EP2510376A1 - Positionnement basé sur la tdoa (différence entre les temps d'arrivée) avec calcul de facteurs de correction pour compenser les décalages d'horloge de stations de réseau non synchronisées - Google Patents

Positionnement basé sur la tdoa (différence entre les temps d'arrivée) avec calcul de facteurs de correction pour compenser les décalages d'horloge de stations de réseau non synchronisées

Info

Publication number
EP2510376A1
EP2510376A1 EP10704912A EP10704912A EP2510376A1 EP 2510376 A1 EP2510376 A1 EP 2510376A1 EP 10704912 A EP10704912 A EP 10704912A EP 10704912 A EP10704912 A EP 10704912A EP 2510376 A1 EP2510376 A1 EP 2510376A1
Authority
EP
European Patent Office
Prior art keywords
signal
user
time
arrival
value
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Withdrawn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
EP10704912A
Other languages
German (de)
English (en)
Inventor
David Bevan
Simon Gale
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.)
Nortel Networks Ltd
Original Assignee
Nortel Networks Ltd
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 PCT/EP2009/066858 external-priority patent/WO2011069552A1/fr
Application filed by Nortel Networks Ltd filed Critical Nortel Networks Ltd
Priority to EP10704912A priority Critical patent/EP2510376A1/fr
Publication of EP2510376A1 publication Critical patent/EP2510376A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • 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
    • G01S5/06—Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements
    • 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
    • G01S5/0205—Details
    • G01S5/021—Calibration, monitoring or correction

Definitions

  • the present invention relates to wireless mobile networks or access points of a wireless local network having mobile user location functions, associated methods and computer program products.
  • One such method is based on a time difference of arrival TDOA and uses the time difference it takes for a signal to travel to two destinations as an ind irect method of calculating a d istance.
  • the difference in time it takes for the signal to reach each tower of a base station can be used to triangulate the position of the mobile unit.
  • TDOA systems do not need any specialized antennas and as such the infrastructure is kept simple.
  • the arrival time of the target mobile signal is recorded by a TDOA location measuring unit at each base station or access point which is able to receive the signal .
  • the method according to the present invention exploits the fact that base stations of a wireless mobile network or access points of a wireless local network are located at known positions and thus are situated in a fixed positional relationship. This allows to calculate signal propagation delays of beacon signals transmitted amongst those stations and received individually. These are calculated based on the known signal propagation speed and the respective distance between the stations.
  • the signals are transmitted wirelessly over the air, which advantageously allows for a very simple infrastructure as no cables and wires need to be deployed.
  • the signal is embodied as a beacon signal, because this allows using normal wireless access points or base stations which already transmit beacon signals to be used in the context of the present invention.
  • a signal is a frame, as frames by nature provide the advantage to possess a unique identification property in their frame number and thus further ease the implementation of the method of the present invention in presently used transmission systems.
  • the frame can be embodied as a frame according to a local area network protocol such as the IEEE 802.1 1 standard, as in this manner standards can be easily adapted by the present invention and commonly used transmission standards are suitable for incorporation in the method according to the present invention.
  • a local area network protocol such as the IEEE 802.1 1 standard
  • a polynomial with least squares may be used because such a polynomial is simple in its mathematical structure while at the same time satisfying the descriptive needs of the dependency of two clocks according to the method of the present invention without sacrificing any accuracy in the modeling process.
  • At least one sig nal is being transmitted before the arbitrary point in time and one is being transmitted after the arbitrary point in time in order to improve the accuracy of the clocking at the arbitrary point in time according to the method of the present invention.
  • the timing difference of arrival at a different pair of receiving stations is used to be able to accurately determine the location of a mobile station by a method of time difference of arrival based location determination. This allows the determination of two hyperbolas and their corresponding intersection point as the location of the mobile device.
  • the present invention provides an arrangement for clocking comprising: - at least a first, a second and a third device;
  • the first device having transmitting means for transmitting at least a first and a second signal with a unique identification
  • the second and third devices having receiving means and a clock for receiving the at least first and second signals and processing means for associating a respective measured second and third local clock at the reception time of the respective signal to it, leading to at least two value pairs of local clocks of the second and third device;
  • the second and third device further being adapted to receiving at an arbitrary point in time a user signal from a user device at the second and third device and associating a reception time measured by the respective second and third local clock of the second and third device to the user signal upon its reception, leading to a user value pair of local clocks of the second and third device, - processing means for calculating a reference time difference of arrival RTDOA for a signal from the first device received at the second and third device from the fixed positional relationship, based on the respective distance between the first and the second device and the first and the third device and the known signal propagation speed; and for calculating a user time difference of arrival UTDOA from the user value pair;
  • processing means is adapted to relate the RTDOA and
  • the arrangement accord ing to the present invention comprises a minimum number of receiving devices to achieve the clocking according to the present invention which provides a simple infrastructure in a competitive manner capable to solve the problem of the present invention.
  • a further development of the arrangement according to the present invention allows employing a server for the computational intensive tasks that need to be performed, which on the other hand allows a further simpl ification of the receiving stations, and only requires correspond ing communications of the respective identification of the received signals together with their associated time information to the computation server for calculating a location of the mobile device.
  • the computer program product of the invention provides a simple means to implement the method of the present invention at respective base stations and access points by providing a means of storage and transport.
  • Fig. 1 shows a simple transmitter and receiver arrangement according to an embodiment of the present invention
  • Fig. 2 gives an example of a relative clock behaviour of two receiving stations
  • Fig . 3 shows an example of signal transm ission accord ing to an embodiment of the present invention
  • Fig. 4 shows a flow-chart explaining the estimation of a user location based on a time difference of arrival according to an embodiment of the present invention
  • Fig. 5 gives an example of a computer program product according to the present invention.
  • Fig. 6 gives an example of a device of an arrangement according to the present invention.
  • top, bottom , over, under and the l i ke in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
  • a basic configuration to embody the method of the present invention comprises or consists of three access points AP1 , AP2 and AP4.
  • these access points can be any stations that are capable of transmitting respectively receiving signals, e.g. wireless signals.
  • the potential to be a transceiver, i.e. as well a transmitter as a receiver has certain advantages in terms of not having to have separate transmitting and receiving stations and thus providing an optimum use of resources.
  • the access points may be access points of a wireless LAN, e.g. according to the IEEE Standard 802.1 1 .
  • the access points may be stations that are capable of transmitting respectively receiving a signal, respectively a number of signals, especially wireless signals wh ich can be provided with a unique identifier or at least an element that enables a signal to be identifiable as a un ique signal . It is for instance conceivable that each signal has a different format and thus the unique identifier of the signal to be a unique signal is the format.
  • the station AP4 transmits a unique signal, respectively a sequence of unique signals that is/are received by stations AP2 and AP1 .
  • the respective stations AP1 and AP2 associate the unique signal with a time measured by their local clock that has been measured at the time of reception of the un ique signal .
  • such an association may be performed for one, two or a plurality of unique signals in order to protocol a dependency of the local clocks of the stations AP2 and AP1 in association to a joint reception of the same individual unique signal from the station AP4.
  • these clocks are subject to a temperature drift to a clock inaccuracy drift, e.g . to a phase drift, and/or to a frequency drift of the clock, which imposes a certain inaccuracy of the clocking of the individual stations AP1 to AP4.
  • the absolute offsets and rate differences of the va riou s clocks of th e station s AP 1 to AP4 may be q ua ntified in microseconds of drift per second, or equivalently, parts per million PPM.
  • offsets can be accumulated or bu ilt up and maintained over long periods of many seconds or minutes when they are measured . Th is provides accurate measurement.
  • the accumulated offsets or any related value thereto can be stored , e .g . in an optional location eng ine .
  • the location eng ine may be implemented in the form of a server performing the calculation of the time difference of arrival at the various stations.
  • a time difference of the signal flight times between a user device (not shown), which may be implemented as a mobile device, and two or more receiving stations, for instance AP2, AP1 , and AP4 may be calculated.
  • 1 10 in the given example the user's position should be somewhere on hyperbola 120.
  • the user's position should also be somewhere on the hyperbola marked by reference sign 130. Therefore, at the intersection of hyperbolas 1 10 and 130 the user's position also ind icated by reference sign 1 40, respectively the position of the mobile device of the user, can be identified.
  • the embodiment of the present invention exploits the fact, that the distances between the known stations AP1 to AP4 are known, as they are in a fixed positional relationship and that based on the separation distances of the stations between each other, an accurate propagation time of a correspondingly transmitted signal can be calculated by taking the distance and the propagation speed .
  • establ ish ing a time d ifference of arrival based on an accurate calculation allows the establ ishment of a relationsh ip of th is accurate time difference of arrival to a time difference of arrival that has been measured by the inaccurate clocks of the two stations in question.
  • an analysis can be made to identify a corresponding error value in the time difference of arrival measured by the inaccurate clocks of the two receiving stations . Further, based on the accurate calculation the system is able to compute a correction value and thus to derive an accurate time difference of arrival at an arbitrary point in time regarding these two receiving stations. For instance, this can be achieved by relating the correct values at an arbitrary point in time to the modeled value at th is point in time to calculate the cu rrent correction value. Mathematical operations in this context are preferably division to relate the values and multiplication to calculate the corrected time difference of arrival for a signal received from a user device with the current correction value.
  • Such a process may be performed for any two receiving stations that are part of the configuration shown in the embodiment of Fig. 1 .
  • Fig. 2 gives an example of a clock behavior at two stations AP1 and AP2 indicated by reference sign 290.
  • the local time of the clock at station AP2 is marked by 275 and on the horizontal axis the time at station AP1 is marked by 265.
  • the triangles in the d iagram ind icated by reference signs 21 5, 220, 230, 235, 240, 245 and 255 represent the reception times of unique signals at the station AP1 respectively AP2. If the clocks at AP1 and AP2 were performing correctly and very accurately, there would be no curve connecting the triangles and they would all lie on a straight line.
  • I n th is case the known propagation time of the sig nal based on a calculation of the signal propagation speed and the distance between respectively AP4 and AP2 and AP4 and AP1 have been subtracted from the reception times of the signal, which may be a beacon signal from AP4.
  • the locations of the station are known such a calculation can be easily performed by a skilled person.
  • the curve represented by reference sign 21 0 connecting the various triangles can be modeled by any su itable regression or interpolation method, e.g. by a simple polynomial.
  • su itable modeling techn iques are conceivable like value approximation by a neural network trained with the value pairs of measured local clocks.
  • Reference sign 250 indicates the time as an arbitrary point in time at which a signal from a mobile device of a user is received at the respective stations AP1 and AP2.
  • a smooth curve between measurements can be obtained by polynomial curve fit which yields a time d ifference between AP1 and AP2 at a user observation time.
  • a dependency of the inaccurate local clocks is for instance further explained in the configuration shown in Fig. 3.
  • a local clock of station AP2 referenced by 321 and a local clock of station AP1 referenced by 31 1 is shown.
  • a signal propagation time between AP4 and AP2 marked by reference sign T p 2 is known based on a calculation of the distance and the propagation speed, which also holds true for the propagation time of a signal transm itted between AP4 and AP1 ind icated by T p ,i .
  • the measu rements ta ken for a sig nal transm itted from station AP4 and the associated timing can for instance be transmitted to a server indicated by reference sign 380 performing the required calculations as well as a suitable modeling function such as a regression analysis of which a polynomial curve fit is one example whereas the transmission is exemplified by an arrow marked by reference sign 350.
  • a relative clock behavior may be obtained by over air measurements.
  • a propagation time correction may be performed in the following manner. It may be assumed, that there are two receiving stations AP1 and AP2 at known locations. The clocks of AP1 and AP2 are ticking in nano seconds and are not synchronized with each other.
  • AP 1 time stamps a frame received from AP4 with the read ing of 629, 1 54,927 ns
  • AP2 time stamps the same frame received from AP4 with the reading of 402,549,572 ns.
  • the fitting of a regression curve such as a polynomial curve to an observed relative AP clock behavior may be performed in the following manner.
  • a relative clock behavior is monitored over a segment of time containing n observations that span the instant when a relative timing of a user observation needs to be established.
  • n observation times wh ich eventually need to be corrected for known propagation times of the same beacon transmissions
  • T A pi,i and T A P2,i a polynomial curve may be fitted to the observed data which is, for example, a least squares fit to the observed data, e.g. in form of
  • TAP2 ao + ai TAPI + B2 (TAPI ) .
  • ao represents a fixed time offset
  • ai represents a fixed frequency offset
  • a2 represents a linear frequency drift with time.
  • ao represents a fixed time offset
  • ai represents a fixed frequency offset
  • a2 represents a linear frequency drift with time.
  • Fig. 4 shows an example of a position determination process in a flowchart according to an embodiment of the present invention.
  • each station measures its inaccurate signal arrival time against its own clock for every signal it receives.
  • the stations send the observations meaning the arrival time of the individual signal and the associated signal identification for instance to a location server which may be employed to calculate a location.
  • the server stores all measurements over a period of time, for instance for the period of some 1 0s of seconds.
  • each station receiving a suitable signal e.g . a user frame, measures the arrival time of each particular user frame, representative of a user signal using its local clock and at 430 sends the observed user signal measurement and the associated identification as well as time to the location server.
  • the server retrieves the values stored for signal transmission between the wireless stations corresponding to the wireless stations that have received the user signal and at 440 corrects the observation regard ing the retrieved com m u n ication between the wireless station by subtracting the known propagation delays based on propagation speed and positional relationship, respectively known distances. Subsequently at 440 a regression analysis such as fitting a polynomial is carried out on the corrected value pairs for each pair of wireless stations wh ich received the common intercomm un ication between the wireless stations . At 450 the server, for instance, uses the polynomials to estimate the clock offsets of the wireless stations at times corresponding to the time where the user signal was received.
  • a time difference of arrival for the user signal is calculated and corrected for the factor determined on the basis of the stored values from the correspond ing pair of wireless stations and the calculated polynomial estimate of the clock offset.
  • the corrected time difference of arrivals information are transmitted to the location algorithm and at 470 the estimated user location is calculated by intersecting the two hyperbolas as shown in Fig. 1 but marked by reference sign 120 and 130 to determine the user location indicated by arrow 140 which is retrieved at 495. Marked by 475 such a process may be repeated to determine various user locations.
  • Fig. 5 shows an example of a computer program product according to the present invention.
  • Reference sign 500 indicates a data carrier which comprises a program code 520 representative of any of the method steps according to the present invention.
  • Such a computer program product constitutes a simple entity to transport the method of the present invention and to implement it on the transmitting and receiving stations AP1 to AP4 of the present invention in case they are equipped with a network interface or a corresponding data reader.
  • the data carrier of the present invention may be a suitable data carrier such as a magnetic- or optical medium or a hardware storage medium such as a flash storage. It may also be represented by a signal that is transmitted on a network according to a certain network protocol implemented on a wired network or on a wireless network for download ing the program code from one computer to another computer.
  • Fig . 6 shows an example of a station that may be employed in an arrangement according to the present invention.
  • Reference sign 600 indicates a wireless station e.g. an access point or any other wireless or wire bound device capable of transmitting and/ or receiving unique signals preferably identifiable by a un ique identifier such as e.g . a frame number. It has an input/ output interface 61 0 of any kind be it mechanical electrical or user specific for data entry and display. Further the station contains a receiver 615 and a transmitter 620 for instance capable of emitting and receiving in the GSM, Bluetooth or WLAN range of frequencies, or to handle standard packet communication over wire or optical media.
  • a wireless station e.g. an access point or any other wireless or wire bound device capable of transmitting and/ or receiving unique signals preferably identifiable by a un ique identifier such as e.g . a frame number. It has an input/ output interface 61 0 of any kind be it mechanical electrical or user specific for data entry and display.
  • the station contains a receiver 615
  • a controller or processor 625 is capable to control the fu nctions of the station 600 and has the power to perform the req u ired computations.
  • a memory 630 is present which may be any optical semiconductor or magnetic device for storing communication and operation data.
  • Reference sign 635 indicates a power supply which may be a battery or a transformer connected to a wal l outlet. All the i nternal com ponents are connected by a suitable system bus 650 ensuring the proper operation of the station 600.

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

Abstract

La présente invention concerne un procédé, une configuration et un produit de programme informatique permettant l'exploitation synchronisée du comportement relatif d'horloges de stations réceptrices individuelles, ainsi qu'une modélisation correspondante servant à dériver une différence entre les temps d'arrivée d'un signal provenant du dispositif d'un utilisateur, qui peut être utilisée pour corriger la différence entre les temps d'arrivée sur la base du comportement modélisé des horloges et obtenir une synchronisation correcte des signaux utilisateurs reçus sans qu'il soit nécessaire de synchroniser les horloges des diverses stations réceptrices. Ce principe peut être appliqué à une pluralité de paires de stations réceptrices et aux signaux de balise qu'elles se transmettent, et permet une estimation correcte de l'emplacement du dispositif d'un utilisateur.
EP10704912A 2009-12-10 2010-01-22 Positionnement basé sur la tdoa (différence entre les temps d'arrivée) avec calcul de facteurs de correction pour compenser les décalages d'horloge de stations de réseau non synchronisées Withdrawn EP2510376A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP10704912A EP2510376A1 (fr) 2009-12-10 2010-01-22 Positionnement basé sur la tdoa (différence entre les temps d'arrivée) avec calcul de facteurs de correction pour compenser les décalages d'horloge de stations de réseau non synchronisées

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
PCT/EP2009/066858 WO2011069552A1 (fr) 2009-12-10 2009-12-10 Procédé, agencement et produit programme d'ordinateur pour cadencement
PCT/EP2010/050747 WO2011069684A1 (fr) 2009-12-10 2010-01-22 Positionnement basé sur la tdoa (différence entre les temps d'arrivée) avec calcul de facteurs de correction pour compenser les décalages d'horloge de stations de réseau non synchronisées
EP10704912A EP2510376A1 (fr) 2009-12-10 2010-01-22 Positionnement basé sur la tdoa (différence entre les temps d'arrivée) avec calcul de facteurs de correction pour compenser les décalages d'horloge de stations de réseau non synchronisées

Publications (1)

Publication Number Publication Date
EP2510376A1 true EP2510376A1 (fr) 2012-10-17

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP10704912A Withdrawn EP2510376A1 (fr) 2009-12-10 2010-01-22 Positionnement basé sur la tdoa (différence entre les temps d'arrivée) avec calcul de facteurs de correction pour compenser les décalages d'horloge de stations de réseau non synchronisées

Country Status (1)

Country Link
EP (1) EP2510376A1 (fr)

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO2011069684A1 *

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