WO2008124316A1 - Différence temporelle d'une estimation basée sur une arrivée d'une vitesse et d'une direction de voyage dans un système de positionnement wlan - Google Patents

Différence temporelle d'une estimation basée sur une arrivée d'une vitesse et d'une direction de voyage dans un système de positionnement wlan Download PDF

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Publication number
WO2008124316A1
WO2008124316A1 PCT/US2008/058345 US2008058345W WO2008124316A1 WO 2008124316 A1 WO2008124316 A1 WO 2008124316A1 US 2008058345 W US2008058345 W US 2008058345W WO 2008124316 A1 WO2008124316 A1 WO 2008124316A1
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Prior art keywords
wlan
enabled device
travel
arrival
time
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PCT/US2008/058345
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English (en)
Inventor
Farshid Alizadeh-Shabdiz
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Skyhook Wireless, Inc.
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Priority claimed from US11/696,832 external-priority patent/US20080248808A1/en
Priority claimed from US11/696,833 external-priority patent/US20080248741A1/en
Application filed by Skyhook Wireless, Inc. filed Critical Skyhook Wireless, Inc.
Publication of WO2008124316A1 publication Critical patent/WO2008124316A1/fr

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W64/00Locating users or terminals or network equipment for network management purposes, e.g. mobility management
    • H04W64/006Locating users or terminals or network equipment for network management purposes, e.g. mobility management with additional information processing, e.g. for direction or speed determination
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W84/00Network topologies
    • H04W84/02Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/10Small scale networks; Flat hierarchical networks
    • H04W84/12WLAN [Wireless Local Area Networks]

Definitions

  • the invention generally relates to using Time Difference Of Arrival (TDOA) to estimate speed, bearing (direction of travel), and location of WLAN enabled mobile devices in a WLAN based positioning system and, more specifically, utilizing the TDOA of packets from the same WLAN access point to estimate speed and bearing of a WLAN enabled mobile device.
  • the invention also includes increasing the accuracy of location, speed, and bearing estimation by combining the results of TDOA based estimations with Received Signal Strength (RSS) based determinations of location, speed and bearing of the WLAN enabled mobile device using a WLAN based positioning system.
  • RSS Received Signal Strength
  • RSS Received Signal Strength
  • TOA Time of Arrival
  • AOA Angle of Arrival
  • a synchronized network means there exists a central reference clock and the timing of all the access points are exactly the same.
  • the synchronization is easy to achieve for small size networks as in a corporate WLAN environment.
  • synchronizing the entire network is not possible and even for municipal networks (a city wide WiFi network installed and managed by one entity) the technique is very difficult to achieve, and none are known to exist. Therefore, TDOA from different access points or TOA is not used.
  • the classic example is having a system that can monitor the exact location of the crash cart within the hospital so that when there is a cardiac arrest the hospital staff doesn't waste time locating the device.
  • the accuracy requirements for these use cases are very demanding, typically calling for 1-3 meter accuracy.
  • These systems use a variety of techniques to fine tune their accuracy including conducting detailed site surveys of every square foot of the campus to measure radio signal propagation. They also require a constant network connection so that the access point and the client radio can exchange synchronization information similar to how A-GPS works. While these systems are becoming more reliable for indoor use cases, they are ineffective in any wide-area deployment.
  • FIG. 1 depicts a WiFi positioning system (WPS).
  • the positioning system includes positioning software [103] that resides on a computing device [101]. Throughout a particular target geographical area, there are fixed wireless access points [102] that broadcast information using control/common channel broadcast signals.
  • the client device monitors the broadcast signal or requests its transmission via a probe request. Each access point contains a unique hardware identifier known as a MAC address.
  • the client positioning software receives signal beacons from the 802.11 access points in range and calculates the geographic location of the computing device using characteristics from the signal beacons. Those characteristics include the unique identifier of the 802.11 access point, known as the MAC address, Time of Arrival (TOA), and the strengths of the signal reaching the client device.
  • TOA Time of Arrival
  • the client software compares the observed 802.11 access points with those in its reference database [104] of access points, which may or may not reside on the device as well.
  • the reference database contains the calculated geographic locations and power profile of all the access points the gathering system has collected.
  • the power profile may be generated from a collection of readings that represent the power of the signal from various locations.
  • the client software calculates the relative position of the user device [101] and determines its geographic coordinates in the form of latitude and longitude readings. Those readings are then fed to location-based applications such as friend finders, local search web sites, fleet management systems and E911 services.
  • a method of estimating a direction of travel of a WLAN-enabled device includes estimating a speed of travel of the WLAN-enabled device and estimating a geographic location of the WLAN-enabled device.
  • the method also includes the WLAN-enabled device receiving signals transmitted by a WLAN access point in range of the WLAN-enabled device. The signals include a first message and a second message.
  • the method further includes accessing a reference database to determine the geographic location of the WLAN access point, determining an actual time of arrival value of the second message, and determining a time difference of arrival value for the second message based on the actual time of arrival of the second message and an expected time of arrival of the second message.
  • the expected time of arrival of the second message is based on an actual arrival time of the first message.
  • the method also calls for estimating the direction of travel of the WLAN-enabled device based on the speed of travel of the WLAN- enabled device, the estimated geographic location of the WLAN-enabled device, the time difference of arrival value, and the geographic location of the WLAN access point.
  • the first and second messages can be data packets. Estimating the expected time of arrival of the second message can be further based on an inter- frame spacing value.
  • the method of estimating the direction of travel includes, for more than one WLAN access point in range of the WLAN-enabled device, estimating corresponding time difference of arrival values for messages received from the more than one WLAN access point and accessing a reference database to determine the geographic location of each of the more than one WLAN access points.
  • the method includes estimating a corresponding direction of travel of the WLAN-enabled device based on the speed of travel of the WLAN-enabled device, the corresponding time difference of arrival values, and the geographic locations of the WLAN access points and estimating the direction of travel of the WLAN-enabled device based on the directions of travel corresponding to the more than one WLAN access points.
  • estimating the direction of travel of the WLAN-enabled device based on the directions of travel corresponding to the more than one WLAN access points includes finding the median value of the corresponding directions of travel.
  • the method of estimating the direction of travel further includes, repetitively determining and monitoring the time difference of arrival values corresponding to the WLAN access points over a period of time and identifying time difference of arrival values associated with line of sight signal components based on the change in time difference of arrival values during the period of time. Determining the direction of travel of the WLAN-enabled device is based on the difference of arrival values associated only with line of sight signal components. [0012J Under one aspect of the invention, the method of estimating the direction of travel also includes determining a plurality of time difference of arrival values based on signals transmitted by the WLAN access point during a window of time and estimating the direction of travel of the WLAN-enabled device based on the plurality of time difference of arrival values.
  • the window of time is based on a maximum expected speed of the WLAN-enabled device and can be about 10 seconds, about 2 seconds, or about 1 second.
  • determining the geographic location of the WLAN-enabled device can be based on the received signals transmitted by the WLAN access point and the geographic location of the WLAN access point, which can include at least one received signal strength of signals transmitted by the WLAN access point. Determining the geographic location of the WLAN-enabled device can be based on information from a Global Navigation Satellite System.
  • determining the speed of travel of the WLAN-enabled device can be based on the received signals transmitted by the WLAN access point and the geographic location of the WLAN access point, which can include at least one received signal strength of signals transmitted by the WLAN access point. Determining the speed of travel of the WLAN-enabled device can be based on information from a Global Navigation Satellite System and/or information from a Doppler system.
  • a method of estimating a speed of travel of a WLAN-enabled device includes the WLAN-enabled device receiving signals transmitted by a WLAN access point in range of the WLAN-enabled device. The signals include a first message and a second message.
  • the method also includes estimating an expected time of arrival of the second message based on an actual arrival time of the first message and determining an actual time of arrival value of the second message.
  • the method further includes determining a time difference of arrival value for the second message based on the actual time of arrival of the second message and the expected time of arrival of the second message and estimating the speed of travel of the WLAN-enabled device based on the time difference of arrival value.
  • the first and second messages can be data packets. Estimating the expected time of arrival of the second message can be further based on an inter- frame spacing value.
  • the method of estimating the speed of travel also includes, for more than one WLAN access point in range of the WLAN-enabled device, estimating corresponding time difference of arrival values for messages received from the more than one WLAN access point.
  • the method calls for estimating a reference speed of travel of the WLAN-enabled device relative to the corresponding WLAN access point based on the time difference of arrival value and determining the estimated speed of travel of the WLAN-enabled device based on the reference speeds of travel.
  • determining the estimated speed of travel of the WLAN-enabled device includes selecting the largest reference speed of travel as the estimated speed of travel of the WLAN-enabled device.
  • the method of estimating the speed of travel also includes repetitively determining and monitoring the time difference of arrival values corresponding to the WLAN access points over a period of time and identifying time difference of arrival values associated with line of sight signal components based on the change in time difference of arrival values during the period of time.
  • T the estimated speed of travel of the WLAN-enabled device is determined based on the reference speeds of travel estimated from time difference of arrival values associated only with line of sight signal components.
  • the method determines a plurality of time difference of arrival values based on signals transmitted by the WLAN access point during a window of time and estimates the speed of travel of the WLAN-enabled device based on the plurality of time difference of arrival values.
  • the window of time is based on a maximum expected speed of the WLAN-enabled device.
  • the window of time can be about 10 seconds, about 2 seconds, or about 1 second.
  • the method of estimating the speed of travel further includes accessing a reference database to determine a geographic location of the WLAN access point, determining a geographic location of the WLAN-enabled device, and determining a direction of travel of the WLAN-enabled device.
  • the method also calls for determining the bearing from the WLAN-enabled device to the WLAN access point based on the geographic location and direction of travel of the WLAN-enabled device and the geographic location of the WLAN access point, wherein estimating the speed of travel of the WLAN-enabled device is further based on the bearing from the WLAN-enabled device to the WLAN access point.
  • determining the geographic location of the WLAN-enabled device is based on the received signals transmitted by the WLAN access point and the geographic location of the WLAN access point. Determining the geographic location of the WLAN-enabled device can be based on at least one received signal strength of signals transmitted by the WLAN access point and/or information from a Global Navigation Satellite System.
  • dete ⁇ nining the direction of travel of the WLAN-enabled device is based on the received signals transmitted by the WLAN access point and the geographic location of the WLAN access point. Determining the direction of travel of the WLAN-enabled device can be based on at least one received signal strength of signals transmitted by the WLAN access point and/or information from a Global Navigation Satellite System.
  • the speed of travel of the WLAN- enabled device is estimated to be zero when the time difference of arrival value is below a threshold value.
  • Figure 1 illustrates an embodiment of a WiFi positioning system
  • Figure 2 illustrates that constant TDOA places a mobile device on a hyperbola
  • Figure 3 illustrates an example of D-TDOA system
  • Figure 4 illustrates an example of estimating TDOA for WiFi networks
  • Figure 5 illustrates that the received signal by a mobile device is impacted by the multi-path effect.
  • Embodiments of the invention estimate speed and bearing of a WLAN enabled mobile device using the Time Difference Of Arrival (TDOA) of packets in a WLAN based positioning system.
  • the WLAN based positioning system can be based on a synchronized network in which a reference clock and the time of all of the WLAN access points used for estimation is synchronized.
  • the WLAN based positioning system can be based on a network without any time and clock synchronization between WLAN access points.
  • Embodiments of the invention can also estimate the speed and bearing of a WLAN enabled mobile device using Time Difference Of Arrival (TDOA) of packets from the same WLAN access point in a WLAN based positioning system.
  • TDOA Time Difference Of Arrival
  • the time of arrival of consecutive packets are measured, and, based on a drift in the difference between the consecutive packets received from the same WLAN access point, the speed and bearing of a WLAN-enabled device are estimated.
  • the WLAN based positioning system can be based on a synchronized network or it can be based on a network without any time and clock synchronization between WLAN access points.
  • Embodiments of the invention further include increasing the accuracy of location, speed, and bearing estimations by combining the results of TDOA based estimations of speed and bearing with Received Signal Strength (RSS) based determinations of location, speed and bearing of a WLAN-enabled mobile device using a WLAN based positioning system.
  • RSS based estimation techniques for determining the location, speed, and bearing of a WLAN mobile device are described in greater detail below.
  • TDOA time difference between receiving packets, which were sent by different WLAN access points at the same time, herein referred to generally as "TDOA".
  • the second definition is the time difference between the times of arrival of multiple packets from the same WLAN access point.
  • TDOA of packets from the same WiFi access point is referred to as "Drift-TDOA” or “D-TDOA” herein to distinguish over the traditional definition of TDOA.
  • D-TDOA the arrival time of a packet, or multiple packets, is used to calculate an expected arrival time of the next packet.
  • the time difference between the expected time of arrival of the next packet and its actual time of arrival is determined; this is the D-TDOA of the later packet. If the expected time of arrival and the actual time of arrival of the later (or next) packet are denoted by TOA e and TOA 3 , respectively, the D-TDOA is calculated as follows:
  • the expected time of arrival of the next packet is calculated based on the time of arrival of the last received packet (or packets) plus the transmission time, Inter Frame Spaces (IFS), and an integer number of time slots, as defined by the 802.11 standard (herein incorporated by reference).
  • IFS Inter Frame Spaces
  • the receiver can calculate the exact expected starting point of the time slots in which the next packet can arrive. If a WiFi enabled mobile device remains stationary, the arrival time of the next packet will be exactly at the beginning of a slot; if the WiFi enabled mobile device moves, there will be a time drift corresponding to its movement. That time drift is used to calculate a change in location.
  • Embodiments of the present invention build on techniques, systems and methods disclosed in earlier filed applications, including but not limited to U.S. Patent Application No. 11/261,848, entitled Location Beacon Database, U.S. Patent Application No. 11/261, 898, entitled Server for Updating Location Beacon Database, U.S. Patent Application No. 11/261,987, entitled Method and System for Building a Location Beacon Database, and U.S. Patent Application No. 11/261,988, entitled Location-Based Services that Choose Location Algorithms Based on Number of Detected Access Points Within Range of User Device, all filed on October 28, 2005, and also including but not limited to U.S. Patent Application No.
  • Embodiments of the present invention also build on techniques, systems and methods disclosed in earlier filed applications, including but not limited to U.S. Patent Application No. U.S. Patent Application No. 11/430,079, entitled Estimation Of Speed and Direction of Travel In A WLAN Positioning System, U.S. Patent Application No. 11/429,862, entitled Estimation of Speed of Travel Using the Dynamic Signal Strength Variation of Multiple WLAN Access Points, U.S. Patent Application No. 11/430,064, entitled Estimation of Speed and Direction of Travel In A WLAN Positioning System Using Multiple Position Estimations, all filed on May 8, 2006, the contents of which are hereby incorporated by reference in their entirety.
  • Embodiments of the invention also provide a system for and a method of continuously maintaining and updating speed and bearing estimation of a WLAN-enabled mobile device based on D-TDOA determinations, and also a method for detecting zero speed or stationary WLAN-enabled devices.
  • the mobile device scans and detects public and private WLAN access points, logs D-TDOA corresponding to each of the WLAN access points, and uses that information to estimate or refine speed and bearing estimates of the mobile device.
  • a WLAN mobile device If a WLAN mobile device is synchronized with a set of WLAN access points, the WLAN mobile device knows the departure time of the received signal.
  • the synchronization of a WLAN mobile device with the WLAN network means synchronizing the reference clock and the reference time of the mobile device with the central time of the entire network. Therefore, because the exact departure time of the packet from the transmitter is known by the receiver (the user's mobile device) and the absolute travel time of the signal can be calculated as a result, the exact distance of the mobile device from the WLAN access point can be found. By knowing the distance from the WLAN access point and also the location of the WLAN access point, the location of WLAN enabled mobile device can be calculated given multiple access points.
  • a synchronized network of WiFi access points for a metro area is considered. This can be, for example, a synchronized municipal network. All the WiFi access points are configured to transmit a given signal (for example a beacon signal) at the given time, and a WiFi enabled mobile device calculates the TDOA of the received signal from different access points.
  • TDOA is equal to the difference between the distances of the user from the access points divided by speed of light. Therefore, by measuring the TDOA values of packets departing from different access points at the synchronized time, a WiFi enabled mobile device can measure its distance from each access point.
  • a WiFi enabled mobile device Referring to Figure 2, the location of a mobile device with a constant difference of distance from two reference points is on a hyperbola.
  • the exact location of the mobile device can be calculated.
  • An example of two access points and a mobile device is shown in Figure 2.
  • the distance of a mobile device [203] from an access point APi [201] is di [202]
  • the distance of a mobile device [203] from an access point AP 2 [205] is d 2 [206].
  • the mobile device can calculate (di-d?). Therefore, the location of mobile device can be anywhere on the hyperbola [204].
  • the RSS based methods incorporated above can be used in combination with this TDOA method to provide a coarse location estimation and improve the estimation results to avoid large errors due to multi-path signals.
  • a wide-area WiFi positioning system leverages existing private and public WiFi access points, which do not operate in a coordinated or synchronized fashion.
  • the TDOA between consecutive received packets from the same WiFi access point is calculated (i.e., D-TDOA).
  • the drift in time of arrival of consecutive packets from the same access point, as defined above, is the D-TDOA value.
  • a mobile device [302] moves from Point A [301] by a distance of d [306] to Point B [302]
  • its distance from an access point [303] changes from dj [305] to ⁇ [304].
  • the speed of light is denoted by C
  • the D-TDOA or ⁇ t s is equal to
  • the time At is the travel time of the distance d. If the distance of movement is much smaller than the distance of the mobile device from the WiFi access point or ⁇ d « dj and di), the following approximation holds true: d ⁇ - d 2 ⁇ d x cos( ⁇ ) .
  • the parameter ⁇ [307] is the angle between the line connecting the mobile device to the access point [303] with the direction of travel.
  • the speed of the mobile device can be estimated as follows:
  • the angle a [307] is known by the mobile device. For example, when a rough location estimate of the WLAN mobile device can be made using other methods, and the access point location is known, a can be calculated. In these cases, the speed of a mobile device can be calculated by detecting only one WiFi access point. If the angle a is not known, the mobile device computes Vcos(a) from the above equation for each detected WiFi access point. The value Vcos(a) is called the "speed reference" to a given access point. The speed reference to an access point is maximized when the angle a [307] is equal to zero or 180.
  • the maximum of multiple speed references to is selected as the best estimate of the speed of the mobile device.
  • the expected time of arrival of a packet is calculated based on the exact time of arrival of the last packet plus Inter- Frame Space (IFS) timing as specified in the WiFi standard and the duration of an integer number of time slots. Slot duration is in the range of microseconds, while the deviation of packet arrival time due to the user's movement is in the range of nanoseconds. Therefore, nanosecond drift of time of arrival of a packet is considered due to the user movement.
  • IFS Inter- Frame Space
  • packet number one [401] and packet number two [404] are apart in time by the end of the transmission time of the first packet plus the length of the DCF Inter-Frame Space [402] (herein "DIFS") and the duration of an integer number of time slots [403] as defined in the WiFi standard. [0048] Therefore, when the mobile device moves and the propagation delay changes, the second packet arrives not exactly inline with start of a time slot, as it is shown by the dashed line of example (b) of Figure 4.
  • DIFS DCF Inter-Frame Space
  • a first packet [405] and a second packet [408] are apart in time from the end of the first packet [405] by the length of the DIFS [406], an integer number of slots [407], and also a small delay due to movement of the mobile device and the corresponding increase of the propagation delay between the mobile device and the access point.
  • a method of determining the direction of travel of a WLAN enabled mobile device equipped with a reference database of WLAN access points in a target area is provided.
  • the direction of travel is estimated by using geographical location information of WLAN access points in the reference database, an estimated location of the WLAN enabled mobile device (determined by, e.g., GPS, methods disclosed in the incorporated applications, or other methods), an estimated speed of travel of the mobile device, and an estimated speed of travel of the device relative to multiple access points (i.e. speed references).
  • a mobile device determines its absolute speed of travel (e.g., by using Doppler, GPS, consecutive position estimations, or some other method) and also calculates its speed references to a number of access points (e.g., by using the D-TDOA techniques provided above), the device can calculate the angles, ⁇ , between the direction of travel and straight lines between the WiFi enabled mobile device and each detected WiFi access point.
  • the angle a is calculated by dividing the speed reference to the access point (Vcos(a)) by the absolute speed of travel (V) and finding the cosine of a.
  • the reference database is accessed to retrieve the corresponding geographical location information of the identified Wi-Fi access points.
  • the geographical locations of the detected Wi-Fi access points, the angles, a, and the estimated location of the WLAN enabled mobile device are used to estimate the direction of travel.
  • the D-TDOA techniques and methods described above can be combined with Received Signal Strength (RSS) based techniques to increase the accuracy of location, speed, and bearing estimations of a WLAN enabled mobile device using a WLAN positioning system.
  • RSS Received Signal Strength
  • the WLAN enabled mobile device scans for and detects public and private WLAN access points and logs both TDOA and RSS values corresponding to each of the detected WLAN access points.
  • the RSS based techniques are used to estimate the location, speed and bearing of the WLAN enabled mobile device, and the D-TDOA methods are also used to estimate the speed and bearing independent of RSS values. These independent sets of values are then combined to provide location, speed, and bearing values of increased accuracy.
  • the RSS based estimation of location, speed and bearing can be used by the D-TDOA based techniques as a rough estimate of speed and bearing.
  • the system can then use these rough values to estimate more accurate speed and bearing determinations employing the D-TDOA methods.
  • These improved speed and bearing values are then fed back to the system for use in further refining the location estimation, thereby also improving the location estimation.
  • a WiFi positioning system operates in a multi-path environment.
  • Figure 5 provides an example of a mobile device [501] receiving two signals from the same WiFi access point [502]. One signal is received directly from the WiFi access point [503], and the other one is received after reflecting off of a building [504]. Therefore, some measurements of TDOA and D-TDOA can be based on a multi-path component and not solely on the direct line of sight component of the received signal.
  • the direction of arrival of a multi-path component is different than the direct line of sight component, because the multi-path component is a reflection of the signal from surrounding objects.
  • the calculated angle, a is between the direction of arrival of the multi-path component and the direction of travel.
  • This component cannot be used to find an accurate direction of travel. If the bearing is calculated based on a multi-path component, the random nature of multi-path causes the bearing value to change randomly over time. Therefore, random change of the bearing or the history of movement of the mobile device can be used as criteria to detect this case and eliminate it from the bearing calculation
  • the bearing calculations based on multi- path components can also be detected.
  • a mobile device can begin by considering the bearing values calculated for all the detected WiFi access points. Access point signals that arrive from paths other than direct lines of site from the corresponding WiFi access points can then be eliminated using the history of movement and coarse bearing calculations derived using other methods (e.g., such as those described in the incorporated applications).
  • the final direction of travel is then calculated by combining all of the valid bearing samples. These valid bearing samples can be combined in different ways. For example, the median of samples can be considered as the final direction of travel.
  • the direct line of sight component of the signal is extracted by knowing a coarse bearing and a coarse speed.
  • the coarse bearing is determined using a method other than one based on D-TDOA (e.g., such as those described in the incorporated applications).
  • the bearings for the different multi-path components are calculated and compared to the coarse bearing information to determine which component among the various multi-path components is the line of sight component.
  • the direct line of sight signal component is then used to calculate D-TDOA and/or TDOA, and, subsequently, the direct line of sight component is used to calculate location, speed and direction of travel of the WiFi mobile device.
  • the time of arrival of a signal is calculated based on the strongest received signal.
  • the strongest received signal can be the direct line of sight signal or it can be a multi-path component.
  • the D-TDOA is determined for both the direct line of sight component and the multi-path components, and these measurements are used to calculate the speed of travel as described above. If the time of arrival of the packets involved in the D- TDOA determination are calculated based on the same multi-path component, the expected time of arrival and the actual time of arrival are compared using the same reference point, and thus, those signals can be used to determine the D-TDOA.
  • T n the duration of T n .
  • the value of T n depends on the mobility model of the mobile device, that is, the end use to which the device is put. For example, if the mobility model is that of a pedestrian, the duration of T n can be ten seconds. However, if the device is to be used in an automobile, the duration of T n is one to two seconds.
  • the T n period depends on the speed of the mobile device and its value can be also changed dynamically based on the estimation of speed of the mobile device.
  • the amount of movement during T n can be known to be negligible. Therefore, all the packets received during the period of T n can be used to calculate TDOA and D-TDOA to increase the accuracy of the estimation of the time of arrival.
  • the accuracy of estimation is increased by considering multiple samples of TDOA or D-TDOA estimations, which are taken during the duration of T n , instead of a single sample. Again, because the mobility of the mobile device during T n is negligible, the estimation results for the duration of T n are correlated. Therefore, combining the multiple estimation results determined during the duration of T n increases the accuracy of overall estimation of TDOA or D-TDOA. For example, the estimation results can be averaged to reduce the impact of noise.

Abstract

L'invention concerne des procédés d'estimation de la vitesse et/ou de support d'un dispositif activé WLAN. Un procédé d'estimation d'un support d'un dispositif activé WLAN comprend la réception de signaux transmis par un point d'accès, comprenant un premier message et un second message. Le procédé consiste en outre à déterminer un temps actuel d'une valeur d'arrivée du second message et de déterminer une différence temporelle d'une valeur d'arrivée pour le second message sur la base du temps actuel d'arrivée du second message et d'un temps d'arrivée prévu du second message, qui est basé sur un temps d'arrivée actuel du premier message. L'estimation du support du dispositif est basée sur la vitesse estimée et l'emplacement du dispositif, la différence temporelle d'une valeur d'arrivée, et l'emplacement du point d'accès. L'estimation de la vitesse du dispositif est basée sur la différence temporelle d'une valeur d'arrivée.
PCT/US2008/058345 2007-04-05 2008-03-27 Différence temporelle d'une estimation basée sur une arrivée d'une vitesse et d'une direction de voyage dans un système de positionnement wlan WO2008124316A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US11/696,832 2007-04-05
US11/696,832 US20080248808A1 (en) 2007-04-05 2007-04-05 Estimation of position, speed and bearing using time difference of arrival and received signal strength in a wlan positioning system
US11/696,833 2007-04-05
US11/696,833 US20080248741A1 (en) 2007-04-05 2007-04-05 Time difference of arrival based estimation of direction of travel in a wlan positioning system

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Cited By (9)

* Cited by examiner, † Cited by third party
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