Abstract:
The present disclosure relates to a sensor network, Machine Type Communication (MTC), Machine-to-Machine (M2M) communication, and technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the above technologies, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. Embodiments of the present invention provide a device and a method for estimating a position between wireless apparatuses using a signal transmitted and received between wireless apparatuses in a wireless communication system. A device of a first wireless apparatus for estimating a position comprises: a transceiver for transmitting and receiving a signal to and from a second wireless apparatus; and a position estimator for estimating a position of the second wireless apparatus using a signal transmitted and received through the transceiver. The position estimator comprises a range estimator for estimating the distance between the first wireless apparatus and the second wireless apparatus on the basis of a first time difference from a time point at which a request range packet is transmitted to the second wireless apparatus to a time point at which the reception of a response range packet transmitted from the second wireless apparatus is sensed and a second time difference from a time point at which the reception of the required range packet is sensed by the second wireless apparatus to a time point at which the response range packet is transmitted.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to the transmission and reception of signals between wireless devices in a wireless communication system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Recently, with the progress of wireless communication technology, there is an increase in the transmission and reception of signals between wireless devices. Users can transmit and receive various data (e.g., multimedia data, such as moving images, music, photographs, documents, etc.) while transmitting and receiving signals through wireless devices enabling wireless access such as smart phones, and thereby can be provided with various services. 
       SUMMARY OF THE INVENTION 
     Technical Problem 
       [0003]    Therefore, embodiments of the present invention provide an apparatus and a method for estimating a location of a wireless device by using signals transmitted and received between wireless devices in a wireless communication system. 
         [0004]    Also, embodiments of the present invention provide an apparatus and a method for measuring, with high resolution, a distance and a direction between wireless devices by using signals transmitted and received between the wireless devices in a wireless communication system. 
         [0005]    Also, embodiments of the present invention provide an apparatus and a method for rapidly measuring a distance and a direction between wireless devices by using signals transmitted and received between the wireless devices in a wireless communication system. 
         [0006]    Also, embodiments of the present invention provide an apparatus and a method for providing information on inaccuracy caused by an effect of a multipath channel when a distance between wireless devices is measured by using signals transmitted and received between the wireless devices in a wireless communication system. 
         [0007]    Also, embodiments of the present invention provide an apparatus and a method for minimizing power consumption when a distance and a direction between wireless devices are measured by using signals transmitted and received between the wireless devices in a wireless communication system. 
         [0008]    Further, embodiments of the present invention provide an apparatus and a method which, in a wireless communication system, estimate a location of a wireless device by using signals transmitted and received between wireless devices and adjust a handover between the wireless devices and power of signals transmitted and received therebetween based on the estimated location. 
       Solution to Problem 
       [0009]    In accordance with an aspect of the present invention, an apparatus of a first wireless device in a wireless communication system is provided. The apparatus includes a transmitter/receiver for transmitting/receiving a signal to/from a second wireless device; and a location estimator that estimates a location of the second wireless device by using a signal transmitted/received by the transmitter/receiver. The location estimator includes a range estimator that estimates a distance between the first wireless device and the second wireless device based on a first time difference between a time point of transmission of a request range packet to the second wireless device and a time point of detection of reception of a response range packet transmitted by the second wireless device, and a second time difference between a time point of detection of reception of the request range packet by the second wireless device and a time point of transmission of the response range packet. 
         [0010]    In accordance with another aspect of the present invention, an operating method of a first wireless device in a wireless communication system is provided. The operating method includes transmitting/receiving a signal to/from a second wireless device, by a transmitter/receiver; and estimating a location of the second wireless device by using a signal transmitted/received by the transmitter/receiver. The estimating of the location of the second wireless device includes estimating a distance between the first wireless device and the second wireless device based on a first time difference between a time point of transmission of a request range packet to the second wireless device and a time point of detection of reception of a response range packet transmitted by the second wireless device, and a second time difference between a time point of detection of reception of the request range packet by the second wireless device and a time point of transmission of the response range packet. 
       Advantageous Effects 
       [0011]    Embodiments of the present invention enable distance estimation having a resolution of several centimeters by using the transmission and reception of signals between wireless devices in a wireless communication system. Also, the embodiments of the present invention enable the estimation of the location of a wireless device on the basis of the estimated distance, and enable the adjustment of a handover between wireless devices and power of signals transmitted and received therebetween on the basis of the estimated location. Further, the embodiments of the present invention enable a distance between wireless devices to be rapidly estimated by using a range packet, enable the inaccuracy (reliability) of distance estimation, which may occur due to an effect of a multipath channel, to be provided to a user, and enable the power consumption of the range estimator to be minimized by using signals used in an existing modem. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For more complete understanding of the present invention and the advantageous effects thereof, the following description will be made with reference to the accompanying drawings, and in these drawings, the same reference numerals denote the same parts. 
           [0013]      FIG. 1  is a view illustrating a location estimation operation performed between wireless devices according to embodiments of the present invention. 
           [0014]      FIG. 2  is a view illustrating a configuration of a first wireless device according to an embodiment of the present invention. 
           [0015]      FIG. 3  is a view illustrating a configuration of a second wireless device according to an embodiment of the present invention. 
           [0016]      FIGS. 4A, 4B, 4C, and 4D  are views each illustrating a processing flow of a distance estimation operation performed by a wireless device according to embodiments of the present invention. 
           [0017]      FIG. 5  is a view illustrating a configuration of a directional multigigabit range element according to an embodiment of the present invention. 
           [0018]      FIG. 6  is a view illustrating a configuration of range capability information field according to an embodiment of the present invention. 
           [0019]      FIG. 7  is a view illustrating a configuration of a request range packet according to embodiments of the present invention. 
           [0020]      FIGS. 8A and 8B  are views each illustrating a distance estimation operation for estimating a distance between wireless devices by a range estimator according to embodiments of the present invention. 
           [0021]      FIGS. 9A to 9C  are views for explaining an operation of detecting a received symbol in order to estimate a distance according to embodiments of the present invention. 
           [0022]      FIGS. 10 and 11  are views for explaining a direction estimation operation according to embodiments of the present invention. 
           [0023]      FIG. 12  is a view illustrating a processing flow of a location estimation operation according to an embodiment of the present invention. 
           [0024]      FIG. 13  is a block diagram of a first wireless device for a location estimation operation according to embodiments of the present invention. 
           [0025]      FIGS. 14A and 14B  are views illustrating examples of displaying the estimated location of a second wireless device in a map according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    In this patent specification,  FIGS. 1 to 14B  used to describe the principles of the present invention are for illustrative purposes only, and should not be construed as limiting the scope of the present invention in any manner. Those having ordinary knowledge in the pertaining field will understand that the principles of the present invention may be implemented even in an optional wireless communication system which is appropriately disposed. 
         [0027]    Embodiments of the present invention, which are to be described below, propose an apparatus and a method which, in a wireless communication system, perform distance estimation having a resolution of several centimeters by using the transmission and reception of signals between wireless devices and estimate a location of a wireless device on the basis of the estimated distance. The above-estimated location information may be used to adjust a handover between the wireless devices and power of signals transmitted and received therebetween. Particularly, embodiments of the present invention propose a signal processing method for distance measurement having a high resolution and a signal processing method for rapidly measuring a distance between wireless devices. Also, embodiments of the present invention propose an apparatus that minimizes power consumption while reducing the inaccuracy of distance measurement which may occur due to an effect of a multipath channel. 
         [0028]    As an example, in an embodiment of the present invention, a wireless device may be a portable electronic device having a wireless access function, such as a smart phone. As another example, the wireless device may be one of a portable terminal, a mobile phone, a mobile pad, a media player, a tablet computer, a handheld computer, a camera enabling wireless access, a smart television, and a Personal Digital Assistant (PDA). As still another example, the wireless device may be an apparatus implemented by combining two or more functions from among those of the above-described apparatuses. 
         [0029]    In an embodiment, a wireless communication system may be a Device-to-Device (D2D) network. In another embodiment, the wireless communication system may be a Local Area Network (LAN). In still another embodiment, the wireless communication system may be a wireless network which supports a group play function between devices. 
         [0030]      FIG. 1  is a view illustrating a location estimation operation performed between wireless devices according to embodiments of the present invention. 
         [0031]    Referring to  FIG. 1 , a first wireless device  100  is an initiator defined as a wireless device that controls location estimation, and includes a location estimator  110  and a transmitter/receiver  120 . A second wireless device  200  is a responder defined as a wireless device that becomes an object of the location estimation, that the first wireless device  100  controls, and includes a location estimator  210  and a transmitter/receiver  220 . Hereinafter, an example will be described in which the first wireless device  100  estimates a location (i.e., a distance and a direction) of the second wireless device  200 . However, conversely, it goes without saying that the second wireless device  200  may estimate a location (i.e., a distance and a direction) of the first wireless device  100 . 
         [0032]    The transmitter/receiver  120  transmits, to the second wireless device  200 , a request signal (e.g., a request range packet) for location estimation, and receives, from the second wireless device  200 , a response signal (e.g., a response range packet) corresponding to the request signal. The transmitter/receiver  220  receives the request signal from the first wireless device  100 , and transmits the response signal to the first wireless device  100 . 
         [0033]    The location estimator  110  estimates a distance and a direction between the first wireless device  100  and the second wireless device  200 , and thereby estimates a location of the second wireless device  200 . In an embodiment, the location estimator  110  estimates a distance between the first wireless device  100  and the second wireless device  200  on the basis of a first time difference Ti between a time point of transmission of a request range packet and a time point of detection of reception of a response range packet; a second time difference Tr between a time point of detection of reception of the request range packet and a time point of transmission of the response range packet, wherein the second time difference Tr is calculated by the location estimator  210  of the second wireless device  200 ; and internal circuit delays of the first wireless device  100  and the second wireless device  200 . 
         [0034]    Also, when estimating the distance between the first wireless device  100  and the second wireless device  200 , the location estimator  110  may further consider a transmission circuit delay, a reception circuit delay, and a processing delay for estimating the detection of reception of a range packet in each of the first wireless device  100  and the second wireless device  200 . Also, when the distance between the first wireless device  100  and the second wireless device  200  is estimated, the location estimator  110  and the location estimator  210  may further consider a predefined Sample Timing Offset (STO). 
         [0035]    In an embodiment, the transmission circuit delay in each of the first wireless device  100  and the second wireless device  200  may include a delay between a Digital to Analog Converter (DAC) and an antenna that are included in each transmitter. In an embodiment, the reception circuit delay in each of the first wireless device  100  and the second wireless device  200  may include a delay between an antenna and an Analog to Digital Converter (ADC) that are included in each receiver. In an embodiment, the processing delay for estimating the detection of the reception of the range packet in each of the first wireless device  100  and the second wireless device  200  may include a delay between the ADC and a range estimator that are included in each receiver. 
         [0036]      FIG. 2  is a view illustrating a configuration of the first wireless device  100  according to an embodiment of the present invention. The configuration illustrated in  FIG. 2 , which is only an example for describing the present invention, may be replaced by various modified configurations, and thus should not be construed as limiting the protection scope of the present invention. 
         [0037]    Referring to  FIG. 2 , the first wireless device  100  includes a Medium Access Control (MAC) processor  105 , a baseband processor  115 , a DAC  125 A, an ADC  125 B, and an antenna  130 . The baseband processor  115  includes a range estimator  110 A and a direction estimator  110 B. For example, the MAC processor  105 , the DAC  125 A, the ADC  125 B, and the antenna  130  configure the transmitter/receiver  120  illustrated in  FIG. 1 . 
         [0038]    The MAC processor  105  generates information for distance estimation and direction estimation. For example, for distance estimation, the MAC processor  105  generates a range start signal during a range estimation period. As another example, for distance estimation, during a capability negotiation period, the MAC processor  105  generates a Directional Multigigabit (DMG) beacon, a probe request, a probe response, and information request or information response, each of which includes a DMG range element. The baseband processor  115  receives, as input, information generated by the MAC processor  105 , and processes the information in a baseband. For example, the baseband processor  115  receives and processes a range start signal, and then generates a request range packet. The DAC  125 A converts a digital signal, which has been provided by the baseband processor  115 , into an analog signal. The antenna  130  transmits the converted analog signal, which has been provided by the DAC  125 A, to the second wireless device  200 . 
         [0039]    The antenna  130  receives a signal from the second wireless device  200 . The ADC  125 B converts the analog signal from the second wireless device  200 , which has been received through the antenna  130 , into a digital signal. The baseband processor  115  processes the converted digital signal, which has been provided by the ADC  125 B, in a baseband. For example, the baseband processor  115  processes the received response range packet and outputs the processed response range packet to the MAC processor  105 . 
         [0040]    The range estimator  110 A estimates a distance between the first wireless device  100  and the second wireless device  200 . In an embodiment, the range estimator  110 A estimates a distance between the first wireless device  100  and the second wireless device  200  on the basis of a first time difference Ti between a time point of transmission of a request range packet and a time point of detection of reception of a response range packet; a second time difference Tr between a time point of detection of reception of the request range packet and a time point of transmission of the response range packet, wherein the second time difference Tr is calculated by the range estimator  210 A of the second wireless device  200 ; and internal circuit delays of the first wireless device  100  and the second wireless device  200 . When estimating the distance between the first wireless device  100  and the second wireless device  200 , the range estimator  110 A may further consider a DAC delay A, a transmission circuit delay B, a reception circuit delay D, an ADC delay E, and a processing delay F for estimating the detection of reception of a request range packet or a response range packet in each of the first wireless device  100  and the second wireless device  200 . Also, when estimating the distance between the first wireless device  100  and the second wireless device  200 , the range estimator  110 A may further consider a predefined STO. 
         [0041]    The direction estimator  110 B transmits, to the second wireless device  200 , a request signal for estimating a direction of the second wireless device  200 , and receives the direction estimation from the second wireless device  200  as a response signal and estimates a direction of the second wireless device  200 . In an embodiment, the direction estimator  110 B measures a strength of a signal transmitted/received between the first wireless device  100  and the second wireless device  200  in one or more beam directions, and estimates direction information of the second wireless device  200  on the basis of the measured strength of the signal. Here, an example is described in which the direction estimator  110 B of the first wireless device  100  estimates the direction of the second wireless device  200 . 
         [0042]      FIG. 3  is a view illustrating a configuration of the second wireless device  200  according to an embodiment of the present invention. The configuration illustrated in  FIG. 3 , which is only an example for describing the present invention, may be replaced by various modified configurations, and thus should not be construed as limiting the protection scope of the present invention. 
         [0043]    Referring to  FIG. 3 , the second wireless device  200  includes a Medium Access Control (MAC) processor  205 , a baseband processor  215 , a DAC  225 A, an ADC  225 B, and an antenna  230 . The baseband processor  215  includes a range estimator  210 A and a direction estimator  210 B. For example, the MAC processor  205 , the DAC  225 A, the ADC  225 B, and the antenna  230  form the transmitter/receiver  220  illustrated in  FIG. 1 . 
         [0044]    The antenna  230  receives a signal from the first wireless device  100 . For example, the antenna  230  receives a signal for location estimation, namely, a request range packet for distance estimation and a signal for direction estimation, from the first wireless device  100 . The ADC  225 B converts the analog signal from the first wireless device  100 , which has been received through the antenna  230 , into a digital signal. The baseband processor  215  processes the converted digital signal, which has been provided by the ADC  225 B, in a baseband. For example, the baseband processor  215  processes the received request range packet and outputs the processed response range packet to the MAC processor  205 . 
         [0045]    The MAC processor  205  receives information for distance estimation and direction estimation. For example, for distance estimation, the MAC processor  205  receives, from the baseband processor  215 , a DMG beacon, a probe request, a probe response, and an information request or an information response, each of which includes a DMG range element. 
         [0046]    Also, the MAC processor  205  generates response information for distance estimation. For example, for distance estimation, the MAC processor  205  generates a DMG beacon, a probe request, a probe response, and an information request or an information response, each of which includes a DMG range element corresponding to the received DMG range element. 
         [0047]    The baseband processor  215  receives, as input, information generated by the MAC processor  205 , and processes the information in a baseband. For example, for distance estimation, the baseband processor  215  generates a response range packet corresponding to the received request range packet. The DAC  225 A converts a digital signal, which has been provided by the baseband processor  215 , into an analog signal. The antenna  230  transmits the analog signal, which has been provided by the DAC  225 A, to the first wireless device  100 . 
         [0048]    The range estimator  210 A calculates a second time difference Tr between a time point of detection of reception of the received request range packet and a time point of transmission of a response range packet. Information on the above-calculated second time difference Tr is transmitted to the first wireless device  100  and is used when the range estimator  110 A performs distance estimation. 
         [0049]    For direction estimation, the direction estimator  210 B receives a signal transmitted by the first wireless device  100 , and transmits, to the first wireless device  100 , a response signal to the received signal. Here, an example is described in which the direction estimator  110 B of the first wireless device  100  estimates a direction of the second wireless device  200 . However, in an identical scheme, the direction estimator  210 B of the second wireless device  200  may estimate a direction of the first wireless device  100 . 
         [0050]      FIGS. 4A, 4B, 4C, and 4D  are views each illustrating a processing flow of a distance measurement operation performed by a wireless device according to embodiments of the present invention. The flows illustrated in  FIGS. 4A, 4B, 4C, and 4D , which are only examples for describing the present invention, may be replaced by various modified flows, and thus should not be construed as limiting the protection scope of the present invention.  FIGS. 4A and 4B  each illustrate a processing flow of a distance measurement operation performed by the wireless device according to an embodiment of the present invention, and in each of  FIGS. 4A and 4B , one period, namely, a range estimation period T 100  during which a distance is measured, is included.  FIGS. 4C and 4D  each illustrate a processing flow of a distance measurement operation performed by the wireless device according to another embodiment of the present invention, and in each of  FIGS. 4C and 4D , two periods, namely, a capability negotiation period T 10  during which capabilities enabling distance measurement are interchanged, and a range estimation period T 100  during which a distance is measured, are included. At this time, it should be noted that as illustrated in  FIGS. 4A and 4B , the range estimation period T 100  may be performed without performing the capability measurement period T 10 . Here, the first wireless device  100  and the second wireless device  200  illustrated in  FIG. 1  are referred to as the “initiator  100 ” and the “responder  200 ,” respectively. 
         [0051]    Referring to  FIG. 4A , the initiator  100  transmits a request range packet to the responder  200  on the basis of a range start signal in step S 110 , and the responder  200 , that has received the request range packet, transmits a response range packet to the initiator  100  in step S 130 . This method may be used when a packet having destination information data is used as the request range packet. At this time, the initiator  100  performs range estimation in step S 140 , and the responder  200  performs range estimation in step S 120 . 
         [0052]    Referring to  FIG. 4B , the initiator  100  transmits a Request To Send (RTS) signal to the responder  200  on the basis of a range start signal in step S 140 , and the responder  200 , that has received the RTS signal, confirms that a destination of a request range packet, that the initiator  100  is to transmit, is the responder  200  while transmitting a DMG Clear To Send (CTS) signal to the initiator  100  in step S 150 . This method may be used when a Null Data Packet (NDP) illustrated in  FIG. 7  below is used as the request range packet. 
         [0053]    Then, the initiator  100  transmits the request range packet to the confirmed destination responder  200  in step S 110 , and the responder  200 , that has received the request range packet, transmits a response range packet to the initiator  100  in step S 130 . At this time, the initiator  100  performs range estimation in step S 140 , and the responder  200  performs range estimation in step S 120 . 
         [0054]    Referring to  FIGS. 4C and 4D , in a distance measurement operation, a period is divided into the capability negotiation period T 10  during which the initiator  100  and the responder  200  interchange capabilities enabling distance measurement, and the range estimation period T 100  during which a distance is measured. 
         [0055]    Since the flow illustrated in each of  FIGS. 4C and 4D  includes a processing flow identical to that of  FIG. 4A , hereinafter, the distance measurement operation will be described with reference to only the capability negotiation period T 10  additionally included in each of  FIGS. 4C and 4D . Referring to  FIGS. 4C and 4D , during the capability negotiation period T 10 , the initiator  100  and the responder  200  exchange respective distance measurement capabilities. For example, the initiator  100  and the responder  200  exchange the respective distance measurement capabilities through a DMG beacon, a probe request, a probe response, and an information request or an information response, each of which includes a DMG range element, which are defined in  FIG. 5  below. 
         [0056]      FIG. 5  is a view illustrating a configuration of a DMG range element according to an embodiment of the present invention. The configuration illustrated in  FIG. 5 , which is only an example for describing the present invention, may be replaced by various modified configurations, and thus should not be construed as limiting the protection scope of the present invention. 
         [0057]    Referring to  FIG. 5 , a DMG range element includes an element IDentifier (ID) field  10 , a length field  20 , and a range capability information field  30 . For example, the element ID field  10 , the length field  20 , and the range capability information field  30  may include one octet, one octet, and two octets, respectively. The DMG range element may be included in a DMG beacon, a probe request, a probe response, and an information request or an information response, and may be defined as an element advertizing range capability. As another example, the DMG range element may also be defined as an element advertizing range capability in an association request/response, a reassociation request/response, and the like. 
         [0058]      FIG. 6  is a view illustrating a configuration of range capability information field according to an embodiment of the present invention. For example, the range capability information field may be the range capability information field  30  illustrated in  FIG. 5 . The configuration illustrated in  FIG. 6 , which is only an example for describing the present invention, may be replaced by various modified configurations, and thus should not be construed as limiting the protection scope of the present invention. 
         [0059]    Referring to  FIG. 6 , the range capability information field  30  illustrated in  FIG. 5  includes a range initiator capable subfield  31 , a range responder capable subfield  32 , a transmit NDP capable subfield  33 , a receive NDP capable subfield  34 , a range feedback request frame capable subfield  35 , a range feedback response frame capable subfield  36 , an expected accuracy subfield  37 , and a reserved subfield  38  for an additional operation. In an embodiment, each of the range initiator capable subfield  31 , the range responder capable subfield  32 , the transmit NDP capable subfield  33 , the receive NDP capable subfield  34 , the range feedback request frame capable subfield  35 , and the range feedback response frame capable subfield  36  may include one bit. The expected accuracy subfield  37  may include two bits. The reserved subfield  38  may include eight bits. The definition and encoding of each subfield may be defined in Table 1 below. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Subfield 
                 Definition 
                 Encoding 
               
               
                   
               
             
             
               
                 Range initiator capable 
                 whether STA is capable of 
                 0: impossible 
               
               
                   
                 operating as initiator 
                 1: possible 
               
               
                 Range responder capable 
                 whether STA is capable of 
                 0: impossible 
               
               
                   
                 operating as responder 
                 1: possible 
               
               
                 Transmit NDP capable 
                 whether STA is capable of 
                 0: impossible 
               
               
                   
                 transmitting NDP 
                 1: possible 
               
               
                 Receive NDP capable 
                 whether STA is capable of 
                 0: impossible 
               
               
                   
                 receiving NDP 
                 1: possible 
               
               
                 Range feedback request 
                 whether STA is capable of 
                 0: impossible 
               
               
                 frame capable 
                 using range feedback 
                 1: possible 
               
               
                   
                 request frame 
               
               
                 Range feedback response 
                 whether STA is capable of 
                 0: impossible 
               
               
                 frame capable 
                 using range feedback 
                 1: possible 
               
               
                   
                 response frame 
               
               
                 Expected accuracy 
                 expected accuracy of 
                 0: not support 
               
               
                   
                 distance measurement 
                 1: 1 cm 
               
               
                   
                   
                 2: 10 cm 
               
               
                   
                   
                 3: 1 m 
               
               
                   
               
             
          
         
       
     
         [0060]    For example, a case where the value of the range initiator capable subfield  31  is equal to 0 indicates that a wireless device or a STAtion (STA) is not capable of operating as an initiator for distance measurement. A case where the value of the range initiator capable subfield  31  is equal to 1 indicates that the wireless device or the STA is capable of operating as the initiator for distance measurement. A case where the value of the range responder capable subfield  32  is equal to 0 indicates that the wireless device is not capable of operating as a responder for distance measurement. A case where the value of the range responder capable subfield  32  is equal to 1 indicates that the wireless device is capable of operating as the responder for distance measurement. A case where the value of the transmit NDP capable subfield  33  is equal to 1 indicates that the wireless device is capable of transmitting an NDP. A case where the value of the transmit NDP capable subfield  33  is equal to 0 indicates that the wireless device is not capable of transmitting an NDP. A case where the value of the receive NDP capable subfield  34  is equal to 1 indicates that the wireless device is capable of receiving an NDP. A case where the value of the receive NDP capable subfield  34  is equal to 0 indicates that the wireless device is not capable of receiving an NDP. A case where the value of the range feedback request frame capable subfield  35  is equal to 1 indicates that the wireless device is capable of using a range feedback request frame. A case where the value of the range feedback request frame capable subfield  35  is equal to 0 indicates that the wireless device is not capable of using the range feedback request frame. A case where the value of the range feedback response frame capable subfield  36  is equal to 1 indicates that the wireless device is capable of using a range feedback response frame. A case where the value of the range feedback response frame capable subfield  36  is equal to 0 indicates that the wireless device is not capable of using the range feedback response frame. A case where the value of the expected accuracy subfield  37  is equal to 1 indicates that the expected accuracy of distance measurement, that the wireless device is capable of providing, is 1 cm. A case where the value of the expected accuracy subfield  37  is equal to 2 indicates that the expected accuracy of distance measurement, that the wireless device is capable of providing, is 10 cm. A case where the value of the expected accuracy subfield  37  is equal to 3 indicates that the expected accuracy of distance measurement, that the wireless device is capable of providing, is 1 m. A case where the value of the expected accuracy subfield  37  is equal to 0 indicates that the wireless device does not support distance measurement. 
         [0061]    Referring back to  FIG. 4C , while exchanging a DMG beacon and a probe request signal for scanning during the capability negotiation period T 10 , through a range capability information field within a DMG range element, the first wireless device  100  as the initiator and the second wireless device  200  as the responder interchange whether an STA is capable of operating as an initiator/responder, whether the STA is capable of receiving/transmitting an NDP, and whether the STA is capable of using a range feedback request/response frame. 
         [0062]    In step S 10 , the initiator  100  includes a DMG range element including capability information thereof in a DMG beacon, and transmits the DMG beacon including the DMG range element to the responder  200 . In step S 20 , in response to the reception of the DMG beacon including the DMG range element, the responder  200  transmits a probe request including a DMG range element to the initiator  100 . In step S 30 , in response to the reception of the probe request including the DMG range element, the initiator  100  may transmit an ACKnowledgement (ACK) signal to the responder  200 . 
         [0063]    Referring to  FIG. 4D , while exchanging an information request signal and an information response signal during the capability negotiation period T 10 , through a range capability information field within a DMG range element, the first wireless device  100  as the initiator and the second wireless device  200  as the responder interchange whether an STA is capable of operating as an initiator/responder, whether the STA is capable of receiving/transmitting an NDP, and whether the STA is capable of using a range feedback request/response frame. 
         [0064]    In step S 40 , the initiator  100  includes a DMG range element including capability information thereof in an information request, and transmits the information request including the DMG range element to the responder  200 . In step S 50 , in response to the reception of the information request including the DMG range element, the responder  200  transmits an ACK to the initiator  100 . In step S 60 , in response to the reception of the information request including the DMG range element, the responder  200  transmits an information response including a DMG range element to the initiator  100 . In step S 70 , in response to the reception of the information response including the DMG range element, the initiator  100  transmits an ACK to the responder  200 . 
         [0065]    The initiator  100  and the responder  200  may interchange the respective pieces of capability information during the capability negotiation period T 10  as described above, and thus, may rapidly enter the range estimation period T 100  appropriately for the capabilities of the initiator  100  and the responder  200  without a separate operation. 
         [0066]      FIG. 7  is a view illustrating a configuration of a request range packet according to embodiments of the present invention. The configuration illustrated in  FIG. 7 , which is only an example for describing the present invention, may be replaced by various modified configurations, and thus should not be construed as limiting the protection scope of the present invention. 
         [0067]    Referring to  FIG. 7 , a request range packet is a packet transmitted by an STA (or a wireless device) for the purpose of measuring a distance. The request range packet may have a format illustrated in  FIG. 7 . The request range packet refers to all packets including only a Short Training Field (STF)  40  and a Channel Estimation (CE) field  50 . 
         [0068]    Due to an oscillator error between the initiator  100  and the responder  200 , it may be difficult for the initiator  100  and the responder  200  to have an accuracy of several centimeters in the case of processing a signal through a packet having a long data length. In this case, for distance measurement having a high-resolution accuracy, it is appropriate to use an NDP which does not have data, including a header  60  illustrated in  FIG. 7 , as a request range packet. 
         [0069]    Meanwhile, since not all wireless devices are capable of transmitting and receiving NDPs, whether an NDP range packet is capable of being used may be determined for each wireless device, according to the range capability information defined in Table 1. Also, although the NDP range packet is not capable of being used, a range field shown in Table 2 below may be placed in the header  60  as illustrated in  FIG. 7  and time required to process a signal through a packet having a long data length may be reduced, so that accuracy can be increased. 
         [0000]    
       
         
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Field 
                 Definition 
                 Encoding 
               
               
                   
                   
               
             
             
               
                   
                 Range 
                 whether packet is range 
                 0: no range packet 
               
               
                   
                   
                 packet 
                 1: range packet 
               
               
                   
                   
               
             
          
         
       
     
         [0070]    For example, when the header  60  illustrated in  FIG. 7  includes a range field  65 , if the value of the range field  65  of the header  60  is equal to 1, the value 1 of the range field  65  represents a range packet. If the value of the range field  65  of the header  60  is equal to 0, the value 0 of the range field  65  represents a case where the packet is not a range packet. 
         [0071]    Referring back to  FIG. 4A , a distance measurement operation is started by a range start signal during the range estimation period T 100 . The first wireless device  100  as the initiator transmits a request range packet to the second wireless device  200  as the responder in step S 110 , and the responder  200  transmits a response range packet to the initiator  100  in response to the request range packet in step S 130 . Step S 110  and step S 130  correspond to a case where the initiator  100  does not use an NDP but use a packet having data as the request range packet. All packets, which enable the responder  200  to respond after the passage of a preset time interval, for example, a Short Interframe Space (SIFS) interval, may be used as the request range packet. For example, an RTS, a probe response, a request action frame, and the like may be used as request range packets, and at this time, a DMG CTS, an ACK, and a response action frame may be used as response range packets, respectively. 
         [0072]    Referring back to  FIG. 4B , a distance measurement operation is started by a range start signal during the range estimation period T 100 . In steps  140  and  150 , while exchanging an RTS and a DMG CTS, the first wireless device  100  as the initiator and the second wireless device  200  as the responder confirm that a destination of a request range packet, that the initiator  100  is to request, is the responder  200 . In steps  110 , the initiator  100  may transmit a NDP as the request range packet to the responder  200 . Since the NDP has an ambiguous destination thereof, it is necessary to perform steps S 140  and S 150 . The responder  200  transmits a response range packet to the initiator  100  in response to the NDP. At this time, an ACK or a response action frame may be used as the response range packet in step S 130 . 
         [0073]      FIG. 8A  is a view illustrating a distance estimation operation for estimating a distance between wireless devices by a range estimator according to an embodiment of the present invention. The distance estimation operation may be performed by the range estimator  110 A illustrated in  FIG. 2  and the range estimator  210 A illustrated in  FIG. 3 . The flow illustrated in  FIG. 8A , which is only an example for describing the present invention, may be replaced by various modified flows, and thus should not be construed as limiting the protection scope of the present invention. 
         [0074]    Referring to  FIG. 8A , the range estimator  110 A of the first wireless device  100  counts a time period from a time point of transmission of a request range packet through the DAC  125  to a time point of detection of reception of a response range packet received by the baseband processor  115 . This time period is Ti. The range estimator  210 A of the second wireless device  200  counts a time period from a time point of detection of reception of a request range packet received by the baseband processor  215  to a time point of transmission of a response range packet through the DAC  225 . This time period is Tr. 
         [0075]    In Table 3 below, A represents each of a delay of the DAC  125 A of the initiator  100  and a delay of the DAC  225 A of the responder  200 . B represents each of a transmit circuit delay between the DAC  125 A of the initiator  100  and the antenna  130  thereof, and a transmit circuit delay between the DAC  225 A of the responder  200  and the antenna  230  thereof. C represents a propagation delay between the initiator  100  and the responder  200 . D represents each of a receive circuit delay between the antenna  230  of the responder  200  and the ADC  225 B thereof, and a receive circuit delay between the antenna  130  of the initiator  100  and the ADC  125 B thereof. E represents each of a delay of the ADC  225 B of the responder  200  and a delay of the ADC  125 B of the initiator  100 . F represents each of a processing delay of BB of the baseband processor  215  of the responder  200  and a processing delay of BB of the baseband processor  115  of the initiator  100 . 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Symbol 
                 Description 
               
               
                   
                   
               
             
             
               
                   
                 Ti 
                 Time for Clock Counter of Initiator 
               
               
                   
                 Tr 
                 Time for Clock Counter of Responder 
               
               
                   
                 A 
                 DAC Delay 
               
               
                   
                 B 
                 Transmit Circuit Delay 
               
               
                   
                 C 
                 Propagation Delay 
               
               
                   
                 D 
                 Receive Circuit Delay 
               
               
                   
                 E 
                 ADC Delay 
               
               
                   
                 F 
                 Processing Delay of BB 
               
               
                   
                   
               
             
          
         
       
     
         [0076]    As described above, the first wireless device  100  and the second wireless device  200  may identify F and may also identify A, B, D, and E, and thus, Equations 1 and 2 below may be derived. 
         [0000]        Ti=Tr+ 2( A+B+C+D+E+F )  Equation 1
 
         [0000]        C =( Ti−Tr )/2−( A+B+D+E+F )  Equation 2
 
         [0077]    A propagation delay C may be obtained from Equation 2. At this time, A, B, D, E, and F represent constants, the value of Ti may be calculated by measurement, the value of Tr may be measured by the second wireless device  200  and may be received from the second wireless device  200 . Accordingly, the first wireless device  100  may estimate a distance between the first wireless device  100  and the second wireless device  200 . 
         [0078]      FIG. 8B  is a view illustrating a distance estimation operation for estimating a distance between wireless devices by a range estimator according to another embodiment of the present invention. The distance estimation operation may be performed by the range estimator  110 A illustrated in  FIG. 2  and the range estimator  210 A illustrated in  FIG. 3 . The flow illustrated in  FIG. 8B , which is only an example for describing the present invention, may be replaced by various modified flows, and thus should not be construed as limiting the protection scope of the present invention. 
         [0079]    When compared with  FIG. 8A , in the processing flow illustrated in  FIG. 8B , each of the initiator  100  and the responder  200  uses an STO to perform more accurate distance estimation. This is for performing more accurate distance estimation by correcting an error and the like, which may occur when a correlation result value in a unit of sampling a received signal is calculated, as expressed by Equation 3 below. 
         [0080]      FIGS. 9A to 9C  are views for explaining an operation of detecting a received symbol, that wireless devices perform in order to estimate a distance, according to embodiments of the present invention. 
         [0081]    Referring to  FIG. 9A , each of the first wireless device  100  and the second wireless device  200  detects a received symbol by using a so-called Golay sequence used in a preamble of a packet of 60 GHz Wi-Fi. What is important in distance estimation is to calculate a propagation delay C, and the first wireless device  100  and the second wireless device  200  may not immediately recognize time points of receptions of packets through the antennas  130  and  230 , respectively. Accordingly, the baseband processor  115  of the initiator  100  or the baseband processor  215  of the responder  200  performs reception detection estimation, and recognizes the time point of the reception of the packet through the antenna  130  or  230  on the basis of a result of the reception detection estimation. A preamble is received through the antenna  130  or  230  and is delivered to the ADC  125 B or  225 B (a time delay D), and a start point of the preamble is delivered to the baseband processor  115  or  215  (a time delay E). The baseband processor  115  or  215  may perform reception detection estimation on the basis of a time point of reception of the start point of the preamble by the baseband processor  115  or  215 . However, for more accurate reception detection, reception detection estimation may be performed by using characteristics of the Golay sequence of the preamble (a time delay F). 
         [0082]      FIGS. 9B and 9C  illustrate a reception detection estimation operation related to a Golay sequence used in a preamble of a packet of 60 GHz Wi-Fi and correlation characteristics of the Golay sequence, respectively. 
         [0083]    Referring to  FIG. 9B , the preamble of the packet of 60 GHz Wi-Fi includes an STF  40  and a CE field  50 . The STF  40  and the CE field  50  include a Ga128 and a Gb128 both having a sample length of 128; and a Gu256  70 , a Gv512  80 , and a Gu512  90 , each including a combination of the Ga128 and the Gb128. 
         [0084]    Referring to correlation characteristics of the Gu256  70  illustrated in  FIG. 9C , a peak P 2  may be expected at an end point of the STF  40  as illustrated in  FIG. 9B , and reception detection may be performed by comparing P 2  with a predetermined threshold. Also, reception detection may be performed by using a phase difference between P 1  and P 2  of correlation characteristics of the Gv256  80  illustrated in (a) of  FIG. 9C . Referring to characteristics of the sum of a correlation of the Gv512  80  and a correlation of the Gu512  90  which are illustrated in (b) of  FIG. 9C , a peak P 3  may be expected at an end point of the Gu512  90  as illustrated in  FIG. 9B , and reception detection may be performed by comparing P 3  with a predetermined threshold. Here, although an embodiment is described in which the reception detection estimation operation is performed by using the particular correlation characteristics of the Golay sequence, a similar modified embodiment may be implemented. For example, for a reception detection estimation operation, correlation characteristics of the Ga128 or the Gb128 may be used, or a signal having a good autocorrelation property, for example, a pseudo random code, may be used. 
         [0085]    Meanwhile, when the baseband processor  115  of the initiator  100  or the baseband processor  215  of the responder  200  performs reception detection estimation, a unit of measurement is a unit of digital sampling, and thus a reception detection estimation error may exist. In this regard, a more accurate reception detection processing delay F of the baseband processor  215  of the responder  200  and a more accurate reception detection processing delay F of the baseband processor  115  of the initiator  100  may be obtained by utilizing an STO as expressed by Equation 3 below. 
         [0000]        F′=F+S   Equation 3
 
         [0086]    Here, F represents each of a processing delay of the baseband processor  215  of the responder  200  and a processing delay of the baseband processor  115  of the initiator  100  in a case where reception detection is performed in a unit of sample, and S represents an STO and has a delay shorter than that of one sample. 
         [0087]      FIGS. 10 and 11  are views for explaining an operation of searching for a direction by the responder  200  according to embodiments of the present invention. The configuration illustrated in  FIGS. 10 and 11 , which is only an example for describing the present invention, may be replaced by various modified configurations, and thus should not be construed as limiting the protection scope of the present invention. A method for searching for a direction by the responder  200 , according to embodiments of the present invention, may be an electric beam-sweep method illustrated in  FIG. 10  and a manual beam-sweep method illustrated in  FIG. 11 . Such a direction estimation operation may be performed by the direction estimator  110 B illustrated in  FIG. 2 . Here, an example is described in which the first wireless device  100  as the initiator estimates a direction of the second wireless device  200  as the responder. However, in an identical scheme, the direction estimator  210 B of the second wireless device  200  illustrated in  FIG. 3  may estimate a direction of the first wireless device  100 . 
         [0088]    Referring to  FIG. 10 , for the electric beam-sweep method, the direction estimator  110 B of the initiator  100  includes multiple sector measurement units  170 - 10 , multiple channel estimators  170 - 12 , multiple Line-of-Sight (LOS) path selectors  170 - 14 , a beam pattern storage unit  170 - 16 , and an Angle of Arrival (AOA) estimator  170 - 18 . The multiple sector measurement units  170 - 10  measure a strength of a signal in a case where the initiator  100  exchanges signals with the reception device while changing an antenna beam direction through antenna beamforming. The multiple channel estimators  170 - 12  respectively correspond to the multiple sector measurement units  170 - 10 , and estimate respective channels. The multiple LOS path selectors  170 - 14  respectively correspond to the multiple channel estimators  170 - 12  and each select a LOS path by searching for a peak of the estimated channel. The AOA estimator  170 - 18  compares a LOS path variation pattern, which has been output from the multiple LOS path selectors  170 - 14 , with a beam pattern, which is pre-stored in the beam pattern storage unit  170 - 16 , and estimates an AOA according to a result of the comparison. Accordingly, the direction of the responder  200  is estimated. 
         [0089]    Referring to  FIG. 11 , for the manual beam-sweep method, the direction estimator  110 B of the initiator  100  includes multiple sector measurement units  170 - 20 , multiple channel estimators  170 - 22 , multiple LOS path selectors  170 - 24 , a direction change measurement unit  170 - 26 , and an AOA estimator  170 - 28 . The multiple sector measurement units  170 - 20  measure a strength of a signal in a case where the initiator  100  exchanges signals with the reception device while a user changes an antenna beam direction with the user&#39;s hand in a state of fixing an antenna beam of the transmission device  100  so as to face the front of the transmission device  100 . The multiple channel estimators  170 - 22  respectively correspond to the multiple sector measurement units  170 - 20 , and estimate respective channels. The multiple LOS path selectors  170 - 24  respectively correspond to the multiple channel estimators  170 - 22  and each select a LOS path by searching for a peak of the estimated channel. The AOA estimator  170 - 28  compares a LOS path variation pattern, which has been output from the multiple LOS path selectors  170 - 24 , with a beam pattern, which has been measured by the direction change measurement unit  170 - 26  that may be implemented by a gyroscope sensor, and estimates an AOA according to a result of the comparison. Accordingly, the direction of the responder  200  is estimated. 
         [0090]      FIG. 12  is a view illustrating a processing flow of a location estimation operation performed between wireless devices according to an embodiment of the present invention. The flow illustrated in  FIG. 12 , which is only an example for describing the present invention, may be replaced by various modified flows, and thus should not be construed as limiting the protection scope of the present invention. The flow may be performed by, for example, the location estimator  110  of the initiator  100  illustrated in  FIG. 1 . An operation of estimating a distance and a direction of the responder  200  by the initiator  100  may be performed by the range estimator  110 A and the direction estimator  110 B included in the baseband processor  115  of the initiator  100  illustrated in  FIG. 2 . A distance estimation operation performed by the range estimator  110 A may be performed according to the above-described flows illustrated in  FIGS. 4A to 8B . A direction estimation operation performed by the direction estimator  110 B may be performed according to the above-described flow illustrated in  FIG. 10 or 11 . 
         [0091]    Referring to  FIG. 12 , in step S 200 , the direction estimator  110 B of the initiator  100  estimates a direction (i.e., an angle) of the responder  200  in order to estimate a location of the responder  200 . 
         [0092]    Then, in steps S 210  to S 240 , the initiator  100  estimates a distance between the initiator  100  and the responder  200 . To this end, it is necessary to know a time period during which a request range packet and a response range packet are in the air. Specifically, it is necessary to know the propagation delay C defined in Table 3. In order to obtain C, in step S 210 , the range estimator  110 A of the initiator  100  calculates a time period Ti from a time point of generation and transmission of a request range packet to a time point of detection of a response range packet transmitted by the responder  200 . In step S 220 , the range estimator  110 A of the initiator  100  receives a time period Tr calculated by the range estimator  210 A of the responder  200 . In step S 230 , the range estimator  110 A of the initiator  100  calculates the propagation delay C from the calculated Ti and Tr by using Equation 2. In step S 240 , the range estimator  110 A of the initiator  100  applies C, which has been calculated by using Equation 2, to Equation 4 below, and thereby estimates the distance between the initiator  100  and the responder  200 . 
         [0000]      Distance= C ×(Speed of light)  Equation 4
 
         [0093]    Here, an example is described in which a distance between the initiator  100  and the responder  200  is estimated once. Alternatively, as another example, a distance between the initiator  100  and the responder  200  may be estimated multiple times, the average of the estimated distances may be used or filtering processing may be performed on the estimated distances, and thereby, a more accurate distance may be estimated. 
         [0094]    In step S 250 , the location estimator  110  of the initiator  100  receives location information of the initiator  100 . For example, the location estimator  110  of the initiator  100  may recognize a location of the initiator  100  by using Global Positioning System (GPS) information or an Access Point (AP). In step S 260 , the location estimator  110  of the initiator  100  may estimate a location of the responder  200 , with a resolution of several centimeters on the basis of the location information of the initiator  100 . 
         [0095]    The location of the responder  200 , that the initiator  100  has estimated as described above, may be externally displayed to enable a user to identify the estimated location of the responder  200 . For example, the location of the initiator  100  and the location of the responder  200  may be displayed on a map as illustrated in  FIGS. 14A and 14B  below. 
         [0096]    Also, the initiator  100  may perform a handover and a signal power adjustment operation on the basis of the estimated location of the responder  200 . For example, the initiator  100  has a high probability of performing smooth communication with smaller signal power as a distance becomes shorter. Accordingly, the initiator  100  may adjust signal power by using a relation formula between a distance and signal power and by using this property. As another example, the initiator  100  may compare a location of the wireless device with locations of base stations, and may use a result of the comparison for a handover so as to communicate with a base station located in a nearby place. 
         [0097]      FIG. 13  is a block diagram illustrating a configuration of a first wireless device for a location estimation operation according to embodiments of the present invention. The configuration illustrated in  FIG. 13 , which is only an example for describing the present invention, may be replaced by various modified configurations, and thus should not be construed as limiting the protection scope of the present invention. The configuration is an exemplified configuration of the first wireless device  100  illustrated in  FIGS. 1 and 2 , does not limit the scope of the present invention, and may use a similar configuration without departing from the scope of the present invention. 
         [0098]    Referring to  FIG. 13 , the first wireless device  100  includes an antenna unit  130 , a beamforming transmitter/receiver  140 , a processor  150 , a memory unit  160 , a user interface module  170 , a range estimator  110 A, and a direction estimator  110 B. The processor  150 , the range estimator  110 A, and the direction estimator  110 B may configure the location estimator  110  illustrated in  FIG. 1 . 
         [0099]    The antenna unit  130  includes multiple antenna arrays, and takes charge of transmission/reception of a signal. For example, the antenna unit  130  transmits/receives a signal in a band of 60 GHz by using mmWave technology. The beamforming transmitter/receiver  140  forms one or more beams, and serves to transmit/receive a signal through the formed beam. For example, the beamforming transmitter/receiver  140  may include an encoder, a modulator, a demultiplexer, a beamformer, a beamforming vector former, an Orthogonal Frequency Division Multiplexing (OFDM) modulator, a Radio frequency (RF) processor, and the like. 
         [0100]    The processor  150  controls an overall operation of the wireless device. Particularly, the processor  150  controls the range estimator  110 A and the direction estimator  110 B, and performs a distance estimation operation and a direction estimation operation according to embodiments of the present invention. For example, the processor  150  of the initiator  100  estimates a direction and a distance of the responder  200  according to the flow illustrated in  FIG. 12 , and thereby estimates a location of the responder  200 . Also, the processor  150  may perform an operation of detecting a location of the initiator  100  by receiving location information of the initiator  100  by using GPS information or an AP, and an operation of displaying the estimated location of the responder  200  on the user interface module  170  by using a map and the like on the basis of the detected location of the initiator  100 . The GPS information may be received through a GPS receiver (not illustrated), and communication with the AP may be performed through the antenna unit  130 . Also, the processor  150  may perform a handover operation or an operation of adjusting power of a signal by using a result of the location estimation. 
         [0101]    The memory unit  160  stores a program for executing an operation of the wireless device, data according to the execution of the operation, and the like. Also, the memory unit  160  stores map information used during the display of the result of the location estimation according to embodiments of the present invention. The user interface module  170  is for an interface between the wireless device and the user, and may include an input module and a display module. The display module may display the result of the location estimation according to embodiments of the present invention together with a map. Through the display of the result of the location estimation, the user may identify the location of the first wireless device  100  and that of the second wireless device  200 . 
         [0102]    The range estimator  110 A estimates distances of nearby wireless devices according to embodiments of the present invention. For example, the range estimator  110 A may estimate a distance of the responder  200  according to the flows illustrated in  FIGS. 4A to 9C . The direction estimator  110 B estimates directions of nearby wireless devices according to embodiments of the present invention. For example, the direction estimator  110 B may estimate a direction of the responder  200  according to the flows illustrated in  FIGS. 10  and  11 . 
         [0103]    The above-described embodiments of the present invention are implemented by using signals, which necessarily need to exist in an existing modem, in order to minimize the power consumption of the range estimator  110 A and that of the range estimator  210 A. A signal which controls Tx of the baseband processor is used to find a time point of transmission of a range packet through the DAC, and adjustment is performed through various offsets. 
         [0104]    Meanwhile, distributions of CIR peak values which are obtained during a distance estimation operation according to embodiments of the present invention may be distinguished from each other according to whether a multipath channel is a LOS channel or a Non-LOS (NLOS) channel. Accordingly, when the initiator for distance measurement receives a response range packet, the initiator may compare a CIR peak value with a particular threshold, and thereby, may represent the CIR peak value so as to be distinguished according to the LOS channel and the NLOS channel, or may represent a reliability on the distance estimated from the CIR peak value. From this result, the user can know the inaccuracy of distance measurement which may occur due to an effect of the multipath channel. 
         [0105]    As described above, embodiments of the present invention enable distance estimation having a resolution of several centimeters by using the transmission and reception of signals between wireless devices in a wireless communication system. The embodiments of the present invention enable the estimation of the location of a wireless device on the basis of the estimated distance, and enable the adjustment of a handover between wireless devices and power of signals transmitted and received therebetween by using the estimated location infirmation. Also, the embodiments of the present invention enable a distance between wireless devices to be rapidly estimated by using a request/response range packet. Also, the embodiments of the present invention enable the inaccuracy (reliability) of distance measurement, which may occur due to an effect of a multipath channel, to be provided to a user. Further, the embodiments of the present invention enable the power consumption of the range estimator to be minimized by using signals used in an existing modem. 
         [0106]    Although the present invention has been described with reference to the limited embodiments and the drawings as described above, the present invention is not limited to the above-described embodiments, and various modifications and changes in form may be made to the embodiments described herein by those having ordinary knowledge in the technical field to which the present invention pertains. As an example, a case has been described in which, in embodiments of the present invention, the wireless device is configured as illustrated in  FIGS. 2 and 3 , operates according to the flows illustrated in  FIGS. 4A, 4B, 4C , and  4 D, and the range estimator of the wireless device measures a distance according to the flows illustrated in  FIGS. 8A and 8B . However, the protection scope of the present invention will not be limited thereto. 
         [0107]    Operations according to an embodiment of the present invention may be implemented by a single controller. In this case, a program instruction for performing an operation implemented by various computers may be recorded in a computer-readable medium. The computer readable medium may include a program command, a data file, a data structure, and the like independently or in combination. The program command may be things specially designed and configured for the present invention, or things that are well known to and can be used by those skilled in the related art. For example, the computer readable recoding medium includes magnetic media such as a hard disk, a floppy disk, and a magnetic tape, optical media such as a CD-ROM and a DVD, magneto-optical media such as a floptical disk, and hardware devices such as a ROM, RAM, and a flash memory, which are specially constructed in such a manner that they can store and execute a program command. Examples of the program command include a machine language code generated by a compiler and a high-level language code executable by a computer through an interpreter and the like. When the whole or part of the base station or the relay described in the present invention is implemented in a computer program, a computer-readable recording medium, that stores the computer program, is included in the present invention. Therefore, the scope of the present invention should not be defined as being limited to the described embodiments, but should be defined by the appended claims and equivalents thereof.