Patent Publication Number: US-7724191-B2

Title: Apparatus and method for tracing position and direction of target object through RF signal

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the priority of Korean Patent Application No. 10-2007-0025034, filed on Mar. 14, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus and a method for tracing position and direction of a target object, and more particularly, to an apparatus and a method for tracing position and direction of a target object through a radio frequency (RF) signal. 
   This work was supported by the IT R&amp;D program of MIC/IITA [2005-S-092-02, USN-based Ubiquitous Robotic Space Technology Development] 
   2. Description of the Related Art 
   In general, an apparatus for tracing position and direction of a target object has been studied in various fields to provide more services to human life, and its technical development is being already in great progress. 
   One of its examples is the global positioning system (GPS). Developed by the United States Department of Defense, the GPS utilizes a constellation of earth orbit satellites that transmit precise microwave signals, and thus enables a GPS receiver to determine its location, speed/direction and time. 
   However, the GPS basically includes various operative errors, and the operative errors increase due to a variety of factors such as arrangements of satellites, weather conditions, buildings, and forests, which may affect a GPS signal reception. Most importantly, The GPS may not be feasible indoors because there are limitations in receiving a GPS signal. 
   Another example is a position tracking system utilizing a camera image. This stores an image of an already-known object in advance, and compares and matches the stored object image with an image that is obtained through a camera in order to search for a corresponding object, such that its existence and direction can be achieved. 
   However, this position tracking system is extremely sensitive to a lighting change. As a result, this may have a limitation in searching for a target object, because it is difficult to recognize direction, position, and a size change of the target object in a dark environment. 
   Furthermore, as circumstances require, the position tracking system may utilize a moving speed of a sound source, and also may place sound source sensors in a circular disposition by using a center axis as a reference line. Then, the position tracking system determines that the target object is disposed close to the one sound source sensor that first detects the sound source of the target object among the sound source sensors. However, this position tracking system is especially sensitive to surrounding noise because of its operating property that utilizes a sound source, and thus may not be appropriately functioned in general environments. 
   Reliability and performance of the position tracking system may vary according to surrounding environments. 
   SUMMARY OF THE INVENTION 
   An aspect of the present invention provides an apparatus and a method for tracing position and direction of a target object with an RF signal transceiver, such that easier tracing can be achieved with the minimum influence of surrounding environments. 
   According to an aspect of the present invention, there is provided an apparatus for tracing position and direction of a target object through a radio frequency (RF) signal, the apparatus including: an antenna rotating and receiving an RF signal transmitted from the target object; and a position and direction determination part calculating an intensity of the received RF signal and determining that the target object is placed in front of the antenna when the RF signal intensity reaches the maximum. 
   According to another aspect of the present invention, there is provided an apparatus for tracing position and direction of a target object through an RF signal, the apparatus including: two loop antennas receiving the RF signal transmitted from the target object and coupled perpendicularly to each other; and a position and direction determination part calculating two RF signal intensities received through the respective two loop antennas for comparison, and then determining that the target object transmitting an RF signal is placed in a center direction between the two loop antennas if the two RF signal intensities are the same, and otherwise determining that the target object is placed in a front direction of the loop antenna having a relatively higher RF signal intensity. 
   According to another aspect of the present invention, there is provided a method for tracing position and direction of a target object through an RF signal, the method including: rotating an antenna to receive an RF signal transmitted from the target object; calculating an intensity of the RF signal; and monitoring a fluctuation of the RF signal intensity and determining that the target object transmitting the RF signal is placed in front of the antenna when the RF signal intensity reaches the maximum. 
   According to another aspect of the present invention, there is provided a method for tracing position and direction of a target object through an RF signal, the method including: receiving an RF signal transmitted from the target object through two perpendicularly-coupled antennas; calculating an intensity of the RF signal received through the respective two antennas; and comparing the two RF signal intensities to determine that the target object transmitting the RF signal is placed in a center direction between the two loop antennas if the two RF signal intensities are the same, and otherwise determine that the target object is placed in a front direction of the loop antenna having a relatively higher RF signal intensity. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a view of an apparatus for tracing position and direction of an RF transceiver according to one embodiment of the present invention; 
       FIGS. 2A and 2B  are views illustrating an RF signal receiving area of a loop antenna of  FIG. 1 , which changes according to a change in an angle between an x-axis of the loop antenna and a transmission direction of an RF signal; 
       FIG. 3  is a graph illustrating an RF signal intensity, which changes according to a change in an angle between an x-axis of a loop antenna and a transmission direction of an RF signal; 
       FIG. 4  is a view of an apparatus for tracing position and direction of an RF transceiver according to another embodiment of the present invention; 
       FIGS. 5A through 5C  are views illustrating an RF signal receiving area of a loop antenna of  FIG. 4 , which changes according to a change in an angle between a reference axis and a rotation axis of the loop antenna; and 
       FIGS. 6A and 6B  are graphs illustrating an RF signal intensity, which changes according to an angular variation between a reference axis and a rotation axis of a loop antenna of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. 
   Accordingly, in some embodiments, well-known processes, well-known device structures, and well-known techniques will not be described in detail to avoid ambiguous interpretation of the present invention. Like reference numerals refer to like elements throughout. 
     FIG. 1  is a view of an apparatus for tracing position and direction of an RF transceiver according to one embodiment of the present invention. 
   Referring to  FIG. 1 , the apparatus for tracing position and direction of an RF transceiver has a plate-shaped and rotatable loop antenna  210 , and a position and direction determination part  220 . The position and direction determination part  220  monitors a fluctuation of an RF signal intensity measured through the loop antenna  210  and determines that a target object is placed in front of the loop antenna  210  when the RF signal intensity reaches the maximum value. 
   The target object may be all kinds of objects that include a radio transmitter  100  to generate an RF signal with a predetermined intensity. 
   When the radio transmitter  100  of the target object transmits the RF signal with a predetermined intensity, the loop antenna  210  rotates and receives the RF signal. According to an angle θx between an x-axis x of the loop antenna  210  and a transmission direction U RF  of the RF signal, magnetic flux of the RF signal passing through a coil in the loop antenna  210  changes, forming a predetermined pattern. Consequently, an intensity of the RF signal, i.e., an induced electromotive force generated by the RF signal, changes, forming a predetermined pattern. 
   For example, as illustrated in  FIG. 2A , if the angle θ x  between the x-axis x of the loop antenna  210  and the transmission direction U RF  of the RF signal is 0° or 180°, the loop antenna  210  may receive almost no RF signal. Therefore, as illustrated in  FIG. 3 , the loop antenna  200  generates the minimum point. Contrarily, as illustrated in  FIG. 2B , if the angle θ x  between the x-axis x of the loop antenna  210  and the transmission direction U RF  of the RF signal is 90°, the loop antenna  210  receives most of the RF signal. Therefore, as illustrated in  FIG. 3 , the loop antenna  200  generates the maximum point. 
   This is because the area S of the loop antenna  210  receiving the RF signal while rotating varies in proportion to S x sin(θ), the position and direction determination part  220  takes this into consideration, and calculates an RF signal intensity V according to Equation 1.
 
V∝CSB|sin(θx)|  Equation 1
 
where C, S, and B represent a constant of a loop antenna, the size of the loop antenna, and electric flux density of an RF signal passing through the loop antenna, respectively, and θ x  represents an angle between an x-axis of the loop antenna and a transmission direction of the RF signal.
 
   The position and direction determination part  220  monitors a fluctuation of the calculated RF signal intensity V, and determines that a target object with the radio transmitter  100  is placed in front of the loop antenna  210  when the RF signal intensity V reaches the maximum. 
     FIG. 4  is a view of an apparatus for tracing position and direction of a target object according to another embodiment of the present invention. 
   Referring to  FIG. 4 , the apparatus for tracing position and direction of a target object includes two loop antennas  311  and  312  and a position and direction determination part  320 . The two loop antennas  311  and  312  have a plate shape and are perpendicularly coupled to each other. The position and direction determination part  320  calculates two RF signal intensities V 1  and V 2  by receiving RF signals through the respective loop antennas  311  and  312  for comparison. Then, the position and direction determination part  320  determines that a radio transmitter  100  transmitting an RF signal is placed in a center direction U c  between the two loop antennas  311  and  312  if the two RF signal intensities V 1  and V 2  are the same, and otherwise determines that the radio transmitter  100  is placed in a front direction Z 1  or Z 2  of one of the loop antennas  311  and  312 , which has a relatively higher RF signal intensity. 
   Here, a reference axis Saxis is set perpendicular to the transmission direction of the RF signal, and a rotation axis Raxis is set at an identical angel with respect to the two loop antennas  311  and  312 . 
   When the radio transmitter  100  of the target object transmits an RF signal with a predetermined intensity, the RF signal intensities received through the respective two loop antennas  311  and  312  varies according to an angle θ R  of the rotation axis Raxis with respect to the reference axis Saxis. 
   For example, as illustrated in  FIG. 5A , if θ R  is less than 0°, the first loop antenna  311  receives an RF signal through its area larger than that of the second loop antenna  312 . As illustrated in  FIG. 5B , if θ R  is 0°, the first and second loop antennas  311  and  312  receive an RF signal through the same area. As illustrated in  FIG. 5C , if θ R  is more than 0°, the second loop antenna  312  receives an RF signal through its area larger than that of the first loop antenna  311 . 
   Accordingly, the position and direction determination part  320  calculates two RF signal intensities V 1  and V 2  by using Equation 2, which vary according to an angle θ R  of the rotation axis Raxis.
 
V 1 ∝C 1 S 1 B 1 |sin(θ R −φ)|
 
V 2 ∝C 2 S 2 B 2 |sin(90°−(θ R −φ))|  Equation 2
 
where C 1  and C 2  represent a constant of the first loop antenna  311  and a constant of the second loop antenna  312 , respectively, S 1  and S 2  represent the size of the first loop antenna  311  and the size of the second loop antenna  312 , respectively, B 1  represents electric flux density passing through the first loop antenna  311 , B 2  represents electric flux density passing through the second loop antenna  312 , θ R  represents an angle of a rotation axis Raxis with respect to a reference axis Saxis, and φ represents an angle of the first loop antenna  311  with respect to the reference axis Saxis.
 
   The position and direction determination part  320  calculates an RF signal intensity ratio V 1,2  through Equation 3 and analyzes the calculated result to locate the target object with the radio transmitter  100 . 
   
     
       
         
           
             
               
                 
                   
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   That is, the position and direction determination part  320  determines that the radio transmitter  100  is placed in a center direction U c  between the two loop antennas  311  and  312  if the RF signal intensity ratio V 1,2  is 1, determines that the radio transmitter  100  is placed in a front direction Z 1  of the first loop antenna  311  if the RF signal intensity ratio V 1,2  is more than 1, and determines that the radio transmitter  100  is placed in a front direction Z 2  of the second loop antenna  312  if the RF signal intensity ratio V 1,2  is less than 1. 
   If necessary, the position and direction determination part  320  calculates an angle φ of the first loop antenna  311  with respect to the reference axis Saxis through Equation 4, and directly determines that the radio transmitter  100  is placed on the position of φ+45°.
 
φ=tan −1 ( V   1,2 )−θ  Equation 4
 
     FIGS. 6A and 6B  are graphs illustrating an RF signal intensity and an RF signal intensity ratio V 1,2 , which change according to a change in an angle θ R  between the reference axis Saxis and the rotation axis Raxis of a loop antenna of  FIG. 4 . 
   First, if an angle OR between the reference axis Saxis and the rotation axis Raxis is less than 0°, the first loop antenna  311  receives an RF signal through an area larger than that of the second loop antenna  312 . 
   Accordingly, since the first RF signal intensity V 1  becomes greater than the second RF signal intensity V 2  as illustrated in  FIG. 6A , the RF signal intensity ratio V 1,2  becomes more than 1. 
   Contrarily, if an angle θ R  between the reference axis Saxis and the rotation axis Raxis is more than 0, the second loop antenna  312  receives an RF signal through its area larger than that of the first loop antenna  311 . Since the first RF signal intensity V 1  becomes greater than the second RF signal intensity V 2  as illustrated in  FIG. 6A , the RF signal intensity ratio V 1,2  becomes less than 1. 
   If the reference axis Saxis and the rotation axis Raxis overlap each other and thus the angle θ R  of the rotation axis with respect to the reference axis is 0°, the first RF signal intensity V 1  and the second RF signal intensity V 2  become the same because the first loop antenna  311  and the second loop antenna receive an RF signal through the same size. Consequently, the RF signal intensity ratio V 1,2  becomes 1. 
   The position and direction determination part  320  utilizes the RF signal intensity ratio V 1,2  to locate the target object with the radio transmitter  100 . 
   The apparatus for tracing position and direction of a target object through an RF signal analyzes a signal intensity change pattern of the RF signal without the influence of surrounding environments and locates position and direction of the target object. Therefore, the target object can be easily located with the minimum influence of surrounding environment. 
   While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.