# US 8,787,930 B2 · Method and apparatus for estimating position of access point in Wi-Fi system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,930 B2 - Document ID: US8787930B2 - Status: Granted - Kind: B2 - Application number: 13/286,716 - Filed: 2011-11-01 - Published: 2012-05-17 - Granted: 2014-07-22 - Earliest claimed: 2010-11-15 - Assignees: Electronics and Telecommunications Research Institute - Applicants: Uzair Ahmad; Wan Sik Choi; Sang Joon Park; Young Su Cho; Do Hyun Kim; Dong Kyoo Kim; Sung Jo Yun; Myung In Ji - Inventors: Uzair Ahmad; Wan Sik Choi; Sang Joon Park; Young Su Cho; Do Hyun Kim; Dong Kyoo Kim; Sung Jo Yun; Myung In Ji - Web page: https://patentgrep.com/patent/US8787930B2 ## CPC - H04W 64/003: {locating network equipment} - G01S 5/14: Determining absolute distances from a plurality of spaced points of known location - G01S 11/06: using intensity measurements - H04W 24/10: Scheduling measurement reports {; Arrangements for measurement reports} - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) - G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES ## Abstract A method and apparatus for estimating a position of an access point (AP) includes (a) measuring a strength of a signal, transmitted by the AP, at three or more measurement points (MPs), (b) selecting an imaginary attenuation factor, (c) calculating a range between the AP and each of the MPs on the basis of the imaginary attenuation factor and a strength of a signal measured at the MP, (d) calculating an intersecting point of ranging circles in each of which a position of the MP is a center and the range between the MP and the AP is a radius, (e) calculating a best intersecting point from among a plurality of the intersecting points obtained by repeating the steps (c) and (d) while changing the imaginary attenuation factor, and (f) estimating the best intersecting point as the position of the AP. ## Claims ### Claim 1 A method of estimating a position of an access point (AP) in a Wi-Fi system, the method comprising: measuring a strength of a signal, transmitted by the AP, at three or more measurement points (MPs); selecting an imaginary attenuation factor; calculating a range between the AP and each of the MPs based on the imaginary attenuation factor and a strength of a signal measured at each of the MP; calculating an intersecting point of ranging circles in each of which a position of the MP is a center and the range between the MP and the AP is a radius; calculating a best intersecting point from among a plurality of the intersecting points obtained by repeating the calculating the range and the calculating the intersecting point of ranging circles while changing the imaginary attenuation factor; and estimating the best intersecting point as the position of the AP. ### Claim 2 (depends on 1) The method of claim 1, wherein the imaginary attenuation factor is changed at an interval of 0.1 between 2 to 6. ### Claim 3 (depends on 1) The method of claim 1, wherein in the calculating the range, the range between the MP and the AP is calculated according to Equation below: d ai = d o ⁢ 10 ( P o - RSS ai 10 × α ) wherein d0 is a standard distance, P0 is a nominal signal strength of the AP, α is an imaginary attenuation factor, and RSSai is an average value of the strength of the signal. ### Claim 4 (depends on 1) The method of claim 1, wherein in the calculating the intersecting point of ranging circles, a number of the intersecting points of the ranging circles is 2. ### Claim 5 (depends on 4) The method of claim 4, further comprising determining whether a number of intersecting points of the ranging circles is 2 and a change of the strength of the signal is smaller than a specific threshold value. ### Claim 6 (depends on 5) The method of claim 5, further comprising changing the strength of the signal by the change, if, as a result of the determination, the number of intersecting points of the ranging circles is not 2 and the change of the strength of the signal is smaller than the specific threshold value. ### Claim 7 (depends on 1) The method of claim 1, wherein in the estimating, the position of the AP is estimated using an iterative Least-Square (LS) algorithm. ### Claim 8 An apparatus for estimating a position of an AP in a Wi-Fi system, the apparatus comprising: a Radio Frequency (RF) unit configured to transmit or receive a radio signal; and a processor, coupled to the RF unit, and configured to: measure a strength of a signal, transmitted by the AP, at three or more MPs, select an imaginary attenuation factor, calculate a range between the AP and each of the MPs based on the selected imaginary attenuation factor and the strength of the signal measured at each of the MP, calculating an intersecting point of ranging circles in each of which a position of the MP is a center and the range between the MP and the AP is a radius; and estimate a best intersecting point, from among the calculated intersection points, as the position of the AP. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein the imaginary attenuation factor is changed at an interval of 0.1 between 2 to 6. ### Claim 10 (depends on 8) The apparatus of claim 8, wherein the range between the MP and the AP is calculated according to Equation below: d ai = d o ⁢ 10 ( P o - RSS ai 10 × α ) wherein d0 is a standard distance, P0 is a nominal signal strength of the AP, α is an imaginary attenuation factor, and RSSai is an average value of the strength of the signal. ### Claim 11 (depends on 8) The apparatus of claim 8, wherein a number of the intersecting points of the ranging circles is 2. ### Claim 12 (depends on 11) The apparatus of claim 11, wherein the processor is further configured to determine whether a number of the intersecting points of the ranging circles is 2 and a change of the strength of the signal is smaller than a specific threshold value. ### Claim 13 (depends on 12) The apparatus of claim 12, wherein the processor is further configured to change the strength of the signal by the change, if, as a result of the determination, the number of intersecting points of the ranging circles is not 2 and the change of the strength of the signal is smaller than the specific threshold value. ### Claim 14 (depends on 8) The apparatus of claim 8, wherein the position of the AP is estimated using an iterative LS algorithm.