OTFS transmission method adaptive to time-varying Doppler channel

Abstract

The invention provides an OTFS transmission method adaptive to a time-varying Doppler channel, and belongs to the technical field of wireless communication. The method comprises the steps that an OTFS downlink receiver estimates the Doppler change rate according to a digital receiving linear frequency modulation sequence, an OTFS downlink transmitter generates an OTFS transmitting signal and sends the OTFS transmitting signal to the OTFS downlink receiver, and the OTFS downlink receiver carries out OTFS demodulation on the OTFS transmitting signal. Compared with the prior art, the time-varying Doppler is considered under the condition that multiple paths exist, the time-varying Doppler is considered while the multipath effect is considered, and the method can adapt to a channel with the Doppler change rate.

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] OTFS (Orthogonal Time Frequency Space) is a new two-dimensional modulation technology that modulates information symbols in the delay-Doppler domain. Many studies have shown that OTFS performs better than OFDM (Orthogonal Frequency Division Multiplexing) technology in high-speed mobile scenarios.

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

[0004] In the paper "Long-time Coherent Integration for Weak Maneuvering Target Detection and High-Order Motion Parameter Estimation Based on Keystone Transform" published by P. Huang et al. in IEEE Transactions on Signal Processing (Volume: 64, Issue: 15, 01 August 2016), the detection and motion parameter estimation problems of weak maneuvering targets with third-order displacement and Doppler shift are considered. First, the Keystone transform is used to compensate for linear range wandering; then, matched filtering is performed in the range frequency and azimuth time domains to eliminate the residual coupling effect between range and azimuth; finally, a clear moving target image is obtained, and three motion parameters, namely velocity, acceleration, and acceleration rate of change, are effectively estimated.

[0005] In the 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. proposed using the second-order Keystone transform to correct the range curvature, and then use the Hough transform to estimate the slope of the range walk trajectory to obtain the target lateral velocity. Finally, the generalized Hough high-order ambiguity function transform is used to convert the target signal into a 2D time-frequency plane, and the slope associated with the third-order Doppler parameter is estimated.

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

[0007] In summary, the prior art only considers the time-varying Doppler when there is a single path, or considers the multipath effect but not the 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 the existence of time-varying Doppler in a wireless channel. To this end, the present invention provides an OTFS transmission method adapted to a time-varying Doppler channel, and the present invention realizes the estimation of the Doppler change rate, so that the system has the ability to resist time-varying Doppler.

[0009] The technical solution adopted by 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 comprises 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 position and connected by wire; the OTFS uplink transmitter and the OTFS downlink receiver are deployed at the same position and connected by wire; 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 (0),…,s k (N 0 -1)} Through digital-to-analog conversion, the kth linear frequency modulation signal is generated and sent 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 (0),…,r k (N 0 -1)}, according to r k Estimated Doppler rate of change Among them, N 0 For k and r k Length;

[0012] Step 2: The OTFS downlink receiver will The OTFS uplink transmitter transmits the data through a wired channel. The OTFS uplink receiver sends the Doppler change rate to the OTFS uplink receiver. Transmitted via wire to 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 The kth group of modulation symbol sequences are sequentially subjected to OTFS modulation and precoding 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 NRepresents 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 number of grid points in 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 a 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 yes, 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, respectively calculate and k The fourth moment F r (η 1 ), F s (η 1 ), the specific steps are:

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

[0022]

[0023] Among them, η 0 ∈(0,N 0 ) is a constant, n∈[-M 0 ,M 0 -η 0 ], conj[×] means conjugation operation;

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

[0025] A s =conj(s k (n))s k (n+η 0 );

[0026] (1023) Calculation The 4th moment of:

[0027]

[0028] in:

[0029] η 1 ∈[-(N 0 -η 0 -1),N 0 -η 0 -1],

[0030] N 1 =max{-M 0 ,-M 0 -η 1},

[0031] N 2 =min{M 0 -η 0 ,M 0 -η 0 -η 1};

[0032] (1024) Calculate s k The 4th moment of:

[0033]

[0034] Step 103, calculate F r (η 1 ), F s (η 1 ) ratio x:

[0035]

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

[0037]

[0038] Step 105, find the maximum value in f, estimate the Doppler change rate, and obtain the estimated value of the Doppler change rate

[0039]

[0040] The following beneficial effects can be obtained by adopting the present invention:

[0041] 1. The present invention realizes the estimation of Doppler change rate, so that the system has the ability to resist time-varying Doppler.

[0042] 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.

[0043] 3. Compared with the prior art, the present invention takes time-varying Doppler into account in the presence of multipath, and considers time-varying Doppler while considering multipath effect, and can adapt to channels with Doppler change rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the structure of the OTFS transmission system;

[0045] Figure 2 It is the overall flow chart of the present invention;

[0046] Figure 3 It is a graph of bit error performance in a time-varying Doppler rate channel. DETAILED DESCRIPTION

[0047] 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.

[0048] 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, comprising the following steps:

[0049] 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, wherein the OTFS downlink transmitter and the OTFS uplink receiver are deployed at the same location and connected by wires; the OTFS uplink transmitter and the OTFS downlink receiver are deployed at the same location and connected by wires. Let k=1.

[0050] In the second step, the OTFS downlink transmitter transmits the kth linear frequency modulation sequence s k ={s k (0),s k (0),…,s k (N 0-1)} Through digital-to-analog conversion, the kth linear frequency modulation signal is generated and sent 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 (0),…,r k (N 0 -1)}, according to r k Estimate the Doppler rate of change. Where N 0 For k and r k The length of the channel is assumed to be U. The specific steps are as follows:

[0051] 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 Of which 1￡u￡U;

[0052] 2.2 Calculate s separately k and The fourth moment F s (η 1 ), F r (η 1 ), the specific steps are:

[0053] 2.2.1 Calculation The instantaneous autocorrelation A r , the calculation method is Among them, η 0 ∈(0,N 0 ) is a constant, selected according to the actual situation, n∈[-M 0 ,M 0 -η 0 ], 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+η 0 );

[0054] 2.2.2 Calculation The fourth-order moment of is calculated as where η 1 ∈[-(N 0 -η 0 -1),N 0 -η 0 -1],N1 =max{-M 0 ,-M 0 -η 1},N 2 =min{M 0 -η 0 ,M 0 -η 0 -η 1}; Calculate s k The fourth-order moment of is calculated as

[0055] 2.3 Calculation of F r (η 1 ), F s (η 1 ) is calculated as

[0056]

[0057] 2.4 Calculate the FFT of x and get in

[0058] 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

[0059]

[0060] In the third step, the OTFS downlink receiver will The OTFS uplink transmitter transmits the data via a cable. The Doppler signal is sent to the OTFS uplink receiver, and the OTFS uplink receiver transmits the Doppler signal to the OTFS downlink transmitter via wire.

[0061] Step 4: OTFS downlink transmitter The kth group of modulation symbol sequences are sequentially subjected to OTFS modulation and precoding 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 the M-order diagonal unit matrix, F N The Fourier transform matrix representing N points has m rows and n columns, and the calculation method of its elements is Indicates F N The conjugate transpose of , P = diag{p}, the i-th element of p is

[0062] Step 5: 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. The OTFS downlink receiver performs OTFS demodulation on the kth OTFS transmission signal. Determine whether the information transmission is completed at this time. If so, end. If not, set k=k+1 and go to the second step.

[0063] 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 the OTFS transmission system not using the method of the present invention. The results are as follows: Figure 3 The horizontal axis represents the signal-to-noise ratio, and the vertical axis represents the bit error rate. The dotted line with a square represents the OTFS transmission system without using the method of the present invention, and the Doppler change rate is 49×10 8 Hz / s; the solid line with “+” indicates an OTFS transmission system without Doppler variation rate; the dotted line with a circle indicates an OTFS transmission system using the method of the present invention, with a Doppler variation rate of 49×10 8 Hz / s. It can be seen that when the method of the present invention is not used, when there is a Doppler change rate, as the signal-to-noise ratio increases, the system bit error rate is still at a relatively high level; when the method of the present invention is used, the system bit error performance is basically the same as when there is no Doppler change rate. This shows that the present invention can adapt to channels with Doppler change rates.

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 comprises 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 position and connected by wire; the OTFS uplink transmitter and the OTFS downlink receiver are deployed at the same position and connected by wire; the method comprises the following steps: Step 1: The OTFS downlink transmitter transmits the kth linear frequency modulation sequence s k ={s k (0),s k (0),…,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 (0),…,r k (N0-1)}, according to r k Estimated Doppler rate of change Where N0 is s k and r k Length; Step 2: The OTFS downlink receiver will The OTFS uplink transmitter transmits the data through a wired channel. The OTFS uplink receiver sends the Doppler change rate to the OTFS uplink receiver. Transmitted via wire to 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 The kth group of modulation symbol sequences are sequentially subjected to OTFS modulation and precoding 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 identity 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 number of grid points in 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 a 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 yes, 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, respectively calculate and 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 conjugation operation; (1022) Calculate s k The instantaneous autocorrelation A s : A s =conj(s k (n))s k (n+η0); (1023) Calculation The 4th 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 4th moment of: Step 103, calculate F r (η1), F s The ratio x of (η1): Step 104, perform fast Fourier transform on x to obtain in Step 105, find the maximum value in f, estimate the Doppler change rate, and obtain the estimated value of the Doppler change rate

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