Method for positioning in a narrow space based on specular reflection and time of arrival estimation

Abstract

The application discloses a positioning method in a long and narrow space based on mirror reflection and time of arrival estimation. The method comprises arranging a microphone and a loudspeaker in the long and narrow space, emitting a linear frequency modulation signal by using the loudspeaker, collecting the positioning signal reflected on the wall surface of the long and narrow space by using the microphone, filtering the collected positioning signal, and obtaining the signal propagation delay time. According to the frequency modulation continuous wave property, the intermediate frequency signal can be more accurately obtained based on the signal propagation delay time, and then the accurate signal arrival time of the signal source is obtained by using the intermediate frequency signal. According to the standard signal arrival time of the signal source, the optimal estimated position of the target is obtained based on the maximum likelihood estimation method, and then the position information of the target to be positioned is obtained. The method introduces a mirror signal source, has high precision and good robustness, and can accurately estimate the position of a moving target.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of indoor positioning, and particularly relates to a positioning method in a narrow space based on mirror reflection and time of arrival estimation. BACKGROUND

[0002] The background of narrow space positioning stems from the challenges faced by traditional indoor positioning techniques in narrow environments. Narrow spaces, such as corridors or alleys, have unique characteristics. Signals are easily affected by multi-path reflections of walls, ceilings, and floors, leading to signal interference and decreased positioning accuracy. Existing indoor positioning techniques, such as those based on LiDAR, UWB, WiFi, etc., often perform poorly in these environments. For example, UWB positioning accuracy decreases significantly in narrow spaces with a rectangular layout due to the increasing aspect ratio. In addition, technologies such as WiFi and Bluetooth can only provide meter-level accuracy, which cannot meet the needs of tasks requiring precise positioning, such as robot navigation and drone control.

[0003] In recent years, acoustic positioning technology has gained attention for its application in indoor environments, particularly in narrow spaces. Acoustic positioning involves base stations transmitting ultrasonic signals, which are received by receivers for position calculation. This technology has strong anti-interference capability and can achieve high-precision positioning even in noisy environments through filtering, cross-correlation, and other technical means. Acoustic positioning technology relies on high-precision time of arrival estimation. However, in narrow spaces, the transmitted signal will undergo multiple reflections on walls, floors, and ceilings before reaching the receiver. Additionally, deploying multiple base stations in narrow spaces not only increases system deployment costs but also further complicates the accurate calculation of signal arrival time at the receiver. Therefore, it is of great significance to utilize the mirror reflection characteristics of acoustic signals to implement virtual base stations and use the geometric constraints of narrow spaces to remove certain multi-path effects for acoustic positioning.

[0004] Some algorithms use special encoding methods to improve signal anti-multipath capability or use other sensors (such as IMU) to roughly estimate device position and correct the time of arrival estimation results based on the rough estimate. However, additional sensors often require strict data calibration and complex processing algorithms. In addition, while special encoding methods can address interference between multiple base stations to some extent, as the system's working range increases and the number of deployed base stations increases, special encoding schemes still cannot handle the interference caused by complex multi-path effects in narrow spaces, which not only leads to poor time of arrival estimation accuracy but also significantly increases the overall cost of the system due to redundant base stations. In summary, there is an urgent need for a method that can achieve position estimation using a single base station in narrow spaces. SUMMARY

[0005] To address the problems existing in the background art, the purpose of this invention is to provide a positioning method in a narrow space based on specular reflection and time of arrival estimation, which accurately estimates the position of the target to be located without relying on additional sensors.

[0006] The technical solution adopted in this invention includes the following steps:

[0007] Step S1: First, set up a microphone and a speaker in the narrow space. Use the speaker to emit a linear frequency modulation signal and use the microphone to collect the positioning signals reflected from the wall of the narrow space and those that are directly received.

[0008] The positioning signal includes echo signals reflected from the walls of the narrow space, as well as direct signals from the speaker to the microphone.

[0009] Step S2: Filter the positioning signal from step S1 to obtain the signal propagation delay time;

[0010] Step S3: Obtain the intermediate frequency signal based on the signal propagation delay time, and then use the intermediate frequency signal to obtain the signal arrival time of the signal source;

[0011] Step S4: Based on the arrival time of the signal from the signal source, obtain the optimal estimated position of the target using the maximum likelihood estimation method, and then obtain the position information of the target to be located.

[0012] The specific steps of S1 are as follows:

[0013] First, a loudspeaker is placed on the inner wall of the narrow space, and a microphone is installed on the target to be located. The loudspeaker emits a linear frequency modulated (LFM) signal, which is reflected on the wall of the narrow space, creating a virtual signal source outside the narrow space. The virtual signal source and the loudspeaker are symmetrically distributed with the inner wall of the narrow space as the plane of symmetry, and the distance between the virtual signal source and the target is equal to the sum of the distance from the LFM signal emitted by the loudspeaker to the reflection point on the inner wall of the narrow space and the distance from the reflection point on the inner wall of the narrow space to the target.

[0014] Both the loudspeaker and the virtual signal source are used as signal sources. The two signal sources emit their own linear frequency modulated signals toward the target. The signals emitted by the signal sources are collected by the microphone installed on the target after propagating in the narrow space.

[0015] The specific steps of step S2 are as follows:

[0016] Step S21: First, bandpass filter is applied to the positioning signal acquired in step S1 to select the signal in the frequency band where the linear frequency modulated signal is located as the frequency band signal s. r (t), frequency band signal s r The expression for (t) is as follows:

[0017]

[0018] Where α represents the attenuation coefficient; f0 represents the starting frequency of the linear frequency modulated (LFM) signal; B represents the bandwidth of the LFM signal; T represents the period of the LFM signal; π represents pi; and t represents the time variable. d Indicates the delay time of signal propagation;

[0019] Step S22: Then, using the linear frequency modulated signal emitted by the signal source as the reference signal x(t), obtain the filtered frequency band signal s. r The cross-correlation function R between (t) and the corresponding reference signal xs (τ):

[0020]

[0021] Where τ represents the time delay parameter;

[0022] Step S23: Finally, the peak extraction algorithm is used to calculate the cross-correlation function R between the frequency band signal and the reference signal. xs (τ) Peak extraction is performed to obtain the cross-correlation function R. xs The peak value of (τ), and according to the cross-correlation function R xs The peak value of (τ) yields the frequency band signal s. r The time difference between (t) and the reference signal is taken as the signal propagation delay time t of the positioning signal. d .

[0023] The specific steps of step S3 are as follows:

[0024] Step S31: First, utilize the signal propagation delay time t d For frequency band signal s r (t) is used for t-segmentation: q -τ a As the starting time for signal interception, t d -τ a +T is used as the termination time for signal interception in the frequency band signal s. r (t) is used to truncate the signal, and the truncated frequency band signal is used as the truncation signal s corresponding to the signal source. j (t), and process it according to the following formula to obtain the intermediate frequency signal s corresponding to the signal source. m (t):

[0025]

[0026] Where, τ ais a preset intercepting time length; T represents a period of the linear frequency modulation signal; a represents an attenuation coefficient; f0 represents a starting frequency of the linear frequency modulation signal; B represents a bandwidth of the linear frequency modulation signal; and t represents a time variable;

[0027] Step S32, performing a fast Fourier transform on the intermediate frequency signal s m (t) so that the intermediate frequency signal s m (t) is converted from a time domain signal to a frequency domain signal, and each frequency peak in the frequency domain signal is obtained as a candidate frequency f p

[0028] In fact, the intermediate frequency signals corresponding to the loudspeaker and the virtual signal source are in the same form.

[0029] Step S33, then, judging whether each candidate frequency f p is qualified, and obtaining a standard frequency f p corresponding to the loudspeaker and the virtual signal source respectively by using the qualified candidate frequency f p .

[0030] Step S34, then, according to the standard frequency f p ', processing the signal arrival time τ k according to the following formula:

[0031]

[0032] wherein τ k represents the time when the linear frequency modulation signal emitted by the signal source reaches the microphone.

[0033] The step S33 is specifically:

[0034] Step S331, first, according to the candidate frequency f p , processing the estimated distance of the signal source to the target according to the following formula:

[0035]

[0036] wherein R O represents the estimated distance of the signal source to the target; and c represents the speed of sound.

[0037] Step S332, judging the candidate frequency f p according to the following constraint condition, wherein the constraint condition of the candidate frequency f p is as follows:

[0038]

[0039] R C > R O,x > R F > R​O,y

[0040] f p ,x>f p ,y>0.2·f max ,f p ∈{f p ,x,f p ,y}

[0041] wherein R O,x represents the estimated distance from the virtual signal source to the target; R O,y represents the estimated distance from the loudspeaker to the target; R w represents the width of the narrow space; R F represents the path length of the linear frequency modulation signal from the loudspeaker to the microphone via the reflection point on the bottom surface in the narrow space; R h represents the distance from the loudspeaker to the bottom surface in the narrow space; R l represents the distance from the loudspeaker to the top surface in the narrow space; R C represents the path length of the linear frequency modulation signal from the loudspeaker to the microphone via the reflection point on the top surface in the narrow space; f p ,xrepresents the candidate frequency of the intermediate frequency signal corresponding to the virtual signal source; f p ,yrepresents the candidate frequency of the intermediate frequency signal corresponding to the loudspeaker; f max represents the frequency corresponding to the maximum energy peak in the intermediate frequency signal;

[0042] If the candidate frequency f p satisfies the above constraint condition, it is considered that the candidate frequency f p is a qualified candidate frequency f p ;

[0043] Step S333, for the loudspeaker and the virtual signal source, taking the minimum value of the qualified candidate frequencies f p as the standard frequency f p ′ corresponding to the loudspeaker, and taking the second minimum value of the qualified candidate frequencies f p as the standard frequency f p ′ corresponding to the virtual signal source.

[0044] The step S4 is specifically: first, according to the signal arrival time, the estimated position of the target is obtained by processing according to the following formula, and the functional expression of the target estimated position is as follows:

[0045]

[0046] R O,y =cτ k,y

[0047] R O,x =cτ k,x

[0048] wherein L(p T ) represents a likelihood function; p T represents an estimated position of the target, p k is a signal source position; p y represents a position of the loudspeaker; p x represents a position of the virtual signal source; R O,k is a distance from the target to the signal source; sigma is a variance of error distribution; R O,y represents an estimated distance from the loudspeaker to the target; R O,x represents an estimated distance from the virtual signal source to the target; tau k,y represents a signal arrival time of the loudspeaker; tau k,x represents a signal arrival time of the virtual signal source; c represents a sound speed.

[0049] Then, the target estimated position p T when the likelihood function L(p T ) is taken to a minimum value is taken as an optimal estimated position of the target, and the position information of the target is determined with the optimal estimated position of the target.

[0050] The expression of the linear frequency modulation signal s(t) in the step S1 is as follows:

[0051]

[0052] wherein f0 represents a starting frequency of the linear frequency modulation signal; B represents a bandwidth of the linear frequency modulation signal; T represents a period of the linear frequency modulation signal; pi represents a circular constant; and t represents a time variable.

[0053] The present application takes a customized frequency linear frequency modulation signal as a transmitting signal, a band-pass filter separates the signal data in the frequency band where the customized signal is located in the received signal; a cross-correlation method is used to estimate the propagation delay time and a peak value extraction algorithm is combined to estimate the peak value frequency corresponding to the signal, the geometric constraint of the loudspeaker and the mirror loudspeaker in the narrow space is used to obtain the accurate signal arrival time, the maximum likelihood method is used to solve the optimal position of the microphone, and the accurate position estimation of the target is realized in the complex indoor scene.

[0054] The present application has the following beneficial effects:

[0055] 1. The present application performs cross-correlation processing on the received positioning signal to obtain the delay time, and the signal data of a period of time is cut off forwardly based on the delay time, so that the constructed intermediate frequency signal is more accurate.

[0056] 2. The present application uses the loudspeaker and the mirror loudspeaker generated in the narrow space to screen the intermediate frequency signal frequency according to the specific geometric constraint of the narrow space, so as to obtain more accurate signal arrival time.

[0057] 3. The application uses the intermediate frequency signal and the known signal source position to construct a likelihood function, and obtains the optimal position estimation of the target by minimizing the likelihood function, the method of the application introduces a mirror signal source, has higher precision and better robustness, and can accurately estimate the position of the moving target.

[0058] 4. The application separates the received signal data with the customized signal frequency band by using a band-pass filter after the customized excitation signal is emitted from the loudspeaker, so that the signal is more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0059] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, without creative labor, other drawings can also be obtained from these drawings.

[0060] Figure 1 is the flow chart of the single base station positioning method in the narrow space of the present application;

[0061] Figure 2 is the waveform diagram and spectrogram of the customized signal. DETAILED DESCRIPTION

[0062] The embodiments of the present application will be described below through specific specific embodiments, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification. The present application can also be implemented or applied by different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0063] The positioning method in the narrow space of the present application comprises the following steps, such as Figure 1 as shown in the figure:

[0064] Step S1, first arrange the microphone and the loudspeaker in the narrow space, use the loudspeaker to emit the customized linear frequency modulation signal, and use the microphone to collect the positioning signal reflected by the wall surface of the narrow space and the direct signal;

[0065] The positioning signal includes the echo signal reflected by the wall surface of the narrow space and the direct signal directly from the loudspeaker to the microphone.

[0066] Step S2, filtering the positioning signal in step S1 to obtain the signal propagation delay time;

[0067] Step S3, obtaining the intermediate frequency signal according to the signal propagation delay time, and then obtaining the signal arrival time of the signal source by using the intermediate frequency signal;

[0068] Step S4, obtaining the optimal estimated position of the target based on the maximum likelihood estimation method according to the signal arrival time of the signal source, and further obtaining the position information of the target to be positioned.

[0069] The narrow space is a horizontally narrow space, that is, the extension direction of the narrow space is parallel to the ground.

[0070] In the step S1, the expression of the linear frequency modulation signal s(t) is as follows:

[0071] Firstly, the loudspeaker is arranged on the inner wall of the narrow space, and the microphone is installed on the target to be positioned, the target being located in the narrow space, the linear frequency modulation signal is emitted by using the loudspeaker, the waveform diagram and the spectrum diagram of the linear frequency modulation signal are as shown in Figure 2 The linear frequency modulation signal emitted by the loudspeaker is reflected on the wall surface of the narrow space, so that a virtual signal source is generated outside the narrow space, the virtual signal source and the loudspeaker are symmetrically distributed with the inner wall of the narrow space opposite to the loudspeaker as the symmetry surface, and the distance between the virtual signal source and the target is equal to the distance from the linear frequency modulation signal emitted by the loudspeaker to the reflection point of the inner wall of the narrow space plus the distance from the reflection point of the inner wall of the narrow space to the target.

[0072] The loudspeaker and the virtual signal source are both regarded as signal sources, wherein the loudspeaker is a real signal source, the signal source includes the real signal source and the virtual signal source, the two signal sources respectively emit their own linear frequency modulation signals to the target, and the signals emitted by the signal sources are collected by the microphone installed on the target after propagating in the narrow space, each signal source generates a positioning signal.

[0073] For the real signal source (such as the loudspeaker), due to the mirror reflection in the narrow space, a virtual signal source is generated on the opposite side of the real signal source, and the processing mode of the virtual signal source for the signal arrival time is the same as that of the real signal source. In step S1, the customized linear frequency modulation signal is an ascending linear frequency modulation signal, the duration time is 40 ms, the frequency of the frequency modulation signal is 16-19 kHz, the sampling frequency is 48 kHz, and the signal refresh rate is 1 Hz.

[0074] In step S1, the expression of the linear frequency modulation signal s(t) is as follows:

[0075]

[0076] Wherein, f0 represents the initial frequency of the linear frequency modulation signal; B represents the bandwidth of the linear frequency modulation signal; T represents the period of the linear frequency modulation signal; π represents the circular constant; t represents the time variable.

[0077] In the specific implementation, the step S2 is specifically:

[0078] Step S21, firstly, a band-pass filter is used to band-pass filter the positioning signal collected in step S1, and the signal in the frequency band of the linear frequency modulation signal is screened out from the positioning signal as the frequency band signal s r (t), the frequency band signal s r (t) is expressed as follows:

[0079]

[0080] Wherein, α represents the attenuation coefficient; f0 represents the starting frequency of the linear frequency modulation signal; B represents the bandwidth of the linear frequency modulation signal; T represents the period of the linear frequency modulation signal; π represents the circular constant; t represents the time variable; t d represents the delay time of signal propagation;

[0081] Wherein, the upper and lower cutoff frequencies of the band-pass filter for separating the frequency band signal are 15.9 kHz and 19.1 kHz respectively, and the order is 20.

[0082] Step S22, then the linear frequency modulation signal transmitted by the signal source is taken as the reference signal x(t), and the filtered frequency band signal s r (t) is obtained. xs (t) is obtained.

[0083]

[0084] Wherein, τ represents the time delay parameter;

[0085] Step S23, finally, the peak extraction algorithm is used to perform peak extraction on the cross-correlation function R xs (τ) between the frequency band signal and the reference signal, to obtain the peak value of the cross-correlation function R xs (τ), and the time difference between the frequency band signal s xs (t) and the reference signal is obtained as the signal propagation delay time t r of the positioning signal. d .

[0086] Specifically, step S3 is specifically:

[0087] Step S31, firstly, the signal propagation delay time t d is used to intercept the frequency band signal s r (t): t d -τ a is taken as the starting time of signal interception, and t d -τ a +T is taken as the termination time of signal interception. r(t) is intercepted, and the intercepted frequency band signal is taken as a truncated signal s j (t) corresponding to the signal source, and is processed according to the following formula to obtain the intermediate frequency signal s m (t) corresponding to the signal source:

[0088]

[0089] Wherein, τ a is a preset truncation duration; T represents the period of the linear frequency modulation signal; the intermediate frequency signal is the result of the point multiplication of the truncated signal and the reference signal s(t); a represents an attenuation coefficient; f0 represents the starting frequency of the linear frequency modulation signal; B represents the bandwidth of the linear frequency modulation signal; and t represents a time variable;

[0090] In an actual signal processing system, due to the limitation of system performance and signal causality, an infinitely long signal cannot be processed, so before the reference signal and the received positioning signal are multiplied, the complete audio data with the linear frequency modulation signal data needs to be intercepted from the received positioning signal stream. In order to ensure the integrity of the intercepted signal, the delay time t d obtained by correlating the received positioning signal with the reference signal as a template is taken as a basis, and signal data with a duration of τ a is further intercepted, and the time t d -τ a is taken as a starting point to construct a signal to improve the accuracy of the intermediate frequency signal calculation. Specifically, τ a may be 10 ms, and the intermediate frequency signal frequency is expanded to 16-20.5 kHz.

[0091] Step S32, performing fast Fourier transform on the intermediate frequency signal s m (t) so that the intermediate frequency signal s m (t) is converted from a time domain signal to a frequency domain signal, and each frequency peak in the frequency domain signal is obtained as a candidate frequency f p ;

[0092] Step S33, then judging whether each candidate frequency f p is qualified, and obtaining the standard frequency f p corresponding to the loudspeaker and the virtual signal source respectively by using the qualified candidate frequency f p ;

[0093] Step S33 specifically includes:

[0094] Step S331, first, according to the candidate frequency f p , the estimated distance from the signal source to the target is obtained according to the following formula:

[0095]

[0096] Among them, R O represents the estimated distance from the signal source to the target; c represents the speed of sound;

[0097] Step S332: Based on the following constraints, evaluate the candidate frequency f. p Make a judgment, candidate frequency f p The constraints are as follows:

[0098]

[0099] R C >R O,x >R F >R O,y

[0100] f p ,x>f p ,y>0.2·f max f p ∈{f p ,x,f p ,y}

[0101] Among them, R O,x R represents the estimated distance from the virtual signal source to the target. O,y R represents the estimated distance from the loudspeaker to the target. w R is the width of the narrow space. F R represents the path length of the linear frequency modulated signal from the loudspeaker, through the reflection point on the bottom surface of the narrow space, to the microphone; h R represents the distance from the loudspeaker to the bottom surface of the narrow space; l R is the distance from the loudspeaker to the top surface of the narrow space; C This represents the path length of a linear frequency modulated signal from the loudspeaker, through the top reflection point within the narrow space, to the microphone. The loudspeaker and microphone are at the same height, and the bottom / top reflection points within the narrow space are reflection points from the inner wall of the narrow space; f p ,x represents the candidate frequency of the intermediate frequency signal corresponding to the virtual signal source; f p ,y represents the candidate frequency of the intermediate frequency signal corresponding to the loudspeaker; f max This indicates the frequency corresponding to the maximum energy peak value in the two intermediate frequency signals;

[0102] If the candidate frequency f p If the above constraints are met, then the candidate frequency f is considered to be... p For a qualified candidate frequency f p ;

[0103] Step S333: Select qualified candidate frequencies f for the speaker and the virtual signal source. p The minimum value in the range is used as the standard frequency f corresponding to the loudspeaker. p ′, select the qualified candidate frequency fp the secondary minimum in the function f (f ) as the standard frequency f corresponding to the virtual signal source p .

[0104] In fact, the mid-frequency signal corresponding to the loudspeaker and the mid-frequency signal corresponding to the virtual signal source are of the same form, so any candidate frequency f that is qualified under any mid-frequency signal can be directly selected to obtain the standard frequency f corresponding to the loudspeaker and the virtual signal source respectively p . p

[0105] Step S34, then, according to the standard frequency f p , the signal arrival time τ is obtained by processing according to the following formula k :

[0106]

[0107] wherein τ k represents the time when the linear frequency modulation signal emitted by the signal source reaches the microphone.

[0108] Considering that the signal emission source is stationary, the mid-frequency signal can also be expressed as:

[0109]

[0110] wherein R represents the distance between the signal source and the microphone;

[0111]

[0112] wherein c represents the speed of sound.

[0113] Step S4 is specifically: first, according to the signal arrival time, the estimated position of the target is obtained by processing according to the following formula, and the functional expression of the target estimated position is as follows:

[0114]

[0115] R O,y = cτ k,y

[0116] R O,x = cτ k,x

[0117] wherein L(p T ) represents the likelihood function; p T represents the estimated position of the target, p k is the signal source position; p y represents the position of the loudspeaker; p x represents the position of the virtual signal source; R O,k is the distance from the target to the signal source; σ is the error distribution variance; R O,y ​denotes the estimated distance of the loudspeaker to the target; R O,x denotes the estimated distance of the virtual signal source to the target; τ k,y denotes the signal arrival time of the loudspeaker; τ k,x denotes the signal arrival time of the virtual signal source, i.e. τ k ∈ {τ k,x ,τ k,y}; c denotes the sound speed;

[0118] The target estimated position p T at which the likelihood function L(p T ) is minimized is then taken as the optimal estimated position of the target, and the position information of the target is determined based on the optimal estimated position of the target.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positioning method in a narrow space based on specular reflection and time-of-arrival estimation, characterized in that, Includes the following steps: Step S1: First, set up a microphone and a speaker in the narrow space. Use the speaker to emit a linear frequency modulation signal and use the microphone to collect the positioning signals reflected from the wall of the narrow space and those that are directly received. Step S2: Filter the positioning signal from step S1 to obtain the signal propagation delay time; Step S3: Obtain the intermediate frequency signal based on the signal propagation delay time, and then use the intermediate frequency signal to obtain the signal arrival time of the signal source; Step S4: Based on the arrival time of the signal from the signal source, obtain the optimal estimated position of the target using the maximum likelihood estimation method, and then obtain the position information of the target to be located.

2. The positioning method in a narrow space based on specular reflection and time of arrival estimation according to claim 1, characterized in that: The specific steps of S1 are as follows: First, a loudspeaker is placed on the inner wall of the narrow space, and a microphone is installed on the target to be located. The loudspeaker emits a linear frequency modulated (LFM) signal, which is reflected on the wall of the narrow space, creating a virtual signal source outside the narrow space. The virtual signal source and the loudspeaker are symmetrically distributed with the inner wall of the narrow space as the plane of symmetry, and the distance between the virtual signal source and the target is equal to the sum of the distance from the LFM signal emitted by the loudspeaker to the reflection point on the inner wall of the narrow space and the distance from the reflection point on the inner wall of the narrow space to the target. Both the loudspeaker and the virtual signal source are used as signal sources. The two signal sources emit their own linear frequency modulated signals toward the target. The signals emitted by the signal sources are collected by the microphone installed on the target after propagating in the narrow space.

3. The positioning method in a narrow space based on specular reflection and time of arrival estimation according to claim 1, characterized in that: The specific steps of step S2 are as follows: Step S21: First, bandpass filter is applied to the positioning signal acquired in step S1 to select the signal in the frequency band where the linear frequency modulated signal is located as the frequency band signal s. r (t), frequency band signal s r The expression for (t) is as follows: Where α represents the attenuation coefficient; f0 represents the starting frequency of the linear frequency modulated (LFM) signal; B represents the bandwidth of the LFM signal; T represents the period of the LFM signal; π represents pi; and t represents the time variable. d Indicates the delay time of signal propagation; Step S22: Then, using the linear frequency modulated signal emitted by the signal source as the reference signal x(t), obtain the filtered frequency band signal s. r The cross-correlation function R between (t) and the corresponding reference signal xs (τ): Where τ represents the time delay parameter; Step S23: Finally, the peak extraction algorithm is used to calculate the cross-correlation function R between the frequency band signal and the reference signal. xs (τ) Peak extraction is performed to obtain the cross-correlation function R. xs The peak value of (τ), and according to the cross-correlation function R xs The peak value of (τ) yields the frequency band signal s. r The time difference between (t) and the reference signal is taken as the signal propagation delay time t of the positioning signal. d .

4. The positioning method in a narrow space based on specular reflection and time of arrival estimation according to claim 1, characterized in that: The specific steps of step S3 are as follows: Step S31: First, utilize the signal propagation delay time t d For frequency band signal s r (t) is used for t-segmentation: d -τ a As the starting time for signal interception, t d -τ a +T is used as the termination time for signal interception in the frequency band signal s. r (t) is used to truncate the signal, and the truncated frequency band signal is used as the truncation signal s corresponding to the signal source. j (t), and process it according to the following formula to obtain the intermediate frequency signal s corresponding to the signal source. m (t): Where, τ a The preset interception duration; T represents the period of the linear frequency modulated signal; α represents the attenuation coefficient; f0 represents the starting frequency of the linear frequency modulated signal; B represents the bandwidth of the linear frequency modulated signal; t represents the time variable; Step S32, for the intermediate frequency signal s m (t) is subjected to a Fast Fourier Transform, making the intermediate frequency signal s m (t) The time-domain signal is converted into a frequency-domain signal, and the peak values ​​of each frequency in the frequency-domain signal are obtained as candidate frequencies f. p ; Step S33: Then determine each candidate frequency f p Whether it is qualified or not, the qualified candidate frequency f is used. p Obtain the standard frequency f corresponding to both the speaker and the virtual signal source. p ′; Step S34: Next, according to the standard frequency f p The signal arrival time τ is obtained by processing it according to the following formula. k : Where, τ k This indicates the time it takes for the linear frequency modulated signal emitted by the signal source to reach the microphone.

5. The positioning method in a narrow space based on specular reflection and time of arrival estimation according to claim 4, characterized in that: The specific steps of S33 are as follows: Step S331: First, based on the candidate frequency f p The estimated distance from the signal source to the target is obtained by processing the signal using the following formula: Among them, R O represents the estimated distance from the signal source to the target; c represents the speed of sound; Step S332: Based on the following constraints, evaluate the candidate frequency f. p The candidate frequency f is determined. p The constraints are as follows: f p ,x>f p ,y>0.2·f max ,f p ∈{f p ,x,f p ,y} Among them, R O,x R represents the estimated distance from the virtual signal source to the target. O,y R represents the estimated distance from the loudspeaker to the target. w R is the width of the narrow space. F R represents the path length of the linear frequency modulated signal from the loudspeaker, through the reflection point on the bottom surface of the narrow space, to the microphone; h R represents the distance from the loudspeaker to the bottom surface of the narrow space; l R is the distance from the loudspeaker to the top surface of the narrow space; C This represents the path length of the linear frequency modulated signal from the loudspeaker, through the reflection point on the top surface within the narrow space, to the microphone; f p ,x represents the candidate frequency of the intermediate frequency signal corresponding to the virtual signal source; f p ,y represents the candidate frequency of the intermediate frequency signal corresponding to the loudspeaker; f max This indicates the frequency corresponding to the maximum energy peak value in the intermediate frequency signal; If the candidate frequency f p If the above constraints are met, then the candidate frequency f is considered to be... p For a qualified candidate frequency f p ; Step S333: Select qualified candidate frequencies f for the speaker and the virtual signal source. p The minimum value in the range is used as the standard frequency f corresponding to the loudspeaker. p ′, select the qualified candidate frequency f p The second smallest value in the range is used as the standard frequency f corresponding to the virtual signal source. p ′.

6. The positioning method in a narrow space based on specular reflection and time of arrival estimation according to claim 1, characterized in that: Step S4 specifically involves: firstly, processing the signal arrival time according to the following formula to obtain the estimated position of the target, the functional expression of the estimated target position is as follows: R O,y =cτ k,y R O,x =cτ k,x Among them, L(p T ) represents the likelihood function; p T p represents the estimated location of the target. k p represents the location of the signal source. y Indicates the position of the speaker; p x Indicates the location of the virtual signal source; R O,k R is the distance from the target to the signal source; σ is the variance of the error distribution; O,y R represents the estimated distance from the loudspeaker to the target. O,x τ represents the estimated distance from the virtual signal source to the target. k,y Indicates the signal arrival time of the loudspeaker; τ k,x The signal arrival time of the virtual signal source is represented by c; c represents the speed of sound. Then the likelihood function L(p) T The estimated target position p when the minimum value is reached. T The optimal estimated position of the target is used to determine the target's location information.

7. The positioning method in a narrow space based on specular reflection and time of arrival estimation according to claim 1, characterized in that: The expression for the linear frequency modulated signal s(t) in step S1 is as follows: Where f0 represents the starting frequency of the linear frequency modulated (LFM) signal; B represents the bandwidth of the LFM signal; T represents the period of the LFM signal; π represents pi; and t represents the time variable.

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