KR102367032B1 - Asynchronous tracking method for wireless terminal and system thereof - Google Patents

Abstract

The present invention relates to an asynchronous wireless terminal location tracking method and a system thereof. According to an embodiment of the present invention, the asynchronous wireless terminal location tracking method, comprises the steps of: transmitting, by a wireless terminal, a plurality of signals including transmission time information in accordance with a wireless terminal reference time at time intervals; transmitting, by a plurality of anchor nodes, the signals, and transmitting time data including reception time information and the transmission time information in accordance with each anchor node reference time to a location tracking server; subtracting, by the location tracking server, the difference of the transmission time from the difference between the reception times of a k^th signal and a (k-1)^th signal to calculate a time difference measured value obtained by eliminating a reference time difference between the wireless terminal and the anchor nodes; and estimating, by the location tracking server, a location of the wireless terminal using the time difference measured value. Therefore, the location of the wireless terminal can be precisely estimated.

Description

Asynchronous wireless terminal location tracking method and system

The present invention relates to an asynchronous wireless terminal location tracking method and system, and more particularly, to an asynchronous wireless terminal location tracking method for accurately estimating the location of a wireless terminal even in a situation in which time synchronization between the wireless terminal and anchor nodes is not performed. and to the system.

In general, the location tracking system using radio waves is divided into a direction finding location tracking system and a location tracking system using a distance. The distance-based location tracking system is a method of estimating a location by obtaining the absolute sum or absolute difference of distances between a transmitter and a receiver. The distance between the transmitter and the receiver can be calculated as the product of the radio wave arrival time and the radio wave. Therefore, by measuring the propagation delay (Time-Of-Arrival, TOA) or the time-difference-of-Arrival (TDOA) of the signal, the distance between the transmitter and the receiver is determined, and from this, the location of the wireless terminal is determined. can be estimated

Measuring the propagation delay of a signal or the difference in propagation delay requires precise time synchronization between the transmitter and receiver. For such precise time synchronization, it is required that each element constituting the positioning system receives a global positioning system (GPS) signal or is connected to a time synchronization server through the Internet, and is maintained periodically to maintain precise time synchronization compensation is needed

In addition, in a network environment in which the satellite navigation system signal is shielded or there is no time synchronization server, such as in an indoor environment, time synchronization of transmitters and receivers is impossible, so it is impossible to determine the location of a wireless terminal using a propagation delay or a difference in propagation delay. there is.

Korean Patent Laid-Open Publication No. 10-2016-0098689 (2016.08.19.) relates to a real-time location tracking system and method, in which a server broadcasts an initialized synchronization information table to a plurality of receivers, a plurality of receivers respectively storing the synchronization information table and updating the synchronization information table, the plurality of receivers transmitting the updated synchronization information table to the server, the plurality of receivers respectively receiving the tag signal from the object, the plurality of receivers receiving the receiver Transmitting the identification information and the reception time of the tag signal to the server, and the server calculating the position of the object using the identification information of the receiver, the reception time of the tag signal, and the updated synchronization information table A method for tracking the location of the liver is provided.

However, this method assumes that a plurality of receivers will perform precise time synchronization using the synchronization information table, and requires a separate network system for transmitting the synchronization information table between the plurality of receivers.

1. Korean Patent Laid-Open Publication No. 10-2016-0098689 (2016.08.19.)

A first technical problem to be solved by the present invention is to provide an asynchronous wireless terminal location tracking method for accurately estimating the location of a wireless terminal even in a situation in which time synchronization between the wireless terminal and anchor nodes is not performed.

A second technical problem to be solved by the present invention is to provide a system for performing the above-described asynchronous wireless terminal location tracking method.

In order to solve the first technical problem described above, an embodiment of the present invention is a step of transmitting, by a wireless terminal, a plurality of signals including transmission time information according to a wireless terminal reference time at a time interval, a plurality of anchor nodes receiving the signals of and transmitting time data including the transmission time information and reception time information according to each anchor node reference time to a location tracking server, wherein the location tracking server is the kth signal and the k-1th signal calculating a time difference measurement value obtained by subtracting the transmission time difference from the reception time difference to remove the reference time difference between the wireless terminal and the anchor nodes, and the location tracking server using the time difference measurement value It provides an asynchronous wireless terminal location tracking method comprising the step of estimating the location of the wireless terminal.

The wireless terminal may transmit the signal at regular time intervals, and in this case, the signal may further include transmission period information.

Alternatively, the wireless terminal transmits the signal at aperiodic time intervals, and in this case, the signal may further include transmission time information of a previous signal.

The step of estimating the location of the wireless terminal by using the time difference measurement by the location tracking server includes: deriving an initial position estimate of the wireless terminal; An asynchronous radio terminal location tracking method comprising the steps of deriving a position prediction value of a terminal, and deriving a final position estimate value of the radio terminal at the time when the k-th signal is transmitted from the time difference measurement value and the position prediction value.

The step of deriving the initial position estimate of the wireless terminal is to derive the initial position estimate using a database-based pattern matching technique, or to derive the initial position estimate using the location of a nearby landmark of the wireless terminal can

The deriving the final position estimate may include estimating the final position estimate using a Bayesian filter-based recursive estimation technique, and for example, correcting the position estimate using a Kalman filter.

When there are a plurality of candidate solutions in the step of deriving the final position estimate, a weight may be assigned to each candidate solution to derive a final position estimate from the weighted sum of the candidate solutions.

An embodiment of the present invention may provide a program recorded in a computer-readable storage medium to execute the above-described method for tracking the position of the asynchronous wireless terminal.

In order to solve the second technical problem described above, an embodiment of the present invention receives a plurality of signals transmitted by a wireless terminal at a time interval, and receives time information according to an internal reference time of each anchor node and the inside of the wireless terminal A plurality of anchor nodes that transmit time data including transmission time information according to the reference time to the location tracking server, and the time difference measured by subtracting the transmission time difference from the reception time difference between the k-th signal and the k-1th signal Calculates and provides an asynchronous wireless terminal location tracking system including a location tracking server for estimating the location of the wireless terminal using the time difference measurement.

The location tracking server derives the initial location estimate of the wireless terminal, derives the location predicted value of the wireless terminal at the time when the k-th signal is transmitted from the initial location estimate, and the k-th from the time difference measurement and the location estimate It is possible to derive the final estimated position of the wireless terminal at the time of transmitting the signal.

In this case, the final position estimate value may be a value obtained by correcting the position prediction value with a Kalman filter using the time difference measurement value.

The asynchronous wireless terminal location tracking method according to the present invention removes the reference time difference between the wireless terminal and each anchor node by calculating a time difference measurement, and uses this to estimate the location of the wireless terminal, thereby estimating the location of the wireless terminal and the anchor nodes. High-resolution wireless terminal location tracking is possible without time synchronization between them. Therefore, separate installation and maintenance for configuring the time synchronization system is not required, and it is applicable even in an indoor environment in which a satellite navigation system signal, etc. is shielded.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned will be clearly understood by those skilled in the art from the following description.

1 is a block diagram illustrating an asynchronous wireless terminal location tracking method according to an embodiment of the present invention.
FIG. 2 is a diagram sequentially illustrating events according to a reference time of each of a wireless terminal and an anchor node in order to explain an asynchronous wireless terminal location tracking method.
FIG. 3 is a block diagram illustrating a step of estimating a location of a wireless terminal in the asynchronous wireless terminal location tracking method shown in FIG. 1 .
4 is a conceptual diagram illustrating an asynchronous wireless terminal location tracking system according to an embodiment of the present invention.

While the invention is susceptible to various modifications and variations, specific embodiments thereof are illustrated and illustrated in the drawings and will be described in detail hereinafter. However, it is not intended to limit the invention to the particular form disclosed, but rather the invention includes all modifications, equivalents and substitutions consistent with the spirit of the invention as defined by the claims.

Although the terms first, second, etc. may be used to describe various elements, regions, layers, and/or steps, such elements, regions, layers and/or steps are not limited by these terms. will understand that no

With reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail. Hereinafter, the same reference numerals are used for the same components in the drawings, and repeated descriptions of the same components are omitted.

1 is a block diagram illustrating an asynchronous wireless terminal location tracking method according to an embodiment of the present invention, and FIG. 2 is an asynchronous wireless terminal location tracking method. It is a drawing showing sequentially.

Referring to Figure 1, in an asynchronous wireless terminal location tracking method according to an embodiment of the present invention, the wireless terminal transmits a signal (S10), a plurality of anchor nodes receive the signal, and time data is stored in the location tracking server Transmitting to (S20), the location tracking server calculating a time difference measurement value obtained by removing the reference time difference between the wireless terminal and the anchor nodes (S30) and using the time difference measurement value of the wireless terminal It includes the step of estimating the position (S40).

First, in the step (S10) of transmitting the signal by the wireless terminal, the wireless terminal transmits a plurality of signals including transmission time information according to the wireless terminal reference time at time intervals. When the reference time of the wireless terminal at one point in time is t[0], the transmission time at which the wireless terminal transmits the k-th signal is t _TX [k] as the wireless terminal reference time.

In an embodiment, the wireless terminal may transmit a plurality of signals at regular time intervals. In this case, the k-th signal transmitted by the wireless terminal may include the transmission time t _TX [k] and the transmission period T information according to the wireless terminal reference time.

In another embodiment, the wireless terminal may transmit a plurality of signals at aperiodic time intervals. In this case, the k-th signal transmitted by the wireless terminal may include the transmission time t _TX [k] according to the wireless terminal reference time and the transmission time t _TX [k-1] of the previous signal.

In the step (S20) of the plurality of anchor nodes receiving the signal and transmitting the time data to the location tracking server, the plurality of anchor nodes receive the signal, and receive time information according to the reference time for each anchor node; The radio terminal transmits time data including the transmission time information recorded according to the reference time of the radio terminal to the location tracking server.

When the reference time of the a-th anchor node at one point is t[0;a], the reception time at which the a-th anchor node receives the k-th signal transmitted by the wireless terminal is the reference time of the a-th anchor node, t _RX It is [k;a].

When the difference between the wireless terminal reference time and the a-th anchor node reference time is τ _a , the difference between the reception time and the transmission time is as follows.

[Formula 1]

In this case, δ _a [k] is the time difference due to the propagation delay time and measurement noise required for the signal to move from the position of the wireless terminal when the signal is transmitted to the position of the a-th anchor node.

[Equation 2]

이고, m[k]는 k번째 신호를 송출할 때 무선 단말의 위치를 나타내는 벡터이고, P _a 는 a번째 앵커노드의 위치를 나타내는 벡터이다.

은 벡터의 크기를 나타내는 유클리디안 놈(Euclidean Norm)이다.here

, m [k] is a vector indicating the position of the wireless terminal when transmitting the k-th signal, and P _a is a vector indicating the position of the a-th anchor node.

is the Euclidean Norm indicating the size of the vector.

n _a [k] is the measurement noise with a normal distribution with mean 0 and variance σ _a ² .

At this time, the difference τ _a between the reference times of the wireless terminal and each anchor node is generated due to the absence of time synchronization, and must be removed for positioning of the wireless terminal.

Each anchor node transmits time data including a transmission time according to the radio terminal reference time and a reception time according to the anchor node reference time to the location tracking server. In this case, the time data may further include transmission time information of a signal transmission period T or a previous signal transmission period by the wireless terminal.

In the step (S30) of the location tracking server calculating the time difference measurement value obtained by removing the reference time difference between the wireless terminal and the anchor nodes, the location tracking server in the difference between the reception times of the k th signal and the k-1 th signal A time difference measurement value obtained by subtracting the difference between the transmission times and the difference τ _a between the reference times between the radio terminal and the anchor node is calculated.

[Equation 3]

The wireless terminal calculates the difference between the reception time t _RX [k;a] when the a-th anchor node receives the k-th signal and the reception time t _RX [k-1;a] when the k-1 signal is received. It can be expressed using the transmitted transmission time t _TX [k] and the transmitted transmission time t _TX [k-1] of the k-1th signal.

At this time, since the reception times t _RX [k;a] and t _RX [k-1;a] and the transmission times t _TX [k] and t _TX [k-1] are measurable values, the measurable values are In summary, the following time difference measurement can be calculated.

[Equation 4]

)에서 송출 시각의 차(

)를 감산하여, 측정 불가능한 값인 무선 단말과 a 번째 앵커노드 사이의 기준 시각의 차이 τ_a를 제거한 값이다.That is, the measured time difference z _a [k;k-1] is the difference (

) to the difference of the transmission time (

_.

The time difference measurement for a total of A anchor nodes is as follows.

[Equation 5]

To rearrange this,

[Equation 6]

이고, 즉 모든 성분의 평균이 0이고, 공분산이

인 잡음 벡터다.At this time,

, that is, the mean of all components is 0, and the covariance is

is a noise vector.

The step of estimating the location of the wireless terminal using the time difference measurement (S40) is to estimate the location m [k] of the time point when the wireless terminal transmits the k-th signal from the time difference measurement value by the location tracking server is a step

The position m [k] at the time point at which the wireless terminal transmits the k-th signal may be estimated using a least-squares method or a recursive estimation method based on a Bayesian filter.

Hereinafter, an embodiment of estimating the location of the wireless terminal using the time difference measurement in the description of FIG. 3 will be described.

FIG. 3 is a block diagram illustrating a step of estimating a location of a wireless terminal in the asynchronous wireless terminal location tracking method shown in FIG. 1 .

Referring to FIG. 3 , the step of estimating the location of the wireless terminal ( S40 ) includes the step of deriving an initial position estimate of the wireless terminal ( S41 ), the step of deriving the predicted position of the terminal from the initial location estimate ( S43 ) and the time difference and deriving a final position estimate from the measured value and the position predicted value (S45).

와 초기 위치 추정값의 분산 C[0]를 도출한다. 이 때, 초기 위치 추정값은 복수의 후보 해를 가질 수 있다.First, in the step of deriving the initial position estimate of the radio terminal (S41), the initial position estimate of the radio terminal

and the variance C [0] of the initial position estimate are derived. In this case, the initial position estimate may have a plurality of candidate solutions.

According to an embodiment of the present invention, an initial position estimate value of a wireless terminal may be derived using a database-based pattern matching technique. The database-based pattern matching technique may be a Wi-Fi fingerprinting technique, video image input, or the like, but is not limited thereto.

This pattern matching technique requires that a database of regions requiring location estimation be established, and when using a Wi-Fi signal, it is difficult to use it for continuous location tracking of a wireless terminal because the signal measurement speed is slow, but the initial location of the wireless terminal It can be used to derive an estimate.

According to another embodiment of the present invention, in order to derive an initial position estimate of the wireless terminal, it is possible to use the location of a landmark around the wireless terminal. The landmark location may be automatically recognized using a wireless network or the like when the wireless terminal moves around the landmark, or may be directly input by a user of the wireless terminal.

The step of deriving the location prediction value of the terminal from the initial location estimation value ( S43 ) is a step of predicting the location of the wireless terminal when the k-th signal is transmitted based on the location variation model (transition model or dynamic model).

According to an embodiment of the present invention, the location variation model may be a random walk model, but is not limited thereto, and may be changed for each application field to which the present invention is applied. In this specification, although the invention is described using a random walk model as a location variation model to help understanding, it is obvious that other location variation models are applied, but are included in the technical spirit of the present invention.

The position prediction values using the random walk model are as follows.

[Equation 7]

이고,

이다.At this time,

ego,

am.

The step (S45) of deriving a final position estimate value from the time difference measurement value and the position prediction value includes the position m [ k] is finally estimated.

The position m [k] at which the wireless terminal transmits the k-th signal may be estimated using a least-squares method or a recursive estimation method based on a Bayesian filter.

The Bayesian filter may be a Kalman filter or a particle filter, but is not limited thereto. In an embodiment of the present invention, the Bayesian filter may be an extended Kalman filter.

In this specification, an exemplary embodiment of the present invention is described using an extended Kalman filter for better understanding. However, it is apparent that other known recursive estimation techniques or least squares methods are also included in the technical spirit of the present invention.

The final position estimate using the extended Kalman filter is as follows.

[Equation 8]

이고, At this time, the variance of the final position estimate is

ego,

인 단위 행렬이다.

is the identity matrix.

가 복수의 후보 해를 가질 경우, 확장 칼만 필터를 이용하여, 위치 추정값의 분산이 임계값 이상일 경우, 후보 해에 대한 추정은 중단하여, 초기 위치 추정값의 해를 좁힐 수 있다.As described above, the initial position estimate of the wireless terminal

If has a plurality of candidate solutions, using the extended Kalman filter, when the variance of the position estimate is equal to or greater than a threshold value, the estimation of the candidate solution may be stopped to narrow the solution of the initial position estimate.

In the present specification, it has been described on the premise of estimating a position in a two-dimensional space, but it can be extended to a three-dimensional space.

When the final position estimation value has a plurality of candidate solutions, the final position estimation value may be derived from the sum of the weights of the candidate solutions by adding a final selection using electronic map information or the like, or by assigning a weight to each candidate solution.

The asynchronous wireless terminal location tracking method according to various embodiments of the present invention shown in FIGS. 1 to 3 can be written as a program that can be executed on a computer, and a computer-readable recording medium is used to operate the program. It can be implemented in the device. The computer-readable recording medium includes a storage medium such as a magnetic storage medium (eg, a ROM, a floppy disk, a hard disk, etc.) and an optically readable medium (eg, a CD-ROM, a DVD, etc.).

4 is a conceptual diagram illustrating an asynchronous wireless terminal location tracking system according to an embodiment of the present invention.

4, the asynchronous wireless terminal location tracking system according to an embodiment of the present invention is a plurality of anchor nodes 21, 22, 23, 24 for receiving a signal transmitted by the wireless terminal 10, and a location tracking server (30).

The wireless terminal 10 transmits a plurality of signals including transmission time information according to the wireless terminal reference time at time intervals.

A plurality of anchor nodes (21, 22, 23, 24) receive a plurality of signals transmitted by the radio terminal 10, and when each signal is received, record reception time information according to the reference time of each anchor node Thus, time data including the transmission time information and the reception time information are created. A plurality of anchor nodes (21, 22, 23, 24) each transmits the time data to the location tracking server (30).

The location tracking server 30 calculates a time difference measurement value obtained by subtracting a transmission time difference from a reception time difference of a k-th signal and a k-1 th signal among a plurality of signals, and using the time difference measurement value, the wireless terminal 10 ) to estimate the location where the k-th signal is transmitted.

When transmitting the k-1th signal, the wireless terminal 10 communicates with each anchor node 21, 22, 23, 24 and d _a1 [k-1], d _a2 [k-1], d _a3 [k-1]. ] and d _a4 [k-1]. At this time, the transmission time according to the reference time of the wireless terminal 10 is t _TX [k-1]. The transmitted signal is received by each anchor node 20, and the reception time according to each anchor node reference time is t _RX [k-1;a]. That is, the reception time of the k-1 th signal of the first anchor node 21 may be expressed as t _RX [k-1;1].

이고,

은 무선 단말 기준 시각과 첫번째 앵커노드 기준 시각의 차이이다.At this time,

ego,

is the difference between the wireless terminal reference time and the first anchor node reference time.

이다.Similarly, when transmitting the k-th signal, the wireless terminal 10' is connected to each anchor node 21, 22, 23, 24 and d _a1 [k], d _a2 [k], d _a3 [k] and d _a4 [ k]. At this time, the transmission time according to the reference time of the wireless terminal 10' is t _TX [k]. The transmitted signal is received by each anchor node 20, and the reception time according to the reference time of each anchor node is t _RX [k; a]. That is, the reception time of the k-th signal of the first anchor node 21 may be expressed as t _RX [k;1]. At this time,

am.

)에서 송출 시각의 차(

)를 감산하여 시간차분 측정치 z_a1[k;k-1]을 산출한다. The location tracking server is the difference between the reception time of the k th signal and the k-1 th signal (

) to the difference of the transmission time (

) to calculate the time difference measurement z _a1 [k;k-1].

이다. 상술한 바와 같이 시간차분 측정치에서, 무선 단말(10)의 기준 시각과 첫번째 앵커노드(21)의 기준 시각이 동기화되지 않아 발생하는 항인

는 제거된다.At this time, the time difference measurement between the first anchor node 21 and the wireless terminal 10 is

am. As described above, in the time difference measurement, the reference time of the wireless terminal 10 and the reference time of the first anchor node 21 are not synchronized.

is removed

The time difference measurements obtained from the plurality of anchor nodes 21, 22, 23 and 24 are as follows.

To rearrange this, the formula is as follows.

The location tracking server 30 may derive an initial location estimate of the wireless terminal 10 by using a database-based pattern matching technique using a Wi-Fi signal or a video image. Alternatively, the location of a nearby landmark of the wireless terminal 10 may be used or may be directly input by the user.

The position tracking server 30 predicts the position of the wireless terminal when transmitting the k-th signal based on the position displacement model from the initial position estimate value, and compares the position estimate value with the measured time difference measurement, and the final position estimates can be derived. In this case, the final position estimate can be derived using a Bayesian filter-based recursive estimation technique, and when the final position estimate has a plurality of candidate solutions, it is finally selected using electronic map information, etc. By weighting, the final position estimate can be derived from the weighted sum of the candidate solutions.

The wireless terminal 10 may receive the final location estimate from the location tracking server 10 and provide it to the user, if necessary.

In this embodiment, four anchor nodes (21, 22, 23, 24) are used, but the number of anchor nodes for estimating the position on a two-dimensional plane is at least two. At least three anchor nodes 20 are required to estimate the position of the wireless terminal 10 in a three-dimensional space. As the number of anchor nodes 20 increases, the accuracy and precision of position estimation may increase.

In the above, the configuration and features of the present invention have been described based on the embodiments according to the present invention, but the present invention is not limited thereto. Various changes or modifications can be made by those skilled in the art to which the present invention pertains within the spirit and scope of the present invention, and therefore such changes or modifications fall within the scope of the appended claims.

10: wireless terminal 21, 22, 23, 24: a plurality of anchor nodes
30: location tracking server

Claims (13)

transmitting, by a wireless terminal, a plurality of signals including transmission time information according to a wireless terminal reference time at time intervals;
receiving, by a plurality of anchor nodes, a plurality of the signals, and transmitting time data including the transmission time information and reception time information according to each anchor node reference time to a location tracking server;
The location tracking server subtracts the difference of the transmission time from the difference between the reception times of the k-th signal and the k-1 th signal to calculate a time difference measurement value obtained by removing the reference time difference between the wireless terminal and the anchor nodes step; and
and estimating, by the location server, the location of the wireless terminal using the time difference measurement. According to claim 1,
The wireless terminal transmits the signal at regular time intervals,
The signal is an asynchronous wireless terminal location tracking method further comprising transmission period information. According to claim 1,
The wireless terminal transmits the signal at aperiodic time intervals,
The signal further includes transmission time information of a previous signal. The method of claim 1,
The step of the location tracking server estimating the location of the wireless terminal using the time difference measurement,
deriving an initial position estimate of the wireless terminal;
deriving a position prediction value of the wireless terminal when a k-th signal is transmitted from the initial position estimate value; and
and deriving a final position estimate of the radio terminal at the time when the k-th signal is transmitted from the time difference measurement value and the position prediction value. 5. The method of claim 4,
The step of deriving the initial position estimate of the wireless terminal comprises:
An asynchronous wireless terminal location tracking method for deriving the initial location estimate using a database-based pattern matching technique. 5. The method of claim 4,
The step of deriving the initial position estimate of the wireless terminal comprises:
An asynchronous wireless terminal location tracking method for deriving the initial location estimate using the location of a nearby landmark of the wireless terminal. 5. The method of claim 4,
The step of deriving the final position estimate is,
An asynchronous wireless terminal location tracking method for estimating a final location estimate using a Bayesian filter-based recursive estimation technique. 5. The method of claim 4,
The step of deriving the final position estimate is,
An asynchronous wireless terminal location tracking method for correcting the location prediction value using a Kalman filter. 9. The method of claim 8,
The step of deriving the final position estimate is,
An asynchronous wireless terminal positioning method for deriving a final position estimate from the weighted sum of the candidate solutions by weighting each candidate solution when there are a plurality of candidate solutions. The wireless terminal receives a plurality of signals transmitted at intervals of time, and time data including reception time information according to the internal reference time of each anchor node and transmission time information according to the internal reference time of the wireless terminal is transmitted to the location tracking server a plurality of anchor nodes for transmitting; and
A location tracking server for calculating a time difference measurement value by subtracting the transmission time difference from the reception time difference of the k-th signal and the k-1 th signal, and estimating the location of the wireless terminal using the time difference measurement value Asynchronous wireless terminal positioning system. 11. The method of claim 10,
The location tracking server derives the initial location estimate of the wireless terminal, derives the location estimate of the wireless terminal at the time when the k-th signal is transmitted from the initial location estimate, and the k-th from the time difference measurement and the location estimate An asynchronous radio terminal positioning system for deriving a final estimate of the position of the radio terminal at the time of signal transmission. 12. The method of claim 11,
The final position estimate value is a value obtained by correcting the position estimate value with a Kalman filter using the time difference measurement value. [10] A program recorded in a computer-readable storage medium for executing the method for locating an asynchronous wireless terminal according to any one of claims 1 to 9.

Images