Source: http://www.google.nl/patents/US20070258421?hl=nl&cl=fr
Timestamp: 2017-12-15 12:00:09
Document Index: 606137507

Matched Legal Cases: ['art 2006', 'art 2012', 'art 2012', 'art 2015', 'art 2016', 'art 2017', 'art 2002', 'art 2010', 'art 2014', 'art 2010']

Patent US20070258421 - Estimation of position using WLAN access point radio propagation ... - Google Patenten
A method for estimating position using WLAN access point radio propagation characteristics in a WLAN location based service is provided. A location-based services system has a plurality of Wi-Fi access points in a target area. The Wi-Fi access points are positioned at geographic locations and have signal...http://www.google.nl/patents/US20070258421?utm_source=gb-gplus-sharePatent US20070258421 - Estimation of position using WLAN access point radio propagation characteristics in a WLAN positioning system
Publicatienummer US20070258421 A1
Publicatiedatum 8 nov 2007
Ook gepubliceerd als CA2651853A1, CA2651853C, EP2022278A2, EP2022278A4, EP2022278B1, US7515578, US7916661, US8155673, US9052378, US20090154371, US20110164522, US20120196621, WO2007133967A2, WO2007133967A3
Publicatienummer 11430222, 430222, US 2007/0258421 A1, US 2007/258421 A1, US 20070258421 A1, US 20070258421A1, US 2007258421 A1, US 2007258421A1, US-A1-20070258421, US-A1-2007258421, US2007/0258421A1, US2007/258421A1, US20070258421 A1, US20070258421A1, US2007258421 A1, US2007258421A1
Oorspronkelijke patenteigenaar Farshid Alizadeh-Shabdiz, Kaveh Pahlavan
Patentcitaties (28), Verwijzingen naar dit patent (90), Classificaties (11), Juridische gebeurtenissen (3)
US 20070258421 A1
1. In a location-based services system having a plurality of Wi-Fi access points in a target area, the Wi-Fi access points being positioned at geographic locations and having signal coverage areas, a method of characterizing at least one of the Wi-Fi access points, comprising:
determining the geographic location of the Wi-Fi access point;
dividing the signal coverage area of the Wi-Fi access point into at least one section; and
determining radio propagation characteristics for each section;
wherein the radio propagation characteristics of each section characterize a radio channel of the Wi-Fi access point and wherein the characterization can be used in a location algorithm.
2. The method of claim 1, wherein the signal coverage area is one section.
3. The method of claim 1, wherein the sections are divided according to at least two radials from the Wi-Fi access point.
4. The method of claim 3, wherein the number of radials is six or less.
5. The method of claim 1, wherein the sections are divided according to at least one distance from the Wi-Fi access point.
6. The method of claim 5, wherein the number of distances is one.
7. The method of claim 1, wherein the sections are divided according to at least two radials and at least one distance from the Wi-Fi access point.
measuring a plurality of received signal power values within the signal coverage area, each received signal power value being measured at an associated position relative to the Wi-Fi access point; and
determining the sections based on the plurality of received signal power values and associated positions.
9. The method of claim 1, wherein the radio propagation characteristics include a signal power-distance gradient.
10. The method of claim 9, wherein the signal power-distance gradient for each section is determined by a method comprising:
measuring a plurality of received signal power values within the signal coverage area, each received signal power value being measured at an associated position relative to the Wi-Fi access point;
performing a linear regression on the plurality of received signal power values and associated positions; and
11. The method of claim 9, wherein the signal power-distance gradient for each section is determined by the method comprising:
calculating a distance corresponding to each of the signal power values, the distances being measured from the associated positions of the signal power values to the geographic locations of the Wi-Fi access points;
estimating an average radius of signal coverage using the standard deviation of the distances;
using the average radius of signal coverage to calculate the signal power-distance gradient.
12. The method of claim 11, wherein the standard deviation of the distances, σ, is calculated according to equations having the form
di is the distance of the associated position of received power value i from the Wi-Fi access point; and
N is the number of signal power values.
13. The method of claim 11, wherein the signal power-distance gradient, α, is calculated using equations having the form
15. A method for estimating the position of a Wi-Fi enabled device, the method comprising:
the Wi-Fi enabled device communicating with Wi-Fi access points within range of the Wi-Fi enabled device to cause the Wi-Fi access points to transmit signals;
the Wi-Fi enabled device receiving the signals transmitted by the Wi-Fi access points;
retrieving calculated locations and estimated radio propagation characteristics of the Wi-Fi access points from a reference database using Wi-Fi access point identifiers; and
using the calculated locations and the estimated radio propagation characteristics to estimate the position of the Wi-Fi enabled device.
16. The method of claim 15, wherein at least one of the Wi-Fi access points has a signal coverage area, the signal coverage area having at least one section, each section having corresponding radio propagation characteristics.
Embodiments of the present invention build on techniques, systems and methods disclosed in earlier filed applications, including but not limited to U.S. patent application Ser. No. 11/261,848, entitled Location Beacon Database, U.S. patent application Ser. No. 11/261, 898, entitled Server for Updating Location Beacon Database, U.S. patent application Ser. No. 11/261,987, entitled Method and System for Building a Location Beacon Database, and U.S. patent application Ser. No. 11/261,988, entitled Location-Based Services that Choose Location Algorithms Based on Number of Detected Access Points Within Range of User Device, all filed on Oct. 28, 2005, the contents of which are hereby incorporated by reference in its entirety. Those applications taught specific ways to gather high quality location data for Wi-Fi access points so that such data may be used in location based services to determine the geographic position of a Wi-Fi-enabled device utilizing such services and techniques of using said location data to estimate the position of a system user. The present techniques, however, are not limited to systems and methods disclosed in the incorporated patent applications. Thus, while reference to such systems and applications may be helpful, it is not believed necessary to understand the present embodiments or inventions.
FIG. 2 represents RSS samples [201] as points on a graph plotting RSS power (in dB) versus distance of the RSS sample from the access point (in dB) [206]. A signal power-distance gradient a can be determined by fitting a line [202] to the RSS sample points [201], where the slope of the line is equal to the signal power-distance gradient. Because a WLAN based positioning system according to embodiments of the invention use radio waves of public and private WLAN access points in order to continuously estimate position of a user, aspects of the invention increase the accuracy of location estimation by using individual radio propagation characteristics of each WLAN access point, rather than a standard value.
When the coverage area is not divided into multiple sections, and the whole area is considered as one area, the standard deviation is calculated based on all of the RSS readings around the access point. If the total number of RSS samples of the access point is denoted by N and corresponding latitude and longitude of RSS sample i are denoted by (lati, longi), the standard deviation, a, of the radius of coverage area is calculated as follows: σ = σ x 2 + σ y 2 , In which σ x 2 = ∑ i = 1 N ( d xi ) 2 N - 1 , N > 1 σ x = 0 , N = 1 , σ y 2 = ∑ i = 1 N ( d yi ) 2 N - 1 , N > 1 σ y = 0 , N = 1 ,
The variables dxi and dyi are the distances of power sample from the WLAN access point in the X and Y directions in Cartesian coordinates. The standard deviation calculation can be simplified as follows: σ = σ lat 2 + σ long 2 , In which σ lat 2 = ∑ 1 N ( lat i - lat ) 2 N - 1 , N > 1 σ lat = 0 , N = 1 , σ long 2 = ∑ 1 N ( long i - long ) 2 N - 1 , N > 1 σ long = 0 , N = 1 ,
In this equation, (lat, long) is the calculated location of the WLAN access point. The average radius of coverage is calculated based on a Cartesian presentation of location. Calculation of the radius of coverage can also be simplified by considering latitude and longitude without converting them to Cartesian coordinates. If the coverage area is divided into multiple sectors, the standard deviation is calculated based on the distance of RSS samples from the WLAN access point, which can be considered in one dimension. Therefore, the standard deviation is calculated as follows: σ = ∑ 1 N ( d i ) 2 N - 1 , N > 1 σ = 0 , N = 1 ,
The standard deviation of a radius of the coverage area is translated to the signal power-distance gradient using following equation: α = α min , if ( σ > σ max ) α = α max , if ( σ < σ min ) α = α max + ( α min - α max ) ( log ( σ ) - log ( σ min ) log ( σ max ) - log ( σ min ) ) , otherwise .
According to embodiments of the invention, signal power-distance gradient(s) for each WLAN access point may be used by the user to find its distance to each WLAN access point in range and consequently locate itself. Signal power-distance gradient can be used in the following equation to find the distance: d = K P RSS α
Under aspects of the invention, the location of access point, (lat, long), may be calculated. If the exact location of an access point is not known, the RSS samples and their corresponding locations can be used to estimate the location of the access point. For example, location of the access point can be found by finding the center of power readings as follows: lat = ∑ i = 1 N lat i N long = ∑ i = 1 N long i N
If a user detects N number of access points with a corresponding RSS value of Pi, a signal power-distance gradient of αi, a latitude of lati, and a longitude of longi, the distance of the user to the access points is calculated as follows: d i = 1 P i α i
Latitude and longitude of the user, Ulat and Ulong, can be found as follows: U lat = ∑ i = 1 N lat i d i ∑ i = 1 N 1 d i U long = ∑ i = 1 N long i d i ∑ i = 1 N 1 d i
Under another aspect of the invention, the RSS value reading by the end user can be normalized, and the RSS power reading can be used to select the correct value of radio propagation characteristics, e.g., a signal power-distance gradient, in the case of multi tier approach. When a coverage area is divided into multiple tiers with piecewise linear estimation of the coverage area, the user must be able to determine in which tier he is located, and use the radio propagation characteristics.
In this case, there is a need to normalize the RSS power reading across different hardware and different Wi-Fi receiver implementations. In order to normalize the RSS power reading, the minimum and the maximum power sensitivity of the user's device are mapped to the dynamic power range of the scanner used to supply data to the reference database [104].
For example, if the standard minimum power and the maximum power values are set to −100 dBm and −40 dBm, respectively, and a user device's minimum and maximum range is between −90 dBm and −60 dBm, the power readings of the user is normalized as follows: P new = [ P old - ( - 90 ) ] ( - 40 - ( - 100 ) - 60 - ( - 90 ) ) + ( - 100 )
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Classificatie in de VS 370/338
Internationale classificatie H04W64/00, G01S19/48, G01S19/25, G01S19/42, G01S5/02
Coöperatieve classificatie H04W64/00, G01S11/06, G01S5/0252