Indoor positioning system and indoor positioning method

Abstract

This invention provides an indoor positioning system and method. A WiFi signal is generated via a WiFi access point. A first leaky-wave antenna converts the received WiFi signal into a first circularly polarized signal and propagates it to a target receiver. A second leaky-wave antenna converts the received WiFi signal into a second circularly polarized signal and propagates it to the target receiver. The second circularly polarized signal is orthogonal to the first circularly polarized signal. The target receiver obtains the target's indoor location information based on the first and second circularly polarized signals. This method eliminates the need for the target to switch between multiple WiFi access points, is less affected by WiFi signal quality, has strong applicability, and provides more accurate positioning.

Description

Technical Field

[0001] This invention relates to the field of indoor positioning technology, and in particular to an indoor positioning system and an indoor positioning method. Background Technology

[0002] With the widespread adoption of IoT technology, the demand for Location Based Services (LBS) is increasing. These services have a wide range of applications, such as smart homes, indoor navigation, and drone tracking. While outdoor positioning is primarily supported by GPS, LBS remains a challenging problem indoors due to the lack of GPS. WiFi-based positioning is one of the most widely used methods for traditional indoor positioning applications, mainly due to the ubiquitous deployment of WiFi access points (APs) and their internet access capabilities. WiFi-based positioning methods can be easily deployed in most indoor scenarios, such as homes and hotels, and can report location to users and LBS providers via wireless LAN.

[0003] In existing WiFi-based indoor positioning methods, those based on Channel State Information (CSI) offer high positioning accuracy and cost savings. However, this method requires line-of-sight signals from WiFi access points (APs) to accurately estimate the target's angle of arrival (Angle of Arrival) or time of flight (Time of Flight), and necessitates the presence of multiple APs to achieve target localization in indoor spaces. Therefore, the actual performance of this method depends heavily on the quantity and quality of available WiFi AP connections, leading to inconsistent positioning accuracy and limiting its application scenarios. Summary of the Invention

[0004] This invention provides an indoor positioning system and method to address the shortcomings of traditional WiFi-based indoor positioning methods, such as unreliable positioning accuracy and limited application scenarios.

[0005] This invention provides an indoor positioning system, comprising:

[0006] WiFi access point, used to generate WiFi signal;

[0007] The first leaky antenna is used to convert the received WiFi signal into a first circularly polarized signal and propagate the first circularly polarized signal to the target receiver.

[0008] The second leaky antenna is used to convert the received WiFi signal into a second circularly polarized signal and propagate the second circularly polarized signal to the target receiver. The second circularly polarized signal is orthogonal to the first circularly polarized signal.

[0009] The target receiver is used to obtain the indoor location information of the target based on the first circularly polarized signal and the second circularly polarized signal.

[0010] An indoor positioning system according to the present invention further includes a WiFi antenna, which is used to transmit the WiFi signal generated by the WiFi access point outward.

[0011] The first leaky antenna and / or the second leaky antenna include:

[0012] Multiple sequentially arranged leakage wave units, a feed port, and a load port, wherein the feed port and the load port are respectively located at both ends of the multiple sequentially arranged leakage wave units;

[0013] The power supply port is used to connect the WiFi antenna to absorb the WiFi signal;

[0014] The load port is used to connect a load, which is used to absorb excess energy.

[0015] According to an indoor positioning system provided by the present invention, the feed ports of the first leaky antenna and the second leaky antenna are located at different positions.

[0016] The first leaky wave antenna is a left-hand circularly polarized antenna, and its feed port is located at the left end of multiple sequentially arranged leaky wave elements;

[0017] The second leaky antenna is a right-hand circularly polarized antenna, and its feed port is located at the right end of multiple sequentially arranged leaky elements.

[0018] The present invention also provides an indoor positioning method, applied to the above-described indoor positioning system, comprising:

[0019] Generate WiFi signal through WiFi access point;

[0020] The WIFI signal is converted into a first circularly polarized signal and a second circularly polarized signal using a first leaky antenna and a second leaky antenna, respectively, wherein the second circularly polarized signal is orthogonal to the first circularly polarized signal.

[0021] The indoor location information of the target is obtained based on the first circular polarization signal and the second circular polarization signal.

[0022] According to an indoor positioning method provided by the present invention, the step of obtaining indoor location information of a target based on a first circularly polarized signal and a second circularly polarized signal includes:

[0023] The estimated frequencies of the first and second circularly polarized signals are input into the positioning model to obtain the indoor location coordinates of the target.

[0024] The positioning model includes a first mathematical equation for a conical surface with the position of the first leaky antenna as the vertex, a second mathematical equation for a conical surface with the position of the second leaky antenna as the vertex, and an equation for the target height horizontal plane.

[0025] The indoor location coordinates of the target are the result of solving the first mathematical equation, the second mathematical equation, and the target height horizontal plane equation simultaneously.

[0026] According to an indoor positioning method provided by the present invention, the method for obtaining the estimated frequency of the first circularly polarized signal and the estimated frequency of the second circularly polarized signal includes:

[0027] Perform circular polarization signal filtering on the signal received by the target receiver;

[0028] The selected circularly polarized signals are then filtered for far-echo signals.

[0029] Filter the near echo signal after filtering the far echo signal;

[0030] The frequencies of the first and second circularly polarized signals after filtering the near-echo signals are estimated and used as the estimated frequencies of the first and second circularly polarized signals, respectively.

[0031] According to an indoor positioning method provided by the present invention, the step of performing circular polarization signal filtering on the signal received by the target receiver includes:

[0032] The first and second leaky antennas are controlled to open and close intermittently;

[0033] Capture the channel state information fluctuation amplitude sequence of the first leaky antenna and the second leaky antenna in the on mode and off mode, respectively;

[0034] The channel state information fluctuation amplitude sequence is subjected to Z-Score normalization.

[0035] Subcarriers with amplitude values ​​greater than a preset threshold in the normalized channel state information fluctuation amplitude sequence are retained as circular polarization signals.

[0036] According to an indoor positioning method provided by the present invention, the step of filtering the selected circularly polarized signals by far-echo signals includes:

[0037] Clustering the subcarriers in the circularly polarized signal yields multiple groups of subcarriers;

[0038] The far echo signal is identified based on the channel state information fluctuation amplitude sequence and bandwidth in each group of subcarriers;

[0039] The far echo signal is filtered to retain subcarrier clusters that meet the amplitude and bandwidth requirements.

[0040] According to an indoor positioning method provided by the present invention, the near echo signal filtering of the signal after filtering the far echo signal includes:

[0041] An intersection operation is performed on the subcarrier clusters in the first circularly polarized signal that meet the amplitude and bandwidth requirements and the subcarrier clusters in the second circularly polarized signal that meet the amplitude and bandwidth requirements, in order to filter out near echo signals outside the intersection and obtain the subcarrier sequence with the largest center frequency.

[0042] According to an indoor positioning method provided by the present invention, estimating the frequency of a first circularly polarized signal and the frequency of a second circularly polarized signal after filtering the near-echo signal includes:

[0043] The weight matrix is ​​obtained by vector multiplication of the subcarrier sequence with the largest center frequency in the first circularly polarized signal and the subcarrier sequence with the largest center frequency in the second circularly polarized signal.

[0044] The weighted average of the subcarrier frequencies in the subcarrier sequence with the largest center frequency corresponding to the first circularly polarized signal is calculated based on the weight matrix to obtain the estimated frequency of the first circularly polarized signal.

[0045] The weighted average of the subcarrier frequencies in the subcarrier sequence with the largest center frequency corresponding to the second circularly polarized signal is calculated based on the weight matrix to obtain the estimated frequency of the second circularly polarized signal.

[0046] The indoor positioning system and method provided by this invention generate WiFi signals through WiFi access points; a first leaky antenna converts the received WiFi signals into a first circularly polarized signal and propagates the first circularly polarized signal to the target receiving end; a second leaky antenna converts the received WiFi signals into a second circularly polarized signal and propagates the second circularly polarized signal to the target receiving end, the second circularly polarized signal being orthogonal to the first circularly polarized signal; the target receiving end obtains the target's indoor location information based on the first and second circularly polarized signals, eliminating the need for the target to switch between multiple WiFi access points, minimizing the impact of WiFi signal quality, enhancing applicability, and providing more accurate positioning. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0048] Figure 1 This is a functional structure diagram of the indoor positioning system provided by the present invention;

[0049] Figure 2 This is a classification and basic schematic diagram of the leaky wave antenna provided by the present invention;

[0050] Figures 3(a) to (d) are polarization characteristic diagrams of electromagnetic waves provided by the present invention;

[0051] Figure 4 This is a graph showing the variation of received signal strength based on the polarization of the signal and the receiving end, as provided by the present invention.

[0052] Figure 5 This is a schematic diagram of the working principle of the indoor positioning system provided by the present invention;

[0053] Figures 6(a) to (c) are functional schematic diagrams of the circularly polarized leaky antenna structure provided by the present invention;

[0054] Figure 7 This is a basic performance diagram of the circularly polarized leaky antenna provided by the present invention;

[0055] Figure 8 This is one of the flowcharts illustrating the indoor positioning method provided by the present invention;

[0056] Figure 9 This is a schematic diagram of wireless signal propagation in the runtime environment provided by the present invention;

[0057] Figure 10 This is the second flowchart illustrating the indoor positioning method provided by the present invention;

[0058] Figures 11(a) and (b) are schematic diagrams of the amplitude and phase of the standardized channel state information provided by the present invention;

[0059] Figures 12(a) to (d) are flowcharts for filtering the correct signal frequency provided by the present invention;

[0060] Figure 13 This is a schematic diagram of the hardware structure of the indoor positioning system provided by the present invention;

[0061] Figure 14 This is a schematic diagram of the hardware structure of the leaky antenna provided by the present invention. Detailed Implementation

[0062] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0063] Figure 1 This is a functional structure diagram of an indoor positioning system provided in an embodiment of the present invention, such as... Figure 1 As shown, the indoor positioning system provided in this embodiment of the invention includes:

[0064] WiFi access point 101 is used to generate WiFi signals;

[0065] The first leaky antenna 102 is used to convert the received WiFi signal into a first circularly polarized signal and propagate the first circularly polarized signal to the target receiver.

[0066] The second leaky antenna 103 is used to convert the received WiFi signal into a second circularly polarized signal and propagate the second circularly polarized signal to the target receiver. The second circularly polarized signal is orthogonal to the first circularly polarized signal.

[0067] The target receiver 104 is used to obtain the indoor location information of the target based on the first circular polarization signal and the second circular polarization signal.

[0068] In this embodiment of the invention, the leaky-wave antenna (LWA) belongs to the category of traveling-wave antennas, where the propagating wave inside the antenna structure can "leak" (i.e., radiate) from the waveguide into free space. It can significantly couple the frequency and radiation direction of the leaky wave signal, generating a frequency-division spatially multiplexed signal, such as... Figure 2 As shown, LWAs with periodic structures typically use dielectric substrates with periodic arrays of metal strips (i.e., slots), similar to antenna arrays. The frequency-division spatially multiplexed signals of this type of LWA can propagate in both forward and backward regions (i.e., [0°. 180°]).

[0069] Specifically, a signal with frequency f The direction of scattering is

[0070]

[0071] Where β(f) and k0(f) are the phase constant of the signal propagating in the LWA and the propagation constant in free space, respectively. The periodic LWA structure, due to its multi-functional slot design and low-cost manufacturing using PCB (printed circuit board) technology, is suitable for the application scenario of this invention to generate circularly polarized signals.

[0072] Polarization is a fundamental characteristic of wireless signals. Polarization represents the direction of the signal's electric field and is denoted as . It can be decomposed into horizontal components. and vertical components There is a phase difference Δφ∈[0,π] between them, resulting in the following ellipse equation.

[0073]

[0074] Where E x0 and E y0 They are and The amplitude.

[0075] When Δφ = 0 or π, we can obtain Therefore, the signal is linearly polarized (LP), as shown in Figure 3(a). The direction of the signal polarization is parallel to... and The angle between related.

[0076] when At that time, one can obtain The signal is circularly polarized (CP) at this point, as shown in Figure 3(b). Furthermore, when Δφ has other values, the signal is elliptically polarized (EP), as shown in Figure 3(c). Similar to the circularly polarized signal, the EP signal can also be divided into left-handed (LHCP) or right-handed (RHCP). Figure 3(d) provides another perspective on how to decompose a circularly polarized signal into two linearly polarized signals. Depending on whether Δφ is positive or negative, the polarization direction of the circularly polarized signal is either left-handed (LHCP) or right-handed (RHCP), which are orthogonal and do not interfere with each other.

[0077] The effect of polarization on the receiver: The polarization of the signal is consistent with the polarization of the transmitting antenna, but it may change during propagation. In order to ensure effective reception, it should be matched with the polarization of the receiving antenna. Figure 4 This explains how polarization mismatch affects received signal strength. For linearly polarized signals and antennas, the received signal strength decreases as the angle between the two polarization directions increases from 0° to 90°. For circularly polarized signals, the signal can be decomposed into two orthogonal linearly polarized signals. Therefore, a linearly polarized antenna can only receive the component whose polarization direction is parallel to itself, losing half of the signal energy. In contrast, a circularly polarized antenna can receive all the signal energy. However, when using LHCP or RHCP antennas to receive circularly polarized signals, since the two polarizations are orthogonal, the theoretical received signal strength is zero, thus eliminating the ambiguity of signals from different leaky-wave antennas.

[0078] A leaky-wave antenna couples the frequency and propagation direction of a signal to form a frequency-division multiplexed signal. The target can calculate its position by capturing the frequencies of the two frequency-division multiplexed signals. Figure 5 As shown. However, due to the similarity of the frequency-division spatially multiplexed signals formed by the two leaky antennas, the target cannot match the frequency-division spatially multiplexed signal with the corresponding signal source, which may lead to position ambiguity and errors. To eliminate this ambiguity, this invention generates frequency-division spatially multiplexed signals with orthogonal circular polarization, left-handed circular polarization (LHCP), and right-handed circular polarization (RHCP), so that they do not interfere with each other, and the source of each frequency-division spatially multiplexed signal can be distinguished and the target position can be accurately calculated.

[0079] To generate a circularly polarized signal, as shown in Figure 6(a), the slot is bifurcated, separating the input signal into two orthogonal linearly polarized signals of equal amplitude. Since a certain distance is required between the two linearly polarized signals... A phase difference is needed to generate a circularly polarized signal, which can be achieved by adjusting the lengths of the two orthogonal slots. A leaky antenna can only generate a good circularly polarized signal when the element size is suitable for the center frequency of the operating band. As shown in Figure 6(b), a double-layer copper-clad substrate structure is used. The substrate material is F4BM-2, with a dielectric constant of 3.02 and a loss tangent of 0.001. The top and bottom of the substrate are made of copper and are tin-plated to prevent oxidation. The bottom copper layer serves as a ground and includes short vias to penetrate the substrate, connecting the top and bottom layers to ground the top layer. These short vias are periodically arranged on the upper and lower boundaries of the substrate and the patch.

[0080] The final structure of the leaky antenna is shown in Figure 6(c), where multiple elements are arranged together to enhance its directivity, which can be likened to an antenna array. For example, there are 11 elements. Each element has two ports at both ends: one is a feed port, connecting to the linearly polarized antenna to absorb the linearly polarized WiFi signal; the other is connected to a matched load, such as a 50Ω load. By changing the signal input port, the polarization of the leaked frequency-division multiplexed signal can be switched between left-hand circular polarization and right-hand circular polarization. If the input signal has passed through all slots and reached the other end, but there is still residual energy, the matched load will absorb the excess signal, preventing the residual signal from re-entering the idle space. By adjusting the spacing between the elements, different WiFi frequency bands can be accommodated, making it universally applicable to multiple frequencies and bandwidths. This invention is designed for the 5.17GHz-5.33GHz WiFi frequency band; however, it should be noted that this invention does not limit the WiFi frequency band. Now, rapid verification is performed using ANSYS HFSS simulation software. The direction of the frequency-division multiplexed signal at different frequencies is shown below. Figure 7As shown in (a), there is a total field of view of 22° in the operating frequency band (5.17 GHz - 5.33 GHz). When the linearly polarized signal is fed to the right or left port, the right-hand circularly polarized signal radiates from 22° to 44° or from 136° to 158°, respectively. Figure 7 (b) shows the energy distribution of the signal at five different frequencies. It is evident that the energy of the leaked signal is concentrated in the correct direction, achieving a gain of over 11.5 dB in all cases. Therefore, the direction can still be easily determined by examining the signal's energy distribution.

[0081] Traditional WiFi-based indoor positioning methods, particularly those based on channel state information, offer high positioning accuracy and cost savings. However, these methods require line-of-sight signals from WiFi access points (APs) to accurately estimate the target's angle of arrival (Angle of Arrival) or time of flight (Time of Flight). Multiple APs are needed to locate the target in indoor spaces. Therefore, the actual performance of this method depends heavily on the quantity and quality of available WiFi AP connections, leading to inconsistent positioning accuracy and limited application scenarios.

[0082] The indoor positioning system provided in this embodiment of the invention generates a WiFi signal through a WiFi access point; a first leaky antenna converts the received WiFi signal into a first circularly polarized signal and propagates the first circularly polarized signal to the target receiving end; a second leaky antenna converts the received WiFi signal into a second circularly polarized signal and propagates the second circularly polarized signal to the target receiving end, the second circularly polarized signal being orthogonal to the first circularly polarized signal; the target receiving end obtains the target's indoor location information based on the first and second circularly polarized signals, without requiring the target to switch between multiple WiFi access points, is less affected by WiFi signal quality, has strong applicability, and provides more accurate positioning.

[0083] The indoor positioning method provided by the present invention is described below. The indoor positioning method described below can be referred to in correspondence with the indoor positioning system described above.

[0084] Figure 8 A flowchart of the indoor positioning method provided in the embodiments of the present invention is shown below. Figure 8 As shown, the indoor positioning method provided in this embodiment of the invention includes:

[0085] Step 801: Generate a WiFi signal through the WiFi access point;

[0086] Step 802: Use the first leaky antenna and the second leaky antenna to convert the WiFi signal into a first circularly polarized signal and a second circularly polarized signal, respectively. The second circularly polarized signal is orthogonal to the first circularly polarized signal.

[0087] Step 803: Obtain the indoor location information of the target based on the first circular polarization signal and the second circular polarization signal.

[0088] The indoor positioning method provided in this embodiment of the invention generates a WiFi signal through a WiFi access point; a first leaky antenna converts the received WiFi signal into a first circularly polarized signal and propagates the first circularly polarized signal to the target receiving end; a second leaky antenna converts the received WiFi signal into a second circularly polarized signal and propagates the second circularly polarized signal to the target receiving end, the second circularly polarized signal being orthogonal to the first circularly polarized signal; the target receiving end obtains the target's indoor location information based on the first and second circularly polarized signals, without requiring the target to switch between multiple WiFi access points, is less affected by WiFi signal quality, has strong applicability, and provides more accurate positioning.

[0089] Based on any of the above embodiments, obtaining the indoor location information of the target according to the first circularly polarized signal and the second circularly polarized signal includes:

[0090] The estimated frequencies of the first and second circularly polarized signals are input into the positioning model to obtain the indoor location coordinates of the target.

[0091] The positioning model includes a first mathematical equation for a conical surface with the position of the first leaky antenna as the vertex, a second mathematical equation for a conical surface with the position of the second leaky antenna as the vertex, and an equation for the target height horizontal plane.

[0092] The indoor location coordinates of the target are the result of solving the first mathematical equation, the second mathematical equation, and the target height horizontal plane equation simultaneously.

[0093] set up and These represent left-hand circularly polarized and right-hand circularly polarized signals, respectively, propagating from the corresponding leaky antennas to the target through the line-of-sight path. The frequencies of these two signals are respectively... and Circularly polarized signals include frequency-division and space-division multiplexed signals, as well as orthogonally circularly polarized signals; these two types of signals do not interfere with each other. Therefore, the target's relative orientation to the two leaky antennas can be estimated based on the received spectrum and the radiation patterns of the two leaky antennas. The target height is known to be z. T The position coordinates of the right-hand circularly polarized leaky antenna are: The position coordinates of the left-hand circularly polarized leaky antenna are Since the radiation mode of the leaky antenna corresponds to the conical surface of the signal at a specific frequency, the target location LOC T (x T ,y T Let be the intersection of the two conical surfaces and the horizontal plane of the target height. The LOC can be estimated by solving the following system of equations.T :

[0094]

[0095] Where z T It is the height of the target, the function and These are the mathematical equations for a conical surface with the positions of the first and second leaky antennas as its vertices. These equations represent the equations for left-handed and right-handed circularly polarized signals, respectively. and The direction of propagation at a given frequency. Taking a right-hand circularly polarized signal as an example, It can be represented as

[0096]

[0097] in

[0098] like Figure 9 As shown, during the positioning process, there are two other types of signals that can affect the positioning process. The first type of interference signal is emitted by the WiFi AP and then received by the target as the LP WiFi signal S. LP This signal establishes data communication between the target and the access point (AP), and also serves as the input signal for the first and second leaky antennas. The first and second leaky antennas convert the input signal into a circularly polarized frequency-division multiplexed signal. The WiFi signal propagates through line-of-sight and multipath paths, where S... LP These represent both line-of-sight and multipath WiFi signals, respectively. The first type of interference signal is a multipath circularly polarized signal. The signal is reflected from the leaky antenna onto the target at a distance or near distance, and then propagates back to the target, forming a far echo signal. and near echo signal

[0099] Therefore, to accurately estimate the target's location, it is necessary to filter out S. LP and Based on any of the above embodiments, such as Figure 10 As shown, the methods for obtaining the estimated frequencies of the first and second circularly polarized signals include:

[0100] Step 1001: Perform circular polarization signal filtering on the signal received by the target receiver;

[0101] In this embodiment of the invention, the circular polarization signal filtering of the signal received by the target receiver includes:

[0102] Step 10011: Control the first and second leaky antennas to open and close intermittently;

[0103] Step 10012: Capture the channel state information fluctuation amplitude sequence of the first leaky antenna and the second leaky antenna in the open mode and the closed mode, respectively;

[0104] Step 10013: Perform Z-Score normalization on the channel state information fluctuation amplitude sequence;

[0105] Step 10014: Retain subcarriers with amplitude values ​​greater than a preset threshold in the normalized channel state information fluctuation amplitude sequence as circular polarization signals.

[0106] In this embodiment of the invention, the leaky-wave antenna requires a linearly polarized WiFi signal S. LP As input, the target may also need it to communicate with the WiFi AP for data. However, this linearly polarized signal may interfere with the reception of circularly polarized signals because the CP antenna on the target can fully receive the linearly polarized signal. To eliminate this interference, the LWA can be controlled to turn on and off intermittently, operating in duty cycle mode. This allows the target to identify frequencies affected by circularly polarized signals by analyzing changes in its received spectrum, while conserving the energy of the leaky antenna. Specifically, WiFi channel state information is utilized, which provides fine-grained information through numerous subcarriers. When the leaky antenna is turned on or off, the center frequency f is respectively... k The channel state information corresponding to the k-th subcarrier is represented as H on (f k ) and H off (f k The former is affected by both circular and linear polarization signals, while the latter is determined only by the linear polarization signal. The relationship is as follows:

[0107]

[0108] Where ||H CP (f k )|| and ∠H CP The amplitude and phase of the channel state information affected by the circularly polarized signal, ||H LP (f k )|| and ∠H LP This represents the amplitude and phase of the CSI affected by the linearly polarized signal. Fluctuations in the acquisition channel state information caused by the circularly polarized signal are quantized as...

[0109]

[0110] In order to accurately analyze ΔH(f) k To mitigate the effects of occasional outliers and noise, Z-score normalization is performed on the phase and amplitude variation sequences, yielding Z(||ΔH(f)). k )||) and Z(∠ΔH(fk )).

[0111] Figure 11 shows the experimental results, where the subcarrier affected by line of sight and multipath signals is at the normalized amplitude Z(||ΔH(f)). k The subcarriers are distinguishable in Z(||). However, the phase changes are not significant, which makes identifying useful subcarriers challenging, as they are often masked by random errors and noise. Therefore, it is sufficient to consider Z(||ΔH(f)). k The changes in Z(||) are obtained. k After processing the sequence Z(||)||), a preliminary screening is performed to quickly filter out subcarriers that are unlikely to be affected by circular polarization signals. A percentage threshold ε∈[0,1] is set to select Z(||ΔH(f) ... k Subcarriers with larger ε values ​​are more susceptible to the effects of circularly polarized signals. It should be noted that the value of ε is empirically chosen based on the multipath effect. Figure 12(a) illustrates the method for selecting subcarriers.

[0112] Step 1002: Filter the selected circularly polarized signals using far-echo signals;

[0113] In this embodiment of the invention, the screening of circularly polarized signals includes far-echo signal filtering, comprising:

[0114] Step 10021: Cluster the subcarriers in the circularly polarized signal to obtain multiple groups of subcarriers;

[0115] Step 10022: Identify the far echo signal based on the channel state information fluctuation amplitude sequence and bandwidth in each group of subcarriers;

[0116] Step 10023: Filter the far echo signal and retain subcarrier clusters that meet the amplitude and bandwidth requirements.

[0117] The presence of abundant indoor reflections introduces severe multipath signals. line of sight signals This causes interference and significant positioning errors. Because multipath signals have weak amplitudes, they attenuate significantly after reflection, resulting in weak amplitudes. Therefore, compared to line-of-sight signals, the changes in subcarriers affected by them are relatively small. Furthermore, multipath signals are frequency-dispersed; due to the special characteristics of frequency-division multiplexed signals, multipath signals are distributed at frequencies different from line-of-sight signals. Multipath signals can be divided into two categories: far-echo signals... (Reflection distance from the target is relatively far) and near echo signal (The reflection distance is relatively close to the target.) The frequencies of these signals are typically sparsely distributed within the operating frequency band because even if reflections occur in many places, only a few signals arrive at the target at discontinuous frequencies. However, The frequency is mainly concentrated in line-of-sight signals The frequency is close to that of the far-echo signal, making direct filtering difficult. Therefore, as shown in Figure 12(a), the far-echo signal forms a cluster of distributed subcarriers with relatively small amplitude variations, while the subcarrier clusters affected by the near-echo signal are very similar to those affected by the line-of-sight (S) signal, forming a cluster with larger variations and higher amplitudes. First, the far-echo signal based on the above observations is processed, and different subcarriers are clustered as shown in Figure 12(b). To find the cluster with the widest bandwidth and highest amplitude, the following integral function is calculated for the i-th cluster.

[0118]

[0119] in and C represents the minimum and maximum frequencies of the i-th cluster, respectively. i The value can be seen as and and The area formed by the curves at the two frequencies. The wider the bandwidth of the cluster and the higher the amplitude, the higher its C... i The larger the value.

[0120] Keep only C i The cluster with the highest value is most likely to contain subcarriers affected by line-of-sight signals. (Far echo signal) They are filtered out due to their more dispersed distribution and widespread attenuation. Conversely, near-echo signals are preserved. and line of sight signals The subcarrier range of the right-hand circularly polarized signal that retains the influence of the retained signal is expressed as: The subcarrier range of a left-hand circularly polarized signal is expressed as:

[0121] Step 1003: Filter the signal after filtering the far echo signal to filter the near echo signal;

[0122] In this embodiment of the invention, filtering the signal after filtering the far echo signal includes:

[0123] An intersection operation is performed on the subcarrier clusters in the first circularly polarized signal that meet the amplitude and bandwidth requirements and the subcarrier clusters in the second circularly polarized signal that meet the amplitude and bandwidth requirements, in order to filter out near echo signals outside the intersection and obtain the subcarrier sequence with the largest center frequency.

[0124] To minimize positioning errors, near-echo signals must be eliminated. The impact. Therefore, the first step is to find... and ||ΔH(f)k The center frequency of the largest subcarrier is shown in Figure 12(c). The index of the selected subcarrier is denoted as K. RH and K LH Since there may be several subcarriers, all of which have high amplitude variations, because... It has a narrow bandwidth and affects multiple subcarriers. In this case, the center frequency of these subcarriers is selected as the chosen frequency. Next, as shown in Figure 12(c), only the intersection of the selected subcarriers of the right-hand circularly polarized signal and the left-hand circularly polarized signal is taken, and then the head and tail are trimmed to obtain the trimmed sequence ||ΔH′(f k )||.

[0125] Step 1004: Estimate the frequencies of the first and second circularly polarized signals after filtering the near-echo signals, and use them as the estimated frequencies of the first and second circularly polarized signals.

[0126] In this embodiment of the invention, estimating the first circularly polarized signal frequency and the second circularly polarized signal frequency after filtering the near-echo signal includes:

[0127] Step 10041: Multiply the subcarrier sequence with the largest center frequency in the first circularly polarized signal by the vector of the subcarrier sequence with the largest center frequency in the second circularly polarized signal to obtain the weight matrix;

[0128] Step 10042: Calculate the weighted average of the subcarrier frequencies in the subcarrier sequence with the largest center frequency corresponding to the first circularly polarized signal according to the weight matrix, and obtain the estimated frequency of the first circularly polarized signal;

[0129] Step 10043: Calculate the weighted average of the subcarrier frequencies in the subcarrier sequence with the largest center frequency corresponding to the second circularly polarized signal based on the weight matrix, and obtain the estimated frequency of the second circularly polarized signal.

[0130] In this embodiment of the invention, the two ||ΔH′(f) of the right-hand circularly polarized signal and the left-hand circularly polarized signal are... k The vectors are multiplied to form a weight matrix G. Each weight in matrix G represents the probability that a pair of frequencies is a line-of-sight signal, as shown in Figure 12(d). The color depth represents the magnitude of the weight. The darker the color, the larger the weight, and the greater the probability that the pair of frequencies is a line-of-sight signal.

[0131]

[0132] Where δ is the vector ΔH′(f) k Half the length.

[0133] Then, through calculation and To estimate by weighted average of the values ​​in and These values ​​are weighted with the corresponding values ​​in matrix G to reduce interference from near-echo signals and noise.

[0134] This invention provides an indoor positioning method that overcomes location estimation errors by filtering out unwanted WiFi signals and multipath frequency division multiplexing (FDM) signals. First, the first and second leaky antennas are intermittently switched on and off with varying duty cycles, allowing the target to distinguish between FDM signals and WiFi signals by analyzing changes in WiFi channel state information. Then, multipath signals are filtered out based on their distribution and amplitude characteristics without requiring any WiFi access point (AP) to send specific signals or require the target to hop between different APs or channels. This extends WiFi functionality to a localized location without hindering data communication between WiFi transceivers.

[0135] Figure 13 The hardware structure diagram of the indoor positioning system provided in the embodiments of the present invention is as follows: Figure 13 As shown, the indoor positioning system provided in this embodiment of the invention includes:

[0136] The left-hand circularly polarized antenna, the right-hand circularly polarized antenna, the WiFi access point, and the low-noise amplifier are all mounted on the antenna bracket of the COMFAST AX210 network card connected to the host computer.

[0137] In an embodiment of the present invention, the leaky antenna is as follows: Figure 14 As shown, the main body is 24.2cm x 5.2cm in length and contains 11 individual units, designed to ensure that most of the energy of the input signal can leak out. One feed port of the leaky antenna is connected to the LP antenna for receiving WiFi signals, while the other port is connected to a 50-ohm matched load to absorb the remaining energy of the signal passing through the entire leaky antenna structure. The feed ports are oriented differently to distribute the output of left-hand and right-hand circularly polarized leaked signals. In some embodiments of the invention, a low-noise amplifier powered by a small rechargeable battery is used to boost the input signal, with a power consumption of 0.43W. A Seeed Studio XIAO and a transistor are used to control the switching state of the amplifier to control the left-hand and right-hand circularly polarized antennas to operate at a 20% duty cycle, thus saving energy.

[0138] The PicoScenes WiFi sensing platform was used to transmit WiFi packets at a power of 20dBm at the WiFi access point and extract channel state information at the target location. Within the operating frequency band, PicoScenes can acquire channel state information data for 2025 subcarriers, indexed [-1012, 1012]. PicoScenes was run on Ubuntu 20.04, and the channel state information data was analyzed. The aforementioned positioning method was then executed on MATLAB 2022b.

[0139] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0140] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0141] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An indoor positioning system, characterized in that, include: WiFi access point, used to generate WiFi signal; The first leaky antenna is used to convert the received WiFi signal into a first circularly polarized signal and propagate the first circularly polarized signal to the target receiver. The second leaky antenna is used to convert the received WiFi signal into a second circularly polarized signal and propagate the second circularly polarized signal to the target receiver. The second circularly polarized signal is orthogonal to the first circularly polarized signal. The target receiver is used for: The estimated frequencies of the first and second circularly polarized signals are input into the positioning model to obtain the indoor location coordinates of the target. The positioning model includes a first mathematical equation for a conical surface with the position of the first leaky antenna as the vertex, a second mathematical equation for a conical surface with the position of the second leaky antenna as the vertex, and an equation for the target height horizontal plane. The indoor location coordinates of the target are the result of solving the first mathematical equation, the second mathematical equation, and the target height horizontal plane equation simultaneously.

2. The indoor positioning system according to claim 1, characterized in that, It also includes a WiFi antenna, which is used to transmit the WiFi signal generated by the WiFi access point outwards; The first leaky antenna and / or the second leaky antenna include: Multiple sequentially arranged leakage wave units, a feed port, and a load port, wherein the feed port and the load port are respectively located at both ends of the multiple sequentially arranged leakage wave units; The power supply port is used to connect the WiFi antenna to absorb the WiFi signal; The load port is used to connect a load, which is used to absorb excess energy.

3. The indoor positioning system according to claim 2, characterized in that, The feed ports of the first and second leaky antennas are located in different positions. The first leaky wave antenna is a left-hand circularly polarized antenna, and its feed port is located at the left end of multiple sequentially arranged leaky wave elements; The second leaky antenna is a right-hand circularly polarized antenna, and its feed port is located at the right end of multiple sequentially arranged leaky elements.

4. An indoor positioning method, applied to the indoor positioning system according to any one of claims 1 to 3, characterized in that, include: Generate WiFi signal through WiFi access point; The WIFI signal is converted into a first circularly polarized signal and a second circularly polarized signal using a first leaky antenna and a second leaky antenna, respectively, wherein the second circularly polarized signal is orthogonal to the first circularly polarized signal. The estimated frequencies of the first and second circularly polarized signals are input into the positioning model to obtain the indoor location coordinates of the target. The positioning model includes a first mathematical equation for a conical surface with the position of the first leaky antenna as the vertex, a second mathematical equation for a conical surface with the position of the second leaky antenna as the vertex, and an equation for the target height horizontal plane. The indoor location coordinates of the target are the result of solving the first mathematical equation, the second mathematical equation, and the target height horizontal plane equation simultaneously.

5. The indoor positioning method according to claim 4, characterized in that, The methods for obtaining the estimated frequency of the first circularly polarized signal and the estimated frequency of the second circularly polarized signal include: Perform circular polarization signal filtering on the signal received by the target receiver; The selected circularly polarized signals are then filtered for far-echo signals. Filter the near echo signal after filtering the far echo signal; The frequencies of the first and second circularly polarized signals after filtering the near-echo signals are estimated and used as the estimated frequencies of the first and second circularly polarized signals, respectively.

6. The indoor positioning method according to claim 5, characterized in that, The circular polarization signal filtering of the signal received by the target receiver includes: The first and second leaky antennas are controlled to open and close intermittently; Capture the channel state information fluctuation amplitude sequence of the first leaky antenna and the second leaky antenna in the on mode and off mode, respectively; The channel state information fluctuation amplitude sequence is subjected to Z-Score normalization. Subcarriers with amplitude values ​​greater than a preset threshold in the normalized channel state information fluctuation amplitude sequence are retained as circular polarization signals.

7. The indoor positioning method according to claim 6, characterized in that, The process of filtering the selected circularly polarized signals for far-echo signals includes: Clustering the subcarriers in the circularly polarized signal yields multiple groups of subcarriers; The far echo signal is identified based on the channel state information fluctuation amplitude sequence and bandwidth in each group of subcarriers; The far echo signal is filtered to retain subcarrier clusters that meet the amplitude and bandwidth requirements.

8. The indoor positioning method according to claim 7, characterized in that, The near-echo signal filtering of the signal after filtering the far echo signal includes: An intersection operation is performed on the subcarrier clusters in the first circularly polarized signal that meet the amplitude and bandwidth requirements and the subcarrier clusters in the second circularly polarized signal that meet the amplitude and bandwidth requirements, in order to filter out near echo signals outside the intersection and obtain the subcarrier sequence with the largest center frequency.

9. The indoor positioning method according to claim 8, characterized in that, The estimation of the first circularly polarized signal frequency and the second circularly polarized signal frequency after filtering the near-echo signal includes: The weight matrix is ​​obtained by vector multiplication of the subcarrier sequence with the largest center frequency in the first circularly polarized signal and the subcarrier sequence with the largest center frequency in the second circularly polarized signal. The weighted average of the subcarrier frequencies in the subcarrier sequence with the largest center frequency corresponding to the first circularly polarized signal is calculated based on the weight matrix to obtain the estimated frequency of the first circularly polarized signal. The weighted average of the subcarrier frequencies in the subcarrier sequence with the largest center frequency corresponding to the second circularly polarized signal is calculated based on the weight matrix to obtain the estimated frequency of the second circularly polarized signal.

Images