CN107819709B - A method and device for moving target detection - Google Patents

Abstract

Embodiments of the present invention provide a method and device for detecting moving objects, which are used to improve the detection accuracy of moving objects and reduce the cost of software and hardware for detection. The method includes: receiving a digital signal transmitted by a radio frequency module, and converting the digital signal into a time-domain digital baseband signal, wherein the digital signal is OTFS modulated on a preset delay Doppler domain symbol, and then passed through a one-dimensional After inverse Fourier transform, the signal transmitted indoors through the radio frequency module after digital-to-analog conversion; OTFS signal demodulation is performed on the time-domain digital baseband signal to obtain a channel estimation in the delayed Doppler domain; based on the channel estimation , to determine the number of moving objects.

Description

A method and device for moving target detection

technical field

The invention relates to the technical field of steel rolling, in particular to a method and a device for detecting moving objects.

Background technique

In the prior art, the non-contact detection of multiple indoor moving objects is realized through wireless signals, and a receiver based on the OFDM (Orthogonal Frequency Division Multiplexing, Orthogonal Frequency Division Multiplexing) technology is usually used to detect the RSSI (Reference Signal of the transmitted signal) Strength Indicator, reference signal strength) changes, and then determine whether there is a moving target. Since the RSSI value deviates greatly within a period of time, it is mainly affected by multiple factors such as target movement, channel fading, and occlusion. The differential method cannot be eliminated. The random jitter of the reference signal strength RSSI cannot accurately detect whether there are multiple moving targets. Therefore, this detection method has a high false detection rate.

In the prior art, moving targets can also be detected by active radar imaging technology, the transmitter actively transmits radar signals, and the receiver detects the number of moving targets by receiving radar echoes reflected by moving objects and stationary objects. The working carrier of the radar signal generally works at a dozen GHz or even dozens of GHz, and the wall penetration performance is poor. Better through-the-wall performance can be achieved by increasing the power or assembling multiple transmitting and receiving antennas, but the goals of miniaturization and low power consumption of the radio frequency module cannot be achieved. In addition, the radar signal needs a strong digital signal processor or FPGA for processing, and the cost of software and hardware is high.

Therefore, the moving target detection method in the prior art has the technical problem that it cannot have both high detection accuracy and low software and hardware implementation cost.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a method and device for detecting moving objects, which are used to improve the detection accuracy of moving objects and reduce the cost of software and hardware for detection.

In a first aspect, the present invention provides a method for moving target detection, the method comprising:

Receive a digital signal transmitted by the radio frequency module, and convert the digital signal into a time-domain digital baseband signal, where the digital signal is an OTFS (Orthogonal Time Frequency Space, orthogonal time-frequency space) performed on a preset delay Doppler domain symbol ) modulation, and then through the one-dimensional inverse Fourier transform, after the digital-to-analog conversion, the signal transmitted indoors by the radio frequency module;

performing OTFS signal demodulation on the time-domain digital baseband signal to obtain a channel estimate in the delayed Doppler domain;

Based on the channel estimates, the number of moving objects is determined.

Optionally, the converting the digital signal into a time-domain digital baseband signal includes:

After performing down-conversion processing and analog-to-digital conversion on the digital signal, a time-domain digital baseband signal is obtained.

Optionally, a preset frame header is added to the digital signal, and the OTFS signal demodulation performed on the time-domain digital baseband signal specifically includes:

Perform frame header detection on the time-domain digital baseband signal through a matched filter;

aligning the time-domain digital baseband signals when the frame header is detected;

OTFS signal demodulation is performed on the aligned time-domain digital baseband signals.

Optionally, the determining the number of moving targets based on the channel estimation includes:

performing a correlation operation on the channel estimate to obtain a correlation matrix;

Perform eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue;

Based on the at least one characteristic value, the number of moving objects is determined.

Optionally, the determining the number of moving targets based on at least one characteristic value includes:

acquiring the number of feature values that are greater than a preset threshold in the at least one feature value;

It is determined that the number of the feature values greater than the preset threshold in the at least one feature value is the number of moving objects.

Optionally, the preset delay Doppler domain symbol is correspondingly set with a preset delay Doppler domain pilot, and the preset delay Doppler domain pilot is based on the number of Doppler positive frequency offsets| v| and the number of channel delays |l| are set, in the delay Doppler domain corresponding to the preset delay Doppler domain symbol, the real numbers A and -A are alternately inserted in the delay Doppler domain position x(v, l), where x(0,0)=A, x(v,1)=-x(ν-1,1), x(1,l)=-x(1,l-1), the rest The position is determined to be 0.

In a second aspect, an embodiment of the present invention provides an apparatus for detecting a moving target, and the apparatus includes:

A radio frequency module, configured to receive a digital signal transmitted by the radio frequency module, and convert the digital signal into a time-domain digital baseband signal, wherein the digital signal is the radio frequency module performing OTFS on a preset delay Doppler domain symbol Modulation, and then through the one-dimensional inverse Fourier transform, the signal transmitted to the room after digital-to-analog conversion;

a channel estimation module, used for performing OTFS signal demodulation on the time-domain digital baseband signal to obtain channel estimation in the delayed Doppler domain;

and a determining module, configured to determine the number of moving objects based on the channel estimation.

Optionally, when the radio frequency module converts the digital signal into a time-domain digital baseband signal, it is specifically used for:

After performing down-conversion processing and analog-to-digital conversion on the digital signal, a time-domain digital baseband signal is obtained.

Optionally, a preset frame header is added to the digital signal, and the channel estimation module is specifically used for performing OTFS signal demodulation on the time-domain digital baseband signal:

Perform frame header detection on the time-domain digital baseband signal through a matched filter;

aligning the time-domain digital baseband signals when the frame header is detected;

OTFS signal demodulation is performed on the aligned time-domain digital baseband signals.

Optionally, when determining the number of moving targets based on the channel estimation, the determining module is specifically configured to:

performing a correlation operation on the channel estimate to obtain a correlation matrix;

Perform eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue;

determining the number of moving objects based on the at least one characteristic value;

Wherein, determining the number of moving targets based on at least one characteristic value includes:

acquiring the number of feature values that are greater than a preset threshold in the at least one feature value;

It is determined that the number of the feature values greater than the preset threshold in the at least one feature value is the number of moving objects.

Optionally, the preset delay Doppler domain symbol is correspondingly set with a preset delay Doppler domain pilot, and the preset delay Doppler domain pilot is based on the number of Doppler positive frequency offsets| v| and the number of channel delays |l| are set, in the delay Doppler domain corresponding to the preset delay Doppler domain symbol, the real numbers A and -A are alternately inserted in the delay Doppler domain position x(v, l), where x(0,0)=A, x(v,1)=-x(ν-1,1), x(1,f)=-x(1,l-1), the rest The position is determined to be 0.

The above-mentioned one or more technical solutions in the embodiments of the present application have at least one or more of the following technical effects:

In the technical solution of the embodiment of the present invention, the radio frequency module transmits the preset delay Doppler domain symbol to the indoor space after OTFS modulation, one-dimensional inverse Fourier transform and digital-to-analog conversion, and the transmitted signal is reflected by the moving target After that, the radio frequency module receives the corresponding digital signal, converts the digital signal into a time-domain digital baseband signal and demodulates the OTFS signal to obtain the corresponding channel estimate, and then analyzes the obtained channel estimate to determine the moving target in space quantity. The solution in this application has lower requirements for the radio frequency module, and can transmit and receive signals only through a single antenna. The digital signal sent by the radio frequency module has a simple structure and has constant envelope characteristics, which can simplify the design of the radio frequency circuit and reduce the RF circuit design requirements. Moreover, it can work in the 2.4GHz and 5.8GHz free frequency bands and has good wall penetration performance, which can ensure high detection accuracy. Therefore, the detection accuracy of the moving target can be effectively improved, and the hardware and software cost of the detection can be reduced.

Description of drawings

1 is a flowchart of a moving target detection method provided by a first embodiment of the present application;

FIG. 2 is a schematic diagram of a pilot frequency design provided by the first embodiment of the present application;

3 is a schematic diagram of OTFS modulation provided by the first embodiment of the present application;

4 is a schematic diagram of a complete example of the moving target detection method provided by the first embodiment of the present application;

FIG. 5 is a schematic structural diagram of a moving target detection apparatus provided by a second embodiment of the present application.

Detailed ways

The embodiment of the present invention provides a method for detecting a moving target, which is used to improve the detection accuracy of the moving target and reduce the cost of software and hardware for detection. The method includes: receiving a digital signal transmitted by a radio frequency module, and converting the digital signal into a time-domain digital baseband signal, wherein the digital signal is OTFS modulated on a preset delay Doppler domain symbol, and then passed through a one-dimensional After inverse Fourier transform, the signal transmitted indoors through the radio frequency module after digital-to-analog conversion; OTFS signal demodulation is performed on the time-domain digital baseband signal to obtain a channel estimation in the delayed Doppler domain; based on the channel estimation , to determine the number of moving targets.

The technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. If there is no conflict, the embodiments of the present application and the technical features in the embodiments may be combined with each other.

The term "and/or" in this article is only an association relationship to describe the associated objects, indicating that there can be three kinds of relationships, for example, A and/or B, it can mean that A exists alone, A and B exist at the same time, and A and B exist independently B these three cases. In addition, the character "/" in this document generally indicates that the related objects are an "or" relationship.

Please refer to FIG. 1 , the method for moving target detection provided by the present invention includes the following steps:

S101: Receive a digital signal transmitted by a radio frequency module, and convert the digital signal into a time-domain digital baseband signal, where the digital signal is OTFS modulated on a preset delay Doppler-domain symbol, and then subjected to one-dimensional inverse Fourier transform After the digital-to-analog conversion, the signal transmitted indoors through the radio frequency module;

S102: Perform OTFS signal demodulation on the time-domain digital baseband signal to obtain a channel estimate in the delayed Doppler domain;

S103: Determine the number of moving objects based on the channel estimation.

Wherein, the preset delay Doppler domain symbol is correspondingly set with a preset delay Doppler domain pilot frequency, and the preset delay Doppler domain pilot frequency is based on the number of Doppler positive frequency offsets |v| and the number of channel delays |l| set, in the delay Doppler domain corresponding to the preset delay Doppler domain symbol, the real numbers A and -A are alternately inserted in the delay Doppler domain position x(v, l) where, x(0,0)=A, x(ν,1)=-x(ν-1,1), x(1,l)=-x(1,l-1), the rest of the positions are determined is 0.

After the radio frequency module performs down-conversion processing and analog-to-digital conversion on the digital signal, a time-domain digital baseband signal is obtained.

Specifically, in this implementation, the transmitting antenna and the receiving antenna of the radio frequency module work at the same time, the radio frequency module performs OTFS modulation on the preset delay Doppler domain symbols, and then converts them into time-domain digital baseband signals through one-dimensional inverse Fourier transform, and then passes The digital-to-analog is converted into a digital signal, and the digital signal is transmitted to the room through the transmitting antenna of the radio frequency module. If there is a moving target in the room, the digital signal will be reflected, and the receiving antenna of the radio frequency module will receive the reflected digital signal, and the radio frequency module will then adjust the signal. After the received digital signal is subjected to down-conversion processing and analog-to-digital conversion, a time-domain digital baseband signal is obtained.

The preset delay Doppler domain symbol in this embodiment is a symbol obtained by mapping the symbol that needs to be subjected to OTFS modulation to the delay Doppler domain, and the preset delay Doppler domain symbol is correspondingly set with a preset delay Doppler domain Domain pilot, the preset delay Doppler domain pilot is set based on the number of Doppler positive frequency offsets |v| and the number of channel delays |l|, and the real numbers A and -A are alternately inserted into the delay Doppler Field corresponding position x(v,l), where x(0,0)=A, x(v,1)=-x(ν-1,1) and x(1,l)=-x(1 , l-1), and the rest of the positions are determined to be 0. When v=5, l=5, a schematic diagram of pilot design is shown in FIG. 2 . The pilot design method can effectively eliminate the influence of stationary channel (channel of non-moving target), and after adopting the simplest two-dimensional new Fourier transform, the channel estimation that eliminates the influence of stationary channel can be obtained.

Further, in this embodiment, OTFS is used to modulate the preset delay Doppler domain symbols, and OTFS modulation is a new modulation method proposed by American cohere company in 2016, which can be used for 5G communication. Different from the OFDM modulation method used in traditional 4G, OTFS modulation first maps the symbols to be modulated to the delay Doppler domain, rather than the frequency domain mapped by the traditional OFDM modulation method. First, the symbols mapped to the delayed Doppler domain are mapped to the entire time-frequency domain through a two-dimensional symplectic Fourier transform. It is then transformed into a time-domain signal through a traditional one-dimensional inverse fast Fourier transform. Finally, the time domain signal is converted into an analog signal through digital-to-analog conversion, and then transmitted through radio frequency. The main difference between the whole process and the traditional OFDM modulation is that a new two-dimensional symplectic Fourier transform module is added. The complete OTFS modulation process is shown in Figure 3.

The two-dimensional symplectic Fourier transform can be described by the following formula (1):

where v is the integer Doppler frequency offset caused by the time-varying channel, l is the lth channel delay, N is the number of OFDM symbols, K is the number of OFDM subcarriers, and n is the nth channel delay At the time of the OFDM symbol, k is represented as the kth OFDM subcarrier. x(n, k) is the signal of the k-th subcarrier at the n-th time, and x(v, l) is the symbol to be modulated with the v-th Doppler frequency integer frequency offset and the l-th channel delay. The symbol can be any modulated constellation symbol such as BPSK, QPSK, QAM and so on.

The one-dimensional inverse Fourier transform can be described by the following formula (2):

信号。Wherein, x(n, t) represents the signal at the t-th time in the n-th OFDM symbol time. After formula (1) and formula (2), the modulation symbol is transformed from the delayed Doppler domain to the time domain. OTFS demodulation is the inverse process of OTFS modulation, so the demodulated

Signal.

Further, in order to accurately receive the digital signal, in this embodiment, after the radio frequency module performs OTFS modulation on the preset delay Doppler domain symbol, and then converts it into a time-domain digital baseband signal through one-dimensional inverse Fourier transform, it also performs OTFS modulation. A preset frame header needs to be added to the time-domain baseband digital signal. Adding a preset frame header is mainly used for frame detection. The frame format used in this embodiment can use a variety of sequences to design the preset frame header. In the specific implementation process, it can be set according to actual needs. Here, this application does not make restrictions.

Furthermore, the digital signal obtained after analog-to-digital conversion of the time-domain baseband digital signal added with the preset frame header has a preset frame header. When performing OTFS signal demodulation on the time-domain digital baseband signal, the following steps can be used to achieve :

Perform frame header detection on the time-domain digital baseband signal through a matched filter;

aligning the time-domain digital baseband signals when the frame header is detected;

OTFS signal demodulation is performed on the aligned time-domain digital baseband signals.

Specifically, after the digital signal is converted into a time-domain digital baseband signal, frame header detection is performed on the time-domain digital baseband signal by a matched filter, and the mathematical expression of the matched filter is described in the following formula (3):

信号。r(t) represents the received digital baseband signal, c ^* (t) represents the conjugate of the time-domain frame header signal, and a(τ) represents the output of the matched filter at the τth moment. Therefore, when a(τ) is greater than a preset threshold B, it can be considered that the preset frame header has been detected, and subsequent digital baseband signal processing can be performed after alignment. Unlike conventional communication signal processing, frequency matching is not required. offset to compensate. Therefore, the OTFS signal demodulation is performed after aligning the time-domain digital baseband signals. The OTFS signal demodulation is the inverse process of the OTFS modulation. Therefore, the demodulated signal can be obtained through the above inverse process.

Signal.

Further, in this embodiment, due to the special design method of the preset pilot frequency, a channel estimation in the delayed Doppler domain including effective v and l numbers can be obtained through a simple two-dimensional inverse symplectic Fourier transform. Assuming that the digital baseband signal corresponding to the receiving antenna is y(n, t), first through one-dimensional Fourier transform, the mathematical expression of the digital baseband signal corresponding to the receiving antenna in the time-frequency domain is shown in formula (4):

即为获得的延迟多普勒域的信道估计，即为还原后的

Then the time-frequency domain signal in formula (4) is subjected to two-dimensional Fourier symplectic transform to obtain the following formula (5),

is the obtained channel estimate in the delayed Doppler domain, which is the restored

Further, after obtaining the channel estimate corresponding to the received digital signal, the number of moving targets may be determined based on the channel estimate, which may specifically include the following steps:

performing a correlation operation on the channel estimate to obtain a correlation matrix;

Perform eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue;

Based on the at least one characteristic value, the number of moving objects is determined.

Wherein, determining the number of moving targets based on at least one characteristic value includes:

acquiring the number of feature values that are greater than a preset threshold in the at least one feature value;

It is determined that the number of the feature values greater than the preset threshold in the at least one feature value is the number of moving objects.

进行相关运算，运算采用公式(6)：Specifically, in this embodiment, it is necessary to estimate the obtained channel

The correlation operation is carried out, and the operation adopts formula (6):

The correlation matrix Ξ is reconstructed according to R _{u, φ} in formula (6). Eigenvalue decomposition is performed on the above-mentioned matrix Ξ to obtain formula (7):

Ξv _i =λ _i v _i (7)

v _i represents the ith eigenvector, and λ _i represents the ith eigenvalue. The above eigenvalue decomposition can effectively separate channel estimation and noise into two domains. Secondly, because the special pilot design has eliminated the influence of the stationary channel, the remaining channel estimation is the channel reflected by the moving target, and the eigenvalue corresponding to the transmitting channel of the moving target is larger, while the eigenvalue corresponding to the noise is relatively large. Small. Therefore, if the characteristic value λ _i > η, and η is a preset threshold, it is considered that the channel is the channel reflected by the moving target, and it can be confirmed that a moving target is detected. Comparing all eigenvalues of i=0, 1, . . . , |v|-1 with the preset threshold η to obtain the final number of detection targets. It should be noted that the DC component causes the value of λ ₀ to be large, so the final number calculation needs to subtract the DC component.

A complete example of the moving target detection method in this embodiment is given below, please refer to FIG. 4 . First, the transmitting antenna and the receiving antenna work simultaneously. After the radio frequency module performs OTFS modulation on the preset delay Doppler domain symbol, it is converted into a time-domain digital baseband signal through one-dimensional inverse Fourier transform, and then the time-domain baseband digital signal is added to the preset frame header, and is converted into digital through digital-to-analog conversion. After the signal is transmitted, it is transmitted to the room through the radio frequency module.

The moving target indoors reflects the digital signal to the receiving antenna. After receiving the digital signal, the receiving antenna performs down-conversion processing and analog-to-digital conversion on the digital signal through the radio frequency module to obtain a time-domain digital baseband signal. The domain digital baseband signal is subjected to frame header detection through a matched filter. When the frame header is detected, the digital signals are aligned.

Furthermore, the aligned digital signals are demodulated by the OTFS signal to obtain a channel estimate in the delayed Doppler domain, the obtained channel estimate is subjected to a correlation operation with its own conjugate, a correlation matrix is obtained, and the correlation matrix is decomposed by eigenvalues, and finally Get eigenvalues.

Finally, the number of moving objects is determined according to the eigenvalue threshold. When the eigenvalue is greater than the preset threshold, that is, λ _i >n, it is determined that there are moving targets, and further, if there are N eigenvalues greater than the preset threshold η, there are N moving targets.

In this way, by setting a special pilot frequency, the influence of the stationary channel is eliminated, and the accurate channel estimation reflected by the moving target is obtained. It is effectively divided into two domains, and then the number of indoor moving targets can be accurately determined according to the accurate channel estimation reflected by the moving target. The solution in this embodiment has lower requirements for the radio frequency module, and can realize signal transmission and reception only through a single antenna. The digital signal sent by the radio frequency module has a simple structure and has constant envelope characteristics, which can simplify the design of the radio frequency circuit. Reduce RF circuit design requirements. Moreover, it can work in the 2.4GHz and 5.8GHz free frequency bands and has good wall penetration performance, which can ensure high detection accuracy. Therefore, the detection accuracy of the moving target can be effectively improved, and the hardware and software cost of the detection can be reduced.

Referring to FIG. 5 , a second embodiment of the present invention provides a moving target detection device, the device includes:

The radio frequency module 501 is configured to receive a digital signal transmitted by the radio frequency module, and convert the digital signal into a time-domain digital baseband signal, wherein the digital signal is the radio frequency module performing preset delay Doppler domain symbols on the signal. OTFS modulation, and then through the one-dimensional inverse Fourier transform, the signal transmitted to the room after digital-to-analog conversion;

a channel estimation module 502, configured to perform OTFS signal demodulation on the time-domain digital baseband signal to obtain a channel estimation in the delayed Doppler domain;

The determining module 503 is configured to determine the number of moving targets based on the channel estimation.

Wherein, the preset delay Doppler domain symbol is correspondingly set with a preset delay Doppler domain pilot frequency, and the preset delay Doppler domain pilot frequency is based on the number of Doppler positive frequency offsets |v| and the number of channel delays |l| set, in the delay Doppler domain corresponding to the preset delay Doppler domain symbol, the real numbers A and -A are alternately inserted in the delay Doppler domain position x(v, l) where, x(0,0)=A, x(v,1)=-x(ν-1,1), x(1,l)=-x(1,l-1), the rest of the positions are determined is 0.

After the radio frequency module performs down-conversion processing and analog-to-digital conversion on the digital signal, a time-domain digital baseband signal is obtained.

Specifically, in this implementation, the transmitting antenna and the receiving antenna of the radio frequency module work at the same time, the radio frequency module performs OTFS modulation on the preset delay Doppler domain symbols, and then converts them into time-domain digital baseband signals through one-dimensional inverse Fourier transform, and then passes The digital-to-analog is converted into a digital signal, and the digital signal is transmitted to the room through the transmitting antenna of the radio frequency module. If there is a moving target in the room, the digital signal will be reflected, and the receiving antenna of the radio frequency module will receive the reflected digital signal, and the radio frequency module will then adjust the signal. After the received digital signal is subjected to down-conversion processing and analog-to-digital conversion, a time-domain digital baseband signal is obtained.

The preset delay Doppler domain symbol in this embodiment is a symbol obtained by mapping the symbol that needs to be subjected to OTFS modulation to the delay Doppler domain, and the preset delay Doppler domain symbol is correspondingly set with a preset delay Doppler domain Domain pilot, the preset delay Doppler domain pilot is set based on the number of Doppler positive frequency offsets |v| and the number of channel delays |l|, and the real numbers A and -A are alternately inserted into the delay Doppler Domain corresponding position x(v,l), where x(0,0)=A, x(ν,1)=-x(ν-1,1) and x(1,l)=-x(1 , l-1), and the rest of the positions are determined to be 0. When v=5, l=5, a schematic diagram of pilot design is shown in FIG. 2 . The pilot design method can effectively eliminate the influence of stationary channel (channel of non-moving target), and after adopting the simplest two-dimensional new Fourier transform, the channel estimation that eliminates the influence of stationary channel can be obtained.

Further, this embodiment uses the OTFS modulation method to modulate the preset delay Doppler domain symbols, and the OTFS modulation is a new modulation method proposed by the American cohere company in 2016 that can be used for 5G communication. Different from the OFDM modulation method used in traditional 4G, OTFS modulation first maps the symbols to be modulated to the delay Doppler domain, rather than the frequency domain mapped by the traditional OFDM modulation method. First, the symbols mapped to the delayed Doppler domain are mapped to the entire time-frequency domain through a two-dimensional symplectic Fourier transform. It is then transformed into a time-domain signal through a traditional one-dimensional inverse fast Fourier transform. Finally, the time domain signal is converted into an analog signal through digital-to-analog conversion, and then transmitted through radio frequency. The main difference between the whole process and the traditional OFDM modulation is that a new two-dimensional symplectic Fourier transform module is added. The complete OTFS modulation process is shown in Figure 3.

The two-dimensional symplectic Fourier transform can be described by the following formula (1):

where v is the integer Doppler frequency offset caused by the time-varying channel, l is the lth channel delay, N is the number of OFDM symbols, K is the number of OFDM subcarriers, and n is the nth channel delay At the time of the OFDM symbol, k is represented as the kth OFDM subcarrier. x(n, k) is the signal of the k-th subcarrier at the n-th time, and x(v, l) is the symbol to be modulated with the v-th Doppler frequency integer frequency offset and the l-th channel delay. The symbol can be any modulated constellation symbol such as BPSK, QPSK, QAM and so on.

The one-dimensional inverse Fourier transform can be described by the following formula (2):

信号。Wherein, x(n, t) represents the signal at the t-th time in the n-th OFDM symbol time. After formula (1) and formula (2), the modulation symbol is transformed from the delayed Doppler domain to the time domain. OTFS demodulation is the inverse process of OTFS modulation, so the channel estimation module 502 can obtain the demodulated

Signal.

Further, in order to accurately receive the digital signal, in this embodiment, after the radio frequency module performs OTFS modulation on the preset delay Doppler domain symbol, and then converts it into a time-domain digital baseband signal through one-dimensional inverse Fourier transform, it also performs OTFS modulation. A preset frame header needs to be added to the time-domain baseband digital signal. Adding a preset frame header is mainly used for frame detection. The frame format used in this embodiment can use a variety of sequences to design the preset frame header. In the specific implementation process, it can be set according to actual needs. Here, this application does not make restrictions.

Furthermore, when the digital signal of the time-domain baseband digital signal added with the preset frame header is obtained after analog-to-digital conversion with the preset frame header, the channel estimation module 502 specifically uses the OTFS signal to demodulate the time-domain digital baseband signal. At:

Perform frame header detection on the time-domain digital baseband signal through a matched filter;

aligning the time-domain digital baseband signals when the frame header is detected;

OTFS signal demodulation is performed on the aligned time-domain digital baseband signals.

Specifically, after the radio frequency module 501 converts the digital signal into a time-domain digital baseband signal, the channel estimation module 502 performs frame header detection on the time-domain digital baseband signal through a matched filter, and the mathematical expression of the matched filter is as follows (3 )describe:

信号。r(t) represents the received digital baseband signal, c ^* (t) represents the conjugate of the time-domain frame header signal, and a(τ) represents the output of the matched filter at the τth moment. Therefore, when a(τ) is greater than a preset threshold B, it can be considered that the preset frame header has been detected, and subsequent digital baseband signal processing can be performed after alignment. Unlike conventional communication signal processing, frequency matching is not required. offset to compensate. Therefore, the channel estimation module 502 performs OTFS signal demodulation after aligning the time-domain digital baseband signals. The OTFS signal demodulation is the inverse process of OTFS modulation. Therefore, the demodulated signal can be obtained through the above inverse process.

Signal.

Further, in this embodiment, due to the special design method of the preset pilot frequency, a channel estimation in the delayed Doppler domain including effective v and l numbers can be obtained through a simple two-dimensional inverse symplectic Fourier transform. Assuming that the digital baseband signal of the receiving antenna is y(n, t), first through the one-dimensional Fourier transform, the mathematical expression of the digital baseband signal of the receiving antenna in the time-frequency domain is shown in formula (4):

即为获得的延迟多普勒域的信道估计，即为还原后的

Then the time-frequency domain signal in formula (4) is subjected to two-dimensional Fourier symplectic transform to obtain the following formula (5),

is the obtained channel estimate in the delayed Doppler domain, which is the restored

Further, after obtaining the channel estimation corresponding to the received digital signal, the determining module 503 may determine the number of moving targets based on the channel estimation, and the determining module 503 is specifically used for:

performing a correlation operation on the channel estimate to obtain a correlation matrix;

Perform eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue;

Based on the at least one characteristic value, the number of moving objects is determined.

Wherein, determining the number of moving targets based on at least one characteristic value includes:

acquiring the number of feature values that are greater than a preset threshold in the at least one feature value;

It is determined that the number of the feature values greater than the preset threshold in the at least one feature value is the number of moving objects.

进行相关运算，运算采用公式(6)：Specifically, in this embodiment, the determining module 503 needs to estimate the obtained channel

The correlation operation is carried out, and the operation adopts formula (6):

The correlation matrix Ξ is reconstructed according to R _{μ, φ} in formula (6). Eigenvalue decomposition is performed on the above-mentioned matrix Ξ to obtain formula (7):

Ξv _i =λ _i v _i (7)

v _i represents the ith eigenvector, and λ _i represents the ith eigenvalue. The above eigenvalue decomposition can effectively separate channel estimation and noise into two domains. Secondly, because the special pilot design has eliminated the influence of the stationary channel, the remaining channel estimation is the channel reflected by the moving target, and the eigenvalue corresponding to the transmitting channel of the moving target is larger, while the eigenvalue corresponding to the noise is relatively large. Small. Therefore, if the determining module 503 determines that the characteristic value λ _i >n, and n is a preset threshold, it is considered that the channel is the channel reflected by the moving target, and it can be confirmed that a moving target is detected. All feature values are compared with the preset threshold η to obtain the final number of detection targets. It should be noted that the DC component causes the value of λ ₀ to be large, so the final number calculation needs to subtract the DC component.

The above-mentioned one or more technical solutions in the embodiments of the present application have at least one or more of the following technical effects:

In the technical solution of the embodiment of the present invention, the radio frequency module transmits the preset delay Doppler domain symbol to the indoor space after OTFS modulation, one-dimensional inverse Fourier transform and digital-to-analog conversion, and the transmitted signal is reflected by the moving target After that, the radio frequency module receives the corresponding digital signal, converts the digital signal into a time-domain digital baseband signal and demodulates the OTFS signal to obtain the corresponding channel estimate, and then analyzes the obtained channel estimate to determine the moving target in space quantity. The solution in this application has lower requirements for the radio frequency module, and can transmit and receive signals only through a single antenna. The digital signal sent by the radio frequency module has a simple structure and has constant envelope characteristics, which can simplify the design of the radio frequency circuit and reduce the RF circuit design requirements. Moreover, it can work in the 2.4GHz and 5.8GHz free frequency bands and has good wall penetration performance, which can ensure high detection accuracy. Therefore, the detection accuracy of the moving target can be effectively improved, and the hardware and software cost of the detection can be reduced.

Although preferred embodiments of the present invention have been described, additional changes and modifications to these embodiments may occur to those skilled in the art once the basic inventive concepts are known. Therefore, the appended claims are intended to be construed to include the preferred embodiment and all changes and modifications that fall within the scope of the present invention.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Thus, provided that these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims (8)

1. a moving target detection method, is characterized in that, comprises: Receive a digital signal transmitted by the radio frequency module, and convert the digital signal into a time-domain digital baseband signal, wherein the digital signal is a digital signal generated by a preset delay Doppler domain symbol conversion based on OTFS modulation, and the preset delay The Doppler domain symbol is correspondingly set with a preset delay Doppler domain pilot, and the preset delay Doppler domain pilot is set based on the number of Doppler positive frequency offsets |v| and the number of channel delays , in the delayed Doppler domain corresponding to the preset delayed Doppler domain symbol, the real numbers A and -A are alternately inserted at the delayed Doppler domain position x(v, l), where x(0, 0) =A, x(v, 1)=-x(v-1, 1), x(1, l)=-x(1, l-1), and the rest of the positions are determined to be 0; performing OTFS signal demodulation on the time-domain digital baseband signal to obtain a channel estimate in the delayed Doppler domain; Based on the channel estimates, the number of moving objects is determined. 2. The method of claim 1, wherein the converting the digital signal into a time-domain digital baseband signal comprises: After performing down-conversion processing and analog-to-digital conversion on the digital signal, a time-domain digital baseband signal is obtained. 3. The method according to claim 1, wherein the digital signal is further added with a preset frame header, and the OTFS signal demodulation is performed on the time-domain digital baseband signal, specifically comprising: Perform frame header detection on the time-domain digital baseband signal through a matched filter; aligning the time-domain digital baseband signals when the frame header is detected; OTFS signal demodulation is performed on the aligned time-domain digital baseband signals. 4. The method according to any one of claims 1-3, wherein the determining the number of moving targets based on the channel estimation comprises: performing a correlation operation on the channel estimate to obtain a correlation matrix; Perform eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue; Based on the at least one characteristic value, the number of moving objects is determined. 5. The method of claim 4, wherein the determining the number of moving targets based on at least one characteristic value comprises: acquiring the number of feature values that are greater than a preset threshold in the at least one feature value; It is determined that the number of the feature values greater than the preset threshold in the at least one feature value is the number of moving objects. 6. A moving target detection device, wherein the device comprises: A radio frequency module, configured to receive a digital signal transmitted by the radio frequency module, and convert the digital signal into a time-domain digital baseband signal, wherein the digital signal is a digital signal generated by a preset delay Doppler domain symbol based on OTFS modulation and conversion signal, the preset delay Doppler domain symbol is correspondingly set with a preset delay Doppler domain pilot frequency, and the preset delay Doppler domain pilot frequency is based on the number of Doppler positive frequency offsets |v| and the number of channel delays |l| set, in the delay Doppler domain corresponding to the preset delay Doppler domain symbol, the real numbers A and -A are alternately inserted in the delay Doppler domain position x(v,l) where, x(0,0)=A, x(v,1)=-x(v-1,1), x(1,l)=-x(1,l-1), the rest of the positions are determined is 0; a channel estimation module, used for performing OTFS signal demodulation on the time-domain digital baseband signal to obtain channel estimation in the delayed Doppler domain; and a determining module, configured to determine the number of moving objects based on the channel estimation. 7. The apparatus according to claim 6, wherein the digital signal is further added with a preset frame header, and the channel estimation module is specifically used for performing OTFS signal demodulation on the time-domain digital baseband signal: Perform frame header detection on the time-domain digital baseband signal through a matched filter; aligning the time-domain digital baseband signals when the frame header is detected; OTFS signal demodulation is performed on the aligned time-domain digital baseband signals. 8. The apparatus according to claim 6 or 7, wherein the determining module is specifically configured to: when determining the number of moving targets based on the channel estimation: performing a correlation operation on the channel estimate to obtain a correlation matrix; Perform eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue; determining the number of moving objects based on the at least one characteristic value; Wherein, determining the number of moving targets based on at least one characteristic value includes: acquiring the number of feature values that are greater than a preset threshold in the at least one feature value; It is determined that the number of the feature values of the at least one feature value greater than the preset threshold is the number of moving objects.

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