EP1647160A1 - Localisation estimative de terminaux sans fil par comparaison de modeles de mesures deduites et empiriques de l'intensite du signal - Google Patents

Localisation estimative de terminaux sans fil par comparaison de modeles de mesures deduites et empiriques de l'intensite du signal

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Publication number
EP1647160A1
EP1647160A1 EP04778274A EP04778274A EP1647160A1 EP 1647160 A1 EP1647160 A1 EP 1647160A1 EP 04778274 A EP04778274 A EP 04778274A EP 04778274 A EP04778274 A EP 04778274A EP 1647160 A1 EP1647160 A1 EP 1647160A1
Authority
EP
European Patent Office
Prior art keywords
signal
strength
wireless terminal
location
estimating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP04778274A
Other languages
German (de)
English (en)
Inventor
David Stevenson Spain, Jr.
Robert Lewis Martin
Tarun Kumar Bhattacharya
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Polaris Wireless Inc
Original Assignee
Polaris Wireless Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US10/668,634 external-priority patent/US8712428B2/en
Priority claimed from US10/798,988 external-priority patent/US7116987B2/en
Application filed by Polaris Wireless Inc filed Critical Polaris Wireless Inc
Publication of EP1647160A1 publication Critical patent/EP1647160A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • 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
    • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
    • G01S5/0252—Radio frequency fingerprinting
    • G01S5/02521—Radio frequency fingerprinting using a radio-map
    • G01S5/02523—Details of interaction of receiver with radio-map

Definitions

  • the present invention relates to telecommunications in general, and, more particularly, to a technique for estimating the location of a wireless terminal.
  • Figure 1 depicts a map of a geographic region that is serviced by a wireless telecommunications system, which system provides wireless telecommunications service to wireless terminals (e.g., wireless terminal 101) within the region.
  • the heart of the telecommunications system is wireless switching center 110, which might also be known as a mobile switching center ("MSC") or a mobile telephone switching office (“MTSO").
  • wireless switching center 111 is connected through a plurality of intermediate network elements (e.g., base station controllers, etc.) to a plurality of base stations (e.g., base stations 102-1, 102-2, and 102-3), which are dispersed throughout the geographic area serviced by the system.
  • base station 102-2 serves wireless terminal 101.
  • wireless switching center 111 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal (which is connected to the system via the local and/or long-distance telephone networks and which are not shown in Figure 1).
  • the salient advantage of wireless telecommunications over wireline telecommunications is the mobility that is afforded to the users of the wireless telecommunications system.
  • the salient disadvantage of wireless telecommunications lies in that fact that because the user is mobile, an interested party might not be able to readily ascertain the location of the user.
  • Such interested parties might include both the user of the wireless terminal and remote parties. There are a variety of reasons why the user of a wireless terminal might be interested in knowing his or her own location. For example, the user might be interested in telling a remote party where he or she is. [0008] There are a variety of reasons why a remote party might be interested in knowing the location of the user. For example, the recipient of a 911 emergency call from a wireless terminal might be interested in knowing the location of the wireless terminal so that emergency services vehicles can be dispatched to that location. [0009] There are many techniques in the prior art for estimating the location of a wireless terminal.
  • the location of a wireless terminal is estimated to be at the center of the cell in which the wireless terminal is located.
  • This technique is advantageous in that it does not require that additional hardware be added to the wireless terminal or to the wireless telecommunications system, and this means that the first technique can be inexpensively implemented in legacy systems.
  • the first technique is only accurate, however, to a few kilometers, and, therefore, it is generally not acceptable for applications (e.g., emergency services dispatch, etc.) that require higher accuracy.
  • the location of a wireless terminal is estimated by triangulating the angle of arrival or the time of arrival of the signals transmitted by the wireless terminal to be located at various receivers.
  • the location of a wireless terminal is estimated by a radio navigation unit, such as a Global Positioning System (GPS) receiver, that is incorporated into the wireless terminal.
  • GPS Global Positioning System
  • This technique is accurate to within tens of meters and is advantageous in that it does not require that additional hardware be added to the telecommunication system's infrastructure.
  • the third technique is disadvantageous, however, in that it cannot be used with legacy wireless terminals that do not comprise a radio navigation unit. [0013] Therefore, the need exists for a technique for estimating the location of a wireless terminal with higher resolution than the first technique and that can be inexpensively implemented in legacy systems.
  • the present invention enables the estimation of the location of a wireless terminal without the addition of hardware to either the wireless terminal or to the telecommunication system's base stations. Some embodiments of the present invention are, therefore, ideally suited for use with legacy telecommunications systems. [0015]
  • the illustrative embodiment of the present invention is based on the observation that the signal strength of a signal from a transmitter is different at some locations, and, therefore, the location of a wireless terminal can be estimated by comparing the signal strength it currently observes against a map or database that correlates locations to signal strengths.
  • a first radio station, Radio Station A transmits a strong signal to Location 1 and Location 2, but a weak signal to Location 3 and Location 4, and a second radio station, Radio Station B, transmits a strong signal to Location 1 and Location 3, but a weak signal to Location 2 and Location 4.
  • This information is summarized in the table below and forms the basis for a map or database that correlates locations to signal strength.
  • a given wireless terminal at an unknown location receives Radio Station A with a weak signal and Radio Station B with a strong signal, it is more likely that the wireless terminal is at Location 3 than it is at either Location 1, 2, or 4.
  • the accuracy of the estimate of the location of a wireless terminal can be enhanced when the signal strength of each signal at each location is quantified. A simplified example illustrates this point.
  • a wireless terminal measures the signal strength of the control channels of the base stations that it can receive and that are not serving it and reports some or all of those signal-strength measurements back to the wireless switching center. In the prior art this is performed so that the wireless switching center can intelligently decide which base station the wireless terminal should be served by.
  • these signal- strength measurements are also used, in conjunction with a map or database that correlates locations to signal strength, to estimate the location of the wireless terminal.
  • a map or database that correlates locations to signal strength, to estimate the location of the wireless terminal.
  • more signal-strength measurements provide a better estimate of the location of the wireless terminal than fewer signal-strength measurements, and, therefore, the acquisition of additional signal-strength measurements is typically advantageous.
  • One way of acquiring an additional signal- strength measurement is to actually physically measure a signal at the wireless terminal, but most legacy terminals are not equipped to measure and report on an arbitrary number of signals.
  • the illustrative embodiment deduces the signal strength of one or more base stations' control channels at the wireless terminal based on the principal of reciprocity, whether or not the wireless terminal can actually receive the base stations' control channels but so long as the base station can receive and measure an uplink traffic channel signal from the wireless terminal. This is accomplished in accordance with the principal of reciprocity.
  • the principal of reciprocity states that the attenuation of a signal transmitted from Point A to Point B is the same as that for a signal that is transmitted from Point B to Point A.
  • the principal of reciprocity indicates that the attenuation of the signal between the base station and the wireless terminal, A D , equals the attenuation of that signal between the wireless terminal and the base station, A ⁇ , as represented by Equation 2:
  • a D Au (Eq.
  • Equation 3 the signal strength of the base station's control channel signal at the wireless terminal, R D
  • the signal strength of the base station's control channel signal at the wireless terminal, R D can be deduced from the strength at which the control channel signal is transmitted by the base station, T D , the strength at which the signal is transmitted by the wireless terminal, T ⁇ , and the signal strength of the uplink traffic channel signal from the wireless terminal as measured by the base station, R Ur as represented by Equation 4:
  • the deduced signal-strength measurements can then used - alone or in combination with the empirical signal-strength measurements - to estimate the location of the wireless terminal.
  • the illustrative embodiment comprises: receiving a signal-strength measurement for a first downlink signal that is received by a wireless terminal and a signal-strength measurement for an uplink signal that is transmitted by the wireless terminal; and estimating the location of the wireless terminal based on the signal- strength measurement for the first downlink signal and on the signal-strength measurement for the uplink signal.
  • Figure 1 depicts a map of a portion of a wireless telecommunications system in the prior art.
  • Figure 2 depicts a map of the illustrative embodiment of the present invention.
  • Figure 3 depicts a block diagram of the salient components of location system 212.
  • Figure 4 depicts a broad overview of the salient operations performed by the illustrative embodiment in ascertaining the location of wireless terminal 201 in geographic region 200.
  • Figure 5 depicts a flowchart of the salient operations performed in operation 401.
  • Figure 6 depicts a map of how geographic region 200 is partitioned into 500 locations in accordance with the illustrative embodiment of the present invention.
  • Figure 7a depicts a graph that shows that the signal strength of an electromagnetic signal decreases, in general, as a function of the distance from the transmitter and in an environment with no radio frequency obstacles.
  • Figure 7b depicts a graph that shows that the signal strength of an electromagnetic signal decreases, in general, as a function of the distance from the transmitter and in an environment with two radio frequency obstacles.
  • Figure 8 depicts a map of the signal-strength measurements of the signal radiated from base station 202-1 at each location in geographic region 200.
  • Figure 9 depicts a map of the signal-strength measurements of the signal radiated from base station 202-2 at each location in geographic region 200.
  • Figure 10 depicts a map of the signal-strength measurements of the signal radiated from base station 202-3 at each location in geographic region 200.
  • Figure 11 depicts a flowchart of the salient operations performed in operation 402
  • Figure 12 depicts a flowchart of the salient operations performed in operation 1102.
  • Figure 13 depicts a flowchart of the salient operations performed in operation 1103.
  • Figure 14 depicts a flowchart of the salient operations performed in operation 404.
  • Figure 2 depicts a map of the illustrative embodiment of the present invention, which comprises: wireless switching center 211, location system 212, base stations 202-1, 202-2, and 202-3, and wireless terminal 201, which are interconnected as shown.
  • the illustrative embodiment provides wireless telecommunications service to most of geographic region 200, in well-known fashion, and is also capable of estimating the location of wireless terminal 201 within geographic region 200.
  • Wireless switching center 211 is a switching center as is well-known to those skilled in the art in most respects but is different in that it is capable of communicating with location system 212 in the manner described below. After reading this disclosure, it will be clear to those skilled in the art how to make and use wireless switching center 211.
  • a wireless switching center is also known by other names, such as a mobile switching center, a mobile telephone switching office, etc.
  • the illustrative embodiment comprises one wireless switching system, but after reading this specification it will be clear to those skilled in the art how to make and use embodiments of the present invention that use two or more systems to obtain signal-strength measurements. Typically, this is useful when a wireless terminal is near the boundary of one or more systems.
  • one wireless switching center can use the IS-41 protocol messages HandoffMeasurementRequest and HandoffMeasurementRequest2 to elicit signal-strength measurements from another.
  • Base stations 202-1, 202-2, and 202-3 are well-known to those skilled in the art and communicate with wireless switching center 211 through cables and other equipment (e.g., base station controllers, etc.) that are not shown in Figure 2.
  • wireless terminal 201 is serviced by base station 202-2.
  • the illustrative embodiment comprises three base stations, it will be clear to those skilled in the art how to make and use embodiments of the present invention that comprise any number of base stations.
  • Each of base stations 202-1, 202-2, and 203-3 is capable, in well-known fashion, of: i. measuring the signal strength of an uplink traffic channel signal as transmitted by wireless terminal 201 and reporting that measurement to wireless switching center 211; and ii.
  • base station 202-1 receives and measures the signal strength of the uplink signal S (depicted as a dashed zig-zag arrow in Figure 2) from wireless terminal 201.
  • Base station 202-1 is in the vicinity of wireless terminal 201, but base station 202-1 is neither (1) the serving base station for wireless terminal 201 nor (2) on wireless terminal 201's list of neighboring base stations.
  • the illustrative embodiment depicts only one base station in the vicinity of wireless terminal 201 for receiving and measuring the strength of the uplink signal S and that is neither (1) the serving base station nor (2) on wireless terminal 201's list of neighboring base stations, it will be clear to those skilled in the art how to make and use embodiments of the present invention that have any number of such base stations.
  • base station 202-2 is the serving base station for wireless terminal 201 and, therefore, base station 202-2 receives and measures the signal strength of the uplink signal S (depicted as a dashed zig-zag arrow in Figure 2) from wireless terminal 201. In accordance with the illustrative embodiment, wireless terminal 201 does not measure the signal strength of the control channel from base station 202-2. In accordance with the illustrative embodiment, wireless terminal 201 receives a downlink traffic channel (depicted as a solid zig-zag arrow in Figure 2) from base station 202-2.
  • base station 202-3 is on wireless terminal 201's list of neighboring base stations, and, therefore, wireless terminal 201 receives and measures the signal strength of the control channel (depicted as a dotted zig-zag arrow in Figure 2) from base station 202-3.
  • Base station 202-3 is in the vicinity of wireless terminal 201, and, therefore, base station 202-3 receives and measures the signal strength of the uplink signal S (depicted as a dashed zig-zag arrow in Figure 2) from wireless terminal 201. This is not a necessary consequence of base station 202-3 being on wireless terminal 201's list of neighboring base stations, but is merely a result of the proximity of base station 202-3 and wireless terminal 201.
  • a base station on a wireless terminal's list of neighboring base stations will be able to receive and measure the signal strength of the uplink signal S from wireless terminal 201 and in some cases it will not. It will be clear to those skilled in the art how to make and use embodiments of the present invention in which some, none, or all of the base stations on a wireless terminal's list of neighboring base stations are able to receive and measure the signal strength of the uplink signal S from wireless terminal 201.
  • Wireless terminal 201 is a standard GSM wireless terminal as it is currently manufactured and used throughout the world.
  • Wireless terminal 201 is equipped, in well-known fashion, with the hardware and software necessary to measure and report to wireless switching center 211 on the signal strength of signals from the base stations that are on its Hst of neighboring base stations.
  • a GSM wireless terminal such as wireless terminal 201, is capable of reporting the signal strength of a signal as one of 64 levels between -47 dBm and -110 dBm. Any signal stronger than -47 dBm is reported as -47 dBm, and any signal weaker than -110 dBm is reported as -110 dBm.
  • Location system 212 is a computer system that is capable of estimating the location of wireless terminal 201, as described in detail below.
  • location system 212 is capable of estimating the location of any number of wireless terminals serviced by wireless switching center 211.
  • location system 212 is depicted in Figure 2 as being distinct from wireless switching center 211, this is done principally to highlight the distinction between the functions performed by wireless switching center 211 and the functions performed by location system 212. In other words, it will be clear to those skilled in the art how to make and use embodiments of the present invention in which location system 212 resides within or without wireless switching center 211 or is a fully- integrated part of wireless switching center 211.
  • FIG. 2 depicts a block diagram of the salient components of location system 212 in accordance with the illustrative embodiment.
  • location system 212 comprises: processor 301, signal-strength database 302, receiver 303, and transmitter 304, which are interconnected as shown.
  • Receiver 303 receives information from wireless switching center 211, as disclosed below and with respect to Figure 4, and forwards this information to processor 302.
  • Processor 301 is a general-purpose processor as is well-known in the art that is capable of performing the operations described below and with respect to Figure 4.
  • Processor 302 receives input from receiver 303 and sends output to transmitter 304 in well-known fashion.
  • Signal-strength database 302 is a non-volatile memory that stores signal-strength measurements as described below and with respect to Figure 4.
  • Transmitter 304 receives output from processor 301 and transmits this output to wireless switching center 211 in well-known fashion.
  • Overview - Figure 4 depicts a broad overview of the salient operations performed by the illustrative embodiment in ascertaining the location of wireless terminal 201 in geographic region 200.
  • the tasks performed by the illustrative embodiment can be grouped for ease of understanding into five operations: i. the population of signal-strength database 302, ii. the querying of the wireless switching center 211 to provide uplink and downlink signal-strength measurements, iii. the deduction of the signal strengths at the wireless terminal for downlink signals whose signal strength was not empirically measured at the wireless terminal, iv.
  • signal-strength database 302 associates each location within geographic region 200 with a tuple of signal-strength measurements for specific signals for that location. Operation 401 is generally complex and potentially expensive, and it is, therefore, preferably performed only occasionally. The details of operation 401 are described in detail below and with respect to Figure 5. [0067] At operation 402, location system 212 queries wireless switching center 211 to learn: i.
  • location system 212 receives the following data (which is summarized in Table 2): i. empirical signal-strength measurements of the (downlink) control channels transmitted by base station 202-3, as received by wireless terminal 201, which is designated as R D (3), respectively; ii.
  • R D (3) 7 D (1), T D (2), and 7 " D (3) are needed along with T ⁇ to deduce R D (1), R D (2), and R D (3).
  • R D (3) was determined empirically and directly by wireless terminal 201, for reasons given below, the deduced value of R D (3) might be preferred.
  • wireless terminal 201 periodically or sporadically provides R D (3) and T ⁇ to wireless switching center 211 in well-known fashion, and the measurements are forwarded to location system 212.
  • the details of operation 402 are described in detail below and with respect to Figures 11, 12, and 13.
  • location system 212 deduces the values of R D ( ⁇ ) based on Tu, Ru(i), and 7 ⁇ (i).
  • R D (i) and R ⁇ (i) are at different frequencies, as in, for example, a frequency-division duplexed system, the effects of fast fading (i.e., Rayleigh fading) must be removed from R ⁇ (i) to ensure that the deduced value of R D (i) is independent of fast fading at the frequency of R u ( ' -
  • the effects of fast fading can be removed from Ru(i) through well-known filtering techniques.
  • the details of operation 403 are described in detail below and with respect to Figure 12.
  • location system 212 estimates the location of wireless terminal 201 based on all of the downlink signal-strength measurements (i.e., the measured signal-strength measurements, R lr . . . R n . t , and the deduced signal-strength measurements, R D (1), . . . R D (3)) r and a map or database that correlates locations to signal-strength measurements.
  • location system 212 will receive an empirical signal- strength measurement for a downlink signal and will be able to deduce the signal strength of that same downlink signal.
  • the deduced value should be used instead of the empirical measurement because the accuracy of the uplink signal-strength measurement is typically better than the accuracy of the downlink signal-strength measurement. It will be clear to those skilled in the art, however, after reading this specification, how to make and use embodiments of the present invention in which one or more empirical measurements are used instead of deduced values for the measurements. [0073]
  • location system 212 transmits the location estimated in operation 405 to an entity (not shown) for use in an application. It is well known to those skilled in the art how to use the estimated location of a wireless terminal in an application.
  • geographic region 200 is partitioned into a grid of 221 square locations that are designated location x lr yx through location x 17 , y 13 .
  • the number of locations into which geographic location 200 is partitioned is arbitrary, subject to the considerations described below.
  • each location is an area of approximately 5 arc-seconds in length by 5 arc-seconds in height. Five arc- seconds near the equator equals approximately 150 meters.
  • the size of the locations defines the highest resolution with which the illustrative embodiment can locate a wireless terminal.
  • the illustrative embodiment can only estimate the location of a wireless terminal to within one location (i.e., 5 by 5 arc-seconds in the illustrative embodiment). If greater resolution is desired, for example 1 arc-second resolution, then geographic region 200 would need to be partitioned into 1 arc-second by 1 arc-second locations. If geographic region 200 were partitioned into 1 arc-second by 1 arc-second locations, there would be 5,525 squares, which is considerably more than the 221 used in the illustrative embodiment. Although the ostensibly higher resolution of 1 arc-second versus 5 arc-seconds is advantageous, there are considerable disadvantages to a large number of locations.
  • the number of locations to partition geographic region 200 into is based on three factors. First, as the size of each location goes down, the resolution of the embodiment increases. Second, as the size of each location decreases, the number of locations in a region increases, and, consequently, the computational complexity of operation 404 increases quickly. Third, each location must be large enough so that it has (at least slightly) different signal-strength characteristics than its adjacent areas. This is because the illustrative embodiment might - but won't necessarily - have difficulty distinguishing between adjacent locations that have the same signal-strength characteristics. It will be clear to those skilled in the art how to consider these three factors when deciding how to partition a geographic region.
  • the signal-strength measurements for a signal from each base station are determined at each location in geographic region.
  • the signal used from each base station is the control channel because it is broadcast at a constant power and because wireless terminal 201 can distinguish it from every other control channel, if it can decode its BSIC (for GSM networks).
  • BSIC for GSM networks
  • the signal strength of an electromagnetic signal decreases as a function of the distance from the transmitter, as is depicted in Figure 7a, but the topography of the region and the presence of buildings, trees, and other radio-frequency obstacles severely alters this generalization, as is depicted in Figure 7b.
  • the tuple of three signal- strength measurements for each location are determined through a combination of: (i) a theoretical radio-frequency propagation model, and (ii) empirical signal-strength measurements. It will be clear to those skilled in the art how to accomplish this.
  • one well-known modeling technique for outdoor radio- frequency signal propagation is adapted from the power-law decay model.
  • the power- law decay model assumes that the base station's antenna is high above the ground and that there is line-of-sight propagation to the wireless terminal.
  • the mean signal-strength, P received at the wireless terminal decays in inverse proportion to the square of the distance from the transmitter, oc — - , (Eq. 5) r ⁇ up to some break-point. Beyond that breakpoint, the mean power at the wireless terminal decays in inverse proportion to the fourth power of the distance from the transmitter:
  • the location of the break-point is determined through empirical signal-strength measurements as the location at which the ground bounce signal interferes with the line- of-sight signal.
  • the signal-strength measurements at each location are determined by taking empirical measurements at various locations and by interpolating for the locations in between the sampled locations. This method is advantageous in that it does not require many empirical measurements to be made, but it is less accurate than taking measurements at every location. [0087] It will be clear to those skilled in the art how to determine the signal- strength measurements for each location in the geographic region whether through: (i) theoretical radio-frequency propagation models, or (ii) empirical signal-strength measurements, or (iii) any combination of i and ii.
  • Figure 8 depicts the signal strength of the signal from base station 202-1 (hereinafter referred to as "Signal 1") at each location in geographic region 200.
  • Signal 1 is stronger near base station 202-1 and weaker far away from base station 202-1.
  • Figure 9 depicts the signal strength of the signal from base station 202-2 (hereinafter referred to as "Signal 2") at each location in geographic region 200.
  • Signal 2 is stronger near base station 202-2 and weaker far away from base station 202-2.
  • Figure 10 depicts the signal strength of the signal from base station 202-3 (hereinafter referred to as "Signal 3") at each location in geographic region 200. Like Signals 1 and 2, Signal 3 is stronger near base station 202-3 and weaker far away from base station 202-3.
  • Signal 3 is stronger near base station 202-3 and weaker far away from base station 202-3.
  • the signal-strength tuples for each location in geographic region 200 have been determined, they are stored in signal-strength database in a data structure that associates each location with the tuple for that location. The data structure is then stored in signal-strength database 302.
  • Table 3 depicts a portion of an illustrative data structure for associating each location with the signal-strength tuple for that location.
  • the three signal-strength measurements in a row of table 1 constitute a "tuple" or non-empty set of ordered elements.
  • the signal-strength tuple at Location x , y 7 are the 3-tuple ⁇ -45, -51, -49 ⁇ .
  • the illustrative embodiment of the present invention estimates the location of a wireless terminal by pattern matching the signal-strength measurements by the wireless terminal at a location against the signal-strength tuples in signal-strength database 302. This process is described in detail below and with respect to operation 402. [0094] From task 502, control passes to operation 402 in Figure 4. [0095] Query of Transmit Strength and Signal-Strength Measurements from Wireless Switching Center - Figure 11 depicts a flowchart of the salient operations performed in operation 402. [0096] At task 1101, location system 212 transmits a request to wireless switching center 211 to provide: i. the uplink transmit signal strength for wireless terminal 201, T ⁇ , ii.
  • the third of these can be requested from wireless switching center 211 in the form of an IS-41 HandoffMeasurementRequest or HandoffMeasurementRequest2 message, in well- known fashion.
  • wireless switching center 211 obtains the uplink transmit signal strength for wireless terminal 201, T ⁇ , and the downlink signal-strength measurements from wireless terminal 201, R D (3) for some or all of the control channels that wireless terminal 201 is able to receive (e.g., base station 202-2 in Figure 2, etc.) in well-known fashion.
  • Task 1102 is described in detail below and with respect to Figure 12.
  • wireless switching center 211 obtains the uplink signal- strength measurements, R ⁇ (l) through R ⁇ (3), in well-known fashion.
  • Task 1103 is described in detail below and with respect to Figure 13.
  • location system 212 receives from wireless switching center 211: i.
  • FIG. 12 depicts a flowchart of the salient operations performed in task 1102.
  • wireless switching center 211 directs wireless terminal 201, in well-known fashion, to (1) attempt to receive the control channels for the base stations on its list of neighboring base stations, (2) report back a signal- strength value for each received control channel, and (3) report back the transmit strength of a signal that it transmits.
  • wireless terminal 201 reports, in well-known fashion, signal-strength measurements Rx . . . R n . ⁇ for some or all of the control channels that it is able to receive to its serving cell's base station (e.g., base station 202-2 in Figure 2, etc.).
  • wireless terminal 201 reports to its serving cell's base station, in well-known fashion, the transmit strength of a signal S transmitted by wireless terminal 201, R ⁇ .
  • wireless terminal 201 regularly transmits signals, and any of these signals can be used as "signal S" with respect to tasks 1103 and 1202, disclosed below.
  • the base station forwards (i) the signal-strength measurements received at task 1102, and (ii) the transmit strength received at task 1103, to wireless switching center 211 in well-known fashion.
  • wireless switching center 211 forwards (i) the signal- strength measurements received at task 1102, and (ii) the transmit strength received at task 1103, to location system 212 in well-known fashion.
  • location system 212 In well-known fashion.
  • control passes to operation 1104 in Figure 11.
  • Receipt of f iii ' Transmit Strength of control channels and f iv " ) Signal-Strength Measurement of Signal S - Figure 13 depicts a flowchart of the salient operations performed in operation 1103.
  • wireless switching center 211 directs the base stations in the vicinity of wireless terminal 201 to measure and report the signal-strength of the uplink signal from wireless terminal 201, in well-known fashion.
  • each of the base stations that are able to measure the signal strength of the uplink signal from wireless terminal 201 reports to wireless switching center 211 the measured signal strength, in well-known fashion.
  • each of the base stations that reported a value in subtask 1302 reports to wireless switching center 211 the transmit strength of the control channel that it transmits, in well-known fashion.
  • operation 404 is described as it is applied to the first report, and finally, operation 404 is described as it is applied to the second report.
  • the signal strength of Signal 1, R D (1) is deduced and equals -98
  • the signal strength of Signal 2, R D (2) is deduced, and equals -64
  • the signal strength of Signal 3, R D (3) is empirically measured, and equals -51.
  • Subtasks 1402 through 1405 can be computationally intense, and the computational burden increases with the number of candidate locations that must be considered. Therefore, location system 212 attempts, at subtask 1401, to reduce the number of candidate locations that must be processed in subtasks 1402 through 1405. [0117] To reduce the number of candidate locations that must be processed in subtasks 1402 through 1405, location system 212 uses the following observation. When a downlink signal is reported with a maximum signal strength (i.e., "-47" in the illustrative embodiment), location system 212 can reasonably eliminate from consideration as a candidate location every location where the signal-strength measurement for that signal is below the maximum (minus a factor for measurement errors and systematic bias).
  • location system 212 can restrict consideration in subtasks 1402 through 1405 to those candidate locations where signal-strength database 302 predicts the signal strength to be greater than or equal to the maximum reportable value (minus a factor for measurement errors and systematic bias).
  • the factor for measurement errors and systematic bias is 3 dBm, and, therefore when a downlink signal is reported with -47, location system 212 can restrict consideration in subtasks 1402 through 1405 to those candidate locations where signal- strength database 302 predicts the signal strength to be greater than or equal to -50 dBm. It will be clear to those skilled in the art how to determine and use other factors for measurement errors and systemic bias.
  • location system 212 computes the signal-strength differentials for all of the downlink signal-strength measurements (i.e., both the empirical signal-strength measurements and the deduced signal-strength measurements) that are not at the maximum signal strength.
  • n-m-1 Eq. 8 pair-wise differentials for the remaining n-m signals are computed, in well-known fashion.
  • location system 212 will have computed n-m-1 pair-wise differentials, ⁇ S2 through ⁇ S n . m . [0119]
  • location system 212 computes the signal-strength differentials for only those locations that were not eliminated from consideration in task 1201.
  • location system 212 only computes the signal-strength differentials corresponding to the differentials computed in subtask 1402; the idea, of course, being to ensure that "apples are compared with apples.”
  • R-k,x,y is the signal-strength of Signal k at location x,y in signal-strength database 302, and R ⁇ , ⁇ r y is the reported signal strength of Signal 1 at location x,y in signal-strength database 302.
  • location system 212 will have computed n-m-1 pair-wise differentials, ⁇ R2 r ⁇ r y through ⁇ R n - m/Xr y, corresponding to the pair-wise differentials computed in subtask 1403, for alf the candidate locations.
  • location system 212 compares the signal-strength differentials computed in subtask 1402, ⁇ S2 through ⁇ S n - m , to the signal-strength differentials in subtask 1403, ⁇ R2 r ⁇ r y through ⁇ R n - m/X/ y, to generate a probability distribution that indicates the goodness of fit between the signal-strength differentials computed from the values received in operations 402 and 403 to the signal-strength differentials computed from the tuples in signal-strength database 302.
  • Equation 10 the Euclidean norm at each of the / candidate locations is computed for the signal- strength differentials computed from the values received in operations 402 and 403 and each of the signal-strength differentials computed from the tuples in signal-strength database 302. This is described in Equation 10.
  • location system 212 estimates the location of wireless terminal 201 based on the probability distribution generated in subtask 1404. In accordance with the illustrative embodiment, location system 212 estimates the location of wireless terminal based on the geometric mean of the probability distribution generated in subtask 1404.
  • location system 212 computes two (2) signal-strength differentials for each of the 221 locations in signal-strength database 302, as depicted in Table 5.
  • location system 212 can restrict consideration in subtasks 1402 through 1305 to those locations in signal-strength database 302 in which Signal 3 is predicted to be -50 dBm or greater.
  • there are only 13 locations (x8,y4; x9,y4; xl0,y4; x7,y5; x8,y5; x9,y5; xl0,y5; x7,y6; x8,y6; x9,y6; xl0,y6; x7,y7; x8,y7; x9,y7) at which Signal 3 is predicted to be -50 dBm or stronger, and, therefore, location system 212 need only perform subtasks 1402 through 1305, in the above-described fashion, on those 13 locations.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)

Abstract

L'invention concerne un procédé qui permet d'estimer l'emplacement d'un terminal sans fil. Le mode de réalisation exemplaire de l'invention est fondé sur l'observation que l'intensité d'un signal émis par un émetteur est différent à certains emplacements et que, par conséquent l'emplacement d'un terminal sans fil peut être estimé par rapprochement de l'intensité du signal actuellement observée à une carte ou une base de données corrélant des emplacements à des intensités du signal. De plus, le mode de réalisation de l'invention déduit l'intensité du signal d'une ou de plusieurs voies de signalisation de stations de base, au niveau du terminal sans fil, sur la base du principe de réciprocité, que le terminal sans fil puisse effectivement recevoir ou non les voies de signalisation des stations de base, pour autant que la station de base puisse recevoir et mesurer le signal ascendant provenant du terminal sans fil. Les mesures d'intensité du signal déduites peuvent être utilisées, seules ou en combinaison avec les mesures d'intensité du signal empiriques, pour estimer l'emplacement d'un terminal sans fil.
EP04778274A 2003-07-19 2004-07-14 Localisation estimative de terminaux sans fil par comparaison de modeles de mesures deduites et empiriques de l'intensite du signal Withdrawn EP1647160A1 (fr)

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US48886603P 2003-07-19 2003-07-19
US10/668,634 US8712428B2 (en) 2003-07-19 2003-09-23 Location estimation of wireless terminals through pattern matching of deduced signal strengths
US10/798,988 US7116987B2 (en) 2003-07-19 2004-03-12 Location estimation of wireless terminals through pattern matching of deduced and empirical signal-strength measurements
PCT/US2004/022676 WO2005011321A1 (fr) 2003-07-19 2004-07-14 Localisation estimative de terminaux sans fil par comparaison de modeles de mesures deduites et empiriques de l'intensite du signal

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