convert the time-delay-Doppler domain data symbols into time-domain signals.

[0027] In step S3), time delay compensation for each branch can be achieved through time shifting. The time delay compensation value for each branch is equal to the maximum time delay value among all grid cells to be aligned, minus the time delay value of the corresponding grid cell for that branch. Doppler frequency shift compensation for each branch can be achieved by multiplying by a time-varying phase shift. The Doppler compensation value for each branch is equal to the negative of the Doppler frequency shift value of the corresponding grid cell for that branch. Based on this, the transmitter uses multiple antennas to design beamforming vectors for each processing branch. This design is based on the minimum mean square error (MMSE) criterion. By constructing and solving an optimization problem aimed at maximizing the signal-to-interference-plus-noise ratio (SINR) at the receiver, the optimal beamforming vector is obtained.

[0028] In step S4), the receiving end directly performs orthogonal time-frequency space demodulation on the received signal, such as through Discrete Zak Transform (DZT), to recover the data symbols in the time-delay-Doppler domain.

[0029] The orthogonal time-frequency space-time transmission method based on time-delay Doppler alignment modulation of the present invention will be described below through specific embodiments.

[0030] Figure 1 This is a schematic diagram illustrating a DDAM-OTFS-based communication system according to an exemplary embodiment. The system is equipped with... Root transmitting antenna ( The base station provides service to user equipment equipped with a single antenna. The wireless channel is... It consists of several dominant scattering clusters, each containing multiple rays with subtle differences, corresponding to different departure angles, time delays, and Doppler shifts. Therefore, the impulse response of the downlink linear time-varying channel... It can be represented as in, and Representing the first The th cluster Complex gain of the ray and corresponding departure angle The transmit array response vector. and These represent the time delay and Doppler frequency shift of the ray, respectively. The equivalent channel response in the time delay-Doppler domain. for here It is the impulse response of the pulse shaping filter. It is the Doppler leakage function. Signals propagating through this type of clustered channel are superimposed at the receiving end.

[0031] Figure 2 This is a schematic diagram of a DDAM-OTFS transmitter and receiver architecture according to an exemplary embodiment. The transmitter sends the signal to be transmitted... Data symbols Carried on a time-delay-Doppler domain grid, it is converted into a time-domain signal by an OTFS modulation module. Subsequently, Parallel input Each DDAM processing branch performs time delay compensation on the signal sequentially. Doppler frequency shift compensation and beamforming After the signals from all branches are combined, the final transmitted signal is formed. The receiving end receives the signal Direct OTFS demodulation, i.e., DZT transform, can output the delay-Doppler domain symbol. .

[0032] The specific implementation steps can be summarized as follows: (1) Based on the equivalent channel impulse response of the communication channel in the time-delay-Doppler domain, select the grid cells that need to be processed by DDAM: The base station selects the grid cells that need to be processed by DDAM based on the known equivalent channel impulse response in the time-delay-Doppler domain. The mesh cells that need to undergo DDAM processing are selected. The specific process is as follows: a) Calculate the grid cell in each time-delay-Doppler domain. Channel response energy at the location .

[0033] b) Set energy threshold ,in This is a preset coefficient. It filters out items with energy greater than or equal to... The grid cells constitute the candidate set. .

[0034] c) In the set In this process, the units whose channel energy is the maximum value in their four neighborhoods are further selected, forming a set of locally strongest units. .

[0035] d) For sets The cells in the array are used to calculate the channel response vectors between each pair of cells. and The spatial correlation coefficient is Set space-related thresholds .like Then the grid cell is considered to be and Those dominated by the same scattering cluster are grouped together. This operation transforms the set... Divided into A group of non-overlapping groups Calculate the grid cell in each time-delay-Doppler domain. Channel response energy at the location For the first Group The unit with the largest channel response energy is selected as the representative unit of the group, and its index is denoted as . ,satisfy Finally obtained A representative grid cell to be aligned and its equivalent channel.

[0036] (2) Determine the pre-compensation parameters and design beamforming vector: a) Calculate the pre-compensation amount: Calculate the maximum time delay index among all mesh cells to be aligned. For the first Each processing branch is configured with a delay compensation amount. Doppler frequency shift compensation .

[0037] b) Beamforming Vector Design: The beamforming vector is designed based on the minimum mean square error (MMSE) criterion to maximize the signal-to-interference-plus-noise ratio (SINR) at the receiver. Define the first... The equivalent channel vector of each branch after phase adjustment is: Aggregate all The channel vectors of each branch constitute The corresponding beamforming vector to be determined is... .and relative alignment point offset The concatenated vectors of all equivalent channels are given. Considering the main residual interference, the interference-noise covariance matrix is ​​constructed. ,in This refers to noise power. (In the total transmit power) Under constraints, the optimal MMSE beamforming vector is From this, the beamforming vectors of each branch can be analyzed. .

[0038] (3) The base station transmits signals for communication: the transmitter performs OTFS modulation on the data symbols to obtain the time domain signal. for Subsequently, the parameters determined in step (2) are used. The final transmit signal is generated by performing DDAM processing. (4) User end receives communication signal: The receiving end receives the signal Then, OTFS demodulation is performed directly to obtain the received symbols in the time-delay-Doppler domain. for The input-output relationship of the system can be characterized as in It is noise.

[0039] like Figure 3 As shown, because DDAM preprocessing effectively compresses the delay spread and Doppler spread of the equivalent channel, it can reshape a multi-cluster channel into a single-cluster channel. Therefore, the DDAM-OTFS transmission technology and system proposed in this invention can effectively compress the delay spread and Doppler spread of the channel, reshape the channel characteristics, greatly expand the feasible domain of OTFS parameter design, and improve communication performance.

[0040] Example 2 This invention also provides a communication system based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation, comprising: The grid cell filtering module is used to filter out the grid cells that need to undergo time-delay Doppler alignment modulation processing based on the equivalent channel impulse response of the communication channel in the time-delay-Doppler domain, and obtain the number of cells to be aligned, as well as the time delay, Doppler frequency shift and channel response vector of the corresponding grid cells. The orthogonal time-frequency modulation module is used to carry the data symbols to be transmitted in the time-delay-Doppler domain and perform orthogonal time-frequency modulation to obtain the time domain signal; The delay-Doppler alignment modulation module is used to introduce corresponding delay compensation and Doppler frequency shift compensation for the symbol string to be transmitted on each branch using a delay and Doppler frequency shift module that is consistent with the number of units to be aligned. It also uses multiple antennas to perform beamforming design based on grid units so that the signal can reach the receiver simultaneously without frequency shift after passing through multiple clustered scattering path channels. The orthogonal time-frequency space demodulation module is used to perform orthogonal time-frequency space demodulation on the received signal and output delay-Doppler domain symbols.

[0041] The time-delay Doppler alignment modulation module includes multiple parallel processing branches, each of which is sequentially equipped with a time-delay compensation module, a Doppler compensation module, and a beamforming module. The delay compensation applied to the signal by the delay compensation module is equal to the maximum delay value in all critical grid cells minus the delay value of the corresponding grid cell of the branch. The Doppler frequency shift compensation amount applied to the signal by the Doppler compensation module is equal to the negative number of the Doppler frequency shift value of the corresponding grid cell of the branch. The beamforming vector of the beamforming module is designed based on the minimum mean square error criterion to maximize the signal-to-interference-plus-noise ratio at the receiver.

[0042] This invention applies OTFS modulation to the symbols to be transmitted at the transmitter and introduces corresponding time delay and Doppler shift compensation to the resulting symbol string, enabling the signal to reach the receiver simultaneously and without Doppler shift after passing through a multi-cluster scattering path channel, thereby significantly reducing inter-symbol interference and inter-carrier interference in broadband transmission. The transmitter utilizes multiple antennas and performs beamforming design based on grid cells. Through time delay Doppler alignment modulation, the multi-scattering cluster channel can be reshaped into a single-cluster channel, greatly reducing the time delay spread and Doppler spread of the equivalent channel. This invention actively suppresses the time delay spread and Doppler spread of the channel through time delay Doppler alignment modulation and grid cell-based beamforming, thereby releasing the performance potential of the OTFS system and improving communication performance in high-speed mobile scenarios.

[0043] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation, characterized in that, The method includes the following steps: Step S1: Based on the equivalent channel impulse response of the communication channel in the time-delay-Doppler domain, select the grid cells that need to undergo time-delay-Doppler alignment modulation processing, and obtain the number of cells to be aligned, as well as the time delay, Doppler frequency shift and channel response vector of the corresponding grid cells. Step S2: The transmitting end carries the data symbols to be transmitted in the time-delay-Doppler domain and performs orthogonal time-frequency conditioning to obtain the time domain signal; Step S3: The transmitter uses a delay and Doppler shift module that matches the number of cells to be aligned to introduce corresponding delay compensation and Doppler shift compensation for the symbol string to be transmitted on each branch. It also uses multiple antennas to perform beamforming design based on grid cells so that the signal can reach the receiver simultaneously without frequency shift after passing through multiple clustered scattering path channels. Step S4: The receiver performs orthogonal time-frequency space demodulation on the received signal and outputs a time-delay-Doppler domain symbol.

2. The communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation according to claim 1, characterized in that, The communication channel in step S1 is a time-frequency dual-selection millimeter wave or terahertz channel, and the scattering paths in the channel are clustered.

3. The communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation according to claim 1, characterized in that, The specific steps in step S1 for selecting the grid cells that need to undergo time-delay Doppler alignment modulation processing are as follows: based on the equivalent channel impulse response, determine the channel response strength of each grid cell in the time-delay-Doppler domain, and select grid cells with strengths exceeding a preset threshold as the cells that need to be aligned.

4. The communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation according to claim 1, characterized in that, In step S1, the channel response vectors on the grid cells to be aligned are spatially weakly correlated and are dominated by different scattering clusters.

5. The communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation according to claim 1, characterized in that, The delay compensation introduced for the symbol string on each branch in step S3 is equal to the maximum delay value among all grid cells to be aligned minus the delay value of the corresponding grid cell of that branch.

6. The communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation according to claim 1, characterized in that, The Doppler frequency shift compensation introduced into the symbol string of each branch in step S3 is equal to the negative of the Doppler frequency shift value of the corresponding grid cell of that branch.

7. The communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation according to claim 1, characterized in that, The beamforming vector design in step S3 is based on the minimum mean square error criterion to maximize the signal-to-interference-plus-noise ratio at the receiver.

8. The communication method based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation according to claim 1, characterized in that, In step S3, the signal after time delay Doppler alignment modulation and beamforming design is propagated through the actual multi-cluster channel and arrives at the receiving end simultaneously. The receiving end receives the time delay aligned and Doppler frequency shift compensated multipath signal, whose time delay is equal to the maximum time delay among all grid cells to be aligned.

9. A communication system based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation, characterized in that, include: The grid cell filtering module is used to filter out the grid cells that need to undergo time-delay Doppler alignment modulation processing based on the equivalent channel impulse response of the communication channel in the time-delay-Doppler domain, and obtain the number of cells to be aligned, as well as the time delay, Doppler frequency shift and channel response vector of the corresponding grid cells. The orthogonal time-frequency modulation module is used to carry the data symbols to be transmitted in the time-delay-Doppler domain and perform orthogonal time-frequency modulation to obtain the time domain signal; The delay-Doppler alignment modulation module is used to introduce corresponding delay compensation and Doppler frequency shift compensation for the symbol string to be transmitted on each branch using a delay and Doppler frequency shift module that is consistent with the number of units to be aligned. It also uses multiple antennas to perform beamforming design based on grid units so that the signal can reach the receiver simultaneously without frequency shift after passing through multiple clustered scattering path channels. The orthogonal time-frequency space demodulation module is used to perform orthogonal time-frequency space demodulation on the received signal and output delay-Doppler domain symbols.

10. The communication system based on time-delay Doppler alignment modulation and orthogonal time-frequency modulation according to claim 9, characterized in that, The time-delay Doppler alignment modulation module includes multiple parallel processing branches, each of which is sequentially equipped with a time-delay compensation module, a Doppler compensation module, and a beamforming module. The delay compensation applied to the signal by the delay compensation module is equal to the maximum delay value in all critical grid cells minus the delay value of the corresponding grid cell of the branch. The Doppler frequency shift compensation amount applied to the signal by the Doppler compensation module is equal to the negative number of the Doppler frequency shift value of the corresponding grid cell of the branch. The beamforming vector of the beamforming module is designed based on the minimum mean square error criterion to maximize the signal-to-interference-plus-noise ratio at the receiver.

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