HK1109547A - Determining a mobile station position based on pertinent location fingerprint data - Google Patents

Abstract

A system, method and device are provided for determining the position of a mobile station through the identification of an approximate position of the mobile station. Thereafter received signal strength (RSSI) fingerprint data for the approximate position is requested and retrieved. The fingerprint data and received signal strength data collected at the mobile station are compared in connection with fixing the position of the mobile station.

Description

Determining mobile station location based on associated location fingerprint data

Cross reference to related applications

This application claims priority to provisional patent application No. 60/622,884, filed on even date 27/10/2004.

Technical Field

Background

Locating personnel, vehicle employees, etc., particularly through mobile phone media, has become an increasingly important issue over the past few years. The Federal Communications Commission (FCC) has stimulated a great deal of interest in locating mobile phones through its mandate that wireless enhanced 911 systems (E911) be established by 11 months of 2005.

There are a variety of techniques available and proposed for mobile station (e.g., mobile phones, Personal Digital Assistants (PDAs) with telecommunications capabilities, portable computers with telecommunications capabilities, pagers, etc.) position determination, from using Global Positioning Systems (GPS) to telephone network-based solutions. Fingerprints provide another way of determining the location of a mobile station.

Radio frequency signal characteristics associated with each zone within the signal transmission zone are collected in a database. Each grouping of signal features of a region is referred to as a fingerprint. Typically, the location of a mobile station is determined by comparing RF data samples collected by the mobile station with fingerprint data in the database. The location of the mobile station is determined to be within the region corresponding to the fingerprint data point having the greatest correlation with the RF data sample.

The comparison is performed by a server that stores the fingerprint data. If the comparison is done conventionally in the mobile station, a large amount of data has to be downloaded from the network-based database to the mobile station. Fingerprinting requires multiple measurements from different base stations or cell sites (e.g., Base Transceiver Stations (BTSs)) at different times of day to capture short-term signal fluctuations (rayleigh fading, etc.) and network load (capacity) fluctuations in an effort to capture each fingerprint calibration point of the fingerprint database. Therefore, downloading the fingerprint database to the mobile station may not be feasible.

Ekahau corporation has used a Received Signal Strength Indicator (RSSI) in network planning and fingerprint establishment. Radio network sample points are collected from different site locations. Each sample point contains RSSI data along with associated map coordinates stored within a database for use in location tracking of people, assets, equipment, etc. within a Wi-Fi network (802.11 a/b/g).

However, such Wi-Fi based Ekahau systems are for small applications, where a program running on a server computes a position determination and interacts with a client device (i.e., laptop, Personal Digital Assistant (PDA), Wi-Fi tag, etc.) in relation to an application program for recording field data (e.g., RSSI data). The returned position determination data may include the speed, direction, building floor, and grid location of the client device. For larger scale applications, many us wireless carriers use RSSI measurements from and by nearby BTSs to determine the location of mobile phones.

Triangulation techniques can result in duplicate computations on network servers, which can unnecessarily burden the system, especially in high traffic networks. While not encountering many of the problems associated with other location identification techniques, fingerprinting requires a considerable amount of work in data collection and is most feasible in highly populated, highly concentrated metropolitan areas. However, fingerprinting benefits from the collection of multipath signal data over the indirect signal path from the transmitter to the receiver. There is a need to take advantage of the benefits of fingerprinting in a manner that improves current RSSI position measurement techniques.

Disclosure of Invention

Drawings

Fig. 1 is a diagram of a mobile station and multiple BTSs organized in a grid with each grid division assigned a lookup token indicated by a subscripted "T".

Fig. 2 is a block diagram of an embodiment of a communication system.

Fig. 3 is a block diagram of a mobile station.

003.2 fig. 4 illustrates a functional block diagram of a mobile station position location system.

FIG. 5 is a chart illustrating the types of data that may be maintained in a fingerprint database.

Fig. 6 is a flow chart of a method for determining the position of a mobile station.

Detailed Description

The present invention provides an improved position determination method, system and apparatus for mobile stations, particularly for densely populated areas exhibiting multipath signal patterns. Familiar locations with these multipath signal patterns include, for example, Chicago, Manhattan, or san Francisco.

In one location determination aspect, fingerprint data is stored in a network database and relevant portions of the database are downloaded to the mobile station in relation to identifying the approximate signal reception area in which the mobile station is located. The fingerprint database includes RSSI data.

Referring to fig. 1, there is illustrated a diagram including a mobile station 2 (assumed to be a car phone) and a plurality of transceiver sites (such as BTSs organized in a grid 5) with each grid partition assigned a look-up token indicated by a subscripted "T". The subscripts refer to the rows and columns of grid 5.

Various embodiments may be used in connection with a variety of different radio access channel systems including, for example, Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Spatial Division Multiple Access (SDMA), or the like.

In the case of a CDMA system, the signal propagates through frequency and is encoded. These features provide the signal with the ability to achieve privacy and interference rejection. The encoding is done using a noise-like code, referred to as a pseudo-random scrambling code or pseudo-noise. Although other mobile systems consider multipath signal characteristics undesirable, for CDMA, multipath signals have certain advantageous aspects-multipath signals may be used to improve the quality of the signal. This is possible because of the wideband nature of CDMA signals. Each BTS site 4 transmits a pseudo-noise (PN) code having a unique code sequence, including a BASE-ID (BASE-ID) that the mobile station 2 can distinguish within the BTS pilot signal on the forward link (communication from BTS to mobile station) pilot channel. The pilot channel constantly transmits a signal 7, which signal 7 is used by the mobile station 2 to acquire the communication system. When the mobile station 2 has acquired the system, signal strength measurements are made using the pilot signal 7. The strength of the pilot signal from the BTS to the mobile station is used to determine the power required to properly adjust the signal transmission strength of the mobile station. Additionally, in accordance with one aspect of the present invention, the pilot signal strength may be used to identify a transmitting BTS in an effort to determine a relevant look-up token from a network database (not shown) containing relevant RSSI database information for comparison with the RSSI data measured at the mobile station 2.

The relevant look-up token information may be determined from a single BTS. For example, the BTS 4A may be defined within a circle 12 (partially shown) that defines a transmission radius 10. The look-up token data within circle 12 for a given radius 10 may be downloaded into mobile station 2. The radius 10 may be a predetermined length-a parameter selection feature particularly suited for multipath signal environments. Alternatively, the length of the radius 10 may be tailored as a function of pilot signal strength. For example, the greater the signal strength, the smaller the radius length required since a closer proximity to the BTS can be inferred and a smaller number of look-up tokens can be analyzed.

The mobile station 2 compares the downloaded look-up token information based on the individual BTS4 with the RSSI data measured at its location to estimate its location. Since each look-up token T corresponds to a mapped location, selecting the look-up token with the closest correlation to the measured RSSI data enables the location to be determined as corresponding to the location of that look-up token. It can be concluded from the look-up token grid 5 in fig. 1 that a greater number of look-up tokens over a given area will result in a tighter grid spacing and thus provide a better basis for more accurate location determination. In an alternative embodiment, the pilot signals from two BTSs are used to determine the relevant look-up token data to be analyzed. As shown in fig. 1, the intersection radii 10 from BTS 4A and BTS 4C, respectively, define an intersection area 6 on the grid 5. Thus, the affected region in region 6 is associated with and includes T_1，1、T_1，2、T_2，1、T_1，3And T_2，2Is correlated with the look-up token. The lookup token in the intersection 6 is downloaded to the mobile station 2. By passingUsing two BTSs to define the relevant look-up tokens, the number of look-up tokens that can be analyzed is reduced compared to look-up tokens within the transmission radius of a single BTS 4. As with the previous embodiment, the radius 10 may be a predetermined length, or it may be customized as a function representative of the pilot signal strength from each BTS. Accordingly, the length of each radius 10 associated with a given BTS4 need not be the same.

In another alternative embodiment, other methods may be used to determine the relevant look-up token data to analyze and thus determine the approximate location of the mobile station. For example, another intersecting circle (not shown) may be established using a pilot signal from a further third BTS (BTS 4B) in a manner that employs Advanced Forward Link Trilateration (AFLT). Using AFLT, the mobile station measures RSSI measurements of signals from nearby cellular base stations (towers) in addition to relative time of arrival measurements, and uses these readings to triangulate the approximate position of the handset.

Additionally, the relevant RSSI fingerprint data for download to the mobile station may also be based on cell ID (cell identification code) information, or enhanced cell ID-by identifying cellular base station towers that are close to the mobile station. Enhanced cell ID is a network technology that combines cell ID with one or more additional technologies. Its level of accuracy is improved compared to the basic cell ID. For example, in a GSM network, the additional techniques for incorporation may include timing advance (which measures the handset's distance from the base station, including whether the handset is connected to the nearest cell) and RSSI.

Table 1 below summarizes the expected performance in terms of average accuracy of position determination according to the illustrated method to obtain an approximation of position. The accuracy defines a search area for RSSI matching and greatly reduces the number of grids provided to and examined by the mobile station.

TABLE 1

Location approximation method	AFLT	Enhanced cell ID	Cell ID
				Average accuracy of position determination	100 to 200 m	150 to 1000 m	750 meters to 3-5 kilometers

Fig. 2 is a block diagram showing a system in which mobile station 2 interaction with BTS4 and database 8 may be remotely located by mobile station 2 and BTS 4. The interaction causes mobile station 2 to make a request for the selected look-up token in connection with analyzing the signal strength data received from the BTS-represented by the exit of double arrow 16 to BTS4 (with the strongest pilot signal strength indication). The same BTS4 may receive lookup token information from the database 8 in relation to a request to the server 11 on which the database resides. Alternatively, the information of the database 8 may be forwarded to the mobile station 2 by another BTS (not shown), as indicated by the dashed arrow 20.

In an alternative embodiment, other unique cellular identifiers may be used in addition to BASE station identifiers (BASE-IDs) to identify areas of interest associated with downloading associated fingerprint data. These include system identification code (SID)/network identification code (NID)/BASE-ID and SID/Mobile switching center identification code (MSC-ID)/BASE-ID.

Fig. 3 is a block diagram of the mobile station 2. As shown, the mobile station 2 includes a location approximation identity portion 30, the location approximation identity portion 30 identifying the relevant portions of the fingerprint database to be downloaded to the mobile station 2 according to one of the location approximation methods described herein (i.e., AFLT, enhanced Cell-ID, etc.). The RSSI section 32 works in conjunction with a radio frequency communication section 34 for providing mobile communications and a processor 36 for processing data within the mobile station 2 to determine RSSI measurements at the mobile station 2. The RSSI measurements, the request for associated fingerprint data, and the determination of the location of the mobile station are made in association with software 42 stored in memory 40.

Fig. 4 is a functional block diagram of a mobile station position location system. As shown, the location estimator 46 identifies an approximate location of the mobile station according to one of the methods described herein. Alternatively, a location estimator may be built into network 54. The fingerprint requestor 48 requests and obtains the associated fingerprint data for the approximate location identified by the location estimator 46. The fingerprint comparator 50 compares the measured RSSI data determined by the RSSI indicator 51 with fingerprint data received from the network 54 through the fingerprint requester 48 relating to the fingerprint request of the requester 48.

The fingerprint comparator 50 determines the location of the mobile station in relation to selecting the look-up token with the greatest correlation to the RSSI data measured by the RSSI indicator 51. Selecting an area corresponding to the look-up token as the location of the mobile station. The location of the mobile station is shown on the location display 52. The location may be displayed in latitude and longitude readings. Additionally, or alternatively, the location may include a representative street address. Alternatively, the location display step may require mapping and displaying the location on a digital map. In yet another embodiment, the position fix may be provided to an application internal or external to the mobile station for further processing and display.

Fig. 5 is a chart illustrating the types of data that may be maintained within the fingerprint database 8, the fingerprint database 8 being used to determine the location of the mobile station. As shown, the database 8 may hold a tower entry indicating the identity of the tower for defining the region of the lookup token of interest. Fig. 5 shows an example of two tower entries. However, more tower entries may be used to define the lookup token region. To further refine the lookup token area, the intersection area between two towers determined by a specified radius defining the BTS antenna coverage area or antenna range outward from each BTS may be recorded. Note, however, that maintaining a single tower entry in database 8 helps to account for situations where a single tower is sufficient to define the lookup token region and situations where only a single tower is involved in reception. RSSI tokens defined by tower intersection areas or individual towers may be maintained in the database 8. A location defined by latitude and longitude readings, along with other measurements, may also be maintained in the database 8.

Fig. 6 is a flow chart showing a method of mobile station position determination. As shown, the mobile station collects RSSI data, 60. Thereafter, an approximate location of the mobile station is determined, 62. The approximate location of the mobile station may be determined in accordance with one of the techniques described previously. For example, in one aspect, the mobile station determines the nearest BTS site based on pilot signal strength from a transmitted pilot signal on a received pilot channel. The second and next closest BTS towers are identified based on the second and next strongest pilot signals. Based on the intersection of overlapping reception areas of two or more identified BTS sites, an area of interest of an associated look-up token is defined and provided to the mobile station.

In another aspect, look-up token data corresponding to an area identified as being proximate the mobile station is defined, 64. These look-up tokens are compared, preferably at a server holding the look-up token database, with RSSI data collected by the mobile station, 66. Correlations between the look-up token data points within the defined region of interest are calculated, 68. The look-up token with the greatest correlation to the collected RSSI data is selected, 70, and compared to a predetermined correlation threshold, 72. For example, if an 80% correlation between the look-up token and the collected RSSI data is sufficient, the selected look-up token indicating the corresponding position fix (street address, longitude and latitude indication, etc.) of the mobile station is selected, 74. If the selected lookup token with the greatest correlation does not meet the threshold, the method is restarted from the mobile station collecting RSSI data (60) in an effort to obtain a position determination for the mobile station. Many known algorithms relating to nearest neighbor search and signal pattern matching are also contemplated herein. These techniques may be employed to further improve the location estimate. Although the description has been made with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims (21)

1. A system for determining a location of a mobile station, comprising:

a location estimator for identifying an approximate location of the mobile station;

a fingerprint requestor for requesting and obtaining, over a radio channel access from a fingerprint database remote from the mobile station, associated location fingerprint data, the associated location fingerprint data being indicative of the approximate location of the mobile station; and

a fingerprint comparator for comparing RSSI data measured at the mobile station with the correlated positioning fingerprint data to determine a location of the mobile station.

2. A system for determining the position of a mobile station as recited in claim 1 further comprising a display operable to indicate the position of said mobile station.

3. The system for determining the position of a mobile station of claim 1 wherein said radio channel access is provided by a technique selected from the group of radio channel access schemes consisting of CDMA, TDMA, FDMA, SDMA, and combinations thereof.

4. A system for determining the location of a mobile station as recited in claim 1 wherein said remote fingerprint database contains RSSI data.

5. The system of claim 1, wherein the mobile station is a mobile communication device selected from the group consisting of a mobile telephone, a personal digital assistant with wireless communication capability, a portable computer with wireless communication capability, and a pager.

6. A mobile station, comprising:

a location approximate identification portion operable to identify a relevant portion of a remote fingerprint database corresponding to a vicinity of the mobile station for download to the mobile station;

an RSSI section for making RSSI measurements at the mobile station;

a memory;

a processor;

software stored in memory and running in the processor for determining a location of the mobile station by comparing the relevant portion of the remote fingerprint database to the RSSI measurements made at the mobile station.

7. A mobile station as recited in claim 6, wherein said location approximation identification component identifies nearby relevant portions of a remote fingerprint database corresponding to said mobile station by an advanced forward link trilateration method.

8. The mobile station of claim 6, wherein the location approximation identification section identifies the relevant portion of the remote fingerprint database by identifying base station sites in the vicinity of the mobile station by measuring base station pilot signal strengths.

9. A mobile station as recited in claim 6, wherein said location approximate identification portion identifies a relevant portion of a remote fingerprint database corresponding to the vicinity of the mobile station by identifying cellular base stations located in the vicinity of the mobile station by a method that uses Cell-IDs.

10. A mobile station as recited in claim 6, wherein the location approximate identification portion identifies nearby relevant portions of a remote fingerprint database that correspond to the mobile station by a method that uses an enhanced Cell-ID.

11. A system for determining a location of a mobile station, comprising:

a fingerprint database containing RSSI data;

a mobile station comprising a location estimator for identifying an approximate location of the mobile station;

a fingerprint requestor for requesting and obtaining, over a radio channel access from a fingerprint database remote from the mobile station, associated location fingerprint data, the associated location fingerprint data indicating an approximate location of the mobile station; and

a fingerprint comparator for comparing RSSI data measured at the mobile station with the correlated positioning fingerprint data to determine a location of the mobile station.

12. A method for determining a position of a mobile station, comprising:

collecting RSSI data at the mobile station;

determining an approximate location of the mobile station;

selecting fingerprint look-up token data corresponding to the approximate location of the mobile station from a database located remotely from the mobile station;

comparing the fingerprint lookup token data with the RSSI data collected at the mobile station; and

determining the location of the mobile station from finding the fingerprint look-up token data having the greatest correlation with the RSSI data.

13. A method of determining the position of a mobile station as recited in claim 12 further comprising determining whether said maximum correlation satisfies a predetermined threshold.

14. A method of determining the position of a mobile station as claimed in claim 13, wherein the method is repeated provided that the maximum correlation fails to meet the predetermined threshold.

15. A method of determining the position of a mobile station as claimed in claim 12, wherein the fingerprint look-up token data comprises RSSI data.

16. A method of determining the position of a mobile station as recited in claim 12, wherein determining the approximate location of the mobile station is accomplished by using an APLT method.

17. A method of determining the position of a mobile station as recited in claim 12, wherein determining the approximate location of the mobile station is accomplished by identifying base station sites in the vicinity of the mobile station by measuring base station pilot signal strengths.

18. A method of determining the position of a mobile station as recited in claim 12, wherein determining the approximate location of the mobile station is accomplished by identifying a cellular base station antenna located proximate to the mobile station.

19. A method of determining the position of a mobile station as recited in claim 12 further comprising displaying the location of said mobile station.

20. A method of determining the position of a mobile station as recited in claim 19, wherein the display of the location of the mobile station includes latitude and longitude readings.

21. A method of determining the position of a mobile station as recited in claim 19 wherein said display of the location of said mobile station includes street location information.