WO2005065320A2 - Tdoa/gps hybrid wireless location system - Google Patents
Tdoa/gps hybrid wireless location system Download PDFInfo
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- WO2005065320A2 WO2005065320A2 PCT/US2004/043709 US2004043709W WO2005065320A2 WO 2005065320 A2 WO2005065320 A2 WO 2005065320A2 US 2004043709 W US2004043709 W US 2004043709W WO 2005065320 A2 WO2005065320 A2 WO 2005065320A2
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Classifications
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- 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
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/03—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers
- G01S19/09—Cooperating elements; Interaction or communication between different cooperating elements or between cooperating elements and receivers providing processing capability normally carried out by the receiver
-
- 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
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
- G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/42—Determining position
- G01S19/45—Determining position by combining measurements of signals from the satellite radio beacon positioning system with a supplementary measurement
- G01S19/46—Determining position by combining measurements of signals from the satellite radio beacon positioning system with a supplementary measurement the supplementary measurement being of a radio-wave signal type
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- 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
- G01S5/0018—Transmission from mobile station to base station
- G01S5/0036—Transmission from mobile station to base station of measured values, i.e. measurement on mobile and position calculation on base station
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- 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
- G01S5/0257—Hybrid positioning
- G01S5/0263—Hybrid positioning by combining or switching between positions derived from two or more separate positioning systems
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- 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
- G01S5/12—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 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
- H04W4/90—Services for handling of emergency or hazardous situations, e.g. earthquake and tsunami warning systems [ETWS]
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- 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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W76/00—Connection management
- H04W76/50—Connection management for emergency connections
Definitions
- the present invention relates generally to wireless location systems, and more particularly to a wireless location system that employs both infrastructure-based and handset- based approaches for locating wireless devices.
- Some of the exemplary aspects of the present invention are particularly suited to a wireless location system and related methods and subsystems compatible with the Global System for Mobile Communication, or GSM.
- GSM Global System for Mobile Communication
- the present invention relates to the determination of the location of a mobile radio-frequency transceiver operating within the operational domain of a wireless communications network.
- the mobile units of primary interest are cellular telephones, personal digital assistants, wireless-equipped laptop computers, and other similar devices equipped with wireless transceivers for normal operation under a "cellularized" telephone system, such as one based on the Global System for Mobile communications (GSM).
- GSM Global System for Mobile communications
- the location-determination technology described herein optimally integrates GPS data together with infrastructure data and collateral data, for enhanced accuracy and robust effectiveness under conditions that could degrade results individually achievable under the distinct approaches.
- Patent Number 4,728,959 and related art.
- the use of collateral information to enhance and even enable location determination in further applications of such infrastructure-based systems was introduced in Maloney, et al., U.S. Patent Number 5,959,580; and further extended in Maloney, et al., U.S. Patent Numbers 6,108,555 and 6,119,013.
- These and related following descriptions of the prior art for infrastructure-based location determination systems enable robust and effective location- determination performance when adequate measurement data can be derived or are otherwise available.
- a dominant benefit in the use of infrastructure-based location systems is the applicability of the technology for the localization of any and all types of mobile wireless communications units.
- the infrastructure technology establishes the facility to locate the mobile units through the measurement of location-related signal characteristics inherent in the normal communications-band transmissions.
- legacy phone models as well as newly emerging wireless communications units can all be equally served with the location facilities.
- the mobile units need only employ the standard wireless communications system signal formats and protocols, and do not require any special, localization-specific modification to support the location capability.
- a difficulty that accrues in the application of the infrastructure-based systems occurs with their use in sparsely populated, rural environments. In these environments, the economic constraints of the underemployed communications facilities only support the deployment of the communications facilities at cellular land stations that are significantly distant from each other.
- the accuracy of the calculated locations is degraded relative to that achievable in urban and suburban environments.
- the spatial densities of the communications cell stations are high in order to service the demand for the communications traffic without routinely exceeding the capacities of the individual cells.
- the location determinations are derived with significantly higher quantities of contributing measurements, extracted at sensing locations with significantly higher signal strengths, providing significantly better cumulative precision for the location evaluations.
- the sparse deployment densities of the infrastructure equipment in rural environments challenge the accuracy capabilities for the infrastructure-based location determination systems.
- GPS Global Positioning System
- the constellation of GPS satellites transmitting from over head provides the signals from which the GPS receiver can determine its location. In rural domains where the view of the sky is open, exemplary GPS accuracy is routinely achievable.
- Significant prior art is available for the use of GPS receivers embedded with mobile wireless communications transceivers to locate the mobile units. Example descriptions of such approaches are included in, e.g., U.S. Patent No. 4,445,118, April 24, 1984, "Navigation System and Method"; and U.S. Patent No.
- GPS augmentations for determining locations for wireless communications units.
- the GPS facilities in the mobile units are distinct from the communications facilities, and hence only phone models that incorporate the additional hardware functionality for the GPS reception can be used to obtain the GPS-based location-determination benefits.
- the signal processing and analysis involved for the GPS signals includes added facilities to receive the GPS frequency band signals with their particular signal formats.
- the wireless unit must support the energy or power demands of this added functionality.
- the GPS reception may not be continuously active, e.g., when not needed for location support.
- acquisition and reception of the GPS signals requires a search for the applicable satellite signals at the time the location service is needed, and this search can result in a comparatively large time to first fix (TTFF) when the GPS receiver has not been actively monitoring the satellite signals for some time.
- TTFF time to first fix
- the GPS receiver should be able to acquire and measure the characteristics of an adequate number of satellite signals across a relatively broad and uniform expanse of the sky in order to support the calculation of a location of acceptable accuracy.
- the assistance provided to the AGPS receiver guides the receiver in the parameters appropriate for acquiring those and only those satellites that are currently "over head.”
- the assistance reduces the signal search processing required to detect the satellite signals and thereby supports enhanced performance with a reduced response TTFF.
- U-TDOA In some rural environments, where cell site densities, network geometries, and coverage areas are very limited, the performance of U-TDOA has proven to degrade without the assistance of other location methods.
- AGPS Assisted Global Position Systems
- AFLT Advanced Forward Link Trilateration
- AGPS Advanced Global Position Systems
- AFLT Advanced Forward Link Trilateration
- U-TDOA technologies have proven to perform well because the SNR of uplink channels remains high and cell site densities are most dense.
- the present invention provides the technology for the integration of information from both types of processing to locate wireless mobile communications units.
- the system architectures implemented for the diverse localization approaches have not readily supported the information integration needs. Rather the system designs have been distinctly focused upon the derivation of the location- related data exclusively for either the GPS calculations or the infrastructure-based calculations, but not both.
- the functional directives, the signal reception approaches, and the facility and approach to extract and analyze the location-related information have been uniquely oriented to one form of system solution or the other, but not both.
- the location of a mobile station (MS) equipped with embedded GPS signal reception capability is determined using both GPS data and extracted location-related signal characteristics.
- the inventive method includes the steps of receiving GPS data at a land station, the GPS data being received from a MS to be located; at a land station equipped with location-measurement facilities, receiving from the MS to be located a communications-band signal, and using the location-measurement facilities to extract location-related characteristic data from the communications-band signal; and at a land station equipped for location-determination calculations, performing location-determination calculations using the GPS data and the extracted location-related characteristic data to derive an estimated location for the MS.
- the method may further include providing assistance data to the MS to be located.
- the assistance data enables the MS to receive GPS coarse/acquisition (C/A) signals and extract TOA or pseudorange measures, which can then be communicated to the land station equipped with location-measurement facilities. Further, where the GPS data and the extracted location-related characteristic data are provided at separate land stations, these may be communicated to the land station equipped for location-determination calculations, thereby enabling the location- determination function to be carried out.
- the location-related characteristic data extracted from the communications-band signal may include time of arrival (TOA) data, time difference of arrival (TDOA) data, angle of arrival (AOA) data, signal strength or propagation loss (PL) data, and/or timing advance (TA) data.
- the inventive method may advantageously include the use of collateral information in performing the location- determination calculations.
- the method may advantageously be employed to achieve applicable Federal Communications Commission (FCC) accuracy requirements for E-911. [0015]
- FIG. 1 depicts the components of one embodiment of the present invention, along with their inter-communication paths.
- FIG. 2 shows the inter-connectivity of the location-determination processing components.
- FIG. 3 illustrates the major functions and their interactions performed for the determination of the location estimates that optimally integrate GPS data and infrastructure information.
- AGPS Assisted GPS
- SN GPS satellite space vehicle
- the present invention provides technology for the determination of the location and motion of a wireless communications mobile station (MS) device, such as a cellular telephone or personal digital assistant, or the like.
- the location parameters are determined through the integrated evaluation of location-related radio-frequency (RF) signal characteristic measurements for a combination of Global Positioning System (GPS) signals together with communications infrastructure signals and associated, location-indicative, collateral, infrastructure and environment information.
- GPS Global Positioning System
- SN GPS satellite space vehicle
- the inherent communications facilities in the MS device as well as in the communications system infrastructure equipment deployed at land station (LS) sites provide communications-band signals that are also processed for the calculation of location- related parameters.
- These infrastructure-based signal characteristics include times or time differences of signal arrival (TOAs or TDOAs), angles of signal arrival (AOAs), received signal power levels (at the MS and/or at the LSs), and communications-system timing advance (TA) information for the MS of interest.
- TOAs or TDOAs times or time differences of signal arrival
- AOAs angles of signal arrival
- received signal power levels at the MS and/or at the LSs
- TA communications-system timing advance
- the present invention describes techniques that enable and apply the integration of measurement information regarding both types of signals, i.e., in both GPS and communications frequency bands, for determination of an optimal estimate of the MS location.
- the present invention determines a location for an MS that has embedded facilities for the reception of GPS signals as well as for the transmission and reception of wireless communications signals in accord with the signal formats and protocols of a wireless communications system (WCS).
- WCS wireless communications system
- the MS 101 receives GPS signals 102 transmitted from GPS SNs 103.
- the MS also transmits wireless communications signals 104 that are received at LSs 105, which are equipped with wireless communications antenna structures. These LSs 105 are also equipped with measurement units to process the received signals and extract signal characteristics that are related to the location of the MS.
- These LSs 105 are additionally equipped with GPS receivers for the reception of GPS signals 106.
- these LS facilities are installed at the same physical cell locations where the base transceiver stations (BTSs) of the cellularized WCS infrastructure are implemented.
- the LSs are networked through links 107 that enable the communication of the location-related measurements and GPS data to a central LS 108 for the integration of all relevant data in the determination of the MS location.
- these logical data links 107 are overlaid upon the inter-station data links of the underlying WCS, and the central LS facilities are installed at the same physical LS where the mobile switching center (MSC) of the cellularized WCS infrastructure is implemented.
- MSC mobile switching center
- the central directive or request to the MS to provide its received GPS signal data is communicated to the MS through a WCS data link 109 to a WCS BTS/LS 110, which is the WCS LS currently serving the MS.
- This serving cell LS 110 which is the optimal cell for the MS to communicate its own GPS data to the central LS 108, may not necessarily be equipped with the same signal characterization facilities as are at the location measurement LSs 105.
- the wireless request 111 sent to the MS from the LS 110 may also include supporting or assisting information described below, which can enhance the GPS sensitivity and response time of the MS. This GPS assistance information is developed in the LS network from timely support analysis of the current GPS configuration.
- the location measurement unit (LMU) 201 is the position-determination equipment (PDE) infrastructure device that is embedded at a networked LS 105 for signal detection and processing.
- PDE position-determination equipment
- each LMU is connected to and receives signals from a GPS antenna 202 and from wireless communications band antenna(s) 203.
- the serving mobile location center (SMLC) 204 facilities at a "central" collection-and-analysis LS 108 assemble the appropriate measurements from the LMU network to calculate the MS location.
- SMLC serving mobile location center
- the SMLC can further exploit additional, collateral or supporting, location- indicative information inferring probable MS locations.
- collateral information enhances the efficacy or even enables the completion of disambiguated location calculations.
- MPC mobile positioning center
- LG location gateway
- the GPS enables calculation of an MS location based upon TOA measurements and the associated "pseudoranges," which a GPS receiver embedded in the MS extracts from the signals continuously transmitted from the constellation of orbiting SNs. Reception of the GPS signals also involves measurement of the Doppler shift associated with each received SN signal, and the Doppler values support determination of the motion of the receiving MS.
- the prior art of record including the initial notice of proposed rule making ( ⁇ PRM) under the U.S. Federal Communications Commission (FCC) Common Carrier Docket Number CC 94-102, describes the use of GPS receivers embedded in the MSs operating under a WCS to provide the MS locations upon request, e.g., for enhanced public safety response to an emergency communication.
- Assisted GPS [0024]
- the simplicity, efficiency, sensitivity, and response time of an MS GPS receiver can be enhanced through the use of assistance obtained from an infrastructure of one or more supporting stations.
- the standard (e.g., non-military) GPS receiver receives the GPS SN coarse/acquisition (C/A) signals and extracts TOA or pseudorange measures through correlative signal processing that is based upon the known transmitted signal waveforms.
- the basic GPS C/A signal consists of a navigation message that is formed by the code division multiple access (CDMA) encoding of a 50 bit per second (bps) data stream.
- CDMA code division multiple access
- Each SN is uniquely associated with a 1023 -bit code or pattern of "chips,” which is applied in the encoding of the C/A message at a 1.023 million chips per second (Mcps) rate.
- Mcps chips per second
- the C/A code repeats every 1.0 millisecond (msec) in the SN transmissions and 20 such repetitions are included for each transmitted bit.
- the CDMA demodulation process applies matched replica correlation to detect the presence of the code in the received signal, with correlation delay lags covering the possible domain of TOA, at a time resolution inversely proportional to the effectively processed signal bandwidth.
- the signal propagation time from an SN to a MS on or near the earth's surface falls in the domain from 67 to 89 msec, i.e., spanning a window under 22 msec with dependence upon the orientation from the MS to the SN (closer for an SN over head and farther for SNs at the horizon).
- the possible domain of Doppler shifted frequency differences ranging from minimal for SNs over head to nearly 4.5 kilohertz (kHz) for SNs at the horizon, must also be covered in the signal correlation calculations, at a Doppler frequency resolution inversely proportional to the effective coherent integration time of the correlation.
- a supporting set of information can be communicated in the message 111 to the MS to indicate which SNs are currently overhead or above approximate horizon to warrant a candidate correlative search, what approximate and limited domain of Doppler frequency shift is reasonable for each candidate SN search, and what approximate and limited domain of TOA is reasonable for each candidate SN search.
- an LS can support such indications of available SN numbers and associated Doppler and delay search windows through the use of its own LMU-embedded GPS receiver and signal monitoring evaluations, which continuously sense and evaluate the information and characteristics of the currently available SNs in the GPS constellation.
- the assisting information is provided to the MS through the embedded WCS facilities in the MS and in the WCS LSs.
- the processing burden on the MS can also be and preferably is further alleviated through implementation of the location-calculation function in the supporting infrastructure of the PDE.
- the MS of the present invention uses its embedded communications facilities to provide to the LS infrastructure its own derived GPS pseudorange measurements, but the MS is not required to also provide a GPS-derived location.
- the MS can also optionally provide its demodulated associated SN navigation message data and/or its calculated MS location or SN locations and clock information as available.
- the LS infrastructure then completes the optimal integration of the GPS information provided by the MS together with the independently derived infrastructure- based LMU measurements and all relevant and available collateral information to determine the MS location.
- FIG. 3 depicts the significant functionality of the dominant components of the PDE of Figure 2, i.e., the LG, the SMLC, and the LMU.
- the request for the location of a particular MS of interest originates at a logical component called the mobile positioning center (MPC), which is external to the PDE.
- the LG 301 receives the location request, and validates the authenticity and authorization for it.
- a valid request identifies the WCS serving cell and associated communications protocol parameters, including assigned frequency usage, that shall apply for the WCS communications with the MS.
- the LG 302 provides the request to the SMLC that is appropriate for the determination of locations for MSs operating in the vicinity of the WCS serving cell.
- the selected SMLC 303 receives and reviews any request to determine the list of cooperating LMUs that are optimal for supporting location requests associated with the identified serving cell. In anticipation of the need to rapidly support a request for assisting GPS data, the SMLC 304 also routinely maintains and evaluates current GPS configuration data that specify the location and motion parameters for the GPS SNs. These data are persistently monitored by the LMUs 305 through their GPS receivers. The LMUs provide to the SMLC the Doppler shifts, pseudoranges, and relevant demodulated navigation message data for the GPS SN telemetry streams received at the LMU positions. The SMLC 306 receives these GPS SN data periodically communicated from the LMUs.
- the SMLC 307 For each potential serving cell, the SMLC 307 periodically or on demand evaluates and derives a current list that specifies the optimal SNs in potential view near the cell site, along with the restricted domains of Doppler shift and pseudorange that are anticipated to be appropriate for assisting in an AGPS reception.
- the preferred embodiment of the present invention exploits the availability of the up-to-date descriptions of the GPS configuration parameters to support a reduced TTFF from the MS GPS receiver.
- the SMLC 308 rapidly responds to a particular location request and provides the AGPS parameters appropriate for the vicinity of the serving WCS cell site. These AGPS parameters are received by the LG 309 and are provided to the MPC and/or the MSC to be communicated to the MS in its GPS data request 111.
- the SMLC 310 also proceeds to request the development of data related to the MS location from all LMUs that are optimally configured to cooperate in the determination of locations served by the identified cell site.
- the LMUs 311 apply their signal acquisition and processing facilities to detect and extract the data appropriate for support of the location-determination calculations.
- These LMU data are then provided to and received by the SMLC 312 for integration into the location processing.
- the GPS data relevant to the MS location is sensed by the MS receiver with whatever assistance its processing facilities are configured to exploit.
- the MS develops this data in response to the request 111, and communicates the data to the serving cell site 110 for inclusion in the location calculations.
- the MS's GPS data may be provided to the PDE by way of the WCS, either through the MPC or directly from the MSC.
- the LG 313 can receive these data from the WCS or, optionally, the LMUs 314 may receive, demodulate, and provide the MS's GPS data from the MS response message.
- the SMLC 315 receives the GPS information that the MS has provided for insertion into the integrated location-determination calculations. [0029] With the data received from the LMUs 312 and from the MS 315, the SMLC 316 integrates all of the data in deriving an optimal probable estimate for the MS location parameters.
- the location-related measurements obtained from the cooperating LMUs may include data of various forms and positional sensitivities from LMU positions and equipment that support various individual accuracies.
- the GPS data may individually define or support stand-alone data location, with potential correctable biases, or may only provide pseudorange and Doppler measurements for a limited, incomplete set of SN signals due to occlusion or distortion of the GPS signal propagation paths.
- the SMLC 316 combines all of the data provided, and integrates them into probability-based evaluations that incorporate whatever additional relevant collateral information is available to further condition the location estimate. The approaches and techniques appropriate for these integrated evaluations are presented in the following descriptions.
- the resultant estimate for the MS location is provided to the LG so that the LG 317 can route the information to the MPC in response to its original location request.
- a measurement of a time of signal arrival (TOA) at a receiving position is directly related to the distance between the location of signal reception and the location of signal transmission.
- the signal transmitter-to-receiver distance, D TR spanned in the propagation of the transmitted signal is represented as the straight-line vector length between the transmitting and receiving locations, X and X R , represented in an earth-centered, inertial (ECI), three-dimensional, Cartesian coordinate system:
- X R (TOA) is the three-dimensional vector coordinate representation of the receiver position at the "epoch” or time TOA
- x ⁇ (TOT) is the vector coordinate representation of the transmitter position at epoch TOT.
- the (constant) propagation speed, "c” may be multiplied by the fundamental time measurements to render the measurements directly in units of distance or length.
- the TOT for the received signal interval is defined, controlled, and known with respect to a specified and precisely maintained time standard, e.g., GPS time or the related Universal Time Coordinated (UTC).
- An MS using an embedded GPS receiver is designed to receive the GPS signals that are transmitted at known times from the SNs, whose positions can be calculated from transmitted orbit-determination parameters.
- a land-based infrastructure that determines MS locations by exploiting TO As measured at separated LS locations for signals transmitted by the MS or at the MS for signals transmitted by the LSs uses time-base synchronization (e.g., synchronized to GPS transmissions) to coordinate the clock standards for separated LS receiving stations and/or time commonality to associate separate signal receptions at the MS.
- time-base synchronization e.g., synchronized to GPS transmissions
- TDOA measurement provides a measure of the difference between two TOAs for two different and distinct signal receptions.
- TDOA 1 the difference in times of arrival, TDOA 1 , is directly related to the difference in signal propagation distances, D R and D ! :
- the TA parameter for an MS which is measured and applied for communications system synchronization, is also directly related to the distance of signal propagation from a controlling LS to the MS of interest, and back, i.e., the MS senses a signal transmitted from an LS, synchronizes itself to this signal, and emits a responding transmission in cooperative time alignment that is sensed at the LS.
- the TA M s is set to this offset and is directly related to twice the location-related propagation distance, D ML , between the MS and LS locations:
- G is a distance-independent factor encapsulating other contributing factors such as receiving and transmitting antenna "system” gains in the relative directions of signal propagation
- PL() is a distance-dependent model of the environmental path losses for the propagating signal strength between the deployed transmitting and receiving antennas.
- ⁇ is the wavelength of signal propagation.
- the distance differences for GPS signal propagations from SNs to a receiving MS are proportionately small, and significant variability exists in GPS signal propagation from the different SNs, with ionospheric and atmospheric effects and with multipath reflections near the MS. These characteristics typically render the use of received GPS power levels inconsequential for MS location determination.
- the location calculations can make effective use of an empirically validated propagation loss model such as Hata's representation of Okumura's data, as documented in the following article, which is incorporated herein by reference: Empirical Formula for Propagation Loss in Land Mobile Radio Services, M.
- a transmitted level may not be known or available from measurement.
- the ratio of received levels for the common transmitted signal that is received by two separate receivers can be exploited as a measure related to the ratio (or dB difference) for the two position-dependent distances between the transmitting and the receiving stations.
- the power level ratio or dB difference is adjusted for gain factors specific to each reception location. Such use of received power ratio or dB difference does not require available information regarding the common transmitted power level.
- MS location-dependent information can be extracted for transmissions from one or more LSs to an MS and/or from an MS to one or more LSs.
- signal AOA measurements also provide MS location-dependent information, and this type of information is nominally independent of the signal propagation distance. Since measurement of an AOA requires the availability of a directionally sensitive, receiving, antenna structure at the reception location, the AOA is typically extracted for a signal transmitted by the MS and received at a LS. Thus the AOAs are measured for communications-band signals propagated "horizontally," approximately along the earth's surface.
- An AOA may be typically represented as the angle of the direction from the point of reception toward the incoming signal, quantified relative to the known fixed direction of true, geodetic North. This relation may be expressed as
- AOATR atan2[(x ⁇ -XR)E / (XT ⁇ XR)N] (7)
- Atan2[] provides the complete four-quadrant arctangent
- () E and () N represent the East and North components for the vector directed toward the transmitter location X T from the receiver location X R .
- Such a measure provides information regarding the locus of the possible or probable transmitting MS locations along the line of bearing (LOB) sensed at the receiving LS, and the measure is nominally independent of the distance along the LOB from the LS to the MS location.
- LOB line of bearing
- GPS SV Transmitter Locations [0038] With the location-dependent relations described above, the determination of an MS location requires knowledge of the transmitter locations when the MS is the point of signal reception, as in GPS and some forms of infrastructure systems measures, and requires knowledge of the receiver locations, when the MS is the transmitter.
- the locations of fixed LS receiver locations can be precisely determined by survey, including GPS-based survey.
- the accuracy of MS locations determined from measurements involving LSs is directly related to the accuracy with which the LS locations are known. Of particular significance for the exploitation of GPS time measurements, the limitation in the accuracy to which a MS location is determined is dependent upon the accuracy to which the SN transmitter positions are known and represented.
- GPS SN positions and velocities at any instant or epoch are described and determined in accord with the ephemeris parameters that are communicated from the GPS in the SN navigation message transmissions.
- Descriptions of the mathematical relations involved in the representation and calculation of the SN elliptical-orbit positions and velocities from the ephemerides are available in texts such as those following: Global Positioning System, Theory and Practice, 5th Ed., Hofmann-Wellenhof, Lichtenegger, and Collins, Springer-Nerlag, 1994; Global Positioning Systems, Inertial Navigation, and Integration, Grewal, Weill, and Andrews, John Wiley, 2001.
- the SN ephemeris parameters are used to produce SN location and motion parameters expressed in accord with the World Geodetic System 1984 (WGS 84) description of the earth's shape and other physical properties.
- the ephemeris parameters include the satellite pseudo-random number (PR ⁇ ) identity, the specification of the GPS reference epoch for which the parametric values are specified, the Keplerian orbital parameters, and the parameters specifying the planar alignment of the Keplerian ellipse and its perigee.
- the ephemeris defines the SN location and motion with respect to the earth-centered, earth- fixed (ECEF) coordinate system, which is itself rotating with respect to the solar-fixed (inertial), vernal-equinox based, ECI coordinate system. While the ephemeris parameters in the GPS almanac data provide the multiple-kilometer accuracy appropriate for acquiring signal contact, it is the broadcast ephemeris from each SN (sans the dither or truncation of selective availability, S A) that typically enables the calculation of the SN's particular ECEF Cartesian position to within a few meters, when used for observation epochs within the appropriate four-hour epoch window from the reference epoch.
- ECEF earth-centered, earth- fixed
- Time Base Alignment As noted in the relations above, for determination of the location of an MS at a specific instant, the times of reception and/or transmission of the signal intervals of interest must be appropriately acquired and tagged to the processed signal data.
- the time base for GPS called GPS time
- the GPS transmissions of each SN occur at instants in synchronization with a time-base established by that SN's clock.
- GPS ground stations around the world monitor the position, time synchronization, and health of each SN, and provide correction terms to the SNs that describe "current" time alignment corrections for the accurate interpretation of the SN transmissions in synchronization with the GPS time standard.
- These time correction parameters, to second order, are included in the navigation messages transmitted from the SNs.
- the position, x, of the MS of interest is determined for a particular instant in time, relevant to the measurements and information from which it is derived, i.e., the MS location is not typically or necessarily presumed or constrained to be constant in time, but rather is taken to be a function of time, x(t).
- An example of this is represented in relation (2).
- the time base of the MS receiver is not inherently synchronous with GPS time, e.g., the MS time base may be, at least, offset (zeroth order correction) and drifting by clock frequency difference (first order correction) from that of GPS.
- a fundamental TOA measurement labeled or "tagged” in accord with the MS time base, is potentially biased relative to its "true” value aligned with GPS time.
- the fundamental TOA measurement in a GPS receiver is said to provide a measurement of "pseudorange" (rather than true range or distance), when used in relation (2) before determination of the MS clock bias or offset for that measurement.
- the present invention can mitigate the typical necessity for a GPS-related location determination to have available at least four, distinct, independent pseudorange measurements.
- the four measurements or position- determining data are required for the completion of the location calculation to derive the MS three-dimensional coordinate position along with the MS clock bias.
- any available pseudorange measurements are integrated into the location calculations, together with whatever relevant location-related measurements are available from infrastructure-based equipment and whatever other relevant location-related collateral information is available about the probable MS location.
- DGPS Differential GPS
- Biases such as these can be mitigated or corrected in calculations of the MS location through the monitoring, evaluation, and application of DGPS adjustments, which are derived from a network of one or more supporting stations.
- DGPS corrections for the MS location calculations are evaluated for a GPS monitoring station through comparative evaluation of currently sensed GPS measurements at the station and derived location parameters for that location.
- the derived values are calculated for the "known" locations of the SNs based upon their ephemerides and are evaluated in association with the "known" values for the support station location, hi preferred embodiments of the present invention with the use of fixed/stationary LSs as the supporting DGPS reference stations, the known LS locations are those obtained through accurate geodetic surveys.
- Each pseudorange measurement can be corrected in accord with the difference observed at some nearby supporting reference LS between its own currently observed pseudorange measurement from that same SN and the current value that would conform with its apriori known location, given the associated current common SN clock bias and ephemeris parameters being transmitted in the SN navigation message. Such differential corrections mitigate the effects of local systematic biases in the pseudorange measurements and enhance the accuracy of the derived MS location.
- Probable Location Determination [0048] With the technology described herein, an optimum estimate of a MS location is derived from the totality of the location-related information available for its determination. The location-related information is available in measurements of received signal characteristics and in collateral information that indicates the relative probabilities or likelihoods of potential MS locations.
- z) represents the probability that the state vector components are those evaluated for x under the condition that the observations have the values actually obtained for the measurement values in z
- x) represents the probability that the values of the vector z would be observed under the condition that the state variables are of the values in x
- p(x) is the total (marginal) relative apriori probability that the state values of x would occur
- p(z) is the total (marginal) probability that the measured parameter values occur for the observation vector, z.
- location-independent factors such as the p(z) term are inconsequential.
- the jointly combined probability or likelihood of the independent data elements together is the product of the probabilities of the independent data sets alone, e.g., with the technology of the present invention, the assembly of data of various types from diverse sources integrates statistically independent data.
- the maximum of the likelihood is derived via the maximum of the logarithm of the likelihood, then the product likelihood relation is accumulated as the sum of the "log likelihoods.”
- the parametric location solution for the maximum or most likely value is typically derived by sampling or calculating the likelihood function value for a grid or set of discrete location parameter values that span the complete domain of possible values.
- the sampling interval or grid spacing typically is started at a coarse mesh that is sufficient to indicate the local region(s) of potentially optimum value, and then the mesh of the sampling grid is progressively refined in subsequent iterations that are focused in the optimal regions of limited extent.
- the ultimate results are evaluated to the resolution that the contributing measurement accuracies support.
- gradient-based calculations can be applied in focusing upon the regions of optimal value and upon the inherent resolution supported by the measurements.
- the function h() is intended to accurately represent the true association between the data and the desired location state parameters.
- the expectation value, "E(),” for the noise is zero (i.e., the noise is unbiased) and, under normal assumptions, the observation uncertainties are represented by a Gaussian covariance matrix, R:
- the state vector x will typically be a four-parameter vector, including three MS location coordinates and one MS clock bias coordinate, and the measurement vector will typically be a vector of four or more measurements.
- the measurement vector will typically be a vector of four or more measurements.
- the dimensionality of the measurement vector can be reduced and still result in an acceptably accurate MS location.
- an optimal estimate for the MS location can be derived for the maximum probability or maximum likelihood state estimate, which maximizes the combined product probability that integrates any available collateral information and all of the available measurement information, both GPS- based and infrastructure-based.
- the optimal integrations of GPS-based measurements and infrastructure-based measurements and associated information enable a MS location to be derived even when there is not sufficient information available from either the infrastructure alone or from GPS measurements alone to determine a location of useful accuracy.
- the typical GPS accuracy with small circular area of uncertainty, is realized when an open view of the sky is available, so that SN signals can be successfully received from an approximately uniform distribution of satellites above and surrounding the MS.
- signal propagation conditions among the urban canyons of high-rise buildings at the centers of large metropolitan regions can result in occluded SN reception, thereby preventing reception of a sufficient suite of GPS SN signals for a stand-alone GPS solution.
- some types of collateral information can be expressed in one or more constraint relations for the MS state parameters, e.g., while the typical GPS solution is calculated in the three dimensions of an ECEF coordinate system, the resultant location estimate can be constrained to be at a distance from the ECEF origin at earth center that effectively places the location at (or nearly at) the earth's surface when the MS is known to be positioned near the ground terrain, rather than in flight.
- constraints can be included in the probability calculations either by pre-conditioning the apriori probabilities associated with candidate locations, or by effectively including "pseudo-measurements" that express various constraints and their extent of uncertainty as a function of location.
- An effective use of known statistics for the potential locations of an MS can be applied in the likelihood calculations.
- the statistical distribution of relevant locations for the phone usage may be available from collected usage statistics or databases, e.g., the statistics of phone usage in heavy urban environments may indicate that MS phones are more likely to be on or beside the streets of the urban road network, and similarly the statistics for operations in sparsely populated rural environments may indicate that MS phones are more likely to be on or beside the highways or arterial thoroughfares passing through a rural region.
- An accurate representation of the roadway positions of a street or highway network may be obtained from standard map databases, including those maintained by civil authorities.
- the imposition of an apriori distribution of probability factors overlaying the candidate domain of possible locations might preferentially condition the likely locations to fall on or beside the roads.
- the two- dimensional description of the roadway locations on the earth's surface can be spatially "lowpass" filtered. This filtering can de-resolve or smooth the apriori likelihood representation so that the probabilities are indeed elevated near or on the roadways, but that the probabilities decrease slowly or are spread/smoothed out to realistic extent in directions transverse to the roadways.
- the effective use of available statistics in the present invention can be recursively augmented, enhanced, and applied in upgrading the probability representations as the statistics are collected from the locations derived with the present invention.
- Coordinate Relations To support the integration of GPS information together with infrastructure- based information, the common coordinate system applied in the location calculations must accurately represent both types of information. As noted above, GPS calculations are typically implemented with the use of an ECEF system of coordinates, which accurately represents the locations and velocities of the SNs and the MS of interest, on land or above. To date, coordinate systems applied in the exploitation solely of information regarding a terrain-based network of LSs for cellular phone location determination have typically invoked planar projections of the earth's surface in the local vicinity of the LSs.
- the geographic extent of the applicable operational domain of the locating system has been confined to a small enough region that the curvature of the earth's surface has not affected the observed relations to a measurable degree.
- the surveyed locations of terrain-based LS antennas are typically expressed in terms of geodetic latitude, longitude, and height above ground level (agl), together with the associated height of the local ground level above mean sea level (amsl).
- Transformations of geodetic coordinates based upon a (e.g., WGS 84) ellipsoid into a system of flat, planar coordinates typically apply conformal projections, such as the Lambert conformal conical or (universal) transverse Mercator (UTM) projections, as described in John P. Snyder's texts: Map Projections - A Working Manual, Snyder, U.S. Geological Survey Professional Paper 1395, US Government Printing Office, 1987; Map Projections, A Reference Manual, Bugayevskiy and Snyder, Taylor & Francis, 1995.
- conformal projections such as the Lambert conformal conical or (universal) transverse Mercator (UTM) projections
- the preferred embodiment of the present invention applies the GPS-standard ECEF coordinate system together with the reliable transformation of local altitude representations to provide an accurate representation of all of the relevant location relations.
- the GPS antenna and receiver at each LMU location provides a direct WGS 84 basis for differential comparison with the height (agl) of the communications antennas at the site.
- the likelihood calculations involving the relations between sensed or statistical information and the candidate MS location can be simply implemented in the three-dimensional, WGS 84-based, ECEF Cartesian coordinate system that is standard for the exploitation of GPS data. All of the location descriptions for the LS antennas and the collateral information are transformed in accord with this system for the location- determination evaluations.
- GPS-related coordinate transformation discussions referenced herein e.g., section 1 of Bugayevskiy and Snyder and section 10 of Hofmann-Wellenhof, Lichtenegger, and Collins, describe calculations involved in relating ECEF coordinate values to corresponding values for horizontal (latitude, longitude) location and altitude or height above mean sea level, expressed in terms of local, geodetic coordinates.
- GPS coordinate transformations are based upon the WGS 84 parametric representation of the earth's shape.
- the WGS 84 representation of the earth as an ellipsoid of revolution provides the geodetic basis in the expression of the calculated location results.
- the results are quantified in terms of the WGS 84 geodetic latitude, the longitude, and the height above the WGS 84 ellipsoid and/or the height above the mean sea level of a local geoid surface, which is itself described in terms of height above the WGS 84 ellipsoid surface.
- the height can be constrained to this locally representative surface level above the WGS 84 ellipsoid, h this case, the locations evaluated in the likelihood considerations need only span the latitude and longitude domains relevant to the ensemble of available observations or measurements.
- the ECEF system values for the instantaneous location and velocity parameters of the SNs could be transformed into an "east- north-up (E ⁇ U)" coordinate system that is convenient for a local region of applicable LSs.
- E ⁇ U east- north-up
- the us ( e of such a system in an alternative embodiment of the present invention would require the additional coordinate system transformation of the SN coordinates from the ECEF system natural for the use of the GPS ephemerides to the local E ⁇ U coordinates tangent and orthogonal to the WGS 84 ellipsoid.
- Such an alternative implementation may exploit the similarity or proximity of such coordinate system to a local, planar, preferably conformal projection of the earth's surface. For such usage, proper consideration of the instantaneous location and velocity vector relations of the SNs with respect to the appropriate direction of "up" is essential.
- Constrained TDOA/FDOA The psuedo-ranges computed by a GPS/ AGPS (even EOTD) receiver may be combined with network-based location measurements, such as TOA, TDOA, AOA, relative power, and round trip delay, to compute a more accurate and robust solution.
- network-based location measurements such as TOA, TDOA, AOA, relative power, and round trip delay
- constrained TDOA/FDOA calculations may be used in a GPS/AGPS environment.
- the constraints can determined by a combination of data collected by an assisting GPS receiver, which limits the effects of time offset or Doppler caused by the position and velocity of the satellites, along with constraints determined using the position computed by GPS/AGPS, a network-based location method, or a combination.
- Constrained TDOA/FDOA can reduce the processing burden on the GPS receiver, and improve sensitivity by eliminating most opportunities for false alarm.
- An enhanced synchronization technique may be employed to increase the system sensitivity to discovering GSM beacons and their respective mapping to GPS time.
- an Abis monitor or Abis Monitoring System, or AMS
- AMS Abis Monitoring System
- the parameters provided by the AMS contain the RFN (reduced frame number, Tl', T2, T3) ⁇ the partial description of GSM frame number.
- This information may be combined with observations and calculations made directly by LMUs monitoring the downlink path to further converge on the timing solution.
- Hybrid AGPS/TDOA/AOA System for Increasing Capacity/Service Levels [0064] In a multiple- vendor GSM environment, a number of location-based services will exist, each with different accuracy, call states, and latency requirements. Also, location technology should be designed to cope with real-world traffic and loading requirements.
- a combined TDOA/AGPS system presents an ideal system for confronting the multiple challenges to a wireless location system. 1. For cases when early, enhanced call routing is required, TDOA is best. 2. When a user is on a call, TDOA is best with no additional traffic loading. 3. When the MS is idle or the position is latency insensitive, AGPS is best. 4. When the system is lightly loaded, AGPS is best/most accurate 5. When the system is heavily loaded, TDOA is best. 6. When the system requires high accuracy, TDOA and AGPS an be used in combination. 7. When a legacy phone (non-GPS capable phone) is in operation, TDOA is best.
- the true scope the present invention is not limited to the presently preferred embodiments disclosed herein.
- the foregoing disclosure of a presently preferred embodiment of a wireless location system uses explanatory terms, such as Location Measurement Unit (LMU), Serving Mobile Location Center (SMLC), and the like, which should not be construed so as to limit the scope of protection of the following claims, or to otherwise imply that the inventive aspects of the system are limited to the particular methods and apparatus disclosed.
- the inventive aspects disclosed herein may be applied in location systems that are not based on TOA and/or TDOA techniques.
- the processes by which the wireless location system determines TDOA and/or FDOA values can be applied to non-TDOA systems.
- the invention is not limited to systems employing LMUs and other subsystems constructed as described above.
- the LMUs, SMLC, etc. are, in essence, programmable data collection and processing devices that could take a variety of forms without departing from the inventive concepts disclosed herein.
- the place of implementation (i.e., the functional element) described herein is merely a designer's preference and not a hard requirement. Accordingly, except as they may be expressly so limited, the scope of protection of the following claims is not intended to be limited to the specific embodiments described above.
Abstract
Description
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BRPI0418136-0A BRPI0418136A (en) | 2003-12-30 | 2004-12-29 | method and system for determining the location of a mobile station (ms) equipped with a built-in gps signal reception capability and equipped to operate within a wireless communications network |
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IL176192A IL176192A (en) | 2003-12-30 | 2006-06-08 | Tdoa/gps hybrid wireless location system |
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Also Published As
Publication number | Publication date |
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EP1704734A2 (en) | 2006-09-27 |
IL176192A0 (en) | 2006-10-05 |
KR101183753B1 (en) | 2012-09-17 |
JP2007518979A (en) | 2007-07-12 |
CA2821652C (en) | 2014-07-22 |
KR20070026345A (en) | 2007-03-08 |
US7925274B2 (en) | 2011-04-12 |
AU2004311881A1 (en) | 2005-07-21 |
GB0612619D0 (en) | 2006-08-23 |
CN1898975A (en) | 2007-01-17 |
GB2426647B (en) | 2008-02-13 |
US20080248811A1 (en) | 2008-10-09 |
EP1704734A4 (en) | 2009-10-21 |
CA2548669C (en) | 2014-05-06 |
CA2548669A1 (en) | 2005-07-21 |
AU2004311881B2 (en) | 2008-07-31 |
WO2005065320A3 (en) | 2006-04-20 |
US20050148346A1 (en) | 2005-07-07 |
CN1898975B (en) | 2010-04-28 |
JP5026086B2 (en) | 2012-09-12 |
IL176192A (en) | 2011-03-31 |
CA2821652A1 (en) | 2005-07-21 |
BRPI0418136A (en) | 2007-04-17 |
US7440762B2 (en) | 2008-10-21 |
MXPA06007257A (en) | 2006-08-18 |
GB2426647A (en) | 2006-11-29 |
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