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WO2023044314A1 - Détermination de position de source éloignée - Google Patents

Détermination de position de source éloignée Download PDF

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Publication number
WO2023044314A1
WO2023044314A1 PCT/US2022/076388 US2022076388W WO2023044314A1 WO 2023044314 A1 WO2023044314 A1 WO 2023044314A1 US 2022076388 W US2022076388 W US 2022076388W WO 2023044314 A1 WO2023044314 A1 WO 2023044314A1
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WIPO (PCT)
Prior art keywords
receiver
far
sources
location
signals
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Ceased
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PCT/US2022/076388
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English (en)
Inventor
Martin C. Alles
John P. Carlson
Abdulwahaab Arif
Sharif Shaher
Zachary Hester
Ryan Riveland
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Parsons Corp
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Parsons Corp
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Priority claimed from US17/931,619 external-priority patent/US12449503B2/en
Application filed by Parsons Corp filed Critical Parsons Corp
Publication of WO2023044314A1 publication Critical patent/WO2023044314A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
    • G01S5/06—Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • 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

Definitions

  • Embodiments of the present invention relate, in general to position determination and more particularly to using imprecisely characterized distant signal sources to determine a position of a receiver.
  • the user of the system determines the location of the source (in this case a GPS satellite) by reading the navigation data embedded in the signal.
  • a read of the same data specifies the timing relationship on the GPS gold codes needed by the user to correlate and make a timing determination.
  • Data in the navigation message is used to correct for deformities (delays due to channel imperfections, as for example, due to the ionosphere). It is at the end of this process that the user can then combine many such carefully made and corrected measurements from multiple satellites in an algorithm to determine user location.
  • the deformities on the signal can be minimized: the MS if in proximity to the Rx can determine these deformities and provide that information to the Rx.
  • Such methods are difficult to implement, and often are impossible to architect without multiple high fidelity MS units observing the signal source from geographically dispersed locations. For example, one can consider the GPS monitor stations placed worldwide which monitor the signals transmitted by GPS satellites, derive the needed information, pass the information to a control station, which then populates the information in the GPS navigation data which the GPS user is then able to read. Effectively, one can consider the GPS monitor stations as providing the same function a local MS attempts to provide in a more limited and localized context for some different signal usable for navigation.
  • a system and method are presented for navigation using a Monitor Station (MS) having a known location and signals impinging on both the MS and User Equipment (UE or Rx) where both entities can make measurements on common signals.
  • MS Monitor Station
  • UE User Equipment
  • a positional determination is achieved by an interpretation of measurements made on such distant sources even when lacking precise information as to the location of the sources or the exact transmission timing of the signals received.
  • the present invention uses signals from far sources without requiring precise ephemeris or signal timing information.
  • These far sources can, for example, be any satellite, whether Highly Elliptical Orbit (HEO), Geosynchronous Orbit (GSO), Geostationary Orbit (GEO), Middle Earth Orbit (MEO) or Low Earth Orbit (LEO).
  • HEO Highly Elliptical Orbit
  • GSO Geosynchronous Orbit
  • GEO Geostationary Orbit
  • MEO Middle Earth Orbit
  • LEO Low Earth Orbit
  • LEO Apogee altitude h A ⁇ 2000 km
  • GEO Perigee altitude h P > 40164 km and apogee altitude h A ⁇ 44164 km
  • MEO Perigee altitude h P > 2000 km and apogee altitude h A ⁇ 40164 km
  • GTO Geographical' Transfer orbit
  • HEO all other objects.
  • the MS and Rx communicate, in one embodiment, on a low bandwidth data channel, exchanging measurement information with respect to common signals.
  • the method described herein can be applied to establish the integrity of any other navigation, positioning, or timing application, such as for example GPS.
  • the inventive technique detailed herein is hereafter referred to as Far Source Navigation (FSN).
  • FSN Far Source Navigation
  • a method for far source positional determination includes measuring one or more time-difference of arrivals of one or more signals from one or more, respective, far sources. Each time-difference of arrival being between difference of arrival of each of the one or more signals at a first receiver and arrival of each of the one or more signals at a second receiver.
  • the process includes, determining for each signal, a loci of points, forming one or more loci of points wherein each loci of points is at a distance from the second receiver (MS) on which the first receiver (Rx) resides based on the respective one or more timedifference of arrivals.
  • the process ends by identifying a relative position of the first receiver from the second receiver based on an intersection of the one or more loci of points. As the location of the second is known, the position of the first receiver can be determined.
  • a wavefront of each of the one or more signals are a planar wavefront.
  • the location of the one or more far sources can be unknown as the location of one or more far sources is substantially irrelevant to identifying the relative position (via the unit vector) of the first receiver.
  • a first clock associated with the first receiver and a second clock associated with the second receiver are synchronized. And responsive to the first clock and the second clock having a relative bias, the process continues by identifying the relative position of the first receiver by examining a plurality of relative positions of the first receiver using a corresponding plurality of clock biases. Moreover, each of the corresponding plurality of clock biases can be applied to each measurement, thereby forming a convergence of solutions at the relative position of the first receiver.
  • Another feature of the invention is that a distance between the first receiver and the second receiver is viewed as a point with respect to the one or more far sources. Also, the content of the one or more signals is irrelevant apart from its structure to identifying the relative position of the first receiver.
  • a system for far source positional determination includes a first and second receiver each configured to receive one or more signals from one or more far sources, respectively.
  • the system also includes a timedifference module configured to measure one or more time-difference of arrivals, each time-difference of arrival being difference between arrival of one of the one or more signals at the first receiver and arrival of the one of the one or more signals at the second receiver.
  • a loci of points module configured to communicate with the -time-difference module and to determine, for each signal, a loci of points is another feature of the present invention.
  • Each formed loci of points is at a distance from the second receiver on which the first receiver resides based on the respective one or more time-difference of arrivals.
  • the system includes a position module, using information gained from the loci of points module, configured to identify a relative position of the first receiver based on an intersection of the one or more loci of points.
  • the system of the present invention assumes that a wavefront of each of the one or more signals is a planar wavefront and is operable even though a precise location of the one or more far sources is unknown. Indeed, the exact location of one or more far sources is irrelevant to identifying the relative position of the first receiver.
  • the system also includes a first clock associated with the first receiver and a second clock associated with the second receiver, wherein the first clock and the second clock are synchronized. Responsive to the first clock and the second clock having a relative bias, the position module is configured to identify the relative position of the first receiver by examining a plurality of relative positions of the first receiver using a corresponding plurality of clock biases, and wherein each of the corresponding plurality of clock biases is applied to each measurement, thereby forming a convergence of solutions at the relative position of the first receiver.
  • One aspect of the present invention is that a distance between the first receiver and the second receiver, with respect to the one or more far sources, is a point and that the content of the one or more signals is irrelevant to identifying the relative position of the first receiver.
  • the second receiver location is known, and the position module is configured to determine a first receiver location based on the second receiver location.
  • Figure 1 depicts a general configuration of the far sources as applied to this disclosure, as well as a Rx and MS wherein the Rx and MS are positioned anywhere in space within a Region of Interest (ROI).
  • ROI Region of Interest
  • Figures 2A-2C depict planar wavefronts representing a signal from a far source according to one embodiment of the present invention along with the relationship of the measurements to the vector distance between the MS and Rx and the common unit vector pointing in the direction of the far source.
  • Figure 3 represents the earth having a MS and a Rx positioned along the Y axis and a far source visible by both MS and Rx, according to one embodiment of the present invention.
  • Figures 4A-4E depict plots of error due to unit vector approximations due to an initial estimate and improved estimations / refinements according to one embodiment of the present invention.
  • Figures 4F - 4H show the achievable location accuracy performance of a mix of far sources in a simulation where the measurement noise at node 2 is 3m, and the measurement noise at node 1 is 6m.
  • Figure 4H shows the ideal performance in this case, when the measurement noise is zero.
  • Figure 5A presents a scenario where several Geosynchronous Earth Orbiting (GEO) satellites are used in a Far Source Navigation context with the unit vectors displayed providing an intuitive understanding of the present invention.
  • GEO Geosynchronous Earth Orbiting
  • Figure 5B provides a high-level view of a GPS denied region (note that GPS denied can be taken to mean GNSS denied, or more generally where the expected navigation signals are denied for one reason or another) and use of Far Source Navigation according to one embodiment of the present invention to determine a position of a node using GPS locations of one or more other nodes.
  • Figure 6 presents the results of a simulation of the FSN technique of the present invention showing the accuracy of the method and its relationship to the size of the ROI.
  • This simulation uses a small configuration of far sources: 2 LEOs and 3GEOs.
  • the noise indicated is the measurement noise.
  • Figure 7 presents a high-level view of a system for far source positional determination according to one embodiment of the present invention.
  • Figure 8 is a block diagram of a computer system suitable for implementation of one or more embodiments of far source positional determination.
  • Figure 9 presents a flow chart of one methodology, according to the present invention, for far source positional determination.
  • Two receivers located within a Region of Interest (ROI) that is sufficiently small as compared to a distance to a source of a signal (a far source) can be considered a “point”. Signals received at that “point” are planar. Accordingly, any difference in the time of arrival of a signal from the source by one receiver as compared to another receiver located within that ROI establishes a locus of points representing a distance between the receivers perpendicular to the vector pointing to the source. Using signals from multiple far sources, multiple loci on which one receiver must exist as compared to the other receiver can be identified.
  • the convergence of these loci identifies a relative position of one receive from the other, and if the geospatial position of other receiver is known, so too is the position of the one receiver.
  • the present invention can be visualized as a pole of fixed length pointing in one 3-D direction, combined with a mutual clock delay. Assume the directional pole to be associated with the clock delay, forming a representation of the space and time relationship between two nodes.
  • ephemeris is meant a tabular statement of the assigned places of a celestial body for regular intervals.
  • a representation of an object s position and velocity over time, or coordinates derived from that, is called an “ephemeris”.
  • ephemeris Historically, the term “ephemeris” referred to a printed table of position coordinates at discrete instants but is now extended to modern computational concepts like representations in time- continuous polynomial data-files. Imprecise ephemeris for satellites can quite easily be obtained from orbital prediction software that uses Two Line Elements (TLEs) as input.
  • TLEs Two Line Elements
  • TLE information is generated by the U.S. Space Surveillance Network, is publicly available for most space sources, and permits the computation of satellite ephemeris.
  • the precision with which ephemeris can be obtained by such a process can result in errors of many km. Errors of that magnitude generally preclude utilization of the ephemeris for navigation in any traditional method of navigation, since that error will be reflected in user location error.
  • any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment.
  • the appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
  • the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion.
  • a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
  • “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present), and B is false (or not present), A is false (or not present), and B is true (or present), and both A and B are true (or present).
  • Figure 1 provides a high-level depiction of a signal generated by a far source and received by two different entities, Rx and MS.
  • a satellite 110 in orbit around the earth receives a signal 115 from a Radio Access Facility (RAF), 120 also described as a gateway, that is relayed to ground stations Rx 130 and MS 140.
  • RAF Radio Access Facility
  • the signal 115 emanates from the RAF 120 at to arriving at the satellite 110 at t s .
  • the signal is retransmitted to the receivers, Rx 130 and MS 140 arriving at t r and t m , respectively.
  • t r and t m and not equal. That is, the time of arrival of the signal at Rx and MS is different.
  • the present invention focuses on the differential measurements between the arrival of the planar signal at Rx and the MS. Many of the specifics of where exactly the signal originated, what time it originated, what delays or deformations the channel or satellite performed on the signal in its long transit from a far source or from the RAF can be ignored.
  • the present invention analyzes the differential of arrival to two locations from one or more far sources.
  • a far source is defined, for the purpose of this discussion, as a source with a distance from a Region of Interest (ROI) in which receivers (Rx and MS) reside, where the transmit antenna is located on the order of thousands of km distant from the receiving antenna. Given several such sources, including those that are in motion, a location for the Rx can be determined in closed form. Alternatively, the system can combine the measurements on the far sources (with the method detailed here) with other available measurements to generate a location estimate, and thus, sequentially navigate.
  • ROI Region of Interest
  • Sources that are not far can also be addressed by this system and method with a slight penalty in achievable accuracy.
  • the present invention can determine a high accuracy location for a receiver in closed form. We note that most satellites can in fact be treated as far sources given a reasonably sized ROI .
  • Imprecise timing is also not a concern since the present invention uses differential measurement of the arrival of a signal at MS and Rx. What is meant by imprecise timing is that far sources are all transmitting signals that are in use by some receiver system, most often communicating data and sometimes voice. Thus, over relatively short period of time, these signal sources produce stable waveforms: the waveforms hew to their design. The present invention simply requires a stable waveform so that both the MS and Rx can perform an arrival time measurement on some segment of the waveform. The invention does not need to know the precise time at which the waveform may have been transmitted from the source, or the entire content of the waveform.
  • a signal 115 in this case generally emanates from a ground-based gateway indicated in Figure 1 as a Radio Access Facility (RAF) 120 at some time t 0 , arrives at the satellite at time t s and the transponded signals arrive at a Monitoring Station, (MS) 140, and at the
  • RAF Radio Access Facility
  • Receiver, (Rx) 130 at times t m and t R respectively.
  • the position of the MS is known perfectly and is represented by P m .
  • the Rx is at some unknown position P R .
  • the satellite ephemeris at the time of signal emission (from the satellite) is E s (t s ).
  • the signal could also originate at the satellite (as for example how it does in GPS), and in fact it is the final leg of the signal travel, from the apparent source (for example the satellite) that is pertinent in the present invention.
  • Figure 1 is deceptive as to the scale of separation of Rx and MS with respect to distance to the transmitting far source.
  • Rx 130 is distant at most from the MS 140 by on the order of 10 km.
  • the satellite 110 is distant 40,000 km (or more) from either the Rx 130 or the MS 140.
  • the region of interest in which Rx and MS exist is therefore essentially a point if drawn to scale. This is fundamental to the present invention.
  • Figure 2A illustrates the reception of a far source signal 215 in the vicinity of a MS 240 and Rx 230 in a typical Concept of Operations (ConOp).
  • the fundamental observation of Figure 2 is that the wavefront 220 of the transmitted signal 215 from the far source 210 is planar.
  • the wavefront is substantially a perfect plane given the massive distance at which the far sources we are considering are located and for the purposes of this invention the wavefront is assumed to be perfectly planar. It is nearly certainly a plane in the small region of interest that encloses both the MS and the Rx.
  • the distance from the Rx 230 to the MS 240 is a vector d 245, and u 248 represents a unit vector pointing towards the far source 210 (from either the MS or the Rx), then the difference in time of arrival of the signal measured at the Rx 230 and the MS 240 is exactly (u t d/c) where d is the vector pointing from the Rx to the MS and c is the speed of light.
  • the vectors here are taken to be column vectors, and the unit vector is transposed by the superscript, denoted as t, in this operation.
  • Figure 2B illustrates the reception of another far source signal in the vicinity of MS 240 and Rx 230.
  • the wavefront 270 is again planar.
  • the planar wavefront 220 of the far source 210 in Figure 2A differs from the planar wavefront 270 in Figure 2B.
  • the distance from the Rx 230 to the MS 240 is a vector d 275
  • u 278 represents a unit vector pointing towards this new far source 260 (from either the MS or the Rx)
  • the difference in time of arrival of the signal measured at Rx 230 and MS 240 is exactly (u t d/c) where d is the vector pointing from the Rx to the MS and c is the speed of light.
  • Figure 2C presents a two-dimensional depiction of the reception of signals from two far sources 210, 260 by Rx 230 and MS 240.
  • Rx 230 exists on a plane perpendicular to u for each far source where this plane is at a distance c ⁇ t from the MS. These planes intersect forming a line extending through the paper on which Rx 230 exists. Assuming Rx resides on the surface of the earth, (in this case the surface of the paper on which the drawing exists) the location of Rx can be determined to be the intersection of the three planes.
  • a fundamental assumption of the present invention is that the unit vector used to derive the measurements that feed Far Source Navigation (FSN) has certain properties.
  • the main assumed property of the unit vector is that within the Region of Interest (ROI), the unit vector to the far source is effectively identical, no matter where one is in the ROI. As the distance to the far source increases the applicable area of the ROI increases.
  • ROI Region of Interest
  • the ROI for this analysis can be anywhere on the surface of the earth 310, and the far source can be anywhere in space with an elevation above some minimum elevation (assume 3 degrees) above the centroid C of the region to ensure reception.
  • C 320 Assume 3 degrees, it is sufficient to place C 320 as shown in Figure 3 on the surface of the earth 310.
  • the circles denote the earth with axes representation as shown. In the upper circle the Y axis is into the paper, whereas in the lower circle the earth is rotated such that the Z axis is now out of the paper.
  • MS Monitor Station
  • Node 2 330 (N2 or Rx) is at a position along the Y-axis distant from point C 320 but also on the surface of the earth. Node 2 330 can have its distance from C 320 randomized uniformly within the region radius, i.e., uniformly selected within 0 - 15km for this example. Given that a far source is a certain elevation, then all geometries of C, N2, and the far source are equivalent to our selection, or mathematically considered homomorphic.
  • the far source in this example, can be represented using spherical coordinates [r, ⁇ , ⁇ ] being the radius, azimuth and elevation of the far source with respect to center of the earth.
  • the azimuth ⁇ can be viewed as a rotation in the [YZ] plane about the [X] axis, and the elevation as the angle subtended at the center of the earth by the far source above the plane [YZ],
  • One way to think about the location of the far source is to consider a plane parallel to the ZY axis through the point C, and that the far source is anywhere to the right of that plane, limited only such that its elevation with respect to C is at least some minimum angle ⁇ min . If the far source is located at some point in space F, (represented by the exact vector F), the ideal time measurements made at C (node 1) and node 2 can be computed as can the unit vector and measurement error.
  • the ideal time difference (converted to distance) at the two nodes can be expressed as: this being the time difference on a given signal burst from the far source measured at the nodes.
  • the unit vector from node 1 to the far source is computed as: where E is the ephemeris error (the error in FSN system knowledge of the far source location).
  • the FSN measurement can now be written as: where the vector d is the vector from node 2 (N2) to node 1 (Nl). Again, note N1 is shown as C in Figure 3. This equation includes error associated with the unit vector approximation (planar wavefront approximation) that can be bound or quantified.
  • the error due to using the unit vector determined at Nl throughout the ROI can be expressed as: and this can be now plotted for various randomizations of the far source location F, and the node 2 position N2.
  • the unit vector approximation can be improved by using a repeated or iterated solution once a first solution has been determined.
  • a positional determination using FSN of the present invention or a combination of one or more FSN measurements with other sources
  • the unit vector approximation can be improved by using a repeated or iterated solution once a first solution has been determined.
  • the MS can be used in Rx positioning, by what is essentially a method of differential positioning.
  • the argument being that the difference in TOAs (Times of Arrival) on the same burst, as observed by the MS and the Rx is directly related to the vector projection of the relative position vector (P m — P R ) in the direction of the satellite from the operational area of interest.
  • the result is of a form given by the position vector of the MS to which is added a differential vector.
  • the latter differential vector is fully defined by the unit vectors and the measurement differences.
  • the matrix U is non-singular as we have previously presented, and constant, so the measurement differences drive the location solution: as they change the estimate changes.
  • the measurements needed to locate any given node (say Node 1) do not all need to be associated with two nodes (the node being located and the already located node). In fact, a set of nodes that have location can provide the needed measurements.
  • Node 1 For each such node, and each far source, this produces an equation needed in the location of Node 1.
  • Node 3 could be obtaining measurements on the signals transmitted by a given far source while Node 2 could be doing the same for a different far source.
  • the network then transfers the data needed to Node 1.
  • Node 1 For each such node outside the region in this example, Node 1, when it also processes against the same set of far sources, obtains one measurement.
  • Node 1 With each such pairing of nodes, Node 1 is placed on a plane a specific distance away from the associated other node.
  • Intelligence in the network can decide on the best allocation of far sources to nodes so as to provide Node 1 with the data needed for location.
  • the modifications to handle clock bias follow exactly as described previously.
  • Another aspect of the present invention is the combining of far source measurements with other sources.
  • u 1 is the unit vector from the ROI to the far source
  • r m is the position vector of the MS
  • r the position vector of the Rx r the position vector of the Rx
  • ⁇ the clock bias of the Rx
  • Figures 4A - 4C show plots of the error due to the unit vector approximation, firstly due to the initial estimate of the vector, and secondly with the improved estimate discussed above after the initial location estimate.
  • Plots for LEO, MEO and GEO satellites show that it is clear how the error varies with distance to the far source. As indicated earlier the satellite geometry is fully randomized in space with respect to the ROI where node 1 and node 2 lie.
  • Figure 4G shows the achievable location accuracy performance of a mix of far sources including LEOs, MEOs and GEOs in a simulation where the measurement noise at node 2 is 3m, and the measurement noise at node 1 is 6m.
  • Figure 4H shows the ideal performance in this case, when the measurement noise is set to zero.
  • Figure 5A provides a perspective view of a plurality of far source satellites orbiting the earth 510 as applied to identify a position of a receiver P 520, according to one embodiment of the present invention.
  • Rx and MS can receive signals from four far sources Satellite Vehicle 3 (“SV3”) 530, SV2 540, SV1 550, SV21 560.
  • SV3 Satellite Vehicle 3
  • Rx and MS are in communication with each other, and the location of MS is known.
  • the clock on Rx drifts. Both are located within a region of interest depicted in Figure 5 A as point P 520.
  • the MS can be used in Rx positioning, by a method of differential positioning.
  • the argument being that the difference in TOAs (Times of Arrival) on the same signal burst, as observed by the MS and the Rx is directly related to the vector projection of the relative position vector (P m — P R ) in the direction of the satellite from the operational area of interest.
  • This example focuses on the case where the Rx clock drifts slowly such that it can perform correlations to signals adequately but develops bias (interpreted here as an excess over the correct value) over time.
  • This bias is represented as a clock error ⁇ (in units of distance) that can be considered constant over some short period of time in which multiple measurements are performed.
  • FSN can also be used to time synchronize nodes. Consider any two such nodes, and assume they have clock time errors given by and ⁇ 2 respectively, the nodes will produce some receive time estimates:
  • the first vector is then off true time by and the second by ⁇ 2 .
  • ⁇ 2 the second by ⁇ 2 .
  • any pair can differ at most by 50 microseconds (the distance divided by the speed of light). This is the worst case bound on receive time for two nodes separated 15 km for each other and occurs only when the signal is directly traveling on the line through one node to the other. In most case of interest this time difference will be much less than 50 microseconds for far sources that are overhead.
  • N will be large for the wrong alignment, and within a few tens of microseconds or at worst 50 microseconds for the correct alignment. If a wrong pairing is made, successive pairings should exhibit the error (a false pairing is not sustained over time).
  • N is small when an observation vector (a vector of differenced arrival times from a set of sources) from one node is paired with the wrong observation vector from another node, then it is extremely unlikely that the computed difference norm N is small. This can be easily seen by constructing some examples.
  • a wrong pairing (effectively resulting in setting the clock of the second node to the first), is unsustainable as new observation vectors come in (they will diverge significantly).
  • the methodology of the present invention can:
  • (b) determine the closeness of nodes; lacking the ability to satisfy the distance requirement of roughly N ⁇ 50 microseconds or some equally small number for any pairing, means that the node likely belongs in a different set (different node grouping), or different AMS, or outside the region of interest,
  • FSN may be used to synchronize time in a network of nodes where the node positions are known. Solving for time or clock bias is inherent to FSN solving for position and time, but if position is already known, then time alone can be solved for with potentially higher accuracy, and hence nodes can be synchronized.
  • the position of a receiver, or node can be located with measurements (the vector distance from receiver to a master station) from three far sources in which node 1 has a synchronized clock with a master station (or node 2 in this example). And even if the clock is not synchronized the location of node 1 can be determined with measurements from four far sources.
  • One aspect of the present invention is that the measurements do not need to come from a single master station or node.
  • the measurements can come from other nodes that have position knowledge. For example, consider the scenario shown in Figure 5B. Node 1 570 in Figure 5 B is in a GPS denied zone 575. Yet several nodes surrounding node 1 570 are aware of their position via various GPS resources, shown here as Satellite Vehicle (SV##).
  • SV Satellite Vehicle
  • Node 1 570 is in communication with each of nodes 2, 3, 4, 5 and 6. Further assume that nodes 2, 3, 4, 5 and 6 each possess their GPS location. Therefore, for each far source and for each node, N, the present invention can determine a measurement of how far node 1570 is from node N. Again, the loci of points are perpendicular to the unit vector to a given source.
  • Each Node N measurement coupled with Node 1 570 measurement on a given far source provides one such loci of points (planes) of positioning. Accordingly, where all these planes intersect is the position solution for Node 1.
  • These candidate positioning planes can derive from measurements from a collection of GPS un-denied nodes, rather than a single node. If Node 1 has a clock bias, the solution proceeds as previously described for handling clock bias, , but now with all nodes N providing the needed measurements.
  • the present invention presents a method and system for the use of far source signals for navigation.
  • the far source generates a planar wavefront in the vicinity of a region of interest containing both a MS and an Rx whose location is to be determined, the solution can be expressed in closed form.
  • the accuracy of the method is primarily governed by the noise on the measurements.
  • the term “far” is inter-related to the size of the ConOp region, the distance to the signal source and the imprecision of the source location. When the distance is large enough, the same systems developed here can be applied. The larger the distance however the more imprecision in the source signal location and the larger the ConOp region that can be included within the system.
  • LOB line of bearing
  • the goal is to solve for the relative position of one of the multiple antennas (Rx antenna in relation to the MS antenna) given a known angle of arrival (interpreted in 3 dimensions, as a unit vector).
  • the arrival angle is not perfectly known, but it is known well enough due to the very distant source location.
  • the analogy is not perfect but may be helpful to understand the physics or provide intuition.
  • LOB the carrier signal phase is the focus of examination while in the present invention the focus rests on the Time of Arrival (TO A) of a signal.
  • the far source can be either near stationary (relative to the earth), such as a GEO satellite, or at the other extreme move rapidly as in the case of a LEO satellite. Approximate ephemeris for such far sources is easily obtained and hence FSN is applicable in each case. In each case, and depending on the set of far sources selected, as well as the desired navigation accuracy, the size of the ROI can be determined. [00126] To better understand the present invention, consider the geometry and its impact on the solution. If the far sources are restricted to near equatorial GEO satellites (and specifically geosynchronous rather than geostationary satellites), the optimum regions for location would be mid-latitude regions on the earth surface, assuming no other sources come into the mix.
  • Mid-latitude regions would provide the best 3-D distribution of the unit vectors. Nearer to the equator, the solution while it can be very good in the East-West axis, may have more problems in the North-South axis. Similarly, as one approaches the poles, the visibility of equatorial source, however distant from the earth diminishes, so these regions may be difficult for the exploitation of the system.
  • the FSN of the present invention performs quite well. For example, if one was to combine GEO satellites with LEO satellites (for example, at an inclination 52 degrees) a much better and dynamic geometry would be created since the sources are not near equatorially concentrated.
  • Figure 6 shows the performance of a configuration with 3 GEO satellites and 2 LEO satellites simulated in each instance over 10,000 runs.
  • the satellite ephemeris error is randomly generated with a magnitude of 10km.
  • Both the Monitor Station (MS) and the Receiver make measurements on the signals from the satellites. Measurement standard deviations from 5m to 25m are considered in steps of 5m. Monitor station to receiver distances are considered from under 15km.
  • the error plotted is the mean absolute error over the stated number of runs.
  • the FSN system of the present invention can be combined with other traditional measurements to provide a navigation solution.
  • Traditional measurements such ranges, time differences of arrival, Doppler measurements, Angle of Arrival (AO A) measurements, etc., can be supplemented with the techniques presented herein.
  • the present invention can be used on signals that are not very far, that is not far sources, provided the ROI is small. For example, with DTV, one can reduce the diameter of the ROI to 1 km and provide accurate navigation within that region.
  • the present invention is also applicable to very distant signals.
  • signals emanating from sources on the moon or other planets will exhibit a planar wavefront over very large dimensions, even hundreds of km.
  • a MS it is also possible for a MS to situate itself at a landmark in a region of interest even in the complete absence of GPS and thus provision the nodes of a mission with data sufficient for each other node to position itself.
  • a mobile MS with specialized CRPA antennas that could dynamically position itself, overcoming GPS jamming and where it is able to receive multiple far source signals, while provisioning data to Rx nodes in the region which can then locate themselves.
  • the unit vectors of interest are to be calculated in such a manner as to account for the time of travel of the signal from the far source to the ROI. This can be easily calculated to a sufficient approximation, given the ephemeris and the ROI.
  • the consideration of interest in these cases is where the far source was positioned in inertial space that amount of time prior to the determined time stamp on the signal burst at the MS or node N. While one could ignore this effect and simply allow it to be absorbed into the ephemeris uncertainty, better accuracy would be obtained by making the known correction.
  • Another application of the present invention is a MS that self-locates using GNSS or other LEO satellites and then serves as the aiding data source to implement the method detailed here to enable navigation for all Rx s in the region of interest.
  • the MS can in this instance continue to improve its self-location, such as would happen when it can observe more than three LEO satellites.
  • the MS continues to improve its estimate of position over time, and as a result and over time, the navigation performance of each Rx also improves.
  • Multiple such MS can be made operational for added robustness and resilience in the solution. Note that multiple MSs would reduce the noise and provide diversity in the measurements.
  • MS can also be used in a different setting to potentially address enhancing the accuracy of the unit vectors. This can enhance the accuracy of FSN.
  • Multiple MS units can jointly compute the best unit vector representation for a signal in a given ROI. The MS know where they are and have good clocks, and hence can solve for the best unit vector representations to be applied. In fact, computing the unit vectors of interest in this manner would be viable even with no knowledge of ephemeris for the far sources. The MS units would jointly compute the unit vectors that best match the FSN equations, and then provide these unit vectors to all nodes requiring positioning.
  • the present invention can provide an alternative or supplement to traditional GPS, thus providing robustness in navigation for consumers. This can also serve as a cross check against GPS derived location, enabling the detection of GPS spoofing.
  • a cellular network is an attractive candidate for FSN since the MS units are available with no build out, the cellular network provides the built-in capability to share measurement information, and with the addition of an App running on smart phones can provide a full implementation of FSN as a resilience and security measure.
  • FSN Far Source Navigation
  • Such an implementation includes two or more spatially distributed receivers as in a typical mission context.
  • Four or more spatially distributed far sources (three if any receiver has a precise clock) are combined with one or more local precise sources (or having precise characterization of one or more of the far sources).
  • a low bandwidth message exchange between receivers enables data exchange and enables receiver motion over time.
  • Another example of an application of one or more embodiments of the present invention is that of a shipping port or an aircraft terminal. At a control tower on land within the port, one could conceive of placement of a MS.
  • each Rx can derive positioning and navigation information. This information can be continuously compared to an available GPS location derived from using a GPS receiver for precise positional determination.
  • a further integrity or resilience determining measure utilizing FSN would be to use the GPS Gold codes directly in FSN (ignoring the embedded navigation data). This will then generate a location estimate that can be compared to the GPS receiver location estimate derived from using the navigation data. This will result in a third mutually conflicting location estimate.
  • Three location estimates are formed: a) the GPS Rx location estimate (blind to the spoofing event), b) the FSN Rx location estimate, c) a Rx location estimate using only the GPS Gold codes, and treating the GPS satellites as far sources, thus applying FSN to the Gold codes and ignoring the GPS navigation data.
  • the present invention is also applicable in instances of GPS jamming.
  • the present invention can perform PNT (navigation) without demodulation of the bits if we have almanac data for coarse satellite position data (which can last many hours or even days), and one could integrate through the jammers enough to get just the detection of the C/A code (perhaps through coherent and non-coherent integration over longer periods). Not having to demodulate the entire signal permits the Rx to implement FSN even if some segments of the signal cannot be recovered, permitting PNT with fragmented (due to jamming) signal components.
  • Another alternative to almanac data would be the use of TLE derived approximate ephemeris as indicated earlier on; any means of obtaining approximate imprecise ephemeris is sufficient.
  • one or more portions of the present invention can be implemented in software.
  • Software programming code which embodies the present invention is typically accessed by a microprocessor from long-term, persistent storage media of some type, such as a flash drive or hard drive.
  • the software programming code may be embodied on any of a variety of known media for use with a data processing system, such as a diskette, hard drive, CD-ROM, or the like.
  • the code may be distributed on such media or may be distributed from the memory or storage of one computer system over a network of some type to other computer systems for use by such other systems.
  • the programming code may be embodied in the memory of the device and accessed by a microprocessor using an internal bus.
  • the techniques and methods for embodying software programming code in memory, on physical media, and/or distributing software code via networks are well known and will not be further discussed herein.
  • Figure 7 presents a high-level view of a system 700 for far source positional determination.
  • a far source signal 710 is received by a first 715 and a second receiver 720.
  • information regarding the time of arrival of the signal at the second receiver is communicated 730 to the first receiver.
  • a time-difference module 740 communicatively coupled to the first receiver 715 is configured to measure one or more time-difference of arrivals, each time-difference of arrival being difference between arrival of one of the one or more signals at the first receiver and arrival of the one of the one or more signals at the second receiver.
  • a loci of points module 750 communicatively coupled to the time-difference module 740, determines, for each signal, a loci of points, forming one or more loci of points wherein each loci of points is a distance from the second receiver on which the first receiver resides based on the respective one or more time-difference of arrivals.
  • a position module 760 communicatively coupled to the loci of points module identifies a relative position 780 of the first receiver from the second receiver based on an intersection of the one or more loci of points.
  • program modules include routines, programs, objects, components, data structures and the like that perform tasks or implement abstract data types.
  • program modules include routines, programs, objects, components, data structures and the like that perform tasks or implement abstract data types.
  • program modules may be in both local and remote memory storage devices.
  • FIG. 8 is a very general block diagram of a computer system in which software-implemented processes of the present invention may be embodied.
  • system 800 comprises a central processing unit(s) (CPU) or processor(s) 801 coupled to a random-access memory (RAM) 802, a graphics processor unit(s) (GPU) 820, a read-only memory (ROM) 803, a keyboard or user interface 806, a display or video adapter 804 connected to a display device 805, a removable (mass) storage device 815 (e.g., floppy disk, CD-ROM, CD-R, CD-RW, DVD, or the like), a fixed (mass) storage device 816 (e.g., hard disk), a communication (COMM) port(s) or interface(s) 810, and a network interface card (NIC) or controller 811 (e.g., Ethernet).
  • a real time system clock is included with the system 800, in a conventional manner.
  • CPU 801 comprises a suitable processor for implementing the present invention.
  • the CPU 801 communicates with other components of the system via a bi-directional system bus 820 (including any necessary input/output (VO) controller 807 circuitry and other "glue” logic).
  • the bus which includes address lines for addressing system memory, provides data transfer between and among the various components.
  • Randomaccess memory 802 serves as the working memory for the CPU 801.
  • the read-only memory (ROM) 803 contains the basic input/output system code (BIOS)— a set of low- level routines in the ROM that application programs and the operating systems can use to interact with the hardware, including reading characters from the keyboard, outputting characters to printers, and so forth.
  • BIOS basic input/output system code
  • Mass storage devices 815, 816 provide persistent storage on fixed and removable media, such as magnetic, optical, or magnetic-optical storage systems, flash memory, or any other available mass storage technology.
  • the mass storage may be shared on a network, or it may be a dedicated mass storage.
  • fixed storage 816 stores a body of program and data for directing operation of the computer system, including an operating system, user application programs, driver, and other support files, as well as other data files of all sorts.
  • the fixed storage 816 serves as the main hard disk for the system.
  • program logic (including that which implements methodology of the present invention described below) is loaded from the removable storage 815 or fixed storage 816 into the main (RAM) memory 802, for execution by the CPU 801.
  • the system 800 accepts user input from a keyboard and pointing device 806, as well as speech-based input from a voice recognition system (not shown).
  • the user interface 806 permits selection of application programs, entry of keyboard-based input or data, and selection and manipulation of individual data objects displayed on the screen or display device 805.
  • the pointing device 808, such as a mouse, track ball, pen device, or the like, permits selection and manipulation of objects on the display device. In this manner, these input devices support manual user input for any process running on the system.
  • the computer system 800 displays text and/or graphic images and other data on the display device 805.
  • the video adapter 804 which is interposed between the display 805 and the system's bus, drives the display device 805.
  • the video adapter 804 which includes video memory accessible to the CPU 801, provides circuitry that converts pixel data stored in the video memory to a raster signal suitable for use by a cathode ray tube (CRT) raster or liquid crystal display (LCD) monitor.
  • CTR cathode ray tube
  • LCD liquid crystal display
  • the system itself communicates with other devices (e.g., other computers) via the network interface card (NIC) 811 connected to a network (e.g., Ethernet network, Bluetooth wireless network, or the like).
  • the system 800 may also communicate with local occasionally connected devices (e.g., serial cable-linked devices) via the communication (COMM) interface 810, which may include a RS-232 serial port, a Universal Serial Bus (USB) interface, or the like.
  • Communication (COMM) interface 810 which may include a RS-232 serial port, a Universal Serial Bus (USB) interface, or the like.
  • Devices that will be commonly connected locally to the interface 810 include laptop computers, handheld organizers, digital cameras, and the like.
  • Figure 9 provides a high-level view of a flowchart of a methodology for far source positional determination. The process begins with measuring 910 one or more time-difference of arrivals of one or more signals from one or more, respective, far sources. Each time-difference of arrival is between the difference of arrival of each of the one or more signals at a first receiver and arrival of each of the one or more signals at a second receiver.
  • the method continues by determining 920, for each signal, a loci of points.
  • Each locus of points is at a distance from the second receiver on which the first receiver resides based on the respective one or more time-difference of arrivals.
  • the process ends by identifying 930 a relative position of the first receiver from the second receiver based on an intersection of the one or more loci of points.
  • a location of the one or more far sources is unknown. wherein a location of one or more far sources is irrelevant to identifying the relative position of the first receiver.
  • a first clock associated with the first receiver and a second clock associated with the second receiver are synchronized. wherein responsive to the first clock and the second clock having a relative bias, further comprising identifying the relative position of the first receiver by examining a plurality of relative positions of the first receiver using a corresponding plurality of clock biases, and wherein each of the corresponding plurality of clock biases is applied to each measurement, thereby forming a convergence of solutions at the relative position of the first receiver. wherein a distance between the first receiver and the second receiver is viewed as a point with respect to the one or more far sources.
  • a system for far source positional determination includes:
  • a first receiver configured to receive one or more signals from one or more far sources, respectively;
  • a second receiver communicatively coupled to the first receiver, configured to receive the one or more signals from the one or more far sources, respectively;
  • a time-difference module communicatively coupled to the first receiver and configured to measure one or more time-difference of arrivals, each time-difference of arrival being difference between arrival of one of the one or more signals at the first receiver and arrival of the one of the one or more signals at the second receiver;
  • a loci of points module communicatively coupled to the time-difference module, configured to determine, for each signal, a loci of points, forming one or more loci of points wherein each loci of points is a distance from the second receiver on which the first receiver resides based on the respective one or more time-difference of arrivals;
  • a position module communicatively coupled to the loci of points module and configured to identify a relative position of the first receiver from the second receiver based on an intersection of the one or more loci of points.
  • a wavefront of each of the one or more signals is a planar wavefront wherein a location of the one or more far sources is unknown. wherein a location of one or more far sources is irrelevant to identifying the relative position of the first receiver.
  • the position module is configured to identify the relative position of the first receiver by examining a plurality of relative positions of the first receiver using a corresponding plurality of clock biases, and to apply each of the corresponding plurality of clock biases to each measurement, thereby forming a convergence of solutions at the relative position of the first receiver.
  • a distance between the first receiver and the second receiver, with respect to the one or more far sources is a point. wherein the content of the one or more signals is irrelevant to identifying the relative position of the first receiver.
  • a second receiver location is known.
  • the position module is configured to determine a first receiver location based on the second receiver location. wherein, within a region of interest, a unique unit vector is associated with each of the one or more far sources and wherein the loci of points for each of the one or more far sources on which the first receiver resides is perpendicular to that unique unit vector. • wherein responsive to the position module identifying the relative position of the first receiver from the second receiver, configuring the position module to refine each unique unit vector using the relative position of the first receiver and the second receiver location.
  • the second receiver is a transceiver configured to transmit to the first receiver times of arrival of one of the one or more signals received at the second receiver.
  • a component of the present invention is implemented as software
  • the component can be implemented as a script, as a standalone program, as part of a larger program, as a plurality of separate scripts and/or programs, as a statically or dynamically linked library, as a kernel loadable module, as a device driver, and/or in every and any other way known now or in the future to those of skill in the art of computer programming.
  • the present invention is in no way limited to implementation in any specific programming language, or for any specific operating system or environment. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention.

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

Abstract

Deux récepteurs (715, 720) situés dans une région d'intérêt qui est suffisamment petite comparativement à une distance à une source d'un signal peuvent être considérés en tant que « point ». Des signaux (710) reçus en ce « point » sont plans. En conséquence, toute différence dans le temps d'arrivée d'un signal (730) provenant de la source par un récepteur comparativement à un autre récepteur situé dans cette région établit un lieu de points représentant une distance entre les récepteurs perpendiculaire au vecteur pointant vers la source. L'utilisation de signaux provenant de multiples lieux à multiples sources éloignées sur lesquels un récepteur doit exister comparativement à l'autre récepteur peut être identifiée. La convergence de ces lieux identifie une position relative d'un récepteur par rapport à l'autre et, lorsque la position géospatiale d'un récepteur est connue, la position de l'autre récepteur l'est également.
PCT/US2022/076388 2021-09-15 2022-09-14 Détermination de position de source éloignée Ceased WO2023044314A1 (fr)

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US17/931,619 US12449503B2 (en) 2021-09-15 2022-09-13 Far-source position determination

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001065271A1 (fr) * 1998-10-09 2001-09-07 Cell-Loc Inc. Procedes et dispositif de positionnement de recepteur mobile a l'aide de signaux de liaison descendante
WO2012003411A2 (fr) * 2010-07-01 2012-01-05 Qualcomm Incorporated Détermination de positions d'émetteurs-récepteurs sans fil à ajouter dans un réseau de communication sans fil
US20200371193A1 (en) * 2019-05-24 2020-11-26 U-Blox Ag Method and apparatus for positioning with wireless signals

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001065271A1 (fr) * 1998-10-09 2001-09-07 Cell-Loc Inc. Procedes et dispositif de positionnement de recepteur mobile a l'aide de signaux de liaison descendante
WO2012003411A2 (fr) * 2010-07-01 2012-01-05 Qualcomm Incorporated Détermination de positions d'émetteurs-récepteurs sans fil à ajouter dans un réseau de communication sans fil
US20200371193A1 (en) * 2019-05-24 2020-11-26 U-Blox Ag Method and apparatus for positioning with wireless signals

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