Communication waveform adjustment method and system based on OTFS

Abstract

The invention relates to the technical field of communication, and particularly discloses an OTFS-based communication waveform adjustment method and system, and the method comprises the steps: defining a to-be-transmitted time delay Doppler domain signal; establishing a channel response function under satellite communication by using satellite-ground statistical channel information; according to the channel response function and the Doppler domain signal, determining the signal-to-noise ratio of the terminal time delay Doppler domain; and solving the optimal weight and the optimal rate of the terminal according to the signal-to-noise ratio and a preset signal constraint condition. Limited spectrum resources can be fully utilized, and the communication rate of a multi-user communication system is improved.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and particularly to a communication waveform adjustment method and system based on OTFS. Background Art

[0002] With the continuous improvement of satellite users' requirements for the quality of communication services, and due to the problem of tight bandwidth resources caused by the large-scale access of users, how to effectively improve the spectral efficiency of satellite communication systems under limited frequency resources has become one of the key problems to be solved urgently at present.

[0003] Orthogonal Time Frequency Space (OTFS) is a new modulation method proposed in recent years. Different from OFDM that transmits information in the frequency domain, OTFS transmits information in the delay-Doppler domain. The advantages of OTFS include, but are not limited to, being able to adapt to high-speed mobile environments and being able to estimate channels with less overhead. Orthogonal Time Frequency Space OTFS provides the possibility of solving the problem of effectively improving the spectral efficiency of satellite communication systems. Summary of the Invention

[0004] In view of the above problems, the purpose of the present invention is to provide a communication waveform adjustment method and system based on OTFS, which can make full use of limited spectral resources and improve the communication rate of multi-user communication systems.

[0005] A communication waveform adjustment method based on OTFS provided by the present invention includes: Defining a delay-Doppler domain signal to be transmitted; Establishing a channel response function for satellite communication by using satellite-ground statistical channel information; Determining the signal-to-noise ratio of the terminal in the delay-Doppler domain according to the channel response function and the Doppler domain signal; Solving the optimal weight and optimal rate of the terminal according to the signal-to-noise ratio and a preset signal constraint condition.

[0006] In a possible implementation manner, the defining a delay-Doppler domain signal to be transmitted includes: Defining a delay-Doppler domain signal to be transmitted according to the following formula: ; ; Wherein, is the delay-Doppler domain signal, is the delay-Doppler domain range, is the delay index, is the Doppler index, is the minimum resolution unit interval in the Doppler domain, is a D-dimensional time-delay Doppler domain plane, is the number of time-domain subcarriers, is the number of samples of the time-domain signal, is the signal sampling time interval.

[0007] In a possible implementation, the establishing of the channel response function for satellite communication by using the satellite-ground statistical channel information includes: Establish the channel response function according to the following formula : ; where, is the channel attenuation of the th path between the satellite and the ground, is the time delay of the th path, is the Doppler frequency shift of the th path, is the total number of paths, is the path index, is the Dirichlet function, is the starting reference time-delay parameter variable, is the starting reference frequency-shift parameter variable.

[0008] In a possible implementation, the establishing of the channel response function for satellite communication by using the satellite-ground statistical channel information further includes: Convert the channel response function to the time-delay Doppler domain, and the formula is as follows: ; where, is the channel response function, is the channel attenuation of the th path between the satellite and the ground, is the time delay of the th path, is the Doppler frequency shift of the th path, is the number of paths from the satellite to the terminal, is the path number index, is the transformation matrix of the th path channel, indicates that the channel dimension is dimensions.

[0009] In a possible implementation, the establishing of the channel response function for satellite communication by using the satellite-ground statistical channel information further includes: Determine according to the following formula: ; Among them, represents conjugate transpose, is the number of paths from the satellite to the terminal, is the point Fourier transform matrix, is the identity matrix of dimension is the th channel conversion matrix of the th path of the th terminal, is the cyclic matrix when the time delay of the th path of the th terminal is th, is the diagonal matrix when the frequency shift of the th path of the th terminal is is the integer Doppler frequency shift index number, is the fractional Doppler index number, is the path number index.

[0010] In a possible implementation, determining the signal-to-noise ratio in the time-delay Doppler domain of the terminal according to the channel response function and the Doppler domain signal includes: Vectorize the time-delay Doppler domain signal to be transmitted from the satellite to the terminal as follows: ; Among them, is the time-delay Doppler domain signal of the th terminal, is the time-delay Doppler domain plane of dimension is the transmitted signal of the th terminal, is a vector of dimension and is the vectorized representation.

[0011] In a possible implementation, determining the signal-to-noise ratio in the time-delay Doppler domain of the terminal according to the channel response function and the Doppler domain signal further includes: Obtain the received signal of the terminal according to the following formula: ; Among them, is the time-delay Doppler domain normalized noise, is the ​The received signal of the terminal is the transmitted signal of the th terminal, is the transmission channel matrix of the th terminal signal, is the weight factor of the terminal and

[0012] is the terminal number. In a possible implementation, determining the signal-to-noise ratio of the terminal in the time-delay Doppler domain according to the channel response function and the Doppler-domain signal further includes: obtaining the signal-to-interference-plus-noise ratio according to the following formula ; wherein, is the total number of terminals, is the terminal index, is the target terminal index, represents the trace function, is the channel strength of the terminal plus the waveform shaping matrix, is the sum of the channel strengths of all other terminals except the terminal plus the waveform shaping matrix, is the th noise existing in the transmission of the terminal.

[0013] In a possible implementation, solving for the optimal weighting and optimal rate of the terminal according to the signal-to-noise ratio and the preset signal constraint conditions includes: obtaining the objective function according to the following formula : ; wherein, is the total shaping matrix, is the total number of terminals, is the terminal index, is the target terminal index, is the weight coefficient of the terminal and and are auxiliary variables, is the trace function, is the channel strength of the terminal plus the waveform shaping matrix, is the sum of the channel strengths of all other terminals except the terminal plus the waveform shaping matrix, represents a constant, is the th noise existing in the transmission of the terminal, is the waveform shaping matrix of the th terminal, is the conjugate transpose form of the waveform shaping matrix of the th terminal, indicates that the matrix is positive semi - definite represents the shaping power limit, is a constant real number, is the transmission channel matrix of the th terminal signal, is the conjugate transpose form of the transmission channel matrix of the th terminal.

[0014] The present invention also provides a communication waveform adjustment system based on OTFS for implementing any of the above - mentioned communication waveform adjustment methods, including: A signal definition module for defining the time - delay Doppler domain signal to be transmitted; A channel response function establishment module for establishing a channel response function in satellite communication by using satellite - ground statistical channel information; A signal - to - noise ratio determination module for determining the signal - to - noise ratio in the time - delay Doppler domain of the terminal according to the channel response function and the Doppler domain signal; A solution module for solving the optimal weight and optimal rate of the terminal according to the signal - to - noise ratio and the preset signal constraint conditions.

[0015] The communication waveform adjustment method and system based on OTFS provided by the present invention are applied to the satellite - ground communication scenario, have good adaptability to large Doppler frequency offsets in high - mobility satellite - ground communication scenarios, can make full use of limited spectrum resources, and improve the communication rate of multi - user communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic flow chart of the communication waveform adjustment method based on OTFS provided by an embodiment of the present invention; Figure 2 is a schematic diagram of OTFS signal processing provided by an embodiment of the present invention; Figure 3 is a communication schematic diagram provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The following further describes in detail the embodiments of the present invention in conjunction with the drawings and embodiments. The detailed description and drawings of the following embodiments are used to exemplarily illustrate the principle of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the described preferred embodiments, and the scope of the present invention is defined by the claims.

[0018] In the description of the present invention, it should be noted that unless otherwise specified, "a plurality of" means two or more; the terms "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance; for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0019] Figure 1 The flowchart of the communication waveform adjustment method based on OTFS provided for the embodiments of the present invention is as Figure 1 shown. A communication waveform adjustment method based on OTFS provided by the present invention includes: Step S1, defining the time-delay Doppler domain signal to be transmitted; In a possible implementation, a low-earth orbit satellite is defined, with an orbital altitude of , and a set of ground terminal users .

[0020] The time-delay Doppler domain signal to be transmitted is defined according to the following formula: ; ; where is the time-delay Doppler domain signal, is the time-delay Doppler domain range, is the time-delay index, is the Doppler index, is the minimum resolution unit interval in the Doppler domain, , is a two-dimensional time-delay Doppler domain plane, is the number of subcarriers in the time domain, is the number of samples of the time-domain signal, is the signal sampling time interval, is the duration of one frame of OTFS data frame, is the signal bandwidth.

[0021] Step S2, establishing a channel response function in satellite communication by using the satellite-ground statistical channel information; The satellite-ground statistical channel information generally includes channel fading coefficients, multipath time delays, Doppler frequency shifts, and typical ones include the TDL model, etc.

[0022] In a possible implementation, the channel response function is established according to the following formula : ; where is the channel attenuation of the th path between the satellite and the ground, is the time delay of the th path, is the Doppler shift of the th path, is the path index, is the Dirichlet function, is the starting reference time delay parameter variable, is the starting reference frequency shift parameter variable.

[0023] During the actual transmission process, the defined time delay Doppler domain signal , through the inverse symplectic Fourier transform ISFFT, converts the time delay Doppler signal to the time-frequency domain, and through the Wigner transform, converts it to the time domain signal and then transmits it. After being transmitted through a channel with time delay and Doppler shift characteristics, at the receiving end, the received time domain signal is converted to the time-frequency domain through the Wigner transform and then to the time delay Doppler domain through the symplectic Fourier transform SFFT to obtain the received time delay Doppler signal . The principle of the OTFS signal processing flow is as shown in Figure 2 .

[0024] Convert the channel response function to the time delay Doppler domain, and the formula is as follows: ; where is the channel response function, is the channel attenuation of the th path between the satellite and the ground, is the time delay of the th path, is the Doppler shift of the th path, is the number of paths from the satellite to the terminal, is the path number index, is the th path channel transformation matrix, indicates that the channel dimension is dimensions.

[0025] In a possible implementation, establishing the channel response function in satellite communication using satellite-ground statistical channel information further includes: Determine according to the following formula: ; where represents the conjugate transpose, is the number of paths from the satellite to the terminal, is point Fourier transform matrix, is The identity matrix of dimension is the th path channel transfer matrix of the th terminal, is the circulant matrix when the delay of the th path of the th terminal is , is the diagonal matrix when the frequency shift of the th path of the th terminal is , is the integer Doppler frequency shift index number, is the fractional Doppler index number, is the number of the terminal, is the path number index.

[0026] ; Among them, is the diagonal matrix function, is to the th power, is the circulant matrix function, is the inverse Fourier transform unit, is the imaginary unit.

[0027] Step S3: Determine the signal-to-noise ratio in the delay-Doppler domain of the terminal according to the channel response function and the Doppler-domain signal; In a possible implementation, vectorize the delay-Doppler domain signal to be transmitted from the satellite to user q, and the formula is as follows: ; Among them, is the delay-Doppler domain signal of the th terminal, is the -dimensional delay-Doppler domain plane, is the transmitted signal of the th terminal, is a vector with a dimension of , is the vectorized representation.

[0028] Define the delay-Doppler domain beamforming vector .

[0029] Assume that one beam only serves one ground user and adopts a one-to-one mode. Then the delay-Doppler domain signal actually transmitted from the satellite to terminal is , .

[0030] The received signal of the terminal is obtained according to the following formula: ; ; where is the normalized noise in the time-delay Doppler domain, , is the received signal of the -th terminal, is the transmitted signal of the -th terminal, is the transmission channel matrix of the -th terminal signal, is the weight factor of the terminal , is the number of the terminal.

[0031] The signal-to-interference-plus-noise ratio is obtained according to the following formula: : ; where is the total number of terminals, is the terminal index, is the target terminal index, represents the trace function, is the channel strength of the terminal plus the waveform shaping matrix, is the sum of the channel strengths of all other terminals except the terminal plus the waveform shaping matrix, is the noise existing in the transmission of the -th terminal.

[0032] Step S4, solve the optimal weight and optimal rate of the terminal according to the signal-to-noise ratio and the preset signal constraint conditions.

[0033] In a possible implementation, by setting the objective function to maximize the weighted sum rate, solve the optimal beamforming vector: ; where is the weight factor of user .

[0034] First, perform a Lagrangian dual transformation on the objective function to transform the fraction inside the log function: ; Then, the objective function is still in a non-convex form. Using the quadratic transformation method, introduce an auxiliary variable to process the third term of the objective function: ; ; Update the objective function: ; Finally, observe the three variables and constraints in the objective function. By successively fixing and 、 and , for 、 take the derivative to calculate the optimal solution of the process: ; Obtain the objective function according to the following formula : ; Among them, is the total shaping matrix, is the total number of terminals, is the terminal index, is the target terminal index, is the weight coefficient of terminal , and are auxiliary variables, is the trace function, is the channel strength of terminal plus the waveform shaping matrix, is the sum of the channel strengths of all terminals except terminal plus the waveform shaping matrix, represents a constant, is the noise existing in the transmission of the th terminal, is the waveform shaping matrix of the th terminal, is the conjugate transpose form of the waveform shaping matrix of the th terminal, represents matrix positive semi-definite represents the shaping power limit, is a constant real number, is the transmission channel matrix of the signal of the th terminal, is the conjugate transpose form of the transmission channel matrix of the th terminal.

[0035] By setting the iterative optimization conditions and the convergence threshold of the objective function, solve the optimal weighted sum and optimal rate of the terminals.

[0036] The present invention also provides a communication waveform adjustment system based on OTFS for implementing the above communication waveform adjustment method, including: A signal definition module, configured to define the time-delay Doppler domain signal to be transmitted; A channel response function establishment module, configured to establish a channel response function for satellite communication by using the satellite-ground statistical channel information; A signal-to-noise ratio determination module, configured to determine the signal-to-noise ratio of the terminal time-delay Doppler domain according to the channel response function and the Doppler domain signal; A solution module, configured to solve the optimal weight and optimal rate of the terminal according to the signal-to-noise ratio and the preset signal constraint conditions.

[0037] The communication waveform adjustment method and system based on OTFS provided by the present invention consider the downlink transmission performance of multi-beam satellite-to-ground communication. Taking the beamforming vector of the satellite transmitting end as the optimization variable, under the constraint of the total satellite transmission power, through means such as Lagrangian dual decomposition and quadratic transformation, the optimization problem of maximizing the user weighted sum rate is solved, so as to achieve the purpose of making full use of satellite resources and maximizing the system weighted sum rate, and improving the performance of the satellite-to-ground communication system.

[0038] The above are only the specific implementation manners of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A communication waveform adjustment method based on OTFS, characterized in that: include: defining a delay-Doppler domain signal to be transmitted; The channel response function of satellite communication is established by using satellite-to-ground statistical channel information; Determining a signal-to-noise ratio in a delay-Doppler domain of a terminal according to the channel response function and the Doppler domain signal; The optimal weight and the optimal rate of the terminal are solved according to the signal-to-noise ratio and the preset signal constraint condition.

2. The communication waveform adjustment method according to claim 1, characterized in that: The definition of the delay-Doppler domain signal to be transmitted includes: The delay-Doppler domain signal to be transmitted is defined according to the following formula: ； ； in, is the delay Doppler domain signal, is the delay-Doppler domain range, is the delay index, is the Doppler index, is the minimum resolution unit interval in the Doppler domain, for dimensional delay-Doppler domain plane, is the number of subcarriers in the time domain, is the number of time domain signal samples, is the signal sampling time interval.

3. The communication waveform adjustment method according to claim 1, characterized in that: The channel response function for satellite communication established by using satellite-to-ground statistical channel information includes: The channel response function is established according to the following formula : ； in, For the Star-Earth The channel attenuation of the path, For the The delay of the path, For the The Doppler shift of the path, is the total number of paths, is the path index, is the Dirichlet function, is the starting reference delay parameter variable, is the starting reference frequency shift parameter variable.

4. The communication waveform adjustment method according to claim 3, characterized in that: The channel response function for establishing satellite communication using satellite-to-ground statistical channel information also includes: The channel response function is converted to the delay-Doppler domain, and the formula is as follows: ； in, is the channel response function, For the Star-Earth The channel attenuation of the path, For the The delay of the path, For the The Doppler shift of the path, is the number of paths from the satellite to the terminal, is the path number index, For the The transformation matrix of the path channel, The channel dimension is dimension.

5. The communication waveform adjustment method according to claim 4, characterized in that: The channel response function for establishing satellite communication using satellite-to-ground statistical channel information also includes: Determine according to the following formula : ； in, represents the conjugate transpose, is the number of paths from the satellite to the terminal, for The point Fourier transform matrix, yes dimensional identity matrix, For the The terminal Path channel conversion matrix, For the The terminal The delay of the path is The circulant matrix when For the The terminal The frequency shift of the path is The diagonal matrix when is the integer Doppler shift index number, is the fractional Doppler index number, is the terminal number, The index of the number of paths.

6. The communication waveform adjustment method according to claim 1, characterized in that: The determining, according to the channel response function and the Doppler domain signal, a signal-to-noise ratio of a terminal delay-Doppler domain comprises: Send the satellite to the terminal The delay-Doppler domain signal is vectorized and the formula is as follows: ； in, For the The delay-Doppler domain signal of each terminal is for dimensional delay-Doppler domain plane, For the The transmitted signal of a terminal, The dimension is The vector of is a vectorized representation.

7. The communication waveform adjustment method according to claim 6, characterized in that: The determining, according to the channel response function and the Doppler domain signal, a signal-to-noise ratio of a terminal delay-Doppler domain further comprises: The terminal is obtained according to the following formula The received signal: ； in, is the delay-Doppler domain normalized noise, For the The received signal of each terminal is For the The transmitted signal of a terminal, For the The transmission channel matrix of the terminal signal is For Terminal The weight factor of The terminal number.

8. The communication waveform adjustment method according to claim 7, characterized in that: The determining, according to the channel response function and the Doppler domain signal, a signal-to-noise ratio of a terminal delay-Doppler domain further comprises: The signal-to-interference-noise ratio is obtained according to the following formula : ； in, is the total number of terminals, is the terminal index, is the target terminal index, represents the trace function, Terminal for adding waveform shaping matrix The channel strength, In addition to the terminal for adding waveform shaping matrix The sum of the channel strengths of all other terminals except For the The noise present in each terminal transmission.

9. The communication waveform adjustment method according to claim 1, characterized in that: The solving the optimal weight and the optimal rate of the terminal according to the signal-to-noise ratio and the preset signal constraint condition comprises: The objective function is obtained according to the following formula : ； is the total shaping matrix, is the total number of terminals, is the terminal index, is the target terminal index, For Terminal The weight coefficient of and is an auxiliary variable, is the trace function, Terminal for adding waveform shaping matrix The channel strength, In addition to the terminal for adding waveform shaping matrix The sum of the channel strengths of all other terminals except represents a constant, For the The noise present in each terminal transmission For the The waveform shaping matrix of each terminal, For the The conjugate transposed form of the waveform shaping matrix of the terminal, Denotes a matrix that is positive semidefinite Indicates shaping power limit, is a constant real number, For the The transmission channel matrix of the terminal signal is For the The conjugate transposed form of the transmission channel matrix of the terminal.

10. A communication waveform adjustment system based on OTFS, used to implement the communication waveform adjustment method according to any one of claims 1 to 9, characterized in that: include: A signal definition module, used to define a delay-Doppler domain signal to be transmitted; A channel response function establishment module is used to establish a channel response function under satellite communication by using satellite-to-ground statistical channel information; A signal-to-noise ratio determination module, configured to determine a signal-to-noise ratio in a delay-Doppler domain of a terminal according to the channel response function and the Doppler domain signal; A solution module is used to solve the optimal weight and optimal rate of the terminal according to the signal-to-noise ratio and preset signal constraints.

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