Signal processing method and system based on modulation domain cyclic time delay doppler shift

Abstract

The application relates to the technical field of wireless communication, and discloses a signal processing method and system based on modulation domain cyclic delay Doppler shift, which comprises the following steps: obtaining a to-be-sent signal vector of a transmitting-end antenna; performing modulation domain cyclic delay Doppler shift on the to-be-sent signal vector to obtain a modulation domain signal vector, wherein the modulation domain cyclic delay Doppler shift comprises cyclic delay shift and cyclic Doppler shift; performing time delay Doppler modulation on the modulation domain signal vector to obtain a first time domain signal vector; adding a cyclic prefix to the first time domain signal vector to obtain a second time domain signal vector; and sending the second time domain signal vector to a double-fading wireless channel. The application not only can obtain full transmit diversity gain, but also can be used in a communication system of all time delay Doppler waveforms, has strong robustness, extremely low calculation complexity and wide application scenarios.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wireless communication technology, in particular to a signal processing method and system based on modulation domain cyclic delay Doppler shift. BACKGROUND

[0002] The waveform on the delay Doppler domain or the transform domain corresponding to the delay Doppler domain is called the delay Doppler (DD) waveform. This kind of waveform has strong anti-Doppler shift capability and is the most potential candidate waveform for the future sixth generation mobile communication system. In the delay Doppler waveform system based on multiple-input multiple-output (MIMO) technology, the diversity gain is a key indicator for the system to provide reliable communication services. The diversity gain refers to the inverse of the ratio of the logarithmic value of the bit error rate to the logarithmic value of the signal-to-noise ratio when the signal-to-noise ratio tends to infinity. The greater the diversity gain, the faster the system bit error rate decreases with the increase of the signal-to-noise ratio, and the better the communication performance. The commonly used method to increase the system diversity gain is to use MIMO technology. However, in the MIMO-based communication system, it is relatively simple and direct to obtain the receive antenna diversity, but it is very difficult to obtain the transmit antenna diversity gain. At present, there is no related method that can effectively obtain the transmit antenna diversity gain. SUMMARY

[0003] To solve the above technical problems, the present application provides a signal processing method and system based on modulation domain cyclic delay Doppler shift. Different cyclic delays and Doppler shifts are performed on the modulation domain symbols in advance, so that the equivalent number of channel paths is increased to the original number of transmit antennas, thereby realizing transmit diversity gain. The present application has low computational complexity and good gain effect.

[0004] In a first aspect, the present application provides a signal processing method based on modulation domain cyclic delay Doppler shift, which comprises:

[0005] obtaining a to-be-sent signal vector of a transmit antenna, performing modulation domain cyclic delay Doppler shift on the to-be-sent signal vector to obtain a modulation domain signal vector, the modulation domain cyclic delay Doppler shift comprising cyclic delay shift and cyclic Doppler shift;

[0006] performing delay Doppler modulation on the modulation domain signal vector to obtain a first time domain signal vector;

[0007] adding a cyclic prefix to the first time domain signal vector to obtain a second time domain signal vector, and sending the second time domain signal vector to a double-fading wireless channel.

[0008] Further, the step of modulating domain cyclic time delay Doppler shifting the to-be-sent signal vector comprises:

[0009] According to the shift step number and the time delay Doppler waveform of the to-be-sent signal vector, a corresponding modulation domain cyclic shift matrix is obtained.

[0010] According to the modulation domain cyclic shift matrix, the to-be-sent signal vector is modulated domain cyclically shifted to obtain a modulation domain signal vector.

[0011] Further, the step of obtaining the corresponding modulation domain cyclic shift matrix according to the shift step number and the time delay Doppler waveform of the to-be-sent signal vector comprises:

[0012] If the time delay Doppler waveform is orthogonal time frequency space, then the to-be-sent signal vector is cyclically time delayed and cyclically Doppler shifted according to the time delay shift step number and the Doppler shift step number respectively to obtain a first cyclic matrix and a second cyclic matrix.

[0013] According to the first cyclic matrix and the second cyclic matrix, a first modulation domain cyclic shift matrix is calculated and obtained.

[0014] If the time delay Doppler waveform is affine frequency division multiplexing, then a transform domain shift step number is calculated according to the time delay shift step number and the Doppler shift step number.

[0015] According to the transform domain shift step number, the to-be-sent signal vector is discretely affine Fourier transform domain cyclically shifted to obtain a third cyclic matrix.

[0016] According to the third cyclic matrix and a phase compensation matrix, a second modulation domain cyclic shift matrix is calculated and obtained.

[0017] Further, the first modulation domain cyclic shift matrix is represented by the following formula:

[0018]

[0019] In the formula, denotes the time delay shift step number, denotes the Doppler shift step number, OTFS denotes orthogonal time frequency space, MD-CDDS denotes modulation domain cyclic time delay Doppler shifting, N OTFS denotes the Doppler sampling number, M OTFS denotes the time delay sampling number, denotes the first cyclic matrix, denotes the second cyclic matrix, denotes the unit matrix;

[0020] The second modulation domain cyclic shift matrix is expressed by the following formula:

[0021]

[0022] In the formula, AFDM represents affine frequency division multiplexing, Δm represents a transform domain shift step number, represents the number of AFDM subcarriers, represents a third cyclic matrix, represents a phase compensation matrix, wherein,

[0023]

[0024] k s represents an interval factor, k max represents a maximum normalized Doppler shift.

[0025] Further, the step of modulating domain cyclic shifting the to-be-sent signal vector according to the modulation domain cyclic shift matrix to obtain a modulation domain signal vector comprises:

[0026] If the time delay Doppler class waveform of the to-be-sent signal is orthogonal time frequency space, the modulation domain signal vector is expressed by the following formula:

[0027]

[0028] x OTFS =vec(X OTFS )

[0029] In the formula, X OTFS represents a to-be-sent signal vector whose time delay Doppler class waveform is orthogonal time frequency space;

[0030] If the time delay Doppler class waveform of the to-be-sent signal is affine frequency division multiplexing, the modulation domain signal vector is expressed by the following formula:

[0031]

[0032] In the formula, X AFDM represents a to-be-sent signal vector whose time delay Doppler class waveform is affine frequency division multiplexing.

[0033] Further, after the second time domain signal vector is sent to a double-fading wireless channel, the method further comprises:

[0034] obtaining a third time domain signal vector from the double-fading wireless channel through a receiving end antenna, and removing a cyclic prefix in the third time domain signal vector to obtain a fourth time domain signal vector;

[0035] performing time-delay Doppler-like demodulation on the fourth time-domain signal vector to obtain a received signal vector.

[0036] Further, the step of performing time-delay Doppler-like demodulation on the fourth time-domain signal vector to obtain a received signal vector comprises:

[0037] If the time-delay Doppler-like waveform of the to-be-sent signal is orthogonal time-frequency-space, the received signal vector is expressed by the following formula:

[0038]

[0039] wherein k represents the index of the Doppler axis, l represents the index of the time-delay axis, P represents the number of branches of the double-fading wireless channel, i represents the i-th branch, and respectively represent the equivalent fading coefficient, the equivalent Doppler and the equivalent time-delay of the i-th branch of the double-fading wireless channel after modulation-domain cyclic time-delay Doppler shifting, represents the actual equivalent Doppler frequency shift, represents the actual equivalent time-domain shift, X OTFS represents the to-be-sent signal vector whose time-delay Doppler-like waveform is orthogonal time-frequency-space, N OTFS represents the number of Doppler samples, M OTFS represents the number of time-delay samples;

[0040] If the time-delay Doppler-like waveform of the to-be-sent signal is affine frequency division multiplexing, the received signal vector is expressed by the following formula:

[0041]

[0042]

[0043]

[0044] wherein m represents the index of the discrete affine Fourier transform domain, and respectively represent the equivalent fading coefficient, the equivalent Doppler and the equivalent time-delay of the i-th branch of the double-fading wireless channel after modulation-domain cyclic time-delay Doppler shifting, X AFDM represents the to-be-sent signal vector whose time-delay Doppler-like waveform is affine frequency division multiplexing, represents the number of AFDM subcarriers, and c1 and c2 are parameters of AFDM.

[0045] In a second aspect, the present application provides a signal processing system based on modulation-domain cyclic time-delay Doppler shifting, which comprises:

[0046] a time delay Doppler shift module, configured to obtain a to-be-sent signal vector of a transmitting antenna, and to perform modulation domain cyclic time delay Doppler shift on the to-be-sent signal vector to obtain a modulation domain signal vector, wherein the modulation domain cyclic time delay Doppler shift comprises cyclic time delay shift and cyclic Doppler shift;

[0047] a time delay Doppler modulation module, configured to perform time delay Doppler modulation on the modulation domain signal vector to obtain a first time domain signal vector;

[0048] a cyclic prefix adding module, configured to add a cyclic prefix to the first time domain signal vector to obtain a second time domain signal vector, and to send the second time domain signal vector to a double-fading wireless channel.

[0049] Further, the time delay Doppler shift module further comprises:

[0050] a shift matrix generating module, configured to obtain a corresponding modulation domain cyclic shift matrix according to a shift step number and a time delay Doppler waveform of the to-be-sent signal vector, wherein the shift step number comprises a time delay shift step number and a Doppler shift step number;

[0051] a cyclic shift module, configured to perform modulation domain cyclic shift on the to-be-sent signal vector according to the modulation domain cyclic shift matrix to obtain a modulation domain signal vector.

[0052] Further, the shift matrix generating module further comprises:

[0053] a first matrix generating module, configured to, if the time delay Doppler waveform is orthogonal time frequency space, perform cyclic time delay shift and cyclic Doppler shift on the to-be-sent signal vector according to the time delay shift step number and the Doppler shift step number respectively to obtain a first cyclic matrix and a second cyclic matrix, and to calculate a first modulation domain cyclic shift matrix according to the first cyclic matrix and the second cyclic matrix;

[0054] a second matrix generating module, configured to, if the time delay Doppler waveform is affine frequency division multiplexing, calculate a transform domain shift step number according to the time delay shift step number and the Doppler shift step number, perform discrete affine Fourier transform domain cyclic shift on the to-be-sent signal vector according to the transform domain shift step number to obtain a third cyclic matrix, and calculate a second modulation domain cyclic shift matrix according to the third cyclic matrix and a phase compensation matrix.

[0055] The application provides a signal processing method and system based on modulation domain cyclic time delay Doppler shift, through which the number of equivalent branches can be increased to improve the diversity order of the system, the application can be regarded as a precoding operation, can be combined with other precoding models to realize joint precoding, does not increase the processing load of the transmitting end, greatly reduces the complexity, and can be applied to all time delay Doppler based antenna systems, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is a single-input single-output time delay Doppler waveform communication system model schematic diagram;

[0057] Figure 2 is a flowchart of the signal processing method based on modulation domain cyclic time delay Doppler shift in the embodiment of the application;

[0058] Figure 3 is a transmitting end model schematic diagram of a multiple-input multiple-output time delay Doppler waveform communication system based on MD-CDDS provided by the embodiment of the application;

[0059] Figure 4 is a table diagram of an information symbol frame of an OTFS system in a time delay Doppler domain;

[0060] Figure 5 is a table diagram of a fast-varying channel in a two-dimensional time domain Doppler domain and a one-dimensional DAFT domain in an AFDM system;

[0061] Figure 6 is a bit error rate comparison schematic diagram of OTFS and AFDM systems under different antenna settings in a numerical simulation experiment;

[0062] Figure 7 is a structure schematic diagram of the signal processing system based on modulation domain cyclic time delay Doppler shift in the embodiment of the application. DETAILED DESCRIPTION

[0063] To make the purpose, technical scheme and advantages of the embodiments of the application clearer, the technical scheme in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are some of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0064] In the field of wireless communication technology, the waveform modulated on the time delay Doppler domain or the transform domain corresponding to the time delay Doppler domain is called time delay Doppler waveform, which has strong anti-Doppler frequency shift capability and is the most potential candidate waveform for the sixth generation mobile communication system. Typical time delay Doppler waveforms include orthogonal time frequency space, affine frequency division multiplexing, etc. In time delay Doppler waveform communication systems, including single-input single-output systems and multiple-input multiple-output systems, the following is an example of a single-input single-output time delay Doppler waveform communication system.

[0065] Please refer to Figure 1 , where the subscript zz of all variables represents any kind of time delay Doppler waveform, such as orthogonal time frequency space (OTFS), affine frequency division multiplexing (AFDM), etc. Assuming x zz is a to-be-sent signal vector composed of N orthogonal amplitude modulation (QAM) symbols in the time delay Doppler modulation domain, and the size of each vector is N x 1. For OTFS, it corresponds to the time delay-Doppler domain, and AFDM corresponds to the discrete affine Fourier transform domain. In the transmitting end of the communication system, x zz is modulated in the time delay Doppler domain, i.e. OTFS corresponds to OTFS modulation, and AFDM corresponds to AFDM modulation, thereby transforming to obtain a time domain signal vector s zz , the size of which is N x 1. Then, a cyclic prefix (CP) with a size equal to the maximum time delay of the channel is added to obtain a time domain signal vector with a cyclic prefix s , which is sent to a double-fading wireless channel through the transmitting antenna; the time domain signal vector received by the receiving antenna from the double-fading wireless channel is d , and the cyclic prefix is cut off to obtain a time domain signal vector d zz , the size of which is N x 1. Then, time delay Doppler demodulation is performed to obtain a received signal vector y zz in the time delay Doppler modulation domain.

[0066] The double-fading wireless channel is modeled in the time delay Doppler domain to obtain:

[0067]

[0068] In the formula, P represents that the double-fading wireless channel is composed of P paths, h i , τ i , and v iLet represent the fading system, time delay, and Doppler of the i-th path, respectively.

[0069] Typical time-delay Doppler waveforms include orthogonal time-frequency space-time (OTFS) and analog radio-frequency multiplexing (AFDM). Due to the differences in waveforms, the input-output relationships within these two different systems will also differ. For the OTFS system, its input-output relationship can be expressed as:

[0070]

[0071] Among them, X OTFS for Figure 1 The transmitted signal x located in the time-delay Doppler modulation domain zz k represents the index of the Doppler axis, l represents the index of the time delay axis, and N OTFS M represents the Doppler sampling number. OTFS Y represents the number of delay samples. OTFS [k, l] is then... Figure 1 The received signal y in the time-delay Doppler modulation domain zz .

[0072] For an AFDM system, its input-output relationship can be expressed as:

[0073]

[0074] Among them, X AFDM for Figure 1 The transmitted signal x located in the Discrete Affine Fourier Transform (DAFT) domain zz Y AFDM Then it is Figure 1 The received signal y in the DAFT domain zz , m represents the index of the DAFT field, This represents the number of AFDM subcarriers, where c1 and c2 are two parameters of AFDM.

[0075]

[0076] In the formula, k max k represents the maximum normalized Doppler frequency shift. s This represents the interval factor, which is a non-negative integer, and can be any irrational number or much smaller than 0. The rational number, and ind i As an index indicator factor, Where, α i This represents the normalized Doppler shift of the i-th path.

[0077] After explaining single-input single-output (SSO) time-delay Doppler waveform communication systems, multiple-input multiple-output (MIMO) systems become easier to understand. MIMO systems refer to wireless communication systems that use multiple antennas to transmit and receive signals. Assuming an MIMO time-delay Doppler waveform communication system has N... t One transmitting antenna and N r There are N receiving antennas. t ×N r In a MIMO system, the only difference between the channels between each pair of transmit and receive antennas is the fading coefficient of each path; the number of paths, the delay of each path, and the Doppler effect of each path are the same. Therefore, regardless of these N paths... t Whether the transmitting antennas transmit the same signal or not, the diversity gain order of the system is always the multipath number P multiplied by the number of receiving antennas, and not the number of transmitting antennas N. r Irrelevant.

[0078] To further improve the reliability of the communication system, increase the diversity gain order, please refer to [link / reference]. Figure 2 The first embodiment of the present invention proposes a signal processing method based on modulation domain cyclic delay Doppler shift, including steps S10 to S30:

[0079] Step S10: Obtain the signal vector to be transmitted from the transmitting antenna, and perform modulation domain cyclic delay Doppler shift on the signal vector to be transmitted to obtain the modulation domain signal vector. The modulation domain cyclic delay Doppler shift includes cyclic delay shift and cyclic Doppler shift.

[0080] Please see Figure 3 This invention is implemented in the modulation domain. Specifically, before modulating the transmitted signal, the transmitted signal symbols in the modulation domain are first modulated using a modulation-domain cyclic delay-Doppler shift (MD-CDDS) at different transmitting antennas, and then modulated into the time domain. That is, assuming that for the t-th symbol (t = 2, ..., N)... t The vector of the signal to be transmitted from the transmitting antenna x zz conduct Step-by-step cyclic delay shift and Step-by-step cyclic Doppler shift, denoted as The modulation domain signal vector is obtained by performing MD-CDDS, and the specific steps are as follows:

[0081] Step S101: Based on the number of shift steps and the time-delay Doppler waveform of the signal vector to be transmitted, obtain the corresponding modulation domain cyclic shift matrix, wherein the number of shift steps includes the number of time-delay shift steps and the number of Doppler shift steps;

[0082] Step S102, performing modulation domain cyclic shift on the to-be-sent signal vector according to the modulation domain cyclic shift matrix, to obtain a modulation domain signal vector.

[0083] The application realizes cyclic time delay shift and cyclic Doppler shift through a designed modulation domain cyclic shift matrix. However, due to different time delay Doppler waveforms of communication antennas, the modulation domain modulation process of the to-be-sent signal is different for different waveforms. Since typical time delay Doppler waveforms include orthogonal time frequency space (OTFS) and affine frequency division multiplexing (AFDM), the modulation of the two waveforms is described as follows.

[0084] Step S1011a, if the time delay Doppler waveform is OTFS, performing cyclic time delay shift and cyclic Doppler shift on the to-be-sent signal vector according to the time delay shift step number and the Doppler shift step number respectively, to obtain a first cyclic matrix and a second cyclic matrix.

[0085] Step S1012a, calculating a first modulation domain cyclic shift matrix according to the first cyclic matrix and the second cyclic matrix.

[0086] (a) OTFS system based on MD-CDDS

[0087] Please refer to Figure 4 OTFS modulates signal symbols in a two-dimensional time delay-Doppler domain, so the to-be-sent signal vector X OTFS is a matrix with a size of N×M, the row direction is the Doppler axis, and the column direction is the time delay axis.

[0088] Define x OTFS = vec(X OTFS ), the vec(.) operator represents that the input matrix is converted into an NM×1 vector along the column direction of the input matrix, and then the NM×1 vector is rearranged into an N×M matrix. Therefore, the OTFS step cyclic time delay shift of X can be obtained by the following operation:

[0089]

[0090] wherein,

[0091]

[0092] The OTFS step cyclic Doppler shift of X can be obtained by the following operation:

[0093]

[0094] where the operator denotes the Hadamard product:

[0095]

[0096] then The implementation of the step MD-CDDS in X OTFS is:

[0097]

[0098] Therefore, the OFTS has The modulation domain cyclic shift matrix of the step MD-CDDS is:

[0099]

[0100] In step S1011b, if the time delay Doppler type waveform is an affine frequency division multiplexing, a transform domain shift step number is calculated according to the time delay shift step number and the Doppler shift step number.

[0101] In step S1012b, a discrete affine Fourier transform domain cyclic shift is performed on the to-be-sent signal vector according to the transform domain shift step number, to obtain a third cyclic matrix.

[0102] In step S1013b, a second modulation domain cyclic shift matrix is calculated according to the third cyclic matrix and a phase compensation matrix.

[0103] (b) MD-CDDS-based AFDM system

[0104] Please refer to Figure 5 In the AFDM system, the expression of the channel in the one-dimensional DAFT domain can be regarded as the dimension reduction of the two-dimensional time delay Doppler channel by means of time delay block splicing, and therefore, the AFDM to-be-sent signal vector X AFDM can be subjected to Δm steps of DAFT domain cyclic shift to realize Step MD-CDDS, wherein

[0105]

[0106] It should be particularly noted that, in order to ensure that the new branch after the cyclic Doppler shift is still in the original time delay block, the k s in the AFDM parameter c1 should be set to that is:

[0107]

[0108] wherein This represents the maximum value of the cyclic Doppler shift made by all transmitting antennas.

[0109] The following is the derivation of AFDM. The modulation domain cyclic shift matrix of MD-CDDS is first processed by X. AFDM The vector representation of a DAFT-domain cyclic shift of Δm steps is as follows:

[0110]

[0111] After performing a DAFT domain cyclic shift, the received signal vector in equation (3) becomes:

[0112]

[0113] in, and These represent the new time delay and the new Doppler, respectively.

[0114] The modulus phase factor ε(m′, Δm) in formula (12) is:

[0115]

[0116] Gain phase factor in formula (12) for:

[0117]

[0118] Since the modulus phase factor ε(m′, Δm) and the channel attenuation factor h i Delay i and Doppler K i Since they are irrelevant, they can be eliminated beforehand at the transmitting end by multiplying by a diagonal phase compensation matrix, which is:

[0119]

[0120] The vector of the signal to be transmitted is processed using formulas (11) and (15). Step MD-CDDS is equivalent to simultaneously performing P-slice path segmentation on the original channel. Step-by-step cyclic delay shift and The step-by-step cyclic Doppler shift, and the exponential constant attached to the equivalent fading coefficient. It will not change the original fading coefficient h i The amplitude of AFDM can be obtained from formulas (11) and (15). The step MD-CDDS modulation domain cyclic shift matrix is:

[0121]

[0122] then Step MD-CDDS in X AFDM is implemented as:

[0123]

[0124] Step S20, time delay Doppler-like modulation is performed on the modulation domain signal vector to obtain a first time domain signal vector.

[0125] Step S30, a cyclic prefix is added to the first time domain signal vector to obtain a second time domain signal vector, and the second time domain signal vector is sent to a double fading wireless channel.

[0126] After the modulation domain cyclic shift is performed on the to-be-sent signal, the modulation domain signal after modulation is subjected to time delay Doppler-like modulation according to the original processing flow of the communication system model, and after a cyclic prefix is added, it is sent to a double fading wireless channel. The time domain signal vector is received by the receiving end antenna from the double fading wireless channel, the cyclic prefix is removed, and time delay Doppler-like demodulation is performed, so as to obtain a received signal vector.

[0127] In the OTFS system based on MD-CDDS, according to The definition of Step MD-CDDS can be obtained as:

[0128]

[0129] Substitute formula (18) into formula (2), then:

[0130]

[0131] That is:

[0132] wherein, which are respectively represented as Step MD-CDDS, the equivalent fading coefficient, the equivalent Doppler, and the equivalent time delay of the i-th branch of the channel after MD-CDDS, denotes the actual equivalent Doppler frequency shift, denotes the actual equivalent time domain shift.

[0133] As can be seen from formula (19), the time delay Doppler domain signal vector in formula (2) is subjected to Step MD-CDDS is equivalent to simultaneously performing Step cyclic time delay shift and Step cyclic Doppler shift on the P branches of the channel originally, and the exponential constant attached by the equivalent fading coefficient does not change the amplitude of the original fading coefficient h i .

[0134] In an AFDM system based on MD-CDDS, the demodulated received signal vector can be represented as:

[0135]

[0136] in, They are respectively represented as The equivalent fading coefficient, equivalent delay, and equivalent Doppler of the i-th path of the channel after step MD-CDDS.

[0137] The following section analyzes the performance of the MD-CDDS method provided by this invention. Let PATH = {(k1, l1), ..., (k P , l P Let )} be the set of time-domain Doppler parameter pairs of the original channel multipath, then This indicates that the antenna at the t-th transmitting end is performing... The set of equivalent time-domain Doppler parameter pairs after step MD-CDDS.

[0138]

[0139] After using MD-CDDS, both the transmitting and receiving ends have There are multiple paths with different time delays or different Doppler frequencies, where |.| represents the cardinality of the set, i.e., the number of elements, therefore N t ×N r The diversity order of the system is

[0140] When the set PATH [ALL] cardinality | PATH [ALL] |=N t When P, the set There are no common elements between any two pairs of N. t ×N r The diversity order of the system is N t PN r In other words, the diversity order obtained using the MD-CDDS method provided by this invention is increased by N compared to the diversity order of the system before MD-CDDS was applied. t This represents a multiple, meaning full transmit diversity gain is achieved. Since the reflectors in the channel are sparse, the condition [PATH]... [ALL] |=N t In practical applications, the number of MD-CDDS steps for each antenna can be adjusted in advance based on experience to obtain full transmit diversity gain.

[0141] As can be seen, the technical solution provided by this invention does not require any changes to the receiving end, and the derived MD-CDDS matrix... is a sparse permutation matrix, i.e. there is only one non-zero value in each row and each column, which is only related to the MD-CDDS step number and is irrelevant to the fast changing channel. Therefore, the MD-CDDS matrix only needs to be calculated once at the transmitting end with extremely low computational complexity and can be used all the time, which is simple to operate. Compared with the classic Alamouti transmit diversity method which needs at least two information symbol vectors time to achieve, the MD-CDDS is completed within one information symbol vector time, has no limit to the number of transmitting antennas, and is particularly suitable for high-mobility scenarios such as vehicle networks, unmanned aerial vehicle clusters and space-air-ground integrated wireless communication systems with high reliability and low transmission delay.

[0142] It should be particularly pointed out that the present application is applied before the modulation operation and can be regarded as a precoding operation on the transmitted signal. Therefore, the present application can be combined with other precoding operations to achieve the effect of joint precoding without increasing the load of the transmitting end, has strong scalability, and provides the derivation of the MD-CDDS matrix of the most typical two delay-Doppler type waveforms OTFS and AFDM at present. The derivation process can provide theoretical guidance for the matrix derivation of other waveforms, thereby laying a theoretical foundation for the expansion of the signal processing method based on MD-CDDS to other delay-Doppler type waveforms.

[0143] The performance of the above-mentioned signal processing method based on modulation domain cyclic delay-Doppler shift in OTFS and AFDM systems is verified by numerical simulation, and the bit-error-rate (BER) is used as the evaluation standard for channel estimation accuracy. The number of paths between each pair of transmitting and receiving antennas is 2, the time-domain Doppler parameter pairs of the two paths are [-1, 0] and [1, 0], the OTFS parameters are: Δf OTFS = 20 kHz, N OTFS = 5, M OTFS = 2, the AFDM parameters are: subcarrier spacing Δf AFDN = 4 kHz, the number of subcarriers is N AFDN = 10, which ensures that the two signals occupy the same communication time-frequency resources, and the corresponding maximum moving speed is 1080 kilometers per hour at the carrier frequency f c = 4 GHz fc. Other main simulation parameters are shown in Table 1, in which the maximum likelihood detector is the most commonly used optimal detector. The ratio of the time-domain received data signal power to the noise power is denoted as SNR (signal-to-noise ratio). The simulation parameters are shown in Table 1:

[0144] System parameters Values Carrier frequency 4 GHz Maximum Doppler shift 4 kHz Maximum moving speed 1,080 kmph Number of multipaths 2 Digital modulation method BPSK Detector Maximum likelihood detector

[0145] Table 1 System parameter settings

[0146] Please refer to Figure 6 , Figure 6 The bit error rate comparison of OTFS and AFDM systems under different antenna settings is shown, auxiliary lines of diversity gain orders p = 2, p = 4 and p = 8 are provided for convenient observation, first, it can be seen that the diversity orders of OTFS and AFDM in a single-input single-output communication system, a 2x1 communication system and a 2x2 communication system are 2, 4 and 8 respectively, which indicates that both the latter two systems obtain full transmit diversity gain 2, that is, the number of transmit antennas, which is consistent with the result of the method provided by the application, and from Figure 5 It can also be seen that the bit error rate of the 2x1 MD-CDDS-OTFS system using the application is much better than that of the traditional 2x1 Alamouti-OTFS system, because the latter requires a fast variable path to remain unchanged within two information symbol vectors time, which is impossible to achieve in a high-speed mobile scenario, which also embodies the great low-latency superiority of the MD-CDDS system provided by the application.

[0147] The signal processing method based on modulation domain cyclic delay Doppler shift provided by the embodiment can obtain full transmit diversity gain, and can be used in all delay Doppler class waveform communication systems, which includes most 6G candidate waveforms and has strong robustness, and the application also provides the derivation of the MD-CDDS matrix of the two most typical delay Doppler class waveforms, which lays a theoretical foundation for the expansion of the signal processing method based on MD-CDDS to other delay Doppler class waveforms, the signal processing method based on modulation domain cyclic delay Doppler shift provided by the application has lower processing complexity, better effect, occupies fewer communication resources, has stronger practical application, and has more abundant practical application scenarios.

[0148] Please refer to Figure 7 , based on the same inventive concept, the signal processing system based on modulation domain cyclic delay Doppler shift provided by the second embodiment of the application comprises:

[0149] The delay Doppler shift module 10 is configured to obtain a to-be-sent signal vector of a transmit-end antenna, perform modulation domain cyclic delay Doppler shift on the to-be-sent signal vector, and obtain a modulation domain signal vector, wherein the modulation domain cyclic delay Doppler shift comprises cyclic delay shift and cyclic Doppler shift.

[0150] a time delay Doppler modulation module 20, configured to perform time delay Doppler modulation on the modulation domain signal vector to obtain a first time domain signal vector;

[0151] a cyclic prefix adding module 30, configured to add a cyclic prefix to the first time domain signal vector to obtain a second time domain signal vector, and send the second time domain signal vector to the double-fading wireless channel.

[0152] Further, the time delay Doppler shifting module 10 further comprises:

[0153] a shift matrix generating module 101, configured to obtain a modulation domain cyclic shift matrix according to a shift step number and a time delay Doppler waveform of the to-be-sent signal vector, the shift step number comprising a time delay shift step number and a Doppler shift step number;

[0154] a cyclic shift module 102, configured to perform modulation domain cyclic shift on the to-be-sent signal vector according to the modulation domain cyclic shift matrix to obtain a modulation domain signal vector.

[0155] Further, the shift matrix generating module 101 further comprises:

[0156] a first matrix generating module 1011, configured to, if the time delay Doppler waveform is orthogonal time frequency space, perform cyclic time delay shift and cyclic Doppler shift on the to-be-sent signal vector according to the time delay shift step number and the Doppler shift step number respectively to obtain a first cyclic matrix and a second cyclic matrix, and calculate a first modulation domain cyclic shift matrix according to the first cyclic matrix and the second cyclic matrix;

[0157] a second matrix generating module 1012, configured to, if the time delay Doppler waveform is affine frequency division multiplexing, calculate a transform domain shift step number according to the time delay shift step number and the Doppler shift step number, perform discrete affine Fourier transform domain cyclic shift on the to-be-sent signal vector according to the transform domain shift step number to obtain a third cyclic matrix, and calculate a second modulation domain cyclic shift matrix according to the third cyclic matrix and a phase compensation matrix.

[0158] The technical features and technical effects of the signal processing system based on modulation domain cyclic time delay Doppler shifting proposed in the embodiments of the present application are the same as those of the method proposed in the embodiments of the present application, and will not be repeated here.

[0159] In summary, the signal processing method and system based on modulation domain cyclic delay Doppler shift proposed in the embodiments of the present application, the method obtains a to-be-sent signal vector of a transmitting end antenna, performs modulation domain cyclic delay Doppler shift on the to-be-sent signal vector to obtain a modulation domain signal vector, the modulation domain cyclic delay Doppler shift includes cyclic delay shift and cyclic Doppler shift, performs delay Doppler modulation on the modulation domain signal vector to obtain a first time domain signal vector, adds a cyclic prefix to the first time domain signal vector to obtain a second time domain signal vector, and sends the second time domain signal vector to a double-fading wireless channel. The present application not only can obtain full transmit diversity gain, but also can be used in a communication system using all delay Doppler waveforms, has strong robustness, the present application also provides derivation of MD-CDDS matrices of two most typical delay Doppler waveforms, lays a theoretical foundation for expansion of the signal processing method based on MD-CDDS to other delay Doppler waveforms, and the signal processing method based on modulation domain cyclic delay Doppler shift provided by the present application has lower processing complexity, better effect, occupies less communication resources, has stronger practical applicability, and has more abundant practical application scenarios compared with the existing signal processing method.

[0160] Each of the embodiments in the specification is described in a progressive manner, and the same or similar parts of each of the embodiments can be referred to each other, and each of the embodiments mainly describes the difference from other embodiments. Especially, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the related parts can be referred to the part of the method embodiment. It should be noted that, each of the technical features of the above embodiments can be combined arbitrarily, in order to make the description simple, each of the technical features of the above embodiments is not described all possible combinations, however, as long as the combination of the technical features does not exist contradictory, it should be considered that it is within the scope of the present application.

[0161] The above-described embodiments only express several preferred embodiments of the present application, the description is more specific and detailed, but it should not be understood as the limitation of the patent scope of the present application. It should be noted that, for ordinary skilled in the art, without departing from the technical principles of the present application, a number of improvements and replacements can be made, and these improvements and replacements should be regarded as the protection scope of the present application. Therefore, the patent protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A signal processing method based on modulation domain cyclic time delay Doppler shift, characterized in that, The method comprises the following steps: obtaining a to-be-sent signal vector of a sending-end antenna, performing modulation-domain cyclic time-delay Doppler shift on the to-be-sent signal vector to obtain a modulation-domain signal vector, wherein the modulation-domain cyclic time-delay Doppler shift comprises cyclic time-delay shift and cyclic Doppler shift; performing time-delay Doppler modulation on the modulation-domain signal vector to obtain a first time-domain signal vector; adding a cyclic prefix to the first time-domain signal vector to obtain a second time-domain signal vector, and sending the second time-domain signal vector to a double-fading wireless channel; wherein the step of performing modulation-domain cyclic time-delay Doppler shift on the to-be-sent signal vector to obtain a modulation-domain signal vector comprises: obtaining a corresponding modulation-domain cyclic shift matrix according to a shift step number and a time-delay Doppler waveform of the to-be-sent signal vector, wherein the shift step number comprises a time-delay shift step number and a Doppler shift step number; performing modulation-domain cyclic shift on the to-be-sent signal vector according to the modulation-domain cyclic shift matrix to obtain a modulation-domain signal vector; the step of obtaining a corresponding modulation-domain cyclic shift matrix according to a shift step number and a time-delay Doppler waveform of the to-be-sent signal vector comprises: if the time-delay Doppler waveform is orthogonal time-frequency-space, performing cyclic time-delay shift and cyclic Doppler shift on the to-be-sent signal vector according to the time-delay shift step number and the Doppler shift step number respectively to obtain a first cyclic matrix and a second cyclic matrix; calculating a first modulation-domain cyclic shift matrix according to the first cyclic matrix and the second cyclic matrix; if the time-delay Doppler waveform is affine frequency division multiplexing, calculating a transform-domain shift step number according to the time-delay shift step number and the Doppler shift step number; performing discrete affine Fourier transform-domain cyclic shift on the to-be-sent signal vector according to the transform-domain shift step number to obtain a third cyclic matrix; calculating a second modulation-domain cyclic shift matrix according to the third cyclic matrix and a phase compensation matrix.

2. The signal processing method based on modulation domain cyclic time delay Doppler shift according to claim 1, characterized in that, The first modulation-domain cyclic shift matrix is expressed by the following formula: In the formula, denotes the time delay shift step number, denotes the Doppler shift step number, OTFS denotes orthogonal time frequency space, MD-CDDS denotes modulation domain cyclic time delay Doppler shift, N OTFS denotes the Doppler sampling number, M OTFS denotes the time delay sampling number, denotes the first cyclic matrix, denotes the second cyclic matrix, denotes the unit matrix; The second modulation-domain cyclic shift matrix is expressed by the following formula: In the formula, AFDM represents affine frequency division multiplexing, and Δm represents a transform domain shift step number. represents the number of AFDM subcarriers, represents a third cyclic matrix, represents a phase compensation matrix, wherein, k s represents an interval factor, k max represents the maximum normalized Doppler shift.

3. The signal processing method based on modulation domain cyclic time delay Doppler shift according to claim 2, characterized in that, the step of performing modulation-domain cyclic shift on the to-be-sent signal vector according to the modulation-domain cyclic shift matrix to obtain a modulation-domain signal vector comprises: if the time-delay Doppler waveform of the to-be-sent signal is orthogonal time-frequency-space, the modulation-domain signal vector is expressed by the following formula: x OTFS = vec(X OTFS ) In the formula, X OTFS represents the time delay Doppler waveform as a quadrature time-frequency space to-be-sent signal vector; if the time-delay Doppler waveform of the to-be-sent signal is affine frequency division multiplexing, the modulation-domain signal vector is expressed by the following formula: In the formula, X AFDM The time delay Doppler waveform is an affine frequency division multiplexing to-be-sent signal vector.

4. The signal processing method based on modulation domain cyclic time delay Doppler shift according to claim 1, characterized in that, after the second time-domain signal vector is sent to the double-fading wireless channel, the method further comprises the following steps: obtaining a third time-domain signal vector from the double-fading wireless channel through a receiving-end antenna, removing the cyclic prefix in the third time-domain signal vector to obtain a fourth time-domain signal vector; performing time-delay Doppler demodulation on the fourth time-domain signal vector to obtain a received signal vector.

5. The signal processing method based on modulation domain cyclic time delay Doppler shift according to claim 4, characterized in that, the step of performing time-delay Doppler demodulation on the fourth time-domain signal vector to obtain a received signal vector comprises: If the time delay Doppler class waveform of the to-be-sent signal is orthogonal time frequency space, the following formula is used to represent the received signal vector: where k represents an index of a Doppler axis, l represents an index of a delay axis, P represents a number of sub-paths of a double-fading wireless channel, i represents an i-th sub-path, and respectively represent an equivalent fading coefficient, an equivalent Doppler, and an equivalent delay of the i-th sub-path of the double-fading wireless channel after modulation-domain cyclic delay-Doppler shifting, representing an actual equivalent Doppler frequency shift, representing an actual equivalent delay shift, OTFS representing a time-delay-Doppler waveform of a to-be-transmitted signal vector of an orthogonal time-frequency-space, N OTFS representing a number of Doppler samples, M OTFS representing a number of delay samples; If the time delay Doppler class waveform of the to-be-sent signal is affine frequency division multiplexing, the following formula is used to represent the received signal vector: wherein m represents an index of a discrete affine Fourier transform domain, and respectively represent an equivalent fading coefficient, an equivalent Doppler and an equivalent delay of the i-th branch of the double-fading wireless channel after modulation-domain cyclic delay Doppler shifting, X AFDM represents a time-delay Doppler waveform, and represents an AFDM subcarrier number, and c1 and c2 are parameters of the AFDM.

6. A signal processing system based on modulation domain cyclic time delay Doppler shift characterized by, The method comprises the following steps: A time delay Doppler shift module is configured to obtain a to-be-sent signal vector of a transmitting end antenna, and to perform modulation domain cyclic time delay Doppler shift on the to-be-sent signal vector to obtain a modulation domain signal vector, wherein the modulation domain cyclic time delay Doppler shift comprises cyclic time delay shift and cyclic Doppler shift; A time delay Doppler modulation module is configured to perform time delay Doppler modulation on the modulation domain signal vector to obtain a first time domain signal vector; A cyclic prefix adding module is configured to add a cyclic prefix to the first time domain signal vector to obtain a second time domain signal vector, and to send the second time domain signal vector to a double-fading wireless channel. The time delay Doppler shift module further comprises: A shift matrix generating module is configured to obtain a corresponding modulation domain cyclic shift matrix according to a shift step number and a time delay Doppler class waveform of the to-be-sent signal vector, wherein the shift step number comprises a time delay shift step number and a Doppler shift step number; A cyclic shift module is configured to perform modulation domain cyclic shift on the to-be-sent signal vector according to the modulation domain cyclic shift matrix to obtain a modulation domain signal vector; The shift matrix generating module further comprises: A first matrix generating module is configured to, if the time delay Doppler class waveform is orthogonal time frequency space, perform cyclic time delay shift and cyclic Doppler shift on the to-be-sent signal vector according to the time delay shift step number and the Doppler shift step number, respectively, to obtain a first cyclic matrix and a second cyclic matrix; and to calculate a first modulation domain cyclic shift matrix according to the first cyclic matrix and the second cyclic matrix; A second matrix generating module is configured to, if the time delay Doppler class waveform is affine frequency division multiplexing, calculate a transform domain shift step number according to the time delay shift step number and the Doppler shift step number; to perform discrete affine Fourier transform domain cyclic shift on the to-be-sent signal vector according to the transform domain shift step number to obtain a third cyclic matrix; and to calculate a second modulation domain cyclic shift matrix according to the third cyclic matrix and a phase compensation matrix.

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