WO2008131414A1 - Concept pour emplacement sans fil à l'aide d'horloges asynchrones - Google Patents

Concept pour emplacement sans fil à l'aide d'horloges asynchrones Download PDF

Info

Publication number
WO2008131414A1
WO2008131414A1 PCT/US2008/061262 US2008061262W WO2008131414A1 WO 2008131414 A1 WO2008131414 A1 WO 2008131414A1 US 2008061262 W US2008061262 W US 2008061262W WO 2008131414 A1 WO2008131414 A1 WO 2008131414A1
Authority
WO
WIPO (PCT)
Prior art keywords
snaps
ranging
transmitter
ranging stations
stations
Prior art date
Application number
PCT/US2008/061262
Other languages
English (en)
Inventor
Roderick Bryant
Bradford Anderson
Frederick Montano
John Riedl
Original Assignee
Signav Pty 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
Application filed by Signav Pty Ltd. filed Critical Signav Pty Ltd.
Publication of WO2008131414A1 publication Critical patent/WO2008131414A1/fr

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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Definitions

  • This invention relates to the use of wireless ranging stations to determine the location of a wireless transmitter.
  • the prime example considered within this specification is that of Special IEEE802.11 Wi-Fi Network Access Points (SNAPs) locating Standard IEEE802.11 Wi-Fi User Devices (SUDs).
  • SNAPs Special IEEE802.11 Wi-Fi Network Access Points
  • SUVs Standard IEEE802.11 Wi-Fi User Devices
  • other examples that could use all or part of this invention include special 802.11 user devices, special cellular network base stations locating standard handsets or modems or two-way radio sets locating each other.
  • this invention involves methods, devices and systems for locating wireless transmitters.
  • a range of applications for IEEE 802.11 WI-FI systems involve the need to locate SUDs with varying levels of accuracy down to 1 foot or 300mm.
  • ranging techniques based on time of flight are necessary rather than ranging based on signal level.
  • the prior art involves both techniques and also methods and apparatus for determining location based on amplitude signatures at multiple NAPs.
  • none of these approaches incorporate mechanisms capable of achieving accuracy in the order of 1 foot.
  • NAPs Network Access Points
  • Prior art for Wi-Fi positioning involves estimation of the ranges between SUDs and NAPs based on the signal powers received at the NAPs. This is necessarily a coarse ranging technique that is seriously affected by walls furniture and other obstructions causing attenuation along the signal paths.
  • Another approach in the prior art involves storing signatures consisting of sets of amplitude measurements at multiple NAPs and correlating these signatures with location. Location is then determined by comparing the amplitude measurements from the NAPs with the signatures. This is potentially more accurate but remains a relatively coarse technique.
  • Ranging based on Time Of Flight has also been explored but is limited by NAP synchronization errors.
  • One solution for the synchronization problem that has been advanced involves measuring changes in range only. Each of these measurements is a measurement of elapsed time made using a single clock. Thus it is not subject to synchronization error. This allows position to be tracked accurately once an initial location is known. However, the accurate initialization of the tracking remains problematic. Furthermore, the errors that do occur will accumulate during the tracking process.
  • the system is intended to provide precise positioning for use in a wide range of applications many or indeed most of which involve indoor locations.
  • the indoor environment complicates the synchronization problem since autonomous GPS timing cannot be used while Assisted GPS timing is both insufficiently reliable and nowhere near accurate enough. It also means that foot level positioning must be achieved in the presence of significant levels of multipath interference.
  • a WI-FI system consists of wireless NAPs at fixed locations providing access to the WLAN for roving SUDs. Wireless signals are transmitted regularly in both directions between the wireless NAPs and the SUDs using the WLAN as part of the normal operation of 802.11.
  • these signals are to be used to estimate the range differences between each of the SUDs and each of at least 3 (for 2D positioning) or at least 4 (for 3D positioning) SNAPs.
  • the differences in the times of flight of the signals are directly proportional (via the speed of light) to these range differences provided the signals travel directly from transmitting antenna to receiving antenna.
  • a computing element in the system would then calculate the position of the SUDs based on the ranges measured.
  • Figure 1 depicts the positioning subsystem of the present invention.
  • Figure 2 depicts the TDOE scheme of the present invention.
  • Figure 3 depicts the measurement of TOF in the present invention.
  • Figure 4 is a block diagram for a typical de-spreading code generator in a correlation receiver incorporating a numerically controlled oscillator (NCO).
  • NCO numerically controlled oscillator
  • the positioning subsystem will consist of several elements as indicated in Figure 1.
  • the elements in the wireless zone consist of the Frequency Reference Beacon Transmitters (FRBTs) which will be described later, the SNAPs and the SUDs.
  • FRBTs Frequency Reference Beacon Transmitters
  • the functions of these elements will be discussed in detail later in this document.
  • the other elements needed include the Position Determining Entity (PDE), a Map database and, optionally, a Track database and a Presentation Layer.
  • PDE Position Determining Entity
  • Map database Map database
  • Track database a Presentation Layer
  • the PDE is typically a server or server farm with computing capability and memory capacity.
  • the functions of the PDE are:
  • a Presentation Layer may be needed depending on the nature of the application to show where the tracked objects are on a plan of the building or tracking environment.
  • locations may be supplied to the application layer on demand.
  • Many applications may be serviced by the one PDE.
  • the PDE may periodically compute the locations of all or selected SUDs or may only do so on command from the application layer.
  • the control database would contain information on which SUDs are to be tracked and at what intervals. This information may be assembled based on queries from the application layer.
  • the Map database registers the locations of walls, floors and SNAPs and is essential to the operation of the PDE.
  • the PDE might control the SNAPs in the following way. Having received a request for position of a specific SUD, the PDE would request responses from those SNAPs receiving from that PDE. Using the locations of walls floors and SNAPs from the Map database and the signal levels from the SNAPs, the PDE would then determine which floor the SUD was on and decide which SNAPs to use for positioning and how they should be paired. The PDE would then instruct the selected SNAPs to perform measurements on signals from the selected SUD. Those SNAPs would then measure TDOEs and return these to the PDE.
  • the PDE would then compute the required TDOAs and solve for the cartesian position coordinates of the SUD.
  • the latter computation would typically be a least squares calculation.
  • the PDE would then convert these cartesian coordinates into user- friendly map coordinates in terms of floor, room and location relative to walls and floor.
  • the PDE needs Time Of Flight (TOF) estimates for the pairs of SNAPs. These could be stored with the SNAP coordinates in the Map database. They could be obtained via regular calibrations as discussed later.
  • TOF Time Of Flight
  • the PDE may store the position data in the Track database for supply to the application layer as required.
  • the precise operation of the major computing and data-base elements is unimportant to the innovation but the functional operation is important.
  • the operating environment will involve a mix of SUDs from many different manufacturers conforming to various substandards of IEEE 802.11 (eg 802. HA, 802. HB and 802.1 IG). There may also be NAPs present from other manufacturers all of which conform to some subset of the 802.11 standards. No variation from the standards is permitted as it could affect interoperability among the SUDs and the NAPs.
  • IEEE 802.11 eg 802. HA, 802. HB and 802.1 IG
  • NAPs present from other manufacturers all of which conform to some subset of the 802.11 standards. No variation from the standards is permitted as it could affect interoperability among the SUDs and the NAPs.
  • the wireless antennas will preferably be integrated into the SNAP assemblies (as opposed to external antenna(s) mounted externally to the building.
  • the system is to be capable of very high positioning accuracy. Application accuracy requirements will vary but accuracy requirements down to 300mm or even better in both horizontal and vertical dimensions is envisaged for some applications.
  • the system must be capable of operating within buildings including warehouses, office buildings and so on. Such buildings may have metal roofs and/or walls and may contain metal structures. There may also be very large buildings.
  • the system ideally will operate with standard SUDs. That is, the system will require special features in the SNAPs only.
  • the primary impediments to achieving the desired accuracy are:
  • IEEE802.11 NAPs are not designed to measure time of arrival of signal instants and will require special receive circuitry to do this to the required accuracy
  • normal 802.11 NAPs are modified to become SNAPs by the addition of circuitry and software and the circuitry will include a precise controllable clock in each SNAP.
  • Synchronizing the SNAP clocks to Ins accuracy is extremely difficult if not impossible using economically viable techniques although the system would work with synchronised clocks.
  • estimation of elapsed times to this accuracy is definitely feasible without such synchronisation. It requires stabilization (as opposed to synchronization) of the SNAP clocks to a degree that is dependent on the elapsed time to be measured. For example, to measure a Is time interval to Ins accuracy requires a clock stabilized to 1 part in one billion (lppb) for the period during which measurements are taken.
  • Typical clock frequencies used to drive wireless systems run at tens of MHz. This implies clock resolution of the order of 10s of ns. This is between 1 and 2 orders of magnitude larger than the desired Ins accuracy for measuring the time of flight.
  • the synchronising clock needs to be accurate to a fraction of a nanosecond so that the aggregate errors do not approach the order of magnitude of that which is being measured.
  • Navigation and time transfer systems like GPS use similar clock frequencies.
  • this problem is overcome by estimating the Time Of Transmission (TOT) to very high precision at a clock edge.
  • the highest resolution element of the TOT is the codephase of the spreading code.
  • the codephase of the receiver-generated replica of the spreading code can only be changed at a clock edge but can be changed to very high precision. In this way the local code can be aligned with the code of the incoming signal to extremely high precision and can be latched on any given clock edge with that same precision.
  • Wi-Fi systems also use spreading codes although the code lengths are much shorter being the length of 1 bit of the data. IfWi-Fi receivers were to establish and maintain code sync with the incoming signal in a similar manner to GPS receivers (ie using correlation receiver techniques) then the misalignment between the clock edges and the chip edges could be established with high precision and taken account of in the time of flight calculations. Standard 802.11 NAPs are not designed with this application in mind. Therefore supplementary receiver circuits are required.
  • correlation receiver circuitry does not guarantee that the desired accuracy will be achieved. This is especially true since the Wi-Fi spreading codes have not been chosen with precise ranging in mind. It may not be possible to reduce the code tracking noise to the necessary level. Therefore supplementary techniques may be required.
  • the WI-FI signals are also subject to multipath.
  • DSSS chipping rates for example, can be as low as 1 IMBPS, depending on the variant of 802.11 which means that the maximum multipath error is around 30m which is very large compared to the desired accuracy. Such large path length differences are also likely in warehousing environments in particular. Significant multipath errors are quite likely unless specific features are built into the system to mitigate them.
  • 802.1 IB has become the most common implementation and uses HR/DSSS with higher chipping rates.
  • the direct signal should invariably be significantly stronger than the delayed multipath signals.
  • multipath mitigation techniques in the signal processing can be very effective.
  • the ranges between the SUDs and the SNAPs are relatively short it should be possible to limit the effects of multipath to an acceptable degree.
  • the TDOE concept is based on the idea of constructing TDOA (Time difference of arrival) measurements from a set of elapsed time measurements using a single clock to measure the elapsed time between pairs of events. The time difference between each pair of events must be measured by a sufficiently stable clock.
  • TDOA Time difference of arrival
  • This scheme involves pairs of SNAPs.
  • One of the pair receives a token from a SUD, transmits another token and and measures the elapsed time between the 2 events. Such a measurement is called a TDOE.
  • the second token is received by a second SNAP which has also received the same token from the SUD and measures the elapsed time between those two events.
  • Figure 2 illustrates the concept. Rather than ranging directly between multiple SNAPs and the SUD whose position is to be determined, in this concept the differences between the ranges from several SNAPs to the SUD are measured. This is the TDOA as is used in cellular positioning. However, rather than measuring the TDOA directly, we measure TDOEs at multiple SNAPs and then compute the TDOAs from the TDOEs. Consider one pair of SNAPs. Each SNAP latches the time of receipt of the same token (Token 1) from the SUD as Tl at API and T2 at AP2. API then transmits a new token (Token 2) to AP2 and latches the Time of Transmission of that token as T3.
  • the elapsed time (T3-T1) between reception of Token 1 and transmission of Token 2 is a TDOE measurement that is available to be taken account of in the TDOA calculation.
  • AP2 then latches the time of receipt of Token 2 (T4).
  • T4 time of receipt of Token 2
  • TDOA (T4-T2) - (T3-T1) - ⁇ T
  • ⁇ T is the time of flight between API and AP2 which is known a-priori.
  • TDOA is directly proportional (via the speed of light) to the difference in ranges to the SUD ofAP2 and APl.
  • TDOA is calculated from TDOE measurements only.
  • Each TDOE measurement is a measurement of elapsed time between 2 events at the same SNAP. No absolute time estimates are required and thus no synchronization is required amongst the SNAPs. This is the key difference between this scheme and a simple TDOA measurement scheme.
  • the tokens to be used are instances in the normal transmissions from the SUDs and SNAPs. No additional wireless traffic is generated for positioning purposes.
  • the tokens could be, for example, the ends of frames. In the case of the SNAP transmissions, the tokens could be the ends of beacon frames.
  • Token 2 from one SNAP to another does not have to be consequential upon the receipt of Token 1. It can precede it. The important thing is that the relative times are measured by stabilised highly accurate clocks that are frequency synchronised rather than time synchronised.
  • An alternative method of operation therefore is that the SNAPs transmit tokens to each other on a continuous and regular basis, latching the relative times of each Token until a SUD token arrives and its relative time of arrival is then latched. There is then no need to transmit another token and the same calculation can be done as above as long as the both Token 1 and Token 2 are within close enough time to each other for the accuracy of the system to be maintained. This time depends upon many factors but is likely to be of the order of a second at the current state of the art.
  • the total elapsed times to be measured may be of the order of a second since normal IEEE802.11 medium access mechanisms may delay the transmission of Token 2 in the first example for some time.
  • the clock stability required is of the order of lppb as required to provide ranging accuracy to 300mm.
  • the solution to this problem is to use one or more Frequency Reference Beacon Transmitters (FRBTs) within the area where SUDs are to be tracked.
  • the FRBT would transmit a suitable signal in the ISR band (for compatibility with the IEEE802.11 antennas and RF sections and to reduce the regulatory demands) but is not necessarily restricted to this band for the purposes of this patent.
  • this signal would be a spread spectrum signal to minimise interference with the IEEE802.11 signals. However, it would be modulated with one or more highly stable frequencies which would be used to stabilize the clocks in the SNAPs via phase or frequency locking. These stable FRBT frequency references could be derived from suitable IPPB oscillators or from GPS receivers. These beacons could also provide time synchronization which may be of use in applications requiring less accuracy and involving special or Custom User Devices (CUDs). One important benefit would be that it would facilitate round trip ranging using much the same TDOE mechanisms. The use of round trip ranging would facilitate location calculations using fewer SNAPs (ie 3 SNAPs for 3D positioning and 2 SNAPs for 2D positioning (albeit with ambiguity)). A master-slave beacon concept could also be employed in which there is only one source of time and frequency references with repeaters extending its range if required.
  • the time of flight between 2 SNAPs is required for the TDOA calculation as indicated earlier. It can be estimated based on the locations of the 2 SNAPs or it can be measured as indicated in Figure 3.
  • AP2 transmits Token 1 to API and latches the time of transmission as T5.
  • API latches the time of receipt of Token 1 as T6 and later transmits Token 2 back to API. It also latches the time of transmission of Token 2 as T3.
  • AP2 then latches the time of receipt of Token 2 as T4.
  • the time of flight between the 2 SNAPs is then computed as:
  • T3 may occur before Tl and T3 may occur before T6.
  • the SNAPs can simply listen to the beacon frames transmitted by each other. These are transmitted at regular intervals as part of the standard IEEE802.11 protocols. If the combined
  • TDOA/TOF scheme is used then the nearest pair of beacon events to any SUD reception event could be reported along with the reception event.
  • the latched times of transmission and times of receipt referred to in the above sections will necessarily be latched at a clock edge.
  • Transmission token events will typically but not necessarily occur at clock edges but reception token events generally will not. This can be overcome by estimating the misalignment between the incoming code chip edge representing the token and the nearest following clock edge at which the token receipt time is latched.
  • the following is one possible implementation of a method of measuring time of receipt with one form of code. Other equivalent methods are available using a combination of hardware and software, the key innovation being the accurate determination of the time differences between nominated parts of the message.
  • FIG. 4 is a block diagram for a typical de-spreading code generator in a correlation receiver incorporating a numerically controlled oscillator (NCO).
  • NCO numerically controlled oscillator
  • This form of de- spreading code generation may not be employed in a conventional NAP but could be employed in the SNAPs in one version of this concept.
  • the NCO is made up of the code frequency register and the sub-chip accumulator. At each clock edge the accumulator adds the value held in the code frequency register to its own contents. The carry from the accumulator clocks the code generator at the chipping rate. Hence the code frequency register determines the chipping rate. The larger its contents, the more frequently the chip counter counts.
  • the chip counter always updates at a clock edge.
  • the code frequency is only maintained on average.
  • the phase of the code generator is controlled to align it with the phase of the incoming signal by manipulating the code frequency.
  • the value in the code frequency register will vary from the nominal value representing the code frequency in order to adjust the codephase alignment with the incoming signal.
  • the state of the code generator (the codephase) can be latched at any time into the codephase register.
  • the bits of the codephase that were latched from the sub-chip accumulator then represent the fraction of a chip since the last chip edge at the latching instant. If this value is M and the nominal value in the code frequency register is N then the fraction of a clock cycle since the last chip edge is given by:
  • this value may be greater than 1.0 since there will generally be multiple clock cycles per chip. However, if we latch the codephase coincident with the carry then this value will represent the fraction of a clock cycle since the last chip edge. If the latching occurred at a token reception event then this number represents the fraction of a clock cycle that the token event occurred before the event time was latched. Hence this fraction of a clock cycle can be subtracted from the latched event time to give the precise event time.
  • PT Pseudo-Token
  • Any code tracking noise will show up in the sub-chip adjustments to the token receipt times and will thus contribute to the ranging error.
  • One approach to reducing these random ranging errors is to employ averaging. For example, averaging over a hundred measurements will reduce the RMS ranging error by a factor of 10.
  • PT Pseudo-Token
  • the effect is the same as measuring the time associated with a token event but the accuracy is much higher.
  • the TDOEs associated with PTs are used in the estimation of TDOA in the same way that TDOEs associated with tokens are used.
  • Tokens 1 to 6 can simply be replaced by PTs 1 to 6 in the above descriptions in order to see how the PTs are used.
  • PTl and PT2 in those descriptions can relate to different fragments of completely different frames. They can even be different lengths. It is only necessary for the transmission times and the reception times of the same PTs to be used in the calculation.
  • PT2 can relate to a beacon frame while PTl can be any convenient frame transmitted from the SUD.
  • the SNAPs In reporting event times to the PDE the SNAPs need a way of identifying the events to which they refer.
  • the events could be identified via the signal source (for examples: SNAP 36 or SUD 531), the frame number and whether the event was a transmission event or a reception event.
  • Care will need to be taken, in some cases, to limit the level of traffic over the ethernet backbone between the PDE and the SNAPs. In a large system and with many SUDs to locate and, possibly, to maintain track of, care should be taken to reduce unnecessarily detailed control of the process by the PDE. However, this may lead to a large amount of ethernet traffic reporting event times to the PDE.
  • the SNAPs could simply report every event. These would include reception of ends of frames from SUDs and transmission and reception of the ends of beacon frames.
  • the PDE would choose groups of event times yielding desired TDOA measurements. This would result in a large number of ethernet transactions and a large amount of data for the PDE to manage and to process.
  • the PDE could command each SNAP in near real time as to which sources it should report events for and even which frame numbers to report events on. That would lead to a large amount of Ethernet traffic simply to manage the process along with a nearly impossible task for the PDE in keeping track of all wireless transactions.
  • the PDE may choose to limit the number of SNAPs reporting its transactions to those closest to its last known location.
  • the PDE could also time division multiplex the system operation across zones thereby limiting the volume of ethernet traffic and its own processing load.
  • each SUD and any custom devices to be tracked will have allocated a scan frequency. For example lap-tops might be scanned and tracked every minute while desk-tops every hour. This allocation would be advised to the relevant SNAPs which would then throw away irrelevant data to unload the Ethernet traffic. Time division multiplexing of operation would be useful here. For example, each group of SNAPs around an SUD that is being tracked would be given a time slot by the PDE in which to track that SUD and would ignore it at other times. If the object starts to move and requires more frequent tracking, then the PDE could uprate the tracking frequency of the relevant SNAPs as well as activate SNAPs in adjacent areas where the SUD might enter.
  • the range between a SUD and a SNAP is a non-linear function of the locations of those two entities.
  • equations can be constructed relating the ranges of multiple SNAPs to their locations and that of the SUD to be located.
  • a location solution algorithm can be derived by linearizing those equations via differentiation and then differencing them to obtain range difference equations.
  • Three range difference equations involving the three coordinates of one SUD location can be solved to determine that location. The most obvious approach is to express the set of equations in matrix terms and to solve the problem via matrix inversion.
  • the locations are all expressed in cartesian coordinates and a more sophisticated equation is set up in which the covariances of the measurement errors and of the location uncertainties are used to weight the measurements.
  • the solution is still performed by matrix inversion but the solution is now an optimal least squares solution.
  • the primary advantage of this approach is that more than 3 sets of range difference measurements can be utilized to obtain an improved solution taking account of the varying reliability of the measurements. The latter would depend on signal strength, for example.
  • this least squares solution process can be formulated as a Kalman filter in which the history of the SUDs motion is taken into account and its dynamic characteristics can also be modelled.
  • Such an algorithm can also be enhanced in various ways to reject or otherwise mitigate multipath effects based on the probability of the measurements.
  • the accuracy of location depends upon the position of the SNAPs and is degraded when they are co-planar. This is a typical situation in an office where all the SNAPs might be located on a ceiling. In this situation, horizontal positioning can be very accurate but vertical may not. Other techniques, such as signal strength are then important to determine the floor on which the SUD is located and to distinguish between SNAP tracking where the SNAPs are on different floors and the floors and ceilings are relatively transparent to signals.
  • the location is computed with poor DOP resulting in poorer accuracy than desired.
  • the SNAPs cannot listen to each other and ranging is performed via TDOA using beacon synchronization rather than TDOE. In this case amplitude may be used to improve the accuracy by initially locating the SUD to a region. This results in poorer accuracy.

Abstract

La présente invention concerne des signaux sans fil utilisés pour estimer les différences de plage entre des SUD et chacun d'au moins 3 (pour le positionnement 2D) ou d'au moins 4 (pour le positionnement 3D) SNAP. A partir des emplacements précis des SNAP, un élément de calcul dans le système calcule la position des SUD en fonction des plages mesurées.
PCT/US2008/061262 2007-04-23 2008-04-23 Concept pour emplacement sans fil à l'aide d'horloges asynchrones WO2008131414A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US91344507P 2007-04-23 2007-04-23
US60/913,445 2007-04-23

Publications (1)

Publication Number Publication Date
WO2008131414A1 true WO2008131414A1 (fr) 2008-10-30

Family

ID=39875969

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2008/061262 WO2008131414A1 (fr) 2007-04-23 2008-04-23 Concept pour emplacement sans fil à l'aide d'horloges asynchrones

Country Status (1)

Country Link
WO (1) WO2008131414A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106535328A (zh) * 2016-12-02 2017-03-22 武汉博思创信息科技有限公司 一种白光led通讯室内定位系统及方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030054832A1 (en) * 2001-09-14 2003-03-20 Stein Jeremy M. Method and apparatus for detecting excess delay in a communication signal
US20040002344A1 (en) * 2002-04-25 2004-01-01 Mark Moeglein Method and apparatus for location determination in a wireless assisted hybrid positioning system
US20050037775A1 (en) * 2003-06-27 2005-02-17 Mark Moeglein Method and apparatus for wireless network hybrid positioning
US20060009235A1 (en) * 2004-06-18 2006-01-12 Leonid Sheynblat Method and apparatus for determining location of a base station using a plurality of mobile stations in a wireless mobile network
US20070121560A1 (en) * 2005-11-07 2007-05-31 Edge Stephen W Positioning for wlans and other wireless networks

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20030054832A1 (en) * 2001-09-14 2003-03-20 Stein Jeremy M. Method and apparatus for detecting excess delay in a communication signal
US20040002344A1 (en) * 2002-04-25 2004-01-01 Mark Moeglein Method and apparatus for location determination in a wireless assisted hybrid positioning system
US20050037775A1 (en) * 2003-06-27 2005-02-17 Mark Moeglein Method and apparatus for wireless network hybrid positioning
US20060009235A1 (en) * 2004-06-18 2006-01-12 Leonid Sheynblat Method and apparatus for determining location of a base station using a plurality of mobile stations in a wireless mobile network
US20070121560A1 (en) * 2005-11-07 2007-05-31 Edge Stephen W Positioning for wlans and other wireless networks

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106535328A (zh) * 2016-12-02 2017-03-22 武汉博思创信息科技有限公司 一种白光led通讯室内定位系统及方法
CN106535328B (zh) * 2016-12-02 2023-10-31 上海灵信数字技术有限公司 一种白光led通讯室内定位系统及方法

Similar Documents

Publication Publication Date Title
US20210006389A1 (en) Methods for nanosecond-scale time synchronization over a network
Yamasaki et al. TDOA location system for IEEE 802.11 b WLAN
US11909852B1 (en) Frequency and gain calibration for time synchronization in a network
JP6166260B2 (ja) 減衰が小さくなったｒｆ技術を用いる物体の測距および追跡におけるマルチパス緩和
AU2012275282B2 (en) Coding in a wide area positioning system (WAPS)
US20190072636A1 (en) Method and system for multipath reduction for wireless synchronization and/or locating
EP2460028B1 (fr) Systèmes de positionnement
EP1451606B1 (fr) Procede et dispositif permettant de synchroniser chronologiquement un reseau de positionnement
US20180295470A1 (en) Multi-path mitigation in rangefinding and tracking objects using reduced attenuation rf technology
JP2021180512A (ja) 低減衰ｒｆ技術を使用する対象の追跡および測距におけるマルチパス緩和
JP2022008675A (ja) Ｒｆを使用する位置発見のための部分同期型の多辺測量／三辺測量法及びシステム
US6185429B1 (en) Method and apparatus for performing a time synchronization of a base site
CN100403664C (zh) 在使用移动gps接收机的蜂窝网络中测量基站频率的方法及装置
US20150085899A1 (en) Coding in a positioning system
CN113949990A (zh) 用于追踪对象的到达角度定位系统
JP2021519422A (ja) 位置サービスのためのネットワークアーキテクチャ及び方法
US20140323152A1 (en) Method and apparatus for relative timing measurements
US11658798B1 (en) Methods for time synchronization and localization in a mesh network
RU2533202C2 (ru) Способ и система позиционирования мобильного терминала внутри зданий на основе глонасс-подобного сигнала
WO2008131414A1 (fr) Concept pour emplacement sans fil à l'aide d'horloges asynchrones
EP2420855A1 (fr) Système de localisation et procédé d'étalonnage correspondant
Zhao et al. Design and implementation of a wireless time synchronization based positioning system
Cui et al. Wifi localization based on ieee 802.11 rts/cts mechanism
Kolakowski et al. Indoor UWB positioning in EIGER localization system
WO2022226233A1 (fr) Procédés de synchronisation et de localisation dans le temps dans un réseau maillé

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: 08746646

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 08746646

Country of ref document: EP

Kind code of ref document: A1