WO2010059439A2 - Système et procédé permettant de déterminer l'emplacement géographique falsifié d'un dispositif mobile - Google Patents

Système et procédé permettant de déterminer l'emplacement géographique falsifié d'un dispositif mobile Download PDF

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Publication number
WO2010059439A2
WO2010059439A2 PCT/US2009/063628 US2009063628W WO2010059439A2 WO 2010059439 A2 WO2010059439 A2 WO 2010059439A2 US 2009063628 W US2009063628 W US 2009063628W WO 2010059439 A2 WO2010059439 A2 WO 2010059439A2
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Prior art keywords
estimated location
satellites
residuals
satellite
wireless device
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PCT/US2009/063628
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English (en)
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WO2010059439A3 (fr
Inventor
Neil Harper
Martin Thomson
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Andrew Llc
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Publication of WO2010059439A2 publication Critical patent/WO2010059439A2/fr
Publication of WO2010059439A3 publication Critical patent/WO2010059439A3/fr

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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
    • G01S19/13—Receivers
    • G01S19/21—Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
    • G01S19/215—Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service issues related to spoofing

Definitions

  • Radio communication systems generally provide two-way voice and data communication between remote locations. Examples of such systems are cellular and personal communication system (“PCS”) radio systems, trunked radio systems, dispatch radio networks, and global mobile personal communication systems (“GMPCS”) such as satellite-based systems. Communication in these systems is conducted according to a pre-defined standard. Mobile devices or stations, also known as handsets, portables or radiotelephones, conform to the system standard to communicate with one or more fixed base stations. It is important to determine the location of such a device capable of radio communication especially in an emergency situation. In addition, in 2001 the United States Federal Communications Commission (“FCC”) required that cellular handsets must be geographically locatable. This capability is desirable for emergency systems such as Enhanced 911 (“E-911").
  • FCC Federal Communications Commission
  • the FCC requires stringent accuracy and availability performance objectives and demands that cellular handsets be locatable within 100 meters 67% of the time for network based solutions and within 50 meters 67% of the time for handset based solutions.
  • Current generations of radio communication generally possess limited mobile device location determination capability.
  • the position of the mobile device is determined by monitoring mobile device transmissions at several base stations. From time of arrival or comparable measurements, the mobile device's position may be calculated. However, the precision of this technique may be limited and, at times, may be insufficient to meet FCC requirements.
  • a mobile device may be equipped with a receiver suitable for use with a Global Navigation Satellite System (“GNSS”) such as the Global Positioning System (“GPS").
  • GPS is a radio positioning system providing subscribers with highly accurate position, velocity, and time (“PVT”) information.
  • FIG 1 is a schematic representation of a constellation 100 of GPS satellites 101.
  • GPS may include a constellation of GPS satellites 101 in non-geosynchronous orbits around the earth.
  • the GPS satellites 101 travel in six orbital planes 102 with four of the GPS satellites 101 in each plane.
  • Each orbital plane has an inclination of 55 degrees relative to the equator.
  • each orbital plane has an altitude of approximately 20,200 km (10,900 miles).
  • the time required to travel the entire orbit is just under 12 hours. Thus, at any given location on the surface of the earth with clear view of the sky, at least five GPS satellites are generally visible at any given time.
  • GPS position determination is made based on the time of arrival ("TOA") of various satellite signals.
  • TOA time of arrival
  • Each of the orbiting GPS satellites 101 broadcasts spread spectrum microwave signals encoded with satellite ephemeris information and other information that allows a position to be calculated by the receiver.
  • GPS measurements corresponding to each correlator channel with a locked GPS satellite signal are available for GPS receivers.
  • the two carrier signals, Ll and L2 possess frequencies of 1.5754 GHz and 1.2276 GHz, or wavelengths of 0.1903 m and 0.2442 m, respectively.
  • the Ll frequency carries the navigation data as well as the standard positioning code, while the L2 frequency carries the P code and is used for precision positioning code for military applications.
  • the signals are modulated using bi-phase shift keying techniques.
  • the signals are broadcast at precisely known times and at precisely known intervals and each signal is encoded with its precise transmission time.
  • the LC2C signal is a second civilian frequency transmitted by GPS satellites.
  • Ll transmits the Coarse Acquisition ("C/A") code.
  • L2C transmits L2CM (civil-moderate) and L2CL (civil long) codes. These codes allow a device to differentiate between satellites that are all transmitting on the same frequency.
  • the C/A code is 1 milliseconds long, the L2CM is 20 milliseconds long and the L2CL is 1.5 seconds long.
  • the L2C codes provide a more robust cross-correlation performance so that reception of weak GPS signals is less affected by simultaneously received strong GPS signals.
  • the civil navigation message (“CNAV”) is the broadcast model that can be transmitted on the L2C and provides a more accurate and frequent message than the legacy navigation message.
  • GPS receivers measure and analyze signals from the satellites, and estimate the corresponding coordinates of the receiver position, as well as the instantaneous receiver clock bias. GPS receivers may also measure the velocity of the receiver. The quality of these estimates depends upon the number and the geometry of satellites in view, measurement error and residual biases. Residual biases generally include satellite ephemeris bias, satellite and receiver clock errors, and ionospheric and tropospheric delays. If receiver clocks were perfectly synchronized with the satellite clocks, only three range measurements would be needed to allow a user to compute a three- dimensional position. This process is known as multilateration.
  • This clock bias is determined by computing a measurement from a fourth satellite using a processor in the receiver that correlates the ranges measured from each satellite. This process requires four or more satellites from which four or more measurements can be obtained to estimate four unknowns x, y, z, b.
  • the unknowns are latitude, longitude, altitude and receiver clock offset.
  • the amount b, by which the processor has added or subtracted time, is the instantaneous bias between the receiver clock and the satellite clock. It is possible to calculate a location with only three satellites when additional information is available.
  • an arbitrary satellite measurement may be included that is centered at the- center of the earth and possesses a range defined as the distance from the center of the earth to the known altitude of the handset or mobile device.
  • the altitude of the handset may be known from another sensor or from information from the cell location in the case where the handset is in a cellular network.
  • A-GPS Assisted-GPS
  • TTFF time to first fix
  • a communications network and associated infrastructure may be utilized to assist the mobile GPS receiver, either as a standalone device or integrated with a mobile station or device.
  • the general concept of A-GPS is to establish, a GPS reference network (and/or a wide-area D-GPS network or a wide area reference network (“WARN”)) including receivers with clear views of the sky that may operate continuously.
  • This reference network may also be connected with the cellular infrastructure, may continuously monitor the real-time constellation status, and may provide data for each satellite at a particular epoch time.
  • the reference network may provide ephemeris information, UTC model information, ionosphere model information, and other broadcast information to the cellular infrastructure.
  • the GPS reference receiver and its server may be located at any surveyed location with an open view of the sky.
  • Typical A-GPS information may include data for determining a GPS receiver's approximate position, time synchronization mark, satellite ephemerides, various model information and satellite dopplers.
  • Different A-GPS services may omit some of these parameters; however, another component of the supplied information is the identification of the satellites for which a device or GPS receiver should search.
  • a mobile device From such assistance data, a mobile device will attempt to search for and acquire satellite signals for the satellites included in the assistance data. If, however, satellites are included in the assistance data that are not measurable by the mobile device (e.g., the satellite is no longer visible, etc.), then the mobile device will waste time and considerable power attempting to acquire measurements for the satellite.
  • GPS signals are widely used by government and private industries for important applications, including, but not limited to, public safety services, navigation, geolocation, hiking, surveying, robotics, tracking, etc.
  • civilian GPS signals are not secure. Since GPS signal strength, measured at the Earth's surface at about -16OdBw (1 x 10 "16 watts), is roughly equivalent to viewing a 25 watt light bulb from a distance of 10,000 miles, GPS signals may be blocked by destroying or shielding a receiver's antenna and may be jammed by a signal of a similar frequency but greater strength. As stated above, however, blocking and jamming are not the greatest security risk.
  • a more pernicious attack involves feeding the receiver fake or forged satellite signals so that the receiver believes it is located somewhere in space and time that it is not.
  • Spoofing may be accomplished by utilizing a GPS satellite simulator. Such simulators are uncontrolled and widely available.
  • an adversary may broadcast a forged satellite signal with a higher signal strength than the true signal, and the GPS receiver believes that the forged signal is actually a true GPS signal. The receiver may then proceed to calculate erroneous position or time information based on this forged signal.
  • embodiments of the present subj ect matter may not prevent spoofing attacks, these embodiments may alert a wireless device user and/or an operator of a location determining system to such suspicious activity thereby decreasing the probability that a spoofing attack succeeds. Further embodiments of the present subject matter may be implemented easily and inexpensively by retrofitting existing GPS receivers and exemplary location determining systems.
  • an embodiment of the present subject matter provides a method for determining whether a wireless device has transmitted one or more forged satellite measurements.
  • the method may comprise determining an estimated location of the wireless device from signals received from a cellular network. For each one of the first set of satellites from which the wireless device receives a signal, expected frequency information may be determined as a function of the estimated location, actual frequency information may be measured, and the expected and measured frequency information compared. The wireless device may then be identified as having transmitted a forged satellite measurement if a difference between the expected and measured frequency information is greater than a predetermined threshold.
  • Another embodiment of the present subject matter provides a method for determining whether a wireless device has transmitted a forged satellite measurement.
  • the method comprises receiving at the wireless device signals from a plurality of satellites and determining an estimated location of the wireless device as a function of signals provided by a cellular network. Expected Doppler shift of ones of the received signals may be compared with the actual Doppler shift of the ones of received signals, and the wireless device identified as having transmitted a forged measurement if the expected and actual Doppler shifts do not substantially correspond within a predetermined threshold.
  • a further embodiment of the present subject matter may provide a method for determining whether an estimated location of a wireless device includes one or more forged satellite measurements.
  • the method may comprise receiving at the wireless device signals from a first set of satellites for a region in which the wireless device is located and determining an estimated location of the wireless device from the signals received from the first set of satellites. The estimated location may then be identified as having a forged satellite measurement if the estimated location is not within the region.
  • One embodiment of the present subject matter provides a system for determining whether a wireless device has transmitted one or more forged satellite measurements.
  • the system may comprise circuitry for determining an estimated location of the wireless device and circuitry for determining expected frequency information as a function of the estimated location.
  • the system may also comprise circuitry for measuring actual frequency information and circuitry for comparing the expected frequency information with the measured frequency information.
  • the system may then include circuitry for identifying the wireless device as having transmitted a forged satellite measurement if the difference between the expected and measured frequency information is greater than a predetermined threshold.
  • a method for determining whether an estimated location of a wireless device includes one or more forged satellite measurements may comprise determining an estimated location of the wireless device from signals received from a first set of satellites and obtaining a set of residuals as a function of the estimated location.
  • the obtained set of residuals may be compared to a reference set of residuals, and the estimated location identified as having one or more forged satellite measurements if the comparison between the obtained set and reference set of residuals is less than a predetermined threshold.
  • An additional embodiment of the present subject matter provides a method for determining whether an estimated location of a wireless device includes a forged satellite measurement.
  • the method may comprise receiving at the wireless device signals from a plurality of satellites and determining an estimated location of the wireless device from the received signals.
  • a set of residuals obtained from the estimated location may be compared with a reference set of residuals, and the estimated location then identified as having a forged satellite measurement if the comparison is less than a predetermined threshold.
  • One further embodiment may also provide a system for determining whether an estimated location of a wireless device includes one or more forged satellite measurements.
  • the system may include circuitry for determining an estimated location of the wireless device from signals received from a set of satellites and circuitry for calculating a set of residuals as a function of the estimated location.
  • the system may also include a database having information from a reference station network, circuitry for comparing the obtained set of residuals to a reference set of residuals provided by the reference network, and circuitry for identifying the estimated location as having one or more forged satellite measurements if the comparison between the obtained set and reference set of residuals is less than a predetermined threshold.
  • An embodiment of the present subject matter may also provide a method for determining whether a wireless device has transmitted one or more forged satellite measurements.
  • the method may include the steps of determining an estimated location of the wireless device and determining acquisition assistance data for a first set of satellites as a function of the estimated location, the assistance data including an uncertainty window.
  • the wireless device may then be identified as having transmitted one or more forged satellite measurements if the measured code phase information substantially correlates to the uncertainty window.
  • An additional embodiment of the present subject matter may provide a method for determining whether a wireless device has transmitted one or more forged satellite measurements.
  • the method may include the steps of determining an estimated location of the wireless device and determining acquisition assistance data for a first set of satellites as a function of the estimated location. For ones of the first set of satellites from which the wireless device receives a signal, measured code phase information may be compared to code phase information in the determined acquisition assistance data. The wireless device may then be identified as having transmitted one or more forged satellite measurements if a difference between measured code phase information for ones of the first set of satellites and code phase information in the determined acquisition assistance data for the same ones of satellites is greater than a predetermined threshold.
  • One further embodiment may provide a system for determining whether a wireless device has transmitted one or more forged satellite measurements.
  • the system may include circuitry for determining an estimated location of the wireless device and circuitry for determining acquisition assistance data for a first set of satellites as a function of the estimated location, the assistance data including an uncertainty window.
  • the system may also include circuitry for identifying the wireless device as having transmitted one or more forged satellite measurements if received code phase information from the wireless device substantially correlates to the uncertainty window.
  • Figure 1 is a schematic representation of a constellation of GPS satellites.
  • Figure 2 is an algorithm according to one embodiment of the present subject matter.
  • Figure 3 is another algorithm according to an embodiment of the present subject matter.
  • Figure 4 is an algorithm according to another embodiment of the present subject matter.
  • Figure 5 is a graphical illustration of the SSR statistics from a NovAtel
  • Figure 6 is an algorithm according to one embodiment of the present subject matter.
  • Figure 7 is an algorithm according to another embodiment of the present subject matter.
  • Figure 8 is an algorithm according to an embodiment of the present subject matter.
  • Figure 9 is another algorithm according to an embodiment of the present subject matter.
  • Figure 10 is a schematic representation for implementing one embodiment of the present subject matter.
  • the disclosure relates to a mobile appliance or device and a location determining system using satellite signals and/or measurements of these satellite signals.
  • Exemplary devices may include, but are not limited to, a cellular device, text messaging device, computer, portable computer, vehicle locating device, vehicle security device, communication device, and wireless transceiver.
  • the satellites may be considered as part of a Global Navigation Satellite System ("GNSS”), such as, but not limited to, the U.S. Global Positioning System (“GPS"). While the following description references the GPS system, this in no way should be interpreted as limiting the scope of the claims appended herewith.
  • GNSS Global Navigation Satellite System
  • GPS Global Positioning System
  • GNSS systems operate, for the purposes of this disclosure, similarly to GPS, such as, but not limited to, the European Satellite project, Galileo; the Russian satellite navigation system, GLONASS; the Japanese Quasi-Zenith Satellite System (“QZSS”), and the Chinese satellite navigation and positioning system called Beidou (or Compass). Therefore, references in the disclosure to GPS and/or GNSS, where applicable, as known to those of skill in the art, apply to the above-listed GNSS systems as well as other GNSS systems not listed above. Further, the terms spoofed, falsified, forged, and various tenses and forms thereof are utilized interchangeably throughout this disclosure and such use should in no way should be interpreted as limiting the scope of the claims appended herewith.
  • TTFF time to forwarding assistance data from an exemplary communications network to assist in locking onto or acquiring satellites quickly.
  • A-GPS devices may include, but are not limited to, a cellular device, text messaging device, computer, portable computer, vehicle locating device, vehicle security device, communication device, and wireless transceiver. These devices may provide satellite measurements back to a location determining system to perform a position calculation.
  • Exemplary network elements that supply the assistance data and/or perform the position calculation may be a location determining system such as a Mobile Location Center (“MLC”), location information server or system (“LIS”), or other comparable network element.
  • MLC Mobile Location Center
  • LIS location information server or system
  • the location determining system may generally be a node in a wireless network that performs the location of a mobile device.
  • the location determining system generally requires a wireless device to provide true and accurate measurements (rather than forged measurements) to determine an accurate location or provide accurate assistance data.
  • true and accurate measurements rather than forged measurements
  • the integrity of the resulting location is important because the location may be used by emergency services operators to find an injured person, for location- based services, etc.
  • an exemplary method may be utilized to determine whether a geographic location of a mobile or wireless device has been spoofed or forged. For example, a determination may be made whether a calculated location of the device is within the boundary of a region, such as, but not limited to, a serving cell. If the geographic location falls outside of this region, then the possibility exists that the calculated location may contain spoofed or forged satellite measurements. If the, geographic location of the device falls within the region, then the location may still be spoofed because the wireless device is geographically located at one place within the region and the measurements result in a calculated location at another place within the same region.
  • Figure 2 is an algorithm according to another embodiment of the present subject matter.
  • a method 200 is provided for determining whether an estimated location of a wireless device includes one or more forged satellite measurements.
  • the wireless device signals may receive signals from a first set of satellites for a region in which the wireless device is located.
  • An exemplary region may be, but is not limited to, a serving area of a base station serving the wireless device, an approximate area of a communications network, a city, a municipality, a county, a state, a country, a continent, and the Earth.
  • an estimated location of the wireless device may then be determined from the signals received from the first set of satellites. The estimated location may then be identified as having a forged satellite measurement if the estimated location is not within the region at step 230.
  • the method may include determining another estimated location of the mobile device from signals received from a second set of satellites. This exemplary method may be further refined by embodiments discussed below.
  • Several* attributes in satellite measurements may be utilized as a source for detecting location spoofing, such as, but not limited to, GNSS signal strength, satellite identification codes, number of satellite signals received, time intervals, clock bias, code phases, Doppler shift, and combinations thereof.
  • code phase measurements may allow a wireless device to derive a range to a satellite relative to the ranges to other satellites and may provide an important input to determining the respective pseudorange measurements.
  • Doppler shift is generally a measured frequency shift between the wireless device and a satellite and is a measure of the relative velocity between the transmitter ⁇ e.g., the satellite) and the device ⁇ e.g., GNSS receiver) along a line of sight vector.
  • Doppler shift occurs because GNSS signals travel at the speed of light and the rate of change of the range between the respective satellite and receiver stretches or compresses the wavelength that is effectively measured at the receiver. For example, when a satellite approaches the receiver, the frequency will increase and when the satellite withdraws from the receiver, the frequency is reduced.
  • An expected Doppler shift may be determined as a function of a calculated geographic location of a wireless device. The measured Doppler shift may then be compared against the expected Doppler shift and if the difference between the shifts is outside a predetermined threshold, then the geographic location of the device and any one, several or all satellite measurements may be identified as being forged or spoofed.
  • the Doppler in hertz (D) may be determined as the dot product of the difference in velocities between a satellite and receiver and an estimated line of sight vector by the following relationship:
  • v s represents the velocity of the satellite
  • v r represents the velocity of the receiver
  • c represents the speed of light
  • / s represents the estimated line of sight unit vector
  • / represents the transmitted frequency of Ll (i.e., 1.5754 GHz).
  • the c and/scalars may convert the result from ms " to Hz.
  • the line of sight vector may be determined as the difference between the satellite and receiver location divided by the norm of the difference as a function of the following relationship:
  • FIG. 3 is another algorithm according to an embodiment of the present subject matter.
  • a method 300 is provided for determining whether a wireless device has transmitted one or more forged satellite measurements.
  • an estimated location of the wireless device may be determined.
  • the estimated location may be determined as a function of coarse acquisition ("C/ A") code phase information and/or signals provided by a cellular network.
  • C/ A coarse acquisition
  • a wireless device may provide a cell identification value in its initial location request, and from a cell table, the latitude, longitude, altitude and range for the cell may be determined to provide the estimated location.
  • expected frequency information may be determined as a function of the estimated location, actual frequency information may be measured, and the expected frequency information compared with the measured frequency information.
  • Exemplary frequency information may include Doppler shift information.
  • the wireless device may then be identified at step 330 as having transmitted a forged satellite measurement if a difference between the expected and measured frequency information is greater than a predetermined threshold. In another embodiment, step 330 may include identifying all forged satellite measurements transmitted by the wireless device.
  • the method 300 may also include the step of determining another estimated location of the wireless device from signals received from a second set of satellites, the second set excluding the satellite having the forged measurement. Any of steps 310 through 330 may be iteratively repeated utilizing signals received from a second set of satellites. This second set of satellites may be a subset of the first set of satellites or may also be mutually exclusive of the first set of satellites.
  • FIG. 4 is an algorithm according to another embodiment of the present subject matter.
  • a method 400 for determining whether a wireless device has transmitted a forged satellite measurement may include receiving at the wireless device signals from a plurality of satellites and determining an estimated location of the wireless device from the signals provided by a cellular network, at step 410.
  • the method may also comprise comparing expected Doppler shift determined as a function of the estimated location with the measured Doppler shift of the ones of received signals at step 420.
  • the wireless device may then be identified as having transmitted a forged measurement if the expected and measured Doppler shifts do not substantially correspond within a predetermined threshold at step 430.
  • the GPS position calculation function is a parametric least squares implementation. Inputs to the PCF is generally four or more satellite measurements with outputs being the location of the receiver and its respective clock bias. Another output of the least squares process is the residuals when there is an over- determined solution (e.g., five or more satellites in view). A simplified and non-limiting description of a residual is the difference between the actual observation and the computed distance between a satellite and the derived satellite position.
  • Residuals generally provide an indication of how much satellite measurements have changed to fit a position solution and thus reflect errors present in each measurement.
  • One aspect of determining whether code phase information has been spoofed is whether the residuals reflect the errors that are normally measured. For example, when the residuals are below a normal or predetermined range, this is an acceptable indicator that certain satellite measurements have been spoofed. Residuals may be determined as a function of the following relationship:
  • A represents partial derivatives of the functional model
  • x represents an estimate of a device's location
  • b represents the observational model.
  • Residuals may also be inputted into an exemplary method or algorithm that determines an uncertainty ellipse at a given confidence, ⁇ n such an embodiment, a spoofed location may be indicative of a small uncertainty ellipse.
  • SSR squared residuals
  • the SSR of a typical receiver in a mobile device calculating a location thereof within ten meters is generally in the range of 200 to 8000 when there are eight satellites in view.
  • Table 1 below is from an independent operational test utilizing Motorola SiRF chipsets.
  • SSRs of a receiver in open-sky conditions may produce statistics as shown in Table 2 below.
  • Table 2 SSR statistics from a NovAtel GPS reference receiver
  • FIG. 5 is a graphical illustration of the SSR statistics from a NovAtel GPS reference receiver.
  • the upward trend in SSR is as expected, e.g., more satellites result in more total error in the measurements.
  • Figure 5 also illustrates a substantially linear relationship between the number of satellites and SSR, i.e., as an extra satellite is considered, the SSR increases by a substantially constant amount.
  • a quality receiver operating in open sky conditions may be considered as a baseline for detection of a spoofing attack. For example, if a mobile device reports eight satellites that results in an SSR of less than 52.46, then the location may be considered as having spoofed or forged satellite measurements.
  • the baseline statistics provided in Table 2 may be compared to the results shown below in Table 3 from an independent operational test utilizing a Sony- Ericsson device running a Broadcomm A-GPS chipset and later discovered as spoofing device. Table 3 - SSR for a Sony-Ericsson (Broadcomm) implementation
  • the mobile device providing the SSR in Table 3 was considered to be a spoofer because the SSR was very low.
  • the chipset supplier confirmed the results that the device was spoofing the code-phases provided to the MLC. Therefore, embodiments of the present subject matter may provide a baseline SSR threshold similar to that shown in Table 2; however, such a disclosure and the respective statistics should not limit the scope of the claims appended herewith as acceptable baselines and/or thresholds may be provided by any number of means, such as, but not limited to, mobile reference receivers, fixed reference receivers, a reference network having both mobile and fixed reference receivers, a wide area reference network, etc.
  • the respective thresholds may also be tuned as a function of the behavior of mobile devices in a communications network.
  • the measured SSR is less than the average provided by a reference network then the respective mobile device may be considered to be a spoofer.
  • Figure 6 is an algorithm according to one embodiment of the present subject matter.
  • a method 600 is provided for determining whether an estimated location of a wireless device includes one or more forged satellite measurements.
  • an estimated location of the wireless device may be determined from signals received from a first set of satellites, and at step 620 a set of residuals obtained as a function of the estimated location.
  • the estimated location may be determined as a function of C/A code phase shift information, Doppler information, and/or signals provided by a cellular network.
  • the obtained set of residuals may then be compared to a reference set of residuals at step 630.
  • the reference set of residuals may be provided by a database having information from an exemplary reference station network including a plurality of geographically dispersed reference stations. These reference stations may be fixed reference stations, mobile reference stations, or combinations thereof. As discussed above, if the comparison between the obtained set and reference set of residuals is less than a predetermined threshold, then at step 640 the estimated location may be identified as having one or more forged satellite measurements. In another embodiment, step 630 may include comparing the SSR for the obtained set to the SSR for the reference set or may include comparing the SSR for the obtained set to an average SSR for a plurality of reference sets.
  • the method 600 may further include determining another estimated location of the wireless device from signals received from a second set of satellites, the second set excluding a satellite having a forged measurement. Any of steps 610 through 640 may be iteratively repeated utilizing signals received from a second set of satellites.
  • This second set of satellites may be a subset of the first set of satellites or may also be mutually exclusive of the first set of satellites.
  • Figure 7 is an algorithm according to another embodiment of the present subject matter.
  • a method 700 is provided for determining whether an estimated location of a wireless device includes a forged satellite measurement.
  • signals may be received at the wireless device from a plurality of satellites and an estimated location thereof determined.
  • a set of residuals obtained from the estimated location may be compared with a reference set of residuals.
  • the estimated location may be identified as having a forged satellite measurement if the comparison is less than a predetermined threshold.
  • acquisition assistance data type is generally an assistance data type where code phases and Doppler shifts are calculated as a function of a given location. The calculation may be provided with an uncertainty area or ellipse utilized to determine the uncertainty in chips (and Doppler) for a mobile device to search.
  • acquisition assistance data may be provided to a mobile device by handset-assisted A-GPS to ensure the device locks onto and acquires signals from appropriate satellites. The assistance data may then be determined as a function of an approximate location of the device and an uncertainty of the approximate location of the device.
  • a spoofer attempting to emulate a specific location is likely to calculate expected code phases (from that location) and provide the expected code phases to the location determining system (e.g., MLC).
  • the location determining system may then compare the reported code phases to its respective acquisition assistance data calculations and if the comparison indicates the code phases are within or outside a predetermined threshold or uncertainty window, then the measurements may be identified as being spoofed.
  • the MLC may compare relative code phases (or the difference between code phases) because, the clock in the respective mobile device may not be properly synchronized to GPS timing.
  • One aspect to note during such a comparison of measured values against server calculated values is whether the differences between the measurements match. For example, if a mobile device reports satellite PRN 5 as 100 chips and PRN 6 as 200 chips, and the location determining system calculates PRN 5 as 400 chips and PRN 6 as 500 chips with a search window of 1 chip, then this may be considered to be a match, as the difference is within the search window, and the mobile device classified as a spoofer.
  • Figure 8 is an algorithm according to an embodiment of the present subject matter.
  • a method 800 is provided for determining whether a wireless device has transmitted one or more forged satellite measurements.
  • an estimated location of the wireless device may be determined.
  • the estimated location may be determined as a function of coarse acquisition ("C/A") code phase information and/or signals provided by a cellular network.
  • C/A coarse acquisition
  • a wireless device may provide a cell identification value in its initial location request, and from a cell table, the latitude, longitude, altitude and range for the cell may be determined to provide the estimated location.
  • acquisition assistance data for a first set of satellites may be determined as a function of the estimated location, the assistance data including an uncertainty window.
  • step 830 if measured code phase information from the wireless device substantially correlates to the uncertainty window, then the wireless device may be identified as havirig transmitted one or more forged satellite measurements.
  • An exemplary uncertainty window may be, but is not limited to, a code phase uncertainty window.
  • step 830 may further include comparing relative code phase information for ones of the first set of satellites from which the wireless device receives a signal, and identifying the wireless device as having transmitted a forged satellite measurement if a difference between the relative code phase information is substantially outside the uncertainty window.
  • the relative code phase information may represent a difference between code phase information reported by the wireless device and code phase information determined by a location information server.
  • the method 800 may further include determining another estimated location of the wireless device from signals received from a second set of satellites, the second set excluding a satellite having a forged measurement. Any of steps 810 through 830 may be iteratively repeated utilizing signals received from a second set of satellites. This second set of satellites may be a subset of the first set of satellites or may also be mutually exclusive of the first set of satellites.
  • Figure 9 is another algorithm according to an embodiment of the present subject matter. With reference to Figure 9, a method 900 is provided for determining whether a wireless device has transmitted one or more forged satellite measurements. At step 910, an estimated location of the wireless device may be determined.
  • the estimated location may be determined as a function of coarse acquisition ("C/A") code phase information and/or signals provided by a cellular network.
  • C/A coarse acquisition
  • a wireless device may provide a cell identification value in its initial location request, and from a cell table, the latitude, longitude, altitude and range for the cell may be determined to provide the estimated location.
  • acquisition assistance data for a first set of satellites may be determined as a function of the estimated location. For ones of the first set of satellites from which the wireless device receives a signal, the measured code phase information may be compared to code phase information in the determined acquisition assistance data at step 930.
  • the wireless device may be identified as having transmitted one or more forged satellite measurements.
  • the method 900 may further include determining another estimated location of the wireless device from signals received from a second set of satellites, the second set excluding a satellite having a forged measurement. Any of steps 910 through 940 may be iteratively repeated utilizing signals received from a second set of satellites. This second set of satellites may be a subset of the first set of satellites or may also be mutually exclusive of the first set of satellites.
  • FIG. 10 is a schematic representation for implementing embodiments of the present subject matter.
  • a satellite system 1010 may communicate with a terrestrial system 1020.
  • An exemplary satellite system 1010 may be a GNSS such as, but not limited to, a GPS, Galileo system, GLONASS system, QZSS, Compass system, Bediou system, etc.
  • the ground system 1020 may include a cellular network having a location center 1021 and may receive information from or include a SBAS, WAAS, EGNOS, digital television network, and combinations thereof.
  • the location center 1021 may be an MLC, LIS or other network component such as a central office configured to communicate with a telecommunications network 1022 and/or at least one base station' 1023.
  • the location center 1021 may include a receiver for receiving signals transmitted from a mobile device 1024, and circuitry for determining the location of the mobile device 1024 as a function of received signals from the device 1024.
  • the location center 1021 may also include a database having information from a reference network such as a WARN.
  • Exemplary reference networks may include a plurality of geographically dispersed reference stations and may include fixed reference stations, mobile reference stations, or combinations thereof.
  • the location center 1021 may include a transmitter for transmitting to the mobile device 1024 acquisition assistance data, a location request, and other information and data.
  • Exemplary devices 1024 may be, but are not limited to, a cellular device, text messaging device, computer, portable computer, vehicle locating device, vehicle security device, communication device, or wireless transceiver.
  • the location center 1021 may also include circuitry for determining expected frequency information as a function of an estimated location, circuitry for measuring actual frequency information, circuitry for comparing the expected frequency information with the measured frequency information, and circuitry for identifying the device 1024 as having transmitted a forged satellite measurement if the difference between the expected and measured frequency information is greater than a predetermined threshold.
  • the location center 1021 may also include circuitry for calculating a set of residuals as a function of an estimated location, circuitry for comparing the obtained set of residuals to a reference set of residuals provided by a reference network, and circuitry for identifying the estimated location as having one or more forged satellite measurements if the comparison between the obtained set and reference set of residuals is less than a predetermined threshold.
  • the location center 1021 may include circuitry for determining an estimated location of the wireless device, circuitry for determining acquisition assistance data as a function of the estimated location, the assistance data including an uncertainty window, circuitry for identifying the wireless device as having transmitted one or more forged satellite measurements if received code phase information from the device 1024 substantially correlates to the uncertainty window, and/or circuitry for comparing received code phase information from the device 1024 to code phase information in the determined acquisition assistance data.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)

Abstract

L’invention concerne un système et procédé permettant de déterminer si l’emplacement supposé d’un dispositif sans fil comporte une ou plusieurs mesures satellites falsifiées. On peut déterminer l’emplacement supposé du dispositif sans fil à partir de signaux reçus d’un premier ensemble de satellites et un ensemble de signaux résiduels obtenus en fonction de l’emplacement supposé. L’ensemble de signaux résiduels obtenu peut alors être comparé à un ensemble de référence de signaux résiduels. Si la comparaison entre l’ensemble obtenu et l’ensemble de référence de signaux résiduels est inférieure à un seuil prédéterminé, alors l’emplacement supposé peut être identifié comme présentant une ou plusieurs mesures satellites falsifiées.
PCT/US2009/063628 2008-11-24 2009-11-06 Système et procédé permettant de déterminer l'emplacement géographique falsifié d'un dispositif mobile WO2010059439A2 (fr)

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US12/276,852 2008-11-24
US12/276,852 US7800533B2 (en) 2008-11-24 2008-11-24 System and method for determining falsified geographic location of a mobile device

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