Patent Publication Number: US-2023152415-A1

Title: Cooperative positioning method and apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of PCT Patent Application PCT/KR2021/006843 filed Jun. 2, 2021, and claims priority to Patent Application No. 10-2020-0091202, filed on Jul. 22, 2020 in Korea, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     a. Technical Field 
     The present disclosure relates to a method and an apparatus for cooperative positioning, and more particularly, to a method and an apparatus for cooperative positioning in which a low-performance device that does not support a high-performance positioning technology can indirectly perform a high-performance positioning technology through a high-performance device. 
     b. Background Art 
     The contents described in the present section simply provide background information on the present disclosure and do not constitute related art. 
     Network-based positioning technology is being used more widely to provide the location of a device in GPS signal shaded areas, such as indoors and underground. In general, a positioning method based on a wireless LAN estimates a location of a device using fingerprint method or multilateration based on received signal strength (RSSI) or timing data (e.g. RTT, ToA, TDoA, ToF, etc.) of beacon signals. 
     A representative method of indoor positioning methods using wireless signals is a method of estimating a location of a device by obtaining a distance between a device and each of the access points (AP) using signals received by the device from the access points and applying multilateration including triangulation to the AP-device distance. 
     In general, communication standards used in network-based positioning technology include Bluetooth, Bluetooth at Low Energy (BLE), geo-magnetic intensity, Wi-Fi, and the like. Here, the WiFi-based positioning technology uses a Received Signal Strength Indicator (RSSI). 
     Recently, research on network-based positioning technology has been actively conducted, and a positioning method based on Wi-Fi Round Trip Time (RTT), a positioning method based on UWB, and the like are being developed. Such positioning methods can accurately estimate the location of a device, but the device needs to be equipped with a high-performance chipset or needs to be able to implement an algorithm. That is, in the case of low-cost or low-performance devices, it is difficult to enjoy the benefits of high-performance positioning technology since they cannot support high-performance positioning technology. 
     Meanwhile, since network-based positioning technologies use radio signals, a device cannot use the positioning technology in an area where no radio signal reaches. In addition, due to the nature of the radio signal, when the signal strength changes according to various factors such as time, weather, or floating population, or when the radio signal is distorted by multipath, non-line of sight (NLOS) or the like, there may be areas where the accuracy of positioning is low in an indoor environment. Specifically, since an indoor space is mostly an NLOS environment with no straight path between devices, there is a high possibility that the distance measurement value and the final position estimation value contain errors. 
     Accordingly, research on a positioning method that can estimate a location of the device using a peripheral device for when a device is a low-cost or low-performance device or is located in an area where it is difficult for the device to receive radio signals is needed. 
     In this case, when the estimated location of the peripheral device is estimated as the location of the target device, a positioning error may occur due to a distance between the target device and the peripheral device. Accordingly, additional research on positioning technology that can reduce the error due to the distance between devices is also needed. 
     SUMMARY 
     An aspect of the present disclosure is directed to providing a method for cooperative positioning performed by a target device including: scanning beacon signal transmitted by at least one peripheral device; determining whether at least one peripheral device exist within a reference radius based on the beacon signal; when the at least one peripheral device is within the reference radius, transmitting a cooperative positioning request to the at least one peripheral device; receiving, in response to transmitting the cooperative positioning request, location of the at least one peripheral device and a degree of reliability for the location of the at least one peripheral device; and determining a location of the target device based on the location and the degree of reliability. 
     Another aspect of the present disclosure is directed to providing a target device using a method for cooperative positioning, the device comprising: a scanning unit configured to scan beacon signal transmitted by at least one peripheral device; a determining unit configured to determine whether at least one peripheral device exist within a reference radius based on the beacon signal; a requesting unit configured to, when the at least one peripheral device is within the reference radius, transmit a cooperative positioning request to the at least one peripheral device; a receiving unit configured to receive, in response to transmitting the cooperative positioning request, location of the at least one peripheral device and a degree of reliability for the location of the at least one peripheral device; and a deciding unit configured to determine a location of the target device based on the location and the degree of reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a configuration diagram of a target device according to one embodiment of the present disclosure. 
         FIG.  2 A  is a diagram illustrating a process of determining a location of a target device through one or more peripheral devices within a reference radius according to one embodiment of the present disclosure. 
         FIG.  2 B  is a diagram illustrating a process of determining a location of a target device through at least three peripheral devices outside a reference radius according to one embodiment of the present disclosure. 
         FIG.  2 C  is a diagram illustrating a process of determining a location of a target device through two device groups outside a reference radius according to one embodiment of the present disclosure. 
         FIG.  3    is a diagram illustrating a process of determining a location of a target device through at least four peripheral devices outside a reference radius according to one embodiment of the present disclosure. 
         FIG.  4    is a diagram illustrating a process of evaluating a degree of reliability of an estimated location of a peripheral device according to one embodiment of the present disclosure. 
         FIG.  5    is a flowchart illustrating a method for cooperative positioning of a target device according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure provide a method and an apparatus for cooperative positioning for improving positioning accuracy by allowing a low-performance device that does not support the high-performance positioning technology to indirectly use the high-performance positioning technology of a high-performance device. 
     Other embodiments of the present disclosure provide a method and an apparatus for cooperative positioning for expanding an area where positioning is feasible by using a positioning technology of a peripheral device when a target device is located in an area where positioning is unfeasible or is difficult. 
     Other embodiments of the present disclosure provide a method and an apparatus for cooperative positioning that can reduce error due to a distance between a low-performance device and a high-performance device by performing a method of determining the location of the low-performance device from the locations of the high-performance devices in two ways depending on the distances between the high-performance devices. 
     Hereinafter, some exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, like reference numerals preferably designate like elements, although the elements are shown in different drawings. Further, in the following description of some embodiments, a detailed description of known functions and configurations incorporated therein will be omitted for the purpose of clarity and for brevity. 
     Additionally, various terms such as first, second, A, B, (a), (b), etc., are used solely to differentiate one component from the other but not to imply or suggest the substances, order, or sequence of the components. Throughout the present specification, when a part ‘includes’ or ‘comprises’ a component, the part is meant to further include other components, not to exclude thereof unless specifically stated to the contrary. The terms such as ‘unit’, ‘module’, and the like refer to one or more units for processing at least one function or operation, which may be implemented by hardware, software, or a combination thereof. 
       FIG.  1    is a configuration diagram of a target device according to one embodiment of the present disclosure. 
     Referring to  FIG.  1   , a target device  10  according to one embodiment of the present disclosure includes a scanning unit  100 , a measuring unit  110 , a determining unit  120 , a requesting unit  130 , a receiving unit  140 , and a deciding unit  150 . The target device  10  according to one embodiment of the present disclosure may further include a selecting unit  160 . 
     The scanning unit  100  scans beacon signals transmitted by a plurality of peripheral devices. Here, the beacon signal includes identification information of the plurality of peripheral devices. The identification information includes one or more of a MAC address, a Service Set Identifier (SSID), or identification information. 
     The measuring unit  110  measures a distance to at least one peripheral device based on the beacon signals. Here, the distance to at least one peripheral device means distances between the target device  10  and each of the peripheral devices. 
     To measure the distance between the target device  10  and each peripheral device, the measuring unit  110  measures at least one of received signal strength indicator (RSSI), round trip time (RTT), time of flight (ToF), time of arrival (ToA), or time difference of arrival (TDoA) of the beacon signals. The measuring unit  110  may measure the distance between the target device  10  and each peripheral device based on at least one of RSSI, RTT, ToF, ToA, or TDoA of the beacon signal. 
     The determining unit  120  is a component that determines whether at least one peripheral devices exist within a reference radius. Furthermore, the determining unit  120  may determine whether there exist at least three peripheral devices having similar distances from the target device outside the reference radius. Here, the reference radius is a distance from the target device  10  and refers to a preset radius. 
     The determining unit  120  identifies a device group including at least three peripheral devices outside the reference radius when the at least one peripheral device is outside the reference radius. Additionally, the determining unit  120  determines whether a differences between distances from two different peripheral devices in the device group to the target device is smaller than a preset distance. This is to determine whether at least three peripheral devices are located at similar distances from the target device. 
     Even though at least one peripheral device exist within the reference radius, when the degree of reliability for the location of the at least one peripheral device are lower than a preset value, the determining unit  120  determines whether a device group including at least three peripheral devices exists outside the reference radius. Additionally, the determining unit  120  determines whether a difference between distances from two different peripheral devices included in the device group to the target device is smaller than the preset distance. 
     Meanwhile, the determining unit  120  may identify a second device group including at least three second peripheral devices outside the reference radius. When a second device group exists, the determining unit  120  determines whether a difference between distances from two different second peripheral devices included in the second device group to the target device is smaller than the preset distance. 
     The requesting unit  130  is a component that, when there exist one or more peripheral devices within the reference radius, transmits a cooperative positioning request to one or more peripheral devices. 
     In addition, when the determining unit  120  determines that there exists a device group outside the reference radius and determines that a difference between distances from two different peripheral devices included in the device group to the target device is smaller than the preset distance, the requesting unit  130  transmits cooperative positioning requests to at least three peripheral devices included in the device group. 
     Moreover, when there exist the device group and the second device group, the requesting unit  130  transmits a cooperative positioning request to peripheral devices included in the device group selected by the selecting unit  160 . 
     The receiving unit  140  is a component that receives the location of at least one peripheral device and a degree of reliability for the location from the at least one peripheral device in response to transmitting the cooperative positioning request. The degree of reliability is explained in detail in  FIG.  4   . 
     Additionally, the receiving unit  140  may receive at least three locations of at least three peripheral devices included in the device group from the at least three peripheral devices. 
     Additionally, when there exist the device group and the second device group, the receiving unit  140  may receive at least three locations of the at least three peripheral devices included in the device group selected by the selecting unit  160  from the at least three peripheral devices. 
     The receiving unit  140  according to one embodiment of the present disclosure may receive locations of peripheral devices from either a peripheral device or an external server. Here, the location is estimated by the external server or the peripheral device through a plurality of APs. In other words, the location of the peripheral device may be estimated by each device through the plurality of APs or by the external server. In this case, the external server estimates the location of the peripheral device after collecting AP beacon signals received by the peripheral device from the plurality of APs. 
     The deciding unit  150  is a component that determines, the location of a target device using the location of at least one peripheral device based on the degree of reliability when there exist at least one peripheral device within the reference radius. Here, the degree of reliability means the accuracy of the location estimated by the peripheral device through the AP. Specifically, the degree of reliability is a value determined based on a differences between a first distances between locations of a plurality of APs and the location of the at least one peripheral device, and a second distances derived by the at least one peripheral device using signals received from the plurality of APs. The degree of reliability is calculated to be higher as the difference between the first distance and the second distance is smaller. 
     In this case, according to one embodiment of the present disclosure, when the degree of reliability of the location of at least one peripheral device is greater than the preset value, the deciding unit  150  may determine the location of the at least one peripheral device as the location of the target device. 
     According to another embodiment of the present disclosure, when there exists a plurality of peripheral devices within the reference radius, the deciding unit  150  may determine a weighted average of locations of the plurality of peripheral devices as the location of the target device using the degree of reliability for the locations of the plurality of peripheral devices as weights. In other words, the deciding unit  150  may determine, as the location of the target device, the calculated weighted average value obtained by reflecting weights proportional to the degrees of reliability of the plurality of peripheral devices to the locations. 
     According to one embodiment of the present disclosure, when there exists a plurality of peripheral devices within the reference radius, the deciding unit  150  may identify locations having a degree of reliability higher than a preset value from the locations of the plurality of peripheral devices, and determine a weighted average of the identified locations as the location of the target device using degrees of reliability for the identified locations as weights. 
     According to one embodiment of the present disclosure, when there exist at least three peripheral devices outside the reference radius, the deciding unit  150  determines circumcenter coordinates of a triangle created using the at least three locations as the location of the target device. 
     When four or more peripheral devices are included in the device group outside the reference radius, the deciding unit  150  may generate a plurality of triangles using the locations of the four or more peripheral devices. Thereafter, the deciding unit  150  may derive circumcenter coordinates of the plurality of triangles, and determine one of a mean position or a median position of the circumcenter coordinates as the location of the target device. Here, the mean position of the circumcenter coordinates refers to coordinates having a dimensional average value of the circumcenter coordinates. The median position of the circumcenter coordinates refers to coordinates having a dimensional median value of the circumcenter coordinates. 
     When there exist the device group and the second device group, the selecting unit  160  is a component that selects a device group having a shorter distance from the target device among the device group and the second device group. Here, each device group needs to satisfy the condition that a difference between distances from two different peripheral devices included in each device group to the target device is less than the preset distance. The receiving unit  140  receives at least three locations of the at least three peripheral devices included in the device group selected by the selecting unit  160  from the at least three peripheral devices. The deciding unit  150  determines, as the location of the target device, the circumcenter coordinates of the triangle generated from the locations of the peripheral devices included in the selected device group. 
       FIG.  2 A  is a diagram illustrating a process of determining a location of a target device through one or more peripheral devices within a reference radius according to one embodiment of the present disclosure. 
     Referring to  FIG.  2 A , a reference radius  200 , a target device  210 , and a plurality of peripheral devices  220 ,  222 ,  230 ,  232 , and  234  are shown. The plurality of peripheral devices  220 ,  222 ,  230 ,  232 , and  234  include two peripheral devices  220  and  222 , and three peripheral devices  230 ,  232  and  234 . The two peripheral devices  220  and  222  include a first peripheral device  220  and a second peripheral device  222 . The three peripheral devices  230 ,  232 , and  234  include a third peripheral device  230 , a fourth peripheral device  232 , and a fifth peripheral device  234 . 
     The target device  210  scans beacon signals transmitted from the plurality of peripheral devices  220 ,  222 ,  230 ,  232 , and  234 . The target device  210  measures distances to the plurality of peripheral devices  220 ,  222 ,  230 ,  232 , and  234  based on the beacon signals. 
     The target device  210  determines whether there exist one or more peripheral devices within the reference radius  200 . In  FIG.  2 A , two peripheral devices  220  and  222  exist within the reference radius  200 . 
     The target device  210  transmits a cooperative positioning request to the two peripheral devices  220  and  222  within the reference radius. Then, the target device  210  receives locations and degrees of reliability of the two peripheral devices  220  and  222  from the two peripheral devices  220  and  222 . 
     The target device  210  may determine one of the two locations of the two peripheral devices  220  and  222  as its location based on the degrees of reliability. 
     When both the degrees of reliability of the two locations are greater than a preset value, the target device  210  may arbitrarily select one of the two locations and determine it as its own location. 
     When both the degrees of reliability of the two locations are greater than the preset value, a location obtained by calculating, using the degrees of reliability, a weighted average of the locations of the two peripheral devices  220  and  222  may be determined as the location of the target device  210 . For example, when the degree of reliability of the location of the first peripheral device  220  is higher than the degree of reliability of the location of the second peripheral device  222 , the target device  210  may assign a higher weight to the location of the first peripheral device  220 . Conversely, the target device  300  may assign a lower weight to the location of the second peripheral device  222 . 
     Meanwhile, in case that there exist three or more peripheral devices within the reference radius  200 , when the degree of reliability of the location of one peripheral device is less than the preset value and the degrees of reliability of the locations of the other peripheral devices are greater than the preset value, a location obtained by calculating, using the degrees of reliability, a weighted average of the locations of the other peripheral devices may be determined as the location of the target device  210 . That is, after excluding the location having the degree of reliability lower than the preset value, the location of the target device  210  is determined from the other peripheral devices. 
     When the degree of reliability of the location of the second peripheral device  222  among the two locations is less than the preset value, the target device  210  may determine the location of the first peripheral device  220  as its own location. 
     When both the degrees of reliability of the two locations are less than the preset value, the target device  210  may determine whether there exists a device group including at least three devices outside the reference radius. This is explained in detail with reference to  FIG.  2 B ,  FIG.  2 C  and  FIG.  3   . 
       FIG.  2 B  is a diagram illustrating a process of determining a location of a target device through at least three peripheral devices outside a reference radius according to one embodiment of the present disclosure. 
     Referring to  FIG.  2 B , a reference radius  200 , a target device  210 , three peripheral devices  230 ,  232 ,  234 , a device group radius  236 , and a triangle  238  are shown. The three peripheral devices  230 ,  232 , and  234  include a third peripheral device  230 , a fourth peripheral device  232  and a fifth peripheral device  234 . The device group radius  236  may be expressed as a single circle, but may also be expressed as a ring shape having a small radius and a large radius. This means that the distances from the target device  210  to each of the peripheral devices may be different from each other. 
     When there is no peripheral device within the reference radius  200  or that there is no peripheral device whose degree of reliability for the location is greater than the preset value, the target device  210 , based on the scanned beacon signal, determines whether there exists a device group including at least three peripheral devices outside the reference radius  200 . In  FIG.  2 B , three peripheral devices  230 ,  232 , and  234  constitute one device group. 
     The target device  210  determines whether a difference between distances from two different peripheral devices included in the device group to the target device  210  is smaller than a preset distance. In other words, the difference between the distances from two different peripheral devices included in the device group to the target device  210  should be less than the preset distance. This is a process for checking whether the three peripheral devices  230 ,  232 , and  234  included in the device group have similar distances from the target device  210 . This is because the circumcenter coordinates of the triangle  238  can be estimated as the location of the target device  210  only when the three peripheral devices  230 ,  232 , and  234  are located at similar distances from the target device  210 . 
     For example, the target device  210  calculates a first distance between the third peripheral device  230  and the target device  210 , and calculates a second distance between the fourth peripheral device  232  and the target device  210 . The target device  210  determines whether a difference between the first distance and the second distance is smaller than the preset distance. In addition, the target device  210  performs the same process for the pair of the fourth peripheral device  232  and the fifth peripheral device  234 , and performs the same process for the pair of the third peripheral device  230  and the fifth peripheral device  234 . When the difference between the distances from two different peripheral devices to the target device  210  is smaller than the preset distance, the target device  210  recognizes that the three peripheral devices  230 ,  232 , and  234  are located at similar distances from the target device  210 . 
     When the three peripheral devices  230 ,  232 , and  234  have similar distances from the target device  210 , the target device  210  transmits a cooperative positioning request to the three peripheral devices  230 ,  232 , and  234 . The target device  210  receives the locations of the three peripheral devices  230 ,  232 , and  234  from the three peripheral devices  230 ,  232 , and  234 . 
     The target device  210  creates the triangle  238  using the locations of the three peripheral devices  230 ,  232 , and  234  and then determines the circumcenter coordinates of the triangle  238  as its own location. 
       FIG.  2 C  is a diagram illustrating a process of determining a location of a target device through two device groups outside a reference radius according to one embodiment of the present disclosure. 
     Referring to  FIG.  2 C , a reference radius  200 , a target device  210 , three first peripheral devices  230 ,  232 , and  234 , a first device group radius  236 , a triangle  238 , and three second peripheral devices  240 ,  242 ,  244  and a second device group radius  246  are shown. The three first peripheral devices  230 ,  232 , and  234  include a third peripheral device  230 , a fourth peripheral device  232 , and a fifth peripheral device  234 . The three second peripheral devices  240 ,  242  and  244  include a sixth peripheral device  240 , a seventh peripheral device  242 , and an eighth peripheral device  244 . 
     The target device  210  determines whether there exist a first device group and a second device group, each including at least three peripheral devices. In this case, the peripheral devices included in the first device group and the second device group should not be completely identical. 
     The target device  210  further determines whether a difference between distances from two different peripheral devices included in each device group to the target device  210  is smaller than a preset distance. That is, it is determined whether the three first peripheral devices  230 ,  232 , and  234  have similar distances from the target device  210 . Additionally, the target device  210  determines whether the distances of the three second peripheral devices  240 ,  242 , and  244  from the target device  210  are similar. The detailed process is the same as the process described with reference to  FIG.  2 B . 
     When the three first peripheral devices  230 ,  232 , and  234  are located within the first device group radius  236  and the three second peripheral devices  240 ,  242 , and  244  are located within the second device group radius  246 , the target device  210  selects a device group closer to the target device  210 . In  FIG.  2 C , since the first device group radius  236  is closer to the target device  210  than the second device group radius  246 , the target device  210  selects the first device group located within the first device group radius  236 . The target device  210  transmits a cooperative positioning request to the three first peripheral devices  230 ,  232 , and  234  included in the selected group and receives locations of three first peripheral devices  230  from three first peripheral devices  230 ,  232 ,  234 . 
     The target device  210  creates the triangle  238  using the locations of the three peripheral devices  230 ,  232 , and  234  included in the selected first device group, and determines the coordinates of the circumcenter of the triangle  238  as the location of the target device  210 . 
       FIG.  3    is a diagram illustrating a process of determining a location of a target device through at least four peripheral devices outside a reference radius according to one embodiment of the present disclosure. 
     Referring to  FIG.  3   , a plurality of device group radii  250 ,  252 ,  254 ,  256 , a plurality of triangles  260 ,  262 ,  264 ,  266 , and a plurality of circumcenter coordinates  270 ,  272 ,  274 ,  276  are shown. The plurality of device group radii  250 ,  252 ,  254 , and  256  include a first device group radius  250 , a second device group radius  252 , a third device group radius  254 , and a fourth device group radius  256 . The plurality of triangles  260 ,  262 ,  264 , and  266  include a first triangle  260 , a second triangle  262 , a third triangle  264 , and a fourth triangle  266 . The plurality of circumcenter coordinates  270 ,  272 ,  274 , and  276  include a first circumcenter coordinate  270 , a second circumcenter coordinate  272 , a third circumcenter coordinate  274 , and a fourth circumcenter coordinate  276 . 
     When there are four or more peripheral devices having similar distances from the target device, a plurality of device group radii  250 ,  252 ,  254 , and  256  may be generated from a combination of at least three peripheral devices among the four or more peripheral devices. Here, a difference between distances from two different peripheral devices among the peripheral devices located in each of the plurality of device group radii  250 ,  252 ,  254 , and  256  to the target device is smaller than a preset distance. 
     The target device may create one triangle from three peripheral devices included in each device group. In  FIG.  3   , the target device may create four triangles using four peripheral devices located at similar distances from the target device. 
     The target device may derive the plurality of circumcenter coordinates  270 ,  272 ,  274 , and  276  for the plurality of triangles  260 ,  262 ,  264 , and  266 . The target device may determine any one of a mean position or a median position of the plurality of circumcenter coordinates  270 ,  272 ,  274 , and  276  as the location of the target device. 
       FIG.  4    is a diagram illustrating a process of evaluating a degree of reliability of an location of a peripheral device according to one embodiment of the present disclosure. 
     Referring to  FIG.  4   , a peripheral device  400  and a plurality of APs  410 ,  420 ,  430 , and  440  are illustrated. Hereinafter, it will be described that the peripheral device  400  performs the degree of reliability calculation process, but this is only one exemplary embodiment, and after an external server receives data from the peripheral device  400  and performs the degree of reliability calculation process, the degree of reliability information may be transmitted to the target device from the external server. 
     The peripheral device  400  according to one embodiment of the present disclosure calculates a first distance between the peripheral device  400  and each of the plurality of APs  410 ,  420 ,  430 , and  440  based on the location of the peripheral device  400  and the pre-stored location coordinates of the plurality of APs  410 ,  420 ,  430 , and  440 . In addition, the peripheral device  400  calculates a second distance from the target beacon signals. The peripheral device  400  calculates the degree of reliability of the estimated location based on the difference between the first distance and the second distance. Here, the peripheral device  400  evaluates the degree of reliability higher as the difference between the first distance and the second distance decreases. For example, the peripheral device  400  obtains a first distance and a second distance to a first AP  410 . The peripheral device  400  calculates a first error that is a difference between the first distance and the second distance. The peripheral device  400  calculates an error between the first distance and the second distance with respect to the plurality of APs  410 ,  420 ,  430 , and  440 , and peripheral device  400  evaluates the degree of reliability of its location higher as the total error is smaller. 
     According to one embodiment of the present disclosure, the peripheral device  400  may calculate the degree of reliability using the following equations that are expressed as Eq. 1 to Eq. 3, but the present disclosure is not limited thereto, and may include all equations that evaluate a degree of reliability higher as the error between the first distance and the second distance is smaller. 
     
       
         
           
             
               
                 
                   
                     
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     In Eq. 1 to Eq. 3, N means the number of APs, i means the index of the plurality of APs, P means the location of the peripheral device  400 , P i  means the location coordinates of the plurality of APs  410 ,  420 ,  430 , and  440 , {circumflex over (d)} i  means the second distance between the plurality of APs  410 ,  420 ,  430 , and  440  and the peripheral device  400 , and ∥P−P i ∥ means the first distance between the peripheral device  400  and the plurality of APs  410 ,  420 ,  430 , and  440 . 
       FIG.  5    is a flowchart illustrating a method for cooperative positioning of a target device according to one embodiment of the present disclosure. 
     Referring to  FIG.  5   , the target device scans beacon signals transmitted by at least one peripheral device (S 500 ). 
     The target device measures distances to the at least one peripheral device based on the beacon signals (S 502 ). 
     The target device determines whether the at least one peripheral device is within reference radius (S 504 ). 
     The target device send a cooperative positioning request to the at least one peripheral device when the at least one peripheral device is within the reference radius (S 506 ). 
     When at least one peripheral device do not exist within the reference radius, the target device identifies device group including at least three peripheral devices outside the reference radius, and determines whether a difference between distances from two different peripheral devices to the target device is smaller than a preset distance. When the difference is less than the preset distance, the target device sends cooperative positioning requests to at least three peripheral devices included in the device group. 
     The target device receives a location of the at least one peripheral device and a degree of reliability for the location (S 508 ). Here, the degree of reliability is a value determined based on differences between first distances between locations of a plurality of access points (APs) and the location of the at least one peripheral device, and second distances derived by the at least one peripheral device using signals received from the plurality of APs. 
     The target device determines a location of target device based on the location of the at least one peripheral device and the degree of reliability for the location (S 510 ). 
     The target device according to one embodiment of the present disclosure may determine the location of the at least one peripheral device as the location of the target device when the degree of reliability for the location of the at least one peripheral device is greater than a preset value. 
     When there exists a plurality of peripheral devices within the reference radius, the target device according to one embodiment of the present disclosure may determine, a weighted average of locations of the plurality of peripheral devices as the location of the target device using the degree of reliability for the locations of the plurality of peripheral devices as weights. 
     When there exists a plurality of peripheral devices within the reference radius, the target device according to one embodiment of the present disclosure may identify locations having a degree of reliability higher than a preset value from locations of the plurality of peripheral devices, and determine a weighted average of the identified locations as the location of the target device using degrees of reliability for the identified locations as weights. 
     When the target device receives the locations and degrees of reliability from at least three peripheral devices outside the reference radius, the target device may determine circumcenter coordinates of a triangle generated from the at least three locations as the location of the target device. When there are several triangles, the target device may derive circumcenter coordinates of the plurality of triangles and determine either a mean position or a median position of the circumcenter coordinates as the location of the target device. 
     As described above, according to one embodiment of the present disclosure, it is possible to increase positioning accuracy by allowing a low-performance device that does not support the high-performance positioning technology to indirectly use the high-performance positioning technology of a high-performance device. 
     According to another embodiment of the present disclosure, when the target device is located in an area where positioning is unfeasible or difficult, the location of the target device can be estimated by using a positioning technology of a peripheral device. 
     According to another embodiment of the present disclosure, the error due to the distance between the low-performance device and the high-performance device can be reduced by performing a method of determining the location of the low-performance device from the location of the high-performance devices in two ways depending on the distances between the high-performance devices. 
     Although it is described in  FIG.  5    that the processes S 500  to S 510  are sequentially executed, this is merely illustrative of the technical idea of one embodiment of the present disclosure. In other words, since a person of ordinary skill in the art to which the embodiment of the present disclosure pertains may make various modifications and changes by changing the order of the processes described in  FIG.  5    or performing one or more of the processes S 500  to S 510  in parallel without departing from the essential characteristics of the embodiment of the present disclosure,  FIG.  5    is not limited to a time-series order. 
     Meanwhile, the processes shown in  FIG.  5    can be implemented as computer readable codes on a computer-readable recording medium. The computer-readable recording medium includes all types of recording devices in which data readable by a computer system is stored. That is, the computer-readable recording medium may be a non-transitory medium such as ROM, RAM, CD-ROM, a magnetic tape, a floppy disk, or an optical data storage device, and may further include a temporary medium such as a carrier wave (e.g., transmission over the Internet) and a data transmission medium. In addition, the computer-readable recording medium may be distributed in a network-connected computer system, and computer-readable codes may be stored and executed in a distributed manner. 
     In addition, the components of the present disclosure may use an integrated circuit structure such as a memory, a processor, a logic circuit, a look-up table, and the like. The integrated circuit structures execute each of the functions described in the present specification through the control of one or more microprocessors or other control devices. Further, the components of the present disclosure may be specifically implemented by a part of a program or codes that include one or more executable instructions for performing a specific logical function and is executed by one or more microprocessors or other control devices. Furthermore, the components of the present disclosure may include or be implemented by a central processing unit (CPU), a microprocessor, etc. that perform each function. In addition, the components of the present disclosure may store instructions executed by one or more processors in one or more memories. 
     Although exemplary embodiments of the present disclosure have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the idea and scope of the claimed invention. Therefore, exemplary embodiments of the present disclosure have been described for the sake of brevity and clarity. The scope of the technical idea of the present embodiments is not limited by the illustrations. Accordingly, one of ordinary skill would understand that the scope of the claimed invention is not to be limited by the above explicitly described embodiments but by the claims and equivalents thereof.