An uplink multiple access transmission method for a multi-user orthogonal time-frequency-space system

Abstract

An uplink multiple access transmission method for a multi-user orthogonal time-frequency-space system includes: mapping a user's transmission signal into an orthogonal amplitude modulation symbol, multiplexing information symbols along the entire delay axis with corresponding Doppler indexes for different users, obtaining an indicator matrix of Doppler division multiple access, and obtaining a time domain transmission signal; processing the time domain received signal, and combining the indicator matrix of Doppler division multiple access to obtain a received signal of the DD domain of DoDMA based on OTFS modulation; applying a serial interference elimination method to the received signal of the DD domain of DoDMA based on OTFS modulation at the base station, judging the signal of each user one by one according to the size of the signal power, and then obtaining the achievable rate of each user by the mutual information theorem and the properties of the trace operation, and performing uplink multiple access transmission based on the achievable rate of each user. The present invention can solve the influence of high Doppler frequency shift and interference between multiple users caused by rapid movement, and improve the transmission rate and bit error rate performance.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to an uplink multiple access transmission method for a multi-user orthogonal time-frequency-space system. Background Art

[0002] With the rapid development of wireless communications, communication scenarios have become more diverse, such as high-speed rail, drones, and vehicle networking in high-mobility scenarios. Traditional orthogonal frequency division multiplexing (OFDM) technology can overcome the inter-symbol interference caused by time dispersion, but the relative motion between the transmitter and the receiver will cause serious inter-subcarrier interference, which greatly reduces the system transmission performance and cannot meet the needs of efficient and reliable wireless communication services in high-mobility scenarios.

[0003] In order to solve the inter-subcarrier interference caused by Doppler frequency shift in OFDM technology, Orthogonal Time-Frequency-Space (OTFS) modulation technology has shown its potential in handling high Doppler frequency shift in the field of 6G wireless communications. OTFS performs modulation in the Delay-Doppler (DD) domain, converting the time-varying channel in the time-frequency domain into the time-invariant channel in the DD domain, and obtaining the full channel diversity gain in time and frequency, so that OTFS modulation technology can resist the influence of high Doppler frequency shift caused by the high mobility of users, and solve the problem of OFDM technology's performance degradation in communication systems under high mobility.

[0004] However, when the delay and Doppler spread are high, the signal transmitted on the delay-Doppler resource block may propagate to the adjacent resource blocks, and as the number of users continues to increase, the transmission efficiency of the traditional multiple access transmission scheme decreases and multi-user interference occurs. Therefore, studying the uplink multiple access transmission method of the multi-user OTFS system in a high mobility scenario is of great significance to the multi-user wireless communication needs. Summary of the invention

[0005] The object of the present invention is to provide an uplink multiple access transmission method for a multi-user orthogonal time-frequency-space system to solve the influence of high Doppler frequency shift and interference between multiple users caused by rapid movement, thereby achieving better achievable rate and bit error rate performance.

[0006] An uplink multiple access transmission method for a multi-user orthogonal time-frequency-space system comprises the following steps:

[0007] Step S1, multiple users perform wireless communication with a base station, obtain a transmission signal of each user, map the transmission signal into an orthogonal amplitude modulation symbol, multiplex information symbols along the entire delay axis with corresponding Doppler indexes for different users, and obtain an indicator matrix of Doppler division multiple access. In addition, the transmission signal is converted from the delay-Doppler domain to the time-frequency domain by an inverse symplectic finite Fourier transform, and then the transmission signal is converted from the time-frequency domain to a time-domain transmission signal by a Heisenberg transform;

[0008] Step S2, after the time domain transmission signal is transmitted through the channel, a time domain reception signal is obtained, and then a Wigner transform is performed on the time domain reception signal to obtain a time-frequency domain signal of the user, and finally the time-frequency domain signal is separated and symplectic finite Fourier transform is performed on the time-frequency domain signal, and combined with the indicator matrix of Doppler division multiple access, a delay-Doppler domain reception signal of Doppler division multiple access based on orthogonal time-frequency space modulation is obtained;

[0009] Step S3, at the base station, a serial interference elimination method is applied to the delay-Doppler domain received signal of Doppler division multiple access based on orthogonal time-frequency space modulation, and the delay-Doppler domain received signal of Doppler division multiple access based on orthogonal time-frequency space modulation of each user is judged one by one according to the size of the signal power to eliminate interference between users, and then the achievable rate of each user is obtained by the mutual information theorem and the properties of the trace operation, and uplink multiple access transmission is performed based on the achievable rate of each user.

[0010] According to the uplink multiple access transmission method of the multi-user orthogonal time-frequency space system provided by the present invention, in a high mobility scenario, a Doppler division multiple access (DoDMA) technology based on OTFS modulation is adopted, and different users multiplex information symbols along the entire delay axis through corresponding Doppler indexes, so that resource allocation can be better performed, and a received signal of the DD domain of DoDMA based on OTFS modulation is obtained by separating and performing symplectic finite Fourier transform on the time-frequency domain signals and combining with the indicator matrix of Doppler division multiple access, and then a serial multiplication is applied to the received signal of the DD domain of DoDMA based on OTFS modulation at the base station. The interference elimination method judges the received signals in the delay-Doppler domain of Doppler division multiple access based on orthogonal time-frequency space modulation of each user one by one according to the size of the signal power to eliminate the interference between users, and then obtains the achievable rate of each user by the mutual information theorem and the properties of trace operation. Uplink multiple access transmission is performed based on the achievable rate of each user, which can effectively solve the influence of high Doppler frequency shift and interference between multiple users caused by rapid movement, achieve higher transmission rate, and significantly improve the bit error rate performance, showing better communication reliability, and meet the wireless communication service needs of uplink transmission in high mobility scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a flow chart of the uplink multiple access transmission method of the multi-user orthogonal time-frequency space system of the present invention. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] See also Figure 1 The uplink multiple access transmission method of the multi-user orthogonal time-frequency-space system provided by the embodiment of the present invention comprises steps S1 to S3:

[0014] Step S1, multiple users conduct wireless communication with the base station, obtain the transmission signal of each user, map the transmission signal into an orthogonal amplitude modulation symbol, multiplex information symbols along the entire delay axis with corresponding Doppler indexes for different users, and obtain an indicator matrix of Doppler division multiple access. In addition, the transmission signal is converted from the delay-Doppler domain to the time-frequency domain through an inverse symplectic finite Fourier transform, and then the transmission signal is converted from the time-frequency domain to a time-domain transmission signal through a Heisenberg transform.

[0015] Wherein, step S1 specifically includes:

[0016] Set the total number of users to K u , the number of subcarriers and time slots in the OTFS frame are M and N The horizontal axis of the delay-Doppler domain grid is defined as the Doppler axis, and the vertical axis of the delay-Doppler domain grid is defined as the delay axis. The horizontal and vertical axes are divided into unit Doppler frequency shifts. and unit delay Grid;

[0017] Obtaining the bit stream of the transmitted signal of each user, mapping the bit stream of the transmitted signal into orthogonal amplitude modulation symbols, then converting the orthogonal amplitude modulation symbols into a symbol sequence, and then placing the symbol sequence on a delay-Doppler domain grid;

[0018] K u The user multiplexes information symbols along the entire delay axis with different Doppler indices, defining k The indicator matrix of Doppler division multiple access for each user for:

[0019] ;

[0020] in, Is the length N , is the identity matrix, is the Kronecker product.

[0021] Specifically, for The column-block matrix of k indivual The block is the identity matrix, and the others are 0; Is the length N The column vector of k The number is 1, and the others are 0.

[0022] The transmitted signal is converted from the delay-Doppler domain to the time-frequency domain by inverse symplectic finite Fourier transform, and the expression is as follows:

[0023] ;

[0024] in, is the signal matrix in the time-frequency domain, for M The point fast Fourier transform matrix, is the transmit signal matrix, for N Point fast inverse Fourier transform matrix, the superscript H indicates conjugate transpose;

[0025] Then the transmitted signal is converted from the time-frequency domain to the time-domain transmitted signal through the Heisenberg transform, and the expression is as follows:

[0026] ;

[0027] in, is the time domain transmit signal matrix, express M Point Fast Inverse Fourier Transform Matrix.

[0028] Step S2, the time domain transmission signal is transmitted through the channel to obtain the time domain reception signal, and then the time domain reception signal is subjected to Wigner transformation to obtain the user's time-frequency domain signal, and finally the time-frequency domain signal is separated and sigmoid finite Fourier transformed, and combined with the indicator matrix of Doppler division multiple access, a delay-Doppler domain reception signal of Doppler division multiple access based on orthogonal time-frequency space modulation is obtained.

[0029] Among them, the modulated time domain transmission signal is first transmitted through the antenna in the wireless channel, and the time domain reception signal is obtained after the multipath effect and noise interference; then the time domain reception signal is transformed to map the multi-user signal from the time domain to the time-frequency domain; finally, the time-frequency domain reception signals of different users are separated, and the time-frequency domain reception signal of each user is subjected to a symplectic finite Fourier transform to obtain the DD domain reception signal of the uplink transmission OTFS-DoDMA in the high mobility scenario.

[0030] Assuming that the transmitted pulse is a rectangular pulse waveform and considering the uplink transmission in a high mobility scenario, we can get k Delay-Doppler domain channel model for a user The expression is:

[0031] ;

[0032] in, P is the path loss number, , , Respectively k User's i The channel gain, delay, and Doppler shift corresponding to each path, is the Dirac function, For delay, is the Doppler shift.

[0033] Furthermore, the time-frequency domain received signals of different users are separated, and the time-frequency domain received signals of each user are subjected to symplectic finite Fourier transform to obtain the delay-Doppler domain received signal of Doppler division multiple access based on orthogonal time-frequency spatial modulation. , the expression is:

[0034] ;

[0035] ;

[0036] ;

[0037] in, is the user's transmission power, For the k The transmitted signal of a user, it should be pointed out that the transmitted signal The transmit signal matrix After vectorization, is the effective channel matrix in the delay-Doppler domain, For the k User , is the equivalent noise in the delay-Doppler domain, express N The point fast Fourier transform matrix, is the time domain channel matrix, is additive white Gaussian noise.

[0038] Step S3, at the base station, a serial interference elimination method is applied to the delay-Doppler domain received signal of Doppler division multiple access based on orthogonal time-frequency space modulation, and the delay-Doppler domain received signal of Doppler division multiple access based on orthogonal time-frequency space modulation of each user is judged one by one according to the size of the signal power to eliminate interference between users, and then the achievable rate of each user is obtained by the mutual information theorem and the properties of the trace operation, and uplink multiple access transmission is performed based on the achievable rate of each user.

[0039] Among them, for uplink transmission in high mobility scenarios, the serial interference cancellation method is applied to the received signal in the delay-Doppler domain at the base station, and the received signal in the delay-Doppler domain based on orthogonal time-frequency spatial modulation Doppler multiple access is judged one by one according to the signal power to eliminate interference between users. Assuming that the signal with the maximum channel gain has the largest power, and the channel gains of all users are sorted in descending order, the expression is:

[0040] ;

[0041] in, Indicates the first user i The fading coefficients associated with each path, Indicates the second user's i The fading coefficients associated with each path, Indicates K u User's i The fading coefficients associated with each path;

[0042] The user signal with the largest channel gain is decoded first, and the user signal with the largest channel gain is affected by the residual K u -1 user signal. Then, the user signal with the second largest channel gain is decoded, and the decoded signal is subtracted. The user signal with the second largest channel gain is affected by the remaining K u -2 signals. And so on, until the interference of all user signals is eliminated.

[0043] Assume that the transmitted symbols are equally likely to be taken from the average symbol energy The complex Gaussian constellation can be obtained by the mutual information theorem. k The closed expression of the user for:

[0044] ;

[0045] Among them, det means to find the determinant of the matrix, is the one-sided power spectral density, For the k The interference power of each user;

[0046] The following formula is obtained from the properties of trace operation:

[0047] ;

[0048] Among them, Tr represents the trace operation, Indicates k User's i The fading coefficients associated with each path;

[0049] Then, according to the k The closed expression of each user and the properties of the trace operation give k Signal-to-interference-noise ratio , the expression is:

[0050] ;

[0051] in, Indicates k +1 user's i The fading coefficients associated with each path.

[0052] Finally, we can get k Achievable rate per user The expression is:

[0053] .

[0054] Through the above method, the base station can optimize uplink multiple access transmission according to the rate requirement of each user, thereby reasonably allocating resources in the delay-Doppler domain.

[0055] In summary, according to the uplink multiple access transmission method of the multi-user orthogonal time-frequency space system provided by the present invention, in a high mobility scenario, the Doppler division multiple access (DoDMA) technology based on OTFS modulation is adopted. Different users multiplex information symbols along the entire delay axis through corresponding Doppler indexes, so that resource allocation can be better performed. By separating and performing symplectic finite Fourier transform on the time-frequency domain signals and combining with the indicator matrix of Doppler division multiple access, the received signal of the DD domain of DoDMA based on OTFS modulation is obtained, and then the received signal of the DD domain of DoDMA based on OTFS modulation is applied at the base station. The serial interference elimination method judges the received signals in the delay-Doppler domain of Doppler division multiple access based on orthogonal time-frequency space modulation of each user one by one according to the size of the signal power to eliminate the interference between users, and then obtains the achievable rate of each user by the mutual information theorem and the properties of trace operation. Uplink multiple access transmission is performed based on the achievable rate of each user, which can effectively solve the influence of high Doppler frequency shift and interference between multiple users caused by rapid movement, achieve higher transmission rate, and significantly improve the bit error rate performance, showing better communication reliability, and meet the wireless communication service needs of uplink transmission in high mobility scenarios.

[0056] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0057] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. An uplink multiple access transmission method for a multi-user orthogonal time-frequency-space system, characterized in that: The steps include: Step S1, multiple users perform wireless communication with a base station, obtain a transmission signal of each user, map the transmission signal into an orthogonal amplitude modulation symbol, multiplex information symbols along the entire delay axis with corresponding Doppler indexes for different users, and obtain an indicator matrix of Doppler division multiple access. In addition, the transmission signal is converted from the delay-Doppler domain to the time-frequency domain by an inverse symplectic finite Fourier transform, and then the transmission signal is converted from the time-frequency domain to a time-domain transmission signal by a Heisenberg transform; Step S2, after the time domain transmission signal is transmitted through the channel, a time domain reception signal is obtained, and then a Wigner transform is performed on the time domain reception signal to obtain a time-frequency domain signal of the user, and finally the time-frequency domain signal is separated and symplectic finite Fourier transform is performed on the time-frequency domain signal, and combined with the indicator matrix of Doppler division multiple access, a delay-Doppler domain reception signal of Doppler division multiple access based on orthogonal time-frequency space modulation is obtained; Step S3, at the base station, a serial interference elimination method is applied to the delay-Doppler domain received signal of Doppler division multiple access based on orthogonal time-frequency spatial modulation, and the delay-Doppler domain received signal of Doppler division multiple access based on orthogonal time-frequency spatial modulation of each user is judged one by one according to the signal power to eliminate interference between users, and then the achievable rate of each user is obtained by the mutual information theorem and the properties of trace operation, and uplink multiple access transmission is performed based on the achievable rate of each user; Step S1 specifically includes: Set the total number of users to K u , the number of subcarriers and time slots in the OTFS frame are M and N The horizontal axis of the delay-Doppler domain grid is defined as the Doppler axis, and the vertical axis of the delay-Doppler domain grid is defined as the delay axis. The horizontal and vertical axes are divided into unit Doppler frequency shifts. and unit delay Grid; Obtaining the bit stream of the transmitted signal of each user, mapping the bit stream of the transmitted signal into orthogonal amplitude modulation symbols, then converting the orthogonal amplitude modulation symbols into a symbol sequence, and then placing the symbol sequence on a delay-Doppler domain grid; K u The user multiplexes information symbols along the entire delay axis with different Doppler indices, defining k The indicator matrix of Doppler division multiple access for each user for: ； in, Is the length N , is the identity matrix, is the Kronecker product; The transmitted signal is converted from the delay-Doppler domain to the time-frequency domain by inverse symplectic finite Fourier transform, and the expression is as follows: ； in, is the signal matrix in the time-frequency domain, for M The point fast Fourier transform matrix, is the transmit signal matrix, for N Point Fast Inverse Fourier Transform Matrix; Then the transmitted signal is converted from the time-frequency domain to the time-domain transmitted signal through the Heisenberg transform, and the expression is as follows: ； in, is the time domain transmit signal matrix, express M Point Fast Inverse Fourier Transform Matrix; In step S3, the channel gains of all users are sorted in descending order, and the user signal with the largest channel gain is decoded first. The user signal with the largest channel gain is decoded by the remaining K u -1 user signal interference, then decode the user signal with the second largest channel gain, and subtract the decoded signal, the user signal with the second largest channel gain will be affected by the remaining K u -2 signals, and so on, until the interference of all user signals is eliminated; In which, it is assumed that the transmitted symbols are equally likely to be taken from the average symbol energy The complex Gaussian constellation is obtained by the mutual information theorem. k The closed expression of the user for: ； Among them, det means to find the determinant of the matrix, is the one-sided power spectral density, For the k The interference power of each user, is the user's transmission power, is the effective channel matrix in the delay-Doppler domain, For the k User , the superscript H indicates the conjugate transpose; The following formula is obtained from the properties of trace operation: ； Among them, Tr represents the trace operation, Indicates k User's i The fading coefficients associated with each path, M is the number of subcarriers in the OTFS frame, P is the path loss number; Furthermore, according to k The closed expression of each user and the properties of the trace operation give k Signal-to-interference-noise ratio , the expression is: in, Indicates k +1 user's i The fading coefficients associated with each path; Finally, the k Achievable rate per user The expression is: 。 2. The uplink multiple access transmission method of a multi-user orthogonal time-frequency-space system according to claim 1, characterized in that: In step S2, k Delay-Doppler domain channel model for a user The expression is: ； in, , , Respectively k User's i The channel gain, delay, and Doppler shift corresponding to each path, is the Dirac function, For delay, is the Doppler shift.

3. The uplink multiple access transmission method of a multi-user orthogonal time-frequency-space system according to claim 2, characterized in that: In step S2, the received signal in the delay-Doppler domain based on the orthogonal time-frequency spatial modulation Doppler division multiple access The expression is: ； ； ； in, For the k The transmitted signal of a user, is the equivalent noise in the delay-Doppler domain, express N The point fast Fourier transform matrix, is the time domain channel matrix, is additive white Gaussian noise.

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