Patent Publication Number: US-2011074634-A1

Title: Wireless positioning method and apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2009-0093230 and 10-2010-0095192 filed in the Korean Intellectual Property Office on Sep. 30, 2009 and Sep. 30, 2010, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to wireless positioning method and apparatus and, more particularly, to a method and apparatus for measuring the location of a terminal on the basis of a type of propagation delay. 
     (b) Description of the Related Art 
     A wireless positioning technique is measuring the location of a terminal in a wireless communication system, and recently, as demand for a location-based service (LBS) is increasing, an applied sector of the wireless positioning technique is expanding. In particular, the wireless positioning technique is getting popular according to the growing demand for a technique of detecting a situation or the location of a user and providing an appropriate service to the user. 
     A global positioning system (GPS), a representative positioning technique, provides positioning results of a high level of accuracy, but with a problem in that a terminal in an indoor area is not able to receive a GPS signal and it can receive the GPS signal only when a GPS receiver is mounted in the terminal. 
     Thus, a received signal strength indicator (RSSI) method and a time difference of arrival (TDOA) method are considered as alternative wireless positioning techniques. The RSSI method is acquiring location information by using the strength of a reception signal. According to the RSSI method, location information can be acquired because it has a simple structure, but an excessive error occurs due to a path loss. 
     The TDOA method is acquiring location information by using the time differences of arrival. According to the TDOA method, time synchronization between a receiver and a transmitter are not required, but transmitters must be necessarily synchronized in time. 
     The foregoing wireless positioning techniques, namely, the GPS, the RSSI method, and the TDOA method, have a problem in that they lack an ability of providing accurate positioning results in a non-line of sight (NLOS) environment or an environment in which a channel state is poor. Thus, a method for providing accurate positioning results reflecting a signal propagation environment is required. 
     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 wireless positioning method and apparatus in consideration of a type of propagation delay. In particular, the present invention provides a wireless positioning method and apparatus having advantages of minimizing a positioning error in a non-line of sight (NLOS) environment. 
     An exemplary embodiment of the present invention provides a wireless positioning method of a receiver, including: receiving signals from a plurality of transmitters; determining a propagation delay tap of each of the plurality of transmitters received from the plurality of transmitters, respectively; calculating the distance between the receiver and each of the transmitters, respectively; correcting the distances by using the propagation delay taps of the respective transmitters to determine a final distance between the receiver and each of the transmitters; and estimating an area, in which circles away by the final distances between the receiver and each of the transmitters on the basis of the center of each of the transmitters overlap with each other, as the location of the receiver. 
     Another embodiment of the present invention provides a wireless positioning method of a receiver, including: receiving signals from a plurality of transmitters; determining a propagation environment between the receiver and each of the transmitters by using types of propagation delay taps with respect to the signals received from the plurality of transmitters; calculating the distance between the receiver and each of the transmitters, respectively, by using an arrival time of a first reached propagation delay tap among the propagation delay taps of the transmitters; correcting the distances on the basis of the propagation environments to determine a final distance between the receiver and each of the transmitters; and estimating an area commonly satisfying the final distances, as the location of the receiver. 
     Yet another embodiment of the present invention provides a wireless positioning apparatus of a receiver, including: a propagation environment determining unit configured to determine propagation delay taps with respect to signals transmitted from a plurality of transmitters; a distance calculation unit configured to calculate the distance between the receiver and each of the transmitters; a distance correction unit configured to correct the distances by using the propagation delay taps of the respective transmitters to calculate a final distance between the receiver and each of the transmitters; and a location estimation unit configured to estimate an area, in which circles away by the final distances between the receiver and each of the transmitters on the basis of the center of each of the transmitters overlap with each other, as the location of the receiver. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1D  are graphs showing types of propagation delay taps. 
         FIG. 2  is a schematic block diagram of a wireless positioning apparatus according to an exemplary embodiment of the present invention. 
         FIG. 3  is a flow chart illustrating the process of a wireless positioning method according to an exemplary embodiment of the present invention. 
         FIGS. 4A and 4B  illustrate how the wireless positioning apparatus calculates the distance between a receiver and a transmitter according to an exemplary embodiment of the present invention. 
         FIGS. 5A and 5B  illustrate how the wireless positioning apparatus calculates the distance between a receiver and a transmitter according to an exemplary embodiment of the present invention. 
         FIG. 6  is a view illustrating a method for estimating a location by a wireless positioning apparatus 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, 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. 
     In the present disclosure, a terminal may be designated as a mobile station (MS), mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), a user equipment (UE), an access terminal (AT), and the like, and include entire or partial functions of the terminal, MS, MT, SS, PSS, UE, AT, and the like. 
     In the present disclosure, a base station (BS) may be designated as a radio access station (RAS), a Node B, an evolved Node B (eNodeB), a base transceiver station (BTS), a mobile multihop relay (MMR)-BS, and the like, and include the entire or partial functions of the BS, RAS, Node B, eNodeB, BTS, MMR-BS, and the like. 
     A wireless positioning method and apparatus according to exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. 
       FIGS. 1A to 1D  are graphs showing types of propagation delay taps. 
     A propagation delay tap refers to a signal in a delay spread form after having been transmitted from a transmitter in a multi-path environment. When there is a geographical obstacle between the transmitter and a receiver, multiple paths are formed due to a reflection or diffraction of a signal by the obstacle. Thus, a signal which has been transmitted from the transmitter is delay-spread through the multiple paths. 
     With reference to  FIG. 1A , a signal strength of a propagation tap  10  which has first arrived at the receiver is the greatest. When there is no obstacle between the transmitter and the receiver, a signal, which has been transmitted from the transmitter, can reach the receiver with a high signal strength within a short time. Thus, the type of the propagation delay tap of  FIG. 1A  may be close to a line of sight (LOS) environment. 
     With reference to  FIG. 1B , a signal strength of a propagation delay tap  21  which has second reached the receiver is the greatest, and a signal strength of a first reached propagation delay tap  20  is smaller than that of the propagation delay tap  21 . 
     With reference to  FIG. 1C , a strength of a propagation delay tap  31  which has third reached the receiver is the greatest, and that of a first reached propagation delay tap  30  is smaller than that of the propagation delay tap  31 . 
     With reference to  FIG. 1D , a signal strength of a propagation delay tap  41  which has reached the receiver the latest is the greatest, and that of a first reached propagation delay tap  40  is smaller than that of the propagation delay tap  41 . 
     As the type of the propagation delay tap is similar to that of  FIG. 1A , the environment between the receiver and the transmitter is close to a line of sight (LOS) environment. As the type of the propagation delay tap is similar to that of  FIG. 1D , namely, as an arrival time of the propagation delay tap having the greatest signal strength is delayed, the environment between the transmitter and the receiver is close to a non-line of sight (NLOS) environment. 
       FIG. 2  is a schematic block diagram of a wireless positioning apparatus according to an exemplary embodiment of the present invention, and  FIG. 3  is a flow chart illustrating the process of a wireless positioning method according to an exemplary embodiment of the present invention. The wireless positioning apparatus may be a part of the receiver. It is assumed that the wireless positioning apparatus knows about the location of a neighboring transmitter. 
     With reference to  FIG. 2 , the wireless positioning apparatus  200  includes a signal receiving unit  210 , a propagation environment determining unit  220 , a distance calculation unit  230 , a distance correction unit  240 , and a location estimation unit  250 . 
     With reference to  FIGS. 2 and 3 , the signal receiving unit  210  receives signals transmitted from a plurality of transmitters (S 300 ). The signals transmitted from the transmitters may be, for example, reference signals for positioning. Hereinafter, a case in which the signal receiving unit  210  receives the reference signals for positioning from the plurality of transmitters will be described as an example, 
     The propagation environment determining unit  220  determines propagation delay taps with respect to signals transmitted from the plurality of transmitters, and determines a propagation environment on the basis of the propagation delay taps (S 310 ). For example, the propagation environment determining unit  220  selects a propagation delay tap having the greatest signal strength from among the propagation delay taps of the respective transmitters, and when the selected propagation delay tap is the first reached propagation delay tap, the propagation environment determining unit  220  determines that the propagation environment of the corresponding transmitter is an LOS environment. Meanwhile, if the selected propagation delay tap is not the first reached propagation delay tap, the propagation environment determining unit  220  determines that the propagation environment of the corresponding transmitter is an NLOS environment. In this case, as the propagation delay tap having the greatest signal strength reaches later then the other propagation delay taps, the propagation environment determining unit  220  may determine that the propagation environment of the corresponding transmitter has a more NLOS tendency. 
     The distance calculation unit  230  calculates the distance between each of the transmitters and the receiver (S 320 ). The distance calculation unit  230  may calculate the distance between each of the transmitters and the receiver by using an arrival time of the first reached propagation delay tap among the propagation delay taps of the respective transmitters. 
     The distance correction unit  240  corrects the distance between the receiver and each of the transmitters by using the propagation delay tap, and calculates a final distance between the receiver and each of the transmitters (S 330 ). For example, when the propagation environment is not the LOS environment, the distance correction unit  240  corrects the distance between the receiver and the corresponding transmitter calculated in step S 320 . In this case, the distance correction unit  240  may correct the distance by reflecting a delay value according to the NLOS environment. Namely, when the propagation environment of the receiver and the corresponding transmitter is the NLOS environment, the arrival time of the first reached propagation delay tap among the propagation delay taps of the transmitters cannot reflect an accurate propagation delay time. Thus, the distance may be corrected by reflecting the error according to the NLOS environment. As discussed above with reference to  FIGS. 1A to 1D , the transition from  FIG. 1B  to  FIG. 1D  becomes closer to the NLSO environment, and as the environment is closer to the NLOS environment, an error with respect to the propagation delay time increases. Thus, in case of the LOS environment, an error in the distance between the receiver and each of the transmitters can be corrected by correcting the difference between an estimated arrival time of a propagation delay tap to reach first and an arrival time of the actually first reached propagation delay tap by using a delay tap distribution. 
     The location estimation unit  250  estimates the location of the receiver by using the final distance between the receiver and each of the transmitters (S 340 ). For example, the location estimation unit  250  may form circles around the respective transmitters on the basis of the center of each of the respective transmitters in which the distance between the receiver and each of the transmitters is radius, and estimate an area, in which the formed circles overlap with each other, as the location of the receiver. 
     Hereinafter, a detailed method for estimating, by the wireless positioning apparatus, the distance between the receiver and each of the transmitters by using each propagation environment between the receiver and each of the transmitters will now be described. In the following description, a receiver, a target of wireless positioning, receives a reference signal for positioning from a transmitter located near the receiver. The receiver analyzes a type of a propagation delay tap with respect to the reference signal which has been received from the transmitter, and determines a propagation environment between the receiver and the transmitter. In this case, it is assumed that the wireless positioning apparatus of the receiver know about the location of the transmitter. 
       FIGS. 4A and 4B  illustrate how the wireless positioning apparatus calculates the distance between a receiver and a transmitter according to an exemplary embodiment of the present invention. 
     With reference to  FIG. 4A , a propagation delay tap  40   a  having the greatest signal strength, among the propagation delay taps from transmitters  410 , has first reached a receiver  400 . Thus, it can be estimated that the environment between the receiver  400  and the transmitter is the LOS environment without any obstacle. 
     With reference to  FIG. 4B , when the propagation environment between the receiver  400  and the transmitter  410  is the LOS environment, the distance between the receiver  400  and the transmitter  410  may be calculated by using an arrival time of the first reached propagation delay tap  40   a  among the propagation delay taps of the transmitters  410  and the speed of light. After the wireless positioning apparatus calculates the distance between the receiver  400  and the transmitter  410 , it forms a circle (A) around the transmitter  410  based on the center of the transmitter  410 , which is away by the distance between the receiver  400  and the transmitter  410  from the receiver  400 . 
       FIGS. 5A and 5B  illustrate how the wireless positioning apparatus calculates the distance between a receiver and a transmitter according to an exemplary embodiment of the present invention. 
     With reference to  FIG. 5A , a propagation delay tap  50   a  having the greatest signal strength, among propagation delay taps received from a transmitter  510 , has reached a middle point with respect to the receiver  500 . Namely, the first reached propagation delay tap  50   b  does not have the greatest signal strength. Thus, it can be assumed that the receiver  500  and the transmitter  510  are in an NLOS environment having an obstacle. 
     With reference to  FIG. 5B , when the propagation environment is the LOS environment, an arrival time of the first reached propagation delay tap is even earlier than that in the NLOS environment. Thus, when the propagation environment between the receiver  500  and the transmitter  510  is the NLOS environment, the distance between the receiver  500  and the transmitter  510  may be calculated by using the arrival time of the first reached propagation delay tap  50   b , among the propagation delay taps of the transmitters  510 , and the speed of light, and then corrected by reflecting a delay value according to the NLOS. 
     Namely, the wireless positioning apparatus calculates the distance between the receiver  500  and the transmitter  510  by using the arrival time of the first reached propagation delay tap  50   b  and then forms a circle (B) around the transmitter  510  on the basis of the center of the transmitter  510 , which is away by the calculated distance. Because the circle (B) does not reflect the delay value according to the NLOS, it is different from the actual distance between the receiver  500  and the transmitter  510 . Thus, a circle (B′) reflecting the delay value according to the NLOS is formed. As for the delay value according to the NLOS, when the propagation environment is the LOS environment, the difference between an estimated arrival time of a propagation delay tap  50   c  to reach first and an arrival time of a propagation delay tap (b) which has first reached actually can be corrected by using a distribution of the delay taps. 
     A method for estimating the location of the receiver by using the estimated distance between the receiver and each of the transmitters will now be described. 
       FIG. 6  is a view illustrating a method for estimating a location by a wireless positioning apparatus according to an exemplary embodiment of the present invention. 
     With reference to  FIG. 6 , it is assumed that a propagation environment between a transmitter  700  and a receiver  600  is the LOS environment, a propagation environment between a transmitter  800  and the receiver  600  and that between a transmitter  900  and the receiver  600  is the NLOS environment, and the receiver  600  knows about the locations of the respective transmitters  700 ,  800 , and  900 . 
     The wireless positioning apparatus calculates the distance between each of the transmitters  700 ,  800 , and  900  and the receiver  600  by using an arrival time of the first reached propagation delay tap among propagation delay taps of reference signals received from the respective transmitters  700 ,  800 , and  900 , and forms circles X, Y, and Z around the transmitters  700 ,  800 , and  900  on the basis of the center of each of the transmitters  700 ,  800 , and  900 , having the calculated distance between each of the transmitters  700 ,  800 , and  900  and the receiver  600  equivalent to the radius. 
     Meanwhile, the wireless positioning apparatus corrects the distance between each of the transmitters  800  and  900  and the receiver  600 , in which the propagation environment is the NLOS environment, by reflecting a delay value according to the NLOS, and calculates the final distance between each of the transmitters  700 ,  800 , and  900  and the receiver  600 . 
     Thereafter, the wireless positioning apparatus forms circles X, Y′ and Z′ around the transmitters  700 ,  800 , and  900  on the basis of the center of each of the transmitters  700 ,  800 , and  900  and having the final distance between the receiver  600  and each of the transmitters  700 ,  800 , and  900  as the radius (or equivalent to the radius), and estimates an area, in which the formed circles overlap with each other, as the location of the receiver  600 . 
     In the above description, it is assumed that the receiver receives reference signals for positioning from three transmitters for the sake of brevity, but the technical idea of the present invention is not meant to be limited thereto. The receiver may receive reference signals for positioning from three or more transmitters, and perform positioning on the basis of the received reference signals. 
     By performing wireless positioning on the basis of the types of the propagation delay taps, an error of wireless positioning caused when the propagation environment is the NLOS environment can be reduced. 
     According to the wireless positioning method and apparatus according to the exemplary embodiments of the present invention, a positioning error in an NLOS environment can be minimized. Thus, accurate positioning results can be obtained by using wireless communication even in a satellite reception is not easy. 
     The exemplary embodiments of the present invention are not implemented only through the apparatus and method, but can be implemented through a program realizing the function corresponding to the configurations of the exemplary embodiments of the present invention or a recording medium storing the program. 
     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.