WO2009020952A1 - Method and apparatus for locating a mobile device without synchronizing base station clocks - Google Patents
Method and apparatus for locating a mobile device without synchronizing base station clocks Download PDFInfo
- Publication number
- WO2009020952A1 WO2009020952A1 PCT/US2008/072185 US2008072185W WO2009020952A1 WO 2009020952 A1 WO2009020952 A1 WO 2009020952A1 US 2008072185 W US2008072185 W US 2008072185W WO 2009020952 A1 WO2009020952 A1 WO 2009020952A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- base station
- message
- pre
- local clock
- time
- Prior art date
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
- G01S5/14—Determining absolute distances from a plurality of spaced points of known location
-
- 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
- G01S5/0009—Transmission of position information to remote stations
- G01S5/0081—Transmission between base stations
-
- 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
-
- 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
Abstract
Description
METHOD AND APPARATUS FOR LOCATING A MOBILE DEVICE WITHOUT SYNCHRONIZING BASE STATION CLOCKS
BACKGROUND [0001] "Wireless" devices can take any of a number of forms, including cellular telephones and pagers, as well as various types of Internet, Web, or other network enabled devices, such as personal digital assistants (PDAs). Generally, a wireless device configured for transmitting, receiving, accessing, or exchanging data via a network may be referred to as a "mobile device" and communications between mobile devices may be referred to as "wireless communications".
[0002] In many situations, it is necessary to monitor the location or position of the mobile device in a given localized area. The position may be of interest for security reasons in order to prevent unauthorized devices located outside of the area from using the network or for other reasons. Typically, position detection and motion tracking of such devices involve signal timing analysis, such as time of arrival (TOA) or time difference of arrival (TDOA) based measurements, such as those used by global positioning systems (GPS) that involve measuring the timing of signals between the mobile device and a set of geo-stationary satellites. However, often GPS techniques cannot be used indoors or underground due to signal unavailability, interference and signal multi-path effects.
[0003] Therefore, detection and location of a mobile device within a defined indoor local area is typically performed using a local area network (LAN) comprised of a set of "base stations" which communicate wirelessly with the mobile device. If the geographical location of each base station is known, the location of the wireless device can be determined by a variety of techniques. For example, received signal strength indicator (RSSI) values may be obtained from the communications between the wireless device and the base stations. The RSSI values of signals between the mobile device and a particular base station vary depending on the distance between the mobile device and that base station. If there are at least three base stations that receive signals from the wireless device, the location of the device can be determined by a well-known process of trilateration. However, location systems that use RSSI techniques are generally relatively imprecise due to a number of factors, such as signal interference and multi-path signals.
[0004] It is also possible to use TOA and TDOA techniques with the signals that pass between the mobile device and the base stations. In this case, the time of arrival of signals generated by the mobile device is measured at each base station relative to a local clock in that base station. Then, all of the timing signals are sent to a central location where trilateration methods are used to determine the location of the mobile device. However, these methods require that the local clocks in the base stations be synchronized relative to each other. This synchronization, in turn, requires additional communications between the devices and between the base stations which adds to the communication burden.
SUMMARY
[0005] In accordance with the principles of the invention, TDOA techniques are used to determine the location of a mobile device relative to a set of base stations at known locations without synchronizing the local clocks via a technique called "clock correction." In accordance with this method, the reception time of a timing signal generated by the mobile device relative to a local clock at each base station is sent via messages to one of the base stations which corrects the reception time relative to its own local clock. Trilateration is then used with the corrected timing signals in order to determine the location of the mobile device.
[0006] In another embodiment, a calibration method is used to compensate for local clock drift between the time that the timing signal generated by the mobile device is received and the time that the message is sent to the base station.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] Figure 1 is a schematic diagram showing the basic layout of the various components of the mobile device locating system.
[0008] Figure 2 is a schematic diagram illustrating clock correction between stations. [0009] Figure 3 is a schematic diagram illustrating local clock drift.
[0010] Figure 4 is a schematic diagram for compensating for clock drift by calibration.
[0011] Figure 5 is a schematic diagram illustrating the process of deriving a clock correction using a clock relational factor derived form a calibration.
[0012] Figure 6 is a schematic diagram illustrating an alternative embodiment using distributed computations.
[0013] Figure 7 is a time line showing the signal timing in the embodiment illustrated in Figure 6. [0014] Figure 8 is a block schematic illustration of an embodiment in which the base stations are wirelessly connected.
[0015] Figure 9 is a block schematic illustration of the components in a base station.
[0016] Figure 10 is a block schematic illustration of an embodiment in which the base stations are connected by a LAN or WAN network.
DETAILED DESCRIPTION
[0017] Figure 1 shows the basic layout of the various components of the mobile device locating system. As shown four base stations (B0, Bi, B2, B3) are used, although more or less base stations can be used as long as at least three base stations are present. The geographical position (x,, y,, Z1) of each base station device B1 is known in advance. The mobile device Tag (T) is moving and, thus, its position (x, y, z) is not known in advance. Each device (B0, Bi, B2, B3 and Tag) in the positioning system runs its own internal clock. In order to determine, the location of the Tag (T), the Tag is instructed by one of the base stations (for example, the closest base station) to generate a timing signal. This timing signal is sent to all base stations as indicated by the transmission signals (1 ) in Figure 1. Each base station records the time of arrival of this timing signals relative to its local clock and then sends this time of arrival encoded in a signal to a pre-selected base station (in this example, base station B0) as indicated by transmissions 2, 3 and 4. Base station B0 then determines the geographical position of the Tag (T).
[0018] Figure 2 illustrates the concept of clock correction. In this figure, two base stations A and B are located at fixed positions with a distance do separating them. Base station B sends a message to base station A. The message contains a coded value representing the value of the local clock in station B at the time the message is sent. In the figure, the value ts B denotes the time at which the first signal of the message is sent from base station B as determined by the local clock of base station B.
The value tr A denotes the time at which the first signal of the message is received at node A as determined by the local clock of base station A. Assuming that the local clock of base station A is faster than the local clock of base station B, then, the difference between the two clock values (denoted as ckA_B in Figure 2) is given by the following equation:
where c is the speed of light.
[0019] Using equation (1 ) the location process proceeds as follows. Assume that do[1] is the physical distance between base stations B0 and B1, do[2] is the physical distance between base stations B0 and B2 and do[3] is the physical distance between base stations B0 and B3 respectively and that do[1], do[2] and do[3] are known in advance. Assume further that ck0, cki, ck2 and ck3 are the local clocks in base stations B0, B1, B2 and B3, respectively and that clock ck0 is the fastest clock.
[0020] Then, from the broadcast of the timing signals from the tag shown as signals (1 ) in Figure 1 , the base stations B0, B1, B2 and B3 each get the time of arrival values of the timing signal from the tag as determined by their local clocks (ck0, Ck1, ck2 and ck3). These values are denoted as tto°, ttΛtt2 2 and tt3 3, respectively.
[0021] Next, base stations B1, B2 and B3 send messages containing these values and the times at which the messages are sent to base station B0. From the communication between B1 and B0 (denoted as signal (2) in Figure 1 ), base station B0 obtains from the message from Bi the time the tag signal is received at station Bi (tti1) and the time that the message is sent from Bi to B0 (denoted as tsi1). Station B0 also records the time of arrival of the message as determined with its local clock ck0 , which is denoted as tr1°. Then, with equation (1 ) as set forth above, station B0 calculates the time of arrival of the timing signal from the Tag to station Bi relative to the station B0 clock Ck0 as the following:
[0022] From the communication between B2 and B0 (denoted as signal (3) in Figure 1 ), base station B0 obtains from the message from B2 the time the tag signal is received at station B2 (tt2 2) and the time that the message is sent from B2 to B0 (denoted as ts2 2). Station B0 also records the time of arrival of the message as determined with its local clock ck0 , which is denoted as tr2°. Then, with equation (1 ) as set forth above, station B0 calculates the time of arrival of the timing signal from the Tag to station B2 relative to the station B0 clock ck0 as the following:
[0023] In a similar manner, from the communication between B3 and B0 (denoted as signal (4) in Figure 1 ), base station B0 calculates the time of arrival of the timing signal from the Tag to station B3 relative to the station B0 clock ck0 as the following:
tξ = ttl + Ck0 3 = ttl + ((tr°3 - ξ3) -^-) [0024] Using the calculated times of arrival relative to the local clock ck0 of the tinning signal sent by the Tag at the four base-stations (denoted as tto°, ttio,tt2°, tt3 0 from the previous equations) and the known coordinates of the four base-stations B0, Bi, B2 and B3, station B0 calculates the position (x, y, z) of the mobile Tag by solving the following equations:
t Ut1° -t Ut0° X C = U(x-xl)2 + (y -yl)2 + (z -zlf -^(x-x0)2 + (y -y0)2 + (z - z0)2 t Ut1 0 -t Ht0° X C = U(x-x2f + (y -y2)2 + (z - z2)2 -^(x-x0)2 + (y -y0)2 + (z -z0f tή -ttl xc = U(x-x3f +(y -y3)2 +(z-z3f
[0025] The aforementioned calculation assumes that the local clock in each base station is stable during the time interval between the time that timing signal is received from the Tag and the time at which a message is sent to the base station B0. However, in general, this is not the case. Figure 3 shows a typical case. Here a timing signal is sent from the Tag at time to as indicated by arrow 300. It arrives at base station Bi at time t1. Some time later, after a delay of duration L that depends on the internal configuration of the base station B1 and/or an intentional delay, a message is sent at time t2 to base station B0 as indicated by arrow 302. Here, tθ, t1 and t2 are absolute times.
[0026] If the local clock cki in base station Bi were perfect, then t2 would be equal to t1 + L. However, during the time period L, drift in the local clock Ck1 results in the clock value t2 at the end of L period being equal to t1 + L + Δ where Δ is the drift in the clock value during the time period L. In order to make the location calculation accurate, the corrected clock value at the beginning of the L period is needed, but, in the process described previously, what is computed is the corrected clock value at the end of the L time period. Without correcting for this drift, the positioning error of the inventive location system will be in the same order as conventional two-way ranging based IPS (TRIPS).
[0027] The clock drift can be compensated by calibration. This process is illustrated in Figure 4. Here base station A sends a message of length L to base station B. This would be done before operation of the system begins and may also be done periodically during operation to adjust the compensation. The values tiA and t2 A are the values of a counter in base station A, which correspond to the time of transmitting the start of the message and the time of transmitting the end of the message, respectively. The values tiB and t2 B are the values of a counter in base station B, which correspond to the time of receiving the beginning of the message and the time of receiving the end of the message, respectively. The values tcyc_A and tcyc_B denote the duration of one cycle of the clock in base station A and base station B, respectively. Then
- K^ x^ -^ ^J and
- = (t2B * tcyc_B - tt * tcyc_A)
[0028] Given these two equations, the relationship η between the two clocks in base station A and base station B is given by:
_ lcyc_A _ I2 1I t lcyc_B t l2A ~ t 1IA
[0029] Using the clock relationship η, the clock corrections between the base station B0 and the other base stations can be compensated for drift as shown in Figure 5. Here base station Bi sends a calibration message to base station B0 before operation of the system begins. This message is used to determine the value of η as set forth above. Then, the mobile device (Tag) sends a timing message to station Bi which is received at time H1 1. Base station B1 then sends a message to station B0 at time tsi 1. The time at which the timing signal arrives at station Bi, as determined relative to the local clock at station B0 and corrected for drift in the clock at station Bi (ttr_tti°) is given by:
ttr O_ttl = C -(ts l l -ttl) x η
where tri° is the time that the message from station Bi is actually received at station B0. This gives a clock correction for the reception of the timing signal at station B1 relative to the local clock at station B0 of:
cktΛ = (ttr° tΛ -tt\)
[0030] Using the correction factor η the aforementioned location process is modified as follows. Again, assume that do[1 ] is the physical distance between base stations B0 and B1, do[2] is the physical distance between base stations B0 and B2 and do[3] is the physical distance between base stations B0 and B3 respectively and that do[1 ], do[2] and do[3] are known in advance. Assume further that ck0, Ck1 , ck2 and Ck3 are the local clocks in base stations B0, B1, B2 and B3, respectively and that clock ck0 is the fastest clock.
[0031] Then, from the broadcast of the timing signals from the tag shown as signals (1 ) in Figure 1 , the base stations B0, B1, B2 and B3 each get the time of arrival values of the timing signal from the tag as determined by their local clocks (ck0, Ck1 , ck2 and ck3). These values are denoted as tto°, tti1 ,tt2 2 and tt3 3, respectively. [0032] Next, base stations B1, B2 and B3 send messages containing these values and the times at which the messages are sent to base station B0. From the communication between B1 and B0 (denoted as signal (2) in Figure 1 ), base station B0 obtains from the message from B1 the time the tag signal is received at station B1 (U1 1) and the time that the message is sent from B1 to B0 (denoted as ts1 1). Station B0 also records the time of arrival of the message as determined with its local clock ck0 , which is denoted as tri°. Then, with equation (1 ) as set forth above, station B0 calculates the time of arrival of the timing signal from the Tag to station Bi relative to the station B0 clock Ck0 as the following:
tt? =
[0033] From the communication between B2 and B0 (denoted as signal (3) in Figure 1 ), base station B0 obtains from the message from B2 the time the tag signal is received at station B2 (tt2 2) and the time that the message is sent from B2 to B0 (denoted as ts2 2). Station B0 also records the time of arrival of the message as determined with its local clock ck0 , which is denoted as tr2°. Then, with equation (1 ) as set forth above, station B0 calculates the time of arrival of the timing signal from the Tag to station B2 relative to the station B0 clock ck0 as the following:
tξ =
[0034] In a similar manner, from the communication between B3 and B0 (denoted as signal (4) in Figure 1 ), base station B0 calculates the time of arrival of the timing signal from the Tag to station B3 relative to the station B0 clock ck0 as the following:
do[3] tξ = ttl + ck0 3 = ttl + {((tr°3 - (ή3 - ttl) x η0 3) - ttl) -
[0035] Using the calculated times of arrival relative to the local clock ck0 of the timing signal sent by the Tag at the four base-stations (denoted as tto°, H1 0^t2 0, tt3 0 from the previous equations) and the known coordinates of the four base-stations B0, Bi, B2 and B3, station B0 can calculate the position (x, y, z) of the mobile Tag by solving the above equations.
[0036] The aforementioned location arrangement requires station B0 to make all of the positioning calculations. It is also possible to decentralize the calculations using the signal transmissions shown on Figure 6. The time line for the transmissions is shown in Figure 7. At time TO the mobile device (Tag) transmits the timing signal to all stations as indicated as transmissions (1 ) in Figure 6. Then, at time T1 stations BO, B1 B2, B3 receive the timing signals (1 ) At time TV station B1 sends a message to stations BO and B2 as indicated by signal (2) in Figure 6. At time T2, stations BO and B2 receive the message (2) from station B1 . Subsequently, at time T2' station B2 sends a message to stations BO and B3 as indicated in Figure 6 by signal (3). At time T3 stations BO and B3 receive the message from station B2. Next, at time T3' station B3 sends a message to station BO shown as signal (4) in Figure 6. Finally, at time T4, station BO receives the message (4) from station B3. This arrangement allows some of the calculations to be performed at stations B2 and B3 as well as station BO.
[0037] The aforementioned arrangement has some significant advantages. For example, it is based on one-way ranging. Therefore, compared with conventional two- way ranging, the inventive location arrangement saves bandwidth. More specifically, at least six communications are needed between stations for positioning via two-way ranging - three two-way communications between the mobile device and three base- stations. However, with one-way based positioning, only four communications between the mobile device and the base stations are needed.
[0038] In addition, there is no requirement to synchronize the local clocks in the base stations, because the local clocks are used to measure the relative time of arrival. [0039] The inventive arrangement also saves power in the mobile device both because only one transmission from the mobile device is required and also because the position computation is performed at the base stations rather than the mobile device. The arrangement is also reliable for a dynamic radio environment, because the three base-stations i.e. B1 , B2, B3, are used as references, which correct the measurement error in real time. [0040] Further, since the time between the reception of the tinning signal in a station and the transmission of a message concerning that timing signal from that station (the time duration L) is adjustable. It is possible to adjust this time to prevent signal overlap of the relayed signals. [0041] Figure 8 shows a block schematic illustration of an embodiment 800 in which all of the base stations 802-808 are wirelessly connected as shown schematically by arrows 810-814. In this embodiment, each base station may be a wireless access point and base station 802 constitutes the pre-selected base station that performs the location calculations. [0042] Figure 9 is a block schematic diagram of the components of a base station 900, which might be the pre-selected base station 802 or, in the case where computations are distributed among the base stations as discussed above, any of the other base stations 804-808. Base station 900 includes a transceiver 904 which is connected to the antenna 902 to both receive and transmit wireless signals between the mobile unit and other base stations. Transceiver 904 is connected to a timing unit 910, which is also connected to the local clock 914. Timing unit 910 determines the time of arrival relative to local clock 914 by detecting the start of a timing signal received by transceiver 902 from the mobile unit or the start of a message received from another base station. [0043] Messages received from the mobile unit or other base stations are placed in message buffer 906 by the transceiver 904. A message decoder 908 processes the messages in buffer 906 in order to extract the timing information as discussed above. The time of arrival information generated by timing unit 910 and the timing information in incoming messages, which is extracted by message decoder 908, are provided to computation unit 912 which, in the case of the pre-selected base station, determines the location of the mobile unit as discussed above. In the case of other base stations, computation unit 912 may generate message to be sent to the preselected base station with timing information as discussed above. These message are placed in the message buffer 906 for transmission by the transceiver 904. [0044] Figure 10 is a block schematic illustration of another embodiment 1000 in which the base stations 1002-1008 are connected by a network 1010, which could be a LAN or a WAN, such as the Internet. Embodiment 1000 eliminates the need for the base stations to communicate wirelessly.
[0045] While the invention has been shown and described with reference to a number of embodiments thereof, it will be recognized by those skilled in the art that various changes in form and detail may be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
[0046] What is claimed is:
Claims
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US95413107P true | 2007-08-06 | 2007-08-06 | |
US60/954,131 | 2007-08-06 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2009020952A1 true WO2009020952A1 (en) | 2009-02-12 |
Family
ID=40341682
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US2008/072185 WO2009020952A1 (en) | 2007-08-06 | 2008-08-05 | Method and apparatus for locating a mobile device without synchronizing base station clocks |
Country Status (1)
Country | Link |
---|---|
WO (1) | WO2009020952A1 (en) |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2009126416A1 (en) * | 2008-04-11 | 2009-10-15 | Cisco Technology, Inc. | Inserting time of departure information in frames to support multi-channel location techniques |
EP2727392A4 (en) * | 2011-06-28 | 2015-06-03 | Qualcomm Inc | Distributed positioning mechanism for wireless communication devices |
US9332383B2 (en) | 2011-09-19 | 2016-05-03 | Qualcomm Incorporated | Time of arrival based positioning system |
WO2016067064A1 (en) * | 2014-10-27 | 2016-05-06 | Umm Al-Qura University | A method and system for 3d position estimation of an object using time of arrival measurements |
US9388042B2 (en) | 2011-02-25 | 2016-07-12 | Rutgers, The State University Of New Jersey | Scalable multiple-inverse diffusion flame burner for synthesis and processing of carbon-based and other nanostructured materials and films and fuels |
FR3043467A1 (en) * | 2015-11-11 | 2017-05-12 | Jan Mennekens | Method and geolocation system of a stamp by tag |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20030222819A1 (en) * | 1996-09-09 | 2003-12-04 | Tracbeam Llc. | Locating a mobile station using a plurality of wireless networks and applications therefor |
US20050192024A1 (en) * | 2002-10-17 | 2005-09-01 | Leonid Sheynblat | Method and apparatus for improving radio location accuracy with measurements |
US20050288033A1 (en) * | 2004-06-15 | 2005-12-29 | Mcnew Justin P | System and method for location determination |
US20070121560A1 (en) * | 2005-11-07 | 2007-05-31 | Edge Stephen W | Positioning for wlans and other wireless networks |
US20070155401A1 (en) * | 2005-12-30 | 2007-07-05 | Trueposition Inc. | User plane uplink time difference of arrival (u-tdoa) |
-
2008
- 2008-08-05 WO PCT/US2008/072185 patent/WO2009020952A1/en active Application Filing
Patent Citations (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20030222819A1 (en) * | 1996-09-09 | 2003-12-04 | Tracbeam Llc. | Locating a mobile station using a plurality of wireless networks and applications therefor |
US20060025158A1 (en) * | 1996-09-09 | 2006-02-02 | Leblanc Frederick W | Locating a mobile station and applications therefor |
US20050192024A1 (en) * | 2002-10-17 | 2005-09-01 | Leonid Sheynblat | Method and apparatus for improving radio location accuracy with measurements |
US20050288033A1 (en) * | 2004-06-15 | 2005-12-29 | Mcnew Justin P | System and method for location determination |
US20070121560A1 (en) * | 2005-11-07 | 2007-05-31 | Edge Stephen W | Positioning for wlans and other wireless networks |
US20070155401A1 (en) * | 2005-12-30 | 2007-07-05 | Trueposition Inc. | User plane uplink time difference of arrival (u-tdoa) |
Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2009126416A1 (en) * | 2008-04-11 | 2009-10-15 | Cisco Technology, Inc. | Inserting time of departure information in frames to support multi-channel location techniques |
US8335173B2 (en) | 2008-04-11 | 2012-12-18 | Cisco Technology, Inc. | Inserting time of departure information in frames to support multi-channel location techniques |
US9388042B2 (en) | 2011-02-25 | 2016-07-12 | Rutgers, The State University Of New Jersey | Scalable multiple-inverse diffusion flame burner for synthesis and processing of carbon-based and other nanostructured materials and films and fuels |
EP2727392A4 (en) * | 2011-06-28 | 2015-06-03 | Qualcomm Inc | Distributed positioning mechanism for wireless communication devices |
US9332383B2 (en) | 2011-09-19 | 2016-05-03 | Qualcomm Incorporated | Time of arrival based positioning system |
WO2016067064A1 (en) * | 2014-10-27 | 2016-05-06 | Umm Al-Qura University | A method and system for 3d position estimation of an object using time of arrival measurements |
FR3043467A1 (en) * | 2015-11-11 | 2017-05-12 | Jan Mennekens | Method and geolocation system of a stamp by tag |
WO2017081418A1 (en) * | 2015-11-11 | 2017-05-18 | Uwinloc | Method and system for the geolocalisation of a beacon by means of time-stamping |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US6420999B1 (en) | Method and apparatus for determining an error estimate in a hybrid position determination system | |
US6801782B2 (en) | Method and apparatus for determining the position of a mobile communication device | |
US6937872B2 (en) | Methods and apparatuses for measuring frequencies of basestations in cellular networks using mobile GPS receivers | |
US5990833A (en) | System for direction determination | |
US20050181810A1 (en) | Mobile terminals and methods for determining a location based on acceleration information | |
US6525688B2 (en) | Location-determination method and apparatus | |
US7593736B1 (en) | Positioning system for digital telephone networks | |
US20140213193A1 (en) | Frequency offset compensation for wifi ranging | |
US20090251364A1 (en) | Method and system of a mobile subscriber estimating position | |
US6070078A (en) | Reduced global positioning system receiver code shift search space for a cellular telephone system | |
US6671620B1 (en) | Method and apparatus for determining global position using almanac information | |
US20080248741A1 (en) | Time difference of arrival based estimation of direction of travel in a wlan positioning system | |
US6185429B1 (en) | Method and apparatus for performing a time synchronization of a base site | |
US7652622B2 (en) | Transfer of position information of mobile terminal | |
US6704547B2 (en) | Wireless communication base station transmission timing offset correction system | |
US20050130669A1 (en) | Positioning system using radio signal sent from node | |
US20060291537A1 (en) | Time transfer utilizing ultra wideband signals | |
US6861982B2 (en) | System for determining position of an emitter | |
US20080309557A1 (en) | Facilitating mobile station location using a ground-based cellular network | |
US20040072582A1 (en) | Method and system for synchronizing location finding measurements in a wireless local area network | |
US20010039192A1 (en) | Time synchronization of radio networks | |
US20080232297A1 (en) | Node location method, node location system and server | |
US6108558A (en) | Method for calculating a location of a remote Unit utilizing observed time difference (OTD) and real time difference (RTD) measurements. | |
US20040087277A1 (en) | Method and apparatus for improving accuracy of radio timing measurements | |
US7616155B2 (en) | Portable, iterative geolocation of RF emitters |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
121 | Ep: the epo has been informed by wipo that ep was designated in this application |
Ref document number: 08797165 Country of ref document: EP Kind code of ref document: A1 |
|
NENP | Non-entry into the national phase in: |
Ref country code: DE |
|
122 | Ep: pct app. not ent. europ. phase |
Ref document number: 08797165 Country of ref document: EP Kind code of ref document: A1 |