Patent Publication Number: US-9851430-B2

Title: Positioning method and apparatus using wireless signal

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2014-0087636 filed in the Korean Intellectual Property Office on Jul. 11, 2014, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a positioning method and apparatus using a wireless signal, and more particularly, to a positioning method and apparatus used to calculate a location of a terminal by measuring phase differences between wireless signals having periods received from three or more base stations adjacent to a terminal. 
     (b) Description of the Related Art 
     In general, methods for enhancing precision of satellite navigation technologies such as the global positioning system (GPS) and the like include differential GPS, a positioning method using a GPS carrier phase, and the like. 
     The D-GPS, a method of correcting a GPS signal error generated due to diffraction of the atmosphere, an abnormality of a satellite orbit, and the like, is known to improve an error level by up to a 1-meter level in good conditions. However, in an environment in which line-of-sight (LOS) with respect to a satellite is not guaranteed, such as a downtown area, an indoor area, or a mountainous area, an error range increases due to an effect such as delay spread due to multiple paths. 
     A GPS broadcast wave phase scheme (or RealTime Kinematics (RTK) method), which calculates the number of wavelengths of a satellite carrier signal ranging from 1.5 GHz to 2 GHz and a phase difference, significantly improves positioning precision to a centimeter level. In a GPS carrier phase method, it is important to accurately synchronize a start point at which a positioning terminal and a reference station starts to count wavelengths of simultaneously received satellite carriers, and here, if the positioning terminal moves at a fast speed or if a satellite signal is temporarily blocked by a nearby obstacle or interfered with by slight noise, a phase slip phenomenon in which the number of wavelengths counted by the positioning terminal is different from that of the reference station occurs, causing a positioning error. In this case, the positioning terminal should again start a phase tracking synchronization process with respect to the reference station from scratch. 
     Meanwhile, in a method of performing positioning using a ground mobile communication base station signal, without relying on the GPS, position coordinates of a positioning terminal are calculated using a cell ID or using a time difference of arrival of signals between a base station and the positioning terminal, and as such, a technique such as observed time difference of arrival (OTDOA) or the like has been known. However, with the positioning methods based on a ground mobile communication base station signal, time synchronization precision between base stations is inferior to that of GPS satellites supporting precise time synchronization by an atomic clock, or the like, and a positioning error of a few meters to tens of meters or greater occurs due to limitations in a bandwidth, a sampling time interval, and the like, of a general broadband mobile communication wireless system. 
     In order to reduce the error limitations of the ground mobile communication base station-based positioning methods, a positioning method based on a phase measurement of a reception signal in a wireless communication network has been proposed. In this method, a positioning terminal calculates phase rotation values of time-synchronized OFDM preamble signals from three or more adjacent base stations, and obtains absolute coordinate values thereof by using differences in the phase rotation values of the three or more base stations and differences in distances converted therefrom. 
     In the positioning method based on phase measurement of a reception signal, since continuous rotation values of a signal phase are used, a time error due to discretized sampling is reduced and more precise time resolving power (or resolution) can be obtained. However, the positioning method fails to improve precision beyond a theoretical sampling time interval limitation, i.e., a bandwidth limitation, and does not provide a method for reducing an error occurring when base stations are not synchronized in time. 
     In general, mobile communication base station systems perform time synchronization based on GPS satellite signals, and in this case, a synchronization error of nanoseconds (ns) or greater may occur on the ground. A resultant positioning error may be a few meters or greater. 
     Also, in the foregoing positioning methods based on satellite and ground base station signals, when positioning is performed in a downtown area or a mountainous area, a signal is subjected to reflection and diffraction with a nearby building or obstacle and reach through various paths. In this case, when a position is calculated on the basis of the reflected or diffracted signal, the calculated position may be different from an actual position, and the resultant positioning error may range from a few meters to tens of meters. Thus, the related art positioning methods based on satellites and base stations generally have a severe positioning error in a downtown area or in a mountainous area or cannot be used in an indoor area. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a positioning method and apparatus having advantages of calculating a location of a terminal by measuring phase differences between wireless signals having periods received from three or more base stations adjacent to a terminal. 
     An exemplary embodiment of the present invention provides a positioning method of a terminal using a wireless signal. The positioning method may include: receiving carrier signals with start point information indicated thereon from three or more base stations (BSs) including a serving BS; calculating a difference in phase angles between carrier signals of two BSs, while changing the two BSs, by using the start point information of the carrier signals of the two BSs among the three or more BSs; calculating differences in distances of arrival from the corresponding two BSs to the terminal by using the calculated differences in phase angles; and calculating coordinates of the terminal by using the calculated differences in distances of arrival. 
     At least one among a phase, an amplitude, and a frequency of the carrier signal may be changed on the basis of the start point period, and the calculating may include detecting the point at which at least one among the phase, the amplitude, and the frequency is changed, as a start point of the carrier signals. 
     The receiving may include: calculating a propagation incident angle range of each of the nearby BSs on the basis of the coordinates of the terminal and coordinates of the nearby BSs; and filtering only a carrier signal received within the propagation incident angle ranges of each of the BSs. 
     The calculating may include: generating diffraction paths from BSs, among the nearby BSs, to the terminal by using 3D map information; calculating differences in lengths between the diffraction paths from two BSs to the terminal, while changing the two BSs, among the nearby BSs; calculating an error between the difference in lengths between the diffraction paths calculated with respect to the same BS subject and a difference in distances of arrival; and calculating coordinates of the terminal by using the error value. 
     The generating of diffraction paths may include: generating a linear vector connecting the coordinates of the terminal and coordinates of any one BS; generating an edge vector forming a plane from plane information of a building adjacent to the terminal, while intersecting the linear vector, by using the 3D map information; calculating an orthogonal projection point to which the linear vector between the terminal and any one BS is projected on the edge vector; and linking the calculated orthogonal projection point, the any one BS, and the terminal to generate a diffraction path from the any one BS to the terminal. 
     The calculating of coordinates of the terminal may include calculating the coordinates of the terminal at which the error value is minimized. 
     The calculating of a difference in distances of arrival may include: receiving an offset value with respect to a difference in phase angles between the serving BS and a neighbor BS of the serving BS, calculated by the serving BS, from the serving BS; and compensating for the difference in phase angles between the carrier signals of the two BSs by using the received offset value. 
     The receiving of the offset value may include: receiving, by the serving BS, the carrier signal from the neighbor BS; calculating, by the serving BS, a phase angle of the carrier signal with respect to a start point of the carrier signal of the neighbor BS; calculating, by the serving BS, an offset value with respect to a difference in phases between a phase angle calculated with respect to the start point of the carrier signal transmitted by the serving BS and a phase angle calculated with respect to the start point of the carrier signal of the neighbor BS; and transmitting, by the serving BS, the offset value. 
     The receiving may include transmitting, by the three or more BSs, carrier signals with frequencies of different bands. 
     The receiving may include transmitting, by the three or more BSs, carrier signals at mutually different times. 
     Another exemplary embodiment of the present invention provides a positioning apparatus of a terminal using a wireless signal. The positioning apparatus may include a reception unit, a phase tracking unit, a plurality of phase clock units, and a control unit. The reception unit may receive carrier signals with start point information indicated thereon from three or more nearby base stations (BSs) including a serving BS. The phase tracking unit may detect a start point and a start point period of each of the carrier signals of the BSs. The plurality of phase clock units may calculate a phase angle of each of the carrier signals of the BSs with respect to a start point of each of the carrier signals of the BSs. The control unit may calculate a difference in phase angles between carrier signals of two BSs, among the nearby BSs, while changing the two BSs, calculate a difference in distances of arrival from the corresponding two BS to the terminal by using the calculated differences in phase angles, and calculate coordinates of the terminal by using the calculated differences in distances of arrival. 
     The control unit may generate diffraction paths from the BSs to the terminal by using the calculated coordinates of the terminal and 3D map information, and correct the coordinates of the terminal by using the diffraction paths from the BSs to the terminal. 
     The control unit may calculate differences in lengths between the diffraction paths from two BSs to the terminal, while changing the two BSs, calculate an error between the difference in lengths between the diffraction paths calculated with respect to the same BS subject and a difference in distances of arrival, and correct coordinates of the terminal by using the error value. 
     The control unit may generate a linear vector connecting the coordinates of the terminal and coordinates of any one BS, generate an edge vector forming a plane from plane information of a building adjacent to the terminal while intersecting the linear vector by using the 3D map information, calculate an orthogonal projection point to which the linear vector between the terminal and any one BS is projected on the edge vector, and link the calculated orthogonal projection point, the any one BS, and the terminal to generate a diffraction path from the any one BS to the terminal. 
     The control unit may control the reception unit to filter only a carrier signal received within a propagation incident angle range of the directions of the nearby BSs. 
     The control unit may calculate a propagation incident angle range of each BS on the basis of the coordinates of the terminal and the coordinates of the nearby BSs received from the serving BS. 
     At least one among a phase, an amplitude, and a frequency of the carrier signal may be changed on the basis of the start point period, and the phase tracking unit may detect the point at which at least one among the phase, the amplitude, and the frequency is changed, as a start point of the carrier signals. 
     Each of the plurality of phase clock units may synchronize a phase clock with respect to the carrier signal of the corresponding BS to a wavelength of the corresponding carrier signal, and when a start point of the carrier signal of the corresponding BS is detected, each of the plurality of phase clock units may reset a phase clock with respect to the carrier signal of the corresponding BS. 
     The reception unit may receive at least one offset value with respect to a difference in phase angles between the serving BS and a neighbor BS of the serving BS, calculated by the serving BS, through the serving BS, and the control unit may compensate for each difference in phase angles between the carrier signals by using the at least one offset value. 
     When the interval of the start point period is converted into a distance, the distance may be longer than a maximum distance between two BSs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating an example of a wireless communication system to which the present invention is applied. 
         FIG. 2  is a view illustrating an example of indicating start points in a carrier signal according to an exemplary embodiment of the present invention. 
         FIG. 3  is a flowchart illustrating a method for calculating an offset value in a base station according to an exemplary embodiment of the present invention. 
         FIG. 4  is a flowchart illustrating a method for synchronizing a phase clock of a carrier signal received by a base station according to an exemplary embodiment of the present invention. 
         FIGS. 5 through 7  are flowcharts illustrating a method for calculating a location of a terminal according to first to third exemplary embodiments of the present invention. 
         FIG. 8  is a view illustrating a method for calculating a diffraction distance of propagation illustrated in  FIG. 7 . 
         FIG. 9  is a view illustrating a base station according to an exemplary embodiment of the present invention. 
         FIG. 10  is a view illustrating a positioning apparatus of a terminal according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
     Throughout the specification, a terminal may refer to user equipment (UE), a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS), a high reliability mobile station (HR-MS), a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), or the like, and may include the entirety or a portion of functions of the UE, MT, MS, AMS, HR-MS, SS, PSS, AT, or the like. 
     Also, a base station (BS) may refer to a node B, an evolved node B (eNB), an advanced base station (ABS), a high reliability base station (HR-BS), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), or the like, and may include the entirety or a portion of functions of the node B, eNB, BS, ABS, HR-BS, AP, RAS, BTS, or the like. 
     Throughout the specification and claims, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. 
     Hereinafter, a positioning method and apparatus using a wireless signal according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a view illustrating an example of a wireless communication system to which the present invention is applied. 
     Referring to  FIG. 1 , a wireless communication system includes a plurality of base stations (BSs)  110 ,  120 , and  130 , and a terminal  200 . 
     The BSs  110 ,  120 , and  130  may provide a communication service to the terminal  200  present in a particular geographical area called a cell, and may be installed and operated in various forms such as a macrocell, a picocell, a microcell, and the like, according to an installation purpose and a size of cell coverage. 
     The terminal  200  is a terminating point of a wireless channel, which is connected to a single BS and provided with a communication service. 
     The BSs  110 ,  120 , and  130  transmit a carrier signal having a period, for the purpose of positioning the terminal  200 . The carrier signal may be a single carrier signal or a plurality of carrier signals. 
     The BSs  110 ,  120 , and  130  may use carrier frequencies of different bands to avoid interference, or in case of using the same carrier frequency, transmission timing is divided in a time division manner among the BSs according to previously agreed rules to transmit carrier signals, thereby avoiding mutual interference. 
     The BSs  110 ,  120 , and  130  may explicitly or indirectly indicate a start point on a carrier signal and transmit the same, such that a neighbor BS or the terminal  200  can easily find the start point from which the number of wavelengths of the carrier signal is counted. 
     The BSs  110 ,  120 , and  130  may receive carrier signals transmitted by neighbor BSs. Each of the BSs  110 ,  120 , and  130  detects start points of carrier signals from neighbor BSs, and calculates an error, i.e., an offset value, with respect to a phase difference between phase angles of carrier signals from neighbor BSs measured with reference to the start points of the carrier signals from the neighbor BSs and phase angles of carrier signals measured with reference to start points of carrier signals transmitted by the BSs  110 ,  120 , and  130 . 
     The BSs  110 ,  120 , and  130  broadcast the calculated offset value to the terminal  200  within a cell radius served by the BSs  110 ,  120 , and  130 . 
     The terminal  200  receives carrier signals from the nearby BSs  110 ,  120 , and  130 . Also, the terminal  200  receives coordinate information of the nearby BSs and an offset value calculated by the serving BS  120  from the serving BS  120 . 
     The terminal  200  tracks a phase and a start point period of each of carrier signals received from the BSs to count the number of wavelengths of each of the carrier signals of the BSs, and calculates a difference in phase angles between the carrier signals of two BSs. The terminal  200  compensates for the difference in phase angles between carrier signals of two BSs, calculated by the terminal  200  itself, by using the offset value received from the serving BS. 
     The terminal  200  calculates a difference in distances of arrival from the two corresponding BSs to the terminal  200  by using the difference in phase angles between the carrier signals, which has been compensated with the offset value. 
     In this manner, the difference in distances of arrival can be calculated from the carrier signals of the two different BSs, and approximate coordinates of the terminal  200  may be calculated using the calculated difference in distances of arrival. 
     In order to reduce an error due to multiple paths of propagation, the terminal  200  may use three-dimensional (3D) geographical information. That is, the terminal  200  may recognize a shape and a position of an obstacle placed in a linear distance between the terminal  200  and the BSs  110 ,  120 , and  130 , and calculate accurate distances of arrival between the terminal  200  and the BSs  110 ,  120 , and  130  in consideration of diffraction paths of propagation, thus enhancing accuracy of positioning. 
       FIG. 2  is a view illustrating an example of indicating start points in a carrier signal according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , the BS  110  transmits a carrier signal having n number of wavelengths, and thereafter, the BS  110  inverts a phase of the carrier signal by 180 degrees to transmit the phase-inverted carrier signal having n number of wavelengths. 
     Then, points at which the phase of the carrier signal is inverted are start points A, B, and C of the carrier signal. 
     In this manner, by inverting the phase of the carrier signal according to the start point period, the start points A, B, and C of the carrier signal may be indicated. 
     The BS  120  also transmits a carrier signal having n number of wavelengths, and thereafter, the BS  120  inverts the phase of the carrier signal by 180 degrees and transmits the phase-inverted carrier signal having n number of wavelengths, thus indicating start points A′, B′, and C′ in the carrier signal. 
     In this manner, the terminal  200 , which receives the carrier signal including the start point information, may detect the phase inverted points of the repeatedly transmitted carrier signal as start points, even in a shadow area in which signal strength is weak or in an environment with severe noise, and count the number of wavelengths of the carrier signal from each of the start points of the carrier signal to measure a phase angle. 
     In addition to the method, various other methods such as a method of using amplitude modulation of the carrier signal, a method of using frequency modulation of the carrier signal, a method of using a phase difference between a plurality of carrier signals having different frequencies, as an indirect start point indicator, and the like, may also be used as a method of indicating start point information on the carrier signal. 
     The intervals between the start points A, B, and C of the carrier signal may be longer than a maximum distance between two neighbor BSs  110  and  120  when the intervals are converted into distances. For example, when it is assumed that the BS  110  transmits the start point (A, B, C) information by using a carrier signal having n number wavelengths in which the length of one wavelength is p, a distance between certain two start points is pxn, and the length (=pxn) is longer than the maximum distance between the two neighbor BSs  110  and  120 . 
       FIG. 3  is a flowchart illustrating a method for calculating an offset value in a base station according to an exemplary embodiment of the present invention. In  FIG. 3 , for the purposes of description, the method of calculating an offset value by the BS  110  will be described, and the other BSs  120  and  130  may also calculate an offset value in the same manner. 
     Referring to  FIG. 3 , the BS periodically counts the number of wavelengths, while transmitting a carrier signal having continuous wavelengths using the method illustrated in  FIG. 2  (S 310 ). 
     When the number of wavelengths of the transmitted carrier signal corresponds to the preset value (n) (S 320 ), the BS  110  initializes a wavelength number counter (S 330 ). 
     The BS  110  repeats the steps S 310 , S 320 , and S 330  by inverting the phase of the carrier signal by 180 degrees and continuously transmitting the wavelengths. 
     In this manner, the BS  110  transmits the carrier signal. 
     The BS  110  receives carrier signals transmitted from the neighbor BSs (e.g.,  120  and  130 ) (S 340 ). 
     The BS  110  tracks phases and start points of the carrier signals received from the neighbor BSs  120  and  130 . 
     When start points of the carrier signals from the BSs  120  and  130  are detected, the BS  110  counts the number of wavelengths of the corresponding carrier signals with respect to the start points of the carrier signals of the neighbor BSs  120  and  130  to measure phase angles (S 350 ). 
     Thereafter, the BS  110  calculates offset values with respect to a relative phase difference between a phase angle measured from a start point of the carrier signal transmitted by the BS  110  and the phase angles measured from the start points of the carrier signals of the neighbor BSs  120  and  130  (S 360 ), and stores the calculated offset values in an internal memory. 
     In this manner, the BS  110  calculates the offset values with respect to all the neighbor BSs and stores the calculated offset values in the internal memory. 
     For example, when it is assumed that a BS A receives a carrier signal from a BS B and calculates an offset value, the offset value may be calculated as expressed by Equation 1 below.
 
 O   B =((φ A −φ B −2π d /λ)+2π n )mod 2π n   (Equation 1)
 
     In Equation 1, (φ A −φ B ) is a phase difference between a phase angle measured from a start point of the carrier signal transmitted from the BS A and a phase angle measured from a start point of the carrier signal received from the BS B. “d” denotes a distance between the BS A and the BS B, and λ denotes a length of a wavelength of a carrier signal. 2πn denotes a start point period, that is, n number of wavelength intervals, and mod denotes a modulo operation. 
     Similarly, when it is assumed that the BS B receives a carrier signal from the BS A and calculates an offset value, the offset value may be calculated as expressed by Equation 2 below.
 
 O   A =((φ B −φ A −2π d /λ)+2π n )mod 2π n   (Equation 2)
 
     The BS  110  broadcasts an offset value list stored in the internal memory to the terminal  200  within a cell radius (S 370 ). The BS  110  may broadcast coordinate information thereof and coordinate information of a neighbor BS, together with the offset value list, to the terminal  200  within the cell radius. The offset value list may be periodically broadcasted. 
     Then, the terminal  200  may receive the offset value list from the serving BS (e.g.,  120 ). 
       FIG. 4  is a flowchart illustrating a method for synchronizing a phase clock of a carrier signal received by a base station according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , the BS  110  receives carrier signals periodically transmitted from the neighbor BSs  120  and  130 . 
     The BS  110 , while tracking phases of the received carrier signals of the neighbor BSs  120  and  130 , synchronizes the phase clocks of the corresponding carrier signals to wavelengths of the corresponding carrier signals (S 410 ). 
     When the BS  110  detects start points of the carrier signals (S 420 ), the BS  110  initializes the phase clocks again (S 430 ). 
     Accordingly, the BS  110  can accurately calculate offset values measured from start points of the carrier signals of the neighbor BSs  120  and  130 . 
       FIG. 5  is a flowchart illustrating a method for calculating a location of a terminal according to a first exemplary embodiment of the present invention. 
     Referring to  FIG. 5 , the terminal  200  receives coordinate information of neighbor BSs including the serving BS and information of an offset value list from the serving BS (S 510 ). The terminal  200  stores the received information in the internal memory. 
     When the terminal  200  receives a carrier signal from a neighbor BS (S 520 ), the terminal  200  synchronizes a phase clock of the carrier signal of each BS to a wavelength of the corresponding carrier signal. 
     Next, when the terminal  200  detects a start point of the carrier signal of each BS (S 530 ), the terminal  200  resets the phase clock of the corresponding carrier signal (S 540 ). 
     The terminal  200  measures a phase angle of the carrier signal of each BS by using the phase clock of the carrier signal of each BS (S 550 ). 
     The terminal  200  calculates a difference in the phase angles between the carrier signals of certain two BSs (S 560 ), and compensates for the calculated difference in the phase angles between the carrier signals of the two BSs with an offset value corresponding to the carrier signals of the two BSs received from the serving BS (S 570 ). 
     The terminal  200  calculates a difference in distances of arrival from the certain two base stations to the terminal  200  by using the offset value-compensated difference in phases between the carrier signals (S 580 ). 
     For example, the difference in distances of arrival from the BS A and the BS B to the terminal  200  may be calculated as expressed by Equation 3 below. 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     
                       d 
                       AB 
                     
                   
                   = 
                   
                     
                       λ 
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                       { 
                       
                         
                           ( 
                           
                             
                               φ 
                               A 
                             
                             - 
                             
                               φ 
                               B 
                             
                             - 
                             
                               O 
                               B 
                             
                             + 
                             
                               2 
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                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               n 
                             
                           
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                         mod 
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                         2 
                         ⁢ 
                         π 
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                         ⁢ 
                         n 
                       
                       } 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
     In Equation 3, Δd AB  denotes a difference in distances of arrival from the BS A and the BS B to the terminal  200 , and λ denotes a length of one wavelength of the carrier signals. φ A  is a phase angle measured using the start point of the carrier signal of the BS A as a reference, and φ B  is a phase angle measured using the start point of the carrier signal of BS B as a reference. O B  denotes an offset value with respect to the BS B calculated by the BS A, and 2πn is a start point period. 
     By using the carrier signals received from three or more BSs including the serving BS, the terminal  200  calculates a plurality of differences in distances of arrival by changing the two BSs on the basis of the method described above. For example, the terminal  200  may calculate a difference in distances of arrival from the BSs  110  and  120  to the terminal  200  by using a difference in phases between the carrier signals of the BSs  110  and  120 , calculate a difference in distances of arrival from the BSs  120  and  130  to the terminal  200  by using a difference in phases between the carrier signals of the BSs  120  and  130 , and calculate a difference in distances of arrival from the BSs  110  and  130  to the terminal  200  by using a difference in phases between the carrier signals of the BSs  110  and  130 . 
     The terminal  200  calculates approximate coordinate information of the terminal  200  by using the plurality of differences in distances of arrival (S 590 ). The terminal  200  may calculate approximate coordinate information of the terminal  200  by applying the plurality of differences in distances of arrival to a hyperbolic secant algorithm. 
       FIG. 6  is a flowchart illustrating a method for calculating a location of a terminal according to a second exemplary embodiment of the present invention. 
     Referring to  FIG. 6 , the terminal calculates approximate coordinates of the terminal  200  on the basis of the method described above with reference to  FIG. 5  (S 610 ). 
     The terminal  200  calculates a propagation incident angle range of each BS with reference to the approximate coordinates of the terminal and coordinates of neighbor BSs (S 620 ). 
     The terminal  200  filters only a carrier signal within the propagation incident angle range in the direction of each BS among multipath waves (S 630 ). 
     The terminal  200  calculates coordinates of the terminal  200  through the method described above with reference to  FIG. 5  by using the filtered carrier signals (S 640 ). 
     In this manner, a delay spread and angle spread error due to multiple paths may be reduced. 
       FIG. 7  is a flowchart illustrating a method for calculating a location of a terminal according to a third exemplary embodiment of the present invention. 
     Referring to  FIG. 7 , the terminal  200  calculates approximate coordinate information of the terminal  200  on the basis of the method described above with reference to  FIG. 5  (S 710 ). 
     The terminal  200  generates a linear vector connecting the approximate coordinates of the terminal  200  and the coordinates of a neighbor BS (S 720 ). 
     The terminal  200  detects plane information of a building which intersects the linear vector and which is adjacent to the terminal  200  by using 3D map information stored in the internal memory (S 730 ). Also, the terminal  200  generates an edge vector forming the plane from the plane information of the building adjacent to the terminal  200  (S 740 ). 
     The terminal  200  calculates an orthogonal projection point to which a linear vector between the terminal  200  and each BS is projected on the edge vector (S 750 ), and generates a diffraction path linking the calculated orthogonal projection point, the corresponding BS, and the terminal  200  (S 760 ). 
     The terminal  200  calculates differences in lengths of diffraction paths between certain two BS and the terminal  200  (S 770 ). The terminal  200  calculates differences in lengths of diffraction paths between certain two BS and the terminal  200 , with respect to all of BSs. 
     The terminal  200  calculates an error value between the difference in lengths between the diffraction paths calculated from two BSs to the terminal  200  and the differences in distances of arrival from the two BSs to the terminal calculated on the basis of Equation 3 (S 780 ). 
     The terminal  200  calculates coordinates of the terminal  200  and an optimal orthogonal projection point minimizing the error value (S 790 ). Here, the terminal  200  may calculate the coordinates of the terminal  200  and the optimal orthogonal projection point minimizing the error value by applying maximum likelihood, or the like. 
     In this manner, a positioning error due to an obstacle in a downtown area or a mountainous area and diffraction of propagation may be minimized. 
       FIG. 8  is a view illustrating a method for calculating a diffraction distance of propagation illustrated in  FIG. 7 . 
     Referring to  FIG. 8 , after the approximate coordinate information of the terminal  200  is calculated, the terminal  200  generates a linear vector V1 connecting the approximate coordinates (x1, y1) of the terminal  200  and coordinates (x2, y2) of the BS A, and a linear vector V2 connecting the approximate coordinates (x1, y1) of the terminal  200  and coordinates (x3, y3) of the BS A. 
     The terminal  200  detects plane information (P1, P2) of a building which intersects the linear vectors V1 and V2 and which is adjacent to the terminal  200 . Also, the terminal  200  generates edge vectors V3 and V4 from a plane from the plane information P1 and P2 of the building adjacent to the terminal  200 . 
     The terminal  200  calculates an orthogonal projection point P3 to which the linear vector V1 between the terminal  200  and the BS A is projected on the edge vector V3, and calculates an orthogonal projection point P4 to which the linear vector V2 between the terminal  200  and the BS B is projected on the edge vector V4. 
     The terminal  200  generates diffraction paths PA and PB linking the calculated orthogonal projection points P3 and P4, the corresponding BSs, and the terminal  200 . 
     The terminal  200  calculates a difference in lengths between the diffraction path PA calculated from the BS A to the terminal  200  and the diffraction path PB calculated from the BS B to the terminal  200 . 
     The terminal  200  calculates an error value between the difference in lengths between the diffraction path PA calculated from the BS A to the terminal  200  and the diffraction path PB calculated from the BS B to the terminal  200 , and the difference λd AB  in distances of arrival from the BS A and the BS B to the terminal  200  calculated on the basis of Equation 3. 
       FIG. 9  is a view illustrating a base station according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 9 , a BS  900  includes a carrier generating unit  910 , a start point control unit  920 , a signal modulating unit  930 , a transmission unit  940 , a reception unit  950 , and an offset calculating unit  960 . The BS  900  corresponds to the BSs  110 ,  120 ,  130 , the BS A, and the BS B described above. 
     The carrier generating unit  910  generates a carrier signal having n number of carrier wavelengths. 
     The start point control unit  920  determines a start point period to be indicated on a carrier. 
     The signal modulating unit  930  differently modulates at least one among a phase, an amplitude, and a frequency of a carrier signal on the basis of the start point period, and transmits the same through the transmission unit  940 . For example, as described above, the signal modulating unit  930  may invert a phase of the carrier signal by 180 degrees on the basis of the start point period. 
     The transmission unit  940  transmits the carrier signal. The transmission unit  940  transmits an offset value list calculated by the offset calculating unit  960 . 
     The reception unit  950  receives a carrier signal from a neighbor BS. 
     The offset calculating unit  960  tracks a phase of the carrier signal of the neighbor BS, and detects a start point. The BS  900  measures the number of wavelengths and a phase angle of the carrier signal with respect to the detected start point of the carrier signal. The offset calculating unit  960  calculates an offset value with respect to a relative difference between a phase angle measured from the start point of the carrier signal transmitted by itself and the phase angle measured from the start point of the carrier signal of the neighbor BS. 
     The offset calculating unit  960  calculates an offset value with respect to every neighbor BS to generate an offset value list, and stores the offset value list in an internal memory. The offset calculating unit  960  transmits the offset value list through the transmission unit  940 . The offset value list may be periodically transmitted. 
       FIG. 10  is a view illustrating a positioning apparatus of a terminal according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 10 , a positioning apparatus  1000  of a terminal includes a reception unit  1110 , a phase tracking unit  1200 , a plurality of phase clock units  1300 , a memory unit  1400 , and a control unit  1500 . 
     The reception unit  1100  receives carrier signals from nearby BSs including a serving BS. The reception unit  1100  may receive coordinate information of nearby BSs and an offset value list from the serving BS. 
     The phase tracking unit  1200  tracks phases of the received carrier signals of the BSs, and detects start points and start point periods. The phase tracking unit  1200  may store the received coordinate information and offset value list of the nearby BSs in the memory unit  1400 . 
     The plurality of phase clock units  1300  correspond to the received carrier signals of the BSs. When a start point of a carrier signal of a corresponding BS is detected, each of the phase clock units  1300  resets a phase clock and counts the number of wavelengths of the carrier signal. The plurality of phase clock units  1300  may include a wavelength number counter (not shown) for counting the number of wavelengths of each of the carrier signals. 
     The memory unit  1400  stores the coordinate information of the nearby BSs and the offset value list received from the serving BS. Also, the memory unit  1400  stores 3D map information. 
     The control unit  1500  calculates a location of the terminal  200 . The control unit  1500  may calculate a location of the terminal  200  on the basis of the method described above with reference to  FIGS. 5 through 7 . In the case of  FIG. 6 , the control unit  1500  may calculate a propagation incident angle range of each BS on the basis of the coordinates of the terminal  200  and the coordinates of the nearby BSs received from the serving BS, and control the reception unit  1100  to filter only a carrier signal received within the propagation incident angle range of each BS. 
     As described above, at least some of functions of the positioning method and apparatus of the terminal according to an exemplary embodiment of the present invention described above may be implemented by hardware or software combined with hardware. For example, a processor realized as a central processing unit (CPU) or any other chip set, a microprocessor, and the like, may perform the functions of the phase tracking unit  1200 , the phase clock unit  1300 , and the control unit  1500 , a transceiver may perform the function of the reception unit  1100 , and a memory or a storage may perform the function of the memory unit  1400 . The memory may be realized as a random access memory (RAM) such as a medium such as a dynamic random access memory (DRAM), a Rambus DRAM (RDRAM), a synchronous DRAM (SDRAM), or a static RAM (SRAM). The storage may be realized as an optical disk such as a hard disk, a compact disk read only memory (CD-ROM), a CD rewritable (CD-RW), a digital video disk ROM (DVD-ROM), a DVD-RAM, a DVD-RW disk, a blue-ray disk, a flash memory, or a permanent or volatile storage such as various types of RAMs. 
     Also, at least some functions of the BS for positioning a terminal may be realized by hardware or software combined with hardware. For example, a processor realized as a CPU or any other chip set, a microprocessor, and the like, may perform the functions of the carrier generating unit  910 , the start point control unit  920 , the signal modulating unit  930 , and the offset calculating unit  960 , and a transceiver may perform the functions of the transmission unit  940  and the reception unit  950 . 
     According to an embodiment of the present invention, a positioning error level can be reduced, compared with the related art positioning method, based on measurement of a signal arrival time. 
     Also, stable and reliable positioning performance can be achieved even in a vehicle moving at a high speed or in a downtown area in which severe multiple paths are generated. 
     The embodiments of the present invention may not necessarily be implemented only through the foregoing devices and methods, but may also be implemented through a program for realizing functions corresponding to the configurations of the embodiments of the present invention, a recording medium including the program, or the like, and such an implementation may be easily made by a skilled person in the art to which the present invention pertains from the foregoing description of the embodiments. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.