An OTFS transmission method adapted to time-varying Doppler channels

Abstract

This invention proposes an OTFS transmission method adapted to time-varying Doppler channels, belonging to the field of wireless communications. The method comprises: an OTFS downlink receiver estimating the Doppler variation rate based on a digital received linear frequency modulation sequence; an OTFS downlink transmitter generating an OTFS transmit signal and transmitting it to the OTFS downlink receiver; and the OTFS downlink receiver performing OTFS demodulation on the OTFS transmit signal. Compared with existing technologies, this method considers time-varying Doppler in the presence of multipath, taking into account both multipath effects and time-varying Doppler, thus adapting to channels with Doppler variation rates.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to an OTFS transmission method adapting to a time-varying Doppler channel. Background Art

[0002] Orthogonal Time Frequency Space (OTFS) is a novel two-dimensional modulation technique that modulates information symbols in the delay-Doppler domain. Numerous studies have shown that OTFS outperforms OFDM (Orthogonal Frequency Division Multiplexing) in high-speed mobility scenarios.

[0003] In scenarios such as low-Earth orbit satellites and millimeter wave systems, the received signal can experience significant time-varying Doppler distortion due to the relative motion between the transmitter and receiver. The Doppler rate, a higher-order motion parameter related to acceleration, must be accounted for in the system model. Consequently, the Doppler shift is no longer a constant but a time-varying variable.

[0004] In their paper, "Long-time Coherent Integration for Weak Maneuvering Target Detection and High-Order Motion Parameter Estimation Based on Keystone Transform," published in IEEE Transactions on Signal Processing (Volume 64, Issue 15, August 1, 2016), P. Huang et al. considered the detection and motion parameter estimation problems of weakly maneuvering targets with third-order displacement and Doppler shift. First, they used the Keystone transform to compensate for linear range wander. Then, they applied matched filtering in the range-frequency and azimuth-time domains to eliminate the residual coupling effects between range and azimuth. Finally, they obtained a clear image of the moving target and effectively estimated three motion parameters: velocity, acceleration, and rate of acceleration.

[0005] In their paper “Ground Maneuvering Target Imaging and High-Order Motion Parameter Estimation Based on Second-Order Keystone and Generalized Hough-HAF Transform,” published in IEEE Transactions on Geoscience and Remote Sensing (Volume: 55, Issue: 1, January 2017), P. Huang et al. address the problem of estimating the motion parameters of ground moving targets using synthetic aperture radar. They propose using a second-order Keystone transform to correct the range curvature, then use the Hough transform to estimate the slope of the range walk trajectory to obtain the target's lateral velocity. Finally, they use a generalized Hough high-order ambiguity function transform to convert the target signal into a 2D time-frequency plane and estimate the slope associated with the third-order Doppler parameter.

[0006] Yaru Shan et al. published a paper titled "Low-Complexity and Low-Overhead Receiver for OTFS via Large-Scale Antenna Array" in IEEE Transactions on Vehicular Technology (Volume: 70, Issue: 6, June 2021). They proposed a method to distinguish OTFS multipath using large-scale antennas, but did not consider the time-varying Doppler channel.

[0007] In summary, existing technologies only consider time-varying Doppler in the presence of a single path, or consider multipath effects without considering time-varying Doppler. Therefore, how to provide an OTFS transmission method that adapts to Doppler-varying channels has become a technical issue of great concern to those skilled in the art. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide an efficient OTFS transmission method for wireless channels with time-varying Doppler. To this end, the present invention provides an OTFS transmission method that adapts to time-varying Doppler channels. The present invention estimates the Doppler change rate, making the system resistant to time-varying Doppler.

[0009] The technical solution adopted in the present invention is:

[0010] An OTFS transmission method adapted to a time-varying Doppler channel is applied to an OTFS transmission system, wherein the OTFS transmission system includes an OTFS downlink transmitter, an OTFS uplink transmitter, an OTFS downlink receiver, and an OTFS uplink receiver, wherein the OTFS downlink transmitter and the OTFS uplink receiver are deployed at the same location and connected via a wired connection; the OTFS uplink transmitter and the OTFS downlink receiver are deployed at the same location and connected via a wired connection. The method comprises the following steps:

[0011] Step 1: The OTFS downlink transmitter transmits the kth linear frequency modulation sequence s k ={s k (0),s k (1),…,s k (N0-1)} generates the kth linear frequency modulation signal through digital-to-analog conversion and sends it to the wireless channel; after the OTFS downlink receiver receives the kth linear frequency modulation signal, it generates the kth digital received linear frequency modulation sequence r through analog-to-digital conversion. k ={r k (0),r k (1),…,r k (N0-1)}, according to r k Estimated Doppler rate of change Where N0 is s k and r k length;

[0012] Step 2: The OTFS downlink receiver will The OTFS uplink transmitter transmits the data via a wired channel. The OTFS uplink receiver sends the Doppler change rate to the OTFS uplink receiver. Transmitted via wire to the OTFS downlink transmitter;

[0013] Step 3: After the OTFS downlink transmitter transmits the kth linear frequency modulation signal, it modulates the information bit stream to be transmitted to generate the kth group of modulation symbol sequences, and then Perform OTFS modulation and precoding on the kth group of modulation symbol sequences in sequence to generate the kth OTFS digital signal y k :

[0014]

[0015] in, is the delay-Doppler domain symbol to be sent, I M is the M-order unit matrix, F N Represents the Fourier transform matrix of N points, whose mth row and nth column elements are M and N are the number of grid points in the delay dimension and the Doppler dimension respectively. Indicates F N The conjugate transpose of represents the Kronecker product, P = diag{p}, where diag{·} represents the diagonalization operation, that is, the vector p is placed on the diagonal of the matrix P, and the other positions of the matrix P are 0. The i-th element of the vector p is Δf is the subcarrier spacing of the OTFS signal;

[0016] Step 4, OTFS downlink transmitter k Perform digital-to-analog conversion and up-conversion in sequence to generate the kth OTFS transmission signal, and send the kth OTFS transmission signal to the OTFS downlink receiver through the wireless channel;

[0017] Step 5: The OTFS downlink receiver performs OTFS demodulation on the kth OTFS transmission signal and determines whether the information transmission is completed at this time. If so, the process ends; if not, k=k+1 is set and steps 1 to 5 are repeated.

[0018] Furthermore, the specific method of step 1 is:

[0019] Step 101: The OTFS downlink receiver distinguishes r k The multipath in r k Divide the signal into U paths to distinguish multipaths Where 1≤u≤U, U is the number of transmission paths in the channel;

[0020] Step 102, calculate and s k The fourth moment F r (η1), F s (η1), the specific steps are:

[0021] (1021) Calculation The instantaneous autocorrelation A r :

[0022]

[0023] Among them, η0∈(0,N0) is a constant, n∈[-M0,M0-η0], conj[·] means conjugation operation;

[0024] (1022) Calculate s k The instantaneous autocorrelation A s :

[0025] A s =conj(s k (n))s k(n+η0);

[0026] (1023) calculation The fourth moment of:

[0027]

[0028] in:

[0029] η1∈[-(N0-η0-1),N0-η0-1],

[0030] N1=max{-M0,-M0-η1},

[0031] N2=min{M0-η0,M0-η0-η1};

[0032] (1024) Calculate s k The fourth moment of:

[0033]

[0034] Step 103, calculate F r (η1), F s The ratio ξ of (η1):

[0035]

[0036] Step 104, perform fast Fourier transform on ξ to obtain in

[0037] Step 105, find the maximum value in f, estimate the Doppler rate of change, and obtain the estimated value of the Doppler rate of change

[0038]

[0039] The following beneficial effects can be achieved by adopting the present invention:

[0040] 1. The present invention realizes the estimation of Doppler change rate, so that the system has the ability to resist time-varying Doppler.

[0041] 2. The present invention precodes the OTFS transmission signal according to the Doppler change rate, so that the complexity of the channel estimation at the receiving end is greatly reduced.

[0042] 3. Compared with the prior art, the present invention takes into account the time-varying Doppler in the presence of multipath. It considers the time-varying Doppler while taking into account the multipath effect, and can adapt to channels with Doppler variation rates. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1It is a schematic diagram of the structure of the OTFS transmission system;

[0044] Figure 2 It is the overall flow chart of the present invention;

[0045] Figure 3 It is a graph of the bit error performance in a time-varying Doppler rate channel. DETAILED DESCRIPTION

[0046] In order to better understand the present invention, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0047] An OTFS transmission method adapted to a time-varying Doppler channel, assuming that the symbol period and subcarrier spacing of the OTFS signal are T and Δf respectively, and the number of grid points in the delay dimension and the number of grid points in the Doppler dimension are M and N respectively, comprises the following steps:

[0048] The first step is to build the OTFS transmission system. Figure 1 As shown, the OTFS transmission system includes an OTFS downlink transmitter, an OTFS uplink transmitter, an OTFS uplink transmitter, and an OTFS uplink receiver. The OTFS downlink transmitter and the OTFS uplink receiver are deployed at the same location and connected by a wired connection; the OTFS uplink transmitter and the OTFS downlink receiver are deployed at the same location and connected by a wired connection. Let k = 1.

[0049] In the second step, the OTFS downlink transmitter transmits the kth linear frequency modulation sequence s k ={s k (0),s k (1),…,s k (N0-1)} generates the kth linear frequency modulation signal through digital-to-analog conversion and sends it to the wireless channel; the OTFS downlink receiver receives the kth linear frequency modulation signal and generates the kth digital received linear frequency modulation sequence r through analog-to-digital conversion. k ={r k (0),r k (1),…,r k (N0-1)}, according to r k Estimate the Doppler rate of change. Where N0 is s k and r k Assuming that the number of transmission paths in the channel is U, the specific steps are:

[0050] 2.1 The OTFS downlink receiver uses the method of background technology 3 to distinguish r k The multipath in r k Divide the signal into U paths to distinguish multipaths Where 1≤u≤U;

[0051] 2.2 Calculate s separatelyk and The fourth moment F s (η1), F r (η1), the specific steps are:

[0052] 2.2.1 Calculation The instantaneous autocorrelation A r , the calculation method is Among them, η0∈(0,N0) is a constant, and n∈[-M0,M0-η0] is selected according to the actual situation. The operation conj[·] means to find the conjugate; calculate s k The instantaneous autocorrelation A s , calculated as A s =conj(s k (n))s k (n+η0);

[0053] 2.2.2 Calculation The fourth moment of Among them, η1∈[-(N0-η0-1),N0-η0-1], N1=max{-M0,-M0-η1}, N2=min{M0-η0, M0-η0-η1}; calculate s k The fourth moment of

[0054] 2.3 Calculation of F r (η1), F s The ratio ξ of (η1) is calculated as

[0055]

[0056] 2.4 Calculate the FFT of ξ and get in

[0057] 2.5 Find the maximum value in f, estimate the Doppler rate of change, and obtain the estimated value of the Doppler rate of change The estimation method is

[0058]

[0059] In the third step, the OTFS downlink receiver will The OTFS uplink transmitter transmits the data via a wire. The signal is sent to the OTFS uplink receiver, which then transmits the Doppler to the OTFS downlink transmitter via a wire.

[0060] Step 4: OTFS downlink transmitter Perform OTFS modulation and precoding on the kth group of modulation symbol sequences in sequence to generate the kth OTFS digital signal y k ,y k The calculation method is is the delay-Doppler domain symbol to be sent, I M is an M-order diagonal unit matrix, F N Represents the Fourier transform matrix of N points, and the calculation method of its m rows and n columns is Indicates F N The conjugate transpose of , P = diag{p}, the i-th element of p is

[0061] Step 5: OTFS downlink transmitter k Perform digital-to-analog conversion and up-conversion sequentially to generate the kth OTFS transmission signal. This signal is then transmitted via a wireless channel to the OTFS downlink receiver. The OTFS downlink receiver performs OTFS demodulation on the kth OTFS transmission signal. The process then determines whether the information transfer is complete. If so, the process ends. If not, set k = k + 1 and proceed to the second step.

[0062] To illustrate the performance of the present invention, simulation experiments were conducted on the performance of the OTFS transmission system using the method of the present invention and not using the method of the present invention. The results are as follows: Figure 3 As shown. The horizontal axis represents the signal-to-noise ratio, and the vertical axis represents the bit error rate. The dotted line with squares represents the OTFS transmission system without the method of the present invention, and the Doppler variation rate is 49×10 8 Hz / s; the solid line with “+” represents the OTFS transmission system without Doppler variation; the dotted line with a circle represents the OTFS transmission system using the method of the present invention, with a Doppler variation of 49×10 8 Hz / s. It can be seen that when the method of the present invention is not used, when the Doppler variation exists, the system bit error rate remains at a relatively high level as the signal-to-noise ratio increases. However, when the method of the present invention is used, the system bit error performance is essentially the same as when the Doppler variation does not exist. This shows that the present invention is adaptable to channels with Doppler variation.

Claims

1. An OTFS transmission method adapted to a time-varying Doppler channel, characterized in that: Applied to an OTFS transmission system, the OTFS transmission system includes an OTFS downlink transmitter, an OTFS uplink transmitter, an OTFS downlink receiver, and an OTFS uplink receiver, wherein the OTFS downlink transmitter and the OTFS uplink receiver are deployed at the same location and connected by wire; the OTFS uplink transmitter and the OTFS downlink receiver are deployed at the same location and connected by wire; the method includes the following steps: Step 1: The OTFS downlink transmitter transmits the kth linear frequency modulation sequence s k ={s k (0),s k (1),…,s k (N0-1)} generates the kth linear frequency modulation signal through digital-to-analog conversion and sends it to the wireless channel; after the OTFS downlink receiver receives the kth linear frequency modulation signal, it generates the kth digital received linear frequency modulation sequence r through analog-to-digital conversion. k ={r k (0),r k (1),…,r k (N0-1)}, according to r k Estimate the Doppler change rate a; where N0 is s k and r k length; Step 2: The OTFS downlink receiver will The OTFS uplink transmitter transmits the data via a wired channel. The OTFS uplink receiver sends the Doppler change rate to the OTFS uplink receiver. Transmitted via wire to the OTFS downlink transmitter; Step 3: After the OTFS downlink transmitter transmits the kth linear frequency modulation signal, it modulates the information bit stream to be transmitted to generate the kth group of modulation symbol sequences, and then Perform OTFS modulation and precoding on the kth group of modulation symbol sequences in sequence to generate the kth OTFS digital signal y k : in, is the delay-Doppler domain symbol to be sent, I M is the M-order unit matrix, F N Represents the Fourier transform matrix of N points, whose mth row and nth column elements are M and N are the number of grid points in the delay dimension and the Doppler dimension respectively. Indicates F N The conjugate transpose of represents the Kronecker product, P = diag{p}, where diag{·} represents the diagonalization operation, that is, the vector p is placed on the diagonal of the matrix P, and the other positions of the matrix P are 0. The i-th element of the vector p is Δf is the subcarrier spacing of the OTFS signal; Step 4, OTFS downlink transmitter k Perform digital-to-analog conversion and up-conversion in sequence to generate the kth OTFS transmission signal, and send the kth OTFS transmission signal to the OTFS downlink receiver through the wireless channel; Step 5: The OTFS downlink receiver performs OTFS demodulation on the kth OTFS transmission signal and determines whether the information transmission is completed at this time. If so, the process ends; if not, k=k+1 is set and steps 1 to 5 are repeated.

2. The OTFS transmission method adapted to a time-varying Doppler channel according to claim 1, characterized in that: The specific method of step 1 is: Step 101: The OTFS downlink receiver distinguishes r k The multipath in r k Divide the signal into U paths to distinguish multipaths Where 1≤u≤U, U is the number of transmission paths in the channel; Step 102, calculate and s k The fourth moment F r (η1), F s (η1), the specific steps are: (1021) Calculation The instantaneous autocorrelation A r : Among them, η0∈(0,N0) is a constant, n∈[-M0,M0-η0], conj[×] means conjugate operation; (1022) Calculate s k The instantaneous autocorrelation A s : A s =conj(s k (n))s k (n+η0); (1023) calculation The fourth moment of: in: η1∈[-(N0-η0-1),N0-η0-1], N1=max{-M0,-M0-η1}, N2=min{M0-η0,M0-η0-η1}; (1024) Calculate s k The fourth moment of: Step 103, calculate F r (η1), F s The ratio ξ of (η1): Step 104, perform fast Fourier transform on ξ to obtain in Step 105, find the maximum value in f, estimate the Doppler rate of change, and obtain the estimated value of the Doppler rate of change

Images