KR101515512B1 - Method for estimating location based on time difference of arrival - Google Patents

Abstract

A method for estimating a location based on time difference of arrival (TDOA) according to the present invention is provided. The purpose of the present invention is to provide a method for estimating a location which is robust to a frequency offset and is capable of improving the estimation accuracy on a location of a receiver or a location of a signal source based on TDOA. The method for estimating a location based on TDOA according to the present invention includes: a step of receiving a plurality of reception signals and configuring a candidate group which includes the reception signals; a step of selecting one among the reception signals included in the candidate group as a reference point and removing a reception signal corresponding to the selected reference point from the candidate group; a step of calculating a measured TDOA value which is a difference between the selected reference point and the rest reception signals; a step of estimating a location based on the calculated measured TDOA value; and a step of determining the final location value based on the multiple estimated location values until the candidate group becomes an empty group.

Description

Field of the Invention < RTI ID = 0.0 > [0002] < / RTI &

The present invention relates to position estimation based on Time Difference of Arrival (TDOA). More particularly, the present invention relates to a TDOA based positioning method that is robust to a frequency offset, Time-difference-based position estimation method capable of improving the accuracy of estimation of the arrival time difference.

There is a growing demand for location-based services in various industrial fields such as mobile communication, aeronautical and defense, and the importance of location measurement of a receiver and position of a signal source is emerging.

When measuring the position of the receiver, different frequency offsets occur due to oscillator differences of the respective base stations. When measuring the position of the signal source, different frequency offsets There is a problem that this occurs.

As a technique for estimating the position of a conventional receiver or the position of a signal source, there is a TDOA-based position estimation method.

The conventional TDOA-based position estimation technique is a technology for calculating a TDOA value through simple cross correlation and estimating a position, and is used in various fields.

However, since the TDOA-based position estimation technique may degrade the position estimation performance when frequency offsets occur, a separate frequency synchronization process must be added to improve the estimation performance.

 In addition, the conventional TDOA-based position estimation technique has a problem that the position estimation can diverge depending on which base station or receiving sensor is used as the reference point when calculating the TDOA measurement value.

Therefore, there is a need for a TDOA based position estimation method robust to the frequency offset without adding the frequency synchronization process.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the conventional art, and it is an object of the present invention to provide a receiver capable of improving the estimation accuracy of the position of the receiver or the position of the signal source based on the TDOA, And to provide a position estimation method based on arrival time difference.

It is another object of the present invention to provide a position estimation method based on arrival time difference which can improve accuracy of estimation of a position of a receiver or a position of a signal source without a separate frequency synchronization process.

It is another object of the present invention to provide a position estimation method based on arrival time difference, which can improve the accuracy of position estimation and prevent divergence of position estimation through reference point selection and iterative estimation.

According to an aspect of the present invention, there is provided a position estimation method based on arrival time difference, comprising: receiving a plurality of received signals and constructing a candidate set including the received plurality of received signals; Selecting one of the plurality of received signals included in the candidate set as a reference point and removing a received signal corresponding to the selected reference point from the candidate set; Calculating a time difference of arrival (TDOA) measurement between the selected reference point and the remaining received signals; Estimating a position value based on the calculated TDOA measurement value; And determining a final position value based on a plurality of position values estimated until the candidate set becomes an empty set.

Advantageously, said determining step may determine an average value for said estimated plurality of position values as said final position value.

Preferably, the determining step may further include a step of removing a position value of the positional variation of the plurality of positional values from a distribution of the estimated plurality of positional values, the positional value being greater than or equal to a predetermined threshold value, It can be determined as the final position value.

Advantageously, the calculating step may calculate a time at which the differential cross-correlation between the reference point and the remaining received signals becomes maximum, as the TDOA measurement value.

Advantageously, said calculating step calculates said TDOA measurement value based on a D differential cross-correlation between said reference point and said remaining received signals, wherein said D value is an oversampling number for said received plurality of received signals Lt; / RTI >

According to another aspect of the present invention, there is provided a position estimation method based on arrival time difference, comprising: receiving a plurality of received signals and constructing a candidate set including the received plurality of received signals; Selecting one of the plurality of received signals included in the candidate set as a reference point and calculating a time difference of arrival (TDOA) measurement between the selected reference point and the remaining received signals; Estimating a position value based on the calculated TDOA measurement value; And determining a final position value based on the estimated plurality of position values until the candidate set becomes vacant.

According to the present invention, the position of the receiver or the position of the signal source is estimated based on the TDOA measurement value using the differential cross-correlation, so that the accuracy of estimation of the position can be improved while being robust to the frequency offset.

Further, the present invention can perform position estimation without frequency synchronization by estimating the position of the receiver or the position of the signal source through the reference point selection and the iterative estimation process, and it is possible to prevent the divergence problem on the position estimation.

FIG. 1 is a flowchart illustrating an operation of a method of estimating a time-difference-based arrival time according to an embodiment of the present invention.
Figs. 2A and 2B illustrate examples of position estimation of a receiver or a signal source.
FIG. 3 illustrates a D-order cross-correlation of a received signal according to an embodiment of the present invention.
FIGS. 4A and 4B illustrate an example of a process for determining a final position value.
FIGS. 5A and 5B illustrate examples of the maximum value detection performance of the cross-correlation when there is no frequency offset for the method of the present invention and the conventional method.

Hereinafter, a TDOA-based position estimation method and an apparatus thereof according to an embodiment of the present invention will be described with reference to the accompanying drawings. The present invention will be described in detail with reference to the portions necessary for understanding the operation and operation according to the present invention.

In describing the constituent elements of the present invention, the same reference numerals may be given to constituent elements having the same name, and the same reference numerals may be given thereto even though they are different from each other. However, even in such a case, it does not mean that the corresponding component has different functions according to the embodiment, or does not mean that it has the same function in different embodiments, and the function of each component is different from that of the corresponding embodiment Based on the description of each component in FIG.

The frequency offset is always generated by oscillator differences in wireless communication, radio navigation, and position detection systems. When such a frequency offset occurs, the conventional TDOA based position estimation technique estimates the accurate position by adding a separate frequency synchronization process.

The present invention intends to improve the accuracy of position estimation by providing a robust position estimation technique for frequency offset based on TDOA without adding a frequency synchronization process.

FIG. 1 is a flowchart illustrating an operation of a TDOA-based position estimation method according to an embodiment of the present invention.

Referring to FIG. 1, a position estimation apparatus according to the present invention may receive a plurality of received signals and construct a candidate set including a plurality of received signals (S110, S120).

Hereinafter, the step of receiving the reception signals in step S110 will be described in detail.

Figs. 2A and 2B illustrate examples of position estimation of a receiver or a signal source.

Referring to FIGS. 2A and 2B, a receiver may receive a signal of each base station as shown in FIG. 2A, or may receive a signal of a signal source at a receiving sensor as shown in FIG. 2B. Of course, the signal of the signal source received by each of the reception sensors of FIG. 2B may be received by a means such as a server for estimating the position of the signal source, for example, Thereby estimating the position of the signal source.

At this time, the received signal y _k (t) to be received can be expressed by the following equation (1).

[Equation 1]

Here, y _k (t) is the means for k-th received signal the signal that is received, and A _k (t) is the size of the k-th received signal α _k (t) in the k-th receiver, or the k-th reception sensor and the phase change It means that the channel characteristics have exp (j2πβ _k), and _{B k (t) = exp (} j2πε k t / t) indicates a phase rotation caused by frequency offset ε _k.

Step S120 is to construct a reference point candidate set using the plurality of received signals, and the reference point candidate set may be a plurality of received signals.

If the candidate set is constructed in step S120, one of the plurality of received signals included in the configured candidate set may be selected as a reference point and the selected reference point may be removed from the candidate set (S130, S140).

For example, when the received signal exists from 1 to K, the reference point candidate set S _Ref can be configured as shown in the following Equation (2).

&Quot; (2) "

When 1 is selected as the reference point in the reference point candidate set, the reference point candidate set can be updated as shown in Equation (3) below.

&Quot; (3) "

That is, when the reference point is selected, the reference point candidate set is updated by removing the reference point selected from the reference point candidate set.

If the reference point is selected in step S130, the TDOA measurement value through the differential cross-correlation is calculated (S150).

At this time, the step S150 may calculate the TDOA measurement value using the D differential cross-correlation, and step S150 is a step of calculating a robust TDOA measurement value with respect to the frequency offset. The step S150 includes receiving a plurality of received signals (S110) May be performed using the received signals, the reference point, and the reference point candidate set obtained in the selection step S130.

At this time, the TDOA measurement value calculated in step S150 can calculate the time when the D differential cross-correlation between the reference point and the remaining received signals included in the candidate set becomes maximum, as the TDOA measurement value.

Hereinafter, it is assumed that the received signal 1 is selected as a reference point for convenience of understanding of the present invention.

In the case of using the conventional simple cross-correlation, the TDOA measurement value between the reference point and another received signal is a time when the cross-correlation value becomes maximum, and the cross-correlation can be expressed as shown in Equation (4) below.

&Quot; (4) "

Here, P _{1 , k} (τ _{1, k} ) denotes cross-correlation between the reference point 1 and the kth received signal, () ^* denotes conjugation, and T denotes a period of a signal .

The TDOA measurement value is a time when the cross-correlation is maximized, and can be represented by the following equation (5) as a sampled discrete signal.

&Quot; (5) "

는 기준점 1과 수신신호 k사이의 TDOA 측정 값을 의미한다.Here, y _k [n] is a discrete signal and the received signal k, and N is the total number of samples,

Means the TDOA measurement value between the reference point 1 and the received signal k.

Therefore, the cross-correlation of Equation (4) can be expressed as a discrete signal sampled as shown in Equation (6) below.

&Quot; (6) "

)은 수신 신호 1의 지연 값과 수신 신호 k의 지연 값으로 표현될 수 있고, B_k[n]은 주파수 옵셋 ε_k으로 인해 발생하는 위상 회전을 의미한다.Here, the channel characteristic A _k [n] can be expressed as A _k because the amount of change during the time for calculating the cross-correlation is not large, and the TDOA measurement value

) Can be expressed by the delay value of the received signal 1 and the delay value of the received signal k, and B _k [n] represents the phase rotation caused by the frequency offset? _K.

If the frequency offset? ₁ =? _K = 0, the cross-correlation value of Equation (6) can be expressed as Equation (7) below.

&Quot; (7) "

As can be seen from Equation (7), when the frequency offset is 0, the maximum value of the cross-correlation can have a maximum value without degradation of performance. If the frequency offset is 竜₁ ≠ 0 and 竜_k ≠ 0, Can be expressed by Equation (8) below. &Quot; (8) "

&Quot; (8) "

As can be seen from Equation (8), when the frequency offset exists, the power of the maximum value of the cross-correlation decreases as compared with the case where there is no frequency offset. This reduces the accuracy of the TDOA measurement value, Which causes deterioration of performance.

FIG. 3 illustrates a D-order cross-correlation of a received signal according to an embodiment of the present invention.

As shown in FIG. 3, it shows the D-order cross-correlation of the i-th received signal shown above and the D-order cross-correlation of the j-th received signal shown at the bottom.

Therefore, the present invention computes the TDOA measurements using the D differential cross-correlation rather than the conventional simple cross-correlation, and the D differential cross-correlation can be expressed as: " (9) "

&Quot; (9) "

The TDOA measurement value is a time when the D differential cross-correlation becomes the maximum, and can be expressed as a following equation (10) as a sampled discrete signal.

&Quot; (10) "

The D differential cross-correlation of Equation (10) can be expressed as a discrete signal sampled as shown in Equation (11) below.

&Quot; (11) "

)은 수신 신호 1의 지연 값과 수신 신호 k의 지연 값으로 표현될 수 있다.Here, the channel characteristic A _k [n] can be expressed as A _k because the amount of change during the time for calculating the cross-correlation is not large, and the TDOA measurement value

Can be expressed by the delay value of the received signal 1 and the delay value of the received signal k.

The D value of the D differential cross-correlation may be determined by the number of oversampling of the receiver of the receiver or the receiver of the receiver that receives the received signal of the receiver, for example, Lt; RTI ID = 0.0 > channel < / RTI > Equation (12) below represents an adaptive D value according to the channel condition.

&Quot; (12) "

는 적응상수를 나타내며, D 차등 상호 상관의 성능을 결정하는 요인으로 적응상수가 작아지면, 계산 복잡도가 감소하지만 상호 상관의 성능은 저하된다. 반대로 적응상수가 커지면, 계산 복잡도는 증가하지만 상호 상관의 성능은 향상된다. 그리고 D 차등 상호 상관의 D 값은 채널 상황이 열악해 지는 경우 예를 들어, 주파수 옵셋이 증가하거나 전체 샘플링 수 N이 감소하는 경우에는 적응 상수를 조절하여 D 값이 작은 값을 갖게 하는 것이 바람직하다. 또한, 상관 성능을 유지하기 위해서 D 값은 오버샘플링 수보다 큰 값으로 설정되는 것이 바람직하다. 또한, 채널 상황을 모르는 경우에는 D 값을 오버샘플링 수와 일치 시키는 것이 바람직하다.Here, round denotes the round-off or down to the nearest whole number, floor represents an abandonment of a near constant, T _S denotes a sampling time.

Represents the adaptation constant, and as the adaptation constant decreases as a factor determining the performance of the D differential cross-correlation, the computational complexity decreases but the performance of the cross correlation decreases. Conversely, as the adaptation constant increases, the computational complexity increases but the cross-correlation performance improves. For example, when the frequency offset increases or the total number of samples N decreases, the D value of the D differential cross-correlation is preferably adjusted to have a small D value by adjusting the adaptation constant . In order to maintain the correlation performance, the D value is preferably set to a value larger than the oversampling number. If the channel condition is not known, it is preferable to match the D value with the oversampling number.

If the frequency offset is? ₁ =? _K = 0, the cross-correlation value of Equation (11) can be expressed by Equation (13) below.

&Quot; (13) "

As can be seen from Equation (13), when the frequency offset is 0, the maximum value of the cross-correlation can have a maximum value without degrading performance. If the frequency offsets ε ₁ ≠ 0 and ε _k ≠ 0, Can be expressed by Equation (14) below. &Quot; (14) "

&Quot; (14) "

1이 될 수 있고, 따라서 주파수 옵셋이 존재하는 경우에도 D 차등 상호 상관의 최대 값은 성능 저하 없이 최대 값을 가질 수 있다. 이는 종래 단순 상호 상관을 이용한 TDOA 측정 값을 계산하는 기술과 다르게 주파수 옵셋이 존재하는 경우에도 TDOA 측정 값의 정확도가 감소되지 않고, 따라서 주파수 옵셋에 강건한 위치 값 추정이 가능하다.Since D << N, exp (j2π (ε ₁ -ε _k ) D / N)

1, so that even when there is a frequency offset, the maximum value of the D differential cross-correlation can have a maximum value without degrading performance. This is different from the technique of calculating the TDOA measurement value using the conventional simple cross-correlation, even when the frequency offset exists, the accuracy of the TDOA measurement value is not reduced, and therefore, it is possible to estimate the position value robust to the frequency offset.

When the TDOA measurement value is calculated in step S150, the position value is estimated using the calculated TDOA measurement value (S160).

In other words, the position value in step S160 is calculated from the TDOA measurement value, and the TDOA measurement value can be expressed as a combination of the previously known coordinates and the coordinates to be estimated as follows.

&Quot; (15) &quot;

Here, (x, y) are (x _i, y _i), means a coordinate to be estimated means the i-th base station or the i-th coordinate of the reception sensor in the coordinates already known and, c denotes the propagation velocity .

The TDOA measurement value shown in Equation (15) can be expressed as a vector as shown in Equation (16) according to a combination of a reference value and each received signal.

&Quot; (16) &quot;

Estimation of the position value using Equation (16) can be performed by Equation (17) below.

&Quot; (17) &quot;

Here, the function G means an inverse function to the function F.

As an example of the function G, it is possible to estimate the position value repeatedly by linearizing the function F through the Taylor Series. In addition to the technique using the Taylor Series function, the technique using the Kalman filter, the least square method And a general technique such as a technique of obtaining a position value by a closed-loop of the sensor.

If the position value is estimated in step S160, it is checked whether the reference point candidate set is an empty set. Otherwise, the steps S130 to S160 are repeated by changing the reference point (S170).

If it is determined in step S170 that the reference point candidate set is an empty set, the final position value is determined based on the estimated position values (S180).

At this time, the step S180 may determine the average value of the plurality of positional values estimated by the steps as the final positional value.

At this time, the step S180 removes a position value of the positional change amount of the plurality of positional values from the distribution of the plurality of positional values estimated by the steps above a predetermined threshold value, Value can be determined as the final position value.

That is, as shown in FIGS. 4A and 4B, the step of determining the final position value (S180) may be such that a position value whose change amount is larger than a predetermined change amount threshold value is removed from the distribution of repeatedly estimated position values, And determines the average of the position values as the final position value.

Therefore, the position estimation method according to the present invention can further improve the position estimation performance because the noise influence is reduced due to the average of the position values that have not been removed.

FIGS. 5A and 5B illustrate examples of the maximum value detection performance of the cross-correlation when there is no frequency offset for the method of the present invention and the conventional method.

Referring to FIGS. 5A and 5B, the comparison of the maximum value of the cross-correlation detection performance according to the frequency offset of the conventional method shown in FIG. 5A and the proposed method according to the present invention shown in FIG. As can be seen, when the method according to the present invention has frequency offsets as compared with the prior art, it is found that the maximum value of cross-correlation detection performance is excellent.

As described above, although the method according to the present invention is described in terms of two-dimensional coordinates, the method according to the present invention is not limited to two-dimensional coordinates, and can be applied to three-dimensional coordinates.

As described above, the TDOA-based position estimation method according to the present invention is robust to the frequency offset and improves the estimation accuracy of the position, estimates the position of the receiver or the position of the signal source through the reference point selection and iterative estimation, It is possible to perform the position estimation without the frequency synchronization process, and it is possible to prevent the divergence problem on the position estimation.

In this embodiment of the present invention, the position estimating apparatus removes the reception signal corresponding to the reference point from the candidate set, but it is not necessarily limited thereto, and only the reference point is selected, and the reception signal corresponding to the selected reference point is not removed from the candidate set It is possible. In addition, the reference point selection can be made by arranging the received signals in descending order of power magnitude in descending order of magnitude of power of the received signal, and selecting the reference point from the order of larger power. This is to ensure the estimation performance even when the number of reference point selection times is smaller than the total number of candidates.

It is to be understood that the present invention is not limited to these embodiments, and all of the elements constituting the embodiments of the present invention described above may be combined or operated in one operation. That is, within the scope of the present invention, all of the components may be selectively coupled to one or more of them. In addition, although all of the components may be implemented as one independent hardware, some or all of the components may be selectively combined to perform a part or all of the functions in one or a plurality of hardware. As shown in FIG. In addition, such a computer program may be stored in a computer-readable medium such as a USB memory, a CD disk, a flash memory, etc., and read and executed by a computer, thereby implementing embodiments of the present invention. As the storage medium of the computer program, a magnetic recording medium, an optical recording medium, a carrier wave medium, or the like may be included.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or essential characteristics thereof. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

Claims (10)

Receiving a plurality of received signals and constructing a candidate set including the received plurality of received signals;
Selecting one of the plurality of received signals included in the candidate set as a reference point and removing a received signal corresponding to the selected reference point from the candidate set;
Calculating a time difference of arrival (TDOA) measurement between the selected reference point and the remaining received signals;
Estimating a position value based on the calculated TDOA measurement value; And
Determining a final position value based on a plurality of estimated position values until the candidate set becomes an empty set;
Wherein the reference points are selected from descending powers of a plurality of received signals included in the candidate set in descending order of power magnitudes of the received signals,
And a TDOA measurement value between the selected reference point and the remaining received signals is calculated. The TDOA measurement value is obtained by removing a received signal corresponding to the selected reference point from the candidate set by selecting any one of the plurality of received signals included in the configured candidate set as the reference point, And calculating TDOA measurement values between the selected reference point and the remaining received signals until the candidate set becomes empty while changing the reference point. The method according to claim 1,
Wherein the determining comprises:
And determining an average value of the estimated plurality of position values as the final position value. The method according to claim 1,
Wherein the determining comprises:
A position value having a variation amount of the position value among the plurality of position values is determined to be equal to or greater than a predetermined threshold value from a distribution of the estimated plurality of position values and an average value with respect to the remaining position values is determined as the final position value Based on the arrival time difference. The method according to claim 1,
Wherein the calculating step comprises:
Calculating a time at which the differential cross-correlation between the reference point and the remaining received signals becomes maximum, as the TDOA measurement value. The method according to claim 1,
Wherein the calculating step comprises:
Calculate the TDOA measurement value based on a D differential cross-correlation between the reference point and the remaining received signals,
Wherein the D value is determined by an oversampling number of the received plurality of received signals. delete delete delete delete delete

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