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CN107819709B - Method and device for detecting moving target - Google Patents

Method and device for detecting moving target Download PDF

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Publication number
CN107819709B
CN107819709B CN201711024002.4A CN201711024002A CN107819709B CN 107819709 B CN107819709 B CN 107819709B CN 201711024002 A CN201711024002 A CN 201711024002A CN 107819709 B CN107819709 B CN 107819709B
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digital baseband
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CN107819709A (en
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李蠡
魏华
黄铫
姚尧
陈功
凌未未
杜江
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Chengdu University of Information Technology
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0222—Estimation of channel variability, e.g. coherence bandwidth, coherence time, fading frequency
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/04—Systems determining presence of a target
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
    • H04L25/023—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols
    • H04L25/0232—Channel estimation using sounding signals with direct estimation from sounding signals with extension to other symbols by interpolation between sounding signals

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Abstract

The embodiment of the invention provides a method and a device for detecting a moving target, which are used for improving the detection precision of the moving target and reducing the software and hardware cost of detection. The method comprises the following steps: 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 a signal which is obtained by performing OTFS modulation on a preset delay Doppler domain symbol, performing one-dimensional inverse Fourier transform, performing digital-to-analog conversion, and transmitting the signal indoors through the radio frequency module; performing OTFS signal demodulation on the time domain digital baseband signal to obtain channel estimation of a delay Doppler domain; based on the channel estimates, the number of moving targets is determined.

Description

Method and device for detecting moving target
Technical Field
The invention relates to the technical field of steel rolling, in particular to a method and a device for detecting a moving target.
Background
In the prior art, a receiver based on an OFDM (Orthogonal Frequency Division Multiplexing) technology is usually used to detect RSSI (Reference Signal Strength) changes of a transmitted Signal, and then determine whether a moving target exists, because the RSSI value is greatly deviated within a period of time and is mainly affected by multiple factors such as target movement, channel fading, and shielding, the random jitter of the RSSI cannot be eliminated by using a differential method, and whether a plurality of moving targets exist cannot be accurately detected, so that the detection method has a high false detection rate.
In the prior art, a moving target can be detected by an active radar imaging technology, a transmitter actively transmits signals of a radar, a receiver detects the number of multiple moving targets by receiving radar echoes reflected by a moving object and a static object, and the wall penetrating performance is poor because the working carrier of the traditional radar signals generally works at tens of GHz or even tens of GHz. Better through-wall performance can be achieved by increasing power or assembling a plurality of transmitting and receiving antennas, but the goals of miniaturization and low power consumption of the radio frequency module cannot be achieved. Moreover, the radar signal needs a strong digital signal processor or FPGA for processing, and the software and hardware implementation cost is high.
Therefore, the moving target detection mode in the prior art has the technical problems that the detection precision is high and the software and hardware realization cost is low.
Disclosure of Invention
The embodiment of the invention provides a method and a device for detecting a moving target, which are used for improving the detection precision of the moving target and reducing the software and hardware cost of detection.
In a first aspect, the present invention provides a method for detecting a moving object, the method comprising:
receiving a digital signal transmitted by a radio Frequency module, converting the digital signal into a Time domain digital baseband signal, wherein the digital signal is a signal which is transmitted indoors by the radio Frequency module after performing OTFS (Orthogonal Time Frequency Space) modulation on a preset delay Doppler domain symbol, performing one-dimensional inverse Fourier transform, and performing digital-to-analog conversion;
performing OTFS signal demodulation on the time domain digital baseband signal to obtain channel estimation of a delay Doppler domain;
based on the channel estimates, the number of moving targets is determined.
Optionally, the converting the digital signal into a time-domain digital baseband signal includes:
and performing down-conversion processing and analog-to-digital conversion on the digital signal to obtain a time domain digital baseband signal.
Optionally, the digital signal is further added with a preset frame header, and the performing OTFS signal demodulation on the time domain digital baseband signal specifically includes:
performing 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;
and performing OTFS signal demodulation on the aligned time domain digital baseband signals.
Optionally, the determining the number of moving targets based on the channel estimation includes:
performing correlation operation on the channel estimation to obtain a correlation matrix;
performing eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue;
based on the at least one characteristic value, a number of moving objects is determined.
Optionally, the determining the number of moving targets based on the at least one feature value includes:
acquiring the number of characteristic values which are larger than a preset threshold value in the at least one characteristic value;
and determining the number of the characteristic values larger than a preset threshold value in the at least one characteristic value as the number of the moving targets.
Optionally, the preset delay doppler domain symbol is correspondingly provided with a preset delay doppler domain pilot frequency, the preset delay doppler domain pilot frequency is set based on the number | v | of doppler positive frequency offset and the number | l | of channel delay, in the delay doppler domain corresponding to the preset delay doppler domain symbol, real numbers a and-a are alternately inserted at a 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), and the rest positions are determined to be 0.
In a second aspect, an embodiment of the present invention provides a moving object detection apparatus, where the apparatus includes:
the radio frequency module is used for receiving a digital signal transmitted by the radio frequency module and converting the digital signal into a time domain digital baseband signal, wherein the digital signal is a signal which is transmitted indoors after the radio frequency module carries out OTFS modulation on a preset delay Doppler domain symbol, and then the signal is subjected to one-dimensional inverse Fourier transform and digital-to-analog conversion;
the channel estimation module is used for carrying out OTFS signal demodulation on the time domain digital baseband signal to obtain channel estimation of a delay Doppler domain;
a determining module for determining the number of moving objects based on the channel estimates.
Optionally, when the radio frequency module converts the digital signal into a time domain digital baseband signal, the radio frequency module is specifically configured to:
and performing down-conversion processing and analog-to-digital conversion on the digital signal to obtain a time domain digital baseband signal.
Optionally, the digital signal is further added with a preset frame header, and the channel estimation module is specifically configured to, when performing OTFS signal demodulation on the time domain digital baseband signal:
performing 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;
and performing OTFS signal demodulation 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 correlation operation on the channel estimation to obtain a correlation matrix;
performing 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 the determining the number of moving objects based on the at least one characteristic value comprises:
acquiring the number of characteristic values which are larger than a preset threshold value in the at least one characteristic value;
and determining the number of the characteristic values larger than a preset threshold value in the at least one characteristic value as the number of the moving targets.
Optionally, the preset delay doppler domain symbol is correspondingly provided with a preset delay doppler domain pilot frequency, the preset delay doppler domain pilot frequency is set based on the number | v | of doppler positive frequency offset and the number | l | of channel delay, in the delay doppler domain corresponding to the preset delay doppler domain symbol, real numbers a and-a are alternately inserted at a delay doppler domain position x (v, l), where x (0, 0) ═ a, x (v, 1) ═ x (v-1, 1), x (1, f) ═ x (1, l-1), and the rest positions are determined to be 0.
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 scheme of the embodiment of the invention, the radio frequency module transmits the preset delay Doppler domain symbol to an indoor space after OTFS modulation, one-dimensional inverse Fourier transform and digital-to-analog conversion, the radio frequency module receives a corresponding digital signal after the transmitted signal is reflected by a moving target, converts the digital signal into a time domain digital baseband signal and demodulates the time domain digital baseband signal through the OTFS signal to obtain a corresponding channel estimation, and the obtained channel estimation is analyzed to determine the number of the moving targets in the space. The scheme in the application has lower requirements on the radio frequency module, can realize the sending and receiving of signals only through a single antenna, has a simple structure of digital signals sent by the radio frequency module, has a constant envelope characteristic, can simplify the design of a radio frequency circuit, and reduces the design requirements of the radio frequency circuit. In addition, the device can work in free frequency bands of 2.4GHz and 5.8GHz, has good wall penetrating performance, and can ensure higher detection precision. Therefore, the detection precision of the moving target can be effectively improved, and the software and hardware cost of detection is reduced.
Drawings
Fig. 1 is a flowchart of a moving object detection method according to a first embodiment of the present application;
fig. 2 is a schematic diagram of a pilot design according to a first embodiment of the present application;
fig. 3 is a schematic illustration of OTFS modulation provided in the first embodiment of the present application;
fig. 4 is a schematic diagram of a complete example of a moving object detection method according to a first embodiment of the present application;
fig. 5 is a schematic structural diagram of a moving object detection apparatus according to a second embodiment of the present application.
Detailed Description
The embodiment of the invention provides a moving target detection method, which is used for improving the detection precision of a moving target and reducing the software and hardware cost of detection. The method comprises the following steps: 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 a signal which is obtained by performing OTFS modulation on a preset delay Doppler domain symbol, performing one-dimensional inverse Fourier transform, performing digital-to-analog conversion, and transmitting the signal indoors through the radio frequency module; performing OTFS signal demodulation on the time domain digital baseband signal to obtain channel estimation of a delay Doppler domain; based on the channel estimates, the number of moving targets is determined.
The technical solutions of the present invention are described in detail below with reference to the drawings and specific embodiments, and it should be understood that the specific features in the embodiments and examples of the present invention are described in detail in the technical solutions of the present application, and are not limited to the technical solutions of the present application, and the technical features in the embodiments and examples of the present application may be combined with each other without conflict.
The term "and/or" herein is merely an association describing an associated object, meaning that three relationships may exist, e.g., a and/or B, may mean: a exists alone, A and B exist simultaneously, and B exists alone. In addition, the character "/" herein generally indicates that the former and latter related objects are in an "or" relationship.
Referring to fig. 1, the method for detecting a moving object provided by the present invention includes the following steps:
s101: 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 a signal which is obtained by performing OTFS modulation on a preset delay Doppler domain symbol, performing one-dimensional inverse Fourier transform, performing digital-to-analog conversion, and transmitting the signal indoors through the radio frequency module;
s102: performing OTFS signal demodulation on the time domain digital baseband signal to obtain channel estimation of a delay Doppler domain;
s103: based on the channel estimates, the number of moving targets is determined.
The preset delay doppler domain symbol is correspondingly provided with a preset delay doppler domain pilot frequency, the preset delay doppler domain pilot frequency is set based on the number | v | of doppler positive frequency offset and the number | l | of channel delay, in the delay doppler domain corresponding to the preset delay doppler domain symbol, real numbers a and-a are alternately inserted at a delay doppler domain position x (v, l), wherein x (0, 0) ═ a, x (ν, 1) ═ x (ν -1, 1), x (1, l) ═ x (1, l-1), and the rest positions are determined to be 0.
And the radio frequency module performs down-conversion processing and analog-to-digital conversion on the digital signal to obtain a time domain digital baseband signal.
Specifically, in this implementation, the transmitting antenna and the receiving antenna of the radio frequency module work simultaneously, the radio frequency module performs OTFS modulation on a preset delay doppler domain symbol, converts the OTFS modulation into a time domain digital baseband signal through one-dimensional inverse fourier transform, converts the time domain digital baseband signal into a digital signal through digital-to-analog conversion, transmits the digital signal to the indoor through the transmitting antenna of the radio frequency module, reflects the digital signal if a moving target exists in the indoor, receives the reflected digital signal through the receiving antenna of the radio frequency module, and performs down-conversion and analog-to-digital conversion on the received digital signal to obtain the time domain digital baseband signal.
The preset delay doppler domain symbol in this embodiment is a symbol obtained by mapping a symbol that needs to be subjected to OTFS modulation to a delay doppler domain, where the preset delay doppler domain symbol is correspondingly provided with a preset delay doppler domain pilot frequency, the preset delay doppler domain pilot frequency is set based on a number | v | of doppler positive frequency offset and a number | l | of channel delay, and real numbers a and-a are alternately inserted into corresponding positions x (v, l) of the delay doppler domain, where x (0, 0) ═ a, x (v, 1) ═ x (v-1, 1) and x (1, l) ═ x (1, l-1), and the remaining positions are determined to be 0. When v is 5 and l is 5, the pilot design diagram is shown in fig. 2. The pilot frequency design method can effectively eliminate the influence of a static channel (a channel which is not a moving target), and the channel estimation for eliminating the influence of the static channel can be obtained after the simplest two-dimensional new Fourier inverse transformation is adopted.
Further, in the present embodiment, OTFS is used to modulate a symbol in a preset delay-doppler domain, and OTFS modulation is a novel modulation method that is proposed by cohere corporation in 2016 and can be used for 5G communication. Unlike the OFDM modulation scheme adopted in the conventional 4G, the OTFS modulation maps the symbol to be modulated to the delay-doppler domain first, instead of the frequency domain mapped by the conventional OFDM modulation scheme. Firstly, the symbols mapped to the delay Doppler domain are mapped to the whole time-frequency domain through two-dimensional sine Fourier transform. And then transformed into a time domain signal by a conventional one-dimensional inverse fast fourier transform. And finally, converting the time domain signal into an analog signal through digital-to-analog conversion, and transmitting the analog signal through radio frequency. The main difference between the whole process and the conventional OFDM modulation is that a novel two-dimensional sinc fourier transform module is added, and the whole OTFS modulation process is shown in fig. 3.
The two-dimensional octree transform can be described by the following equation (1):
Figure GDA0002443063990000071
wherein v represents integer Doppler frequency offset caused by a time-varying channel, l represents the l-th channel delay, N represents the number of OFDM symbols, K represents the number of OFDM subcarriers, N represents the nth OFDM symbol time, and K represents the kth OFDM subcarrier. x (n, k) is the signal of the kth subcarrier at the nth time, and x (v, l) is the symbol to be modulated delayed by the ith channel of the vth integer frequency shift of Doppler frequency. The symbol may be any modulated constellation symbol such as BPSK, QPSK, QAM, etc.
The one-dimensional inverse fourier transform can be described by the following equation (2):
Figure GDA0002443063990000072
where x (n, t) is represented as the signal at the t-th time instant within the n-th OFDM symbol time. Through the formula (1) and the formula (2), the modulation symbols are transformed from the delay-Doppler domain to the time domain. The OTFS demodulation is the inverse process of OTFS modulation, so that the demodulated OTFS can be obtained by the above inverse process
Figure GDA0002443063990000073
A 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 converts the symbol into a time domain digital baseband signal through one-dimensional inverse fourier transform, a preset frame header needs to be added to the time domain baseband digital signal. The frame format adopted in the embodiment can adopt various sequences to design the preset frame header, and can be set according to actual needs in the specific implementation process, so that the method is not limited in the application.
Furthermore, the digital signal obtained by performing analog-to-digital conversion on the time domain baseband digital signal added with the preset frame header has the preset frame header, and when the OTFS signal is demodulated on the time domain digital baseband signal, the method can be realized by the following steps:
performing 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;
and performing OTFS signal demodulation on the aligned time domain digital baseband signals.
Specifically, after converting the digital signal into a time domain digital baseband signal, performing frame header detection on the time domain digital baseband signal through a matched filter, where a mathematical expression of the matched filter is described in the following formula (3):
Figure GDA0002443063990000081
r (t) represents the received digital baseband signal, c*(t) represents the conjugate of the time domain frame header, and a (τ) represents the output of the matched filter at the τ -th time instant. Therefore, when a (τ) is greater than a predetermined threshold B, the frame header is considered to have been detected, and the alignment is followed by subsequent digital baseband signal processing, whereUnlike conventional communication signal processing, no compensation for frequency offset is required. Therefore, the time domain digital baseband signals are aligned and then subjected to OTFS signal demodulation, and the OTFS signals are demodulated into the inverse process of OTFS modulation, so that the demodulated OTFS signals can be obtained through the inverse process
Figure GDA0002443063990000082
A signal.
Further, in this embodiment, due to the special design method of the default pilot, a channel estimate including delay doppler domains with effective v and l numbers can be obtained through a simple two-dimensional inverse fourier transform. Assuming that the digital baseband signal corresponding to the receiving antenna is y (n, t), firstly, through one-dimensional fourier transform, the mathematical expression of the digital baseband signal corresponding to the receiving antenna in the time-frequency domain is as shown in equation (4):
Figure GDA0002443063990000083
then, the time-frequency domain signal in the formula (4) is subjected to two-dimensional Fourier transform to obtain the following formula (5),
Figure GDA0002443063990000084
i.e. the obtained channel estimate of the delay-doppler domain, i.e. the recovered one
Figure GDA0002443063990000085
Figure GDA0002443063990000086
Further, after obtaining the channel estimation corresponding to the received digital signal, the method may determine the number of moving targets based on the channel estimation, and specifically may include the following steps:
performing correlation operation on the channel estimation to obtain a correlation matrix;
performing eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue;
based on the at least one characteristic value, a number of moving objects is determined.
Wherein the determining the number of moving objects based on the at least one characteristic value comprises:
acquiring the number of characteristic values which are larger than a preset threshold value in the at least one characteristic value;
and determining the number of the characteristic values larger than a preset threshold value in the at least one characteristic value as the number of the moving targets.
Specifically, in this embodiment, it is necessary to obtain channel estimates
Figure GDA0002443063990000091
And (3) carrying out correlation operation, wherein the operation adopts the formula (6):
Figure GDA0002443063990000092
according to R in formula (6)u，φThe correlation matrix xi is reconstructed. Decomposing the eigenvalues of the matrix xi to obtain formula (7):
Ξvi＝λivi(7)
videnotes the ith feature vector, λiIndicating the ith characteristic value. The eigenvalue decomposition described above can effectively separate the channel estimate and noise into two domains. Secondly, because the special pilot design already eliminates the influence of the static channel, the residual channel estimation is the channel reflected by the moving target, and the transmission channel of the moving target has a larger eigenvalue and the noise has a smaller eigenvalue. Therefore, if the eigenvalue λiIf the value is greater than η, the channel is considered to be a channel reflected by a moving target, and it can be confirmed that a moving target is detected0The value is large and therefore the dc component needs to be subtracted from the final number calculation.
A complete embodiment of the moving object detection method in this embodiment is given below, and referring to fig. 4, first, the transmitting antenna and the receiving antenna operate simultaneously. The radio frequency module carries out OTFS modulation on a preset delay Doppler domain symbol, converts the symbol into a time domain digital baseband signal through one-dimensional inverse Fourier transform, then adds a preset frame header to the time domain baseband digital signal, converts the signal into a digital signal through a digital-analog mode, and transmits the digital signal to the indoor through the radio frequency module.
The indoor moving target reflects the digital signal to a receiving antenna, after the receiving antenna receives the digital signal, the receiving antenna performs down-conversion processing and analog-to-digital conversion on the digital signal through a radio frequency module to obtain a time domain digital baseband signal, and performs frame header detection on the time domain digital baseband signal through a matched filter. And aligning the digital signals after detecting the frame headers.
And then, performing OTFS signal demodulation on the aligned digital signals to obtain channel estimation of a delay Doppler domain, performing correlation operation on the obtained channel estimation and the conjugate of the channel estimation to obtain a correlation matrix, and performing eigenvalue decomposition on the correlation matrix to finally obtain an eigenvalue.
And finally, judging the number of the moving targets according to the characteristic value threshold. When the characteristic value is greater than a predetermined threshold value, i.e. λiη, determining that there are moving targets, and if N eigenvalues are greater than the preset threshold η, then there are N moving targets.
In such a way, the influence of a static channel is eliminated by setting a special pilot frequency, accurate channel estimation reflected by the moving target is obtained, and when eigenvalue decomposition is carried out on a matrix reconstructed by channel estimation, the channel estimation and noise can be effectively separated into two domains, so that the quantity of the indoor moving targets can be accurately determined according to the accurate channel estimation reflected by the moving target. The scheme in the embodiment has low requirements on the radio frequency module, can realize the transmission and the reception of signals only through a single antenna, has a simple structure of digital signals transmitted by the radio frequency module, has a constant envelope characteristic, can simplify the design of the radio frequency circuit, and reduces the design requirements of the radio frequency circuit. In addition, the device can work in free frequency bands of 2.4GHz and 5.8GHz, has good wall penetrating performance, and can ensure higher detection precision. Therefore, the detection precision of the moving target can be effectively improved, and the software and hardware cost of detection is reduced.
Referring to fig. 5, a second embodiment of the present invention provides a moving object detecting apparatus, including:
a radio frequency module 501, configured to 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 a signal that is transmitted indoors after the radio frequency module performs OTFS modulation on a preset delay doppler domain symbol, and then performs one-dimensional inverse fourier transform and 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 of a delay doppler domain;
a determining module 503, configured to determine the number of moving objects based on the channel estimation.
The preset delay doppler domain symbol is correspondingly provided with a preset delay doppler domain pilot frequency, the preset delay doppler domain pilot frequency is set based on the number | v | of doppler positive frequency offset and the number | l | of channel delay, in the delay doppler domain corresponding to the preset delay doppler domain symbol, real numbers a and-a are alternately inserted at a delay doppler domain position x (v, l), wherein x (0, 0) ═ a, x (v, 1) ═ x (v-1, 1), x (1, l) ═ x (1, l-1), and the rest positions are determined to be 0.
And the radio frequency module performs down-conversion processing and analog-to-digital conversion on the digital signal to obtain a time domain digital baseband signal.
Specifically, in this implementation, the transmitting antenna and the receiving antenna of the radio frequency module work simultaneously, the radio frequency module performs OTFS modulation on a preset delay doppler domain symbol, converts the OTFS modulation into a time domain digital baseband signal through one-dimensional inverse fourier transform, converts the time domain digital baseband signal into a digital signal through digital-to-analog conversion, transmits the digital signal to the indoor through the transmitting antenna of the radio frequency module, reflects the digital signal if a moving target exists in the indoor, receives the reflected digital signal through the receiving antenna of the radio frequency module, and performs down-conversion and analog-to-digital conversion on the received digital signal to obtain the time domain digital baseband signal.
The preset delay doppler domain symbol in this embodiment is a symbol obtained by mapping a symbol that needs to be subjected to OTFS modulation to a delay doppler domain, where the preset delay doppler domain symbol is correspondingly provided with a preset delay doppler domain pilot frequency, the preset delay doppler domain pilot frequency is set based on a number | v | of doppler positive frequency offset and a number | l | of channel delay, and real numbers a and-a are alternately inserted into corresponding positions x (v, l) of the delay doppler domain, where x (0, 0) ═ a, x (ν, 1) ═ x (ν -1, 1) and x (1, l) ═ x (1, l-1), and the remaining positions are determined to be 0. When v is 5 and l is 5, the pilot design diagram is shown in fig. 2. The pilot frequency design method can effectively eliminate the influence of a static channel (a channel which is not a moving target), and the channel estimation for eliminating the influence of the static channel can be obtained after the simplest two-dimensional new Fourier inverse transformation is adopted.
Further, in the present embodiment, an OTFS modulation method is used to modulate a symbol in a preset delay-doppler domain, and the OTFS modulation is a novel modulation method that is proposed by the american coehere company in 2016 and can be used for 5G communication. Unlike the OFDM modulation scheme adopted in the conventional 4G, the OTFS modulation maps the symbol to be modulated to the delay-doppler domain first, instead of the frequency domain mapped by the conventional OFDM modulation scheme. Firstly, the symbols mapped to the delay Doppler domain are mapped to the whole time-frequency domain through two-dimensional sine Fourier transform. And then transformed into a time domain signal by a conventional one-dimensional inverse fast fourier transform. And finally, converting the time domain signal into an analog signal through digital-to-analog conversion, and transmitting the analog signal through radio frequency. The main difference between the whole process and the conventional OFDM modulation is that a novel two-dimensional sinc fourier transform module is added, and the whole OTFS modulation process is shown in fig. 3.
The two-dimensional octree transform can be described by the following equation (1):
Figure GDA0002443063990000121
wherein v represents integer Doppler frequency offset caused by a time-varying channel, l represents the l-th channel delay, N represents the number of OFDM symbols, K represents the number of OFDM subcarriers, N represents the nth OFDM symbol time, and K represents the kth OFDM subcarrier. x (n, k) is the signal of the kth subcarrier at the nth time, and x (v, l) is the symbol to be modulated delayed by the ith channel of the vth integer frequency shift of Doppler frequency. The symbol may be any modulated constellation symbol such as BPSK, QPSK, QAM, etc.
The one-dimensional inverse fourier transform can be described by the following equation (2):
Figure GDA0002443063990000122
where x (n, t) is represented as the signal at the t-th time instant within the n-th OFDM symbol time. Through the formula (1) and the formula (2), the modulation symbols are transformed from the delay-doppler domain to the time domain. The OTFS demodulation is the inverse process of the OTFS modulation, so the channel estimation module 502 can obtain the demodulated OTFS modulation through the above inverse process
Figure GDA0002443063990000123
A 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 converts the symbol into a time domain digital baseband signal through one-dimensional inverse fourier transform, a preset frame header needs to be added to the time domain baseband digital signal. The frame format adopted in the embodiment can adopt various sequences to design the preset frame header, and can be set according to actual needs in the specific implementation process, so that the method is not limited in the application.
Furthermore, when the digital signal channel estimation module 502 with the preset frame header, which is obtained after the analog-to-digital conversion of the time domain baseband digital signal added with the preset frame header, performs OTFS signal demodulation on the time domain digital baseband signal, the module is specifically configured to:
performing 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;
and performing OTFS signal demodulation 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, where a mathematical expression of the matched filter is described in the following formula (3):
Figure GDA0002443063990000131
r (t) represents the received digital baseband signal, c*(t) represents the conjugate of the time domain frame header, and a (τ) represents the output of the matched filter at the τ -th time instant. Therefore, when a (τ) is greater than a predetermined threshold B, it can be considered that the predetermined frame header has been detected, and subsequent digital baseband signal processing can be performed after alignment, where unlike conventional communication signal processing, frequency offset does not need to be compensated. Therefore, the channel estimation module 502 aligns the time domain digital baseband signals and then demodulates the OTFS signals, and the OTFS signals are demodulated to be the inverse process of the OTFS modulation, so that the demodulated signals can be obtained through the inverse process
Figure GDA0002443063990000132
A signal.
Further, in this embodiment, due to the special design method of the default pilot, a channel estimate including delay doppler domains with effective v and l numbers can be obtained through a simple two-dimensional inverse fourier transform. Assuming that the receiving antenna digital baseband signal is y (n, t), firstly, through one-dimensional fourier transform, the mathematical expression of the receiving antenna digital baseband signal in the time-frequency domain is as shown in equation (4):
Figure GDA0002443063990000133
then, the time-frequency domain signal in the formula (4) is subjected to two-dimensional Fourier transform to obtain the following formula (5),
Figure GDA0002443063990000134
i.e. the obtained channel estimate of the delay-doppler domain, i.e. the recovered one
Figure GDA0002443063990000135
Figure GDA0002443063990000136
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 configured to:
performing correlation operation on the channel estimation to obtain a correlation matrix;
performing eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue;
based on the at least one characteristic value, a number of moving objects is determined.
Wherein the determining the number of moving objects based on the at least one characteristic value comprises:
acquiring the number of characteristic values which are larger than a preset threshold value in the at least one characteristic value;
and determining the number of the characteristic values larger than a preset threshold value in the at least one characteristic value as the number of the moving targets.
Specifically, in this embodiment, the determining module 503 needs to obtain the channel estimation
Figure GDA0002443063990000142
And (3) carrying out correlation operation, wherein the operation adopts the formula (6):
Figure GDA0002443063990000141
according to R in formula (6)μ，φThe correlation matrix xi is reconstructed. Decomposing the eigenvalues of the matrix xi to obtain formula (7):
Ξvi＝λivi(7)
videnotes the ith feature vector, λiIndicating the ith characteristic value. The eigenvalue decomposition described above can effectively separate the channel estimate and noise into two domains. Secondly, because the special pilot design already eliminates the influence of the static channel, the residual channel estimation is the channel reflected by the moving target, and the transmission channel of the moving target has a larger eigenvalue and the noise has a smaller eigenvalue. Thus, if the determination module 503 determines the eigenvalues λiIf the channel is greater than η and is considered to be the channel reflected by the moving object, it can be confirmed that a moving object is detected, all the characteristic values are compared with η to obtain the number of the final detected objects0The value is large and therefore the dc component needs to be subtracted from the final number calculation.
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 scheme of the embodiment of the invention, the radio frequency module transmits the preset delay Doppler domain symbol to an indoor space after OTFS modulation, one-dimensional inverse Fourier transform and digital-to-analog conversion, the radio frequency module receives a corresponding digital signal after the transmitted signal is reflected by a moving target, converts the digital signal into a time domain digital baseband signal and demodulates the time domain digital baseband signal through the OTFS signal to obtain a corresponding channel estimation, and the obtained channel estimation is analyzed to determine the number of the moving targets in the space. The scheme in the application has lower requirements on the radio frequency module, can realize the sending and receiving of signals only through a single antenna, has a simple structure of digital signals sent by the radio frequency module, has a constant envelope characteristic, can simplify the design of a radio frequency circuit, and reduces the design requirements of the radio frequency circuit. In addition, the device can work in free frequency bands of 2.4GHz and 5.8GHz, has good wall penetrating performance, and can ensure higher detection precision. Therefore, the detection precision of the moving target can be effectively improved, and the software and hardware cost of detection is reduced.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such 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 such modifications and variations.

Claims (8)

1. A method for detecting a moving object, comprising:
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 generated by converting a preset delay doppler domain symbol based on OTFS modulation, the preset delay doppler domain symbol is correspondingly provided with a preset delay doppler domain pilot frequency, the preset delay doppler domain pilot frequency is set based on the number | v | of doppler positive frequency offset and the number of channel delays, and in a delay doppler domain corresponding to the preset delay doppler domain symbol, real numbers a and-a are alternately inserted at a 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), and the rest positions are determined to be 0;
performing OTFS signal demodulation on the time domain digital baseband signal to obtain channel estimation of a delay Doppler domain;
based on the channel estimates, the number of moving targets is determined.
2. The method of claim 1, wherein said converting the digital signal to a time-domain digital baseband signal comprises:
and performing down-conversion processing and analog-to-digital conversion on the digital signal to obtain a time domain digital baseband signal.
3. The method according to claim 1, wherein a preset frame header is further added to the digital signal, and the performing OTFS signal demodulation on the time-domain digital baseband signal specifically includes:
performing 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;
and performing OTFS signal demodulation on the aligned time domain digital baseband signals.
4. The method of any of claims 1-3, wherein the determining the number of moving objects based on the channel estimate comprises:
performing correlation operation on the channel estimation to obtain a correlation matrix;
performing eigenvalue decomposition on the correlation matrix to obtain at least one eigenvalue;
based on the at least one characteristic value, a number of moving objects is determined.
5. The method of claim 4, wherein determining the number of moving objects based on the at least one eigenvalue comprises:
acquiring the number of characteristic values which are larger than a preset threshold value in the at least one characteristic value;
and determining the number of the characteristic values larger than a preset threshold value in the at least one characteristic value as the number of the moving targets.
6. A moving object detecting apparatus, characterized in that the apparatus comprises:
a radio frequency module for receiving the digital signal transmitted by the radio frequency module and converting the digital signal into a time domain digital baseband signal, wherein the digital signal is generated by converting a preset delay Doppler domain symbol based on OTFS modulation, the preset delay Doppler domain symbol is correspondingly provided with a preset delay Doppler domain pilot frequency, the preset delay Doppler domain pilot frequency is set based on the number | v | of Doppler positive frequency offset and the number | l | of channel delay, in the delay Doppler domain corresponding to the preset delay Doppler domain symbol, real numbers A and-A are alternately inserted at a delay Doppler domain position x (v, l), wherein x (0, 0) ═ a, x (v, 1) ═ x (v-1, 1), x (1, l) ═ x (1, l-1), and the remaining positions are determined to be 0;
the channel estimation module is used for carrying out OTFS signal demodulation on the time domain digital baseband signal to obtain channel estimation of a delay Doppler domain;
a determining module for determining the number of moving objects based on the channel estimates.
7. The apparatus of claim 6, wherein the digital signal is further added with a preset frame header, and the channel estimation module is specifically configured to, when performing OTFS signal demodulation on the time-domain digital baseband signal:
performing 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;
and performing OTFS signal demodulation on the aligned time domain digital baseband signals.
8. The apparatus of claim 6 or 7, wherein the determining module, when determining the number of moving objects based on the channel estimate, is specifically configured to:
performing correlation operation on the channel estimation to obtain a correlation matrix;
performing 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 the determining the number of moving objects based on the at least one characteristic value comprises:
acquiring the number of characteristic values which are larger than a preset threshold value in the at least one characteristic value;
and determining the number of the characteristic values larger than a preset threshold value in the at least one characteristic value as the number of the moving targets.
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