Cell switching method and device based on leaky coaxial cable positioning

Abstract

The present invention provides a cell switching method and device based on leaky coaxial cable positioning, the method comprising the following steps: the receiver positions itself according to the received time code division orthogonal frequency division multiplexing (TC-OFDM) signal to obtain the current positioning result and the historical positioning error index; the receiver determines whether to capture the TC-OFDM signal of the next leaky coaxial cable (LCX) cell according to the obtained current positioning result and the historical positioning error index; in the case of determining to capture the TC-OFDM signal of the next LCX cell, the receiver captures the TC-OFDM signal of the next LCX cell, and positions according to the captured signal, and obtains the receiver speed based on the change rate of the positioning result; in the case that the change of the receiver speed meets the predetermined condition, it is determined to switch the LCX positioning cell. The cell switching method based on the change trend of the leaky coaxial cable positioning result of the present invention has higher switching accuracy and lower switching delay.

Description

Technical Field

[0001] The present invention relates to the technical field of leaky coaxial cable positioning, and in particular to a cell switching method and device based on leaky coaxial cable positioning. Background Art

[0002] When positioning trains or mine cars in narrow and long scenes such as subway tunnels and mines, plate antennas or rod antennas are usually used as positioning antennas. The positioning signals emitted by the antennas are transmitted in narrow and long environments, resulting in multipath effects and uneven signal coverage, which greatly reduces the positioning accuracy. Leaky coaxial cable (LCX) is more suitable as a positioning antenna in the above environment because of its advantages such as uniform signal radiation and weak signal coverage. At present, the positioning method based on LCX can be divided into LCX positioning method based on time difference of arrival (TDOA), LCX positioning method based on electromagnetic induction and LCX positioning method based on received signal strength (RSS). Among them, the LCX positioning method based on TDOA is more suitable as a positioning antenna in the above scene because of its strong anti-noise ability and high positioning accuracy.

[0003] The positioning principle of the LCX positioning method based on TDOA is to use transmitters (such as Figure 1 The transmitters 11 and 12 in the LCX transmit different time code division-orthogonal frequency division multiplexing (TC-OFDM) signals containing positioning signals. The positioning signals are transmitted by the LCX and arrive near the receiver. They are radiated to the outside world through the slots on the LCX and then received by the receiver. The receiver uses the TDOA of different signals arriving at the receiver to calculate its own position. According to the above principle, when the receiver is in the LCX positioning cell, if Figure 1 The receiver 21 can locate itself; when the receiver is outside the LCX positioning cell, such as Figure 1 For the receiver 21 in the example, the TDOA of the signal 1 and the signal 2 received by the receiver 21 will always be equal to the arrival time (TOA) of the signal propagating from one end of the LCX to the other end. At this time, the receiver will not be able to use the signal of the LCX positioning cell to locate itself. Therefore, when the receiver leaves a certain LCX positioning cell, it is necessary to immediately switch the cell. In order to reduce the positioning error caused by the cell switching, it is necessary to shorten the switching delay as much as possible and improve the switching accuracy.

[0004] The switching principle of the RSS-based cell switching algorithm is to determine whether the RSS of the current LCX cell received by the receiver is less than the threshold to determine whether to perform cell switching. When the RSS is less than the threshold, the cell switching is performed. However, when the environmental noise intensity is large, the accuracy of the receiver's judgment of the RSS will be reduced, especially when the signal-to-noise ratio (SNR) is less than 0dB, the signal will be submerged in the noise, making it impossible for the receiver to immediately determine whether the receiver has crossed the cell boundary, resulting in a large switching delay. Therefore, this method is affected by factors such as environmental noise and multipath effects, and has low switching accuracy and large switching delay, which cannot meet the requirements of low switching delay and high switching accuracy in the LCX positioning scenario based on TDOA.

[0005] How to improve the handover accuracy and shorten the handover delay, and thus improve the positioning accuracy of the LCX-based positioning method using TC-OFDM signals at the boundary of two LCX cells, is an urgent problem to be solved. Summary of the invention

[0006] In view of this, an embodiment of the present invention provides a cell switching method based on leaky coaxial cable positioning to improve the cell switching accuracy and shorten the switching delay.

[0007] One aspect of the present invention provides a cell switching method based on a change trend of a leaky coaxial cable positioning result, the method comprising the following steps:

[0008] The receiver locates itself according to the time code division orthogonal frequency division multiplexing TC-OFDM signal received in the current leaky coaxial cable LCX cell, obtains the current positioning result, and obtains the historical positioning error index based on the historical positioning results;

[0009] The receiver determines whether to capture the TC-OFDM signal of the next LCX cell based on the current positioning result and the historical positioning error index;

[0010] In the case of determining to capture the TC-OFDM signal of the next LCX cell, the receiver captures the TC-OFDM signal of the next LCX cell, performs positioning according to the captured signal, obtains a change trend of the positioning result, and determines whether to switch the LCX positioning cell based on the change trend of the positioning result.

[0011] In some embodiments of the present invention, the receiver determines whether to capture the next LCX positioning cell signal according to the obtained current positioning result and the historical positioning error indicator, including:

[0012] The receiver is positioned by estimating the position range in which the receiver can capture signals based on the transmission attenuation and propagation loss of the LCX and the sensitivity of the receiver. The receiver is then positioned based on the positioning result of the receiver and the standard deviation of the historical positioning error to determine whether to capture the next LCX cell signal.

[0013] In some embodiments of the present invention, the determining whether to capture the next LCX cell signal according to the positioning result of the receiver and the standard deviation of the historical positioning error includes:

[0014] When the difference between the change of the signal power received by the receiver with the position and the standard deviation of the historical positioning error is greater than or equal to a predetermined threshold, it is determined to capture the next LCX cell signal.

[0015] In some embodiments of the present invention, determining whether to switch the LCX positioning cell based on the changing trend of the positioning result includes: obtaining the receiver speed based on the changing trend of the positioning result, and determining to switch the LCX positioning cell when the change of the receiver speed meets a predetermined condition; the predetermined condition is that the speed of the receiver has a falling edge, or the speed change of the receiver is greater than a predetermined threshold.

[0016] In some embodiments of the present invention, the positioning of the receiver according to the time code division orthogonal frequency division multiplexing TC-OFDM signal received in the current leaky coaxial cable LCX cell includes: the receiver correlates the local PRN code with the PRN code of the received TC-OFDM signal, obtains the propagation delay of the TC-OFDM signal according to the code phase of the local PRN code when the correlation result is maximum, and calculates the position of the receiver based on the propagation delay.

[0017] In some embodiments of the present invention, the process in which the terminal receiver correlates the received signal with the local pseudo-random code satisfies the following formula:

[0018]

[0019] Where M is the number of discrete data points involved in the correlation, C PRN represents the local PRN code, m represents the mth correlation result, z represents the sampling time epoch, represents the I-channel baseband digital signal obtained based on the received signal, represents a Q-channel baseband digital signal obtained based on the received signal;

[0020] The baseband digital signal of the I path is expressed as:

[0021]

[0022] The Q-path baseband digital signal is expressed as:

[0023]

[0024] Among them, T s Represents the sampling period of the terminal receiver, R i represents the amplitude attenuation of the TC-OFDM signal propagating through the i-th groove of LCX, s() represents the TC-OFDM signal superimposed with positioning auxiliary information, τ i represents the propagation delay of the TC-OFDM signal propagating through the i-th groove of LCX, w I (zT s ) and w Q (zT s ) represents the noise signal after sampling.

[0025] In some embodiments of the present invention, the receiver captures the next LCX cell signal by calculating the maximum distance at which the receiver can capture the next LCX cell signal based on the capture sensitivity of the receiver and the attenuation model of the LCX radiated signal in free space.

[0026] In some embodiments of the present invention, the method further comprises filtering the positioning result using a moving average filtering method to reduce the speed measurement error, and the filtering principle of the moving average filtering method satisfies the following formula:

[0027]

[0028] Where n represents the nth time epoch, 2q+1 represents the average filter window, and v smooth (n) represents the filtered receiver velocity and v(i) represents the unfiltered velocity measured at the i-th time epoch.

[0029] Another aspect of the present invention provides a cell switching device based on the changing trend of the leakage coaxial cable positioning results, the device includes a processor and a memory, the memory stores computer instructions, the processor is used to execute the computer instructions stored in the memory, when the computer instructions are executed by the processor, the device implements the steps of the method.

[0030] Another aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the above-mentioned method when executed by a processor.

[0031] The cell switching method and device based on leaky coaxial cable positioning of the present invention can realize low-delay and high-precision LCX cell switching at the edge of an adjacent LCX cell when the LCX positioning method using TC-OFDM signals is used for positioning, and reduce the positioning error at the boundary of the adjacent LCX cell. Therefore, compared with the cell switching method based on RSS, the present invention has low switching delay, high switching accuracy and low error, thereby better improving the positioning accuracy of equipment traveling in one direction along the track, such as subway trains and mining cars.

[0032] Additional advantages, purposes, and features of the present invention will be described in part in the following description, and will become apparent to those skilled in the art after studying the following, or may be learned from the practice of the present invention. The purposes and other advantages of the present invention may be achieved and obtained by the structures specifically indicated in the specification and the accompanying drawings.

[0033] Those skilled in the art will appreciate that the objectives and advantages that can be achieved with the present invention are not limited to the above specific description, and the above and other objectives that can be achieved by the present invention will be more clearly understood from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of the present application, and do not constitute a limitation of the present invention. In the drawings:

[0035] Figure 1 This is the positioning principle diagram of the LCX positioning method based on TDOA.

[0036] Figure 2 The figure is a flow chart of a cell switching method based on a changing trend of a leaky coaxial cable positioning result in one embodiment of the present invention.

[0037] Figure 3 FIG. 1 is a step diagram of a cell switching algorithm based on a change trend of an LCX positioning result in an embodiment of the present invention.

[0038] Figure 4 This is a diagram showing the relationship between power attenuation and terminal receiver position in one embodiment of the present invention.

[0039] Figure 5 This is a diagram of train positioning simulation results in one embodiment of the present invention.

[0040] Figure 6 This is a diagram of train speed measurement simulation results in one embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0042] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0043] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0044] In order to solve the problem of long cell switching delay and low switching accuracy when using the LCX-based positioning method using TC-OFDM signals to locate equipment such as subway trains and mine cars that travel one-way along fixed tracks in underground spaces. The present invention provides a cell switching method based on the change trend of leaky coaxial cable positioning results that can improve switching accuracy and shorten switching delay. The method is based on the positioning results of the LCX positioning method. According to the characteristic that the positioning results tend to remain unchanged after the receiver crosses the LCX positioning cell boundary, the receiver speed obtained based on the change rate of the positioning results is used to judge whether the boundary of the LCX positioning cell has been reached. When the change of the receiver speed meets the predetermined conditions (such as the occurrence of a falling edge, etc.), the LCX positioning cell is switched. Thereby, the positioning cell switching has higher switching accuracy, shorter switching delay and higher accuracy, thereby improving the positioning accuracy of the LCX-based positioning method using TC-OFDM signals at the boundary of two LCX cells, and better improving the positioning accuracy of equipment such as subway trains and mine cars that travel one-way along tracks.

[0045] In one embodiment of the present invention, the position range where the receiver can capture the signal is estimated based on the transmission attenuation and propagation loss of the LCX and the sensitivity of the receiver, and it is determined whether the next LCX cell signal can be captured based on the positioning result of the receiver and the standard deviation of the historical positioning error. Then, it is determined whether the LCX positioning cell can be switched based on whether the speed measurement result calculated using the LCX positioning result of the TC-OFDM signal has a falling edge.

[0046] Figure 2 FIG. 1 is a flow chart of a cell switching method based on a change trend of a leaky coaxial cable positioning result according to an embodiment of the present invention. Figure 2 As shown, the method of this embodiment includes the following steps:

[0047] In step S110, the receiver positions itself according to the TC-OFDM signal received in the current leaky coaxial cable LCX cell to obtain a current positioning result, and obtains a historical positioning error indicator based on the historical positioning results.

[0048] The TC-OFDM signal after LCX propagation can be expressed as:

[0049]

[0050] Where n(t) represents additive Gaussian white noise, which has a mean of zero and a variance of σ 2 . R i is the amplitude attenuation of the TC-OFDM signal propagating through the i-th notch of LCX, τ i is the propagation delay of the TC-OFDM signal propagating through the i-th notch of the LCX, is the phase of the carrier of the TC-OFDM signal propagating through the i-th notch of the LCX, s i (t) represents the TC-OFDM signal with superimposed positioning assistance information propagated through the i-th groove of LCX. The TC-OFDM signal with superimposed positioning assistance information can be expressed as:

[0051] s(t)=d(t)p(t) (2)

[0052] Wherein, d(t) represents positioning auxiliary information such as navigation message, p(t) represents TC-OFDM signal, and the formula of p(t) is expressed as:

[0053] p(t)=p c (t)+c PRN (t) (3)

[0054] Among them, p c (t) is the communication signal, C PRN (t) is the positioning signal, which is a PRN code with good autocorrelation. During the positioning process, the receiver correlates the local PRN code with the PRN code of the TC-OFDM signal. According to the code phase of the local PRN code when the correlation result is maximum, the propagation delay of the TC-OFDM signal can be estimated, and then the position of the receiver can be calculated.

[0055] The amplitude attenuation R of the TC-OFDM signal propagating through the i-th notch of LCX i It can be expressed as:

[0056]

[0057] Among them, K2 is a constant, which is caused by the loss of the internal components of the terminal receiver and the gain of the internal amplifier of the terminal receiver; K1 can be expressed by the formula:

[0058]

[0059] In the formula, λ represents the wavelength of the signal transmitted in the LCX, G represents the gain of the receiver antenna, h represents the distance from the receiver to the LCX, l represents the distance from the receiver to the initial point, d represents the spacing of the LCX grooves, α represents the transmission attenuation of the LCX, and E1 represents the electric field strength on the surface of the first groove.

[0060] The phase of the carrier of the TC-OFDM signal propagating through the i-th notch of the LCX It can be expressed as:

[0061]

[0062] Where k0 is the free space propagation constant, represents the initial phase of the carrier of the TC-OFDM signal, ε r Represents the relative dielectric constant of the medium in the leaky coaxial cable.

[0063] The propagation delay τ of the TC-OFDM signal propagating through the i-th notch of LCX i It can be expressed as:

[0064]

[0065] Where c is the speed of electromagnetic wave propagation in free space, v is the speed of electromagnetic wave propagation in LCX, and v can be expressed by the following formula:

[0066]

[0067] The carrier frequency f of the signal propagating through the i-th groove of LCX i It can be expressed by the formula:

[0068]

[0069] Where f is the frequency of the signal transmitted in the leaky coaxial cable.

[0070] After the receiver receives the TC-OFDM signal, it will go through the RF front end, down conversion, low pass filtering, analog-to-digital conversion (ADC), etc. in sequence to perform capture and tracking steps. In the RF front end stage, the terminal receiver amplifies and filters the received signal. In the down conversion stage, the terminal receiver will use the local carrier in the I and Q channels to down-convert the RF signal to the intermediate frequency. The carrier phase difference between the I and Q channels is 0.5π. Since the signal after LCX propagation is a signal composed of multiple superimposed signals, the terminal receiver cannot completely remove the carriers of all superimposed signals in the down conversion stage. Assume that the phase of the local carrier of the receiver is The frequency is f c , then the signal radiated by each groove in formula (1) will have residual carrier after down-conversion

[0071]

[0072] The high-frequency signal generated after down-conversion will be filtered out in the low-pass filtering stage, so that only the low-frequency signal is retained.

[0073] The receiver samples and quantizes the intermediate frequency analog signal in the analog-to-digital conversion stage and converts it into a digital signal. The converted baseband digital signals of the I and Q channels can be expressed as:

[0074]

[0075] and

[0076]

[0077] Among them, T s represents the sampling period of the terminal receiver, z represents the sampling time epoch, and w I (zT s ) and w Q (zT s ) represents the noise signal of I and Q paths after sampling; s(zT s -τ i ) represents the TC-OFDM signal superimposed with positioning assistance information.

[0078] The receiver then captures the sampled and converted signal in the capture phase. In the capture phase, the receiver correlates the received signal with the local pseudo-random code. The correlation process can be expressed as:

[0079]

[0080] Where M is the number of discrete data points involved in the correlation, c PRN represents the local PRN code, j represents a complex number, because the baseband digital signals of I and Q are calculated on different channels, the meaning of this formula is to correlate the baseband digital signals of I and Q respectively, and then calculate the square sum to obtain a correlation result, m represents the mth correlation result, and ||·|| represents the modulo operation.

[0081] Since the two TC-OFDM signals arrive at the receiver at different times, the code phases of the TC-OFDM signals are also different when they arrive at the receiver. The receiver continuously adjusts the code phase of the local PRN code and correlates it with the received TC-OFDM signal. When the code phase of the local PRN code is the same as the code phase of the TC-OFDM signal, the correlation result will be amplified M times, that is, a peak value will appear. The TDOA of the receiver is obtained by using the time difference corresponding to the local PRN code phase difference of the receiver when the peaks of the two signals appear, and the position of the receiver is calculated according to the following formula (13):

[0082]

[0083] Wherein, Δt is the TDOA of two TC-OFDM signals received by the terminal receiver, and L is the length of the leaky coaxial cable.

[0084] After the receiver locates itself based on the above process, the current positioning result can be obtained. Based on the historical positioning results, the historical positioning error index can be obtained, for example, the standard deviation of the historical positioning error of the receiver can be obtained.

[0085] Step S120: The receiver determines whether to capture the next leaky coaxial cable (LCX) cell TC-OFDM signal according to the current positioning result and the historical positioning error index.

[0086] Different from the tracking stage, during the receiver's capture of the LCX cell signal, the receiver needs to continuously calculate the correlation results between the pseudo-random codes of all code phases within a period and the received signal, so as to roughly estimate the code phase of the received signal. Therefore, this process is a very time-consuming process. Therefore, under the premise of successfully completing the LCX positioning cell switching, the terminal receiver on the train or mine car should start capturing the next LCX cell signal as late as possible.

[0087] The embodiment of the present invention calculates the maximum distance at which the receiver can capture the next LCX cell signal based on the capture sensitivity of the receiver and the attenuation model of the signal radiated by the LCX in free space.

[0088] For the convenience of analysis, it is assumed that only one signal in formula (1) is sampled, and the RF signal after sampling by the receiver can be expressed as:

[0089]

[0090] According to the power calculation formula of digital signals, the signal power received by the receiver is expressed as:

[0091]

[0092] Combining the above formulas (4), (6), (7), and (9), we can convert R in formula (16) into i , τ i , They are all expressed as functions of i, d, h and l. Since i, d and h are all known quantities, as long as the position x of the receiver (i.e. l ​​in the previous formula) is calculated, the power value received by the receiver at that location can be calculated.

[0093] Based on the power value received by the receiver, the trend of power value changing with position can be obtained. In order to more clearly see the trend of power value changing with position, P cx and They represent the power measured when the terminal receiver on the train or mine car is at position x and position x0 respectively. The power attenuation in decibel form when the terminal receiver moves from position x = x0 to x is expressed as:

[0094]

[0095] It represents the power attenuation in decibels when the terminal receiver moves from position x = x0 to x. When x0 = 5m, we get The simulation results as x changes are shown in the figure Figure 4 As shown, Figure 4 The horizontal axis represents the position of the receiver, the vertical axis represents the power attenuation, the triangle curve represents the attenuation curve when the distance between the terminal receiver on the train and the LCX is h = 0.5m, the square curve represents the attenuation curve when h = 1m, and the star curve represents the attenuation curve when h = 2m. Figure 4 It can be seen from the figure that when the receiver is within the LCX positioning cell (x>0), the signal strength received by the receiver is roughly equal, and when the terminal receiver is outside the LCX positioning cell, as the distance between the receiver and the LCX positioning cell increases, the strength of the signal radiated by the LCX positioning cell received by the receiver decreases rapidly. Therefore, power attenuation The expression that changes with the receiver position is:

[0096]

[0097] Among them, F h (x) is the functional relationship of the signal power received by the receiver as it varies with position and can be obtained based on formula (16).

[0098] It can be concluded that when the terminal receives a line-of-sight signal from LCX radiation at a distance from the signal transmitter that is 20 dBm higher than the minimum power that the terminal can capture, the receiver can capture the minimum position x of the next LCX positioning cell signal. min :

[0099] x min =lF h -1 (-20) (19)

[0100] In one embodiment of the present invention, assuming that the standard deviation of the historical positioning error of the receiver is σ, the judgment condition for judging whether the receiver starts to capture the next LCX positioning cell signal can be expressed as:

[0101]

[0102] That is, when the difference between the signal power received by the receiver and the standard deviation of the historical positioning error is greater than or equal to the predetermined threshold When the TC-OFDM signal of the next LCX cell is captured, it is determined that the terminal receiver on the train or mining car starts to capture the signal of the next LCX cell as late as possible.

[0103] Step S130: When it is determined to capture the TC-OFDM signal of the next LCX cell, the receiver captures the TC-OFDM signal of the next LCX cell, performs positioning according to the captured signal, obtains a change trend of the positioning result, and determines whether to switch the LCX positioning cell based on the change trend of the positioning result.

[0104] For example, when the change trend of the positioning result meets the predetermined condition, it is determined to switch the LCX positioning cell.

[0105] In this step, when the change trend of the positioning result of the receiver meets the predetermined condition (switching condition), it is determined to switch the LCX positioning cell. When setting the predetermined condition for switching the LCX positioning cell, the following two conditions can be considered:

[0106] Condition 1: Ideally, when the positioning result of the receiver is equal to the maximum position that the LCX positioning cell where the receiver is located can locate, the receiver starts to switch the positioning cell. However, in reality, the positioning result of the receiver has errors. If the positioning result of the receiver is used alone to determine whether the LCX cell switching is required, the switching position will be biased. Therefore, in the process of setting the switching conditions, the error of the positioning result can be further considered.

[0107] Condition 2: When the receiver crosses the boundary of two LCX positioning cells, the time difference between the signal of the original LCX positioning cell reaching the receiver will remain unchanged. At this time, the positioning result of the train will tend to remain unchanged, which is reflected in the changing trend of the positioning result. The rate of change of the positioning result decreases rapidly. Therefore, in the process of determining the switching conditions, whether the changing trend of the positioning result suddenly slows down can be considered to determine whether the train meets the switching conditions.

[0108] Ideally, the position where the receiver switches the positioning cell should be the maximum position x that can be measured by the LCX positioning cell. max , the positioning result of the known receiver is Assuming that the historical positioning error of the receiver satisfies the Gaussian distribution, then when When the following conditions are met:

[0109]

[0110] It can be considered that the receiver has traveled to the vicinity of the boundary between two LCX positioning cells, and it is determined that the LCX positioning cell can be switched at this time.

[0111] Based on the above-mentioned LCX positioning cell switching conditions, since speed reflects the amplitude of position change, in one embodiment of the present invention, the receiver speed can be obtained based on the change trend of the positioning result, and whether the train needs to switch the positioning cell can be determined according to the speed change trend.

[0112] In this step, the speed of the receiver is calculated based on the positioning result of the receiver, based on the fact that the speed is a reflection of the amplitude of the position change. Assume that the positioning result of the receiver at time t1 is The positioning result at time t2 is Where x1 and x2 represent the actual position of the receiver, σ1 and σ2 represent the historical positioning error indicators (such as standard deviation) of the receiver, and t1<t2. 2- If t1 is small enough, it can be considered that the speed of the train remains unchanged from t1 to t2. In this way, the speed calculated by the positioning result of the receiver can be written as follows:

[0113]

[0114] The right side of the equal sign in formula (22) is divided into two parts by a plus sign. The first half represents the actual speed of the train from t1 to t2, and the second half represents the speed measurement error caused by the positioning error of the train. 2- When t1 is small enough, factors such as multipath effect and environmental noise have roughly the same influence on the positioning result of the receiver. It can be considered that the probability distribution of the positioning error of the train from t1 to t2 is basically unchanged. At this time, the larger the value of t2-t1 is, the smaller the error of the speed measurement of the receiver is; but on the other hand, the larger the value of t2-t1 is, the longer it takes for the receiver to calculate the speed once. In this way, the receiver needs more time to determine whether to switch the LCX positioning cell, which leads to a longer switching delay. In the simulation process, the value of t2-t1 is designed to be 10ms, but the present invention is not limited to this.

[0115] In order to further reduce the speed measurement error, the present invention uses a moving average filtering method to filter the positioning result. The filtering principle of the moving average filtering method can be expressed by the formula:

[0116]

[0117] Where n represents the nth time epoch, 2q+1 represents the averaging filter window, and v smooth (n) represents the filtered receiver velocity and v(i) represents the unfiltered velocity measured at the i-th time epoch.

[0118] When the change in the receiver speed meets a predetermined condition, it is determined to switch the LCX positioning cell.

[0119] In one embodiment of the present invention, the predetermined condition is that the speed of the receiver has a falling edge. In another embodiment of the present invention, the predetermined condition is that the speed change (decrease) of the receiver is greater than a predetermined threshold. The above predetermined conditions are only examples, and the present invention is not limited thereto.

[0120] In the embodiment of the present invention, it is assumed that the receiver is placed on the top of the train, the train speed is 36 km / h, the length of a single LCX positioning cell is 60 m, and the train starts running at a constant speed from the starting point of the leaky coaxial cable positioning cell. The positioning result measured by the receiver is as follows: Figure 5 As shown in Figure 2, it can be seen that when the receiver crosses the boundary of two LCX positioning cells, the positioning result will tend to remain unchanged. The corresponding speed measured using the positioning result will be Figure 6 The receiver can detect the rapid descent in the Figure 6 The falling edge shown in determines the LCX positioning cell switching.

[0121] From the above, we can see that Figure 3 As shown, in the cell switching method based on the change trend of the leaky coaxial cable positioning result of the present invention, firstly, it is determined whether the condition for capturing the next LCX cell signal is met based on the positioning result. If the difference between the change of the signal power received by the receiver with the position and the standard deviation of the historical positioning error is greater than or equal to the predetermined threshold (the condition for capturing the next LCX cell signal), the signal of the next LCX cell is captured. After the receiver captures the signal of the next LCX cell, the receiver determines whether the speed measurement result calculated by the positioning result has a falling edge to determine whether the receiver has reached the boundary of the LCX positioning cell. When it is determined to be yes, the LCX cell is switched, the tracking of the original LCX cell signal is cut off, and the signal of the new LCX cell is used to locate itself.

[0122] The cell switching method based on the change trend of the leaky coaxial cable positioning result of the present invention can realize low-delay and high-precision LCX cell switching at the edge of an adjacent LCX cell when the LCX positioning method using the TC-OFDM signal is used for positioning, and reduce the positioning error at the boundary of the adjacent LCX cell. Therefore, compared with the cell switching method based on RSS, the present invention has low switching delay, high switching accuracy and low error, thereby better improving the positioning accuracy of equipment traveling one-way along the track, such as subway trains and mine cars.

[0123] Corresponding to the above method, the present invention also provides a cell switching device based on the changing trend of the leakage coaxial cable positioning results, the device includes a computer device, the computer device includes a processor and a memory, the memory stores computer instructions, the processor is used to execute the computer instructions stored in the memory, when the computer instructions are executed by the processor, the device implements the steps of the method described above.

[0124] The embodiment of the present invention also provides a computer-readable storage medium on which a computer program is stored, and when the computer program is executed by a processor, the steps of the aforementioned edge computing server deployment method are implemented. The computer-readable storage medium can be a tangible storage medium, such as a random access memory (RAM), a memory, a read-only memory (ROM), an electrically programmable ROM, an electrically erasable programmable ROM, a register, a floppy disk, a hard disk, a removable storage disk, a CD-ROM, or any other form of storage medium known in the technical field.

[0125] It should be understood by those skilled in the art that the exemplary components, systems and methods described in conjunction with the embodiments disclosed herein can be implemented in hardware, software or a combination of the two. Whether it is performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention. When implemented in hardware, it can be, for example, an electronic circuit, an application specific integrated circuit (ASIC), appropriate firmware, a plug-in, a function card, etc. When implemented in software, the elements of the present invention are programs or code segments used to perform the required tasks. The program or code segment can be stored in a machine-readable medium, or transmitted on a transmission medium or a communication link via a data signal carried in a carrier.

[0126] It should be clear that the present invention is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present invention.

[0127] In the present invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with features of other embodiments or replace features of other embodiments.

[0128] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the embodiments of the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A cell switching method based on leaky coaxial cable positioning, characterized in that: The method comprises the following steps: The receiver locates itself according to the time code division orthogonal frequency division multiplexing TC-OFDM signal received in the current leaky coaxial cable LCX cell, obtains the current positioning result, and obtains the historical positioning error index based on the historical positioning results; The receiver determines whether to capture the TC-OFDM signal of the next LCX cell based on the current positioning result and the historical positioning error index; In the case of determining to capture the TC-OFDM signal of the next LCX cell, the receiver captures the TC-OFDM signal of the next LCX cell, performs positioning according to the captured signal, obtains a change trend of the positioning result, and determines whether to switch the LCX positioning cell based on the change trend of the positioning result; The positioning of the system according to the time code division orthogonal frequency division multiplexing (TC-OFDM) signal received in the current leaky coaxial cable LCX cell includes: The receiver correlates the local pseudo-random code with the received TC-OFDM signal, obtains the propagation delay of the TC-OFDM signal according to the code phase of the local pseudo-random code when the correlation result is maximum, and calculates the position of the receiver based on the propagation delay; wherein the process of the receiver correlating the local pseudo-random code with the received TC-OFDM signal satisfies the following formula: Where M is the number of discrete data points involved in the correlation, C PRN represents the local pseudo-random code, j represents a complex number, m represents the mth correlation result, z represents the sampling time epoch, represents the I-channel baseband digital signal obtained based on the received signal, represents a Q-channel baseband digital signal obtained based on the received signal, and ||·|| represents a modulo operation.

2. The method according to claim 1, characterized in that The receiver determines whether to capture the next LCX positioning cell signal according to the current positioning result and the historical positioning error index, including: The receiver is positioned by estimating the position range in which the receiver can capture signals based on the transmission attenuation and propagation loss of the LCX and the sensitivity of the receiver. The receiver is then positioned based on the positioning result of the receiver and the standard deviation of the historical positioning error to determine whether to capture the next LCX cell signal.

3. The method according to claim 2, characterized in that The determining whether to capture the next LCX cell signal according to the positioning result of the receiver and the standard deviation of the historical positioning error includes: When the difference between the change of the signal power received by the receiver with the position and the standard deviation of the historical positioning error is greater than or equal to a predetermined threshold, it is determined to capture the next LCX cell signal.

4. The method according to claim 1, characterized in that: Determining whether to switch the LCX positioning cell based on the change trend of the positioning result includes: The receiver speed is obtained based on the change trend of the positioning result, and when the change of the receiver speed meets a predetermined condition, the switching of the LCX positioning cell is determined; The predetermined condition is that a falling edge occurs in the speed of the receiver, or a speed change of the receiver is greater than a predetermined threshold.

5. The method according to claim 1, characterized in that The I-channel baseband digital signal is expressed as: The Q-path baseband digital signal is expressed as: Among them, T s Represents the sampling period of the receiver, R i represents the amplitude attenuation of the TC-OFDM signal propagating through the i-th groove of LCX, s() represents the TC-OFDM signal superimposed with positioning auxiliary information, τ i represents the propagation delay of the TC-OFDM signal propagating through the i-th groove of LCX, represents the residual carrier phase of the signal radiated by each groove of LCX after down-conversion, w I (zT s ) and w Q (zT s ) represents the noise signal after sampling.

6. The method according to claim 1, characterized in that The receiver captures the next LCX cell signal by calculating the maximum distance at which the receiver can capture the next LCX cell signal based on the capture sensitivity of the receiver and the attenuation model of the signal radiated by the LCX in free space.

7. The method according to claim 1, characterized in that The method further includes filtering the positioning result using a moving average filtering method to reduce the speed measurement error. The filtering principle of the moving average filtering method satisfies the following formula: Where n represents the nth time epoch, 2q+1 represents the average filter window, and v smooth (n) represents the filtered receiver velocity and v(i) represents the unfiltered velocity measured at the i-th time epoch.

8. A cell switching device based on the change trend of leaky coaxial cable positioning results, comprising a processor and a memory, characterized in that: The memory stores computer instructions, and the processor is used to execute the computer instructions stored in the memory. When the computer instructions are executed by the processor, the device implements the steps of the method as claimed in any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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