A reference time optimized mobile phone sound wave time difference of arrival measurement method

Abstract

The application is a kind of reference time optimized mobile phone sound wave arrival time difference measurement method, belonging to the field of indoor positioning technology; the method comprises the following steps: firstly, setting up the system and setting the system parameters; then, designing, generating and transmitting the chirp signal; thirdly, receiving the chirp signal by the microphone; fourthly, performing cross-correlation operation to obtain the arrival time difference relative to the reference time initial value; fifthly, optimizing the reference time to obtain the reference time optimized value; finally, performing cross-correlation operation to obtain the arrival time difference relative to the reference time optimized value. Compared with the arrival time difference measurement method, the application has the beneficial effect of being able to always keep the reference time shortest, significantly reducing the measurement error of the arrival time difference.

Description

TECHNICAL FIELD

[0001] A reference time optimized mobile phone sound wave time difference of arrival measurement method belongs to the field of indoor positioning technology. BACKGROUND

[0002] Indoor positioning and service are concerned because of its significant application background, but it is far from satisfactory because of its great technical difficulty. At present, indoor positioning technology develops from two aspects. On the one hand, in terms of technical principles, it mainly includes sound wave, infrared, ultra-wideband, radio frequency positioning technology, among which sound wave positioning is the most accurate solution for indoor positioning. On the other hand, in terms of system hardware implementation scheme, it is divided into two ways. Although the special hardware approach has made great progress in the production field, it is extremely inconvenient to carry a separate positioning device alone, which brings obstacles to indoor positioning and service in life. The approach of using existing devices becomes the natural choice of the public. Mobile phones, as universally owned and powerful mobile devices, are undoubtedly the first choice, and mobile phones can transmit and receive sound waves, which can realize sound wave positioning scheme, and become an inevitable choice.

[0003] The attractive prospect of mobile phone indoor positioning attracts researchers to start research on mobile phone ranging. At present, the mobile phone sound wave indoor positioning technology scheme based on time difference of arrival measurement method is widely used. Its principle is to use the mobile phone speaker to emit sound wave signals, and to set K non-coplanar and fixed microphones to receive sound wave signals, and K≥5, select one of the microphones as the reference, and take the propagation time of the sound wave signal emitted by the mobile phone speaker to the reference microphone as the reference time, measure the difference between the propagation time of the sound wave signal to other microphones and the reference time, which is called time difference of arrival measurement method. Then, the time difference of arrival and the sound wave propagation speed of indoor medium are used to calculate the measured point position according to the ranging intersection principle. Obviously, positioning depends on the measurement of time difference of arrival, and positioning error mainly depends on the measurement error of time difference of arrival, so accurate measurement of time difference of arrival is crucial.

[0004] Smartphones can directly perform time difference of arrival (TDOA) measurements based on cross-correlation analysis (CDE). CDE measures TDOA based on the signal waveform, avoiding the low anti-interference capability issues caused by single-point amplitude judgment. However, in TDOA measurement, the selected reference microphone's position remains fixed. The reference time varies depending on the measurement point, while the power of the sound wave signal emitted by the phone attenuates significantly with increasing reference time. This results in the CDE always containing a severely attenuated microphone signal, significantly increasing the probability of error in determining the maximum value of the cross-correlation function, thus leading to a larger measurement error in TDOA. Therefore, maintaining the shortest possible reference time ensures that the CDE always contains a high signal-to-noise ratio microphone signal with minimal attenuation, which helps reduce TDOA measurement error. Summary of the Invention

[0005] To keep the reference time as short as possible, this invention discloses a mobile phone sound wave arrival time difference measurement method with reference time optimization. Compared with the arrival time difference measurement method, the method of this invention does not use a fixed reference microphone, but optimizes the selection of the reference microphone to use the shortest time among the sound wave propagation times from the mobile phone speaker to each microphone as the reference time, thus always keeping the reference time as short and significantly reducing the measurement error of arrival time difference.

[0006] The objective of this invention is achieved as follows:

[0007] A method for measuring the time difference of arrival of mobile phone sound waves with optimized reference time includes the following steps:

[0008] Step a: According to the usage requirements, set a three-dimensional spatial coordinate system XYZO; set the mobile phone speaker to be located at the point being measured (X,Y,Z); set the microphone n to be located at the known point (X... n ,Y n Z n ), where n = 1, 2, 3, ..., N and N ≥ 5;

[0009] Step b: Set the chirp signal according to the phone's performance specifications. Where A0 is the amplitude, Let f1 be the initial phase, f2 be the frequency range and B = f2 - f1, f1 be the starting frequency, f2 be the cutoff frequency, and K be the rate of frequency change and K = B / T. e T e Let t be the duration of the signal and t be the time variable. The mobile phone generates and transmits the chirp signal x0(t) through the speaker.

[0010] Step c: All microphones synchronously receive the chirp signal x0(t) emitted by the mobile phone speaker for the same duration, thus obtaining the chirp signal of microphone n. Among them, An , f1 and K are the chirp signals x of microphone n, respectively. n The amplitude, initial phase, starting frequency, and rate of frequency change of (t);

[0011] Step d: Select microphone i as the reference microphone, and use the propagation time of the sound wave from the phone speaker to microphone i as the initial reference time to obtain the chirp signal x of microphone i. i (t) and the chirping signal x of microphone n n Cross-correlation function between (t) Where i∈{1,2,3,…,N}, and τ is the chirped signal x. n (t) and the chirping signal x i The time difference variable between (t) is then calculated; the cross-correlation function z is then obtained. ni The maximum value of (τ) z ni (τ ni )=max[z ni (τ)], where max[] is the function for finding the maximum value, τ ni For chirp signal x n (t) and the chirping signal x i The time difference between (t) and τ; then, τ ni The time difference τ is the difference between the propagation time of the sound wave signal from the phone speaker to the microphone n and the initial reference time. ni ;

[0012] Step e: Calculate τ ni The minimum value τ mi =min[τ ni ], where min[] is the minimum value function, m∈{1,2,3,…,N}; then, for the propagation time of the sound wave from the mobile phone speaker to the microphone n, the propagation time of the sound wave from the mobile phone speaker to the microphone m is the shortest. The shortest propagation time is used as the benchmark time optimization value, and the microphone m is used as the optimized benchmark microphone.

[0013] Step f: Obtain the chirp signal x from microphone m. m (t) and the chirping signal x of microphone n n Cross-correlation function between (t) Where τ′ is the chirped signal x n (t) and the chirping signal x m The time difference variable between (t) is then calculated; the cross-correlation function z is then obtained. nm The maximum value of (τ′) z nm (τ′ nm )=max[z nmwhere max[] is the maximum function, τ' nm is the chirp signal x n (t) and the time difference between the chirp signal x m (t); then, τ' nm is the difference between the propagation time of the acoustic signal from the phone speaker to the microphone n and the reference time optimization value, and the arrival time difference relative to the reference time optimization value is τ' nm .

[0014] Beneficial effects: In the arrival time difference measurement method, the reference time length varies with the position of the measured point, and the power of the acoustic signal emitted by the phone is seriously attenuated with the increase of the reference time, resulting in a large measurement error of the arrival time difference. In contrast, the method of the present application always keeps the reference time shortest, which significantly reduces the measurement error of the arrival time difference. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is the flow chart of the method of the present application;

[0016] Figure 2 is the system arrangement diagram;

[0017] Figure 3 is the waveform of the chirp signal x0(t) and its amplitude spectrum;

[0018] Figure 4 is the average of the absolute values of the measurement errors of the first microphone at each node in the arrival time difference measurement method for 40 times;

[0019] Figure 5 is the average of the absolute values of the measurement errors of the second microphone at each node in the arrival time difference measurement method for 40 times;

[0020] Figure 6 is the average of the absolute values of the measurement errors of the third microphone at each node in the arrival time difference measurement method for 40 times;

[0021] Figure 7 is the average of the absolute values of the measurement errors of the fourth microphone at each node in the arrival time difference measurement method for 40 times;

[0022] Figure 8 is the average of the absolute values of the measurement errors of the fifth microphone at each node in the arrival time difference measurement method for 40 times;

[0023] Figure 9 is the average of the absolute values of the measurement errors of the first microphone at each node in the method of the present application for 40 times;

[0024] Figure 10This is the average of the absolute values ​​of the measurement errors of the second microphone at each node in the method of the present invention, which is the value of 40 measurements of the absolute value of the error.

[0025] Figure 11 This is the average of the absolute values ​​of the measurement errors of the third microphone at each node in the method of the present invention, which is the value of 40 measurements of absolute value of error.

[0026] Figure 12 This is the average of the absolute values ​​of the measurement errors of the fourth microphone at each node in the method of the present invention, which is the value of 40 measurements of absolute value of error.

[0027] Figure 13 This is the average of the absolute values ​​of the measurement errors of the fifth microphone at each node in the method of the present invention (40 measurements).

[0028] In the picture, 1 is the first microphone, 2 is the second microphone, 3 is the third microphone, 4 is the fourth microphone, 5 is the fifth microphone, 6 is the sixth microphone, and 7 is the phone speaker. Detailed Implementation

[0029] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0030] The reference time-optimized method for measuring the time difference of arrival of mobile phone sound waves under this specific implementation is as follows: Figure 1 As shown, it includes the following steps:

[0031] Step a: According to the usage requirements, set a three-dimensional spatial coordinate system XYZO, set the mobile phone speaker 7 to be located at the measured point (X,Y,Z), and set the microphone n to be located at the known point (X,Y,Z). n ,Y n Z n ), where n = 1, 2, 3, ..., 6; for example Figure 2 As shown, specifically: the mobile phone speaker 7 is located at the test point (X,Y,Z); the first microphone 1, the second microphone 2, the third microphone 3, the fourth microphone 4, the fifth microphone 5 and the sixth microphone 6 are located at fixed points (0,0,0), (20m,0,3m), (40m,0,0), (40m,20m,0), (20m,20m,3m) and (0,20m,0) respectively;

[0032] Step b: Set the chirp signal according to the phone's performance specifications. Where A0 = 1V is the amplitude, The initial phase is given by B = 4 kHz, the frequency range is given by B = f2 - f1, the starting frequency is given by f1 = 2 kHz, the cutoff frequency is given by f2 = 6 kHz, and the frequency change rate is given by K = 80 kHz / s and K = B / T. e T e=0.05s is the signal duration, t is the time variable, and the unit is seconds. The mobile phone generates and transmits the chirp signal x0(t) through the speaker. The unit of the chirp signal x0(t) is V. See the waveform and amplitude spectrum for details. Figure 3 ;

[0033] Step c: All microphones synchronously receive the chirp signal x0(t) emitted by the mobile phone speaker 7 for the same duration, thus obtaining the chirp signal of microphone n. Among them, A n , f1 = 2kHz and K = 80kHz / s are the chirp signals x of microphone n, respectively. n The amplitude, initial phase, starting frequency, and rate of frequency change of (t); at this time... x n The unit of (t) is V, and the unit of t is s;

[0034] Step d: Select microphone i as the reference microphone, and use the propagation time of the sound wave from the mobile phone speaker 7 to microphone i as the initial reference time value to obtain the chirp signal x of microphone i. i (t) and the chirping signal x of microphone n n Cross-correlation function between (t) Where i∈{1,2,3,…,6}, and τ is the chirped signal x. n (t) and the chirping signal x i The time difference variable between (t) is then calculated; the cross-correlation function z is then obtained. ni The maximum value of (τ) z ni (τ ni )=max[z ni (τ)], where max[] is the function for finding the maximum value, τ ni For chirp signal x n (t) and the chirping signal x i The time difference between (t) and τ; then, τ ni The time difference τ is the difference between the propagation time of the sound wave signal from the phone speaker 7 to the microphone n and the initial reference time. ni ;

[0035] Step e: Calculate τ ni The minimum value τ mi =min[τ ni ], where min[] is the minimum value function, m∈{1,2,3,…,6}; then, for the propagation time of the sound wave from the mobile phone speaker 7 to the microphone n, the propagation time of the sound wave from the mobile phone speaker to the microphone m is the shortest. The shortest propagation time is taken as the benchmark time optimization value, and the microphone m is taken as the optimized benchmark microphone.

[0036] Step f: Obtain the chirp signal x from microphone m. m (t) and the chirping signal x of microphone n n Cross-correlation function between (t) Where τ′ is the chirped signal x n (t) and the chirping signal x m The time difference variable between (t) is then calculated; the cross-correlation function z is then obtained. nm The maximum value of (τ′) z nm (τ′ nm )=max[z nm (τ′)], where max[] is the function for finding the maximum value, τ′ nm For chirp signal x n (t) and the chirping signal x m The time difference between (t); then, τ′ nm The time difference between the sound wave signal's propagation time from the phone's speaker 7 to the microphone n and the optimized reference time is τ′. nm .

[0037] It should be noted that the technical field corresponding to the technical solution of the present invention is the field of indoor positioning technology. For those skilled in the art, the specific parameters and instruments used in each step of the method of the present invention can be selected and applied by those skilled in the art based on their professional knowledge. There is no need to provide specific numerical descriptions and instrument descriptions in the present invention. The cross-correlation function calculations used in steps d and f of the present invention are well-known and mature technologies in the field. Those skilled in the art can fully implement them independently. The present invention has been fully disclosed.

[0038] The following simulation experiment demonstrates that, compared with the time difference of arrival measurement method, the method of the present invention has the technical advantages of maintaining the shortest reference time and having a smaller measurement error in the time difference of arrival.

[0039] The simulation experiment was conducted according to a specific embodiment of the present invention. A total of 1326 nodes were formed on the Z=5m plane with a step size of 0.8m. The three-dimensional coordinates of the nodes are (α×0.8m, β×0.8m, 5m), where α = 0, 1, 2, ..., 50 and β = 0, 1, 2, ..., 25. The nodes were used as the test points. At the test points, the mobile phone speaker 7 emitted a chirp signal x0(t):

[0040] x0(t)=sin[2π(2000+40000t)]

[0041] Where t is in seconds (s) and x0(t) is in volts (V), the waveform and amplitude spectrum of the chirped signal x0(t) can be found in [reference needed]. Figure 3All microphones synchronously receive the chirp signal emitted by the mobile phone speaker 7 for the same duration. Based on the attenuation law of the chirp signal x0(t) with propagation distance, the chirp signal x of microphone n is obtained. n (t):

[0042]

[0043] Where, d n The distance from the phone speaker 7 to the microphone n; the chirp signal x of microphone n. n An independent 0.01V Gaussian white noise is introduced into (t) as an error source to evaluate the resulting time difference of arrival measurement error, so as to compare and evaluate the technical advantages of the method of the present invention.

[0044] First, a simulation measurement was performed using the time difference of arrival (TDOA) method. The propagation time of the sound wave from the phone speaker to microphone 6 was always used as the reference time to obtain the time difference of arrival τ between microphone n and the reference time. n6 Then, the average absolute value of the arrival time difference measurement error of microphone n at each node for 40 times is obtained, such as... Figure 4 (when n=1) Figure 5 (when n=2) Figure 6 (when n=3) Figure 7 (when n=4) Figure 8 (When n=5) is shown; further, the average absolute value of the arrival time difference measurement error of microphone n at all nodes is obtained as 2.7092×10. -6 s (when n=1), 3.1324×10 -6 s (when n=2), 3.8956×10 -6 s (when n=3), 2.4405×10 -6 s (when n = 4), 4.8175 × 10 -6 s (when n = 5).

[0045] Then, simulation measurements are performed using the method of this invention. Taking the propagation time of the sound wave from the phone speaker to microphone 6 as the initial reference time, the arrival time difference of microphone n relative to the optimized reference time value is obtained. This yields the average absolute value of the measurement error of microphone n at each node across 40 measurements. Figure 9 (when n=1) Figure 10 (when n=2) Figure 11 (when n=3) Figure 12 (when n=4) Figure 13 (As shown when n=5); further, the average absolute value of the arrival time difference measurement error of microphone n at all nodes is 1.2842×10. -6 s (when n=1), 0.9552×10 -6s (n=2), 1.4310 x 10 -6 s (n=3), 0.9735 x 10 -6 s (n=4), 1.3305 x 10 -6 s (n=5).

[0046] Comparative analysis Figure 4 and Figure 9 , Figure 5 and Figure 10 , Figure 6 and Figure 11 , Figure 7 and Figure 12 , Figure 8 and Figure 13 , obviously the time difference of arrival measurement error of the method of the present application is smaller; in comparison, the average of the absolute value of the time difference of arrival measurement error of microphone n at all nodes is only 47% (n=1), 30% (n=2), 37% (n=3), 25% (n=4), 28% (n=5) of the time difference of arrival measurement method. This verifies that the method of the present application can significantly reduce the measurement error of the time difference of arrival because the reference time is always the shortest.

Claims

1. A method for reference time optimized mobile phone sound wave time difference of arrival measurement, characterized by, comprising the steps of: Step a, according to the use requirements, set a three-dimensional coordinate system X-Y-Z-O; set the mobile phone speaker at the measured point (X, Y, Z); set the microphone n at the known point (X n ,Y n ,Z n ), where n = 1, 2, 3,..., N, and N ≥ 5; Step b, setting chirp signal according to mobile phone performance index wherein A0 is amplitude, is initial phase, B is frequency range and B = f2-f1, f1 is start frequency, f2 is cut-off frequency, K is frequency change rate and K = B / T e , T e is signal duration, t is time variable, the mobile phone generates and emits the chirp signal x0(t) through the speaker; Step c, all microphones synchronously receive the chirp signal x0(t) emitted by the mobile phone speaker for the same length of time, and the chirp signal of microphone n is obtained wherein A n , f1and K are the amplitude, initial phase, starting frequency and frequency change rate of the chirp signal x n (t) of microphone n, respectively Step d, select microphone i as the reference microphone, take the propagation time of the sound wave from the mobile phone speaker to microphone i as the reference time initial value, and obtain the chirp signal x of microphone i i (t) and the chirp signal x n (t) of microphone n Wherein, i ∈ {1, 2, 3, …, N}, τ is the time difference variable between the chirp signal x n (t) and the chirp signal x i (t); then the cross-correlation function z ni (τ) is calculated ni (τ ni ) = max[z ni (τ)], wherein max[] is the maximum value function, τ ni is the time difference between the chirp signal x n (t) and the chirp signal x i (t); then τ ni is the difference between the propagation time of the sound wave from the mobile phone speaker to microphone n and the reference time initial value, and the arrival time difference relative to the reference time initial value is τ ni ; Step e, finding the minimum value τ ni of τ mi = min[τ ni ], where min[] is a minimum value function, and m ∈ {1, 2, 3, …, N}; then, for the propagation time of the sound wave from the speaker of the mobile phone to the microphone n, the propagation time of the sound wave from the speaker of the mobile phone to the microphone m is the shortest, and the shortest propagation time is taken as the reference time optimization value, and the microphone m is taken as the optimized reference microphone; Step f, obtain chirp signal x of microphone m m (t) with chirp signal x n (t) of microphone n where τ' is the time difference between chirp signal x n (t) and chirp signal x m (t); re-calculate the cross-correlation function z nm (τ') of the maximum value nm (τ' nm ) = max[z nm (τ' nm )], where max[] is the maximum value function, τ' n is the time difference between chirp signal x m (t) and chirp signal x nm (t); then τ' nm is the difference between the propagation time of the sound wave signal from the phone speaker to microphone n and the reference time optimization value, and the arrival time difference relative to the reference time optimization value is τ'.

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