Indoor positioning system based on distributed ultrasonic sensing

Abstract

The invention relates to the technical field of optical fiber communication and sensing, in particular to an indoor positioning system based on distributed ultrasonic sensing, which is characterized in that a detection pulse is modulated to light for emission, the detection pulse is amplified by an erbium-doped optical fiber amplifier and then is sent to a to-be-detected optical fiber through an optical circulator; and the received Rayleigh backscattering signal is coupled with the local oscillator after being amplified, and finally demodulation processing is carried out. According to the invention, limitation of sensing distance and sensing frequency can be broken through in a traditional DAS system, effective sampling and recovery of high-frequency signals are realized, a distributed ultrasonic sensing technology is applied to indoor positioning, and a new application direction is developed for the field of real-time detection.

Description

Technical Field

[0001] The present application relates to the field of optical fiber communication and sensing technology, and in particular to an indoor positioning system based on distributed ultrasonic sensing. Background Art

[0002] In recent years, with the development of positioning technology, indoor positioning has gradually become a hot topic of research. Indoor positioning technology aims to solve the problems of satellite signals being difficult to penetrate and weak signals in buildings, and provide reliable support for the precise positioning of objects or people. Intersection technology based on wireless signals, database matching technology, and heading estimation technology based on inertial sensors are the main methods of indoor positioning. However, the application of these technologies in complex indoor environments still faces certain limitations. With the continuous emergence of high-precision, wide-band, and large-range sensing needs, distributed acoustic sensing technology has gradually become an important technical means to solve the problem of indoor positioning. Distributed acoustic sensing (DAS) technology is an efficient monitoring method that uses optical fiber as a sensor to sense external sound waves and vibration signals by detecting the backscattered light in the optical fiber. It has been applied in many fields.

[0003] Currently commonly used DAS frameworks include Figure 1 As shown in the figure, the laser output by the narrow linewidth laser is divided into two parts after passing through the optical coupler, of which 99% is used as the detection light and 1% is used as the local oscillator light. The detection light is modulated into an optical pulse and frequency-shifted by an acousto-optic modulator (AOM) driven by an arbitrary waveform generator (AWG). After being amplified by an erbium-doped fiber amplifier (EDFA) and filtered by an optical bandpass filter (BPF), the detection pulse is sent to the fiber under test (FUT) through an optical circulator. Near the end of the FUT, a section of optical fiber is wrapped around a piezoelectric fiber stretcher (PZT) for vibration stimulation, and then a pigtail is reserved to prevent signal distortion caused by reflection. The Rayleigh backscattered (RBS) light reaches the receiving end through the optical circulator. After being amplified by the second EDFA and filtered by the BPF, the RBS light and the local oscillator light are combined at the 2×2 optical coupler. Finally, the interference light is received by a balanced photon detector (BPD). This framework has been widely used to detect low-frequency signals in the range of a few hertz to more than ten kilohertz, meeting common needs such as communication sensing. However, when detecting high-frequency signals (such as ultrasonic signals), the effectiveness of signal acquisition and processing faces significant challenges due to limitations in fiber length and sampling rate.

[0004] In order to explore the nature of this challenge, Nyquist sampling theorem is introduced for research. According to Nyquist sampling theorem, in order to restore a signal losslessly, it must be sampled at a sampling rate greater than twice its bandwidth, otherwise it will cause an aliasing effect, causing the spectrum of the high-frequency signal to overlap with the low-frequency signal, and the original signal cannot be correctly restored. Figure 2As shown in the figure, in the traditional distributed fiber optic ultrasonic sensing system, the detection frequency of the pulse not only determines the maximum vibration frequency allowed to be detected by the system, but is also inversely proportional to the maximum sensing distance of the system. When the sensing distance is long, the sampling rate is limited and the Nyquist sampling requirements cannot be met. High-frequency signals are prone to spectrum aliasing, making it difficult to restore the original vibration or sound signal. Therefore, the traditional DAS system has significant limitations in high-frequency signal processing. Summary of the invention

[0005] This application provides an indoor positioning system based on distributed ultrasonic sensing, which can break through the limitations of sensing distance and sensing frequency in traditional DAS systems, achieve effective sampling and recovery of high-frequency signals, and apply distributed ultrasonic sensing technology to indoor positioning, opening up new application directions in the field of real-time detection. This application provides the following technical solutions:

[0006] In a first aspect, the present application provides an indoor positioning system based on distributed ultrasonic sensing, the system comprising:

[0007] A laser, for outputting an optical signal;

[0008] A modulator, used for modulating a continuous optical signal into a detection pulse with a specific frequency shift;

[0009] An erbium-doped fiber amplifier is used to amplify the power of the modulated detection pulse;

[0010] An optical circulator is used to guide the detection light signal into the optical fiber to be tested, and at the same time separate the Rayleigh backscattered signal returned from the optical fiber to be tested and guide it to the receiving end;

[0011] The optical fiber to be tested is a sensitive medium used to sense vibration signals;

[0012] Ultrasonic vibration loader, used to generate ultrasonic vibration at a specific position of the optical fiber to be tested to simulate the target signal;

[0013] The second stage amplifier is used to amplify the Rayleigh backscattered light signal returned from the optical fiber to be tested to the receiving end;

[0014] A local oscillator light source, used to interfere with the Rayleigh backscattered light signal;

[0015] An optical coupler is used to combine the amplified Rayleigh backscattered light signal with the local oscillator light to form an interference light signal;

[0016] A coherent receiving module is used to receive and process the interference light signal and extract the target vibration information contained therein;

[0017] The digital signal processor is used to process the demodulated signal, analyze the frequency, amplitude and phase information in the signal, and restore the ultrasonic vibration signal.

[0018] In a specific implementation scheme, the detection frequency needs to satisfy the following formula:

[0019]

[0020] Among them, c, n and L are the speed of light, the refractive index of the optical fiber and the length of the optical fiber respectively. The bandwidth of the vibration signal carried by the ultrasonic wave is less than f max / 2.

[0021] In a specific embodiment, the probe pulse is a rectangular pulse, which is shifted to a certain frequency by an acousto-optic modulator. The incident field at a distance Z along the optical fiber and a time t can be expressed as follows:

[0022]

[0023] Where E0 is the scalar amplitude of the pulse, f0 is the original optical frequency, and f is the intermediate frequency of AOM modulation. is the initial phase, α is the average attenuation coefficient of the sensing fiber, and β is the propagation constant related to the optical frequency and the local effective refractive index.

[0024] In a specific embodiment, the incident field E i The Rayleigh scattered field excited from a scatterer at position z can be expressed as follows:

[0025]

[0026] Where ρ is the backscattering coefficient in complex form, which is a circular complex Gaussian distribution variable; the phase of ρ is uniformly distributed within 0 to 2π.

[0027] In a specific implementation scheme, the return electric field at the optical fiber input end is the interference of the scattered fields propagated by multiple scatterers in the rectangular window, which can be written as follows:

[0028]

[0029] The optical pulse is transmitted back and forth in the optical fiber. The actual pulse width in the optical fiber is twice the rectangular window length. N is the number of scatterers, z i is the position of the i-th scatterer.

[0030] In a specific implementation scheme, the sum is calculated over the entire rectangular window, and the received field can be viewed as the convolution of the propagated scattered field and a rectangular window, where:

[0031] β(z)=2π(f0+f)n eff (z) / c.

[0032] In a specific implementation scheme, assuming that the vibration signal s(t) is superimposed on the ultrasonic carrier, then

[0033]

[0034] The detection results returned by the optical fiber input end are as follows:

[0035]

[0036] The local oscillator (LO) from the same laser can be described as follows:

[0037]

[0038] Where E1 is the scalar amplitude of the local oscillator, is the initial phase of the local oscillator.

[0039] In a specific implementation scheme, after heterodyne detection, the received signal can be expressed as follows:

[0040]

[0041] where ρ tot is a Rayleigh distributed random variable, In order to evenly distribute the comprehensive phase, when the optical fiber is disturbed by the surrounding vibration, The vibration waveform is obtained by differential calculation and eliminated in the differential operation and Recover the vibration signal.

[0042] In a second aspect, the present application provides an electronic device, comprising a processor and a memory; the memory stores a program, and the program is loaded and executed by the processor to implement an indoor positioning system based on distributed ultrasonic sensing as described in the first aspect.

[0043] In a third aspect, the present application provides a computer-readable storage medium, in which a program is stored. When the program is executed by a processor, it is used to implement an indoor positioning system based on distributed ultrasonic sensing as described in the first aspect.

[0044] In summary, the beneficial effects of this application include at least:

[0045] 1) Traditional distributed fiber optic sensing technology is mainly used for the detection of low-frequency signals, and there is an inherent inverse relationship between the perception frequency and the perception distance (the higher the detection frequency, the shorter the perception distance). This application proposes to use ultrasound as a carrier, combined with the bandpass Nyquist sampling theorem, to embed the vibration signal into high-frequency ultrasound, thereby effectively improving the utilization rate of the signal bandwidth. Through ultrasonic carrier technology, the detection of vibration signals is extended from low frequency to high frequency range (>20kHz), significantly improving the perception frequency range of distributed fiber optic sensing systems. At the same time, the signal processing link is optimized, the risk of signal aliasing is reduced, and the contradiction between perception frequency and perception distance is broken from the perspective of signal processing, laying the foundation for the realization of high-resolution, long-distance distributed fiber optic ultrasonic sensing.

[0046] 2) Existing indoor positioning technologies mainly rely on the three-point positioning method of wireless signals (such as Wi-Fi, Bluetooth or UWB), and calculate the target position by measuring the time or distance for the signal to reach multiple reference points. However, these methods have high requirements on the complexity of hardware equipment and are easily affected by factors such as signal blocking in indoor environments. This application makes full use of the continuity and spatial resolution capabilities of distributed fiber optic sensing technology, uses optical fiber as the detection medium, and combines ultrasonic carriers to achieve indoor personnel positioning. By analyzing the signal vibration information distributed by the optical fiber, the dynamic position and behavior of the target are accurately extracted to achieve real-time and continuous positioning functions. This technology innovatively avoids the problem of traditional wireless signal blocking and provides a low-cost, distributed solution for indoor positioning.

[0047] 3) The signal recovery efficiency of traditional distributed fiber optic sensors is low, especially when facing complex signals, they are easily interfered by phase noise and amplitude attenuation. This application uses heterodyne detection based on Rayleigh backscattering, combined with precise phase differential technology, to demodulate the returned interference signal, eliminate interference items (such as noise phase and amplitude randomness), and thus accurately recover the vibration signal. It effectively solves the noise interference and aliasing problems of traditional distributed fiber optic sensors in high-frequency signal demodulation, can quickly extract target vibration signals, improve the accuracy and reliability of signal demodulation, and provide technical support for the application of ultrasonic sensing.

[0048] Optical fiber is used as the sensing medium, and a detection pulse is generated by a laser. The optical signal is frequency-shift modulated and pulse-shaped by combining an acousto-optic modulator (AOM). After being amplified by an erbium-doped fiber amplifier (EDFA), it enters the fiber under test (FUT). When the ultrasonic vibration signal acts on the optical fiber, a Rayleigh backscattered light signal is generated. After coupling with the optical circulator and the local oscillator light, the vibration information is demodulated and restored through coherent reception and digital signal processing. By applying the bandpass Nyquist sampling theorem, the vibration signal is loaded onto a high-frequency ultrasonic carrier, which solves the contradiction between the limited detection frequency, the sensing distance and the sensing frequency in the traditional distributed optical fiber sensing system. It can effectively sense high-frequency vibration signals and realize long-distance indoor personnel positioning, opening up a new direction for optical fiber sensing technology in the field of real-time monitoring.

[0049] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present application in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a framework diagram of a DAS commonly used in the prior art.

[0051] Figure 2 It is a use case diagram of the alias-free sampling criterion of the Nyquist sampling theorem.

[0052] Figure 3 It is a structural block diagram of an indoor positioning system based on distributed ultrasonic sensing in an embodiment of the present application.

[0053] Figure 4 It is a spectrum diagram of the vibration signal in the embodiment of the present application.

[0054] Figure 5 It is a vibration position diagram of the optical fiber extension distance change in the embodiment of the present application.

[0055] Figure 6 This is a diagram of vibration signal recovery results in an embodiment of the present application.

[0056] Figure 7 It is a block diagram of an electronic device for indoor positioning based on distributed ultrasonic sensing in an embodiment of the present application. DETAILED DESCRIPTION

[0057] The specific implementation methods of the present application are further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application but are not intended to limit the scope of the present application.

[0058] Optionally, the present application takes the distributed ultrasonic sensing-based indoor positioning system provided in each embodiment as an example of being used in an electronic device, where the electronic device is a terminal or a server. The terminal may be a computer, a tablet computer, etc. This embodiment does not limit the type of electronic device.

[0059] Reference Figure 3 , is a structural block diagram of an indoor positioning system based on distributed ultrasonic sensing provided by an embodiment of the present application, the system comprising:

[0060] Laser, used to output optical signals.

[0061] The modulator, which is an acousto-optic modulator AOM in this application, is used to modulate the continuous optical signal into a detection pulse with a specific frequency offset, and at the same time adjust the shape of the pulse to be rectangular.

[0062] Erbium-doped fiber amplifier (EDFA) is used to amplify the power of the modulated detection pulse to compensate for the signal attenuation during optical fiber transmission.

[0063] The optical circulator is used to guide the detection light signal into the fiber under test (FUT), and at the same time separate the Rayleigh backscattered signal returned from the fiber under test and guide it to the receiving end.

[0064] The fiber under test (FUT) is a sensitive medium used to sense vibration signals. When the ultrasonic carrier signal acts on the optical fiber, it will induce tiny vibrations in the optical fiber.

[0065] The ultrasonic vibration loader is used to generate ultrasonic vibration at a specific position of the optical fiber to be tested to simulate the target signal.

[0066] Second stage amplifier (EDFA), when the Rayleigh backscattered light signal returns from the optical fiber to be tested to the receiving end, it needs to be amplified by the second stage EDFA due to the attenuation generated during the transmission process.

[0067] The local oscillator light source is used to interfere with the Rayleigh backscattered light signal.

[0068] The optical coupler is used to combine the amplified Rayleigh backscattered light signal with the local oscillator light to form an interference light signal.

[0069] The coherent receiving module is used to receive and process the interfered optical signal to extract the target vibration information contained therein.

[0070] The digital signal processor (DSP) is responsible for processing the demodulated signal, analyzing the frequency, amplitude and phase information in the signal, and restoring the ultrasonic vibration signal.

[0071] In the implementation, the detection pulse is modulated onto light for transmission. After being amplified by an erbium-doped fiber amplifier, the detection pulse is sent into the optical fiber to be tested through an optical circulator. The received Rayleigh backscattered signal is amplified and coupled with the local oscillator, and finally demodulated.

[0072] Specifically, the system first generates a narrow linewidth laser through a laser, and the laser is modulated by a modulator to form a detection pulse signal. This modulator can be implemented by an acousto-optic modulator (AOM) or other types of modulators. The specific function is to modulate the frequency of the laser pulse to meet the detection requirements of the system. The modulated detection pulse is amplified by an erbium-doped fiber amplifier (EDFA) to enhance the signal strength, thereby ensuring that the pulse light can maintain sufficient signal strength during the optical fiber transmission process. The amplified detection pulse is injected into the optical fiber to be tested (sensing fiber) through an optical circulator. At this time, the optical fiber to be tested will respond to its external environment (such as vibration or ultrasonic carrier signal) and generate a Rayleigh backscattered light signal. The Rayleigh backscattered signal is transmitted back through the optical circulator and amplified again by the erbium-doped fiber amplifier (EDFA). The amplified Rayleigh scattered light is coupled with the local oscillator light and interferes in the 2×2 optical coupler. The interfered optical signal enters the coherent receiving module for demodulation. The demodulated signal is extracted through the digital signal processing (DSP) module to extract the required information, such as the ultrasonic vibration signal and the information attached to its carrier (such as a voice signal). The innovation of the system is to transmit vibration signals through ultrasound as carrier waves, and to effectively detect and decode high-frequency signals through distributed sensing. This system can not only sense vibrations, but also realize application expansion through the recovery of high-frequency signals, such as indoor positioning or voice transmission.

[0073] At present, distributed optical fiber sensing often uses the method of single pulse multiple detection, and the detection frequency must satisfy the following formula:

[0074]

[0075] Among them, c, n and L are the speed of light, the refractive index of the fiber and the length of the fiber, respectively. However, the frequency range of ultrasound is relatively high (>20kHz), which means that the low-frequency demodulation method suitable for traditional distributed fiber optic sensing cannot meet the needs of fiber optic ultrasonic sensing. However, according to the bandpass Nyquist sampling theorem, a sampling frequency greater than twice the bandwidth can achieve aliasing-free reception, so it is recommended that the bandwidth of the vibration signal carried by ultrasound be less than f max / 2.

[0076] Usually the probe pulse is a rectangular pulse, which is shifted to a certain frequency by an acousto-optic modulator (AOM). The incident field at the distance Z and time t along the fiber can be expressed as follows:

[0077]

[0078] Where E0 is the scalar amplitude of the pulse, f0 is the original optical frequency, and f is the intermediate frequency of AOM modulation. is the initial phase, α is the average attenuation coefficient of the sensing fiber, and β is the propagation constant related to the optical frequency and the local effective refractive index. i The Rayleigh scattered field excited from a scatterer at position z can be expressed as follows:

[0079]

[0080] Where ρ is the backscattering coefficient in complex form, which is a circular complex Gaussian distribution variable. The phase of ρ is uniformly distributed within 0 to 2π. This application separates its amplitude term and phase term into the following:

[0081]

[0082] The return electric field at the input end of the optical fiber is the interference of the scattered fields propagated by multiple scatterers in the rectangular window, which can be written as follows:

[0083]

[0084] The optical pulse is transmitted back and forth in the optical fiber. The actual pulse width in the optical fiber is twice the rectangular window length. N is the number of scatterers, z i is the position of the i-th scatterer. The sum is calculated within the entire rectangular window, and the received field can be regarded as the convolution of the propagated scattered field and a rectangular window. Where:

[0085] β(z)=2π(f0+f)n eff (z) / c

[0086] Assuming that the vibration signal s(t) is superimposed on the ultrasonic carrier, then

[0087]

[0088] The detection results returned by the optical fiber input end are as follows:

[0089]

[0090] The local oscillator (LO) from the same laser can be described as follows:

[0091]

[0092] Where: E1 is the scalar amplitude of the local oscillator, is the initial phase of the local oscillator. After heterodyne detection, the received signal can be expressed as follows:

[0093]

[0094] where ρtot is a Rayleigh distributed random variable, To evenly distribute the comprehensive phase. When the optical fiber is disturbed by the surrounding vibration, The vibration waveform is obtained by differential calculation and eliminated in the differential operation and The vibration signal can be restored.

[0095] In summary, the present application uses optical fiber as a sensing medium, generates detection pulses through a laser, and combines an acousto-optic modulator (AOM) to perform frequency shift modulation and pulse shaping on the optical signal, which is amplified by an erbium-doped fiber amplifier (EDFA) and enters the optical fiber under test (FUT). When an ultrasonic vibration signal acts on the optical fiber, a Rayleigh backscattered light signal is generated, which is coupled with the optical circulator and the local oscillator light, and then demodulated and the vibration information is restored through coherent reception and digital signal processing. By applying the bandpass Nyquist sampling theorem, the vibration signal is loaded onto a high-frequency ultrasonic carrier, which solves the contradiction between the limited detection frequency, the sensing distance and the sensing frequency in the traditional distributed optical fiber sensing system, can effectively sense high-frequency vibration signals, and realize long-distance indoor personnel positioning, opening up a new direction for optical fiber sensing technology in the field of real-time monitoring.

[0096] Next, let's take an example: Assuming the fiber length is 20km and the detection pulse width is 100ns, the formula shows that the ideal detection time interval is every 0.2ms. To prevent the two detections from interfering with each other, it is recommended to set the detection time interval to every 0.3ms. At the same time, the signal bandwidth for non-aliasing detection is recommended to be set to less than 1.5KHz. Taking sinusoidal vibration as an example, first generate a sine wave with a frequency of 100Hz and superimpose it on a 20KHz carrier as a vibration signal. Figure 4 Shown is the frequency spectrum of the vibration signal.

[0097] Then, the vibration signal is loaded at 5km and 10km of the optical fiber. After simulation, the vibration position diagram of the optical fiber along the distance can be obtained as shown in the figure below: Figure 5 As shown in the figure, the vibration signal recovery result is shown in the figure Figure 6 As shown, the red line is the applied sinusoidal wave signal and the blue line is the restored sinusoidal wave signal.

[0098] Figure 7 4 is a block diagram of an electronic device provided by an embodiment of the present application. The device at least includes a processor 401 and a memory 402.

[0099] The processor 401 may include one or more processing cores, such as a 4-core processor, an 8-core processor, etc. The processor 401 may be implemented in at least one hardware form of DSP (Digital Signal Processing), FPGA (Field-Programmable Gate Array), and PLA (Programmable Logic Array). The processor 401 may also include a main processor and a coprocessor. The main processor is a processor for processing data in the awake state, also known as a CPU (Central Processing Unit); the coprocessor is a low-power processor for processing data in the standby state. In some embodiments, the processor 401 may be integrated with a GPU (Graphics Processing Unit), which is responsible for rendering and drawing the content to be displayed on the display screen. In some embodiments, the processor 401 may also include an AI (Artificial Intelligence) processor, which is used to process computing operations related to machine learning.

[0100] The memory 402 may include one or more computer-readable storage media, which may be non-transitory. The memory 402 may also include a high-speed random access memory, and a non-volatile memory, such as one or more disk storage devices, flash memory storage devices. In some embodiments, the non-transitory computer-readable storage medium in the memory 402 is used to store at least one instruction, which is used to be executed by the processor 401 to implement the indoor positioning system based on distributed ultrasonic sensing provided in the embodiment of the present application.

[0101] Of course, the electronic device may also include fewer or more components, which is not limited in this embodiment.

[0102] Optionally, the present application also provides a computer-readable storage medium, in which a program is stored, and the program is loaded and executed by a processor to implement the indoor positioning system based on distributed ultrasonic sensing of the above embodiment.

[0103] Optionally, the present application also provides a computer product, which includes a computer-readable storage medium, in which a program is stored, and the program is loaded and executed by a processor to implement the indoor positioning system based on distributed ultrasonic sensing of the above embodiment.

[0104] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0105] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. An indoor positioning system based on distributed ultrasonic sensing, characterized in that: The system comprises: A laser, for outputting an optical signal; A modulator, used for modulating a continuous optical signal into a detection pulse with a specific frequency shift; An erbium-doped fiber amplifier is used to amplify the power of the modulated detection pulse; An optical circulator is used to guide the detection light signal into the optical fiber to be tested, and at the same time separate the Rayleigh backscattered signal returned from the optical fiber to be tested and guide it to the receiving end; The optical fiber to be tested is a sensitive medium used to sense vibration signals; Ultrasonic vibration loader, used to generate ultrasonic vibration at a specific position of the optical fiber to be tested to simulate the target signal; The second stage amplifier is used to amplify the Rayleigh backscattered light signal returned from the optical fiber to be tested to the receiving end; A local oscillator light source, used to interfere with the Rayleigh backscattered light signal; An optical coupler is used to combine the amplified Rayleigh backscattered light signal with the local oscillator light to form an interference light signal; A coherent receiving module is used to receive and process the interference light signal and extract the target vibration information contained therein; The digital signal processor is used to process the demodulated signal, analyze the frequency, amplitude and phase information in the signal, and restore the ultrasonic vibration signal.

2. The indoor positioning system based on distributed ultrasonic sensing according to claim 1 is characterized in that: The detection frequency must satisfy the following formula: Among them, c, n and L are the speed of light, the refractive index of the optical fiber and the length of the optical fiber respectively. The bandwidth of the vibration signal carried by the ultrasonic wave is less than f max / 2.

3. The indoor positioning system based on distributed ultrasonic sensing according to claim 1, characterized in that: The detection pulse is a rectangular pulse, which is shifted to a certain frequency by an acousto-optic modulator. The incident field at the distance Z along the optical fiber and the time t can be expressed as follows: Where E0 is the scalar amplitude of the pulse, f0 is the original optical frequency, and f is the intermediate frequency of AOM modulation. is the initial phase, α is the average attenuation coefficient of the sensing fiber, and β is the propagation constant related to the optical frequency and the local effective refractive index.

4. The indoor positioning system based on distributed ultrasonic sensing according to claim 3 is characterized in that: Incident field E i The Rayleigh scattered field excited from a scatterer at position z can be expressed as follows: Where ρ is the backscattering coefficient in complex form, which is a circular complex Gaussian distribution variable; the phase of ρ is uniformly distributed within 0 to 2π.

5. The indoor positioning system based on distributed ultrasonic sensing according to claim 4, characterized in that: The return electric field at the input end of the optical fiber is the interference of the scattered fields propagated by multiple scatterers in the rectangular window, which can be written as follows: The optical pulse is transmitted back and forth in the optical fiber. The actual pulse width in the optical fiber is twice the rectangular window length. N is the number of scatterers, z i is the position of the i-th scatterer.

6. The indoor positioning system based on distributed ultrasonic sensing according to claim 5, characterized in that: The sum is calculated over the entire rectangular window, and the received field can be viewed as the convolution of the propagated scattered field and a rectangular window, where: β(z)=2π(f0+f)n eff (z) / c。 7. The indoor positioning system based on distributed ultrasonic sensing according to claim 6, characterized in that: Assuming that the vibration signal s(t) is superimposed on the ultrasonic carrier, then The detection results returned by the optical fiber input end are as follows: The local oscillator (LO) from the same laser can be described as follows: Where E1 is the scalar amplitude of the local oscillator, is the initial phase of the local oscillator.

8. The indoor positioning system based on distributed ultrasonic sensing according to claim 7, characterized in that: After heterodyne detection, the received signal can be expressed as follows: where ρ tot is a Rayleigh distributed random variable, In order to evenly distribute the comprehensive phase, when the optical fiber is disturbed by the surrounding vibration, The vibration waveform is obtained by differential calculation and eliminated in the differential operation and Recover the vibration signal.

9. An electronic device, characterized in that: The device includes a processor and a memory; a program is stored in the memory, and the program is loaded and executed by the processor to implement an indoor positioning system based on distributed ultrasonic sensing as described in any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that: The storage medium stores a program, which, when executed by a processor, is used to implement an indoor positioning system based on distributed ultrasonic sensing as described in any one of claims 1 to 8.

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