Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/14—Relay systems
  • H04B7/15—Active relay systems
  • H04B7/185—Space-based or airborne stations; Stations for satellite systems
  • H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
  • H04B7/18545—Arrangements for managing station mobility, i.e. for station registration or localisation
  • H04B7/18547—Arrangements for managing station mobility, i.e. for station registration or localisation for geolocalisation of a station
  • H04B7/1855—Arrangements for managing station mobility, i.e. for station registration or localisation for geolocalisation of a station using a telephonic control signal, e.g. propagation delay variation, Doppler frequency variation, power variation, beam identification
• • 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
  • G01S1/00—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith
  • G01S1/02—Beacons or beacon systems transmitting signals having a characteristic or characteristics capable of being detected by non-directional receivers and defining directions, positions, or position lines fixed relatively to the beacon transmitters; Receivers co-operating therewith using radio waves
  • G01S1/022—Means for monitoring or calibrating
• • 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
• • 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
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
  • G01S13/76—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted
  • G01S13/767—Responders; Transponders
• • 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
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
  • G01S13/76—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted
  • G01S13/78—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted discriminating between different kinds of targets, e.g. IFF-radar, i.e. identification of friend or foe
• • 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
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/87—Combinations of radar systems, e.g. primary radar and secondary radar
  • G01S13/878—Combination of several spaced transmitters or receivers of known location for determining the position of a transponder or a reflector

Definitions

• the present invention relates generally to methods and systems for performing geolocation. and more particularly to a method and system for performing global geolocation via a non-geostationary earth orbiting satellite
• GPS Global Positioning System
• the prior art systems perform their geolocation functions using two or more transmitter and/or receiver platforms that are located at distant positions
• at least three and preferably four m-view satellites must be available to the geolocation receiver at all times in order to achieve a position solution
• the use of prior art satellite based systems will not penetrate building structures, thick vegetation, or sheltered areas
• the present invention is therefore directed to the problem of developing a method and apparatus for performing enhanced global geolocation, which does not require large mobile devices or multiple satellites and which will operate indoors and in numerous types of environments SUMMARY OF THE INVENTION
• the present invention solves this problem by determining an error vector representing a difference between a known location of a fixed reference station and a measured location and applying that error vector to a measured location of the mobile unit Bv so doing, the present invention relies onlv on a single satellite, does not require GPS based receivers/transmitters, which keeps the size and power small and can operate at frequencies that penetrate numerous environments, while providing an accurate position measurement
• a method for locating a mobile unit includes determining the location of a reference unit, calculating an error vector that represents the difference between the actual known position and the measured position estimating the position of the mobile unit using the same technique used to measure the location of the reference unit and applying the error vector to the estimate position of the mobile unit to determine the final position of the mobile unit
• the present invention measures the doppler shift in a signal transmitted from the ground units to a satellite to obtain a first position curve on the surface of the earth on which the ground unit may be located, uses the time of arrival of the signal transmitted from the ground unit to the satellite to determine a second position curve on the surface of the earth on which the ground unit may be located, and determines a point of intersection of the first position curve and the second position curve which defines an estimate of a location of the ground unit
• a system for determining with a high degree of accuracy a location of a mobile unit based upon signals transmitted from a low earth orbiting satellite, which is disposed in a known orbit about the earth, the mobile unit being capable of moving selectively throughout a geographical area includes a command center, a transmitter for transmitting geolocation information and other data from the command center to the mobile unit, a receiver for receiving Doppler frequency shift, time of arrival, and angle of arrival data, and other data from the mobile unit via the iow earth orbiting satellite to the command center, and a measurement/geoloca ⁇ on/ service processor residing in the command center
• the processor determines a Doppler frequency shift component of a plurality of geolocation parameters, a time of arrival component of the plurality of geolocation parameters, an angle of arrival component of the plurality of geolocation parameters and an approximate position of the mobile unit transmitter signal traveling between the mobile unit and the low earth orbiting satellite
• the command center includes a receiver for receiving differential data regarding a plurality of fixed reference stations and
• FIG 1 graphically depicts the LEO satellite global coverage of the LEO satellite constellation used in the present invention
• FIG 2 graphically depicts the LEO satellite beam footprint of the satellite constellation used in the present invention
• FIG 3 shows the geolocation system of the present invention
• FIG 4 shows the mobile transceiver unit of the present invention
• FIG 5 illustrates the range measurement technique used in the present invention
• FIG 6 illustrates the Doppler measurement technique used in the present invention
• FIG 7 shows the combined range and Doppler measurement of the present invention
• FIG 8 illustrates the location algorithm for the mobile unit of the present invention
• FIG 9 shows the error correction vector method of the present invention
• FIG 10 shows a map of a typical placement of differential Doppler base stations
• a method and an apparatus for providing an improved satellite-based tracking system uses a reference transmitter at a site with a known location to provide an error correction vector, which can be applied to improve the position estimate of a transmitter at unknown locations
• a transmitter/receiver (transceiver) is interrogated via a satellite ground station through a satellite transponder in Earth orbit Upon reception of the transceiver's unique identification code broadcast by the satellite, the transceiver will transmit its identification code back to the satellite ground station via the satellite transponder
• the round trip response time is used to calculate the range from the satellite to the transceiver
• the Doppler shift of the received signal due to the satellite motion of a satellite in non- geostationary orbit, is used to calculate the angle-of-ar ⁇ val at the satellite
• the range and angle-of-arrival are combined to calculate the position estimate of the location of the transceiver
• This geolocation process is repeated for a transceiver at a known reference site and for all mobile and/or fixed transceivers at unknown sites
• the position estimate generated for the reference transceiver is compared to the a-p ⁇ or known position reference transceiver The difference between the
• the transmitter can be made low power, l e , less than one watt Furthermore, the battery life will be in the range of approximately 30 days as a result of the architecture of the system
• the satellite system employed bv the present invention is independent of the Global Positioning System (GPS) for determination of position and provides the military with a positioning capability, as well as a means for reporting position to the command center without broadcasting a position coordinate set To prevent others from detecting the broadcasts, the present invention employs secure spread spectrum communications
• the present invention inexpensively locates a previously tagged missing person or object Whenever a user is disabled or injured on a covert mission or otherwise needs to be tracked, the mobile unit of the present invention is interrogated by satellite to determine the user's position This requires no action by the user
• the communication between the satellite and the user's mobile unit is performed using inherently secure spread spectrum communications, thus preventing eavesdroppers from listening Since the position is not broadcast, there is nothing to listen to The location determination is performed at the satellite's ground station, which then alerts the rescuers or is monitored for tracking applications
• the following chain of events occur in order to locate a user once a request has been received
• the customer calls the system of the present invention with a request
• the ground station then signals the satellite, which broadcasts the communicator identification code
• the mobile unit receives the broadcast and transmits a response
• the satellite retransmits the mobile unit s signal back to the ground station which then calculates the position
• the downlink to the communicator is in the S-Band (2500 MHZ) and the uplink from the communicator is in the L-Band ( 1600 MHZ) These frequencies enable the use of very small antennas
• CDMA code division multiple access
• the present invention uses the Doppler geolocation technique developed bv the U S Navy T ransit Navigation Satellite System of the 1 60's and 1970's This system was replaced bv the AVSTAR/GPS satellites for navigation
• the present invention uses the Doppler technique because it is simple and low cost, while providing satisfactory positional accuracy
• the present invention adds a Differential Doppler technique, which is discussed below
• the Doppler technique relies upon a shift in frequency between the satellite and the mobile unit As the satellite orbits the earth, the shift of a signal received from a transmitter on the surface of the earth is detected
• the Doppler shift resulting from the relative velocity between the satellite and the transmitter represents a surface of a cone that the transmitter must he upon
• the transmitter is assumed to be on the surface of the earth, which eliminates most of the cone's surface as possible points Consequently, a line of position can be determined from one Doppler measurement, which is the line the cone and the earth intersect A short interval later (e g , one minute) a second Doppler measurement is made, and a second line of position can be determined
• the intersection of the two resulting lines of position represents a position estimate for the mobile unit Since the mobile unit is not moving fast under most circumstances this is sufficient to locate the mobile unit
• the present invention uses pseudo ranging techniques to determine the position of the mobile unit By combining the aforementioned Doppler technique and the ranging technique the present invention is able to provide an instant
• the present invention employs a differential Doppler technique, which relies upon providing a second fixed location communicator to the operational scenario discussed above
• the second communicator is placed in a fixed known reference location
• both the unknown communicator and the reference communicator are interrogated
• the Doppler measurement of the reference tag provides an error correction vector that can be applied to the position estimate of the unknown tag Using this Differential Doppler approach, it is estimated that the position uncertainty can be reduced from 1000 meters to 30 meters
• the present invention minimizes the operational requirements for the transceiver for the mobile unit, thus enabling a wristwatch sized unit This is possible because the satellite performs the geolocation rather than imposing that requirement (and adding GPS) on the mobile unit
• the satellites used in the present invention are low- or mid-earth orbiting satellites due to the higher elevation angles that are achievable In addition, less transmitter power is required, and the omni-directional antennas eliminate the need for tracking antennas
• One example of the low earth orbiting satellite-based digital telecommunications system is Globalstar It will provide telephony and other digital telecommunications services, such as data transmission, paging and facsimile Globalstar service will be delivered through a 48-satelhte constellation at 1419 km altitudes Globalstar, will begin launching satellites in the second half of 1997 and will commence initial commercial operations in 1998 Globalstar is licensed to operate at L and S bands in the United States using spread spectrum communications Odyssey is essentially the same as Globalstar, except for the higher altitude of the satellites Its first launch is scheduled for 2000 FIG 1 shows the low earth orbiting satellite global coverage, and the footprint
• the satellite used in the present invention is one of a series of low earth orbiting satellites orbiting the earth
• satellites are assigned identification numbers that are unique
• the placement of the satellites is such that all points on the earth lie within the coverage area of at least one satellite
• multiple satellites are m view of each point
• Each satellite in the constellation can cover a continent-sized portion of the earth's surface as shown in FIG 2, which shows the low earth orbiting satellite beam footprint 200 and the associated spot beams 202
• the system 300 includes a satellite ground station 302, a low earth orbiting satellite 304, a reference transceiver unit 306 and a mobile transceiver unit 310
• the two transceivers 306, 3 10 are identical, except for the fact that the reference transceiver 306 is placed in a known location, whereas the mobile transceiver 310 can be moved to any point on the earth
• the system of the present invention permits one or more of each of these elements, e g , the ground station 302, the reference unit 306 and the mobile unit 310
• the satellite ground station gateways 302, which also reside on the surface of the earth, are in data communications with in-view low earth orbiting satellites 304 through RF communications channels 308
• the number of mobile units 3 10 is not limited Consequently, the number of mobile units 310 could be in the millions
• the mobile unit 3 10 is portable, battery powered, consumes relatively low power, and includes a relatively small
• FIG 2 shows a LEO satellite footprint 200 of the satellite spot beam 202 formed on the surface of the earth
• Each spot beam 204-232 is formed by a single satellite as it moves along satellite footprint 200 MG 1 shows the global coverage of the entire satellite constellation
• Each spot beam 204-232 within the satellite footprint 200 occupies a unique position within the satellite footprint 200, hence these positions can be distinguished from one another by assigning each spot beam 204-232 a unique identification code Consequently, one can obtain a first cut in locating a particular mobile unit by determining which spot beam the mobile unit lies within This information defines a position relative to a satellite, whose position is usually known from known orbital calculations and tracking
• a spot beam location 204-232 within a satellite footprint 200 with the satellite's position, one can determine the mobile unit ' s position on the earth within a large area
• the location information determined by the unique spot beam 204-232 can be used to perform ambiguity resolution during a geopositioning measurement such as differential Doppler, wherein there are two positions determined, a real position and an image position, I e , the math predicts two positions (a real and an imaginary position), only one of which is real, the other is termed an image position
• the unique spot beam information can be used to choose the real position Mobile Transceiver Unit
• FIG 4 shows a block diagram of the mobile unit 10
• the mobile unit 3 10 consists of a receive antenna 402, a receiver 404 a digital signal processor 406, a crystal reference 408.
• local oscillators 410 a transmitter 412, a power supply/batterv 414 and a transmit antenna 416
• the receiver 404 receives signals from the satellites in low earth orbit via the receive antenna 402
• the receiver 404 couples these signals to the digital signal processor 406, which converts the received electromagnetic energy to data and performs all data demodulation and processing
• the digital signal processor 406 also performs all of the mobile unit 3 10 control and status functions and controls all receive parameters such as frequency, timing, Doppler tracking and the like
• the digital signal processor 406 is also coupled to the transmitter 412 and converts the data to electromagnetic energy and performs all modulation that is used to transmit signals to the satellite in low earth orbit via the transmit antenna 416
• the digital signal processor 406 also controls all transmit parameters such as frequency timing, and the like
• the local oscillators 410
• a range sphere 501 represents the time of arrival of the transmitter's 310 signal at the satellite 304 Since electromagnetic signals propagate at a constant velocity equal to the speed of light, a given propagation duration dictates that the source of the signal must lie on the surface of a sphere having a radius equal to the propagation duration times the speed of light and centered at the point where the signal is received
• the source of the electromagnetic signal may be the mobile unit 310 located on the surface 503 of the earth and the signal may be received at the satellite 304 orbiting the earth
• a time of arrival circle represents the intersection of a sphere centered at the satellite 304 and having a radius equivalent to the speed of light times the propagation duration with the earth's surface This is shown in FIG 5 where the time of arrival circle 501 determines the range between the satellite 304 and the mobile unit 310
• the coordinates of a point in space can be determined bv making a minimum of three range measurements between that point and three known points Each range measurement describes
• the range sphere 501 intersects the surface of the Earth 503 and produces a circular line of position 505, 507 A transmitter 310 on the ground must lie on this circular line of position 505, 507 in order to produce the time of arrival measured at the satellite
• the intersection 509 of the two lines of position 505, 507 represents the position measurement
• the time of arrival of the signal at the satellite is measured by sending a signal from a satellite ground station 302, through the satellite transponder 304, to the transmitter 310 instructing the transmitter 310 to reply with an acknowledgment (an interrogation)
• the total time delay measured includes the transmit time from the ground station 302 to the satellite 304 the transponder delay time, and the transmit time from the satellite 304 to the transceiver 310 on the ground
• the transmit time from the ground station 302 to the satellite 304 can be removed since both the positions of the satellite 304 and the ground station 302 are known Likewise the transponder time delay is known through ranging calibration measurements
• the time of arrival of the signal at the satellite 304 can be determined
• FIG 6 shows a portion of the geolocation process according to the present invention using a single satellite 304
• the geolocation system of the present invention activates the geolocation process with respect to a specific mobile unit 3 10 when a measurement record relating to that mobile unit 310 is received
• the geolocation process determines a frequency of arrival parabola to fit the Doppler component data contained in the measurement record This frequency of arrival parabola or line of position 616 is shown in FIG 6
• the satellite 304 is orbiting the earth and the mobile units 310 are located on the surface 503 of the earth
• the direction with which a satellite 304 moves with respect to a mobile unit 310 continually changes Since this direction continually changes but the satellite orbital velocity remains relatively constant, the component of satellite velocity in a radial direction toward the mobile unit 3 10 continually changes
• the satellite 304 has a particular velocity or range rate vector 614
• the Doppler component continually changes relative to a stationary mobile unit 310 on the surface of the earth
• the Doppler shift of the signal is represented by
• Doppler cone 610 is produced by measuring the Doppler shift of the received signal
• the position of the mobile unit 310 can be determined with only one combined measurement of Doppler and range Assuming that the transceiver unit 310 is on the surface 503 of the earth, the Doppler cone 610 and range sphere 501 will intersect at two possible transceiver unit positions 701 703 on the earth s surface The intersection of the frequency of arrival curve with the time of arrival circle provides a two position solution to the location determination problem One will be the true position and the other will be an image position For a given satellite *• > pass and mobile unit-to-satellite geometry these two positions will be at the same orthogonal distance from the satellite ground track where the range rate (hence Doppler shift) will be zero at the time of closest approach One of these positions resides to the right of the ground track and the other resides to the left of the ground track
• the ground track represents the axis of Doppler symmetry which is offset from the true satellite ground track by the ea ⁇ h's rotation In the absence of earth's rotation, the two solutions would be indistinguishable
• a low Earth orbiting satellite beam footprint 200 is shown with a number of spot beams 202
• SARSAT Search and Rescue Satellite System
• FIG 8 depicts the method of the present invention
• the method of the present invention includes four main parts First, the position of the reference transceiver is determined using two measurements ( 1 ) the range to the reference transceiver via the transceiver response time (803 ), and (2) the angle of arrival of the reference transceiver via the Doppler shift measurement (805 ) After the two measurements are made, the position is calculated (807) Second, the Error Vector is generated by comparing the known position of the reference transceiver with the position determined in the first part (809)
• the position of the transceiver in the unknown location is estimated using the same two measurements, l e , ( 1 ) the range to the reference transceiver via the transceiver response time (81 1 ), and (2) the angle of arrival of the reference transceiver via the Doppler shift measurement (813)
• the position estimate is the calculated for the transceiver in the unknown position (815)
• the Error Vector is applied to the estimated position to obtain the final position of the transceiver in the unknown location (817)
• the Error Correction vector 903 is depicted that is measured when the reference transceiver is interrogated is used to correct the position of mobile customer transceivers in the local area
• Correlated errors include all systematic errors such as satellite position and velocity errors, ionospheric propagation delay errors, troposphe ⁇ c propagation delay errors, and Earth surface elevation modeling errors
• the error correction vector 903 first the position of the reference transceiver is measured This is the "measured position" 905 Next, the difference between the measured position 905 and the known position 901 is determined, which represents the error correction vector 903 The error correction vector is then used to correct the position of the customer transceiver 310 based on the initial position estimate 91 1 to obtain the improved position estimate 907
• FIG 10 depicts a representative map of possible reference transceiver locations in a representative five state area Representative sites include Washington. D C (4). Blacksburg. Virginia (3). Richmond. Virginia (2) and mid West Virginia ( 1 )
• the accuracy of the geolocation technique of the present invention as described above may not be sufficient to locate the mobile unit 310 to the desired degree of accuracy in all cases
• the various sources of location error are random errors that can be expressed through standard deviations or other statistical variance terms Several more position calculations may be made before concluding that sufficient position accuracy has been achieved Additional location measurements may be performed through repetition measurements and a given mobile unit 3 10 Thus, the location process may perform additional measurements in order to average the results The averaging of location estimates determined from a plurality of location parameter sets reduces the inaccuracies associated with the position estimation and causes the location accuracy to improve
• an error ellipse is established for the averaged measurements taken up to a given point in time This error ellipse is determined by the number of measurements averaged, the variance terms that characterize the location parameters, and the currently estimated position location This error distribution is an ellipse centered around the estimated location It is more circular and covers a relatively small area when the error is minimal Where the error is greater, the ellipse ' s area increases (less circular) and its shape becomes more flattened
• the performance of geolocation measurement is based upon a unique combination of techniques for geolocation and the estimation of the geolocation errors associated with each technique
• These position techniques and their respective errors are specified in terms of the satellite operational orbital dynamics and geometry, the measurement of signal-to-noise ratios and their accuracies, the position errors of the satellites 304 based upon the GPS errors from which the satellite ephemeris is derived, satellite platform and mobile unit synchronization models, and the methods of computing mobile unit geolocation (i e , frequency of arrival and time of arrival curves)
• the performance analvsis consists ol several distinct steps These steps include development of models that reflect operational concepts and provides root mean square (RMS) error estimates determination of sensitivities of error sources to location errors and parametric error analvsis selection of geometries and parameters to obtain the expected results of actual measurements and perform calibration of the models to actual measured data
• RMS root mean square
• a key benefit of this model is that actual geolocation processing algorithms are employed, while error sources are represented by statistical distributions
• Calibrations for error analysis is performed by adjusting the error distributions and removing biases
• Using differing geolocation techniques provides the mechanism for determining algorithm performance as a function of the operational scenario This provides the RMS errors as well as the mobile unit location estimates The RMS errors statistically match the distributions of the mobile unit locations
• the error distribution can be adjusted and biases removed to adequately reflect the mobile unit RMS location error while properly modeling the individual error distributions
• the relative contribution of each error source to the actual mobile unit location error can determined as a function of the time duration of the measurement
• the method for establishing mobile unit geolocation accuracy will combine the error factors from the various geolocation techniques
• the biases are removed and the resulting RMS errors are propagated throughout the algorithm
• all RMS errors for an estimate will be converted into orthogonal RMS errors
• the associated estimated and orthogonal RMS errors will be projected onto a common orthogonal coordinate system and the resulting estimate and RMS errors computed by using sum of estimated and square root of the sum of projected RMS errors squared along each
• the RMS for the absolute mobile unit geolocation error is obtained by combining mutually independent RMS errors for the absolute geolocation error in the single satellite estimates and the relative mobile unit geolocation RMS errors
• the geolocations of the mobile unit 310 and the relative RMS errors are computed from the set of loci determined by the measured parameter, associated RMS measurement errors, and the relative RMS location errors Projecting all RMS parameter errors onto a common Euclidean coordinate system the estimate of the mobile unit location is found by minimizing its weighted (bv the product projections if RMS error) distance to each loci
• the resulting RMS parameter error of the mobile unit location estimate in each coordinate is given bv N( ⁇ , , ⁇ , ' ) ' , where N is the number of loci used and ⁇ , is the RMS parameter error along a coordinate at the estimated mobile unit location normal with its loci (I to N)
• the RMS error weights used in the estimate and resulting RMS parameter error depend on the RMS error value of the measurement at the line normal to
• Position accuracies are typically specified as circular error probable (CEP), in which position accuracy is defined as a circle centered on a position measurement
• CEP circular error probable
• the error definition such as the error ellipse is compared with the position accuracy such as the CEP
• the CEP position accuracy
• the error is less if a predetermined percentage of the area of the error ellipse fits within the CEP I urther refinement is needed unless the area of the error ellipse is sufficiently confined within the CEP
• the measurement process is instructed to perform another measurement This refinement will cause the area of the error ellipse to shrink At some point the error ellipse will shrink to a point where it is determined that the error is less than the position accuracy
• the geolocation system requires no further refinement of the location of the mobile unit 3 10, the position is declared, and the process is te ⁇
• the present invention is independent of GPS, the bulk, power consumption and cost of a GPS receiver is unnecessary Differential GPS requires that the GPS receiver have an additional reference signal that is received at each GPS receiver for that receiver to operate By computing the position of the transceiver at the central satellite ground station the transceiver of the present invention is kept simple, inexpensive and has no power consumption associated with processing an additional reference signal Consequently, its battery life is extended relative to differential GPS receivers
• GPS requires that signals be simultaneously acquired from multiple satellites to calculate a position fix
• the combined range and Doppler technique used in the present invention only requires communication with one non- geostationary orbiting satellite
• the combined range and Doppler technique produces a position estimate while GPS cannot

Landscapes

• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• Computer Networks & Wireless Communication (AREA)
• Astronomy & Astrophysics (AREA)
• Aviation & Aerospace Engineering (AREA)
• Signal Processing (AREA)
• Position Fixing By Use Of Radio Waves (AREA)
• Radio Relay Systems (AREA)

Applications Claiming Priority (5)

Publications (1)

Family

ID=26694906

Family Applications (1)

Country Status (4)

Cited By (6)

Families Citing this family (41)

Family Cites Families (1)

• 1997
  • 1997-07-03 EP EP97945181A patent/EP0908022A2/de not_active Withdrawn
  • 1997-07-03 WO PCT/US1997/011711 patent/WO1998002762A2/en not_active Application Discontinuation
  • 1997-07-03 AU AU46439/97A patent/AU4643997A/en not_active Abandoned
  • 1997-07-03 CN CN 97196336 patent/CN1238868A/zh active Pending

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events