Methods and systems for improving the accuracy of expected error estimation in a hybrid positioning system   

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/059,580, filed on Jun. 6, 2008, entitled Integrated WLAN-based and Satellite-based Positioning System, which is herein incorporated by reference in its entirety.

This application is related to the following references:

U.S. patent application Ser. No. (TBA), filed concurrently herewith and entitled “Method and System for Determining Location Using a Hybrid Satellite and WLAN Positioning System by Selecting the Best WLAN-PS Solution;”

U.S. patent application Ser. No. (TBA), filed concurrently herewith and entitled “Systems and methods for Using Environmental Information in a Hybrid Positioning System;”

U.S. patent application Ser. No. (TBA), filed concurrently herewith and entitled “Systems and Methods for Maintaining Clock Bias Accuracy in a Hybrid Positioning System;”

U.S. patent application Ser. No. (TBA), filed concurrently herewith and entitled “System and Method for Refining a WLAN-PS Estimated Location Using Satellite Measurements in a Hybrid Positioning System;”

U.S. patent application Ser. No. (TBA), filed concurrently herewith and entitled “Method and System for Determining Position Using a WLAN-PS Estimated Position as an Initial Position in a Hybrid Positioning System;”

U.S. patent application Ser. No. (TBA), filed concurrently herewith and entitled “Methods and Systems for Stationary User Detection in a Hybrid Positioning System;” and

U.S. patent application Ser. No. (TBA), filed concurrently herewith and entitled “System and Methodfor Using a Satellite Positioning System to Filter WLAN Access Points in a Hybrid Positioning System.”

1. Field

The disclosure generally relates to hybrid positioning systems and, more specifically, to methods of integrating wireless local area network (WLAN)-based positioning system (WLAN-PS) and satellite-based positioning system (SPS) to improve accuracy of location estimates, increase availability of the positioning service to more users, reduce power consumption, and also to improve estimation of the expected error in a user\'s position estimate.

2. Description of Related Art

In recent years the number of mobile computing devices has increased dramatically, creating the need for more advanced mobile and wireless services. Mobile email, walkie-talkie services, multi-player gaming, and call-following are examples of how new applications are emerging for mobile devices. In addition, users are beginning to demand/seek applications that not only utilize their current location but also share that location information with others. Parents wish to keep track of their children, supervisors need to track the locations of the company\'s delivery vehicles, and a business traveler looks to find the nearest pharmacy to pick up a prescription. All of these examples require an individual to know his own current location or the location of someone else. To date, we all rely on asking for directions, calling someone to ask their whereabouts or having workers check-in from time to time to report their positions.

Location-based services are an emerging area of mobile applications that leverage the ability of new devices to calculate their current geographic positions and report them to a user or to a service. Examples of these services range from obtaining local weather, traffic updates, and driving directions to child trackers, buddy finders, and urban concierge services. These new location-sensitive devices rely on a variety of technologies that all use the same general concept. By measuring radio signals originating from known reference points, these devices can mathematically calculate the user\'s position relative to these reference points. Each of these approaches has its strengths and weaknesses, depending upon the nature of the signals and measurements, and the positioning algorithms employed.

The Navstar Global Positioning System (GPS) operated by the US Government leverages about two-dozen orbiting satellites in medium-earth orbits as reference points. A user equipped with a GPS receiver can estimate his three-dimensional position (latitude, longitude, and altitude) anywhere at any time within several meters of the true location, as long as the receiver can see enough of the sky to have four or more satellites “in view.” Cellular carriers have used signals originating from and received at cell towers to determine a user\'s or a mobile device\'s location. Assisted GPS (AGPS) is another model that combines both GPS and cellular tower techniques to estimate the locations of mobile users who may be indoors and must cope with attenuation of GPS signals on account of sky blockage. In this model, the cellular network attempts to help a GPS receiver improve its signal reception by transmitting information about the satellite positions, their clock offsets, a precise estimate of the current time, and a rough location of the user based on the location of cell towers. No distinction is made in what follows between GPS and AGPS.

All positioning systems using satellites as reference points are referred to herein as Satellite-based Positioning System (SPS). While GPS is the only operational SPS at this writing, other systems are under development or in planning. A Russian system called GLONASS and a European system called Galileo may become operational in the next few years. All such systems are referred to herein as SPS. GPS, GLONASS and Galileo are all based on the same basic idea of trilateration, i.e., estimating a position on the basis of measurements of ranges to the satellites whose positions are known. In each case, the satellites transmit the values of certain parameters which allow the receiver to compute the satellite position at a specific instant. The ranges to satellites from a receiver are measured in terms of the transit times of the signals. These range measurements can contain a common bias due to the lack of synchronization between the satellite and receiver (user device) clocks, and are referred to as pseudoranges. The lack of synchronization between the satellite clock and the receiver (user device) clock results in a difference between the receiver clock and the satellite clock, which is referred to as internal SPS receiver clock bias or receiver clock bias, here. In order to estimate a three dimensional position there is a need for four satellites to estimate receiver clock bias along with three dimensional measurements. Additional measurements from each satellite correspond to pseudorange rates in the form of Doppler frequency. References below to raw SPS measurements are intended generally to mean pseudoranges and Doppler frequency measurements. References to SPS data are intended generally to mean data broadcast by the satellites. References to an SPS equation are intended to mean a mathematical equation relating the measurements and data from a satellite to the position and velocity of an SPS receiver.

WLAN-based positioning is a technology which uses WLAN access points to determine the location of mobile users. Metro-wide WLAN-based positioning systems have been explored by a several research labs. The most important research efforts in this area have been conducted by the PlaceLab (www.placelab.com, a project sponsored by Microsoft and Intel); the University of California, San Diego ActiveCampus project (ActiveCampus—Sustaining Educational Communities through Mobile Technology, technical report #CS2002-0714); and the MIT campus-wide location system. There is only one commercial metropolitan WLAN-based positioning system in the market at the time of this writing, and it is referred to herein as the WPS (WiFi positioning system) product of Skyhook Wireless, Inc. (www.skyhookwireless.com).

FIG. 1 depicts a conventional WLAN-based positioning system based on WiFi signals. The positioning system includes positioning software 103 that resides on a mobile or user device 101. Throughout a particular target geographical area, there are a plurality of fixed wireless access points 102 that transmit information using control/common channel signals. The device 101 monitors these transmissions. Each access point contains a unique hardware identifier known as a MAC address. The client positioning software 103 receives transmissions from the 802.11 access points in its range and calculates the geographic location of the computing device using the characteristics of the radio signals. Those characteristics include the MAC addresses, the unique identifiers of the 802.11 access points, the Time of Arrival (TOA) of the signals, and the signal strength at the client device 101. The client software 103 compares the observed 802.11 access points with those in its reference database 104 of access points. This reference database 104 may or may not reside in the device 101. The reference database 104 contains the calculated geographic locations and power profiles of all access points the system has collected. A power profile may be generated from a collection of measurements of the signal power or signal TOA at various locations. Using these known locations or power profiles, the client software 103 calculates the position of the user device 101 relative to the known positions of the access points 102 and determines the device\'s 101 absolute geographic coordinates in the form of latitude and longitude or latitude, longitude, and altitude. These readings then can be fed to location-based applications such as friend finders, local search web sites, fleet management systems, and an E911 service.

In the discussion herein, raw WLAN measurements from an access point are generally intended to mean received signal strength (RSS) and/or times of arrival (TOAs) and/or time differences of arrival (TDOAs). References to data are generally intended to mean the MAC address, one or more record(s) of it, one or more power profile(s), and other attributes based on previous measurements of that access point. References to a WLAN-PS equation are intended to mean a mathematical equation relating the WLAN-PS measurements and data to the location of the mobile device.

A WLAN-based positioning systems can be used indoor or outdoor. The only requirement is presence of WLAN access points in the vicinity of the user. The WLAN-based position systems can be leveraged using existing off-the-shelf WLAN cards without any modification other than to employ logic to estimate position.

FIG. 2 illustrates a conventional way of integrating WLAN-PS and SPS, which consists of a WLAN-PS 201 and a SPS 206, and a location combining logic 210.

WLAN-PS 201 and SPS 206 are stand-alone systems and each can operate independently of the other system. Thus the result of each system can be calculated independent of the other system. The estimated location along with the expected error estimation of each system can be fed to the location combining logic 210. The expected error estimation is also referred to as HPE (horizontal positioning error) herein. The nominal rate of location update of SPS 206 and WLAN-PS 201 is once a second. The location combining logic 210 combines location estimates calculated in the same second by both systems.

WLAN-PS 201 is a conventional system which estimates the location of a mobile device by using WLAN access points. WLAN-PS 201 can include a scanner of WLAN APs 202, a device to select WLAN APs 203, a trilateration module 204, and HPE estimation device 205.

WLAN Scanner 202 detects WLAN APs surrounding the mobile device by detecting the received power (RSS, received signal strength) and/or time of arrival (TOA) of the signal. Different methods can be used to detect WLAN APs including active scanning, passive scanning, or combination of passive and active scanning.

The select WLAN APs device 203 selects the best set of WLAN APs to estimate location of the mobile device. For example, if ten WLAN APs are detected and one AP is located in Chicago and the others are located in Boston, without any other information, the Boston APs are selected. This is an indication that Chicago AP has been moved to Boston. In the conventional system the best set of WLAN APs is selected based on geographical distribution of WLAN APs in addition to corresponding parameters of WLAN APs, including received signal strength, signal to noise ration, and the probability of being moved.

Trilateration module 204 uses WLAN APs and corresponding measurements and characteristics to estimate location of the mobile device. Received signal strength or TOA measurements from WLAN AP are used to estimate distance of the mobile device to the WLAN AP. The aggregation of distance estimates from different WLAN APs with known location is used to calculate location of the mobile device. Trilateration 204 also can use a method which is called nearest neighbor, in which a location with a power profile similar or closest to the power reading of the mobile device is reported as the final location of the mobile device. The power profile of each WLAN AP or entire coverage area can be found in the calibration phase of the system by detailed survey of the coverage area.

HPE estimation device 205 is the module which estimates the expected error of the position estimate of the mobile device. The HPE, or Horizontal Positioning Error is calculated based on previously scanned APs and their characteristics and also characteristics of the received signal, as it was explained in co-pending Skyhook Wireless application Ser. No. 11/625,450 entitled “System and Method for Estimating Positioning Error Within a WLAN Based Positioning System,” the entire disclosure of which is hereby incorporated by reference.

SPS system 206 consists of a satellite signal receiver and measurement device 207, trilateration device 208, and the SPS HPE estimation module 209.

The satellite signal receiver and measurement device 207 receives signals from the satellites in view of the device, decodes the received signal, and measures the satellite parameters from each satellite. The measurements can include pseudorange, carrier frequency, and Doppler frequency.

The trilateration device 208 uses measurements from at least four satellites and location of the satellites in view to estimate location of the user device, velocity, and direction of travel of the mobile device.

HPE estimation device 209 estimates the expected error of the estimated location. The HPE estimation device 209 is conventional and calculates expected error based on geometry of the satellites and signal quality of the received signal from satellites, for example, DOP (dilution of precision), and C/N (carrier to noise ratio).

Location combining logic 210 receives location and HPE estimates calculated for almost the same second from WLAN-PS 201 and SPS 206. In other words, measurements and estimations which are made at the same time are compared and combined. Practically, measurements and estimations within one second can be considered the same time. The location combining logic 210 of the user device reports one estimated location by selecting one of them or linearly combining them. For example, location combining logic might select one of the estimated locations provided by WLAN-PS 201 or SPS 206 based on reported expected error or HPE, or it might report weighted average of estimated locations by both systems according to the HPE.

SUMMARY

This disclosure describes methods and systems for improving the accuracy of expected error estimation in a hybrid positioning system. In some embodiments, the method of determining an expected error in a location determination of a WLAN and satellite enabled device can include determining a WLAN location estimate and an expected error estimate for the WLAN location estimate, obtaining measurements from at least two satellites, and determining the expected error of the location determination by evaluating the consistency of the satellite positioning system measurements to the WLAN positioning system location estimation.

In some embodiments, consistent measurements between the WLAN location estimate and the satellite positioning system measurements can result in a lower expected error in the location determination.

In some embodiments, inconsistent measurements between the WLAN location estimate and the satellite positioning system measurements can result in a higher expected error in the location determination.

In some embodiments, consistency of the measurements can include the distance between the WLAN positioning system location estimation and a region of possible solutions provided by the satellite positioning system measurements.

In some embodiments, the consistency of the internal SPS receiver clock for the WLAN based position estimate can be used as an indication of consistency between the WLAN based position estimate and the satellite measurements.

In some embodiments, the method can include determining a WLAN based location estimate and an expected error estimate for the WLAN location estimate, determining a satellite based location estimate and an expected error estimate for the satellite based location estimate, determining the expected error of the location determination by evaluating the consistency of the satellite positioning system location estimate to the WLAN positioning system location estimation.

In some embodiments, the position estimate with the lower expected error can be selected as the location of the WLAN and satellite enabled device.

In some embodiments, the method can include determining the expected error of the location determination by comparing the WLAN location estimate and the satellite positioning system location estimate.

In some embodiments, consistent measurements between the WLAN location estimate and the satellite positioning system location estimate can result in a lower expected error in the location determination.

In some embodiments, inconsistent measurements between the WLAN location estimate and the satellite positioning system location estimate can result in a higher expected error in the location determination.

In some embodiments, the consistency of the estimates can include the distance between the satellite positioning system location estimate and the WLAN positioning system location estimation.

In some embodiments, the method can include the internal SPS receiver clock for the WLAN based position estimate is used as an indication of consistency between the WLAN based position estimate and the satellite positioning system location.

Some embodiments relate to a system for increasing the accuracy of a WLAN based position estimate using satellite positioning information. The system can include a positioning module including a WLAN module for receiving information from one or more WLAN access points to calculate a WLAN location estimate, a satellite positioning module for obtaining satellite information from at least two different satellites, and logic located in the positioning module for determining the expected error of the location determination by evaluating the consistency of the satellite positioning system measurements to the WLAN positioning system location estimation.

Some embodiments relate to a system for increasing the accuracy of a WLAN based position estimate using satellite positioning information. The system can include a positioning module including a WLAN module for receiving information from one or more WLAN access points and to calculate a WLAN position estimate, a satellite positioning module for obtaining satellite information from at least four different satellites to calculate a satellite position estimate, and logic located in the positioning module for determining the expected error of the location determination by evaluating the consistency of the satellite positioning system location estimate to the WLAN positioning system location estimation.

For a more complete understanding of various embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:

FIG. 1 illustrates a high-level architecture of a WLAN positing system;

FIG. 2 illustrates a system for a conventional way of integrating WLAN-PS and SPS;

FIG. 3 illustrates a system for providing a WLAN-PS and SPS integrated solution according to some embodiments of the disclosed subject matter;

FIG. 4 illustrates an example of selecting a solution between possible WLAN-PS solutions using raw SPS measurements from two satellites according to some embodiments of the disclosed subject matter;

FIG. 5 illustrates a system for integrating WLAN-PS and SPS in which raw SPS measurements are provided to WLAN-PS to select the best solution according to some embodiments of the disclosed subject matter;

FIG. 6 illustrates an example of selecting a solution between possible WLAN-PS solutions based on SPS possible solutions according to some embodiments of the disclosed subject matter;

FIG. 7 illustrates an example of selecting the best set of WLAN APs based on raw SPS measurements according to some embodiments of the disclosed subject matter;

FIG. 8 illustrates a system for integrating WLAN-PS and SPS and using raw SPS measurements from two or more satellites to select a set of WLAN APs in WLAN-PS according to some embodiments of the disclosed subject matter;

FIG. 9 illustrates a system for examining the location estimate and uncertainty provided by WLAN-PS against SPS in order to find the best estimate of the location of a mobile device according to some embodiments of the disclosed subject matter;

FIG. 10 illustrates a system for examining the location estimate and uncertainty provided by WLAN-PS against SPS in order to find the best estimate of the location of a mobile device by using the grid method according to some embodiments of the disclosed subject matter;

FIG. 11 illustrates a system for integrating WLAN-PS and SPS, in which raw SPS measurements are used to refine WLAN-PS location estimate according to some embodiments of the disclosed subject matter;

FIG. 12 illustrates a system for integrating WLAN-PS and SPS, in which as WLAN-PS location estimate is provided as initial location estimate according to some embodiments of the disclosed subject matter;

FIG. 13 illustrates an example for increasing accuracy of the estimation of expected error by using SPS and WLAN-PS information according to some embodiments of the disclosed subject matter;

FIG. 14 illustrates a system for increasing accuracy of the estimation of expected error by using SPS and WLAN-PS information according to some embodiments of the disclosed subject matter;

FIG. 15 illustrates a system for stationary user detection based on two or more satellites according to some embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

Embodiments of the disclosed subject matter provide a method of integrating a WLAN-based positioning system (WLAN-PS) and a satellite-based positioning system (SPS) to create a hybrid positioning system. An integrated or hybrid system refers to a system which combines the measurements from one or more systems to improve the accuracy of the positioning and velocity and bearing estimates and the accuracy of expected error estimate, and to reduce consumed power as compared to each individual system working independently. The method of integrating a WLAN-PS and SPS to create a hybrid positioning system can add raw SPS measurements as another input to WLAN-PS and WLAN-PS final estimations as another input to SPS. Raw SPS measurements from two or more satellites can assist the WLAN-PS to increase the accuracy of position estimate, HPE, and stationary user detection. WLAN-PS initial position estimate and other estimations also can help SPS to reduce time to first fix (TTFF) and power consumption. A hybrid positioning system also can reduce power consumption compared to WLAN-PS and SPS working independently by deactivating WLAN-PS or SPS when they are not adding value in terms of increasing accuracy or other estimations.

FIG. 3 illustrates a block diagram of the hybrid system of a WLAN-PS 301 and a SPS 306.

SPS 306 is an off-the-shelf, conventional satellite positioning device which consists of the same devices as SPS 206 in FIG. 2, with addition of an output 311 and an input 312 from the WLAN-PS (discussed in more detail herein). Satellite receiver and measurement device 207 is part of every conventional SPS receiver 306, and raw SPS measurements are an essential part of the SPS measurement. However, here the raw SPS measurements are used outside the SPS 306, as is shown by output 311. Not all the commercial SPS receivers expose the raw SPS measurements to devices outside SPS 306. For example, Star III GPS manufactured by SiRF Technology, Inc. (San Jose, Calif.) provides raw SPS measurements as part of its standard interface. However there are some other GPS receivers that do not provide such measurements. For the SPS receivers that do not expose raw SPS measurements as part of their standard interface, the SPS receiver 306 is modified to permit access to the raw SPS measurements.

The WLAN-PS 301 functions in a similar manner as the WLAN-PS 201 shown in FIG. 2 except that it is configured to receive raw SPS measurements 311. The integration of the raw SPS measurement with WLAN-PS 301 changes the design of WLAN APs selection device 303, trilateration device 304, and HPE estimation device 305. The WLAN-PS 301 can take advantage of the raw SPS measurements when at least two satellites are acquired, even without any fix or solution from the SPS 306.

This design change of WLAN-PS 301 after receiving raw SPS measurements is discussed in more detail herein.

Under one embodiment, the disclosed method integrates a WLAN-based positioning system (WLAN-PS) and a satellite-based positioning system (SPS) in which the WLAN-PS provides a set of possible locations of a mobile device, and among the possible locations, the one which fits the SPS measurements the best is selected as the final position estimate.

This embodiment also can provide a method to integrate WLAN-based positioning system (WLAN-PS) and satellite-based positioning system (SPS) in which the WLAN-PS provides a set of possible locations for the mobile device, and the possible locations are weighted according to their distance to a plurality of possible SPS device location solutions. In other words, weights are assigned to WLAN-PS possible solutions according how well they correspond to the satellite measurements. After assigning a weight to each possible location, various algorithms can be used to combine or select WLAN-PS possible locations. For example, the final reported location can be weighted by an average of all possible locations, low weight locations can be removed from the weighted average, or only the highest weighted location can be reported. Selection can be a special case of weighting, in which the respective weights are zero and one.

For example, because of the high density of WLAN APs in some areas, WLAN-PS can detect tens of WLAN APs in a given location. The detected WLAN APs may form more than one cluster. A cluster is defined as a set of APs in the coverage area of each other. If the coverage of a WLAN AP is not known, a nominal coverage can be considered. Nominal coverage or typical coverage of a WLAN AP is found statistically by measuring coverage for thousands of WLAN APs, and it is reported numbers between 100 m and 250 m at the time of writing this document. For example, if a mobile device detects fifteen WLAN APs, in which ten of them are located in a high-rise building and the other five are located in an office building far from the high-rise building (for example, 500 meters away from the high rise building), the detected WLAN APs can be considered as two clusters with a size of ten and five, respectively. Conventional positioning algorithms would select the cluster with a higher number of APs: the cluster of ten APs. Under the conventional approach, the location would be somewhere in the high-rise building. However, if raw SPS measurements from two or more satellites are considered with the cluster information, even with no location estimate from SPS, the raw SPS measurements can be used to select the appropriate cluster of WLAN APs from the plurality of clusters. In this example, the cluster of five WLAN APs might be selected as the closest cluster to the location of the mobile device, because it also satisfies the SPS equations. SPS measurements also can be used to assign a weight to the clusters of five and ten APs according to their estimated distance from possible SPS solutions. After assigning a weight to clusters, logic can be used to combine the estimation results of clusters and report only one location. For example, the weighted average of estimation results of clusters, estimations of the cluster with maximum weight, or average of estimation of clusters with higher weights can be reported as final estimation results.

The first step is detecting WLAN access points, which will be used as reference points to locate the user device. WLAN access points are randomly distributed, and they also might move over time. Therefore, the WLAN positioning system applies a clustering algorithm to identify all the clusters of WLAN access points that are detected by the end user.

A cluster of WLAN access points is a set of WLAN access points which are in the coverage area of each other. WLAN access points which are farther than a normal coverage of an access point from the cluster are considered as a new cluster.

For example, a user detects four access points and three of them are located in Boston and one of them in Seattle. Therefore, they form two clusters: one in Boston with three WLAN access points and one in Seattle with one WLAN access point. Each cluster of WLAN access point can result to a separate location in a WLAN positioning system. If the mobile device also acquires signals from two or more satellites, the satellite measurements can be used to select the cluster of WLAN access points or reject clusters of WLAN access points. Two or more satellite measurements provide a set of solutions in a form of a region (volume, surface or a curve). The proximity of possible WPS solutions to SPS possible solutions can be criteria to weight, select, or reject WPS solutions. In other words, the closer the WLAN-PS solution to the SPS solutions, the higher the quality of the WLAN-PS solution.

For example, FIG. 4 shows a WLAN-PS 401, which consists of five WLAN access points 404. The WLAN access points form two clusters in this example, a first cluster 402 and a second cluster 403. Each cluster can be used to estimate the location of the user device. If the user device acquires a signal from at least two satellites 405, the possible solutions of the two or more satellites 406 can be used to select or eliminate some clusters. In this example, possible solution of the two or more satellites is shown as a band 406. Cluster 402 is closer to the possible satellite solutions band 406 than cluster 403. Therefore, cluster 402 can be selected and cluster 403 can be rejected.

FIG. 5 illustrates block diagram of integrated solution of SPS and WLAN-PS. SPS 506 can be a standard, off-the-shelf device, but it has to be able to provide raw SPS measurements as discussed in FIG. 3. The raw SPS measurements 311 are directed to WLAN APs 503 and trilateration device 504.

The WLAN APs selection devices 503 receives the data from WLAN scanner 202 as an input. The WLAN APs selection device 503 clusters WLAN APs based on the distance between the access points. The WLAN APs selection device 503 not only identifies clusters, but also selects a different set of WLAN APs for each cluster. Each different cluster may result in a different location estimate. All of the different sets of clusters can be used in the trilateration device 504 and may result in a different location estimate. The location estimates based on clusters can be weighted according to the cluster distance from the SPS possible solutions or can be selected according to their cluster distance from SPS possible solutions. A cluster can be assigned a high weight if it is considered close (at a small distance) from the satellite distance solution. For example, if the cluster is located on the order of 10 meters away from the satellite distance solution. A cluster can be assigned a low weight if it is considered far (at a large distance) from the satellite distance solution, for example, if it is located on the order of 100 or 1,000 meters away from the satellite distance solution.

The SPS solutions can be found as follows. In each satellite measurement, there are generally four unknowns coordinates of location of the mobile device, (x,y,z) and internal clock bias of SPS receiver. The raw SPS measurements from two or more satellites can be used to eliminate the internal clock bias of the SPS receiver from the equations. In this case, the result is going to be a function of coordinates of the location of the user device, (x,y,z), which can be written as a general form as follows:

F(x,y,z)=0.

This function can represent an area, a surface, or a curve based on number of satellites. Therefore, raw SPS measurements from two or more satellites can result in a set of possible solutions, even without having a final location estimate.

The distance between the different solutions of WLAN-PS and possible solutions of SPS can be used as criteria to weigh each WLAN-PS solution. After assigning a weight to each WLAN-PS possible solution, logic can be used to combine the solution or select the solution from the possible solutions.

Further, the consistency between the SPS measurements and the locations provided by the WLAN-PS can be used as an indication of distance between the locations provided by the WLAN-PS and location of the mobile device. The location of the user device can be calculated by (1) using the possible WLAN-PS locations as rough estimates of the location of the user device (i.e., using each possible WLAN-PS location as the x,y,z) and (2) calculating the final unknown, internal satellite receiver clock bias, for each WLAN-PS location estimate using the measurements from each satellite. The consistency between the calculated internal satellite receiver clock biases (calculated for each satellite in view) for each WLAN location estimate can be used as an indicator of distance between WLAN-PS\'s location estimate and the mobile device actual location. Good WLAN-PS estimates will have consistent receiver clock bias estimates, i.e., when that WLAN-PS estimated location is used as the x,y,z location, for each satellite, the receiver clock bias will be substantially the same, for example, within about 10% of each other. However, if the WLAN-PS location is a poor estimate of the location of the user device, the WLAN-PS location will produce varied satellite receiver clock bias estimates for each satellite, for example, the receiver clock biases will vary by at more than 10%.

If clock bias which is found for each satellite measurement is denoted by Ci, the consistency of Ci can be used as a measure of distance between a given position (in this case, locations determined by the WLAN-PS) and the locations that satisfy the satellite equations. The consistency of Ci can be measured with different mathematical approaches, like standard deviation of Ci, or mean square error of Ci estimation as follows:

C _ = ∑ i = 1 N  C i N M   S   E = ∑ i = 1 N  ( C i - C _ ) 2 N

The value of MSE can be used as an indicator of the consistency of the Ci samples. Therefore, all possible locations of WLAN-PS can be examined with SPS raw measurements, and the consistency of Ci can be used as an indicator of the solution\'s distance to the actual mobile device location. This distance can be used with other WLAN AP parameters to weight or select or deselect (remove) an AP in the process of calculating the mobile device location.

FIG. 6 shows SPS solution in form of a region 606 and a WLAN positioning system 601, in which WLAN access points 604 form a first cluster 602 and a second cluster 603. The mobile device acquisition of two or more satellites 605 also can result in a set of possible satellite device solutions 606. The consistency between the SPS solutions 606 and WLAN-PS solutions 602 is used to select the best solution, which is the 602 solution of WLAN-PS in this example. The consistency between the SPS and WLAN-PS means both of them report the same location as part of their solutions or that the final estimated position is one of the solutions of both systems. Further, a cluster of APs can be weighted according to their distance to possible solutions of SPS.

Another embodiment of the disclosed subject matter provides a method to weigh WLAN access points by using raw SPS measurements. Selecting the best set of WLAN access points to estimate end user\'s location by using raw SPS measurements can be a specific case of assigning a weight to WLAN APs. In addition to other criteria used to weight or select the best set of WLAN access points to estimate the mobile device location, raw SPS measurements can be used or combined with the other criteria. Other criteria and weights are weight based on received signal strength or weight based on round trip time of received signal. The WLAN-PS uses WLAN APs and their characteristics to estimate the location of a mobile device.

The characteristics of a WLAN AP might include, but are not limited to, received signal strength (RSS), location or estimation of location, signal to noise ratio, and time of arrival (TOA). Raw SPS measurements from two or more satellites are used to calculate an indication of distance between location (or estimated location) of WLAN APs and actual location of the mobile device. This indication of distance can be used to select the best set of WLAN APs to estimate location of the mobile device, or the indicator of distance can be used to weight WLAN APs according to their distance from the device location. The raw SPS measurements from at least two satellites can be used in this process, with or without having a location estimate from SPS. The distance is considered far if the distance is more than an order of magnitude larger than the coverage area of the WLAN AP. A distance is considered close or not far is the distance is within an order of magnitude of the coverage area of the WLAN AP. WLAN APs that are considered far can be eliminated from the positioning calculation.

FIG. 7 shows an example of an integrated solution of WLAN-PS and SPS, in which the mobile device detects five WLAN access points 702 and has acquired a signal and raw measurements from two satellites 704. In this example, the WLAN access points are randomly spread around the mobile device, and distance between WLAN access points 702 and possible solutions of two satellites 703 can be used as an indication of distance between WLAN access point and actual location of the mobile device. A region of possible SPS solutions 703 is calculated using measurements from two satellites. The distance between the WLAN access point 702 and SPS possible solution 703 is used as an indicator of distance between WLAN access point and actual location of the mobile device. In this example, all the WLAN access points 702-1 are very close to SPS possible solutions 703, but one WLAN access point 702-2 is not. Therefore, the longer distance between WLAN access point 702-2 and possible SPS solutions 703 is an indicator of a larger distance between WLAN access point 702-2 and the location of the mobile device compared to other detected WLAN access points 702-1. Thus, WLAN access point 702-2 can be weighted according to its distance to SPS possible solutions, or it can be removed from the set of APs to calculate the mobile device location.

FIG. 8 illustrates WLAN-PS 801 and SPS 806 integrated solution, in which all the modules are the same as FIG. 2, except for selecting WLAN APs 803. Selecting WLAN APs 803 also receives raw SPS measurements 311 as an input. These raw measurements are used to estimate the distance between the location (or estimated location) of WLAN APs and the location of the mobile device.

As discussed in the previous embodiment, in this embodiment there is a need to calculate an indication of the distance between WLAN APs location (or estimated location) and actual location of the mobile device using SPS measurements from two or more satellites. The consistency between the raw SPS measurements and the WLAN APs can be used as an indication of distance between the location of WLAN APs and the location of the mobile device. The consistency can be calculated by (1) using the WLAN AP\'s location as an estimation of the location of the mobile device and (2) calculating the receiver clock bias for each WLAN AP location based on the measurements from each satellite. The consistency between calculated receiver clock biases can be used as an indicator of distance between WLAN APs location and the mobile device\'s actual location.

In other words, after applying the location of a WLAN AP as an initial position in SPS equations using pseudorange measurements, the only remaining unknown is the receiver clock bias, which is the same for all SPS raw measurements. If clock bias which is found for each satellite measurement is denoted by Ci, the consistency of Ci is used as a measure of distance between the given position (in this case, location of WLAN AP) and the location that satisfies the satellite equations. Consistency of Ci can be measured with different mathematical approaches, like standard deviation of Ci, or mean square error of Ci estimation as follows:

C _ = ∑ i = 1 N  C i N M   S   E = ∑

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