WO2004105273A1

WO2004105273A1 - Method and system for tracking the position of mobile communication terminal

Info

Publication number: WO2004105273A1
Application number: PCT/KR2004/001202
Authority: WO
Inventors: Myeoung-Keun Oh; Su-Hwan Lim; Sung-Chul Kim; Hyung-Eon Baek
Original assignee: NEO TELECOM CO Ltd
Current assignee: NEO TELECOM CO Ltd
Priority date: 2003-05-20
Filing date: 2004-05-20
Publication date: 2004-12-02
Anticipated expiration: 2005-11-20

Abstract

The present invention relates to a system and method for tracking the position of a mobile communication terminal, which can minimize a position tracking error that may be produced upon tracking the position of the mobile communication terminal due to a propagation delay time in a repeater for transmitting and receiving a reverse or forward signal between the mobile communication terminal and a base station. The position tracking system of the present invention comprises a repeater (200) that relays a signal between the terminal (100) and the base station (400) and includes a terminal discriminating device (300) for receiving information from the base station (400) to determine whether the user terminal (100) is present; and a position tracking server (500) that tracks the position of the user terminal and includes a database (510) for storing geographical position information on the respective repeaters based on repeater identification information. According to the present invention, it is possible to minimize a position tracking error which may be produced upon tracking the position of the mobile communication terminal due to a propagation delay time caused by the repeater and to provide efficient position-based services such as urgency and emergency rescue services, and the like.

Description

METHOD AND SYSTEM FOR TRACKING THE POSITION OF MOBILE COMMUNICATION TERMINAL

Technical field

The present invention relates to a system and method for tracking the position of a mobile communication terminal, and more particularly, to a system and method for tracking the position of a mobile communication terminal, which can minimize a position tracking error that may be produced upon tracking the position of the mobile communication terminal due to a propagation delay time in a repeater for transmitting and receiving a reverse or forward signal between the mobile communication terminal and a base station.

Background Art In mobile communication systems, a position-based service such as Enhanced-911

(E-911) tracking the actual position of a terminal to perform rescue upon the occurrence of an accident is currently in the spotlight. The United States and other countries have additionally specified that various mobile communication devices essentially include functionality for such a position-based service as requirements for the devices. Particularly, the introduction of a repeater, which is one of ways of spreading communication coverage at a low cost at sites under poor propagation environment, has been considered in earnest on recent U.S. markets. For this reason, studies on a scheme for solving a position distortion phenomenon caused by the repeater have become an important issue. Conventional schemes for tracking the position of a terminal are classified into a handset-based position tracking scheme that uses a global positioning system (GPS) receiver mounted on a terminal to track the position of a user, a network-based position tracking scheme that tracks the position of a transmitter using three or more receivers and the transmitter on a reverse link (three or more transmitters and one receiver on a forward link), and a GPSone scheme available from SnapTrack (which is Qualcomm at present) which is a hybrid scheme using a combination of the above two schemes.

The handset-based position tracking scheme is a positioning scheme that obtains a distance between a receiver and a signal source by measuring a time of arrival between the signal source and the receiver. Here, the latitude and longitude of the receiver is found by calculating distances to respective GPS satellites using the times of arrival of signals sent from three or more GPS satellites, exact positions of GPS transmitters, and the like. Such a scheme for tracking the position of a terminal using GPS satellites requires a terminal capable of discriminately receiving three or more GPS satellite signals, correct synchronization, and time-stamps indicating the time when the signals leave. There is another problem in that the scheme requires significantly complicated receiver and arithmetic units to process the data received from the satellites in real time.

The network-based position tracking scheme is a position tracking scheme based on a base station in which the position of a user is tracked using the relative time or angles of arrival of the signals received from a number of base stations. It includes a time-of-arrival (TOA) scheme, a time-difference-of-arrival (TDOA) scheme, and an angle-of-arrival (AOA) scheme.

The TOA scheme is a scheme for determining a distance between a terminal and base stations by measuring a propagation delay time therebetween, in which the position of the terminal is determined by obtaining an intersection point of circles which will be drawn using measured distances from the base stations.

The TDOA scheme is a scheme for determining a position using the time difference of arrival of signals transmitted from different places. The TDOA scheme is capable of determining the position of a terminal by measuring a propagation time difference of arrival, which is in proportion to the difference of the distances from a number of base stations to the terminal, drawing curves of places where the differences of distances from two facing base stations are constant, namely, two or more hyperbolas centered on the two base stations, and selecting an intersection place of such hyperbolas. The position of the terminal is generally determined using the TDOA scheme by means of triangulation based on the time difference when a correlation value becomes largest in a cross-correlation method. The AOA scheme is a positioning scheme for determining a position by a signal source measuring the angles of arrival of signals sent from a receiver. There is a probability that the path of an actual line-of-sight signal is obstructed by multi-path components in a fading environment such as urban zone. In this case, the AOA scheme makes a determination in a multi-path component direction having the strongest intensity of the signal, which causes a positioning error. In addition, even though there is a line-of-sight signal component, the multi-paths act as obstruction factors that interfere with the measurement of the angle. Thus, there is a problem in that a minor change in the AOA contributes to the increase of the error as the distance between the base station and the mobile station increases.

The hybrid position tracking scheme is an algorithm considered to solve a shaded zone problem, which is the greatest shortcoming of a GPS method, using the TDOA scheme of an existing network method while reflecting the accuracy of the GPS method. It is an excellent position-tracking scheme having advantages of position tracking systems of the above two methods. However, in this hybrid position tracking scheme, there may be the following problems in a mobile communication system using a variety of repeaters.

That is, repeaters are generally placed at sites where propagation environments are poor. For this reason, reception of a GPS signal may not be easy and there may be a deviation of maximum several kilometers depending on the actual positions of repeaters and the positions of antennas. In this case, a large error is caused due to propagation delay in tracking the position of a terminal served in cells of the repeaters.

Fig. 1 is a diagram illustrating propagation delay between a base station and a mobile communication terminal. In a case of using the TDOA scheme in the network-based position tracking method mentioned above, the distance from the base station to the terminal without passing through a repeater is as follows.

D_air= (3xl0⁸)[m/s] x t_air[s] (1)

That is, the distance D_ai_r between the base station and the terminal can be determined from a propagation delay time t_aj_r between the base station and the terminal without passing through a repeater. On the other hand, a propagation delay time tb₀ from the base station to the terminal via the repeater is determined by the sum of a propagation delay time t_br between the base station and the repeater and a propagation delay time t_re between the repeater and the terminal. The propagation delay time t_bc from the base station to the terminal via the repeater is larger than the propagation delay time t_aj_r between the base station and the terminal without passing through the repeater.

This is due to a propagation delay time τ caused by the repeater. The distance between the base station and the terminal is determined by equation 2 from the propagation delay time caused by the repeater.

D_BC = (3xl0⁸)[m/s] x (t_air+ τ )[s] (2) That is, the distance between the base station and the tenninal is recognized to be larger than an actual distance due to the propagation delay time τ through the repeater.

Therefore, a service of determining the position of a mobile communication terminal using a repeater has limitations due to the propagation delay time caused by the repeater in providing accurate and reliable position information.

Disclosure of Invention

The present invention is conceived to solve the aforementioned problems. An object of the present invention is to provide a system and method for tracking the position of a mobile communication terminal, wherein the position of the terminal can be accurately tracked by correcting a position tracking error due to propagation delay in a repeater upon tracking the position of the terminal using a network-based position tracking scheme (e.g., TOA or TDOA) in a mobile communication network.

Another object of the present invention is to provide a user terminal discriminating device which is arranged in a repeater to discriminate whether a user terminal that has requested a call is present in a cell area of the relevant repeater through rapid synchronization with the terminal, and a method for determining elementary data for use in tracking the position of a mobile communication terminal using the device.

According to an aspect of the present invention for achieving the objects, there is provided a system for tracking the position of a terminal, which includes repeaters for transmitting a signal received from the terminal to base stations and transmitting signals received from the base stations to the terminal. Each of the repeaters comprises a terminal discriminating device which includes a user discriminating unit for receiving information from the base station and determining whether the user terminal is present so as to track the position of the terminal, a transceiver unit for transmitting and receiving position correction parameters for the user terminal, a control unit for controlling the user discriminating unit and the transceiver unit, and a memory unit for storing data. The system comprises a position tracking server for tracking the position of the user terminal. The position tracking server includes a database for storing geographical position information on the respective repeaters based on repeater identification information. According to another aspect of the present invention, there is provided a method for tracking the position of a terminal using a network-based position tracking system including repeaters for relaying forward and reverse signals between a terminal and a base station, and a terminal discriminating device included in the repeater for discriminating whether the terminal is present. The method comprises a first step of, by the base station, calculating a propagation delay time between the user terminal requesting a call and the base station, and receiving information on an assignment frequency (FA) number and an electrical identification number (ESN) of the relevant terminal from a position tracking server; a second step of, by the base station, transmitting the propagation delay time information between the base station and the user terminal, the assignment frequency (FA) number of the user terminal, and the electrical identification number (ESN) of the user terminal to repeaters in cells or sectors of a coverage area of the base station so as to request the repeaters to confirm whether the relevant user terminal is present; and a third step of, by the base station, receiving repeater identification information from the relevant repeater where the user terminal is positioned, obtaining a propagation delay time between the relevant repeater and the base station, and determining the position of the user terminal based on geographical position information on the repeater, a propagation delay time between the repeater and the terminal, and unique delay times of other neighboring base stations or repeaters.

According to a further aspect of the present invention, there is provided a user terminal discriminating device for tracking a position, comprising couplers for extracting signals transmitted and received from and to antennas of a repeater that relays the signals between a terminal and a base station; a transceiver unit for transmitting and receiving position correction parameters of the user terminal in the base station; a user discriminating unit for determining whether the user terminal is present; a control unit for controlling the transceiver unit and the user discriminating unit; and a memory unit for storing data on a propagation delay time between the base station and the repeater, and data on a unique propagation delay time of the repeater.

According to a still further aspect of the present invention, there is provided a method for determining elementary data for tracking the position of a terminal using a network-based position tracking system including repeaters for relaying forward and reverse signals between a terminal and a base station, a terminal discriminating device included in the repeater for discriminating the presence or absence of the user terminal, and a position tracking server for performing tracking the position of the terminal. The method comprises a first step of, by the terminal discriminating device, receiving a request for determining whether a terminal requesting a call is present in a cell area of the repeater from the base station by receiving an assignment frequency (FA) number of the user terminal, an electrical identification number (ESN) of the terminal device, and data on a propagation delay time between the user terminal and the base station; and a second step of confirming whether the user terminal is present in the cell area using the assignment frequency (FA) number of the relevant user terminal, the electrical identification number (ESN) of the terminal device, and information on the propagation delay time between the user terminal and the base station, and responding to the base station.

Brief Description of Drawings Fig. 1 is a diagram illustrating propagation delay between a base station and a mobile communication terminal.

Fig. 2 is a diagram showing a configuration of a system for tracking the position of a mobile communication terminal according to the present invention.

Fig. 3 is a diagram showing configurations of a terminal discriminating device and a repeater of the present invention. Fig. 4 is a diagram showing an example in which a terminal discriminating device is disposed outside a repeater according to the present invention.

Fig. 5 is a diagram showing propagation delay considered between a mobile communication terminal and a base station in a position tracking system of the present invention.

Fig. 6 is a flowchart showing a method for tracking the position of a mobile communication terminal using a position tracking system of the present invention.

Fig. 7 is a diagram showing a data flow among a base station, a repeater, and a mobile communication terminal in the method for tracking the position of the mobile communication terminal using the position tracking system of the present invention.

Fig. 8 is a diagram showing tracking the position of a mobile communication terminal using a position tracking system according to a preferred embodiment of the present invention.

Figs. 9 to 11 are diagrams showing other examples of tracking the position of a mobile communication terminal using a position tracking system of the present invention.

Best Mode for Carrying out the Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Referring to Fig. 2, a system for tracking the position of a mobile communication terminal according to the present invention comprises a repeater 200 for relaying reverse and forward signals between a mobile communication terminal 100 and a base station 400; a terminal discriminating device 300 connected to the repeater 200 for discriminating the presence or absence of the user terminal; and a position tracking server 500 for performing position tracking in response to reception of an emergency call from the user terminal 100.

Fig. 3 is a diagram showing a configuration of a repeater having a terminal discriminating device mounted thereon according to the present invention. The repeater

200 comprises a link antenna 210 for transmitting and receiving a signal to and from a base station via a wireless channel; a serving antenna 220 for transmitting and receiving a signal to and from a terminal; duplexers 230 and 240 for splitting transmission and reception frequencies input from the link antenna 210 and the serving antenna 220; and forward and reverse signal processing units 250 and 260 for processing forward and reverse signals, respectively. This repeater 200 comprises a terminal discriminating device 300 capable of discriminating the presence or absence of a user terminal. The forward signal processing unit 250 comprises a low-noise amplifier (LNA) for amplifying power at a very low voltage level output from the duplexer 230 while maintaining its low-noise characteristics, a filter and an amplifier for removing a spurious wave signal to minimize affects on neighboring frequencies of an RF signal, a high power amplifier (HP A) for amplifying an actual RF signal, and the like. The reverse signal processing unit 260 has the same configuration and function as the forward signal processing unit 250 but performs signal processing in a reverse direction.

Next, the terminal discriminating device 300 can comprise couplers 310 for extracting signals transmitted and received from and to the antenna of the repeater; a transceiver unit 320 for transmitting and receiving the user terminal's position correction parameter in a base station; a user discriminating unit 330 for discriminating the presence or absence of the user terminal; a control unit 340 for controlling the transceiver unit 320 and the user discriminating unit 330; a memory unit 350 for storing propagation delay time data between the base station and the repeater and repeater's unique propagation delay time data; and a power supply unit 360 for supplying power.

The transceiver unit 320 transmits and receives the position correction data to and from the position tracking server 500. A code division multiple access (CDMA) terminal or a dedicated wireless modem may be used for the transceiver unit 320.

The user discriminating unit 330 receives position tracking information on the user terminal of which the position will be tracked from the base station to determine whether a particular terminal is present in the cell of the repeater.

A method by which the user discriminating unit 330 determines whether a particular terminal is present in a particular repeater will be described in detail.

The memory unit 350 stores synchronization-related data to enable rapid synchronization with a relevant terminal upon deteπnining whether the user terminal is present in a cell area of the repeater. Specifically, the propagation delay time data between the base station and the repeater, and the repeater's unique propagation delay time data may be written in the memory unit. The method for rapid synchronization with a terminal using such data will be further described in detail. For such a terminal discriminating device, a mobile communication terminal with hardware and software for an RF range added or modified using a received signal-resolving capability of the terminal is employed. Alternatively, couplers 310 and a divider 360 are provided at the link antenna 210 and the serving antenna 220 of the conventional repeater, and a terminal discriminating device 300 is separately disposed, as shown in Fig. 4. This makes it possible to correct the position of the terminal even in an existing mobile communication network so that emergency rescue and terminal's position-based services can be provided.

The position tracking server 500 shown in Fig. 2 tracks the position of the user terminal. In order to track the position of the terminal, the following information is stored in a database 510:

1) actual geographical position information 511 on repeaters, and

2) identification information 512 on respective repeaters.

This information may be provided by constructing the geographical information on the repeaters into a database based on mobile identification numbers (MINs) of the repeaters upon arrangement of the repeaters.

Particularly, the identification information on the respective repeaters is intended to discriminate the respective repeaters from one another. To this end, terminal discriminating devices connected to the respective repeaters may be used.

Specifically, the terminal discriminating device 300 at each repeater comprises a transceiver unit 320 for transmitting and receiving the user terminal's position correction parameter to and from the position tracking server. A CDMA terminal or a dedicated wireless modem having a mobile identification number (MIN) may be used for such a transceiver unit.

That is, the mobile identification number of the transceiver unit in the terminal discriminating device 300 connected to each repeater may be used as identification information on the repeater.

The position tracking server 500 decomposes an emergency call from a terminal of which the position will be tracked, and stores a frequency assignment (FA) number, an electrical serial number (ESN) of the terminal device, and offset time information on a long code according to terminal propagation delay time, which are used by a relevant user terminal, in a separate memory unit to be used as position tracking information on the user terminal.

The base station's controller 600 has the function of performing connection with an existing wired network and performs the management of wireless resources, the control and management of the base station, the function of performing matching between the base station and a switch, and the like.

Meanwhile, although the position tracking server 500 is separately shown in Fig. 2, this is only intended to assist in understanding the present invention and it will be easily understood by those skilled in the art that a known base station or base station controller may comprise the aforementioned database for storing the data for use in tracking the position of the terminal to perform the function of a position tracking server.

Hereinafter, a method for determining elementary data for use in determining the position of a mobile communication terminal in the system for tracking the position of the terminal according to the present invention will be described. Information on a propagation delay time from the repeater to the mobile communication terminal, which is one of elementary data for use in tracking the position of the terminal, can be obtained from information on a propagation delay time between the terminal and the base station, which is measured in the base station when an emergency call is originated from the user terminal, and a propagation delay time caused when the repeater where the terminal is positioned sends an acknowledgement to the base station.

Specifically, by way of example, if a user terminal requests an emergency call, a base station receiving the emergency call can know information on a propagation delay time between the base station and the user terminal. Then, the base station requests repeaters, which are positioned in cells or sectors in its coverage area, to confirm the presence or absence of the user terminal that has requested the emergency call. At this time, the base station sends position tracking information for the user terminal, including information on a propagation delay time between the base station and the user terminal, an assignment frequency (FA) number of the user terminal that has requested the emergency call, and an electrical identification number (ESN) of the user terminal, to the respective repeaters.

Next, the terminal discriminating device at each of the repeaters confirms whether the user terminal that has requested the emergency call is present in the cell area of the repeater, and the repeater sends an acknowledgement to the base station if the user terminal is present in its own cell area. Meanwhile, the base station that has received the acknowledgement calculates information on propagation delay time between the relevant repeater and the base station generated while the base station receives the acknowledgement from the repeater.

Thus, a propagation delay time t_rc from the serving antenna of the repeater to the user terminal can be obtained as in the following equation 3: t_rc = tbc - tbr (3) where t_bC is a propagation delay time between the base station and the user terminal, and t_br indicates a propagation delay time due to the distance between the base station and the repeater that has sent the acknowledgement.

For reference, in equation 3, it should be noted that the propagation delay time t_br due to the distance between the base station and the repeater that has sent the acknowledgement needs to be discriminated from data on the propagation delay time between the base station and the repeater stored in the memory unit 350 of the terminal discriminating device 300.

That is, the data on the propagation delay time between the base station and the repeater, which are stored in the memory unit 350 of the terminal discriminating device 300, are data that are obtained by measuring propagation delay times between the base station and the repeater and storing its average value upon arranging the repeater and are needed to obtain timing of synchronization with the user terminal and acquire rapid synchronization upon discriminating whether the user terminal is present in the cell area of the repeater. On the other hand, in equation 3, the propagation delay time tbr due to the distance between the base station and the repeater that has sent the acknowledgement is data calculated by the base station and used to determine the position of the user terminal and to remove inefficiency of an information storage space in the base station and a complicated process for information delivery due to the increase of data to be written in the position tracking server.

Next, a method by which the terminal discriminating device of the present invention determines whether a particular terminal is positioned in a cell area of a particular repeater among a number of repeaters placed in the base station will be described.

The terminal discriminating device of the repeater determines whether the terminal is present in the cell area of the repeater using FA number and ESN information, which have been received from the base station, on the user terminal that has requested the emergency call, and the signal received from the user terminal within the cell area of the repeater, and responds to the request from the base station to confirm whether the relevant user terminal is present.

Specifically, the user discriminating unit 330 of the terminal discriminating device 300 receives, from the base station, the FA number of the terminal of which the position will be tracked, the electrical serial number (ESN) of the terminal device, offset time information on a long code depending on propagation delay time information on the terminal, and a time stamp indicating a time when the base station has measured the long code offset, and recognizes whether the particular terminal is present in the cell of the relevant repeater.

That is, the user discriminating unit 330 shifts a frequency according to the user terminal's FA number sent from the base station, produces a long code using the electrical serial number (ESN) of the terminal and the offset information, despreads the received signal, compares a correlation value output through a correlation detector with a threshold value, and determines that the relevant user terminal is positioned in the repeater if the correlation value is larger than the threshold value. If there are two or more neighboring base stations, it is determined as described above whether a user terminal is present, after a cell area of a repeater has been recognized in consideration of a geographical position. Here, the synchronization between the received signal and the long code is performed by a code searcher of the user discriminating unit. Meanwhile, the synchronization of a clock used in the user discriminating unit 330 is accomplished by a signal from the base station. To discriminate whether the user terminal is present, the user discriminating unit should be synchronized with the long code according to the electrical serial number (ESN) of the terminal device. However, since the number of long codes that are used currently is 2⁴²-l, synchronization for every chip takes much time and thus there is a need for a more efficient synchronization method.

Thus, the user discriminating unit of the present invention can acquire synchronization by means of the following two methods using the code searcher to facilitate rapid synchronization with the long code.

A first method is a method of acquiring synchronization at approximate timing of the long code synchronized with a forward signal through the user discriminating unit in the repeater.

Generally, the terminal acquires initial time synchronization using pilot channel and synchronous channel signals transmitted from the base station. The terminal is synchronized with a delay during a propagation delay time due to the distance between the base station and the terminal.

Thus, the repeater can acquire synchronization using the electrical serial number

(ESN) of the terminal device received from the base station, the propagation delay time between the repeater and the terminal, and information on the propagation delay time between the base station and the repeater and the unique propagation delay time of the repeater stored in the memory unit 350 of the terminal discriminating device 300.

Hereinafter, a method of acquiring synchronization using the terminal discriminating device will be described in greater detail with reference to Fig. 5.

Fig. 5 is a diagram showing propagation delays considered between the mobile communication terminal and the base station in the position tracking system of the present invention. It shows propagation delays that may be produced among the base station, the repeater, and the user's mobile communication terminal. ti to t₅ indicate propagation delays of a forward signal. Here, ti is a transmitting stage delay in the base station itself, t₂ is a propagation delay between the base station and the repeater, t₃ is a forward propagation delay in the repeater, t₄ is a propagation delay between the repeater and the terminal, and t₅ is a forward receiving stage delay in the terminal. t₆ to tio indicate propagation delays of a reverse signal. Here, t₆ is a reverse transmitting stage delay in the terminal, t is a propagation delay between the terminal and the repeater, t₈ is a reverse propagation delay in the repeater, t is a propagation delay between the repeater and the base station, and t₁₀ is a reverse receiving stage delay in the base station. tπ and t₁₂ indicate propagation delays from forward and reverse outputs of the repeater to the user discriminating unit, respectively.

Referring to Fig. 5, when establishing a reverse communication channel, the base station can recognize the propagation delay time t₆+t between the repeater and the terminal by measuring a signal from the terminal based on a reference time of the base station to recognize a delay time τ*_π between the base station and the terminal and by subtracting the propagation delay time t₈+t +t₁₀ between the base station and the repeater stored in the memory unit 350 of the terminal discriminating device 300 from the recognized delay time.

Thus, the user discriminating unit can derive the synchronization timing of a long code from the following equation 4: trev ⁼ tfwd " ( + t₅ + t₆ + t + t₈)

= tf_wd - {(t₆ + t₇) x 2 + t₈} (4) where t_rev is synchronization timing when the reverse user discriminating unit that desires to acquire synchronization is synchronized with the long code, and t_fwd indicates the acquired forward synchronization timing.

In equation 4, since the delay times over the respective forward and reverse fading channels between the repeater and the mobile terminal are substantially identical to each other, calculation can be made with t₄ + t₅ + t₆ + t = (t₆ + t ) x 2. The synchronization timing, which will be derived from equation 4, when the reverse user discriminating unit is synchronized with the long code is advanced by a certain time from the forward synchronization timing.

The reverse propagation delay time t₈ in the repeater is measured upon arranging the terminal discriminating device and is stored in the memory unit of the user discriminating device as unique propagation delay time information on the repeater.

A second method is a method of acquiring synchronization using the offset time information provided by the base station. The base station sets synchronization timing of the base station as a reference time based on a GPS reference time, and stores an offset between a time when the base station has received a signal from the user terminal over the reverse communication channel and the reference time, and a time stamp at which the offset is measured.

If the base station transmits the reference time, the offset of the long code, and the time stamp along with the ESN of the user terminal to the user discriminating unit, the user discriminating unit can recognize timing of the long code based on a known time and the received information.

Thus, the user discriminating unit can obtain the synchronization timing with the long code from the following equation 5: trev ⁼ toff + (tde " t_ab) - (ti + t₂ + t₃ + t + t₁₀) = (t_Ofr+ (tde - tab) - {(t9 + tι₀) x 2 + t₃} (5) where t_rev is synchronization timing of the user discriminating unit with the long code in the reverse signal, t_0ff is an offset time for a time when the base station has received the signal from the user terminal, from the reference time of the base station, t _e is a time when the user discriminating unit tries to initiate the synchronization with the forward long code of the user terminal of which the position is required to be tracked by the user discriminating unit, and t_ab is a time stamp at which the base station has measured the offset.

In equation 5, since the delay times of the forward and reverse fading channels between the base station and the repeater are substantially identical to each other, calculation can be made with t₁+t₂+t₉+t₁o = (t₉+t₁₀) x 2. The forward propagation delay time t₃ of the repeater is measured upon establishing the terminal discriminating device and is written in the memory unit of the user discriminating device as information on a unique propagation delay time of the repeater. A position tracking method using the system for tracking the position of a mobile communication terminal of the present invention constructed as above will be described with reference to Fig. 6.

For reference, the following description will be made under the assumption that a position tracking server and a base station need not to be discriminated from each other as the base station includes the database of the position tracking server, and the base station performs the function of the position tracking server.

In step S10, if a request for tracking the position of a particular terminal is made according to an emergency rescue call from the terminal, the request is delivered to the base station. The base station recognizes physical feature information such as FA number, ESN and the like of a relevant user's mobile communication terminal, and measures and writes a propagation delay time between the user terminal and the base station.

In step S20, the base station transmits a message containing position tracking information on a user terminal, which has issued the emergency rescue call, to repeaters positioned in its cell or sector using a multimedia messaging service (MMS), a short messaging service (SMS) or data communication, requests the repeaters to confirm the presence or absence of the user terminal, and waits for an response thereto.

Meanwhile, each of the respective repeaters in the cell area of the base station, which has received a request from the base station to confirm whether the user terminal is present, analyses a relevant reverse FA number to determine whether the relevant user terminal is positioned in a cell area of the repeater.

Specifically, the terminal discriminating device 300, which is included in each repeater and determines whether the user terminal is present, shifts a frequency according to the user terminal's FA number received from the base station, produces a long code using the electrical serial number (ESN) of the terminal device, despreads the received signal, compares a correlation value output through a correlation detector with a threshold value to determine whether the user terminal is present.

At this time, if the terminal discriminating device in each repeater confirms that the relevant terminal is present in the cell, it sends an acknowledgement to the base station. If the terminal discriminating device does not find a matched terminal, it does not send a response signal.

In order to improve the reliability of the response processing as to whether the relevant user terminal is present, each repeater causes the base station to send its own identification information and a non-acknowledgement signal if it does not find a terminal corresponding to the relevant user terminal information. Further, if the information received from the base station is not correct, the terminal discriminating device can discard the request from the base station and request the base station to retransmit infonnation.

The user discriminating unit 330, which will determine whether the terminal is present, can acquire synchronization approximately at timing of the long code synchronized with the forward signal, as described above. Alternatively, it can be rapidly synchronized with the long code using the offset time information received from the base station.

Step S30 comprises the process of, by the base station, receiving an answer to whether the user tenninal is present from the relevant repeater where the user terminal is positioned (S31), and a process of determining the position of the user mobile communication terminal using the position information and propagation delay time information on the repeater (S32).

That is, the base station receives an acknowledgement from the repeater where the terminal is positioned, and at the same time, obtains a propagation delay time between the repeater and the base station.

Next, the base station calculates information on a propagation delay time between the repeater and the user terminal. The obtained information on the propagation delay time between the repeater and the user terminal is used as positioning elementary information for tracking the position of the user terminal, along with identification information (e.g., geographical position information) on the repeater. The exact position of the user terminal is determined using propagation delay time information of other neighboring base stations or repeaters in addition to this information on the propagation delay time between the repeater and the user terminal.

Fig. 7 is a schematic diagram illustrating a data flow among a base station, a repeater and a mobile communication terminal in the method for tracking the position of a mobile communication terminal using the position tracking system of the present invention.

Fig. 8 is a diagram showing an example of tracking the position of a mobile communication terminal using the network-based position tracking scheme according to the present invention, in which solid lines indicate cell areas of respective base stations or. repeaters, and dotted lines indicate hyperbolas for recognizing the position of a terminal using differences in time from the respective base stations and repeaters to the terminal.

Specifically, Fig. 8 shows an example of tracking the position of a terminal using the TDOA scheme. A reverse signal from the terminal MSI, which has requested an emergency call, is repeated by a first repeater RPT1 and is transmitted to a first base station BTS 1. The first base station BTS 1 requests first and second repeaters RPT1 and

RPT2 positioned in the base station BTSl to discriminate whether the terminal MSI requesting the emergency call is present in the cell areas of the repeaters, as described above. The first repeater RPT1 that has recognized the terminal MSI requesting the emergency call sends its own identification information to the first base station BTSl along with an acknowledgment signal.

Meanwhile, second and third other base stations BTS2 and BTS3 adjacent to the first base station BTSl do not send an acknowledgement for the presence or absence of the terminal MSI because the user terminal MSI is not positioned in their own cell areas, but recognize the call and write propagation delay time differences between the second and third base stations and the terminal MSI.

Thus, since the first base station BTSl knows the geographical position of the first repeater RPT1 and the propagation delay time difference between the first repeater RPT1 and the terminal MSI, the first base station BTSl draws a hyperbola R12 using the propagation delay time difference between the first repeater RPTl and the user terminal MSI and a propagation delay time difference between the second base station BTS2 and the user terminal MSI. In addition, a hyperbola R13 may be drawn using a propagation delay time difference between the third base station BTS3 and the user terminal MSI. It is possible to uniquely determine a point where the two hyperbolas R12 and R13 which have been drawn using the propagation delay time differences between the terminal MSI and each of the first repeater RPTl and the second and third base stations BTS2 and BTS3. Thus, the position of the tenninal MSI that has requested the emergency call is accurately determined. For reference, if a hyperbola is drawn using the propagation delay time difference between the first base station BTS 1 and the terminal without considering the propagation delay time in the repeater, the terminal is recognized as being at a position farther than the actual position, resulting in an error in the position tracking of the terminal.

Figs. 9 to 11 are diagrams showing other examples of tracking the position of a mobile communication terminal using the network-based position tracking system of the present invention, in which solid lines indicate cell areas of respective base stations or repeaters and dotted lines indicate propagation delay times with respect to the user terminal measured at the respective base stations or repeaters. Hereinafter, a description will be made in connection with Figs. 9 to 11. Fig. 9 is a diagram showing tracking the position of a terminal using the TOA scheme in a case where the terminal MSI that has requested an emergency call is positioned in cell areas of the first and second repeater RPTl and RPT2 in the first base station BTSl.

If the terminal MS 1 requests a call, the call is delivered to the first base station BTS 1 via the first repeater RPTl and the second repeater RPT2. The first base station BTS 1 that has received the call sets up a call from a repeater signal having better receiving power among the signals through the first repeater RPTl and the second repeater RPT2.

However, upon tracking the position, the distance is estimated using the propagation delay times in both the repeaters RPTl and RPT2. At this time, the position of the terminal is tracked using only propagation delay time information of the neighboring base station BTS2.

That is, the first base station BTS 1 sets up a call from only a signal through either the first repeater RPTl or the second repeater RPT2, and draws three circles Rl, R2 and R3 centered on the first and second repeaters RPTl and RPT2 and the second base station BTS2 by converting respective propagation delay times into distances based on information on a propagation delay time of another repeater and information on a propagation delay time of the second neighboring base station BTS2 that has received the emergency call from the terminal MSI, thereby determining the exact position of the terminal MSI. Fig. 10 is a diagram showing terminal position tracking in a case where two and more repeaters are included between base stations and a terminal and a repeater of a cell area where the terminal is positioned is connected to the base stations using other repeaters as links.

A call originated from the terminal MSI, which is positioned in the cell area of the first repeater RPTl, is set up to the first base station BTSl via the first repeater RPTl and the second repeater RPT2. Further, a signal is delivered to the second base station BTS2 via the third repeater RPT3, and also to the third base station BTS3. If the first base station BTS 1 transmits a signal for requesting an acknowledgement for position tracking, the first repeater RPTl and the second repeater RPT2 inform the first base station BTSl that the terminal MS 1 is positioned in its own cell area. At this time, because the second repeater RPT2 acts as a link between the first repeater RPTl and the first base station BTSl, the second repeater RPT2 sends an acknowledgement signal in response to the request from the first base station BTSl to confirm whether the terminal MSI requesting the emergency call is present even through the terminal is not positioned in the cell area of the second repeater RPT2.

However, the distance obtained by the second repeater RPT2 belonging to the first base station BTSl is calculated as being larger due to the propagation delay time in the first repeater RPTl, and is indicated by a circle designated by reference numeral R4. This may be ignored since the position of the terminal is determined to be on a point where three circles Rl, R2 and R3, which are drawn by converting propagation delay times measured at the first repeater RPTl, the third repeater RPT3 and the third base station BTS3 with respect to the terminal MSI into distances, are intersected.

Fig. 11 is a diagram showing terminal position tracking using the TOA scheme in a case where repeaters are divided into a master repeater and a slave repeater in the same manner as a digital optical repeater and an emergency rescue call is incoming via the repeaters.

As described in Fig. 10, in a case where there are acknowledgements from a number of repeaters in response to a request from the first base station BTS 1 to confirm whether the terminal MSI is present, circles will be drawn using information on propagation delay times measured in all the repeaters. However, the circles drawn in all the repeaters except for the first repeater RPTl will not be intersected with circles drawn in the second and third neighboring base stations BTS2 and BTS3. Thus, these values are ignored, and the accurate position of the terminal is determined to be on a position where three circles Rl, R2 and R3 are intersected with one another, considering the propagation delay times in the first repeater RPTl and the second and third neighboring base stations BTS2 and BTS3.

As described above, in the method for tracking the position of a mobile communication terminal according to the present invention, the positioning information can be delivered using communication between the base station and the repeater. Moreover, in a case where a communication environment for SMS or MMS is not configured, it is possible to perform data connection (TCP/IP) and data transmission/reception by calling a particular terminal in a simple IP environment.

Generally, in the simple IP environment of the mobile communication network that does not support a mobile IP, it is impossible to directly call a terminal because the terminal does not have a unique IP address. Therefore, if a server calls a particular terminal by sending a message containing its own IP address using SMS or MMS, the receiving terminal recognizes that the call is a request for wireless Internet connection and requests data communication connection. Accordingly, the terminal is assigned its IP by a dynamic host configuration protocol (DHCP) and is capable of performing consecutive data transmission/reception. In the system and method for tracking the position of a mobile communication terminal according to the present invention described above, recognition is made as to whether a mobile communication terminal that has requested an emergency call is present in a cell area of a repeater and then an error in a propagation delay time caused by the repeater is corrected in tracking the position of the terminal based on an existing network-based position tracking scheme, thereby minimizing the position tracking error of the mobile communication terminal and more efficiently providing a position-based service upon occurrence of urgency calls and emergency rescue calls.

Furthermore, in the position tracking system of the present invention, a terminal discriminating device that is capable of determining whether a particular terminal is present in a cell area of the repeater is simply mounted on the conventional repeater by using a coupler, which makes it possible to implement the position tracking system without modifying a conventional mobile communication system including an existing mobile communication terminal, thereby providing an economical and efficient position-based service.

Claims

1. A system for tracking the position of a terminal, the system including repeaters for transmitting a signal received from the terminal to base stations and transmitting signals received from the base stations to the terminal, wherein: each of the repeaters comprises a terminal discriminating device, the terminal discriminating device including a user discriminating unit for receiving information from the base station and determining whether the user terminal is present so as to track the position of the terminal, a transceiver unit for transmitting and receiving position correction parameters for the user terminal, a control unit for controlling the user discriminating unit and the transceiver unit, and a memory unit for storing data, and the system comprises a position tracking server for tracking the position of the user terminal, the position tracking server including a database for storing geographical position information on the respective repeaters based on repeater identification information.

2. The system as claimed in claim 1, wherein the memory unit stores data on propagation delay times between the base stations and the repeaters, and data on unique propagation delay times of the repeaters.

3. A method for tracking the position of a terminal using a network-based position tracking system including repeaters for relaying forward and reverse signals between a terminal and a base station, and a terminal discriminating device included in the repeater for discriminating whether the terminal is present, the method comprising: a first step of, by the base station, calculating a propagation delay time between the user terminal requesting a call and the base station, and receiving information on an assignment frequency (FA) number and an electrical identification number (ESN) of the relevant terminal from a position tracking server; a second step of, by the base station, transmitting the propagation delay time information between the base station and the user terminal, the assignment frequency (FA) number of the user terminal, and the electrical identification number (ESN) of the user terminal to repeaters in cells or sectors of a coverage area of the base station so as to request the repeaters to confirm whether the relevant user terminal is present; and a third step of, by the base station, receiving repeater identification information from the relevant repeater where the user terminal is positioned, obtaining a propagation delay time between the relevant repeater and the base station, and determining the position of the user terminal based on geographical position information on the repeater, a propagation delay time between the repeater and the terminal, and unique delay times of other neighboring base stations or repeaters.

4. A user terminal discriminating device for tracking a position, comprising: couplers for extracting signals transmitted and received from and to antennas of a repeater that relays the signals between a terminal and a base station; a transceiver unit for transmitting and receiving position correction parameters of the user terminal in the base station; a user discriminating unit for determining whether the user terminal is present; a control unit for controlling the transceiver unit and the user discriminating unit; and a memory unit for storing data on a propagation delay time between the base station and the repeater, and data on a unique propagation delay time of the repeater.

5. A method for determining elementary data for tracking the position of a terminal using a network-based position tracking system including repeaters for relaying forward and reverse signals between a terminal and a base station, a terminal discriminating device included in the repeater for discriminating the presence or absence of the user terminal, and a position tracking server for performing tracking the position of the terminal, the method comprising: a first step of, by the terminal discriminating device, receiving a request for determining whether a terminal requesting a call is present in a cell area of the repeater from the base station by receiving an assignment frequency (FA) number of the user terminal, an electrical identification number (ESN) of the terminal device, and data on a propagation delay time between the user terminal and the base station; and a second step of confirming whether the user terminal is present in the cell area using the assignment frequency (FA) number of the relevant user terminal, the electrical identification number (ESN) of the terminal device, and information on the propagation delay time between the user terminal and the base station, and responding to the base station.

6. The method as claimed in claim 5, wherein the terminal discriminating device acquires timing when the terminal discriminating device is synchronized with a long code of a reverse user terminal by the following equation: trev = tj vd - {(t_rc X 2) + τ} where, t_rev is timing when the reverse terminal discriminating device that tries to acquire synchronization is synchronized with the long code, t_fwd is acquired forward synchronization timing, t_rc is a propagation delay time between a serving antenna of the repeater and the terminal, and τ is a unique reverse delay time of the repeater.

7. The method as claimed in claim 5, wherein the terminal discriminating device acquires timing when the terminal discriminating device is synchronized with a long code of a reverse user terminal by the following equation: trev = toff + (t_de - tab) -{(tbr 2) + τ} where, t_rev is timing when the reverse terminal discriminating device that tries to acquire synchronization is synchronized with the long code, t_0ff is an offset time of a time when the base station has received a signal from the user terminal, from a reference time of the base station, t_de is a time when the terminal discriminating device tries to initiate synchronization with a forward long code of the user terminal of which the position is required to be tracked by the user discriminating unit, t_ab is a time stamp at which the base station has measured the offset, t_br is a propagation delay time between the base station and a serving antenna of the repeater, and τ is a unique forward delay time of the repeater.